Dorianis M. Perez, Jesse M. Canfield, Rodman R. Linn, Kevin Speer
In wildfires, atmospheric turbulence plays a major role in the transfer of turbulent kinetic energy. Understanding how turbulence feeds back into a dynamical system is important, down to the varying small scales of fuel structures (i.e. pine needles, grass). Large eddy simulations (LES) are a common way of numerically representing turbulence. The Smagorinsky model (1963) serves as one of the most studied sub-grid scale representations in LES. In this investigation, the Smagorinsky model was implemented in HIGRAD/FIRETEC, LANL's coupled fire-atmosphere model. The Smagorinsky turbulent kinetic energy (TKE) was compared to FIRETEC's 1.5-order TKE eddy-viscosity subgrid-scale model, known as the Linn turbulence model. This was done in simulations of flow over flat terrain with a homogeneous, cuboidal canopy in the center of the domain. Examinations of the modeled vertical TKE profile and turbulent statistics at the leading edge, and throughout the canopy, show that the Smagorinsky model provides comparable results to that of the original closure model posed in FIRETEC.
{"title":"Characterizing Turbulence at a Forest Edge: Comparing Sub-filter Scale Turbulence Models in Simulations of Flow over a Canopy","authors":"Dorianis M. Perez, Jesse M. Canfield, Rodman R. Linn, Kevin Speer","doi":"arxiv-2409.06047","DOIUrl":"https://doi.org/arxiv-2409.06047","url":null,"abstract":"In wildfires, atmospheric turbulence plays a major role in the transfer of\u0000turbulent kinetic energy. Understanding how turbulence feeds back into a\u0000dynamical system is important, down to the varying small scales of fuel\u0000structures (i.e. pine needles, grass). Large eddy simulations (LES) are a\u0000common way of numerically representing turbulence. The Smagorinsky model (1963)\u0000serves as one of the most studied sub-grid scale representations in LES. In\u0000this investigation, the Smagorinsky model was implemented in HIGRAD/FIRETEC,\u0000LANL's coupled fire-atmosphere model. The Smagorinsky turbulent kinetic energy\u0000(TKE) was compared to FIRETEC's 1.5-order TKE eddy-viscosity subgrid-scale\u0000model, known as the Linn turbulence model. This was done in simulations of flow\u0000over flat terrain with a homogeneous, cuboidal canopy in the center of the\u0000domain. Examinations of the modeled vertical TKE profile and turbulent\u0000statistics at the leading edge, and throughout the canopy, show that the\u0000Smagorinsky model provides comparable results to that of the original closure\u0000model posed in FIRETEC.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"27 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212699","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}
Paula Reis, Gaute Linga, Marcel Moura, Per Arne Rikvold, Renaud Toussaint, Eirik Grude Flekkøy, Knut Jørgen Måløy
Drainage in porous media can be broken down into two main mechanisms: a primary piston-like displacement of the interfaces through the bulk of pore bodies and throats, and a secondary slow flow through corners and films in the wake of the invasion front. In granular porous media, this secondary drainage mechanism unfolds in connected pathways of pendular structures, such as capillary bridges and liquid rings, formed between liquid clusters. To represent both mechanisms, we proposed a dynamic dual-network model for drainage, considering that a gas displaces a wetting liquid from quasi-2D granular porous media. For this model, dedicated analyses of the capillary bridge shapes and hydraulic conductivity were conducted so that the secondary drainage mechanism could be properly quantified at finite speeds. With the model, an investigation of the wetting-phase connectivity and flow during drainage was carried out, covering a broad range of flow conditions. Results indicate that the span of liquid-connected structures in the unsaturated region, as well as their ability to contribute to flow, varies significantly with Capillary and Bond numbers.
{"title":"Interaction between corner and bulk flows during drainage in granular porous media","authors":"Paula Reis, Gaute Linga, Marcel Moura, Per Arne Rikvold, Renaud Toussaint, Eirik Grude Flekkøy, Knut Jørgen Måløy","doi":"arxiv-2409.05574","DOIUrl":"https://doi.org/arxiv-2409.05574","url":null,"abstract":"Drainage in porous media can be broken down into two main mechanisms: a\u0000primary piston-like displacement of the interfaces through the bulk of pore\u0000bodies and throats, and a secondary slow flow through corners and films in the\u0000wake of the invasion front. In granular porous media, this secondary drainage\u0000mechanism unfolds in connected pathways of pendular structures, such as\u0000capillary bridges and liquid rings, formed between liquid clusters. To\u0000represent both mechanisms, we proposed a dynamic dual-network model for\u0000drainage, considering that a gas displaces a wetting liquid from quasi-2D\u0000granular porous media. For this model, dedicated analyses of the capillary\u0000bridge shapes and hydraulic conductivity were conducted so that the secondary\u0000drainage mechanism could be properly quantified at finite speeds. With the\u0000model, an investigation of the wetting-phase connectivity and flow during\u0000drainage was carried out, covering a broad range of flow conditions. Results\u0000indicate that the span of liquid-connected structures in the unsaturated\u0000region, as well as their ability to contribute to flow, varies significantly\u0000with Capillary and Bond numbers.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"51 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212730","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}
Shyam S. Nair, Vishal A. Wadhai, Robert F. Kunz, Xiang I. A. Yang
We report direct numerical simulation (DNS) results of the rough-wall channel, focusing on roughness with high $k_{rms}/k_a$ statistics but small to negative $Sk$ statistics, and we study the implications of this new dataset on rough-wall modelling. Here, $k_{rms}$ is the root-mean-square, $k_a$ is the first order moment of roughness height, and $Sk$ is the skewness. The effects of packing density, skewness and arrangement of roughness elements on mean streamwise velocity, equivalent roughness height ($z_0$) and Reynolds and dispersive stresses have been studied. We demonstrate that two-point correlation lengths of roughness height statistics play an important role in characterizing rough surfaces with identical moments of roughness height but different arrangements of roughness elements. Analysis of the present as well as historical data suggests that the task of rough-wall modelling is to identify geometric parameters that distinguish the rough surfaces within the calibration dataset. We demonstrate a novel feature selection procedure to determine these parameters. Further, since there is not a finite set of roughness statistics that distinguish between all rough surfaces, we argue that obtaining a universal rough-wall model for making equivalent sand-grain roughness ($k_s$) predictions would be challenging, and that each rough-wall model would have its applicable range. This motivates the development of group-based rough-wall models. The applicability of multi-variate polynomial regression and feedforward neural networks for building such group-based rough-wall models using the selected features has been shown.
{"title":"Rough surfaces in under-explored surface morphology space and their implications on roughness modelling","authors":"Shyam S. Nair, Vishal A. Wadhai, Robert F. Kunz, Xiang I. A. Yang","doi":"arxiv-2409.06089","DOIUrl":"https://doi.org/arxiv-2409.06089","url":null,"abstract":"We report direct numerical simulation (DNS) results of the rough-wall\u0000channel, focusing on roughness with high $k_{rms}/k_a$ statistics but small to\u0000negative $Sk$ statistics, and we study the implications of this new dataset on\u0000rough-wall modelling. Here, $k_{rms}$ is the root-mean-square, $k_a$ is the\u0000first order moment of roughness height, and $Sk$ is the skewness. The effects\u0000of packing density, skewness and arrangement of roughness elements on mean\u0000streamwise velocity, equivalent roughness height ($z_0$) and Reynolds and\u0000dispersive stresses have been studied. We demonstrate that two-point\u0000correlation lengths of roughness height statistics play an important role in\u0000characterizing rough surfaces with identical moments of roughness height but\u0000different arrangements of roughness elements. Analysis of the present as well\u0000as historical data suggests that the task of rough-wall modelling is to\u0000identify geometric parameters that distinguish the rough surfaces within the\u0000calibration dataset. We demonstrate a novel feature selection procedure to\u0000determine these parameters. Further, since there is not a finite set of\u0000roughness statistics that distinguish between all rough surfaces, we argue that\u0000obtaining a universal rough-wall model for making equivalent sand-grain\u0000roughness ($k_s$) predictions would be challenging, and that each rough-wall\u0000model would have its applicable range. This motivates the development of\u0000group-based rough-wall models. The applicability of multi-variate polynomial\u0000regression and feedforward neural networks for building such group-based\u0000rough-wall models using the selected features has been shown.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"114 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142226912","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}
Arnout Franken, Erwin Luesink, Sagy Ephrati, Bernard Geurts
In this paper, we study geostrophic turbulence without external forcing or dissipation, using a Casimir-preserving numerical method. The research examines the formation of large zonal jets, common in geophysical flows, especially in giant gas planets. These jets form due to the east-west stretching of vortices, influenced by the gradient of the Coriolis parameter, leading to a critical latitude beyond which jets do not form. Using a global quasi-geostrophic model with a fully latitude-dependent Coriolis parameter, we investigate this critical latitude, which is theorized to depend only on the product of the Rossby number and the Lamb parameter. By simulating random flow fields, the critical latitude was identified through zonally averaged zonal velocity profiles. Results align with geostrophic theory, especially near typical Rossby and Lamb parameter values for Earth's atmosphere. However, in the regime of weak rotation (high Rossby numbers) and strong stratification (high Lamb values), no clear critical latitude emerges; instead, zonal jet amplitude and width decrease gradually towards the poles. This research paves the way for further study of jet dynamics under a fully latitude-dependent Coriolis parameter.
{"title":"Critical latitude in global quasi-geostrophic flow on a rotating sphere","authors":"Arnout Franken, Erwin Luesink, Sagy Ephrati, Bernard Geurts","doi":"arxiv-2409.05432","DOIUrl":"https://doi.org/arxiv-2409.05432","url":null,"abstract":"In this paper, we study geostrophic turbulence without external forcing or\u0000dissipation, using a Casimir-preserving numerical method. The research examines\u0000the formation of large zonal jets, common in geophysical flows, especially in\u0000giant gas planets. These jets form due to the east-west stretching of vortices,\u0000influenced by the gradient of the Coriolis parameter, leading to a critical\u0000latitude beyond which jets do not form. Using a global quasi-geostrophic model with a fully latitude-dependent\u0000Coriolis parameter, we investigate this critical latitude, which is theorized\u0000to depend only on the product of the Rossby number and the Lamb parameter. By\u0000simulating random flow fields, the critical latitude was identified through\u0000zonally averaged zonal velocity profiles. Results align with geostrophic theory, especially near typical Rossby and\u0000Lamb parameter values for Earth's atmosphere. However, in the regime of weak\u0000rotation (high Rossby numbers) and strong stratification (high Lamb values), no\u0000clear critical latitude emerges; instead, zonal jet amplitude and width\u0000decrease gradually towards the poles. This research paves the way for further\u0000study of jet dynamics under a fully latitude-dependent Coriolis parameter.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212731","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}
Dorianis M. Perez, Jesse M. Canfield, Rodman R. Linn, Kevin Speer
Vorticity is a key characteristic of flow patterns that determine wildland fire behavior, frontal evolution, and wind-canopy interaction. Investigating the role of vorticity in the flow fields around vegetation can help us better understand fire-atmosphere feedback and the influences of vegetation on this feedback. In modeling vorticity, ``perhaps the greatest knowledge gap exists in understanding which terms in the vorticity equation dominate [...] (and) when one or the other might dominate" (Potter, 2012). In this study, we investigate the role of vorticity in boundary layer dynamics and canopy/forest edge effects using HIGRAD/FIRETEC, a three-dimensional, two-phase transport model that conserves mass, momentum, energy, and chemical species. A vorticity transport equation was derived and discretized. Simulations were performed over a cuboidal homogeneous canopy surrounded by surface vegetation. This derivation led to the discovery of a drag tilting and stretching term, which shows that gradients in the aerodynamic drag of the vegetation, tied to heterogeneities in surface area-to-volume ratio, play an important role in the generation of vorticity. Results from the vorticity budget analysis show that this term contributes significantly in the areas where these gradients are present, namely the edges of the canopy.
{"title":"Characterizing Turbulence at a Forest Edge: A Vorticity Budget Analysis around a Canopy","authors":"Dorianis M. Perez, Jesse M. Canfield, Rodman R. Linn, Kevin Speer","doi":"arxiv-2409.06044","DOIUrl":"https://doi.org/arxiv-2409.06044","url":null,"abstract":"Vorticity is a key characteristic of flow patterns that determine wildland\u0000fire behavior, frontal evolution, and wind-canopy interaction. Investigating\u0000the role of vorticity in the flow fields around vegetation can help us better\u0000understand fire-atmosphere feedback and the influences of vegetation on this\u0000feedback. In modeling vorticity, ``perhaps the greatest knowledge gap exists in\u0000understanding which terms in the vorticity equation dominate [...] (and) when\u0000one or the other might dominate\" (Potter, 2012). In this study, we investigate\u0000the role of vorticity in boundary layer dynamics and canopy/forest edge effects\u0000using HIGRAD/FIRETEC, a three-dimensional, two-phase transport model that\u0000conserves mass, momentum, energy, and chemical species. A vorticity transport\u0000equation was derived and discretized. Simulations were performed over a\u0000cuboidal homogeneous canopy surrounded by surface vegetation. This derivation\u0000led to the discovery of a drag tilting and stretching term, which shows that\u0000gradients in the aerodynamic drag of the vegetation, tied to heterogeneities in\u0000surface area-to-volume ratio, play an important role in the generation of\u0000vorticity. Results from the vorticity budget analysis show that this term\u0000contributes significantly in the areas where these gradients are present,\u0000namely the edges of the canopy.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212704","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}
Craters form as the lander's exhaust interacts with the planetary surfaces. Understanding this phenomenon is imperative to ensure safe landings. We investigate crater morphology, where a turbulent air jet impinges on the granular surfaces. To reveal the fundamental aspect of this phenomenon, systematic experiments are performed with various air jet velocities, nozzle positions, and grain properties. The resultant crater morphology is characterized by an aspect ratio. We find a universal scaling law in which the aspect ratio is scaled by the dimensionless variable consisting of air velocity at the nozzle, speed of sound in air, nozzle diameter, nozzle tip distance from the surface, grain diameter, the density of grains, and density of air. The obtained scaling reveals the crossover of the length scales governing crater aspect ratio, providing a useful guideline for ensuring safe landings. Moreover, we report a novel drop shaped subsurface cratering phenomenon.
{"title":"Air jet impact craters on granular surfaces: a universal scaling","authors":"Prasad Sonar, Hiroaki Katsuragi","doi":"arxiv-2409.04988","DOIUrl":"https://doi.org/arxiv-2409.04988","url":null,"abstract":"Craters form as the lander's exhaust interacts with the planetary surfaces.\u0000Understanding this phenomenon is imperative to ensure safe landings. We\u0000investigate crater morphology, where a turbulent air jet impinges on the\u0000granular surfaces. To reveal the fundamental aspect of this phenomenon,\u0000systematic experiments are performed with various air jet velocities, nozzle\u0000positions, and grain properties. The resultant crater morphology is\u0000characterized by an aspect ratio. We find a universal scaling law in which the\u0000aspect ratio is scaled by the dimensionless variable consisting of air velocity\u0000at the nozzle, speed of sound in air, nozzle diameter, nozzle tip distance from\u0000the surface, grain diameter, the density of grains, and density of air. The\u0000obtained scaling reveals the crossover of the length scales governing crater\u0000aspect ratio, providing a useful guideline for ensuring safe landings.\u0000Moreover, we report a novel drop shaped subsurface cratering phenomenon.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"99 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212709","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}
Models for solving the Reynolds-averaged Navier-Stokes equations are popular tools for predicting complex turbulent flows due to their computational affordability and ability to provide or estimate quantities of engineering interest. However, results depend on a proper treatment of unclosed terms, which require progress in the development and assessment of model forms. In this study, we consider the Reynolds stress transport equations as a framework for second-moment turbulence closure modeling. We specifically focus on the terms responsible for decay of the Reynolds stresses, which can be isolated and evaluated separately from other terms in a canonical setup of homogeneous turbulence. We show that by using anisotropic forcing of the momentum equation, we can access states of turbulence traditionally not probed in a triply-periodic domain. The resulting data span a wide range of anisotropic turbulent behavior in a more comprehensive manner than extant literature. We then consider a variety of model forms for which these data allow us to perform a robust selection of model coefficients and select an optimal model that extends to cubic terms when expressed in terms of the principal coordinate Reynolds stresses. Performance of the selected decay model is then examined relative to the simulation data and popular models from the literature, demonstrating the superior accuracy of the developed model and, in turn, the efficacy of this framework for model selection and tuning.
{"title":"Reynolds stress decay modeling informed by anisotropically forced homogeneous turbulence","authors":"Ty Homan, Omkar B. Shende, Ali Mani","doi":"arxiv-2409.05179","DOIUrl":"https://doi.org/arxiv-2409.05179","url":null,"abstract":"Models for solving the Reynolds-averaged Navier-Stokes equations are popular\u0000tools for predicting complex turbulent flows due to their computational\u0000affordability and ability to provide or estimate quantities of engineering\u0000interest. However, results depend on a proper treatment of unclosed terms,\u0000which require progress in the development and assessment of model forms. In\u0000this study, we consider the Reynolds stress transport equations as a framework\u0000for second-moment turbulence closure modeling. We specifically focus on the\u0000terms responsible for decay of the Reynolds stresses, which can be isolated and\u0000evaluated separately from other terms in a canonical setup of homogeneous\u0000turbulence. We show that by using anisotropic forcing of the momentum equation,\u0000we can access states of turbulence traditionally not probed in a\u0000triply-periodic domain. The resulting data span a wide range of anisotropic\u0000turbulent behavior in a more comprehensive manner than extant literature. We\u0000then consider a variety of model forms for which these data allow us to perform\u0000a robust selection of model coefficients and select an optimal model that\u0000extends to cubic terms when expressed in terms of the principal coordinate\u0000Reynolds stresses. Performance of the selected decay model is then examined\u0000relative to the simulation data and popular models from the literature,\u0000demonstrating the superior accuracy of the developed model and, in turn, the\u0000efficacy of this framework for model selection and tuning.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"273 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212706","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}
M. Atif, N. H. Maruthi, P. K. Kolluru, C. Thantanapally, S. Ansumali
The hydrodynamic limit of a discrete kinetic equation is intrinsically connected with the symmetry of the lattices used in construction of a discrete velocity model. On mixed lattices composed of standard lattices the sixth-order (and higher) moment is often not isotropic and thus they are insufficient to ensure correct imposition of the hydrodynamic moments. This makes the task of developing lattice Boltzmann model for transonic flows quite challenging. We address this by decoupling the physical space lattice from the velocity space lattice to construct a lattice Boltzmann model with very high isotropy. The model is entirely on-lattice like the isothermal models, achieves a Mach number of two with only $81$ discrete velocities, and admits a simple generalization of equilibrium distribution used in isothermal equilibrium. We also present a number of realistic benchmark problems to show that the lattice Boltzmann model with a limited number of velocities is not only feasible for transonic flow but is also quite simple and efficient like its subsonic counterpart.
{"title":"Lattice Boltzmann Model for Transonic Flows","authors":"M. Atif, N. H. Maruthi, P. K. Kolluru, C. Thantanapally, S. Ansumali","doi":"arxiv-2409.05114","DOIUrl":"https://doi.org/arxiv-2409.05114","url":null,"abstract":"The hydrodynamic limit of a discrete kinetic equation is intrinsically\u0000connected with the symmetry of the lattices used in construction of a discrete\u0000velocity model. On mixed lattices composed of standard lattices the sixth-order\u0000(and higher) moment is often not isotropic and thus they are insufficient to\u0000ensure correct imposition of the hydrodynamic moments. This makes the task of\u0000developing lattice Boltzmann model for transonic flows quite challenging. We\u0000address this by decoupling the physical space lattice from the velocity space\u0000lattice to construct a lattice Boltzmann model with very high isotropy. The\u0000model is entirely on-lattice like the isothermal models, achieves a Mach number\u0000of two with only $81$ discrete velocities, and admits a simple generalization\u0000of equilibrium distribution used in isothermal equilibrium. We also present a\u0000number of realistic benchmark problems to show that the lattice Boltzmann model\u0000with a limited number of velocities is not only feasible for transonic flow but\u0000is also quite simple and efficient like its subsonic counterpart.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212708","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}
Zonal winds on Jovian planets play an important role in governing the cloud dynamics, transport of momentum, scalars, and weather patterns. Therefore, it is crucial to understand the evolution of the zonal flows and their sustainability. Based on studies in two-dimensional (2D) $beta$ plane setups, zonal flow is believed to be forced at the intermediate scale via baroclinic instabilities, and the inverse cascade leads to the transfer of energy to large scales. However, whether such a process exists in three-dimensional (3D) deep convection systems remains an open and challenging question. To explore a possible answer, we perform Large Eddy Simulations at the geophysically interesting regime of $Ra=$$10^{12}$, $Ek=$$10^{-6}$,$10^{-7}$ and $10^{-8}$ in horizontally rotating Rayleigh-B'enard convection setup and discover the existence of natural forcing through buoyancy and inverse cascade. The turbulent kinetic energy budget analysis and the spectral space assessment of the results corroborate the emanation of a strong mean flow from chaos.
{"title":"Inverse cascade in zonal flows","authors":"Siddhant Mishra, Anikesh Pal","doi":"arxiv-2409.05127","DOIUrl":"https://doi.org/arxiv-2409.05127","url":null,"abstract":"Zonal winds on Jovian planets play an important role in governing the cloud\u0000dynamics, transport of momentum, scalars, and weather patterns. Therefore, it\u0000is crucial to understand the evolution of the zonal flows and their\u0000sustainability. Based on studies in two-dimensional (2D) $beta$ plane setups,\u0000zonal flow is believed to be forced at the intermediate scale via baroclinic\u0000instabilities, and the inverse cascade leads to the transfer of energy to large\u0000scales. However, whether such a process exists in three-dimensional (3D) deep\u0000convection systems remains an open and challenging question. To explore a\u0000possible answer, we perform Large Eddy Simulations at the geophysically\u0000interesting regime of $Ra=$$10^{12}$, $Ek=$$10^{-6}$,$10^{-7}$ and $10^{-8}$ in\u0000horizontally rotating Rayleigh-B'enard convection setup and discover the\u0000existence of natural forcing through buoyancy and inverse cascade. The\u0000turbulent kinetic energy budget analysis and the spectral space assessment of\u0000the results corroborate the emanation of a strong mean flow from chaos.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"31 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212707","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}
Hao Liu, Mireille Bossy, Bernhard Vowinckel, Christophe Henry
Particle resuspension refers to the physical process by which solid particles deposited on a surface are, first, detached and, then, entrained away by the action of a fluid flow. In this study, we explore the dynamics of large and heavy spherical particles forming a complex sediment bed which is exposed to a laminar shear flow. For that purpose, we rely on fine-scale simulations based on a fully-resolved flow field around individual particles whose motion is explicitly tracked. Using statistical tools, we characterize several features: (a) the overall bed dynamics (e.g. the average particle velocity as a function of the elevation), (b) the evolution of the top surface of the sediment bed (e.g. distribution of the surface elevation or of the surface slope) and (c) the dynamics of individual particles as they detach from or re-attach to the sediment bed (including the frequency of these events, and the velocity difference / surface angle for each event). These results show that particles detach more frequently around the peaks in the top surface of the sediment bed and that, once detached, they undergo short hops as particles quickly sediment towards the sediment bed. A simple model based on the surface characteristics (including its slope and elevation) is proposed to reproduce the detachment ratio.
{"title":"Particle resuspension from complex multilayer deposits by laminar flows: statistical analysis and modeling","authors":"Hao Liu, Mireille Bossy, Bernhard Vowinckel, Christophe Henry","doi":"arxiv-2409.05094","DOIUrl":"https://doi.org/arxiv-2409.05094","url":null,"abstract":"Particle resuspension refers to the physical process by which solid particles\u0000deposited on a surface are, first, detached and, then, entrained away by the\u0000action of a fluid flow. In this study, we explore the dynamics of large and\u0000heavy spherical particles forming a complex sediment bed which is exposed to a\u0000laminar shear flow. For that purpose, we rely on fine-scale simulations based\u0000on a fully-resolved flow field around individual particles whose motion is\u0000explicitly tracked. Using statistical tools, we characterize several features:\u0000(a) the overall bed dynamics (e.g. the average particle velocity as a function\u0000of the elevation), (b) the evolution of the top surface of the sediment bed\u0000(e.g. distribution of the surface elevation or of the surface slope) and (c)\u0000the dynamics of individual particles as they detach from or re-attach to the\u0000sediment bed (including the frequency of these events, and the velocity\u0000difference / surface angle for each event). These results show that particles\u0000detach more frequently around the peaks in the top surface of the sediment bed\u0000and that, once detached, they undergo short hops as particles quickly sediment\u0000towards the sediment bed. A simple model based on the surface characteristics\u0000(including its slope and elevation) is proposed to reproduce the detachment\u0000ratio.","PeriodicalId":501125,"journal":{"name":"arXiv - PHYS - Fluid Dynamics","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142212725","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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