Pub Date : 2019-07-28DOI: 10.1115/ajkfluids2019-5306
N. Kamatani, S. Ogata
The purpose of this study is to clarify the formation characteristics and production conditions of two-layer droplets using coaxial nozzle. In this study, we focus on Newtonian fluid only to pay attention to the fundamental formation characteristics of two-layer droplet. Also, the three liquids flowing in the apparatus were assumed to have the same viscosity and density. First, theoretical equations concerning the outer diameters of the single layer droplet and the two-layer droplet were obtained, and a conditional expression for detaching both nozzles simultaneously from the nozzle in dripping was obtained. These theoretical equations were verified using numerical analysis. By analyzing with various parameters changed, the following six formation modes could be confirmed. 2 interface both dripping, 2 interface both jetting, Outer interface is jetting and The inner interface is dripping, 2 interface comes into contact and the encapsulated liquid is discharged to the outside, Two or more droplets are formed in the interior, Liquid droplets containing liquid droplets and liquid droplets not containing liquid droplets are alternately formed. The validity of each theoretical expression and conditional expression was also be confirmed.
{"title":"Formation Characteristics of Two-Phase Drops From Coaxial Nozzles","authors":"N. Kamatani, S. Ogata","doi":"10.1115/ajkfluids2019-5306","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5306","url":null,"abstract":"\u0000 The purpose of this study is to clarify the formation characteristics and production conditions of two-layer droplets using coaxial nozzle. In this study, we focus on Newtonian fluid only to pay attention to the fundamental formation characteristics of two-layer droplet. Also, the three liquids flowing in the apparatus were assumed to have the same viscosity and density. First, theoretical equations concerning the outer diameters of the single layer droplet and the two-layer droplet were obtained, and a conditional expression for detaching both nozzles simultaneously from the nozzle in dripping was obtained. These theoretical equations were verified using numerical analysis. By analyzing with various parameters changed, the following six formation modes could be confirmed. 2 interface both dripping, 2 interface both jetting, Outer interface is jetting and The inner interface is dripping, 2 interface comes into contact and the encapsulated liquid is discharged to the outside, Two or more droplets are formed in the interior, Liquid droplets containing liquid droplets and liquid droplets not containing liquid droplets are alternately formed. The validity of each theoretical expression and conditional expression was also be confirmed.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"128 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":"114494908","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/ajkfluids2019-4913
Xie Zhenqiang, Xuewen Cao, Fachun Liang, Jun Zhang
The problem of accumulated liquid is very common in wet gas gathering pipelines which varies with the topography, this phenomenon is much more serious especially in upward inclined pipelines. The existence of accumulated liquid at the bottom of the pipeline would decrease the area of the cross section that gas flows through. This makes the gas velocity fluctuate unpredictably and even results in shocks and blocks in pipelines which may cause danger in the safety management of oil and gas production. Swirl tool is a kind of rigid tool which can transfer different flow patterns to a flow pattern similar to annular flow and it has been successfully used to exhaust accumulated liquid in oil fields. However, the mechanism of swirling flow generation in a swirl tool is not fully understood and few researchers have explained how the annular-similar flow decays. In this paper, the formation mechanism of swirling flow in a swirl tool is analyzed using a physical method. The flow pattern transfer procedure and distribution of gas and liquid in the cross section of the pipeline in the swirl tool is simulated with FLUENT (a commercial CFD code). Following the swirling flow formation analysis, the decay of the annular-similar flow from the outlet of the swirl tool is also simulated with FLUENT (a commercial CFD code). Also, the effects of different superficial gas velocities and different liquid rates on the decay of the annular-similar flow are studied with the swirl tool fixed at the bottom of the upward inclined pipeline. The results show that the formation of swirling flow in a swirl tool is mostly affected by the geometric structure of the swirl tool. The centrifugal force is the main force which transfers different flow patterns to a flow pattern similar to annular flow. The centrifugal force that acts on liquid is larger than that of gas since the density of the liquid is much bigger than gas. The annular-similar flow starts to take shape in the swirl tool after the first thread pitch, but the annular-similar flow is nonuniform. After about three thread pitches, the annular-similar flow becomes uniform with liquid surrounding the inner wall of the pipe and gas flowing in the core region of the pipe. The distance of the annular-similar flow sustains longer when the superficial gas velocity increases which means the decay of the swirling flow is slower. Since sufficient liquid rate is critical to maintain annular-similar flow after the tool when the gas flow rate is fixed, the distance of the annular-similar flow goes longer if there is a little increase in liquid rate.
{"title":"The Study of Exhausting Accumulated Liquid in Upward Inclined Pipe Using a Swirl Tool","authors":"Xie Zhenqiang, Xuewen Cao, Fachun Liang, Jun Zhang","doi":"10.1115/ajkfluids2019-4913","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4913","url":null,"abstract":"\u0000 The problem of accumulated liquid is very common in wet gas gathering pipelines which varies with the topography, this phenomenon is much more serious especially in upward inclined pipelines. The existence of accumulated liquid at the bottom of the pipeline would decrease the area of the cross section that gas flows through. This makes the gas velocity fluctuate unpredictably and even results in shocks and blocks in pipelines which may cause danger in the safety management of oil and gas production.\u0000 Swirl tool is a kind of rigid tool which can transfer different flow patterns to a flow pattern similar to annular flow and it has been successfully used to exhaust accumulated liquid in oil fields. However, the mechanism of swirling flow generation in a swirl tool is not fully understood and few researchers have explained how the annular-similar flow decays.\u0000 In this paper, the formation mechanism of swirling flow in a swirl tool is analyzed using a physical method. The flow pattern transfer procedure and distribution of gas and liquid in the cross section of the pipeline in the swirl tool is simulated with FLUENT (a commercial CFD code). Following the swirling flow formation analysis, the decay of the annular-similar flow from the outlet of the swirl tool is also simulated with FLUENT (a commercial CFD code). Also, the effects of different superficial gas velocities and different liquid rates on the decay of the annular-similar flow are studied with the swirl tool fixed at the bottom of the upward inclined pipeline.\u0000 The results show that the formation of swirling flow in a swirl tool is mostly affected by the geometric structure of the swirl tool. The centrifugal force is the main force which transfers different flow patterns to a flow pattern similar to annular flow. The centrifugal force that acts on liquid is larger than that of gas since the density of the liquid is much bigger than gas. The annular-similar flow starts to take shape in the swirl tool after the first thread pitch, but the annular-similar flow is nonuniform. After about three thread pitches, the annular-similar flow becomes uniform with liquid surrounding the inner wall of the pipe and gas flowing in the core region of the pipe. The distance of the annular-similar flow sustains longer when the superficial gas velocity increases which means the decay of the swirling flow is slower. Since sufficient liquid rate is critical to maintain annular-similar flow after the tool when the gas flow rate is fixed, the distance of the annular-similar flow goes longer if there is a little increase in liquid rate.","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":"130800559","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/ajkfluids2019-4971
T. Uchiyama, R. Kano, T. Degawa, K. Takamure
This study investigates the flow past two cylinders arranged in tandem within a microbubble plume inside a tank. Microbubbles with a mean diameter of 0.055 mm are released by water electrolysis from electrodes placed at the bottom of the tank. Upon rising, these microbubbles induce an upward water flow around them due to buoyancy. Orthogonally to the axis of this microbubble plume, two cylinders with a diameter D of 30 mm are arranged in tandem. The distance between the cylinders, L, ranges between 1.5D and 3D. The bubbles and the water flow around the cylinders are visualized, and the bubble velocity distribution is measured. The experiments reveal the water and bubble shear layers originating at the sides of the lower cylinder, and allow the elucidation of their behavior around the upper cylinder. Furthermore, this study makes clear the effects of L on the flow around the two cylinders, such as the stagnant bubbly flow and the bubbly wake.
{"title":"Flow Past Two Cylinders Arranged in Tandem Within a Microbubble Plume","authors":"T. Uchiyama, R. Kano, T. Degawa, K. Takamure","doi":"10.1115/ajkfluids2019-4971","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-4971","url":null,"abstract":"\u0000 This study investigates the flow past two cylinders arranged in tandem within a microbubble plume inside a tank. Microbubbles with a mean diameter of 0.055 mm are released by water electrolysis from electrodes placed at the bottom of the tank. Upon rising, these microbubbles induce an upward water flow around them due to buoyancy. Orthogonally to the axis of this microbubble plume, two cylinders with a diameter D of 30 mm are arranged in tandem. The distance between the cylinders, L, ranges between 1.5D and 3D. The bubbles and the water flow around the cylinders are visualized, and the bubble velocity distribution is measured. The experiments reveal the water and bubble shear layers originating at the sides of the lower cylinder, and allow the elucidation of their behavior around the upper cylinder. Furthermore, this study makes clear the effects of L on the flow around the two cylinders, such as the stagnant bubbly flow and the bubbly wake.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"19 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":"126955089","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/ajkfluids2019-5256
C. Kawakita, T. Hamada
The air lubrication method, which mixes millimeter bubbles into the flow around the hull and reduces frictional resistance, is expected to have a large energy saving effect among a number of marine energy saving technologies. Concerning the frictional drag reduction effect using the air lubrication method, in this study, the frictional drag reduction effect was experimentally investigated for gas-liquid two phase flow considering the influence of inclination and curved surface of the ship bottom. Measurement of local shear stress and measurement of void fraction distribution near the wall surface were carried out and the correlation between local shear stress and local void fraction distribution was grasped.
{"title":"Experimental Investigation on Influence of Inclination and Curved Surface of Ship Bottom in Air Lubrication Method","authors":"C. Kawakita, T. Hamada","doi":"10.1115/ajkfluids2019-5256","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5256","url":null,"abstract":"\u0000 The air lubrication method, which mixes millimeter bubbles into the flow around the hull and reduces frictional resistance, is expected to have a large energy saving effect among a number of marine energy saving technologies. Concerning the frictional drag reduction effect using the air lubrication method, in this study, the frictional drag reduction effect was experimentally investigated for gas-liquid two phase flow considering the influence of inclination and curved surface of the ship bottom. Measurement of local shear stress and measurement of void fraction distribution near the wall surface were carried out and the correlation between local shear stress and local void fraction distribution was grasped.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"11 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":"125884326","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/ajkfluids2019-5225
Thomas G. Shepard, Aleksey Garbaly
In an effervescent atomizer, a bubbly two-phase mixture flows through a convergent section before exhausting from an exit orifice. It is commonly believed that one of the key effects of including bubbles is in the substantial decrease in the speed of sound experienced by the two-phase flow allowing for choked flow conditions at the exit. The existence of choked conditions would result in under-expanded bubbles that would further expand upon exiting the atomizer and provide additional forces to aid in the break-up of the bulk liquid into droplets. This study examines how the homogenous two-phase flow model of speed of sound, and thus critical conditions, compare with experiments in order to better understand the fundamental physics of effervescent atomization. In these experiments, an effervescent atomizer is connected to a vacuum chamber allowing for internal atomizer pressure, liquid flow rate and air flow rate to be monitored as the post-exit pressure is decreased. Experiments reveal that the flow remains subcritical well beyond conditions that the homogenous flow theory might predict being choked. High-speed imaging is used to capture internal atomizer bubble size.
{"title":"Experimental Investigation of Choked Flow Conditions for Bubbly Flow","authors":"Thomas G. Shepard, Aleksey Garbaly","doi":"10.1115/ajkfluids2019-5225","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5225","url":null,"abstract":"\u0000 In an effervescent atomizer, a bubbly two-phase mixture flows through a convergent section before exhausting from an exit orifice. It is commonly believed that one of the key effects of including bubbles is in the substantial decrease in the speed of sound experienced by the two-phase flow allowing for choked flow conditions at the exit. The existence of choked conditions would result in under-expanded bubbles that would further expand upon exiting the atomizer and provide additional forces to aid in the break-up of the bulk liquid into droplets. This study examines how the homogenous two-phase flow model of speed of sound, and thus critical conditions, compare with experiments in order to better understand the fundamental physics of effervescent atomization. In these experiments, an effervescent atomizer is connected to a vacuum chamber allowing for internal atomizer pressure, liquid flow rate and air flow rate to be monitored as the post-exit pressure is decreased. Experiments reveal that the flow remains subcritical well beyond conditions that the homogenous flow theory might predict being choked. High-speed imaging is used to capture internal atomizer bubble size.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"12 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":"121860786","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 : 2019-06-19DOI: 10.1115/ajkfluids2019-5455
A. Harrison
The Lagrangian hydrocode FLAG employs a subgrid model to represent the ejection of particulate mass (“ejecta”) from a shocked metal surface. With a conforming mesh used in typical simulations, the calculations of ejecta production, properties and launch are carried out independently on each mesh face lying on the surface of the metal. Based on experimental evidence [1] that ejecta production is greatest when the shock releases to the liquid state, the ejection process is modeled as a Richtmyer-Meshkov instability (RMI) of the liquid metal surface, in which the metal spikes that form break up to become ejecta. The model applies to the case in which surface perturbations such as machining grooves can be well approximated as a single-mode sinusoidal perturbation; in this case the RMI spikes are actually sheets. The FLAG model includes (1) a description of RMI spike and bubble growth rates [2] and (2) the Self-Similar Velocity Distribution (SSVD) model of the velocity field within a spike as varying linearly from zero (in the fluid frame) at the base to a maximum value at the tip [3]. We report here on the improvement of this model by incorporating (3) a spike breakup treatment based on the Taylor Analogy Breakup (TAB) model [5], as extended to apply to sheet breakup [6,7], and (4) a new model for the inflow of metal into the base of the spikes. Combining all these elements allows us to self-consistently reconcile the evolving shape of the spikes (elongation and thinning) with the inflow, and with the corresponding properties of the bubbles, under the assumption of incompressibility. Since the model describes the motion of each fluid element into and along the spike, and subsequent fragmentation of the spike into ejecta, it predicts not only mass ejection rate but also the sizes and velocities of the particles launched in this process. We describe the new self-consistent model and its implementation in FLAG.
{"title":"The Spike Dynamics Source Model for Ejecta in the FLAG Code","authors":"A. Harrison","doi":"10.1115/ajkfluids2019-5455","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5455","url":null,"abstract":"\u0000 The Lagrangian hydrocode FLAG employs a subgrid model to represent the ejection of particulate mass (“ejecta”) from a shocked metal surface. With a conforming mesh used in typical simulations, the calculations of ejecta production, properties and launch are carried out independently on each mesh face lying on the surface of the metal. Based on experimental evidence [1] that ejecta production is greatest when the shock releases to the liquid state, the ejection process is modeled as a Richtmyer-Meshkov instability (RMI) of the liquid metal surface, in which the metal spikes that form break up to become ejecta. The model applies to the case in which surface perturbations such as machining grooves can be well approximated as a single-mode sinusoidal perturbation; in this case the RMI spikes are actually sheets.\u0000 The FLAG model includes (1) a description of RMI spike and bubble growth rates [2] and (2) the Self-Similar Velocity Distribution (SSVD) model of the velocity field within a spike as varying linearly from zero (in the fluid frame) at the base to a maximum value at the tip [3]. We report here on the improvement of this model by incorporating (3) a spike breakup treatment based on the Taylor Analogy Breakup (TAB) model [5], as extended to apply to sheet breakup [6,7], and (4) a new model for the inflow of metal into the base of the spikes. Combining all these elements allows us to self-consistently reconcile the evolving shape of the spikes (elongation and thinning) with the inflow, and with the corresponding properties of the bubbles, under the assumption of incompressibility. Since the model describes the motion of each fluid element into and along the spike, and subsequent fragmentation of the spike into ejecta, it predicts not only mass ejection rate but also the sizes and velocities of the particles launched in this process. We describe the new self-consistent model and its implementation in FLAG.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115141896","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 : 2014-11-25DOI: 10.1115/ajkfluids2019-5451
F. Grinstein
Accurate predictions with quantifiable uncertainties are essential to many practical turbulent flow applications exhibiting extreme geometrical complexity and broad ranges of length and time scales. Under-resolved computer simulations are typically unavoidable in such applications, and implicit large-eddy simulation (ILES) often becomes the effective strategy. We focus on ILES initialized with well-characterized 2563 homogeneous isotropic turbulence datasets generated with direct numerical simulation (DNS). ILES is based on the LANL xRAGE code, and solutions are examined as function of resolution for 643, 1283, 2563, and 5123 grids. The ILES performance of new directionally-unsplit high-order numerical hydrodynamics algorithms in xRAGE is examined. Compared to the initial 2563 DNS, we find longer inertial subranges and higher turbulence Re for directional-split 2563 & 5123 xRAGE — attributed to having linked DNS (Navier-Stokes based) solutions to nominally inviscid (higher Re) Euler based ILES solutions. Alternatively — for fixed resolution, we find that significantly higher simulated turbulence Re can be achieved with unsplit (vs. split) discretizations.
{"title":"Implicit Large-Eddy Simulation of Transition and Turbulence Decay","authors":"F. Grinstein","doi":"10.1115/ajkfluids2019-5451","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5451","url":null,"abstract":"\u0000 Accurate predictions with quantifiable uncertainties are essential to many practical turbulent flow applications exhibiting extreme geometrical complexity and broad ranges of length and time scales. Under-resolved computer simulations are typically unavoidable in such applications, and implicit large-eddy simulation (ILES) often becomes the effective strategy. We focus on ILES initialized with well-characterized 2563 homogeneous isotropic turbulence datasets generated with direct numerical simulation (DNS). ILES is based on the LANL xRAGE code, and solutions are examined as function of resolution for 643, 1283, 2563, and 5123 grids. The ILES performance of new directionally-unsplit high-order numerical hydrodynamics algorithms in xRAGE is examined. Compared to the initial 2563 DNS, we find longer inertial subranges and higher turbulence Re for directional-split 2563 & 5123 xRAGE — attributed to having linked DNS (Navier-Stokes based) solutions to nominally inviscid (higher Re) Euler based ILES solutions. Alternatively — for fixed resolution, we find that significantly higher simulated turbulence Re can be achieved with unsplit (vs. split) discretizations.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115887007","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 : 1900-01-01DOI: 10.1115/ajkfluids2019-5345
Yu Katano, K. Ando
Underwater ultrasound causes various physical phenomena in megasonic cleaning baths, e.g. cavitation inception, bubble translation and free-surface deformation (FSD) due to acoustic radiation pressure. Because FSD is especially noticeable in the case of high frequency ultrasound due to its high directivity, it is essential to investigate the interaction between FSD and bubble translation in megasonic cleaning bath. In our present experiments, we construct a typical setup for megasonic cleaning and irradiate water with 1 MHz ultrasound vertically upwards. We visualize FSD and bubbles and analyze the height of FSD and the translational velocity in frequency space. The bubbles translate in both short and long time scales caused by bubble-bubble interaction and periodic FSD, respectively, and the latter has periodicity. The most dominant frequency component in FSD shows good agreement with that in the translational velocity of the bubbles and does not depend on whether cavitation occurs or not. Therefore, it is suggested that FSD causes periodicity of bubble translation.
{"title":"Experimental Study of Free-Surface Deformation and Cavitation Bubble Dynamics in a Megasonic Cleaning Bath","authors":"Yu Katano, K. Ando","doi":"10.1115/ajkfluids2019-5345","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5345","url":null,"abstract":"\u0000 Underwater ultrasound causes various physical phenomena in megasonic cleaning baths, e.g. cavitation inception, bubble translation and free-surface deformation (FSD) due to acoustic radiation pressure. Because FSD is especially noticeable in the case of high frequency ultrasound due to its high directivity, it is essential to investigate the interaction between FSD and bubble translation in megasonic cleaning bath. In our present experiments, we construct a typical setup for megasonic cleaning and irradiate water with 1 MHz ultrasound vertically upwards. We visualize FSD and bubbles and analyze the height of FSD and the translational velocity in frequency space. The bubbles translate in both short and long time scales caused by bubble-bubble interaction and periodic FSD, respectively, and the latter has periodicity. The most dominant frequency component in FSD shows good agreement with that in the translational velocity of the bubbles and does not depend on whether cavitation occurs or not. Therefore, it is suggested that FSD causes periodicity of bubble translation.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121040037","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 : 1900-01-01DOI: 10.1115/ajkfluids2019-5200
Yoichiro Fukuchi, T. Kondo, K. Ando
In semiconductor industry, liquid jet cleaning plays an important role because of its high cleaning efficiency and low environmental load. However, its cleaning mechanism is not revealed in detail because the experimental observation of high-speed and sub-micron droplets is challenging. Furthermore, higher impact velocity may give rise to surface erosion due to water-hammer shock loading from the impingement. To study cleaning mechanisms and surface erosion, numerical simulation of droplet impingement accounting for both viscosity and compressibility is an effective approach. In the previous study, wall-shear-flow generation has evaluated from the simulation of high-speed single droplet impingement. To evaluate more practical model of jet cleaning application, simulation of two droplets simplifying mono-dispersed splay of droplet train is favorable. Here, we numerically simulated impingement of two droplets, which allows for evaluating water-hammer pressure and wall shear stress. We consider the case of two water droplets (200 μm in diameter) that collides continuously, at speed 50 m/s, at the inter-droplet distance from 250 to 400 μm, with a no-slip rigid wall covered with a water layer (100 μm in thickness). The simulation is based on compressible Navier-Stokes equations for axisymmetric flow and the mixture of two components appears in numerically diffusion interface expressed by the volume average and advection equation. The simulation is solved by finite-volume WENO scheme that can capture both shock waves and material interface. In our simulation, the impingement of second droplet impingement gain higher shear stress than the single droplet impingement. At the case that the inter-droplet distance is 300 μm, maximum shear stress is 30.22 kPa (at the second droplet impingement), which is much larger than at the first droplet impingement (8.42 kPa). This result indicates how the second droplet impingement make wall shear flow induced by first droplet impingement stronger. From the parameter study of the inter-droplet distance, we can say that wall shear stress gets stronger as water layer thickness decreases. Furthermore, the maximum wall pressure is 1.96 MPa at the second droplet impingement, which is larger than at the first droplet impingement (1.46 MPa). From this study, the evaluation of surface erosion caused by jet cleaning is expected. The simulation suggests that multiple droplets impingement continuously may gain higher cleaning efficiency, which will give us a fundamental insight into liquid jet cleaning technologies. For further study, simulation of water column impingement and comparing the result of impingement of two droplets are expected.
{"title":"Comparison in High-Speed Droplet Impact Between Single and Multiple Collisions Against a Wall Covered With a Liquid Film","authors":"Yoichiro Fukuchi, T. Kondo, K. Ando","doi":"10.1115/ajkfluids2019-5200","DOIUrl":"https://doi.org/10.1115/ajkfluids2019-5200","url":null,"abstract":"\u0000 In semiconductor industry, liquid jet cleaning plays an important role because of its high cleaning efficiency and low environmental load. However, its cleaning mechanism is not revealed in detail because the experimental observation of high-speed and sub-micron droplets is challenging. Furthermore, higher impact velocity may give rise to surface erosion due to water-hammer shock loading from the impingement. To study cleaning mechanisms and surface erosion, numerical simulation of droplet impingement accounting for both viscosity and compressibility is an effective approach. In the previous study, wall-shear-flow generation has evaluated from the simulation of high-speed single droplet impingement. To evaluate more practical model of jet cleaning application, simulation of two droplets simplifying mono-dispersed splay of droplet train is favorable. Here, we numerically simulated impingement of two droplets, which allows for evaluating water-hammer pressure and wall shear stress. We consider the case of two water droplets (200 μm in diameter) that collides continuously, at speed 50 m/s, at the inter-droplet distance from 250 to 400 μm, with a no-slip rigid wall covered with a water layer (100 μm in thickness). The simulation is based on compressible Navier-Stokes equations for axisymmetric flow and the mixture of two components appears in numerically diffusion interface expressed by the volume average and advection equation. The simulation is solved by finite-volume WENO scheme that can capture both shock waves and material interface. In our simulation, the impingement of second droplet impingement gain higher shear stress than the single droplet impingement. At the case that the inter-droplet distance is 300 μm, maximum shear stress is 30.22 kPa (at the second droplet impingement), which is much larger than at the first droplet impingement (8.42 kPa). This result indicates how the second droplet impingement make wall shear flow induced by first droplet impingement stronger. From the parameter study of the inter-droplet distance, we can say that wall shear stress gets stronger as water layer thickness decreases. Furthermore, the maximum wall pressure is 1.96 MPa at the second droplet impingement, which is larger than at the first droplet impingement (1.46 MPa). From this study, the evaluation of surface erosion caused by jet cleaning is expected. The simulation suggests that multiple droplets impingement continuously may gain higher cleaning efficiency, which will give us a fundamental insight into liquid jet cleaning technologies. For further study, simulation of water column impingement and comparing the result of impingement of two droplets are expected.","PeriodicalId":322380,"journal":{"name":"Volume 5: Multiphase Flow","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127344107","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 : 1900-01-01DOI: 10.1115/ajkfluids2019-4943
J. Horwitz, S. Vanka, Purushotam Kumar
In recent years, Lattice Boltzmann Methods (LBM’s) have emerged as a popular class of paradigms for the simulation of multiphase flows. These methods rely on discretized Boltzmann equations to represent the individual multiphase species. Among LBM’s advantages is its ability to explicitly account for interfacial physics and its local streaming/collision operations which make it ideally suited for parallelization. However, one drawback of LBM is in the simulation of incompressible multiphase flow, whereby the density should remain constant along material characteristics. Because LBM uses a state equation to relate pressure and density, incompressibility cannot be enforced directly. This is true even for incompressible single-phase LBM calculations, in which a finite density drop is needed to drive through the flow. This is also the case for compressible Navier-Stokes algorithms when applied to low Mach number flow. To mitigate compressibility effects, LBM can be used in low Mach regimes which should keep material density variation small. In this work, we demonstrate that the assumption of low Mach number is not sufficient in multiphase internal flows. In such flows, in the absence of a Pressure Poisson constraint to enforce incompressibility, LBM predicts a compressible solution whereby a density gradient must develop to conserve mass. Imposition of inflow/outflow boundary conditions or a mean body force can ensure that mass is conserved globally, thereby quelling density variation. The primary numerical problem we study is the deformation of a liquid droplet immersed in another fluid. Though LBM is not typically conducted with a pressure Poisson equation, we incorporate one in this work and demonstrate that its inclusion can significantly lower the density variation in view of maintaining an incompressible flow.
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