Pub Date : 2019-11-25DOI: 10.1142/9789814623285_0012
A. Dhruv, E. Balaras, A. Riaz, Jungho Kim
{"title":"Gravity Effects on Pool Boiling Heat Transfer","authors":"A. Dhruv, E. Balaras, A. Riaz, Jungho Kim","doi":"10.1142/9789814623285_0012","DOIUrl":"https://doi.org/10.1142/9789814623285_0012","url":null,"abstract":"","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"67 1","pages":"217-252"},"PeriodicalIF":0.0,"publicationDate":"2019-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91103770","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 : 2019-11-25DOI: 10.1103/physrevfluids.5.110515
N. Sharp
{"title":"Adopting a communication lifestyle","authors":"N. Sharp","doi":"10.1103/physrevfluids.5.110515","DOIUrl":"https://doi.org/10.1103/physrevfluids.5.110515","url":null,"abstract":"","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81904238","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}
{"title":"Evaluation of a non-equilibrium multi-component evaporation model for blended diesel/alcohol droplets","authors":"Hongyuan Zhang, Ping Yi, Suo Yang","doi":"10.2514/6.2020-2049","DOIUrl":"https://doi.org/10.2514/6.2020-2049","url":null,"abstract":"","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78157862","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}
Controlled flight in unsteady environments presents a challenge that has gained interest in recent years. Unsteady flight conditions exist in many scenarios including urban areas, airwakes, and extreme weather. In cases such as these, large force transients on wings and other lifting surfaces occur due to rapid variations in effective angle of attack resulting in flow separation and the formation of large-scale vortices. The growth and motion of these vortices can have a large impact on the resulting force transient and recovery, and often requires advanced control either locally via flow control or more globally at the vehicle level. Current research efforts focus on the effect of large wind gusts that result in changes to the relative flow that are of the same order of magnitude as the freestream flow. In these large-amplitude gust encounters, flow separation is significant, so the classical linear solution for the flow does not apply. Separated shear layers emanating from the wing tend to roll up into leading and trailing edge vortices that are shed into the wake. The formation and motion of these vortices are characterized via a series of canonical experiments in an attempt to better understand their contribution to aerodynamic forcing.
{"title":"Overview of NATO AVT-282: Unsteady Aerodynamic Response of Rigid Wings in Gust Encounters","authors":"Anya R. Jones","doi":"10.2514/6.2020-0078","DOIUrl":"https://doi.org/10.2514/6.2020-0078","url":null,"abstract":"Controlled flight in unsteady environments presents a challenge that has gained interest in recent years. Unsteady flight conditions exist in many scenarios including urban areas, airwakes, and extreme weather. In cases such as these, large force transients on wings and other lifting surfaces occur due to rapid variations in effective angle of attack resulting in flow separation and the formation of large-scale vortices. The growth and motion of these vortices can have a large impact on the resulting force transient and recovery, and often requires advanced control either locally via flow control or more globally at the vehicle level. Current research efforts focus on the effect of large wind gusts that result in changes to the relative flow that are of the same order of magnitude as the freestream flow. In these large-amplitude gust encounters, flow separation is significant, so the classical linear solution for the flow does not apply. Separated shear layers emanating from the wing tend to roll up into leading and trailing edge vortices that are shed into the wake. The formation and motion of these vortices are characterized via a series of canonical experiments in an attempt to better understand their contribution to aerodynamic forcing.","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"37 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80018584","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 : 2019-11-25DOI: 10.1016/J.NUCENGDES.2021.111177
Raphael Zanella, H. Henry, R. L. Tellier, M. Plapp
{"title":"Three-dimensional numerical simulation of droplet formation by Rayleigh–Taylor instability in multiphase corium","authors":"Raphael Zanella, H. Henry, R. L. Tellier, M. Plapp","doi":"10.1016/J.NUCENGDES.2021.111177","DOIUrl":"https://doi.org/10.1016/J.NUCENGDES.2021.111177","url":null,"abstract":"","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90818406","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 : 2019-11-24DOI: 10.1103/physrevfluids.4.124304
C. Marchioli, G. Sardina, Luca Brandt, A. Soldati
In this work, we use direct-numerical-simulation-based Eulerian-Lagrangian simulations to investigate the dynamics of small gyrotactic swimmers in free-surface turbulence. We consider open-channel flow turbulence in which bottom-heavy swimmers are dispersed. Swimmers are characterized by different vertical stability, so that some realign to swim upward with a characteristic time smaller than the Kolmogorov timescale, while others possess a reorientation time longer than the Kolmogorov timescale. We cover one order of magnitude in the flow Reynolds number and two orders of magnitude in the stability number, which is a measure of bottom heaviness. We observe that large-scale advection dominates vertical motion when the stability number, scaled on the local Kolmogorov timescale of the flow, is larger than unity: This condition is associated to enhanced migration toward the surface, particularly at low Reynolds number, when swimmers can rise through surface renewal motions that originate directly from the bottom-boundary turbulent bursts. Conversely, small-scale effects become more important when the Kolmogorov-based stability number is below unity: Under this condition, migration toward the surface is hindered, particularly at high Reynolds, when bottom-boundary bursts are less effective in bringing bulk fluid to the surface. In an effort to provide scaling arguments to improve predictions of models for motile microorganisms in turbulent water bodies, we demonstrate that a Kolmogorov-based stability number around unity represents a threshold beyond which swimmer capability to reach the free surface and form clusters saturates.
{"title":"Role of large-scale advection and small-scale turbulence on vertical migration of gyrotactic swimmers","authors":"C. Marchioli, G. Sardina, Luca Brandt, A. Soldati","doi":"10.1103/physrevfluids.4.124304","DOIUrl":"https://doi.org/10.1103/physrevfluids.4.124304","url":null,"abstract":"In this work, we use direct-numerical-simulation-based Eulerian-Lagrangian simulations to investigate the dynamics of small gyrotactic swimmers in free-surface turbulence. We consider open-channel flow turbulence in which bottom-heavy swimmers are dispersed. Swimmers are characterized by different vertical stability, so that some realign to swim upward with a characteristic time smaller than the Kolmogorov timescale, while others possess a reorientation time longer than the Kolmogorov timescale. We cover one order of magnitude in the flow Reynolds number and two orders of magnitude in the stability number, which is a measure of bottom heaviness. We observe that large-scale advection dominates vertical motion when the stability number, scaled on the local Kolmogorov timescale of the flow, is larger than unity: This condition is associated to enhanced migration toward the surface, particularly at low Reynolds number, when swimmers can rise through surface renewal motions that originate directly from the bottom-boundary turbulent bursts. Conversely, small-scale effects become more important when the Kolmogorov-based stability number is below unity: Under this condition, migration toward the surface is hindered, particularly at high Reynolds, when bottom-boundary bursts are less effective in bringing bulk fluid to the surface. In an effort to provide scaling arguments to improve predictions of models for motile microorganisms in turbulent water bodies, we demonstrate that a Kolmogorov-based stability number around unity represents a threshold beyond which swimmer capability to reach the free surface and form clusters saturates.","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"96 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85303747","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}
Core annular flow theory is used to model the parallel flow of fluids of different phases and has been used to describe drag reduction in the context of internal flows bounded by superhydrophobic surfaces. The work presented here is an extension of core annular flow theory to the study of the adiabatic section of heat pipes. Our aim is to develop a first-principles estimate of the conditions necessary to maximize the (counter) flow of liquid and vapor and, by extension, the axial flow of heat. The planar and axisymmetric geometries are examined as are heat pipes containing vs being devoid of a wick. In the wick vs no-wick cases, the peripheral return flow of liquid is, respectively, driven by capillarity and by gravity. Our model is used to predict velocity profiles and the flux-maximizing pressure gradient ratio (vapor-to-liquid). We further obtain estimates for the optimum thickness of the liquid layer. Note finally that when the liquid flow occurs via capillary pumping, there is a minimum surface tension below which the wick cannot supply a sufficient flow of liquid. We characterize this critical point in terms of the properties of the working fluid and of the wick.
{"title":"Core annular flow theory as applied to the adiabatic section of heat pipes","authors":"Aishwarya Rath, M. Flynn","doi":"10.1063/5.0017375","DOIUrl":"https://doi.org/10.1063/5.0017375","url":null,"abstract":"Core annular flow theory is used to model the parallel flow of fluids of different phases and has been used to describe drag reduction in the context of internal flows bounded by superhydrophobic surfaces. The work presented here is an extension of core annular flow theory to the study of the adiabatic section of heat pipes. Our aim is to develop a first-principles estimate of the conditions necessary to maximize the (counter) flow of liquid and vapor and, by extension, the axial flow of heat. The planar and axisymmetric geometries are examined as are heat pipes containing vs being devoid of a wick. In the wick vs no-wick cases, the peripheral return flow of liquid is, respectively, driven by capillarity and by gravity. Our model is used to predict velocity profiles and the flux-maximizing pressure gradient ratio (vapor-to-liquid). We further obtain estimates for the optimum thickness of the liquid layer. Note finally that when the liquid flow occurs via capillary pumping, there is a minimum surface tension below which the wick cannot supply a sufficient flow of liquid. We characterize this critical point in terms of the properties of the working fluid and of the wick.","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"161 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87602062","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}
Roman W. Morse, T. Moreira, Kristofer M. Dressler, G. Ribatski, Louise Mccarrol, E. Hurlburt, G. Nellis, A. Berson
{"title":"Liquid Film Dryout in Vertical Two-Phase Annular Flow in a Rectangular Channel","authors":"Roman W. Morse, T. Moreira, Kristofer M. Dressler, G. Ribatski, Louise Mccarrol, E. Hurlburt, G. Nellis, A. Berson","doi":"10.1115/1.0001518v","DOIUrl":"https://doi.org/10.1115/1.0001518v","url":null,"abstract":"","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87928786","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 : 2019-11-24DOI: 10.1103/physrevfluids.5.110517
P. Yeung, K. Ravikumar
{"title":"Advancing understanding of turbulence through extreme-scale computation: Intermittency and simulations at large problem sizes","authors":"P. Yeung, K. Ravikumar","doi":"10.1103/physrevfluids.5.110517","DOIUrl":"https://doi.org/10.1103/physrevfluids.5.110517","url":null,"abstract":"","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"120 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73453393","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}
We consider the periodic gaits of a microswimmer formed by two rotating cylinders, placed apart at a fixed width. Through a combination of theoretical arguments and numerical simulations, we derive semi-analytic expressions for the system’s instantaneous translational and rotational velocities, as a function of the rotational speeds of each cylinder. We can then integrate these relations in time to find the speed and efficiency of the swimmer for any imposed gait. Here, we focus particularly on identifying the periodic gaits that lead to the highest efficiency. To do so, we consider three stroke parameterizations in detail: alternating strokes, where only one cylinder rotates at a time; tilted rectangle strokes, which combine co- and counter-rotation phases; and smooth strokes represented through a set of Fourier series coefficients. For each parameterization, we compute maximum efficiency solutions using a numerical optimization approach. We find that the parameters of the global optimum, and the associated efficiency value, depend on the average mechanical input power. The globally optimal efficiency asymptotes toward that of a steadily counter-rotating cylinder pair as the input power increases. Finally, we address a possible three-dimensional (3D) extension of this system by evaluating the efficiency of a counter-rotating 3D cylinder pair with spherical end caps. We conclude that the counter-rotating cylinder pair combines competitive efficiency values and high versatility with simplicity of geometry and actuation, and thus forms a promising basis for engineered microswimmers.
{"title":"Locomotion of a rotating cylinder pair with periodic gaits at low Reynolds numbers","authors":"Li-Jun Ji, W. M. van Rees","doi":"10.1063/5.0022681","DOIUrl":"https://doi.org/10.1063/5.0022681","url":null,"abstract":"We consider the periodic gaits of a microswimmer formed by two rotating cylinders, placed apart at a fixed width. Through a combination of theoretical arguments and numerical simulations, we derive semi-analytic expressions for the system’s instantaneous translational and rotational velocities, as a function of the rotational speeds of each cylinder. We can then integrate these relations in time to find the speed and efficiency of the swimmer for any imposed gait. Here, we focus particularly on identifying the periodic gaits that lead to the highest efficiency. To do so, we consider three stroke parameterizations in detail: alternating strokes, where only one cylinder rotates at a time; tilted rectangle strokes, which combine co- and counter-rotation phases; and smooth strokes represented through a set of Fourier series coefficients. For each parameterization, we compute maximum efficiency solutions using a numerical optimization approach. We find that the parameters of the global optimum, and the associated efficiency value, depend on the average mechanical input power. The globally optimal efficiency asymptotes toward that of a steadily counter-rotating cylinder pair as the input power increases. Finally, we address a possible three-dimensional (3D) extension of this system by evaluating the efficiency of a counter-rotating 3D cylinder pair with spherical end caps. We conclude that the counter-rotating cylinder pair combines competitive efficiency values and high versatility with simplicity of geometry and actuation, and thus forms a promising basis for engineered microswimmers.","PeriodicalId":9375,"journal":{"name":"Bulletin of the American Physical Society","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90270773","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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