Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

A study of erosion mechanism during the liquid droplet impingement (LDI) on a rough surface was conducted using both numerical simulation and experiments. The numerical simulation was carried out for the LDI on single groove roughness utilizing the two-phase full Eulerian approach based on the high-resolution finite volume method to understand the evolution of the droplet deformation and the wall pressure distribution. The numerical results for the LDI on a large groove roughness showed that the first and the second impacts occurred close to the first contact location of the droplet on the wall, which was similar to the LDI on a smooth surface. The largest impact occurred by the third impact at the groove bottom, which was caused by the side-jet focusing and droplet focusing generated from the contact edge of the droplet. It was also found that the maximum wall pressure at the groove bottom increased with the increase in the groove roughness parameter that represented the geometrical ratio of the groove depth to the droplet diameter. In addition to the numerical studies, the erosion behavior of LDI on single groove roughness was observed experimentally using a Scanning Electron Microscope (SEM) after spray jet impingement on an aluminum specimen with various groove roughness parameter. The experimental results showed that the LDI erosion on the large groove roughness started from the groove bottom, while the LDI erosion on the small groove roughness started from the groove edge and the groove bottom. These experimental findings are well correlated with the maximum wall pressure distributions obtained from the numerical results.

DOI： 10.1016/j.nucengdes.2018.02.021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Inc.  

In order to understand the flow structure of a flickering flame, time-resolved observations are carried out of the velocity and density fields in a diffusion flame in co-flow using particle image velocimetry (PIV) and shadowgraph imaging, respectively. The PIV measurement combined with invalid velocity vector analysis using proper orthogonal decomposition (POD) allows for the high spatial resolution measurement of the velocity field in the flame, while the shadowgraph images show the high-temperature contour and soot formation of the flame. These experimental results indicate a periodic variation in the flow field and soot structure of the flickering flame. The observation of the velocity field shows that the periodic inflow and outflow are generated in the outer layer of the flame near the burner, which promotes the flow acceleration in the vertical direction leading to clip-off behavior. It is found that the vorticity contour evaluated from the velocity field matches well with the high-temperature contour observed in the shadowgraph images. Further examination of the flow structure is carried out using the first two POD modes, which demonstrate the presence of counter-rotating vortices in the outer flame contributing to stretching of the flame due to the clip-off motion in the flame.

DOI： 10.1016/j.expthermflusci.2017.11.026

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

Liquid droplet impingement (LDI) erosion on a rough surface was studied experimentally in the initial stage of erosion using spray-jet impingement on various levels of sandpaper roughness and single groove roughness. The experimental results using an aluminum specimen indicated that the incubation period decreased and the erosion rate increased with increasing the relative roughness, defined as the ratio of roughness height to droplet diameter, in a range of small relative roughness. The growth of the erosion rate in a large relative roughness is almost constant for the sandpaper roughness with increasing the relative roughness, while the erosion rate for the groove roughness decreased at large relative roughness. Therefore, the erosion rate of the groove roughness indicated a peak at small relative roughness. This might be due to the influence of smooth surface surrounding the single groove roughness. A scanning electron microscope (SEM) observation for the small relative roughness of groove showed that erosion was started on the sidewall of the grooves and was followed by the penetration of erosion perpendicular to the groove. The erosion initiation points shifted from the sidewall to the bottom of the groove with increasing the relative roughness, which might be due to the effective impact angle variation across the groove.

DOI： 10.1016/j.wear.2017.12.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

Mass and momentum transfer characteristics in a 90° elbow with a radius to pipe diameter ratio of 1.5 are studied experimentally with the aid of the plaster dissolution method, planar velocity measurement by particle image velocimetry (PIV), and surface flow visualization in the Reynolds number (Re) range of 5 × 104 to 20 × 104. The experimental results indicate that the most significant change in mass transfer distribution occurs on the inner wall of the elbow. The mass transfer coefficient increases along the centerline of the first half of the elbow and decreases in the second half with increasing Reynolds number. The near-wall velocity measurements by PIV show that the flow accelerates on the first half of the inner wall and decelerates on the second half, which contributes to the growth of the turbulent intensities on the second half of the inner wall. The surface flow visualization indicates that the secondary flow is weak on the inner wall of the elbow with higher Reynolds number. These results show that the mass transfer characteristics change on the inner wall of the elbow with increase in the Reynolds number, even when it is larger than Re = 5 × 104.

DOI： 10.1016/j.icheatmasstransfer.2017.11.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Time-resolved observations of pit formation and cloud structure in a cavitating jet are carried out to understand the erosion mechanism of a cavitating jet issuing from a converging and diverging nozzle in a still water environment. Pit formation is detected by a sensor made of gold film (0.2 mu m in thickness) glued to a transparent glass plate, and the number and size of the pits are evaluated from digital image analysis. High-speed camera shadowgraph imaging allows observation of the cloud structure in the cavitating jet, which captures the cavitation cloud collapse combined with the time-difference analysis. The radial distribution of pits is in close agreement with the erosion depth distribution evaluated from the weight-loss profiles of an aluminum specimen in a cavitating jet. The pit distribution in the cloud collapse is well reproduced in the time-difference analysis. Furthermore, simultaneous observations of the pit and cloud structures show that pits are formed on the wall at the instant of cloud collapses during the periodic behavior of the cavitating jet.

DOI： 10.1016/j.wear.2017.06.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Mass and momentum transfer characteristics in and downstream of a 90 elbow are studied experimentally with the aid of the plaster dissolution method, surface flow visualization in the elbow and the cross-sectional velocity field measurement by stereo particle image velocimetry (SPIV) downstream of the elbow. The experiments are carried out for the elbow with the radius to diameter ratio 1.5 at moderate Reynolds number Re = 5 x 10(4). The mass transfer measurements in the elbow indicate that the major change of mass transfer coefficient is observed along the inner wall of the elbow, where low mass transfer coefficient is found in the first half of the inner wall and it increases abruptly in the second half of the elbow, which is followed by a gradual recovery of the mass transfer in the downstream, while the mass transfer on other wall does not change so much with that of the straight pipe. These features are mainly due to the flow acceleration in the first half of the inner wall and the following flow separation in the second half of the inner wall, where the high turbulent energy production is expected from the SPIV measurement downstream of elbow. These results indicate that the mass transfer coefficient in and downstream of the elbow is highly modified by the flow separation and secondary flow in the elbow, which may generate the high turbulent energy production in the second half of the inner wall in the elbow. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2016.11.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The exchange flows in a buoyancy driven forced flow in vertical pipes of circular and square cross-sections were studied experimentally and the flow structure was examined by proper orthogonal decomposition (POD) analysis. The experiments were carried out in the vertical pipes issuing into a still brine water environment and the flow fields were visualized by the laser-induced fluorescence (LIF) technique. The flow visualization study showed that the critical inflow condition was deviated from the purging boundary due to the influence of hysteresis, and they are shifted to the high Froude numbers in the square pipe compared to the circular one. The POD analysis of the exchange flow indicates that the fluctuating energy is increased in the lower POD modes due to the formation of large-scale structure of the exchange flow. It is found from the analysis that the exchange flow in the low Reynolds number is promoted at the corners of the cross section in the square pipe, while it is randomly distributed in the circular pipe. This corresponds to an increased critical Froude number in the square pipe than that of the circular pipe, which is due to the presence of exchange flow through the corners. With increasing the Reynolds numbers, the flow becomes turbulent and the scale of the exchange flow is decreased and restricted to the near-wall region, while the location of the exchange flow becomes random along the pipe wall irrespective of the cross-sectional shape of the pipes. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.icheatmasstransfer.2017.02.011

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In order to understand the mechanisms of non-axisymmetric pipe-wall thinning in the Mihama nuclear power plant accident of 2004, a numerical simulation of pipe-wall thinning in an elbow-orifice pipeline with swirling flow was carried out based on mass and momentum transfer equations with a standard k-epsilon model of turbulence at a Reynolds number of 5.8 x 10(6). The pipe-wall thinning was evaluated on the basis of the mass transfer coefficient using the diffusion coefficient of ferrous iron in bulk water flow. The numerical simulation revealed that swirling flow with a certain level of swirl intensity generates a spiral motion downstream of the elbow and sustains a longer distance than expected from an elbow flow without swirl. This type of non-axisymmetrical flow triggers strongly biased flow at the orifice, which results in non-axisymmetric pipe-wall thinning downstream of the orifice. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.anucene.2016.09.040

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This paper describes the mass transfer characteristics on periodic roughness in a circular pipe and that downstream of an orifice. The mass transfer enhancement ratio of the rough pipe with respect to the smooth pipe are measured by the plaster dissolution method for various combinations of roughness height and wavelength of the periodic roughness, and the influence of roughness on the mass transfer enhancement is examined experimentally. The mass transfer enhancement on periodic roughness is highly increased with increasing the roughness parameter, defined by the roughness height to the wavelength. It is found that the mass transfer enhancement of rough pipe is more than 2 times larger than that of the smooth pipe, which is due to 3the formation of the local recirculating region over the periodic roughness. On the other hand, minor mass transfer enhancement is observed on the flow downstream of an orifice. The examination of the flow and mass transfer over the periodic roughness and that downstream of orifice is carried out by the numerical simulation with low-Reynolds number k-epsilon model. The result indicates that the formation of local recirculating region on the periodic roughness is the major source of mass transfer enhancement on the rough pipe, while the minor mass transfer enhancement downstream of the orifice is attributed to the effect of separating shear layer originating from the orifice edge on the wall, which is dominant over the local effect of recirculating flow on the periodic roughness downstream of the orifice. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2016.10.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The influence of air co-flow on flickering methane diffusion flame was studied experimentally using the image processing technique and the proper orthogonal decomposition (POD) analysis. The flickering of the flame is characterized by the mean height, the oscillation amplitude and the Strouhal number, which are measured by the digital image analysis of the diffusion flame. The experiments are carried out for various combinations of burner diameters, fuel velocities and co-flow velocities. With increasing the velocity ratio of the co-flow to the fuel flow, the oscillation amplitude is decreased and the Strouhal number is increased slightly in proportional to the inverse Froude number, while the frequency jump occurs in the low co-flow velocity ratio. These results are commonly observed in all the burners of different diameters, while the critical co-flow velocity ratio to suppress the flickering is found to be increased with increasing the burner diameters due to the influence of Froude number. The POD analysis of the flickering flame shows that the flickering energy is dominant in the first two POD modes and they are axisymmetric except for the zero co-flow velocity case and fully suppressed case. The correlation of POD coefficients in the first two fluctuating POD modes suggests the suppression of large-scale structure of flickering due to the influence of co-flow.

DOI： 10.1007/s10494-016-9730-9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The variations of cloud structure and erosion characteristics of a cavitating jet are experimentally studied by optical and SEM microscope observations, measurement of erosion characteristics and simultaneous shadowgraph imaging combined with the acceleration pulse measurement. The time difference image analysis of the shadowgraphs allows the detection of the near-wall collapsed bubbles in the periodic development of the cavitating jet, while the simultaneous acceleration pulse measurement indicates the generation of acceleration pulses at the same instant of bubble collapse near specimen surface. These results indicate that the generation of acceleration pulses are highly correlated with the collapsed bubbles behind the cloud in the shrinking motion, which triggers the cavitation bubble collapse and leads to the erosion damage on the specimen. It is found from the image analysis that the erosion distributions on the test specimen are well reproduced in the time-difference images of the shadowgraphs, which indicates the sudden intensity growth near the wall due to the cavitation collapse. This result suggests that the collapse of the cavitation bubbles near the specimen surface is correlated with the erosion distribution on the specimen surface in the cavitating jet. (C) 2016 Published by Elsevier B.V.

DOI： 10.1016/j.wear.2016.03.036

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This paper presents a numerical analysis of liquid droplet impingement (LDI) erosion in the pipeline of nuclear/fossil power plants. The numerical method is based on combining a Eulerian/Lagrangian computational fluid dynamics (CFD) model with an erosion model to consider various aspects of LDI erosion, such as the influence of the droplet velocity, diameter, number density, impingement angle, material hardness, liquid-film thickness, and erosion depth on the wall-thinning rate. A numerical analysis of the erosion depth distribution was carried out for the LDI erosion of a bent pipe downstream of an orifice at the Onagawa power plant incident in 2007. The results were compared with existing erosion models, and the variations in the peak erosion depths were examined. The present model results showed reasonable agreement with the prototype results at the location and the erosion depth distribution of the bent pipe. The comparison showed the importance of the liquid film and erosion depth to predicting the LDI erosion characteristics. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.engfailanal.2016.01.005

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This paper describes an experimental study on the wall-thinning rate in deep erosion by liquid droplet impingement (LDI) in a pipeline for application to nuclear/fossil power plant. The experiment is carried out in a spray jet apparatus, which allows the evaluation of local wall-thinning rate by the LDI erosion. The surface contour of erosion and the wall-thinning rate are measured and the observation by scanning electron microscope (SEM) is carried out in this experiment. The experimental result indicates that the wall-thinning rate is highly attenuated and the macro structure on the erosion surface grows with an increase in the erosion depth, which is due to the influence of the liquid film over the erosion surface. The erosion model for predicting the wall-thinning rate in deep erosion is proposed by introducing the attenuation factor with a function of erosion depth. The introduction of attenuation factor with liquid-film effect shows a better correlation with the experimental data, and the accuracy of correlation is improved by a factor of 2. (c) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.anucene.2015.10.024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The onset of exchange flow and the flow structure in a combined buoyancy and forced pipe flow are experimentally studied at Reynolds number up to 7000. The experiment is carded out in a vertical pipe flow of water issuing into a still brine water environment of various concentrations and flow rates. The critical Froude number for the onset of exchange flow is evaluated by the laser-induced fluorescence technique and the velocity fields near the pipe exit are measured by the particle-image velocimetry. The critical Froude number in the laminar regime increases with increasing the Reynolds number and the onset of inflow and the purging of the exchange flow are deviated due to the hysteresis effect, while it is not observed in the turbulent regime. It is found that the laminar exchange flow is characterized by the large-scale structure and the turbulent exchange flow is featured by the small-scale structure near the wall. The enhancement of velocity fluctuation near the pipe exit is clearly observed in the laminar regime due to the occurrence of exchange flow, while it is limited to the near-wall region in the turbulent regime. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.icheatmasstransfer.2015.11.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The influence of swirling flow on mass and momentum transfer downstream of a pipe with elbow and orifice is studied experimentally. The experiments are carried out in the pipe at Reynolds number Re = 3 x 10(4) for various magnitudes of swirl intensity up to 0.9 driven by the rotary swirler. The mass transfer coefficient and the cross-sectional velocity field downstream of the orifice are measured by the plaster dissolution method and the stereo PIV, respectively. It is found that the mass transfer coefficient and the turbulent energy increases gradually with increasing the swirl intensity, while they become non-axisymmetric downstream of the orifice for the swirl intensity larger than 0.6 at the inlet of the elbow, which is followed by the saturation at higher swirl intensity. The maximum mass transfer coefficient is found to have a peak at one diameter downstream of the orifice and it reaches 6 times larger value than that of the straight pipe without swirling flow. The behavior of the maximum mass transfer coefficient with respect to the swirl intensity is similarly observed in the near-wall turbulent energy. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2015.08.087

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Springer Netherland  

This paper deals with the extraction of turbulent structure correlated with the wall mass transfer in a curved swirling pipe flow behind an orifice. The crosssectional velocity field behind the orifice is measured by the Stereo Particle Image Velocimetry (SPIV) and the results are analyzed by the proper orthogonal decomposition (POD). The instantaneous velocity field shows the asymmetric vortex structure in the cross section due to the combined effect of the swirling flow and the secondary flow generated at the upstream elbow. The POD analysis indicates that the highly turbulent flow is generated on the upper left-hand side of the pipe in the lower POD modes suggesting the occurrence of high wall-thinning rate due to the mass transfer enhancement, while that of the higher modes do not show such asymmetry. This result suggests that the lower POD modes of the velocity field contribute to the non-axisymmetric pipe-wall thinning behind an orifice in a curved swirling flow.

DOI： 10.1007/978-3-319-20388-1_20

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This paper describes the experimental study on the liquid droplet impingement erosion of metal materials to understand the influence of material hardness on the erosion rate. The experiment is carried out using a water spray jet apparatus with a condition of relatively thin liquid film thickness. The metal materials tested are pure aluminum, aluminum alloy, brass, mild steel, carbon steel and stainless steel. The liquid droplets considered are 30 +/- 5 mu m in volume average diameter of water, which is the same order of droplet diameter in the actual pipeline in nuclear/fossil power plants. In order to understand the influence of material hardness on the liquid droplet impingement erosion, the scanning electron microscope (SEM) observation on the eroded surface and the measurement of erosion rate are carried out in the terminal stage of erosion. The experimental results indicate that the erosion rates are expressed by the droplet velocity, volume flux, Vickers hardness and the liquid film thickness, which are fundamentals of the liquid droplet impingement erosion. The empirical formula shows that the power index for droplet velocity dependency is found to be 7 with a scattering from 5 to 9 depending on the materials, while the power index for Vickers hardness dependency is found as -4.5. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nucengdes.2015.03.016

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The non-axisymmetric wall-thinning leading to a pipeline break is studied in a scaled model experiment in a water tunnel. The pipeline consists of an elbow, an orifice and a straight pipe between them. The measurement of velocity field is carried out downstream of the orifice using stereo Ply and the spatial correlation of velocity fluctuations is analyzed by snapshot Proper Orthogonal Decomposition (POD), while the mass transfer coefficient is measured by a benzoic acid dissolution method. These measurements are carried out at Reynolds number Re = 3 x 10(4) with and without swirl. It is found that the non-axisymmetric flow and mass transfer is found downstream of the orifice due to the combined influence of the secondary flow in the elbow and the swirling flow. The POD analysis indicates that non-axisymmetric velocity field is generated in the first two POD modes, which suggests the structural change in the velocity field downstream of the orifice, such as the non-axisymmetric growth of the velocity and turbulent energy in the lower POD modes. It is also found that the near-wall turbulent energy distribution is correlated with the measurement of mass transfer coefficient. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.anucene.2015.01.043

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In this study, the mechanism of non-axisymmetric pipe-wall thinning that led to a pipeline break in the Mihama nuclear power plant in 2004 is evaluated in a scale-model experiment in a water tunnel having an elbow and orifice under the influence of swirling flow. The velocity fields are measured by stereo particle image velocimetry, and the mass transfer rate is measured by a benzoic acid dissolution method at Reynolds number Re = 3 x 10(4) with and without swirling flow. The non-axisymmetric swirling flow is found to be generated behind the elbow, even when the axisymmetric swirling flow is supplied in the upstream of the elbow. The secondary flow generated in the elbow is not suppressed in the pipeline 10 diameters downstream of elbow in the swirling flow, and in this flow geometry, the non-axisymmetry of the flow is greatly magnified downstream of the orifice. The measured mass transfer rates downstream of the orifice under the influence of swirling flow indicate that the Sherwood number distribution on one side of the pipe is enhanced and that on the other side is reduced owing to the appearance of the non-axisymmetric swirling flow, which results in the occurrence of non-axisymmetric pipe-wall thinning downstream of the orifice. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nucengdes.2014.12.036

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

The flow characteristics and the structure of highly buoyant jet of low density fluid issuing into a stagnant surrounding of high density fluid is studied by scanning stereo My combined with proper orthogonal decomposition (POD) analysis. The experiment is carried out at Froude number of 0.3 and Reynolds number of 200, which satisfies the inflow condition due to the unstable density gradient near the nozzle exit. An increase in the maximum mean velocity occurs and the vertical velocity fluctuation is highly amplified near the nozzle exit, which suggests the influence of inflow due to the unstable density gradient. The POD analysis indicates that the vertical velocity fluctuation is the major source of fluctuating energy contributing to the development of the highly buoyant jet. The examination of the POD modes show that the longitudinal structure of the vertical velocity fluctuation is generated along the jet axis having the opposite sign of velocity fluctuation on both sides of the jet axis. The vertical scale of the POD mode decreases with increasing the mode number and results in the frequent appearance of cross-flow across the buoyant jet. The reconstruction flow from the POD modes indicates that the vortex structure is caused by the highly sheared layer between the upward and downward velocity and the inflow is induced by the vortex structure. The magnitude of the vortex structure seems to be weakened with an increase in the distance from the nozzle and the buoyant jet approaches to an asymptotic state in the further downstream. (C) 2014 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.ijheatfluidflow.2014.12.003

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The three-dimensional (3D) temperature field of the flickering flame with and without coflow can be measured using the flame reaction technique combined with tomographic reconstruction. This combined experimental technique facilitates the non-intrusive measurement of the unsteady 3D temperature field of a premixed methane/air flame. The target flame visualization, which was achieved by the flame reaction of sodium in the supplied mists of sodium chloride solution and line-of-sight intensity images of the flame, was transformed into the temperature field using calibration with the sodium D-line reversal method combined with imaging from six CCD cameras located around the flame. The uncertainty in tomographic temperature measurement was confirmed for the steady axisymmetric flame under the influence of strong coflow. Tomographic temperature measurements were applied to the flickering flame with and without coflow, and the results were analyzed using proper orthogonal decomposition (POD) to understand the unsteady behavior of the temperature field of the flickering flame. The flickering energy was found to be dominant in the first two POD modes. Flame flickering with and without coflow was found to be dominant in the axisymmetric and non-axisymmetric modes, respectively. The characteristics of the flickering flame with and without coflow are discussed in this paper, based on spectrum analysis. The results suggest that the structure of the flickering flame is highly modified by the presence of even a small magnitude of coflow.

DOI： 10.1007/s10494-014-9568-y

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The flickering characteristics and the temperature field of an axisymmetric premixed methane/air flame under the influence of co-flow are studied experimentally using the image analysis and the flame reaction technique. The premixed flame is visualized by the alkali metal solution of sodium (Na) for characterizing the flickering characteristics. The temperature measurement of the flame is carried out using the flame reaction technique combined with the relationship between the local intensity of the flame and the temperature from the sodium D-line reversal method, and the influence of the number density distribution of Na on the measured temperature field is corrected by the measurement integrated analysis of the flame with the iterative procedure. This technique is validated by the local temperature measurement in the steady flame under the influence of co-flow using the thermocouple calibrated by the sodium D-line reversal method. The flame visualization and temperature measurement in the flickering flame of the premixed methane/air flame indicates that the flame contour and the temperature field oscillate periodically with the flickering frequency due to the Kelvin-Helmholtz instability of the flame. The oscillation amplitude decreases and the frequency increases gradually with the co-flow velocity increases similar to the observation in the diffusion flame in literature, while the oscillation amplitude grows with the equivalence ratio increases. These changes in the flickering characteristics of the flame are caused by the variations of the temperature field in the premixed flame. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.enconman.2013.10.059

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Experimental and numerical studies are carried out to understand the mass transfer characteristics in a circular pipe behind an orifice, which is often encountered in pipe-wall thinning due to flow accelerated corrosion in pipelines of nuclear/fossil power plants. The measurement of mass transfer coefficient is conducted by using benzoic acid dissolution method in a water flow, which allows the measurement of mass transfer behind the orifice in a circular pipe at the Schmidt number near the actual operating condition of the pipeline. The measurement of mass transfer coefficient behind the orifice shows a maximum Sherwood number in the region 1-2 pipe diameters downstream of the orifice due to the flow turbulence, and it decreases gradually in the downstream, which agrees qualitatively with the feature of pipe-wall thinning in the pipeline in literature. The present result indicates that the Sherwood number behind the orifice is greatly increased by increasing the Schmidt number and the Reynolds number, though the geometrical factor, which is the ratio of the thinning rate of the orifice flow with respect to that of the fully developed pipe flow, is weakly dependent of these parameters. It is also found that the experimental Sherwood number profiles and the mean velocity distribution behind the orifice are well reproduced in the numerical simulation by the k-epsilon model with the empirical modification of high-Schmidt-number flows, though the maximum Sherwood number is slightly overpredicted, reflecting the higher prediction of turbulence energy behind the orifice. These results demonstrate the usefulness of the numerical simulation for predicting the pipe-wall thinning due to the flow accelerated corrosion in the orifice flow. (C) 2013 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.expthermflusci.2013.09.017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In the present paper, the pipe-wall thinning due to liquid droplet impingement erosion is studied experimentally by using a high-speed conical spray under the influences of liquid film on the target specimen. The size of the droplets considered is an order of tens of micrometers in diameter, which is the same order as those expected in the pipeline of nuclear/fossil power plants. In order to evaluate the erosion rate by the liquid droplet impingement under the influence of liquid film, the experiments are conducted by various combinations of the specimen diameters and the standoff distances of the spray from the nozzle. The experimental results show that the erosion depth increases linearly with the local flow volume, indicating the presence of terminal stage of erosion. The present results indicate that the erosion rate increases with decreasing the specimen diameter and increases slightly with increasing the standoff distance. This result combined with the theoretical consideration of the liquid film on the specimen leads to the conclusion that the erosion rate increases with decreasing the liquid film thickness, which supports the numerical result of liquid droplet impingement erosion in literature. Then, the erosion model for predicting the erosion rate by the liquid droplet impingement is proposed considering the influence of the liquid film. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nucengdes.2013.07.039

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This study examined an experimental method for locating aerodynamic sound sources from a bluff body in a stream. The sound sources are evaluated from cross-correlation analysis of the pressure fluctuations on and around the flow field and the sound pressure fluctuations. Measurements are carried out in the sound field emitted from the circular cylinder at Reynolds number Re=4×104. The pressure fluctuations around the circular cylinder are evaluated by measuring the instantaneous velocity field using particle image velocimetry combined with the pressure Poisson equation, while the sound pressure fluctuations are measured simultaneously by a microphone in the far field. The experimental results showed that sound sources were found near the flow separation on both sides of the cylinder and in the near wake. The experimental results were validated by direct measurement of the pressure fluctuations on the cylinder surface using a pressure transducer. The sound sources obtained from the cross-correlation analysis agreed well with those of the direct measurement of pressure fluctuations on the cylinder surface and those around the cylinder in previous studies. © 2013 Elsevier Ltd.

DOI： 10.1016/j.jweia.2013.04.003

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In this paper, the mechanism of asymmetric pipe-wall thinning caused by flow accelerated corrosion behind an orifice in a circular pipe is studied by measuring the velocity fields by PIV and the mass transfer coefficients by naphthalene sublimation method. An attention is placed on the variations of the velocity fields and mass flux under the combined effect of swirling flow and orifice bias. The present measurement indicates that the flow field become asymmetric about the pipe axis due to the influence of swirling flow at large swirl intensity S = 0.3 in combination with an allowable orifice bias as small as 0.8% of a pipe diameter of standard steel pipes. This flow phenomenon results in the asymmetric distribution of mass transfer coefficient along the pipe-wall behind the orifice. The position of enhanced mass transfer occurs on the shorter orifice side near the orifice due to the flow reattachment, while the flow on the longer orifice side remains the same distribution of mass transfer coefficient as the case without swirl. These variations of velocity field and mass transfer data suggest that the mechanism of asymmetric pipe-wall thinning behind the orifice is due to the combined effect of swirling flow and orifice bias. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nucengdes.2012.07.001

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In the present paper, liquid droplet impingement erosion is studied by using a high-speed spray. This experiment allows the evaluation of erosion rate of solid materials due to the impingement of liquid droplets having an order of tens of micrometer in diameter, which corresponds to those of actual conditions in nuclear power plants. The droplet properties are characterized by measuring the droplet velocity by particle image velocimetry, the diameter by shadowgraph and the number of impinging droplets in a unit area by sampling probe. The erosion rate of aluminum material by water droplets is tested by the high-speed spray in some combinations of the distances from the nozzle and droplet velocities. Although the experimental erosion rate in the far field of the nozzle is reproduced by the theoretical erosion model, the erosion rate in the near field does not. This suggests the damping effect of liquid film over the test specimen in the near field. The experimental result also indicates that the erosion rate increases in proportional to the power of 7.0 of droplet velocity in the maximum rate stage. The result indicates a certain degree of deviation from the previous experiment in literature, which may suggest the influence of the droplet diameter and the liquid film on the liquid droplet impingement erosion. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nucengdes.2012.06.022

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The time-resolved scanning stereo PIV system, which consists of a CW Nd:YAG laser, two high-speed CMOS cameras, a Galvano mirror and a pulse controller, is developed for time-sequential three-dimensional velocity field measurement of liquid flow. This experimental technique is validated by the measurement of a laminar non-buoyant jet, and is applied to the 3D velocity measurement of a highly buoyant jet at Froude number 0.3 and Reynolds number 200, which satisfy the inflow condition due to the unstable density gradient. The measurement of statistical properties of velocity field shows the growth of turbulence intensities near the nozzle exit, which indicates the presence of inflow motion near the nozzle exit due to the unstable density gradient. The vorticity contours about the horizontal axis shows the presence of counter-rotating vortices on both sides of the jet centerline, while the vorticity contour about the vertical axis indicates the presence of spiral growth of a pair of vortices along the jet centerline. The growth of the spiral structure along the jet centerline is recognized in the iso-vorticity contours obtained from the time-resolved measurement of 3D velocity field.

DOI： 10.1007/s12650-012-0129-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

A pipe-wall thinning phenomenon behind an orifice in a circular pipe is studied by measuring the mass transfer using the naphthalene sublimation method. An attention is placed on an asymmetric increase of local mass transfer behind the orifice, which is combined with the influence of swirling flow and the orifice bias. The present results indicate that the mass transfer is generally increased with an increase in swirl intensity. However, it becomes asymmetric by the combined effect of the orifice bias for the bias larger than 0.4% of the pipe diameter and the swirl intensity larger than approximately 0.2. The enhanced mass transfer is found on the shorter orifice side behind a biased orifice, and the maximum mass transfer is increased 40% in comparison with the case without swirl and orifice bias.

DOI： 10.1299/jpes.6.402

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An experimental technique for measuring a temperature field in an axisymmetric non-luminous flame is developed using the flame reaction technique combined with the inverse Abel transformation. Flame visualization is carried out using alkali metal solution of Potassium (K), which is supplied to a premixed methane/air flame in a form of spray mist. The basic principle of this technique is based on the measurement of local emission intensity distribution visualized by the flame reaction, which is a function of temperature according to the Maxwell-Boltzmann statistics of thermodynamics. The relationship between the local intensity and the temperature is obtained from the calibration study, in which the local intensity is evaluated from the line of sight intensity by the inverse Abel transformation, and the temperature is measured by thermocouple. This technique is successfully applied to the measurement of local temperature distribution in steady and flickering premixed methane/air flame. The temperature field in the flickering flame indicates that the local temperature oscillates periodically with the flickering frequency, and the highest temperature is found along the flame front and in the merging region.

DOI： 10.1007/s12650-011-0109-7

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In the present paper, the onset of inflow in the near field of a vertical buoyant jet issuing from a square duct is studied by experimental flow visualization and numerical simulation. The experimental critical condition for the onset of inflow is obtained from the scanning LIF visualization in the near field of the buoyant jet at various combinations of Froude numbers and Reynolds numbers. The experimental result shows that the critical Froude number increases with an increase in Reynolds number of the buoyant jet. The critical condition is also examined by numerical simulation based on the Navier-Stokes equation and energy conservation equation, under the assumption that the flow separation occurs at the duct exit. The main feature of the inflow observed by experiment is well reproduced in the numerical results.

DOI： 10.1007/s12650-011-0104-z

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SOC RHEOLOGY, JAPAN  

In this work, entrance flows of viscoelastic fluids from a cavity to a slot in a slot die coating were investigated experimentally and numerically. Aqueous solutions of polyethylene glycol (PEG) and polyethylene oxide (PEO) mixtures, having viscoelasticity and Newtonian viscosity, were tested in order to clarify the effects of viscoelastic characteristics to the excess pressure drops at the entrance. The measured excess pressure drop changes corresponded to the flow pattern changes from a Newtonian-like flow pattern to vortex generation and growth patterns in an asymmetric entrance flow with a submillimeter slot. Numerical predictions of the transitions in the flow patterns and the pressure drops were also made utilizing exponential Phan-Thien-Tanner (EPTT) model with a finite element method. The predictions qualitatively indicated the increase in excess pressure drop and the vortex generation and growth.

DOI： 10.1678/rheology.40.91

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In the present paper, the characteristics of liquid droplet impingement erosion are studied experimentally to propose a new model for predicting the pipe-wall thinning The spray droplets used in this study is an order of tens of micrometers in diameter. In order to obtain an accurate estimation of erosion rate, an experiment is carried out under the condition of the circular specimen in uniformly sprayed droplets. The experiments on erosion rate indicate that the wall thinning increases linearly with respect to the local droplet volume, which is measured by the sampling probe. It is found that the erosion rate is proportional to the power of 4.0 with respect to the local flow rate of the droplets. This power number is found to be equivalent to 7.2 for the droplet velocity. The present experiment also showed the influence of the liquid film on the erosion, which reduces the erosion rate of the material.

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In this paper, combined influence of swirling flows and orifice biases is investigated by a mass transfer experiment and a numerical simulation. In the mass transfer experiment, pipe wall thinning behind an orifice in a circular pipe is evaluated with benzoic acid instead of steel. In addition, a numerical simulation for velocity and concentration fields is performed to estimate mass transfer behind the orifice. The numerical simulation using the standard k-epsilon model of turbulence well reproduces the distributions of Keller coefficient behind the orifice, which agree with those of the experiment in no-swirling flows. Experimental results show asymmetric pipe wall thinning is occurred under combined influence of a swirling flow and a slight orifice bias, while a symmetric pipe wall thinning is seen in the no-swirling flows even with the orifice bias.

DOI： 10.1115/ICONE20-POWER2012-54681

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In the present paper, the inflow phenomenon in the near-field of a buoyant jet issuing from a square duct is studied by using scanning LIP and scanning Ply measurements. The scanning LIF visualization allows an insight into the critical condition of the inflow phenomenon in a wide range of Froude number and Reynolds number. While, the scanning PIV allows the quantitative information on the inflow rate through the duct exit. The experimental result shows that the critical Froude number increases with an increase in Reynolds number in the duct exit up to Reynolds number 2,000, though it is weakened at higher Reynolds number. The examination of the inflow rate indicates that the large magnitude of the inflow rate occurs in the lower Froude number and Reynolds number.

DOI： 10.1115/ICONE20-POWER2012-55245

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In this paper, the flow behavior of viscoelastic fluid in asymmetric planar contraction geometry is studied by flow visualization and PIV measurement. Experiments are carried out for three channels of different contraction widths. The experimental results indicate that the flow field in the contraction channel is characterized by the Weissenberg number to Newtonian-like flow, transitional flow and vortex formation flow. It is found that the vortex formation flow occurs over the critical Weissenberg number, which is independent of the Reynolds number. However, the critical Weissenberg number decreases with increasing the contraction width due to the influence of velocity acceleration in the entry channel in the upstream of the contraction.

DOI： 10.1299/jfst.6.1011

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The flow accelerated corrosion in a pipe is an important topic of interest associated with pipe-wall thinning phenomenon in a highly aged nuclear power plant. In the present study, the velocity field behind an orifice in a pipe is studied by PIV measurement in some combinations of swirl flow magnitudes and orifice bias. The flow observations along the flow axis and across the pipe indicate that the effect of orifice bias is not so influential on the flow behavior behind the orifice at small swirl flow magnitude. However, the asymmetrical flow pattern is observed in the flow behind the orifice at large swirl flow magnitude. The accelerated flow behind the orifice reattaches on the pipe wall of shorter orifice height and the corresponding velocity fluctuation decreases at large swirl flow magnitude, which occurs even at the small orifice bias of 0.7% of pipe diameter. This phenomenon is expected to promote the asymmetrical distribution of pipe-wall thickness due to flow accelerated corrosion in a prototype pipe flow. © 2011 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.77.386

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In the present paper, experiment on liquid droplet impinging erosion is described using high-speed spray. The droplet parameters of this phenomenon, such as droplet velocity, diameter and number of impinging droplets, are measured by using optical techniques, such as particle image velocimetry, shadowgraph and laser-light extinction method, respectively. The present measurement of droplet parameters indicates that the droplet velocity is up to 230m/s and the droplet diameter is tens of micrometers, which are expected to be those of prototype pipeline condition in nuclear power plant. The number density of impinging droplets is an order of 106-108 (mm-2s-1). The observation of erosion on a stainless steel in the laboratory test shows a pear-like surface roughness pattern having a few hundred um, which is found to be much larger than the impinging droplet diameter of a tens of um.

DOI： 10.3154/tvsj.31.63

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DOI： 10.1007/s12650-010-0058-6

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The flow accelerated corrosion in a pipe is an important topic of interest associated with pipe-wall thinning phenomenon in a highly aged nuclear power plant. In the present study, the velocity field behind an orifice in a pipe is studied by PIV measurement in some combinations of swirl flow magnitudes and orifice bias. The flow observations along the flow axis and across the pipe indicate that the effect of orifice bias is not so influential on the flow behavior behind the orifice at small swirl flow magnitude. However, the asymmetrical flow pattern is observed in the flow behind the orifice at large swirl flow magnitude. The accelerated flow behind the orifice reattaches on the pipe wall of shorter orifice height and the corresponding velocity fluctuation decreases at large swirl flow magnitude, which occurs even at the small orifice bias of 0.7% of pipe diameter. This phenomenon is expected to promote the asymmetrical distribution of pipe-wall thickness due to flow accelerated corrosion in a prototype pipe flow. © 2011 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.77.386

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In this paper, simultaneous visualization technique for temperature and velocity fields of a premixed methane air flame is described. The temperature field is visualized by the flame reaction of potassium combined with inverse Abel transformation, while the velocity field of the flame is simultaneously measured by particle image velocimetry (PIV). This new experimental technique allows an insight into the structure of temperature and velocity fields of the flickering flame. It is found that the temperature and the velocity fields in the flickering flame indicate nonlinear oscillation of the flame. During the flame flickering, the temperature in the flame fronts increases to the highest temperature in the merging region, which is followed by the entrainment of the surrounding air into the flame. This fluid motion contributes to the decrease in temperature and self-sustained oscillation of the flame. © 2011 by Begell House, Inc.

DOI： 10.1615/JFlowVisImageProc.2012003801

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The near-field structure of strongly buoyant jet issuing from a square nozzle at low Froude and Reynolds numbers is studied by using LIF flow visualization and time-resolved scanning PIV. These experimental techniques allow the visualization of unsteady three-dimensional flow phenomenon occurring in the near-field of strongly buoyant jet. It is found that the buoyant jet is unstable to the positive buoyancy forces, which promote the inflow motion near the nozzle exit. The surrounding low temperature fluid moves into the nozzle inside along the nozzle corner and mixes with the high temperature fluid deep into the nozzle. Then, the flow pattern inside the nozzle becomes highly complex to promote the laminar to turbulent transition of the jet. The statistical flow characteristics of the strongly buoyant jet are evaluated from the scanning PIV measurement, and the result indicates the presence of axisymmetric distributions of mean flow and velocity fluctuations in the circle of diameter equal to the square side of the nozzle.

DOI： 10.1007/s12650-010-0027-0

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DOI： 10.1007/s12650-010-0028-z

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This paper deals with measurement-integrated (MI) simulation, which is based on the observer in dynamical system theory to obtain the exact and detailed information of real flows. In this study, we propose the MI simulation coupled with Particle Image Velocimetry (PIV) for a flow with the Karman vortex street behind a square cylinder at Reynolds number of 1200 based on the cylinder width. The validity of the PIV-MI simulation is first examined in two-dimensional numerical experiment. The effect of feedback data rate is investigated by changing the feedback frequency and the feedback area. Then effectiveness of the PIV-MI simulation is validated in experiment. As a result, the PIV-MI simulation with full feedback shows good agreement with the standard solution for both the mean velocity and the velocity fluctuation. From the viewpoint of the reduced feedback data rate, spatially limited feedback shows better results than temporarily limited feedback. It is also confirmed that the information around the cylinder is important to reproduce the wake behind the cylinder. In the result of the experimental validation, the PIV-MI simulation reproduces the experimentally obtained flow field, showing the same effect of the feedback in accordance with the numerical experiment.

DOI： 10.1299/jfst.3.477

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This paper deals with the hybrid wind tunnel which combines wind tunnel experiment and numerical simulation to obtain the exact and detailed information of real flows. The hybrid wind tunnel, which is based on the observer theory, utilizes partial pressure measurement of a real flow for the numerical simulation. The measured pressure is included by the simulation through a feedback loop to overcome the difficulty of specifying exact boundary or initial conditions as well as the effect of modeling error. In this paper, the reproducibility of a pressure field on the hybrid wind tunnel, which treats a fundamental flow with the Karman vortex street behind a square cylinder, is investigated by comparison with pressure measurement on the side wall of the wind tunnel. As compared with ordinary simulation, mean pressure and pressure fluctuation reproduced by the hybrid wind tunnel agree well with that of experiment with large time steps which are inappropriate for ordinary simulations. Especially, the oscillation of the pressure synchronizes with that of experiment at -4<I>D</I>?x?3<I>D</I> (<I>D</I> : cylinder width) on the side wall of the wind tunnel, showing positive correlation with the experiment. The reduction of computational cost by using large time steps enables the hybrid wind tunnel to perform real time analysis of real flows.

DOI： 10.1299/kikaib.74.362

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The influence of the swirling intensity on non-axisymmetric mass transfer rate behind the orifice in a curved swirling flow is investigated experimentally. The experimental results indicate that the high mass transfer rate is observed on one side of the pipe behind the orifice in a strong swirling flow, although the mass transfer rate keeps almost axisymmetric distribution in a weak swirling flow.

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This paper presents an experimental study on the liquid droplet impingent erosion of aluminum material using the high-speed spray jet. The flow configuration studied is the pin-hole type erosion, which has the erosion depth comparatively larger than the spray width. The experimental result shows that the growth rate of the erosion is decreased with an increase in the erosion depth due to the influence of liquid film and their relationship is formulated.

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This paper describes the critical consideration on the past studies in literature related to the wall thinning rate of the metal materials due to the liquid droplet impingement erosion. It is found that the power index of droplet velocity on the wall thinning rate ranges from 6 to 8 for the water jet and spray tests, while that of the rotating disk test shows smaller power index 5.8 which is closer to the theoretical value 5. The difference in the power indices is expected due to the influence of liquid film over the test specimen.

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In the present paper, the mass transfer phenomenon behind an orifice in a pipe flow is studied by measuring the mass transfer coefficient along the pipe wall using naphthalene sublimation method. An attention is placed on the asymmetrical pipe-wall thinning behind an orifice under the influence of swirling-flow intensity and allowable orifice bias. The present measurement indicates that the mass transfer coefficient becomes asymmetric about the pipe axis by the combined effect of swirling flow and allowable orifice bias. It is found that the enhancement of mass transfer coefficient is observed on the shorter side of the orifice plate and the reduction is found on the opposite side. This phenomenon is found to be consistent with the flow-field observation in the previous study.

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In the present paper, an experimental technique for measuring flame temperature contour is proposed using the flame reaction. This method allows the temperature measurement by visualizing the flame by the luminescence of Na supplied to the form of mist. An example of temperature measurement is shown for the premixed flickering flame of methane and air. The results indicate the unsteady behavior of the temperature contour during the flickering motion.

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Inflow phenomenon in near field of buoyant jet issuing into still surrounding of water is studied experimentally and numerically. The experimental visualization is carried out using 3D LIF technique, which visualizes the three-dimensional inflow phenomenon in the near field of buoyant jet. It is found from the experiment that the inflow phenomenon starts in the near field of buoyant jet when the Froude number becomes lower than the critical inflow condition. In order to understand the physics of inflow phenomenon, numerical simulation is carried out. The numerical result reproduces well the critical inflow condition observed by experiment. With further decrease in Froude and Reynolds numbers, the vigorous fluid mixing is found in the experiment, which is due to the appearance of turbulence in the jet caused by the inflow phenomenon.

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DOI： 10.1299/jsmehs.2010.47.475

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In the present paper, the erosion rate due to liquid droplet impingement has been evaluated in a small diameter range of tens of micrometers using the newly developed spray-jet apparatus. The erosion rate of aluminum material is tested with respect to the droplet parameters, such as the droplet velocity, the diameter and the number density, which are measured by optical imaging techniques. It is found that the non-dimensional erosion rate increases in proportional to the 5th power of droplet velocity, which agrees closely with that of previous study using large droplet diameters.

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This paper deals with the hybrid wind tunnel which combines wind tunnel experiment and numerical simulation to obtain the exact and detailed information of real flows. The hybrid wind tunnel, which is based on the observer theory, utilizes partial pressure measurement of a real flow for the numerical simulation. The measured pressure is included by the simulation through a feedback loop to overcome the difficulty of specifying exact boundary or initial conditions as well as the effect of modeling error. In this paper, the reproducibility of a pressure field on the hybrid wind tunnel, which treats a fundamental flow with the Karman vortex street behind a square cylinder, is investigated by comparison with pressure measurement on the side wall of the wind tunnel. As compared with ordinary simulation, mean pressure and pressure fluctuation reproduced by the hybrid wind tunnel agree well with that of experiment with large time steps which are inappropriate for ordinary simulations. Especially, the oscillation of the pressure synchronizes with that of experiment at -4D≦x≦3D (D: cylinder width) on the side wall of the wind tunnel, showing positive correlation with the experiment. The reduction of computational cost by using large time steps enables the hybrid wind tunnel to perform real time analysis of real flows.

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This study deals with the hybrid wind tunnel which combines wind tunnel experiment and numerical simulation to obtain the exact and detailed information of real flows. The hybrid wind tunnel based on the observer theory utilizes partial information of the real flow from pressure measurement for the numerical simulation through a feedback loop to overcome the difficulty of specifying exact boundary or initial conditions as well as the effect of modeling error. In previous two-dimensional analyses on the hybrid wind tunnel, the difference between computation and experiment in regard to perturbation velocity increased with the computational grid of a high resolution due to the inappropriateness of the two-dimensional model. In this paper, three-dimensional analyses with three grid systems of different resolutions are performed on the hybrid wind tunnel for a fundamental flow with the Karman vortex street behind a square cylinder. The reproducibility of a velocity field on the hybrid wind tunnel is improved in three-dimensional analysis by using the high resolution grid system. In addition, three-dimensional analysis with the coarse grid system on the hybrid wind tunnel effectively reduces the error due to the insufficient grid resolution for ordinary numerical simulation.

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Numerical simulation and experiment are important tools in flow analysis, but they have advantages and disadvantages. We have proposed Measurement-Integrated simulation that integrates numerical simulation and measurement to reproduce the real flows. This new methodology reproduced the velocity field of Karman vortex street behind a square cylinder in far better agreement with the real flow than the ordinary simulation. In this paper, the pressure field obtained by the MI simulation is validated in comparison with pressure measurement on the sidewall of the wind tunnel. Results show the MI simulation successfully reproduces the pressure oscillation near the cylinder although the root-mean-square pressure is degraded in the downstream region. In addition, the pressure field of Karman vortex street is analyzed and visualized in real-time using the hybrid wind tunnel.

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Detailed information of the velocity and pressure field of the blood flow is essential to establish an advanced diagnosis and treatment of serious circulatory diseases. Commonly used medical measurement equipments does not provide complete information of blood flow in real-time. In this report, we develop a new blood flow measurement system applying Ultrasonic- Measurement-Integrated (UMI) simulation, that integrates ultrasonography and numerical simulation. The system consists of ultrasonic diagnostic imaging equipment, a graphics workstation, and a calculation server. Computer programs for measurement data acquisition, flow simulation, and visualization are synchronized using socket communication scheme. By considering blood flow velocity measured, the system adjusted the phase of a flow rate waveform automatically to match the cycle of pulsation in real diagnostic images.

DOI： 10.1299/jsmemecjo.2005.5.0_91

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Language：Japanese   Publisher：日本流体力学会  

In order to understand precise frictional characteristics of the red blood cells in blood capillaries, the inclined centrifuge microscope has been developed, and the frictional characteristics of blood cells on a glass plate were measured as the first step. In that research, it was the subject of discussion whether the cells glide or roll on the glass plate since the resolution of the microscope was not sufficient to distinguish the cell motion. This report deals with improvement of the observation technique for cell motion. The magnification of the inclined centrifuge microscope is increased by 5 times. The shape of red blood cells under movement can be seen clearly and cells seem to glide on the glass plate, although it is still difficult to exclude the possibility of cell rolling.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, the simulation of the cavitating jet flow which is the high speed submerged jet and spouting from nozzle is carried out, and the effects of the nozzle parallel section length on the cavitating jet is examined by the discrete vortex method the calculating results on high Reynolds number also tend to become stable easily. The result shows that the nozzle length the clear vortex structure keeps downstream exists.

DOI： 10.1299/jsmemecjo.2002.3.0_243

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