Pub Date : 2019-11-20DOI: 10.1115/ajkfluids2019-4774
Taiki Maeda, T. Kanagawa
The present study theoretically carries out a derivation of the Korteweg–de Vries–Burgers (KdVB) equation and the nonlinear Schrödinger (NLS) equation for weakly nonlinear propagation of plane (i.e., one-dimensional) progressive waves in water flows containing many spherical gas bubbles that oscillate due to the pressure wave approaching the bubble. Main assumptions are as follows: (i) bubbly liquids are not at rest initially; (ii) the bubble does not coalesce, break up, extinct, and appear; (iii) the viscosity of the liquid phase is taken into account only at the bubble–liquid interface, although that of the gas phase is omitted; (iv) the thermal conductivities of the gas and liquid phases are dismissed. The basic equations for bubbly flows are composed of conservation equations for mass and momentum for the gas and liquid phases in a two-fluid model, the Keller-Miksis equation (i.e., the equation for radial oscillations as the expansion and contraction), and so on. By using the method of multiple scales and the determination of size of three nondimensional ratios that are wavelength, propagation speed and incident wave frequency, we can derive two types of nonlinear wave equations describing long range propagation of plane waves. One is the KdVB equation for a low frequency long wave, and the other is the NLS equation for an envelope wave for a moderately high frequency short carrier wave.
{"title":"An Effect of Flow Velocity on Propagation Properties of Weakly Nonlinear Waves in Bubbly Flows","authors":"Taiki Maeda, T. Kanagawa","doi":"10.1115/ajkfluids2019-4774","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4774","url":null,"abstract":"\u0000 The present study theoretically carries out a derivation of the Korteweg–de Vries–Burgers (KdVB) equation and the nonlinear Schrödinger (NLS) equation for weakly nonlinear propagation of plane (i.e., one-dimensional) progressive waves in water flows containing many spherical gas bubbles that oscillate due to the pressure wave approaching the bubble. Main assumptions are as follows: (i) bubbly liquids are not at rest initially; (ii) the bubble does not coalesce, break up, extinct, and appear; (iii) the viscosity of the liquid phase is taken into account only at the bubble–liquid interface, although that of the gas phase is omitted; (iv) the thermal conductivities of the gas and liquid phases are dismissed. The basic equations for bubbly flows are composed of conservation equations for mass and momentum for the gas and liquid phases in a two-fluid model, the Keller-Miksis equation (i.e., the equation for radial oscillations as the expansion and contraction), and so on. By using the method of multiple scales and the determination of size of three nondimensional ratios that are wavelength, propagation speed and incident wave frequency, we can derive two types of nonlinear wave equations describing long range propagation of plane waves. One is the KdVB equation for a low frequency long wave, and the other is the NLS equation for an envelope wave for a moderately high frequency short carrier wave.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117232031","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-4776
R. Akutsu, T. Kanagawa, Y. Uchiyama
The present paper theoretically treats weakly nonlinear propagation of plane progressive waves in an initially quiescent compressible liquid containing a tremendously large number of spherical gas bubbles, focusing on the derivation of an amplitude evolution equation (i.e., nonlinear wave equation). We emphasize the following points: (i) the compressibility of the liquid phase, which has long been neglected, is considered; (ii) the wave propagates with a large phase velocity exceeding the speed of sound in pure water; (iii) bubbles are not created or annihilated. From the method of multiple scales with an appropriate scaling of three nondimensional parameters, we can derive an attenuated nonlinear Schrödinger (NLS) equation, where the phase velocity is larger than the speed of sound in a pure liquid.
{"title":"Derivation of an Amplitude Equation for Weakly Nonlinear Pressure Waves of a Very High Frequency in a Compressible Liquid Containing Many Microbubbles","authors":"R. Akutsu, T. Kanagawa, Y. Uchiyama","doi":"10.1115/ajkfluids2019-4776","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4776","url":null,"abstract":"\u0000 The present paper theoretically treats weakly nonlinear propagation of plane progressive waves in an initially quiescent compressible liquid containing a tremendously large number of spherical gas bubbles, focusing on the derivation of an amplitude evolution equation (i.e., nonlinear wave equation). We emphasize the following points: (i) the compressibility of the liquid phase, which has long been neglected, is considered; (ii) the wave propagates with a large phase velocity exceeding the speed of sound in pure water; (iii) bubbles are not created or annihilated. From the method of multiple scales with an appropriate scaling of three nondimensional parameters, we can derive an attenuated nonlinear Schrödinger (NLS) equation, where the phase velocity is larger than the speed of sound in a pure liquid.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122485528","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-4655
G. Haider, Alireza Asgharpour, Jun Zhang, S. Shirazi
During production of oil and gas from wells, solid particles such as removed scales or sand may accompany petroleum fluids. These particles present in this multiphase flow can impact inner walls of transportation infrastructure (straight pipelines, elbows, T-junctions, flow meters, and reducers) multiple times. These repeated impacts degrades the inner walls of piping and as a result, reduce wall thickness occur. This is known as solid particle erosion, which is a complex phenomenon involving multiple contributing factors. Prediction of erosion rates and location of maximum erosion are crucial from both operations and safety perspective. Various mechanistic and empirical solid particle erosion models are available in literature for this purpose. The majority of these models require particle impact speed and impact angle to model erosion. Furthermore, due to complex geometric shapes of process equipment, these solid particles can impact and rebound from walls in a random manner with varying speeds and angles. Hence, this rebound characteristic is an important factor in solid particle erosion modeling which cannot be done in a deterministic sense. This challenge has not been addressed in literature satisfactorily. This study uses experimental data to model particle rebound characteristics stochastically. Experimental setup consists of a nozzle and specimen, which are aligned at different angles so particles impact the specimen at various angles. Information regarding particle impact velocities before and after the impacts are obtained through Particle Tracking Velocimetry (PTV) technique. Distributions of normal and tangential components of particle velocities were determined experimentally. Furthermore, spread or dispersion in these velocity components due to randomness is quantified. Finally, based on these experimental observations, a stochastic rebound model based on normal and tangential coefficients of restitutions is developed and Computational Fluid Dynamics (CFD) studies were conducted to validate this model. The model predictions are compared with experimental data for elbows in series. It is found that the rebound model has a great influence on erosion prediction of both first and second elbows especially where subsequent particle impacts are expected.
{"title":"A Statistical Approach for Modeling Stochastic Rebound Characteristics of Solid Particles","authors":"G. Haider, Alireza Asgharpour, Jun Zhang, S. Shirazi","doi":"10.1115/ajkfluids2019-4655","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4655","url":null,"abstract":"\u0000 During production of oil and gas from wells, solid particles such as removed scales or sand may accompany petroleum fluids. These particles present in this multiphase flow can impact inner walls of transportation infrastructure (straight pipelines, elbows, T-junctions, flow meters, and reducers) multiple times. These repeated impacts degrades the inner walls of piping and as a result, reduce wall thickness occur. This is known as solid particle erosion, which is a complex phenomenon involving multiple contributing factors. Prediction of erosion rates and location of maximum erosion are crucial from both operations and safety perspective. Various mechanistic and empirical solid particle erosion models are available in literature for this purpose. The majority of these models require particle impact speed and impact angle to model erosion. Furthermore, due to complex geometric shapes of process equipment, these solid particles can impact and rebound from walls in a random manner with varying speeds and angles. Hence, this rebound characteristic is an important factor in solid particle erosion modeling which cannot be done in a deterministic sense. This challenge has not been addressed in literature satisfactorily. This study uses experimental data to model particle rebound characteristics stochastically. Experimental setup consists of a nozzle and specimen, which are aligned at different angles so particles impact the specimen at various angles. Information regarding particle impact velocities before and after the impacts are obtained through Particle Tracking Velocimetry (PTV) technique. Distributions of normal and tangential components of particle velocities were determined experimentally. Furthermore, spread or dispersion in these velocity components due to randomness is quantified. Finally, based on these experimental observations, a stochastic rebound model based on normal and tangential coefficients of restitutions is developed and Computational Fluid Dynamics (CFD) studies were conducted to validate this model. The model predictions are compared with experimental data for elbows in series. It is found that the rebound model has a great influence on erosion prediction of both first and second elbows especially where subsequent particle impacts are expected.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"125 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131197453","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-5272
Taiji Tanaka, H. Park, Y. Tasaka, Y. Murai
To investigate the development process of a void wave, spatio-temporal fluctuation of void fraction, we examined experimentally a turbulent boundary layer with bubble injections. The experiments performed on a flat bottom of 4-mlong transparent model ship towed in a tank of 100 m length with the speed of up to 3.00 m/s. In bubbles injection with constant air flow rate, void fluctuations with 4 Hz or 8 Hz appeared dependent on the towing speed. With periodically fluctuated air flow rate, artificial void waves were provided into the turbulent boundary layer and their frequency was maintained during the downstream propagation. The attenuation rate of the fluctuation evaluated using Fourier analysis of the wave took the minimum value at specific injection frequency conditions.
{"title":"Void Waves Developing in Gas-Liquid Two-Phase Turbulent Boundary Layers Beneath a Flat Bottom Model Ship","authors":"Taiji Tanaka, H. Park, Y. Tasaka, Y. Murai","doi":"10.1115/ajkfluids2019-5272","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5272","url":null,"abstract":"\u0000 To investigate the development process of a void wave, spatio-temporal fluctuation of void fraction, we examined experimentally a turbulent boundary layer with bubble injections. The experiments performed on a flat bottom of 4-mlong transparent model ship towed in a tank of 100 m length with the speed of up to 3.00 m/s. In bubbles injection with constant air flow rate, void fluctuations with 4 Hz or 8 Hz appeared dependent on the towing speed. With periodically fluctuated air flow rate, artificial void waves were provided into the turbulent boundary layer and their frequency was maintained during the downstream propagation. The attenuation rate of the fluctuation evaluated using Fourier analysis of the wave took the minimum value at specific injection frequency conditions.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133466687","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-5153
Chang Wang, Yuan Liu, T. Du, Yiwei Wang
With the increasing demand of higher performance and efficiencies for marine propulsion and hydropower system, structures became more flexible and were subjected to high flow rates. Cavitation-structure interaction has become one of the major issues for most engineering applications. In order to analyze the characteristics of unsteady cavitating flow induced vibration, the cloud cavitation flow over three dimensional NACA66 hydrofoil is studied by numerical simulation in this paper. The cavitating flow is modeled by large eddy simulation method and Zwart cavitation model, and the structural vibration model of three dimensional hydrofoil is established. The numerical calculation of fluid-solid coupling is realized based on ANSYS Workbench. The main dimensionless parameters of three-dimensional hydrofoil cavitation flow-induced vibration are obtained by means of dimensional analysis, including density ratio, cavitation number, Reynolds number, and the frequency ratio of flow to structure. The changes of cavity morphology during the cloud cavitation development of flexible hydrofoil and the flow-induced vibration characteristics under cloud cavitation flow of flexible hydrofoil are analyzed. The results showed that the periodic development of cavitation can be divided into three stages: the growth of attached cavity, the development of re-entrant jet and the shedding of cavity in cloud cavitaion stage. The centroid displacement of the free end of the flexible hydrofoil varies periodically with time at the stage of cloud cavitation. The hydrofoil vibration is affected by the development of cloud cavitation, and the vibration frequency corresponds to the shedding frequency of cloud cavitation.
{"title":"Numerical Study on Flow-Induced Vibration Characteristics of Three-Dimensional Hydrofoil in Cavitating Flow","authors":"Chang Wang, Yuan Liu, T. Du, Yiwei Wang","doi":"10.1115/ajkfluids2019-5153","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5153","url":null,"abstract":"\u0000 With the increasing demand of higher performance and efficiencies for marine propulsion and hydropower system, structures became more flexible and were subjected to high flow rates. Cavitation-structure interaction has become one of the major issues for most engineering applications. In order to analyze the characteristics of unsteady cavitating flow induced vibration, the cloud cavitation flow over three dimensional NACA66 hydrofoil is studied by numerical simulation in this paper. The cavitating flow is modeled by large eddy simulation method and Zwart cavitation model, and the structural vibration model of three dimensional hydrofoil is established. The numerical calculation of fluid-solid coupling is realized based on ANSYS Workbench. The main dimensionless parameters of three-dimensional hydrofoil cavitation flow-induced vibration are obtained by means of dimensional analysis, including density ratio, cavitation number, Reynolds number, and the frequency ratio of flow to structure. The changes of cavity morphology during the cloud cavitation development of flexible hydrofoil and the flow-induced vibration characteristics under cloud cavitation flow of flexible hydrofoil are analyzed. The results showed that the periodic development of cavitation can be divided into three stages: the growth of attached cavity, the development of re-entrant jet and the shedding of cavity in cloud cavitaion stage. The centroid displacement of the free end of the flexible hydrofoil varies periodically with time at the stage of cloud cavitation. The hydrofoil vibration is affected by the development of cloud cavitation, and the vibration frequency corresponds to the shedding frequency of cloud cavitation.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123716918","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-5013
Mitsuru Tanaka, Akira Matsuura, K. Tajiri, H. Nishida, M. Yamakawa
A particle-resolved simulation is performed on the motion of spherical particles with an eccentric internal mass distribution in laminar and turbulent vertical flows subjected to horizontal shear in order to examine the effects of mass eccentricity on the motion of particles in shear flows. A spherical shell/hollow particles with an inner spherical core is focused on as a typical example of mass eccentric particles. The Navier-Stokes equations and the Newton-Euler equations are solved for the fluid phase and the particles, respectively. An immersed boundary method is adopted to represent the shell particle. The Newton-Euler equations are solved using the body-fixed coordinate system and four quaternion parameters, considering the deviation of the mass center from the center of the spherical shell particle. Numerical results show that a particle tends to stop its rotation when the torque acting on the particle due to the gravity exceeds that due to the shear. It is found that the transverse migration of mass-eccentric particles becomes less vigorous in both laminar and turbulent flows since the effect of the Magnus force is also weakened for mass-eccentric particles. It is also found that the evolution of fluid kinetic energy is significantly affected by the mass-eccentricity of particles in laminar flows.
{"title":"Effects of Mass Eccentricity on the Motion of Spherical Particles in Shear Flows","authors":"Mitsuru Tanaka, Akira Matsuura, K. Tajiri, H. Nishida, M. Yamakawa","doi":"10.1115/ajkfluids2019-5013","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5013","url":null,"abstract":"\u0000 A particle-resolved simulation is performed on the motion of spherical particles with an eccentric internal mass distribution in laminar and turbulent vertical flows subjected to horizontal shear in order to examine the effects of mass eccentricity on the motion of particles in shear flows. A spherical shell/hollow particles with an inner spherical core is focused on as a typical example of mass eccentric particles. The Navier-Stokes equations and the Newton-Euler equations are solved for the fluid phase and the particles, respectively. An immersed boundary method is adopted to represent the shell particle. The Newton-Euler equations are solved using the body-fixed coordinate system and four quaternion parameters, considering the deviation of the mass center from the center of the spherical shell particle. Numerical results show that a particle tends to stop its rotation when the torque acting on the particle due to the gravity exceeds that due to the shear. It is found that the transverse migration of mass-eccentric particles becomes less vigorous in both laminar and turbulent flows since the effect of the Magnus force is also weakened for mass-eccentric particles. It is also found that the evolution of fluid kinetic energy is significantly affected by the mass-eccentricity of particles in laminar flows.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"88 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126012515","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-5465
F. Darihaki, S. Shirazi, Q. Feng
Water-in-oil dispersion modeling is critical to assess the internal corrosion in pipelines, specifically for the oil and gas industry applications. In many oil transportation facilities, a small amount of water could be entrained in production fluids. Turbulence can break out the water into the form of tiny droplets. Under certain conditions in horizontal or inclined pipelines, water droplets can settle and contact the wall which may lead to CO2 and/or O2 or other forms of corrosion and damage the transport system integrity. In the present study, a novel transient approach has been developed that provides water concentrations across the pipe section. A one-dimensional transient finite-difference computational model has been used to determine concentration distribution in a vertical direction across the pipe. Calculated water fractions using the transient model is compared to experimental data and more comprehensive 3-D Computational Fluid Dynamics (CFD) approach for various flow conditions and watercuts that shows the viability of the simplified one-dimensional approach. The proposed model is capable of predicting water dispersion at different locations and could be utilized for various pipe-flow systems. Furthermore, water in the form of droplets or liquid film can result in corrosion when it wets the pipeline surface. Consequently, the calculated water concentration at the bottom of the pipe assists in determining wettability of the pipe surface by water and evaluating the corrosion risk along the pipeline.
{"title":"A Transient Approach for Estimating Concentration of Water Droplets in Oil and Corrosion Assessment in the Oil and Gas Industry","authors":"F. Darihaki, S. Shirazi, Q. Feng","doi":"10.1115/ajkfluids2019-5465","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5465","url":null,"abstract":"\u0000 Water-in-oil dispersion modeling is critical to assess the internal corrosion in pipelines, specifically for the oil and gas industry applications. In many oil transportation facilities, a small amount of water could be entrained in production fluids. Turbulence can break out the water into the form of tiny droplets. Under certain conditions in horizontal or inclined pipelines, water droplets can settle and contact the wall which may lead to CO2 and/or O2 or other forms of corrosion and damage the transport system integrity.\u0000 In the present study, a novel transient approach has been developed that provides water concentrations across the pipe section. A one-dimensional transient finite-difference computational model has been used to determine concentration distribution in a vertical direction across the pipe. Calculated water fractions using the transient model is compared to experimental data and more comprehensive 3-D Computational Fluid Dynamics (CFD) approach for various flow conditions and watercuts that shows the viability of the simplified one-dimensional approach. The proposed model is capable of predicting water dispersion at different locations and could be utilized for various pipe-flow systems.\u0000 Furthermore, water in the form of droplets or liquid film can result in corrosion when it wets the pipeline surface. Consequently, the calculated water concentration at the bottom of the pipe assists in determining wettability of the pipe surface by water and evaluating the corrosion risk along the pipeline.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114062524","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-5399
J. Nahon, M. Zangeneh, M. Nohmi, Hiroyoshi Watanabe
Cavitation commonly manifests itself as vapour structures attached to the suction surfaces of impeller, runner or propeller blades. The numerical study carried out here seeks to correlate the changes in the behaviour of sheet cavitation to variations in blade geometry. The analysis is run for a two-dimensional stationary cascade. The streamwise loading distribution is the metric used to characterise the geometry. It determines the rate and amount of work generated across the channel and is directly connected to blade surface pressure. In this study, the test sample consists of a set of varying blade profiles characterised by specific loading configurations: foreloaded, aft-loaded or bespoke distributions. Time-resolved simulations of the cavitating flow are generated to study cavity behaviour. Computations are run through Fluent using the SST URANS formulation. The Zwart-Gerber-Belamri homogeneous cavitation model is used to treat cavitation. A range of behaviours are observed for the cavitation patterns. Variations are found in inception conditions, shape and sheet stability. For the latter, two dynamic regimes are identified with a transition point that varies according to the loading profile. A pair of tradeoff relations are also observed: hydrodynamic efficiency versus suction performance and suction performance versus cavity stability. The results demonstrate the capacity of the loading distribution to affect cavitation dynamics.
{"title":"Numerical Investigation on the Effect of Blade Loading on Unsteady Sheet Cavitation Patterns","authors":"J. Nahon, M. Zangeneh, M. Nohmi, Hiroyoshi Watanabe","doi":"10.1115/ajkfluids2019-5399","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5399","url":null,"abstract":"\u0000 Cavitation commonly manifests itself as vapour structures attached to the suction surfaces of impeller, runner or propeller blades. The numerical study carried out here seeks to correlate the changes in the behaviour of sheet cavitation to variations in blade geometry. The analysis is run for a two-dimensional stationary cascade. The streamwise loading distribution is the metric used to characterise the geometry. It determines the rate and amount of work generated across the channel and is directly connected to blade surface pressure.\u0000 In this study, the test sample consists of a set of varying blade profiles characterised by specific loading configurations: foreloaded, aft-loaded or bespoke distributions. Time-resolved simulations of the cavitating flow are generated to study cavity behaviour. Computations are run through Fluent using the SST URANS formulation. The Zwart-Gerber-Belamri homogeneous cavitation model is used to treat cavitation. A range of behaviours are observed for the cavitation patterns. Variations are found in inception conditions, shape and sheet stability. For the latter, two dynamic regimes are identified with a transition point that varies according to the loading profile. A pair of tradeoff relations are also observed: hydrodynamic efficiency versus suction performance and suction performance versus cavity stability. The results demonstrate the capacity of the loading distribution to affect cavitation dynamics.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"553 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116503965","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-5386
Joel R. Karp, E. Mancilla, P. H. Santos, M. M. Neto, R. Morales
The interactions between dispersed oil droplets and gas bubbles was experimentally studied in this work. An experimental set-up was built in the Multiphase Flow Research Center (NUEM) in the Federal University of Technology – Paraná (UTFPR) to conduct a fundamental evaluation of the interactions between sessile gas bubbles and oil droplets employing side-view flow visualization. Tap water was used as the continuous phase, whereas pure nitrogen and colored vegetable oil were employed as the dispersed phases. The bubble-droplet attachment consisted in the encapsulation of the bubble by the droplet, presenting phenomenological similarities to droplet-droplet coalescence. The contact between the dispersed phases induces the formation of a connecting bridge, which grows rapidly with time, with the height of the bridge being comparable to the size of the droplet after 57.0 ms. The inherent asymmetry of the phenomenon induced a significant horizontal displacement of the bubble towards the droplet, whose position remained unaltered. The evaluation of the bridge meniscus corroborated to this observation, since the contact angle on the droplet side decayed faster with time in comparison to the contact angle on the bubble side. The hydrodynamics of the rising aggregate is also evaluated, by the obtainment of its size, three-dimensional trajectory and terminal velocity. The stable aggregates formed presented an increase factor of 150 to 180%, based on the terminal velocity of the individual droplet. The radius of the bubble was found to be the major influence on the hydrodynamics of the aggregate, allowing the definition of a critical bubble radius based on trajectory instabilities.
{"title":"Experimental Study of Bubble-Droplet Interactions in Improved Primary Oil Separation","authors":"Joel R. Karp, E. Mancilla, P. H. Santos, M. M. Neto, R. Morales","doi":"10.1115/ajkfluids2019-5386","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5386","url":null,"abstract":"\u0000 The interactions between dispersed oil droplets and gas bubbles was experimentally studied in this work. An experimental set-up was built in the Multiphase Flow Research Center (NUEM) in the Federal University of Technology – Paraná (UTFPR) to conduct a fundamental evaluation of the interactions between sessile gas bubbles and oil droplets employing side-view flow visualization. Tap water was used as the continuous phase, whereas pure nitrogen and colored vegetable oil were employed as the dispersed phases. The bubble-droplet attachment consisted in the encapsulation of the bubble by the droplet, presenting phenomenological similarities to droplet-droplet coalescence. The contact between the dispersed phases induces the formation of a connecting bridge, which grows rapidly with time, with the height of the bridge being comparable to the size of the droplet after 57.0 ms. The inherent asymmetry of the phenomenon induced a significant horizontal displacement of the bubble towards the droplet, whose position remained unaltered. The evaluation of the bridge meniscus corroborated to this observation, since the contact angle on the droplet side decayed faster with time in comparison to the contact angle on the bubble side. The hydrodynamics of the rising aggregate is also evaluated, by the obtainment of its size, three-dimensional trajectory and terminal velocity. The stable aggregates formed presented an increase factor of 150 to 180%, based on the terminal velocity of the individual droplet. The radius of the bubble was found to be the major influence on the hydrodynamics of the aggregate, allowing the definition of a critical bubble radius based on trajectory instabilities.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115087574","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 : 2019-11-20DOI: 10.1115/ajkfluids2019-5397
V. Matoušek, J. Krupička, J. Konfršt, P. Vlasák
Partially stratified flows like flows of sand-water slurries exhibit non-uniform distribution of solids (expressed as a vertical profile of local volumetric concentration) in a pipe cross section. The solids distribution in such flows is sensitive to pipe inclination. The more stratified the flow is the more sensitive its concentration profile is to the pipe slope. In general, the distribution tends to become more uniform (less stratified) if the inclination angle increases from zero (horizontal pipe) to positive values (ascending pipe) up to 90 degree (vertical pipe). In a pipe inclined to negative angles (descending pipe) the development is different. The flow tends to stratify more if it changes from horizontal flow to descending flow down to the angle of about −35 degree. If the angle further decreases towards −90 degree, then the flow becomes less stratified reaching uniform distribution at the vertical position. This also means that the same flow exhibits a very different degree of stratification in ascending and descending pipes inclined to the same (mild) slope say between ±10 and ±40 degree. The rather complex development of the solids distribution with the variation of the inclination of pipe is insufficiently documented experimentally and described theoretically in predictive models for a concentration profile in partially stratified flow. In order to extend the existing limited data set with experimental data for partially stratified flow of medium sand slurry, we have carried out a laboratory experiment with the slurry of narrow graded fraction of sand with the mean grain size of 0.55 mm in our test loop with an invert U-tube inclinable to arbitrary angle between 0 and 90 degree. A pipe of the loop has an internal diameter of 100 mm. Both legs of the U-tube have a measuring section over which differential pressures are measured. Radiometric devices mounted to both measuring sections sense concentration profiles across a pipe cross section. Furthermore, the discharge of slurry is measured in the test loop. In the paper, experimental results are presented for various inclination angles with a small step between 0 and ±45 degree and a development in the shape of the concentration profiles with the changing inclination angle is analyzed. For the analysis, it is critical to distinguish between suspended load and contact load in the flow as the two loads tend to react differently to the flow inclination. The measured concentration profiles and pressure drops are compared with predictions by the layered model adapted for taking the flow inclination into account.
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