Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-5593
Daiki Makii, H. Sasaki, Y. Iga
Cavitation is a phenomenon in which phase change occurs in a liquid by pressure decrease due to flow acceleration. The phase change is caused by mainly evaporation of the liquid but sometimes by liberation of dissolved non-condensable gas in the liquid. In particular, unsteady cavitation causes vibration, noise, erosion and performance deterioration, which has been a serious problem in the development of fluid machinery. Therefore, it is important to research the characteristics of cavitation generation and develop methods to suppress or control it. In the current CFD (computational fluid dynamics) model of cavitating flow, the saturated vapor pressure has been used as a criterion for determining the cavitation generation or disappearance based on the idea of phase equilibrium, however it is well known that these calculation results don’t agree well with experimental results. For example, it is reported that the cavitation inception pressure is higher than its saturated vapor pressure in water. This is predicted to be resulting from the generation of gaseous cavitation which is caused by liberation of dissolved air, however this has not been taken into consideration in the current CFD model. Here, liberation of non-condensable gas is supposed to be treated by MD (molecular dynamics) then it is not suitable for CFD. Thus, in order to develop a more accurate CFD model for cavitating flow, it is necessary to develop a macroscopic and coarse-grained model of liberation should be developed, which may be related to flow dynamic-stimulation of the unsteady flow field with cavitation. In the present study, we focus attention on relationship between liberation of dissolved gas and unsteadiness of cavitation. Experiment is conducted in high-temperature water cavitation tunnel in which in-situ measurement of the amount of dissolved oxygen can be performed during the operation with cavitation. The variation of dissolved oxygen is used as one of the indexes of liberation of dissolved non-condensable gas during the experiment. The degree of cavitation unsteadiness is judged by calculation based on the FFT (Fast Fourier Transform) of the downstream fluctuation pressure and the RMS (root mean square) of brightness value using images taken with a high-speed camera. In addition, in order to eliminate the factors of dissolved gas liberation other than cavitation unsteadiness, the mainstream pressure, the mainstream temperature and volume of the cavity are made to be equal, respectively. Under the above preconditions, the time evolution of dissolved oxygen amount is measured in several kinds of cavitating flow fields around NACA0015 and NACA16012 hydrofoils.
{"title":"In-Situ Measurement of Liberation of a Dissolved Gas in Unsteady Cavitating Flow in Water","authors":"Daiki Makii, H. Sasaki, Y. Iga","doi":"10.1115/ajkfluids2019-5593","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5593","url":null,"abstract":"\u0000 Cavitation is a phenomenon in which phase change occurs in a liquid by pressure decrease due to flow acceleration. The phase change is caused by mainly evaporation of the liquid but sometimes by liberation of dissolved non-condensable gas in the liquid. In particular, unsteady cavitation causes vibration, noise, erosion and performance deterioration, which has been a serious problem in the development of fluid machinery. Therefore, it is important to research the characteristics of cavitation generation and develop methods to suppress or control it.\u0000 In the current CFD (computational fluid dynamics) model of cavitating flow, the saturated vapor pressure has been used as a criterion for determining the cavitation generation or disappearance based on the idea of phase equilibrium, however it is well known that these calculation results don’t agree well with experimental results. For example, it is reported that the cavitation inception pressure is higher than its saturated vapor pressure in water. This is predicted to be resulting from the generation of gaseous cavitation which is caused by liberation of dissolved air, however this has not been taken into consideration in the current CFD model. Here, liberation of non-condensable gas is supposed to be treated by MD (molecular dynamics) then it is not suitable for CFD. Thus, in order to develop a more accurate CFD model for cavitating flow, it is necessary to develop a macroscopic and coarse-grained model of liberation should be developed, which may be related to flow dynamic-stimulation of the unsteady flow field with cavitation.\u0000 In the present study, we focus attention on relationship between liberation of dissolved gas and unsteadiness of cavitation. Experiment is conducted in high-temperature water cavitation tunnel in which in-situ measurement of the amount of dissolved oxygen can be performed during the operation with cavitation. The variation of dissolved oxygen is used as one of the indexes of liberation of dissolved non-condensable gas during the experiment. The degree of cavitation unsteadiness is judged by calculation based on the FFT (Fast Fourier Transform) of the downstream fluctuation pressure and the RMS (root mean square) of brightness value using images taken with a high-speed camera. In addition, in order to eliminate the factors of dissolved gas liberation other than cavitation unsteadiness, the mainstream pressure, the mainstream temperature and volume of the cavity are made to be equal, respectively. Under the above preconditions, the time evolution of dissolved oxygen amount is measured in several kinds of cavitating flow fields around NACA0015 and NACA16012 hydrofoils.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125137784","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-4782
Shota Moriguchi, T. Endo, Hironori Miyazawa, Takashi Furusawa, S. Yamamoto
In this study, we numerically investigated moist-air flow through the transonic compressor rotors of NASA Rotor 37, assuming whole-annulus rotor blade rows and non-uniform inlet wetness. This is an extension of our previous study, which assumed only a single passage and uniform inlet wetness. The amount of water droplets streaming into the compressor was changed in circumferentially non-uniform inlet condition. Numerical results indicated that non-uniform inlet wetness induced non-uniform temperature in the passages due to absorption of latent heat by droplet evaporation. Moreover, shock locations varied, depending on the local amount of wetness. Furthermore, turning angles of the flow and torque on the rotor blades were influenced by the wetness. Therefore, unsteady forces on the rotor blades were resultantly obtained by considering non-uniform inlet wetness conditions.
{"title":"Numerical Simulation of Unsteady Moist-Air Flows Through Whole-Annulus Rotor Blade Rows in Transonic Compressor","authors":"Shota Moriguchi, T. Endo, Hironori Miyazawa, Takashi Furusawa, S. Yamamoto","doi":"10.1115/ajkfluids2019-4782","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4782","url":null,"abstract":"\u0000 In this study, we numerically investigated moist-air flow through the transonic compressor rotors of NASA Rotor 37, assuming whole-annulus rotor blade rows and non-uniform inlet wetness. This is an extension of our previous study, which assumed only a single passage and uniform inlet wetness. The amount of water droplets streaming into the compressor was changed in circumferentially non-uniform inlet condition. Numerical results indicated that non-uniform inlet wetness induced non-uniform temperature in the passages due to absorption of latent heat by droplet evaporation. Moreover, shock locations varied, depending on the local amount of wetness. Furthermore, turning angles of the flow and torque on the rotor blades were influenced by the wetness. Therefore, unsteady forces on the rotor blades were resultantly obtained by considering non-uniform inlet wetness conditions.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129389377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-5528
J. Onishi, N. Shikazono
Numerical simulation of drop motion on surfaces with micro patterns is conducted. The results are compared with existing experimental and analytical studies to validate the reliability of the numerical simulations. In the comparison of the liquid phase morphology on a surface with straight grooves, it is confirmed that a variety of liquid shapes, including droplets, filaments with positive/negative Laplace pressure and so on are successfully reproduced by the numerical simulation. Moreover, the numerically observed transition between these morphologies in a broad range of the groove aspect ratio and the static contact angle agrees with the morphology diagram which is obtained by a semi-analytic approach based on the surface free energy minimization. Furthermore, in the comparison of the spreading behaviors of a liquid drop on a surface with square pillars, it is shown that the numerical simulations can predict the time-dependent drop deformation during the spreading process. The comparison of the length of two spreading modes shows a quantitative agreement with the experimental results.
{"title":"Validation of Numerical Simulation of Drop Motion on Surfaces With Micro Patterns","authors":"J. Onishi, N. Shikazono","doi":"10.1115/ajkfluids2019-5528","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5528","url":null,"abstract":"\u0000 Numerical simulation of drop motion on surfaces with micro patterns is conducted. The results are compared with existing experimental and analytical studies to validate the reliability of the numerical simulations. In the comparison of the liquid phase morphology on a surface with straight grooves, it is confirmed that a variety of liquid shapes, including droplets, filaments with positive/negative Laplace pressure and so on are successfully reproduced by the numerical simulation. Moreover, the numerically observed transition between these morphologies in a broad range of the groove aspect ratio and the static contact angle agrees with the morphology diagram which is obtained by a semi-analytic approach based on the surface free energy minimization. Furthermore, in the comparison of the spreading behaviors of a liquid drop on a surface with square pillars, it is shown that the numerical simulations can predict the time-dependent drop deformation during the spreading process. The comparison of the length of two spreading modes shows a quantitative agreement with the experimental results.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"103 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124975689","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-4840
Yuki Furuya, T. Sanada, Masao Watanabe
Wet cleaning methods using fluid are widely applied in many industrial fields. For a cleaning inside closed-end holes, it is first necessary to fill the holes to be cleaned with the liquid. However, in structures with small holes, it is difficult to discharge inside the gas due to surface tension. In our early studies, we have found that the discharging a gas inside a closed-end hole was promoted by an impingement of droplet train. And the pressure fluctuation near the gas-liquid interface due to droplet impingement was important. In this study, we attempted the gas discharge from closed-end holes due to acoustic wave irradiation. First, we theoretically estimated the oscillation of the gas column inside the hole during acoustic wave irradiation. We modeled the natural frequency of the gas column using a spring-mass system. Then we experimentally measured the fluctuation of the gas-liquid interface for the evaluation of the model. In addition, we compared the gas discharge ratio with different frequency and pressure level. The fluctuation of gas-liquid interface and discharging the gas were observed with a high-speed video camera. As results, the natural frequencies of a gas column were depending on the length of the gas column and the diameter of the hole. From the experiments, we confirmed that the acoustic wave certainly propagated into the hole, and the frequency of the irradiated acoustic wave and the experimentally obtained natural frequency were in good agreement except for extremely low gas discharge ratio condition. Moreover, we observed gas discharge process and found that the high gas discharge ratio were achieved using the acoustic wave close to natural frequency. From these results, we concluded that the assumption based on a spring-mass system is valid.
{"title":"A Model for a Gas Column Oscillation Inside a Hole by Irradiating an Acoustic Wave","authors":"Yuki Furuya, T. Sanada, Masao Watanabe","doi":"10.1115/ajkfluids2019-4840","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4840","url":null,"abstract":"\u0000 Wet cleaning methods using fluid are widely applied in many industrial fields. For a cleaning inside closed-end holes, it is first necessary to fill the holes to be cleaned with the liquid. However, in structures with small holes, it is difficult to discharge inside the gas due to surface tension. In our early studies, we have found that the discharging a gas inside a closed-end hole was promoted by an impingement of droplet train. And the pressure fluctuation near the gas-liquid interface due to droplet impingement was important.\u0000 In this study, we attempted the gas discharge from closed-end holes due to acoustic wave irradiation. First, we theoretically estimated the oscillation of the gas column inside the hole during acoustic wave irradiation. We modeled the natural frequency of the gas column using a spring-mass system. Then we experimentally measured the fluctuation of the gas-liquid interface for the evaluation of the model. In addition, we compared the gas discharge ratio with different frequency and pressure level. The fluctuation of gas-liquid interface and discharging the gas were observed with a high-speed video camera.\u0000 As results, the natural frequencies of a gas column were depending on the length of the gas column and the diameter of the hole. From the experiments, we confirmed that the acoustic wave certainly propagated into the hole, and the frequency of the irradiated acoustic wave and the experimentally obtained natural frequency were in good agreement except for extremely low gas discharge ratio condition. Moreover, we observed gas discharge process and found that the high gas discharge ratio were achieved using the acoustic wave close to natural frequency. From these results, we concluded that the assumption based on a spring-mass system is valid.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"37 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128418224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-4882
W. Strasser
Under certain conditions in preferred three-stream geometries, a non-Newtonian airblast atomization flowfield violently pulses (axially and radially) by self-generating and self-sustaining interfacial instability mechanisms. The pulsing is severe enough to send acoustic waves throughout feed piping networks. The most recent work on this system instructed that exothermic chemical reactions enhance this moderate Mach number atomization. Explored herein is the potential to further enhance reaction-assisted disintegration by independently superimposing both sinusoidal and randomized mass flow fluctuations of +/− 50% of the mean onto otherwise constant gas feed streams. Two nozzle geometries (low versus high prefilming distance) and multiple superimposed feed frequencies (ranging from below to above the naturally dominant tone) are considered for each gas stream, making twenty-one total long-running unsteady PLIC-VOF CFD models. Droplet size, plus nine other temporal measures, were considered for assessing atomizer performance in our energy production process. Results indicate that superimposed frequencies have potential to enhance chaotic atomization in a statistically significant manner. Depending on the geometry, the largest effect was about a 10% reduction in droplet size; however, some combinations experienced a droplet size increase. Only marginal differences were seen in the nine other measures, such as injector face heat exposure. In addition to the immediate industrial benefit from modulation, dramatic changes in acoustics were produced by imposed feed perturbations at frequencies lower than the natural tone. A detailed study of start-up flow reveals new mechanisms which explain performance differences.
{"title":"Can Naturally Pulsating Prefilming Slurry Atomization Be Enhanced by Artificial External Modulation?","authors":"W. Strasser","doi":"10.1115/ajkfluids2019-4882","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4882","url":null,"abstract":"\u0000 Under certain conditions in preferred three-stream geometries, a non-Newtonian airblast atomization flowfield violently pulses (axially and radially) by self-generating and self-sustaining interfacial instability mechanisms. The pulsing is severe enough to send acoustic waves throughout feed piping networks. The most recent work on this system instructed that exothermic chemical reactions enhance this moderate Mach number atomization. Explored herein is the potential to further enhance reaction-assisted disintegration by independently superimposing both sinusoidal and randomized mass flow fluctuations of +/− 50% of the mean onto otherwise constant gas feed streams. Two nozzle geometries (low versus high prefilming distance) and multiple superimposed feed frequencies (ranging from below to above the naturally dominant tone) are considered for each gas stream, making twenty-one total long-running unsteady PLIC-VOF CFD models. Droplet size, plus nine other temporal measures, were considered for assessing atomizer performance in our energy production process. Results indicate that superimposed frequencies have potential to enhance chaotic atomization in a statistically significant manner. Depending on the geometry, the largest effect was about a 10% reduction in droplet size; however, some combinations experienced a droplet size increase. Only marginal differences were seen in the nine other measures, such as injector face heat exposure. In addition to the immediate industrial benefit from modulation, dramatic changes in acoustics were produced by imposed feed perturbations at frequencies lower than the natural tone. A detailed study of start-up flow reveals new mechanisms which explain performance differences.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116231468","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-5167
Aniket S. Ambekar, Shabina Ashraf, J. Phirani
Imbibition of viscous fluids in capillaries is important in diagnostics, design of microfluidic devices and enhanced oil recovery. The imbibition of a viscous wetting fluid in a capillary follows Lucas-Washburn law. The Lucas-Washburn regime is only observed when the viscous forces are balanced by the capillary forces. This has been previously described for capillary driven flow as a function of the Ohnesorge number (Oh), the length imbibed by the fluid (x) and the radius (r), for a capillary initially filled with fluid of negligible viscosity, i.e., Ohxr∼1. We show using VOF simulations that, in a capillary of length L initially filled with a viscous fluid, the modified Lucas-Washburn law is observed only if the criterion OhLr∼1 is fulfilled. We use VOF simulations to show the deviation of capillary driven flow from the classical Lucas-Washburn behavior for OhLr∼0.1. VOF simulations for forced imbibition in the regime preceding the Lucas-Washburn regime for a single capillary show that with increase in the applied pressure, the advancement of the meniscus is faster. Forced imbibition dynamics in the interacting capillary geometry are also investigated in this study using VOF simulations. We observe that the leading meniscus in the interacting capillaries is significantly dependent on the applied pressures. We also show using VOF simulations that the wettability of the imbibing fluid plays a crucial role in determining the dynamics in an interacting capillary system.
{"title":"Dynamics of Forced Imbibition in Interacting Pores","authors":"Aniket S. Ambekar, Shabina Ashraf, J. Phirani","doi":"10.1115/ajkfluids2019-5167","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5167","url":null,"abstract":"\u0000 Imbibition of viscous fluids in capillaries is important in diagnostics, design of microfluidic devices and enhanced oil recovery. The imbibition of a viscous wetting fluid in a capillary follows Lucas-Washburn law. The Lucas-Washburn regime is only observed when the viscous forces are balanced by the capillary forces. This has been previously described for capillary driven flow as a function of the Ohnesorge number (Oh), the length imbibed by the fluid (x) and the radius (r), for a capillary initially filled with fluid of negligible viscosity, i.e., Ohxr∼1. We show using VOF simulations that, in a capillary of length L initially filled with a viscous fluid, the modified Lucas-Washburn law is observed only if the criterion OhLr∼1 is fulfilled. We use VOF simulations to show the deviation of capillary driven flow from the classical Lucas-Washburn behavior for OhLr∼0.1. VOF simulations for forced imbibition in the regime preceding the Lucas-Washburn regime for a single capillary show that with increase in the applied pressure, the advancement of the meniscus is faster. Forced imbibition dynamics in the interacting capillary geometry are also investigated in this study using VOF simulations. We observe that the leading meniscus in the interacting capillaries is significantly dependent on the applied pressures. We also show using VOF simulations that the wettability of the imbibing fluid plays a crucial role in determining the dynamics in an interacting capillary system.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126508562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-4632
M. Pace, K. Matveev
Air cavities employed under ship hulls can result in significant decrease of the water frictional drag by reducing the hull wetted area. However, these cavities usually perform well only in a limited range of the ship speed and attitude. In off-design states and in the presence of sea waves, efficient air cavities covering large areas of the hull are difficult to form and maintain. This problem can be potentially addressed with help of hydrodynamic actuators, such as compact hydrofoils, tabs, and spoilers, which can assist with forming and maintaining air cavities under ship hulls. In this study, exploratory tests have been conducted with a simplistic small-scale hull having a bottom recess. Air was supplied into the recess to produce an air cavity, and several actuators were implemented and manually controlled during the tests. Subjected to external water flow, the air cavity under the hull was found to be responsive to variable positions of the actuators. Positive effects on the air cavity produced with specific actuator settings are identified and discussed in the paper. A series of experimental photographs of the air-water interface are shown for various actuator settings. The air flow rates needed to establish and maintain a large air cavity under the model hull are also reported.
{"title":"Modification of Air Cavity Flow Under Model Hull With Hydrodynamic Actuators","authors":"M. Pace, K. Matveev","doi":"10.1115/ajkfluids2019-4632","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4632","url":null,"abstract":"\u0000 Air cavities employed under ship hulls can result in significant decrease of the water frictional drag by reducing the hull wetted area. However, these cavities usually perform well only in a limited range of the ship speed and attitude. In off-design states and in the presence of sea waves, efficient air cavities covering large areas of the hull are difficult to form and maintain. This problem can be potentially addressed with help of hydrodynamic actuators, such as compact hydrofoils, tabs, and spoilers, which can assist with forming and maintaining air cavities under ship hulls. In this study, exploratory tests have been conducted with a simplistic small-scale hull having a bottom recess. Air was supplied into the recess to produce an air cavity, and several actuators were implemented and manually controlled during the tests. Subjected to external water flow, the air cavity under the hull was found to be responsive to variable positions of the actuators. Positive effects on the air cavity produced with specific actuator settings are identified and discussed in the paper. A series of experimental photographs of the air-water interface are shown for various actuator settings. The air flow rates needed to establish and maintain a large air cavity under the model hull are also reported.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"144 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128330676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-5290
Hiroaki Kusuno, T. Sanada
The aim of this study is to investigate a velocity distribution of velocity boundary layer on a spherical bubble using numerical simulation and to compare the results with the theoretical model. In this study, we calculated the axisymmetric flow around a spherical bubble, the Reynolds number ranged from 50–1000. We selected Navier-Stokes equations written in the vorticitystream function to capture small vorticity generated on the bubble surface. We described bubble surface with boundary-fitted coordinate system. As a preliminary test, we guaranteed the accuracy of calculation method adopted in this study. Previous study showed that it needs three calculation points in the theoretical boundary layer to describe the boundary layer with second order accuracy. Our study, however, shows that the it needs seven points to describe the boundary layer even if forth order accuracy. We compared the velocity distribution of numerical result to that of theoretical model. The velocity in the vicinity of bubble is divided into potential solution and perturbed velocity component. At bubble side, the absolute value of the perturbation velocity estimated by numerical result is slightly larger than that of the theoretical model in any Reynolds numbers. When we defined bubble boundary layer thickness as the region below to 99% velocity of the potential solution, we find that value of the boundary layer thickness proposed in this study is two to three times larger than that of theoretical model. In the vicinity of the rear stagnant region (i.e. in the wake of bubble), numerical and the theoretical velocity distribution does not match at all.
{"title":"A Computational Estimation of Velocity Distribution of Boundary Layer on a Spherical Bubble","authors":"Hiroaki Kusuno, T. Sanada","doi":"10.1115/ajkfluids2019-5290","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5290","url":null,"abstract":"\u0000 The aim of this study is to investigate a velocity distribution of velocity boundary layer on a spherical bubble using numerical simulation and to compare the results with the theoretical model. In this study, we calculated the axisymmetric flow around a spherical bubble, the Reynolds number ranged from 50–1000. We selected Navier-Stokes equations written in the vorticitystream function to capture small vorticity generated on the bubble surface. We described bubble surface with boundary-fitted coordinate system.\u0000 As a preliminary test, we guaranteed the accuracy of calculation method adopted in this study. Previous study showed that it needs three calculation points in the theoretical boundary layer to describe the boundary layer with second order accuracy. Our study, however, shows that the it needs seven points to describe the boundary layer even if forth order accuracy.\u0000 We compared the velocity distribution of numerical result to that of theoretical model. The velocity in the vicinity of bubble is divided into potential solution and perturbed velocity component. At bubble side, the absolute value of the perturbation velocity estimated by numerical result is slightly larger than that of the theoretical model in any Reynolds numbers. When we defined bubble boundary layer thickness as the region below to 99% velocity of the potential solution, we find that value of the boundary layer thickness proposed in this study is two to three times larger than that of theoretical model. In the vicinity of the rear stagnant region (i.e. in the wake of bubble), numerical and the theoretical velocity distribution does not match at all.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130524827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-5030
A. Kendoush
Phenomenological equations derived for the convective heat and mass transfer to Taylor bubbles (TB) rising in vertical cylindrical pipes. Three models presented; first for the bubble thin liquid layer region, second for the rounded nose region, and third for the wake region. The solution is confined to flat-ended Taylor bubbles under laminar flow and constant heat flux conditions. The results compared reasonably well with the experimental data of other investigators.
{"title":"Phenomenological Prediction of Convective Heat and Mass Transfer to Taylor Bubbles Rising in Vertical Pipes","authors":"A. Kendoush","doi":"10.1115/ajkfluids2019-5030","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5030","url":null,"abstract":"\u0000 Phenomenological equations derived for the convective heat and mass transfer to Taylor bubbles (TB) rising in vertical cylindrical pipes. Three models presented; first for the bubble thin liquid layer region, second for the rounded nose region, and third for the wake region. The solution is confined to flat-ended Taylor bubbles under laminar flow and constant heat flux conditions. The results compared reasonably well with the experimental data of other investigators.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114651998","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-4972
Lile Cao, R. Ito, T. Degawa, Y. Matsuda, K. Takamure, T. Uchiyama
This study experimentally investigates the mixing of a two-layer density-stratified fluid of water (upper layer) and aqueous sodium chloride (NaCl) solution (lower layer) induced by the interaction between a vortex ring and the density interface. The vortex ring, which consists of water, is launched from an orifice in the upper layer toward the density interface, after which its motion, along with the behavior of the lower fluid, is visualized through a planar laser-induced fluorescence method. The Atwood number that expresses the nondimensional density jump across the density interface is set at 0.0055, and the Reynolds number Re of the vortex ring is varied from 2050 to 3070. The visualization experiment clarifies that the vortex ring penetrating the density interface is bounced while collapsing in the lower fluid. Furthermore, it elucidates that the bounced upper fluid entrains the lower fluid into the upper layer by inducing a second vortex ring consisting of the lower fluid. Thus, this study reveals the effect of Re on the mixing of the upper and lower fluid induced by the launched vortex ring.
{"title":"Experimental Study of Mixing of Two-Layer Density-Stratified Fluid by a Vortex Ring","authors":"Lile Cao, R. Ito, T. Degawa, Y. Matsuda, K. Takamure, T. Uchiyama","doi":"10.1115/ajkfluids2019-4972","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4972","url":null,"abstract":"\u0000 This study experimentally investigates the mixing of a two-layer density-stratified fluid of water (upper layer) and aqueous sodium chloride (NaCl) solution (lower layer) induced by the interaction between a vortex ring and the density interface. The vortex ring, which consists of water, is launched from an orifice in the upper layer toward the density interface, after which its motion, along with the behavior of the lower fluid, is visualized through a planar laser-induced fluorescence method. The Atwood number that expresses the nondimensional density jump across the density interface is set at 0.0055, and the Reynolds number Re of the vortex ring is varied from 2050 to 3070. The visualization experiment clarifies that the vortex ring penetrating the density interface is bounced while collapsing in the lower fluid. Furthermore, it elucidates that the bounced upper fluid entrains the lower fluid into the upper layer by inducing a second vortex ring consisting of the lower fluid. Thus, this study reveals the effect of Re on the mixing of the upper and lower fluid induced by the launched vortex ring.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130011982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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