In this paper, we construct a pretraining framework for fluid environment perception, which includes an information compression model and the corresponding pretraining method. We test this framework in a two-cylinder problem through numerical simulation. The results show that after unsupervised pretraining with this framework, the intelligent agent can acquire key features of surrounding fluid environment, thereby adapting more quickly and effectively to subsequent multi-scenario tasks. In our research, these tasks include perceiving the position of the upstream obstacle and actively avoiding shedding vortices in the flow field to achieve drag reduction. Better performance of the pretrained agent is discussed in the sensitivity analysis.
{"title":"Improving agent performance in fluid environments by perceptual pretraining","authors":"Jin Zhang, Jianyang Xue, Bochao Cao","doi":"arxiv-2409.03230","DOIUrl":"https://doi.org/arxiv-2409.03230","url":null,"abstract":"In this paper, we construct a pretraining framework for fluid environment\u0000perception, which includes an information compression model and the\u0000corresponding pretraining method. We test this framework in a two-cylinder\u0000problem through numerical simulation. The results show that after unsupervised\u0000pretraining with this framework, the intelligent agent can acquire key features\u0000of surrounding fluid environment, thereby adapting more quickly and effectively\u0000to subsequent multi-scenario tasks. In our research, these tasks include\u0000perceiving the position of the upstream obstacle and actively avoiding shedding\u0000vortices in the flow field to achieve drag reduction. Better performance of the\u0000pretrained agent is discussed in the sensitivity analysis.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142226913","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}
A methodology is built to model and simulate the dynamics of domain coarsening of a two-phase ternary liquid with an arbitrary phase diagram. High numerical performance is obtained through the use of the phase field-method for interface capturing, a lattice Boltzmann method numerical scheme for all the model equations, and a portable, parallel simulation code running on multiple GPUs. The model is benchmarked against an analytic solution for a ternary diffusion couple. It also reproduces the well-known power law for droplet coarsening during Ostwald ripening without fluid flow. Large-scale simulations with flow illustrate the effects of momentum transport and buoyancy, as well as droplet coalescence and sedimentation.
{"title":"Grand-potential phase field simulations of droplet growth and sedimentation in a two-phase ternary fluid","authors":"Werner Verdier, Alain Cartalade, Mathis Plapp","doi":"arxiv-2409.03401","DOIUrl":"https://doi.org/arxiv-2409.03401","url":null,"abstract":"A methodology is built to model and simulate the dynamics of domain\u0000coarsening of a two-phase ternary liquid with an arbitrary phase diagram. High\u0000numerical performance is obtained through the use of the phase field-method for\u0000interface capturing, a lattice Boltzmann method numerical scheme for all the\u0000model equations, and a portable, parallel simulation code running on multiple\u0000GPUs. The model is benchmarked against an analytic solution for a ternary\u0000diffusion couple. It also reproduces the well-known power law for droplet\u0000coarsening during Ostwald ripening without fluid flow. Large-scale simulations\u0000with flow illustrate the effects of momentum transport and buoyancy, as well as\u0000droplet coalescence and sedimentation.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212738","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}
Esther Lagemann, Julia Roeb, Steven L. Brunton, Christian Lagemann
The accurate quantification of wall-shear stress dynamics is of substantial importance for various applications in fundamental and applied research, spanning areas from human health to aircraft design and optimization. Despite significant progress in experimental measurement techniques and post-processing algorithms, temporally resolved wall-shear stress dynamics with adequate spatial resolution and within a suitable spatial domain remain an elusive goal. To address this gap, we introduce a deep learning architecture that ingests wall-parallel velocity fields from the logarithmic layer of turbulent wall-bounded flows and outputs the corresponding 2D wall-shear stress fields with identical spatial resolution and domain size. From a physical perspective, our framework acts as a surrogate model encapsulating the various mechanisms through which highly energetic outer-layer flow structures influence the governing wall-shear stress dynamics. The network is trained in a supervised fashion on a unified dataset comprising direct numerical simulations of statistically 1D turbulent channel and spatially developing turbulent boundary layer flows at friction Reynolds numbers ranging from 390 to 1,500. We demonstrate a zero-shot applicability to experimental velocity fields obtained from Particle-Image Velocimetry measurements and verify the physical accuracy of the wall-shear stress estimates with synchronized wall-shear stress measurements using the Micro-Pillar Shear-Stress Sensor for Reynolds numbers up to 2,000. In summary, the presented framework lays the groundwork for extracting inaccessible experimental wall-shear stress information from readily available velocity measurements and thus, facilitates advancements in a variety of experimental applications.
{"title":"A deep learning approach to wall-shear stress quantification: From numerical training to zero-shot experimental application","authors":"Esther Lagemann, Julia Roeb, Steven L. Brunton, Christian Lagemann","doi":"arxiv-2409.03933","DOIUrl":"https://doi.org/arxiv-2409.03933","url":null,"abstract":"The accurate quantification of wall-shear stress dynamics is of substantial\u0000importance for various applications in fundamental and applied research,\u0000spanning areas from human health to aircraft design and optimization. Despite\u0000significant progress in experimental measurement techniques and post-processing\u0000algorithms, temporally resolved wall-shear stress dynamics with adequate\u0000spatial resolution and within a suitable spatial domain remain an elusive goal.\u0000To address this gap, we introduce a deep learning architecture that ingests\u0000wall-parallel velocity fields from the logarithmic layer of turbulent\u0000wall-bounded flows and outputs the corresponding 2D wall-shear stress fields\u0000with identical spatial resolution and domain size. From a physical perspective,\u0000our framework acts as a surrogate model encapsulating the various mechanisms\u0000through which highly energetic outer-layer flow structures influence the\u0000governing wall-shear stress dynamics. The network is trained in a supervised\u0000fashion on a unified dataset comprising direct numerical simulations of\u0000statistically 1D turbulent channel and spatially developing turbulent boundary\u0000layer flows at friction Reynolds numbers ranging from 390 to 1,500. We\u0000demonstrate a zero-shot applicability to experimental velocity fields obtained\u0000from Particle-Image Velocimetry measurements and verify the physical accuracy\u0000of the wall-shear stress estimates with synchronized wall-shear stress\u0000measurements using the Micro-Pillar Shear-Stress Sensor for Reynolds numbers up\u0000to 2,000. In summary, the presented framework lays the groundwork for\u0000extracting inaccessible experimental wall-shear stress information from readily\u0000available velocity measurements and thus, facilitates advancements in a variety\u0000of experimental applications.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212734","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}
Providing a compelling derivation of Kolmogorov turbulence is a fascinating open challenge in field theory. Here, we pose a more modest question: if we had a field-theoretic description of Kolmogorov turbulence, could we use it to describe deviations caused, for example, by adding a polymer additive or by relativistic corrections? To investigate this issue, we assume a description of developed, homogeneous, and isotropic turbulence along the lines of Martin, Siggia, and Rose, and we work out the first corrections to the equal-time, two-point spectrum caused by adding non-Newtonian terms to the fluid stress tensor. While the results are not conclusive, they show a promising resemblance to turbulent spectra found in both experiments and large-scale numerical simulations.
{"title":"Field Theory of Non-Newtonian Turbulence","authors":"Esteban Calzetta","doi":"arxiv-2409.03150","DOIUrl":"https://doi.org/arxiv-2409.03150","url":null,"abstract":"Providing a compelling derivation of Kolmogorov turbulence is a fascinating\u0000open challenge in field theory. Here, we pose a more modest question: if we had\u0000a field-theoretic description of Kolmogorov turbulence, could we use it to\u0000describe deviations caused, for example, by adding a polymer additive or by\u0000relativistic corrections? To investigate this issue, we assume a description of\u0000developed, homogeneous, and isotropic turbulence along the lines of Martin,\u0000Siggia, and Rose, and we work out the first corrections to the equal-time,\u0000two-point spectrum caused by adding non-Newtonian terms to the fluid stress\u0000tensor. While the results are not conclusive, they show a promising resemblance\u0000to turbulent spectra found in both experiments and large-scale numerical\u0000simulations.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"31 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212736","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}
Sofía Angriman, Sarah E. Smith, Patricio Clark di Leoni, Pablo J. Cobelli, Pablo D. Mininni, Martín Obligado
Active grids operated with random protocols are a standard way to generate large Reynolds number turbulence in wind and water tunnels. But anomalies in the decay and third-order scaling of active-grid turbulence have been reported. We combine Laser Doppler Velocimetry and hot-wire anemometry measurements in a wind tunnel, with machine learning techniques and numerical simulations, to gain further understanding on the reasons behind these anomalies. Numerical simulations that incorporate the statistical anomalies observed in the experimental velocity field near the active grid can reproduce the experimental anomalies observed later in the decay. The results indicate that anomalies in experiments near the active grid introduce correlations in the flow that persist for long times, and result in the flow being statistically different from homogeneous and isotropic turbulence.
{"title":"Active grid turbulence anomalies through the lens of physics informed neural networks","authors":"Sofía Angriman, Sarah E. Smith, Patricio Clark di Leoni, Pablo J. Cobelli, Pablo D. Mininni, Martín Obligado","doi":"arxiv-2409.03919","DOIUrl":"https://doi.org/arxiv-2409.03919","url":null,"abstract":"Active grids operated with random protocols are a standard way to generate\u0000large Reynolds number turbulence in wind and water tunnels. But anomalies in\u0000the decay and third-order scaling of active-grid turbulence have been reported.\u0000We combine Laser Doppler Velocimetry and hot-wire anemometry measurements in a\u0000wind tunnel, with machine learning techniques and numerical simulations, to\u0000gain further understanding on the reasons behind these anomalies. Numerical\u0000simulations that incorporate the statistical anomalies observed in the\u0000experimental velocity field near the active grid can reproduce the experimental\u0000anomalies observed later in the decay. The results indicate that anomalies in\u0000experiments near the active grid introduce correlations in the flow that\u0000persist for long times, and result in the flow being statistically different\u0000from homogeneous and isotropic turbulence.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212735","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}
Ding-Yi Pan, Yi-Fei Huang, Ze Lyu, Juan-Cheng Yang, Ming-Jiu Ni
In the present study, by adopting the advantage of ultrasonic techniques, we developed a Multichannel Pulsed Ultrasonic Doppler Velocimetry (MPUDV) to measure the 2D2C velocity fields of liquid metal flow. Due to the specially designed Ultrasonic host and post-processing scheme, the MPUDV system can reach a high spatiotemporal resolution of 50 Hz and 3 mm. The flow loop contains a cavity test section to ensure a classical recirculating flow was built to validate the accuracy of MPUDV in velocity field measurement. In the initial phase of the study, water with tracer particles was selected as the working liquid to ensure the velocity field measurements by the well-developed Particle Image Velocimetry (PIV). A comparison of the data obtained from the PIV and MPUDV methods revealed less than 3 differences in the 2D2C velocity field between the two techniques during simultaneous measurements of the same flow field. This finding strongly demonstrates the reliability of the MPUDV method developed in this paper. Moreover, the ternary alloy GaInSn was selected as the working liquid in the flow loop to validate the efficacy of the MPUDV in measuring 2D-2C velocity fields. A series of tests were conducted in the cavity at varying Reynolds numbers, ranging from 9103 to 24123. The measurements demonstrated that the MPUDV could accurately measure the flow structures characterized by a central primary circulation eddy and two secondary eddies in the opaque liquid metal. Furthermore, it was found that the vortex center of the primary circulating eddy and the size of the secondary eddies undergo significant alterations with varying Reynolds numbers, indicating the influence of inertial force on the flow characteristics in the recirculating flow. It is therefore demonstrated that the current MPUDV methodology is applicable for measuring a 2D2C velocity field in opaque liquid metal flows.
{"title":"Development of the Multichannel Pulsed Ultrasonic Doppler Velocimeter for the measurement of liquid metal flow","authors":"Ding-Yi Pan, Yi-Fei Huang, Ze Lyu, Juan-Cheng Yang, Ming-Jiu Ni","doi":"arxiv-2409.02815","DOIUrl":"https://doi.org/arxiv-2409.02815","url":null,"abstract":"In the present study, by adopting the advantage of ultrasonic techniques, we\u0000developed a Multichannel Pulsed Ultrasonic Doppler Velocimetry (MPUDV) to\u0000measure the 2D2C velocity fields of liquid metal flow. Due to the specially\u0000designed Ultrasonic host and post-processing scheme, the MPUDV system can reach\u0000a high spatiotemporal resolution of 50 Hz and 3 mm. The flow loop contains a\u0000cavity test section to ensure a classical recirculating flow was built to\u0000validate the accuracy of MPUDV in velocity field measurement. In the initial\u0000phase of the study, water with tracer particles was selected as the working\u0000liquid to ensure the velocity field measurements by the well-developed Particle\u0000Image Velocimetry (PIV). A comparison of the data obtained from the PIV and\u0000MPUDV methods revealed less than 3 differences in the 2D2C velocity field\u0000between the two techniques during simultaneous measurements of the same flow\u0000field. This finding strongly demonstrates the reliability of the MPUDV method\u0000developed in this paper. Moreover, the ternary alloy GaInSn was selected as the\u0000working liquid in the flow loop to validate the efficacy of the MPUDV in\u0000measuring 2D-2C velocity fields. A series of tests were conducted in the cavity\u0000at varying Reynolds numbers, ranging from 9103 to 24123. The measurements\u0000demonstrated that the MPUDV could accurately measure the flow structures\u0000characterized by a central primary circulation eddy and two secondary eddies in\u0000the opaque liquid metal. Furthermore, it was found that the vortex center of\u0000the primary circulating eddy and the size of the secondary eddies undergo\u0000significant alterations with varying Reynolds numbers, indicating the influence\u0000of inertial force on the flow characteristics in the recirculating flow. It is\u0000therefore demonstrated that the current MPUDV methodology is applicable for\u0000measuring a 2D2C velocity field in opaque liquid metal flows.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212740","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}
Unsteady cloud cavitating flow is detrimental to the efficiency of hydraulic machinery like pumps and propellers due to the resulting side-effects of vibration, noise and erosion damage. Modelling such a unsteady and highly turbulent flow remains a challenging issue. In this paper, cloud cavitating flow in a venturi is calculated using the Detached Eddy Simulation (DES) model combined with the Merkle model. The Adaptive Mesh Refinement (AMR) method is employed to speed up the calculation and investigate the mechanisms for vortex development in the venturi. The results indicate the velocity gradients and the generalized fluid element strongly influence the formation of vortices throughout a cavitation cycle. In addition, the cavitation-turbulence coupling is investigated on the local scale by comparing with high-fidelity experimental data and using profile stations. While the AMR calculation is able to predict well the time-averaged velocities and turbulence-related aspects near the throat, it displays discrepancies further downstream owing to a coarser grid refinement downstream and under-performs compared to a traditional grid simulation . Additionally, the AMR calculations is unable to reproduce the cavity width as observed in the experiments. Therefore, while AMR promises to speed the process significantly by refining grid only in regions of interest, it is comparatively in line with a traditional calculation for cavitating flows. Thus, this study intends to provide a reference to employing AMR as a tool to speed up calculations and be able to simulate turbulence-cavitation interactions accurately.
非稳定云气蚀流会产生振动、噪音和侵蚀破坏等副作用，从而影响泵和螺旋桨等液压机械的效率。对这种不稳定的高湍流进行建模仍然是一个具有挑战性的问题。本文使用分离涡模拟（DES）模型结合梅克尔模型计算文丘里管中的云空化流。采用自适应网格细化（AMR）方法加快了计算速度，并研究了文丘里管中涡流发展的机制。结果表明，速度梯度和广义流体元素对整个空化循环中涡流的形成有很大影响。此外，通过与高保真实验数据比较和使用剖面站，研究了局部尺度上的空化-湍流耦合。虽然 AMR 计算能够很好地预测喉部附近的时均速度和湍流相关方面，但由于下游网格细化较粗，它在更下游显示出差异，与传统网格模拟相比表现不佳。此外，AMR 计算无法再现实验中观察到的空腔宽度。因此，虽然 AMR 可通过仅在感兴趣的区域细化网格来显著加快计算过程，但相对而言，它与传统的空化流计算方法并不一致。因此，本研究旨在为利用 AMR 作为工具加快计算速度并准确模拟湍流与空化相互作用提供参考。
{"title":"Investigation of cloud cavitating flow in a venturi using Adaptive Mesh Refinement (AMR)","authors":"Dhruv Apte, Mingming Ge, Olivier Coutier-Delgosha","doi":"arxiv-2409.02369","DOIUrl":"https://doi.org/arxiv-2409.02369","url":null,"abstract":"Unsteady cloud cavitating flow is detrimental to the efficiency of hydraulic\u0000machinery like pumps and propellers due to the resulting side-effects of\u0000vibration, noise and erosion damage. Modelling such a unsteady and highly\u0000turbulent flow remains a challenging issue. In this paper, cloud cavitating\u0000flow in a venturi is calculated using the Detached Eddy Simulation (DES) model\u0000combined with the Merkle model. The Adaptive Mesh Refinement (AMR) method is\u0000employed to speed up the calculation and investigate the mechanisms for vortex\u0000development in the venturi. The results indicate the velocity gradients and the\u0000generalized fluid element strongly influence the formation of vortices\u0000throughout a cavitation cycle. In addition, the cavitation-turbulence coupling\u0000is investigated on the local scale by comparing with high-fidelity experimental\u0000data and using profile stations. While the AMR calculation is able to predict\u0000well the time-averaged velocities and turbulence-related aspects near the\u0000throat, it displays discrepancies further downstream owing to a coarser grid\u0000refinement downstream and under-performs compared to a traditional grid\u0000simulation . Additionally, the AMR calculations is unable to reproduce the\u0000cavity width as observed in the experiments. Therefore, while AMR promises to\u0000speed the process significantly by refining grid only in regions of interest,\u0000it is comparatively in line with a traditional calculation for cavitating\u0000flows. Thus, this study intends to provide a reference to employing AMR as a\u0000tool to speed up calculations and be able to simulate turbulence-cavitation\u0000interactions accurately.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"104 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212749","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}
Robert Hunt, Roberto Camassa, Richard M. McLaughlin, Daniel M. Harris
The vertical transport of solid material in a stratified medium is fundamental to a number of environmental applications, with implications for the carbon cycle and nutrient transport in marine ecosystems. In this work, we study the diffusion-limited settling of highly porous particles in a density-stratified fluid through a combination of experiment, analysis, and numerical simulation. By delineating and appealing to the diffusion-limited regime wherein buoyancy effects due to mass adaptation dominate hydrodynamic drag, we derive a simple expression for the steady settling velocity of a sphere as a function of the density, size, and diffusivity of the solid, as well as the density gradient of the background fluid. In this regime, smaller particles settle faster, in contrast with most conventional hydrodynamic drag mechanisms. Furthermore, we outline a general mathematical framework for computing the steady settling speed of a body of arbitrary shape in this regime and compute exact results for the case of general ellipsoids. Using hydrogels as a highly porous model system, we validate the predictions with laboratory experiments in linear stratification for a wide range of parameters. Lastly, we show how the predictions can be applied to arbitrary slowly varying background density profiles and demonstrate how a measured particle position over time can be used to reconstruct the background density profile.
{"title":"Diffusion-limited settling of highly porous particles in density-stratified fluids","authors":"Robert Hunt, Roberto Camassa, Richard M. McLaughlin, Daniel M. Harris","doi":"arxiv-2409.02419","DOIUrl":"https://doi.org/arxiv-2409.02419","url":null,"abstract":"The vertical transport of solid material in a stratified medium is\u0000fundamental to a number of environmental applications, with implications for\u0000the carbon cycle and nutrient transport in marine ecosystems. In this work, we\u0000study the diffusion-limited settling of highly porous particles in a\u0000density-stratified fluid through a combination of experiment, analysis, and\u0000numerical simulation. By delineating and appealing to the diffusion-limited\u0000regime wherein buoyancy effects due to mass adaptation dominate hydrodynamic\u0000drag, we derive a simple expression for the steady settling velocity of a\u0000sphere as a function of the density, size, and diffusivity of the solid, as\u0000well as the density gradient of the background fluid. In this regime, smaller\u0000particles settle faster, in contrast with most conventional hydrodynamic drag\u0000mechanisms. Furthermore, we outline a general mathematical framework for\u0000computing the steady settling speed of a body of arbitrary shape in this regime\u0000and compute exact results for the case of general ellipsoids. Using hydrogels\u0000as a highly porous model system, we validate the predictions with laboratory\u0000experiments in linear stratification for a wide range of parameters. Lastly, we\u0000show how the predictions can be applied to arbitrary slowly varying background\u0000density profiles and demonstrate how a measured particle position over time can\u0000be used to reconstruct the background density profile.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"182 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142226915","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}
Alessandro Chiarini, Simone Tandurella, Marco Edoardo Rosti
We investigate the fluid-solid interaction of suspensions of Kolmogorov-size spherical particles moving in homogeneous isotropic turbulence at a microscale Reynolds number of $Re_lambda approx 140$. Two volume fractions are considered, $10^{-5}$ and $10^{-3}$, and the solid-to-fluid density ratio is set to $5$ and $100$. We present a comparison between interface-resolved (PR-DNS) and one-way-coupled point-particle (PP-DNS) direct numerical simulations. We find that the modulated energy spectrum shows the classical $-5/3$ Kolmogorov scaling in the inertial range of scales and a $-4$ scaling at smaller scales, with the latter resulting from a balance between the energy injected by the particles and the viscous dissipation, in an otherwise smooth flow. An analysis of the small-scale flow topology shows that the particles mainly favour events with axial strain and vortex compression. The dynamics of the particles and their collective motion studied for PR-DNS are used to assess the validity of the PP-DNS. We find that the PP-DNS predicts fairly well both the Lagrangian and Eulerian statistics of the particles motion for the low-density case, while some discrepancies are observed for the high-density case. Also, the PP-DNS is found to underpredict the level of clustering of the suspension compared to the PR-DNS, with a larger difference for the high-density case.
{"title":"Kolmogorov-size particles in homogeneous and isotropic turbulence","authors":"Alessandro Chiarini, Simone Tandurella, Marco Edoardo Rosti","doi":"arxiv-2409.02467","DOIUrl":"https://doi.org/arxiv-2409.02467","url":null,"abstract":"We investigate the fluid-solid interaction of suspensions of Kolmogorov-size\u0000spherical particles moving in homogeneous isotropic turbulence at a microscale\u0000Reynolds number of $Re_lambda approx 140$. Two volume fractions are\u0000considered, $10^{-5}$ and $10^{-3}$, and the solid-to-fluid density ratio is\u0000set to $5$ and $100$. We present a comparison between interface-resolved\u0000(PR-DNS) and one-way-coupled point-particle (PP-DNS) direct numerical\u0000simulations. We find that the modulated energy spectrum shows the classical\u0000$-5/3$ Kolmogorov scaling in the inertial range of scales and a $-4$ scaling at\u0000smaller scales, with the latter resulting from a balance between the energy\u0000injected by the particles and the viscous dissipation, in an otherwise smooth\u0000flow. An analysis of the small-scale flow topology shows that the particles\u0000mainly favour events with axial strain and vortex compression. The dynamics of\u0000the particles and their collective motion studied for PR-DNS are used to assess\u0000the validity of the PP-DNS. We find that the PP-DNS predicts fairly well both\u0000the Lagrangian and Eulerian statistics of the particles motion for the\u0000low-density case, while some discrepancies are observed for the high-density\u0000case. Also, the PP-DNS is found to underpredict the level of clustering of the\u0000suspension compared to the PR-DNS, with a larger difference for the\u0000high-density case.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142226914","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}
Naoki Takeishi, Kenta Ishimoto, Naoto Yokoyama, Marco Edoardo Rosti
We present numerical analysis of the lateral movement of spherical capsule in the steady and pulsatile channel flow of a Newtonian fluid, for a wide range of oscillatory frequency. Each capsule membrane satisfying strain-hardening characteristic is simulated for different Reynolds numbers Re and capillary numbers Ca. Our numerical results showed that capsules with high Ca exhibit axial focusing at finite Re similarly to the inertialess case. We observe that the speed of the axial focusing can be substantially accelerated by making the driving pressure gradient oscillating in time. We also confirm the existence of an optimal frequency which maximizes the speed of axial focusing, that remains the same found in the absence of inertia. For relatively low Ca, on the other hand, the capsule exhibits off-centre focusing, resulting in various equilibrium radial positions depending on Re. Our numerical results further clarifies the existence of a specific Re for which the effect of the flow pulsation to the equilibrium radial position is maximum. The roles of channel size and viscosity ratio on the lateral movements of the capsule are also addressed.
我们对球形胶囊在牛顿流体的稳定和脉动通道流中的横向运动进行了数值分析，分析的振荡频率范围很宽。我们模拟了不同雷诺数 Re 和毛细管数 Ca 条件下满足应变硬化特性的各胶囊膜。我们的数值结果表明，与无惯性情况类似，高 Ca 值的胶囊在有限 Re 值下表现出轴向聚焦。我们观察到，通过使驱动压力梯度在时间上振荡，可以大大加快轴向聚焦的速度。我们还证实了一个最佳频率的存在，该频率能最大限度地提高轴向聚焦的速度，并且在无惯性的情况下保持不变。另一方面，在 Ca 相对较低的情况下，胶囊表现出偏离中心的聚焦，导致取决于 Re 的不同径向平衡位置。我们的数值结果进一步证明了存在一个特定的 Re 值，在该值下，流动脉冲对平衡径向位置的影响最大。我们还讨论了通道大小和粘度比对胶囊横向运动的影响。
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