Pub Date : 2023-06-12DOI: 10.1080/14685248.2023.2224019
YaLu Fu, Qingqing Zhou, M. Yu, H. Su, Qilong Guo, Xianxu Yuan
This paper investigates the influences of the distribution of the grooves on the wall on the turbulent statistics, transport of turbulent kinetic energy, and flow structures in supersonic turbulent channel flows at the bulk Mach number of 3.0 by performing direct numerical simulations. It is found that the existence of the grooves leads to the enhancement of the turbulent kinetic energy close to the wall and the abatement thereof above the buffer layer. The density and temperature fluctuations are also enhanced, but only within the buffer layer, above which the influences of the grooves can be disregarded. The pressure fluctuations, however, are significantly increased, which is attributed to the radiated acoustic waves from the wall generated by the disturbances on the wall. Such inference is substantiated by the fact that the inclination angles of the phase averaged pressure are related to the Mach number. Nevertheless, the acoustic and dynamic processes seem to be decoupled, leading to insignificant pressure-dilatation terms in the transport of turbulent kinetic energy.
{"title":"Effects of groove distributions on supersonic turbulent channel flows","authors":"YaLu Fu, Qingqing Zhou, M. Yu, H. Su, Qilong Guo, Xianxu Yuan","doi":"10.1080/14685248.2023.2224019","DOIUrl":"https://doi.org/10.1080/14685248.2023.2224019","url":null,"abstract":"This paper investigates the influences of the distribution of the grooves on the wall on the turbulent statistics, transport of turbulent kinetic energy, and flow structures in supersonic turbulent channel flows at the bulk Mach number of 3.0 by performing direct numerical simulations. It is found that the existence of the grooves leads to the enhancement of the turbulent kinetic energy close to the wall and the abatement thereof above the buffer layer. The density and temperature fluctuations are also enhanced, but only within the buffer layer, above which the influences of the grooves can be disregarded. The pressure fluctuations, however, are significantly increased, which is attributed to the radiated acoustic waves from the wall generated by the disturbances on the wall. Such inference is substantiated by the fact that the inclination angles of the phase averaged pressure are related to the Mach number. Nevertheless, the acoustic and dynamic processes seem to be decoupled, leading to insignificant pressure-dilatation terms in the transport of turbulent kinetic energy.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47228864","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-05-28DOI: 10.1080/14685248.2023.2214399
A. Grenouilloux, J. Leparoux, V. Moureau, G. Balarac, T. Berthelon, R. Mercier, M. Bernard, P. Bénard, G. Lartigue, O. Métais
With the constant increase of computational power for the past years, Computational Fluid Dynamics (CFD) has become an essential part of the design in complex industrial processes. In this context, among the scale resolving numerical methods, Large-Eddy Simulation (LES) has become a valuable tool for the simulation of complex unsteady flows. To generalise the industrial use of LES, two main limitations are identified. First, the generation of a proper mesh can be a difficult task, which often relies on user-experience. Secondly, the ‘time-to-solution’ associated with the LES approach can be prohibitive in an industrial context. In this work, these two challenges are addressed in two parts. In this Part I, an automatic procedure for mesh definition is proposed, whereas the Part II is devoted to numerical technique to reduce the LES ‘time-to-solution’. The main goal of these works is then to develop an accurate LES strategy at an optimised computational cost. Concerning the mesh definition, because LES is based on separation between resolved and modelled subgrid-scales, the quality of the computed solution is then directly linked to the quality of the mesh. However, the definition of an adequate mesh is still an issue when LES is used to predict the flow in an industrial complex geometry without a priori knowledge of the flow dynamics. This first part presents a user-independent approach for both the generation of an initial mesh and the convergence of the mesh in the LES framework. An automatic mesh convergence strategy is proposed to ensure LES accuracy. This strategy is built to guarantee a mesh-independent mean field kinetic energy budget. The mean field kinetic energy is indeed expected to be mesh independent since only turbulent scales should be unresolved in LES. The approach is validated on canonical cases, a turbulent round jet and a turbulent pipe flow. Finally, the PRECCINSTA swirl burner is considered as a representative case of complex geometry. First, an algorithm for the generation of an unstructured mesh from a STL file is proposed to generate a coarse initial mesh, before applying the mesh convergence procedure. The overall strategy including automatic first mesh generation and its automatic adaptation paves the way to use LES approach as a decision support tool for various applications, provided that the ‘time-to-solution’ is compatible with the applications constraint. A second paper, referred as Part II, is devoted to the reduction of this time.
{"title":"Toward the use of LES for industrial complex geometries. Part I: automatic mesh definition","authors":"A. Grenouilloux, J. Leparoux, V. Moureau, G. Balarac, T. Berthelon, R. Mercier, M. Bernard, P. Bénard, G. Lartigue, O. Métais","doi":"10.1080/14685248.2023.2214399","DOIUrl":"https://doi.org/10.1080/14685248.2023.2214399","url":null,"abstract":"With the constant increase of computational power for the past years, Computational Fluid Dynamics (CFD) has become an essential part of the design in complex industrial processes. In this context, among the scale resolving numerical methods, Large-Eddy Simulation (LES) has become a valuable tool for the simulation of complex unsteady flows. To generalise the industrial use of LES, two main limitations are identified. First, the generation of a proper mesh can be a difficult task, which often relies on user-experience. Secondly, the ‘time-to-solution’ associated with the LES approach can be prohibitive in an industrial context. In this work, these two challenges are addressed in two parts. In this Part I, an automatic procedure for mesh definition is proposed, whereas the Part II is devoted to numerical technique to reduce the LES ‘time-to-solution’. The main goal of these works is then to develop an accurate LES strategy at an optimised computational cost. Concerning the mesh definition, because LES is based on separation between resolved and modelled subgrid-scales, the quality of the computed solution is then directly linked to the quality of the mesh. However, the definition of an adequate mesh is still an issue when LES is used to predict the flow in an industrial complex geometry without a priori knowledge of the flow dynamics. This first part presents a user-independent approach for both the generation of an initial mesh and the convergence of the mesh in the LES framework. An automatic mesh convergence strategy is proposed to ensure LES accuracy. This strategy is built to guarantee a mesh-independent mean field kinetic energy budget. The mean field kinetic energy is indeed expected to be mesh independent since only turbulent scales should be unresolved in LES. The approach is validated on canonical cases, a turbulent round jet and a turbulent pipe flow. Finally, the PRECCINSTA swirl burner is considered as a representative case of complex geometry. First, an algorithm for the generation of an unstructured mesh from a STL file is proposed to generate a coarse initial mesh, before applying the mesh convergence procedure. The overall strategy including automatic first mesh generation and its automatic adaptation paves the way to use LES approach as a decision support tool for various applications, provided that the ‘time-to-solution’ is compatible with the applications constraint. A second paper, referred as Part II, is devoted to the reduction of this time.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47469437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-05-25DOI: 10.1080/14685248.2023.2215530
R. Vicente Cruz, E. Lamballais
The development of implicit approaches has prompted debate on the actual usefulness of any explicit subgrid-scale modelling in large-eddy simulation. This question is addressed here by considering two generic turbulent flows: (i) the Taylor-Green vortex problem; (ii) the pipe flow. For both flow configurations, implicit modelling is found to overtake the very popular Smagorinsky model. To understand this robust observation, an analysis in the Fourier space is presented for the Taylor-Green vortex problem. The concept of spectral eddy viscosity, widely used in the pioneer work of Marcel Lesieur in two-point closure and subgrid-scale modelling, is revisited in a general framework based on explicit/implicit subgrid-scale modelling. In particular, the essentially anisotropic nature of implicit modelling is exhibited, as a favourable feature in terms of consistency with the computational mesh. Smagorinsky's model, considered as a generic explicit subgrid-scale model in the framework of Boussinesq's hypothesis, is found to be highly sensitive to numerical errors. Removing the latter is easy but makes computationally inefficient this type of explicit modelling. Comparisons between a priori and a posteriori spectral eddy viscosities show that neither Smagorinsky's model nor implicit modelling can mimic the expected spectral behaviour. Smagorinsky's model is observed to be weakly scale-selective with a poor ability to actually filter the solution. The feature of scale-selectivity is well replicated by implicit modelling which exhibits excellent capabilities for filtering. However, its lack of influence at the largest scales is against the expected behaviour for the spectral eddy viscosity at low wavenumber through the establishment of a non-zero plateau value. This lack of consistency of implicit LES could be overcome thanks to an extra explicit modelling but the attempt to mix Smagorinsky's model and implicit LES is not successful in this study. The potential of implicit large-eddy simulation is also exhibited for the accurate computation of near-wall turbulence inside a pipe flow despite the use of a regular Cartesian mesh with an immersed boundary method. Interestingly, the resulting coarse wall-normal resolution in the near-wall direction does not prevent the reliable prediction of statistical profiles up to the capture of subgrid-scale details. It is suggested that the regularisation associated with implicit modelling is a necessary condition to reach numerical accuracy. However, to faithfully represent the large-scale dynamics, present results confirm that non-local triad interactions must be taken into account as widely discussed in the inspiring textbook Lesieur [Turbulence in fluids. 4th ed. Springer; 2008] of Marcel Lesieur.
{"title":"Physical/numerical duality of explicit/implicit subgrid-scale modelling","authors":"R. Vicente Cruz, E. Lamballais","doi":"10.1080/14685248.2023.2215530","DOIUrl":"https://doi.org/10.1080/14685248.2023.2215530","url":null,"abstract":"The development of implicit approaches has prompted debate on the actual usefulness of any explicit subgrid-scale modelling in large-eddy simulation. This question is addressed here by considering two generic turbulent flows: (i) the Taylor-Green vortex problem; (ii) the pipe flow. For both flow configurations, implicit modelling is found to overtake the very popular Smagorinsky model. To understand this robust observation, an analysis in the Fourier space is presented for the Taylor-Green vortex problem. The concept of spectral eddy viscosity, widely used in the pioneer work of Marcel Lesieur in two-point closure and subgrid-scale modelling, is revisited in a general framework based on explicit/implicit subgrid-scale modelling. In particular, the essentially anisotropic nature of implicit modelling is exhibited, as a favourable feature in terms of consistency with the computational mesh. Smagorinsky's model, considered as a generic explicit subgrid-scale model in the framework of Boussinesq's hypothesis, is found to be highly sensitive to numerical errors. Removing the latter is easy but makes computationally inefficient this type of explicit modelling. Comparisons between a priori and a posteriori spectral eddy viscosities show that neither Smagorinsky's model nor implicit modelling can mimic the expected spectral behaviour. Smagorinsky's model is observed to be weakly scale-selective with a poor ability to actually filter the solution. The feature of scale-selectivity is well replicated by implicit modelling which exhibits excellent capabilities for filtering. However, its lack of influence at the largest scales is against the expected behaviour for the spectral eddy viscosity at low wavenumber through the establishment of a non-zero plateau value. This lack of consistency of implicit LES could be overcome thanks to an extra explicit modelling but the attempt to mix Smagorinsky's model and implicit LES is not successful in this study. The potential of implicit large-eddy simulation is also exhibited for the accurate computation of near-wall turbulence inside a pipe flow despite the use of a regular Cartesian mesh with an immersed boundary method. Interestingly, the resulting coarse wall-normal resolution in the near-wall direction does not prevent the reliable prediction of statistical profiles up to the capture of subgrid-scale details. It is suggested that the regularisation associated with implicit modelling is a necessary condition to reach numerical accuracy. However, to faithfully represent the large-scale dynamics, present results confirm that non-local triad interactions must be taken into account as widely discussed in the inspiring textbook Lesieur [Turbulence in fluids. 4th ed. Springer; 2008] of Marcel Lesieur.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43773875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-05-04DOI: 10.1080/14685248.2023.2212982
Nikhil Oberoi, Walter Arias-Ramírez, J. Larsson
ABSTRACT A computationally affordable approach to estimate parametric sensitivities of engineering relevant quantities of interest for a large eddy simulation (LES) is explored. The method is based on defining a Reynolds-averaged Navier–Stokes (RANS) problem that is constrained to reproduce the LES mean flow field. The proposed method is described and assessed for a shock/boundary layer interaction problem, where the shock angle and wall temperature are considered variable or uncertain. In the current work, we show that the proposed method offers improved sensitivity predictions for certain flow features as compared to standalone RANS simulations, while using a fraction of the LES cost.
{"title":"Multi-fidelity parametric sensitivity estimation for large eddy simulation with the Spalart–Allmaras model","authors":"Nikhil Oberoi, Walter Arias-Ramírez, J. Larsson","doi":"10.1080/14685248.2023.2212982","DOIUrl":"https://doi.org/10.1080/14685248.2023.2212982","url":null,"abstract":"ABSTRACT A computationally affordable approach to estimate parametric sensitivities of engineering relevant quantities of interest for a large eddy simulation (LES) is explored. The method is based on defining a Reynolds-averaged Navier–Stokes (RANS) problem that is constrained to reproduce the LES mean flow field. The proposed method is described and assessed for a shock/boundary layer interaction problem, where the shock angle and wall temperature are considered variable or uncertain. In the current work, we show that the proposed method offers improved sensitivity predictions for certain flow features as compared to standalone RANS simulations, while using a fraction of the LES cost.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46441354","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-04-20DOI: 10.1080/14685248.2023.2203497
Amandine Capogna, O. Doche, J. Schillings, L. Davoust, S. Tardu
ABSTRACT The effect of a permanent, localised and non-uniform magnetic field on the near-wall turbulence in a fully developed channel flow is analysed through direct numerical simulations. The magnetic field distribution is obtained by an arrangement of magnets placed on the upper and lower channel walls, producing preferentially either a streamwise (i.e. in the main flow direction) or a spanwise magnetic field component. The wall shear stress is drastically reduced under the effect of the streamwise arrangement of the wall magnets wherein both streamwise and wall-normal magnetic fields are involved. The magnetic braking effect leads to an important increase of the body force. Paradoxically enough, the small-scale turbulent activity is significantly increased above the low buffer layer in this case. On the opposite, imposing a magnetic field with a predominant spanwise component reduces tremendously the population of the turbulent shear stress producing eddies by directly affecting the regeneration of the buffer layer quasi-streamwise vortices. The flow is quasi-relaminarised between the magnets in the low-buffer and viscous sublayers. The wall shear increases in a predictable and deterministic way over the magnets, wherein the wall normal magnetic field component induces electric current loops.
{"title":"Influence of streamwise and spanwise wall magnet arrays on near-wall MHD turbulence","authors":"Amandine Capogna, O. Doche, J. Schillings, L. Davoust, S. Tardu","doi":"10.1080/14685248.2023.2203497","DOIUrl":"https://doi.org/10.1080/14685248.2023.2203497","url":null,"abstract":"ABSTRACT The effect of a permanent, localised and non-uniform magnetic field on the near-wall turbulence in a fully developed channel flow is analysed through direct numerical simulations. The magnetic field distribution is obtained by an arrangement of magnets placed on the upper and lower channel walls, producing preferentially either a streamwise (i.e. in the main flow direction) or a spanwise magnetic field component. The wall shear stress is drastically reduced under the effect of the streamwise arrangement of the wall magnets wherein both streamwise and wall-normal magnetic fields are involved. The magnetic braking effect leads to an important increase of the body force. Paradoxically enough, the small-scale turbulent activity is significantly increased above the low buffer layer in this case. On the opposite, imposing a magnetic field with a predominant spanwise component reduces tremendously the population of the turbulent shear stress producing eddies by directly affecting the regeneration of the buffer layer quasi-streamwise vortices. The flow is quasi-relaminarised between the magnets in the low-buffer and viscous sublayers. The wall shear increases in a predictable and deterministic way over the magnets, wherein the wall normal magnetic field component induces electric current loops.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-04-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44344877","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-04-03DOI: 10.1080/14685248.2023.2202404
Julie E. Duetsch-Patel, A. Gargiulo, Aurélien Borgoltz, Christopher J. Roy, W. Devenport, K. Lowe
Many turbulence theories in use today are based on two-dimensional equilibrium flows and have limitations when applied to three-dimensional flows. A three-dimensional law of the wall would help to improve simulation fidelity, but while several versions have been proposed, none have been widely accepted. In this study, the three-dimensional attached boundary layer flow over the windward side of the BeVERLI (Benchmark Validation Experiments for RANS/LES Investigations) Hill bump model was measured using near-wall laser Doppler velocimetry in the Virginia Tech Stability Wind Tunnel to study the mean flow and turbulence structure. These mean velocity measurements are compared with the predictions of the proposed three-dimensional (3D) law of the wall of van den Berg [A three-dimensional law of the wall for turbulent shear flows. J Fluid Mech. 1975;70(1):149–160.], which incorporates pressure gradients and inertial effects but assumes alignment of the mean flow gradient and shear-stress angles, and to the sublayer momentum equations, which are exact in the limit of wall-normal . In regions with mild stress/strain misalignment, the van den Berg model compares favourably with the experimental data up to a maximum of , and the sublayer momentum relationship compares favourably with the experimental data in the linear sublayer.
目前使用的许多湍流理论都是基于二维平衡流，并且在应用于三维流时存在局限性。墙的三维定律将有助于提高模拟逼真度，但尽管已经提出了几个版本，但没有一个被广泛接受。在本研究中，在弗吉尼亚理工大学稳定风洞中使用近壁激光多普勒测速仪测量了BeVERLI（RANS/LES调查基准验证实验）Hill bump模型迎风面上的三维附边界层流动，以研究平均流量和湍流结构。将这些平均速度测量值与所提出的van den Berg壁的三维（3D）定律[湍流剪切流的壁的三维定律.J Fluid Mech.1975；70（1）:149–160.]的预测值进行了比较，该定律结合了压力梯度和惯性效应，但假设平均流梯度和剪切应力角对齐，以及精确到壁法线极限的子层动量方程。在具有轻度应力/应变失准的区域中，van den Berg模型与实验数据相比是有利的，最大值为，并且子层动量关系与线性子层中的实验数据相比也是有利的。
{"title":"Boundary layer flow over a bump and the three-dimensional law of the wall","authors":"Julie E. Duetsch-Patel, A. Gargiulo, Aurélien Borgoltz, Christopher J. Roy, W. Devenport, K. Lowe","doi":"10.1080/14685248.2023.2202404","DOIUrl":"https://doi.org/10.1080/14685248.2023.2202404","url":null,"abstract":"Many turbulence theories in use today are based on two-dimensional equilibrium flows and have limitations when applied to three-dimensional flows. A three-dimensional law of the wall would help to improve simulation fidelity, but while several versions have been proposed, none have been widely accepted. In this study, the three-dimensional attached boundary layer flow over the windward side of the BeVERLI (Benchmark Validation Experiments for RANS/LES Investigations) Hill bump model was measured using near-wall laser Doppler velocimetry in the Virginia Tech Stability Wind Tunnel to study the mean flow and turbulence structure. These mean velocity measurements are compared with the predictions of the proposed three-dimensional (3D) law of the wall of van den Berg [A three-dimensional law of the wall for turbulent shear flows. J Fluid Mech. 1975;70(1):149–160.], which incorporates pressure gradients and inertial effects but assumes alignment of the mean flow gradient and shear-stress angles, and to the sublayer momentum equations, which are exact in the limit of wall-normal . In regions with mild stress/strain misalignment, the van den Berg model compares favourably with the experimental data up to a maximum of , and the sublayer momentum relationship compares favourably with the experimental data in the linear sublayer.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45411082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-16DOI: 10.1080/14685248.2023.2189731
L. Fang, W. Bos
The energy cascade from large to small scales is a robust feature of three-dimensional turbulence. In statistically steady turbulence, the average dissipation is in equilibrium with the energy injected in the system. A global quantity measuring the deviations from such a flux equilibrium is the normalised dissipation rate , corresponding to the viscous dissipation, normalised by quantities associated with the largest scales of the system. Recent investigations have pointed out how this normalised dissipation rate varies in unsteady flows. We focus on two test-cases to assess non-equilibrium in isotropic turbulence. These cases are, respectively, turbulence in the presence of a large-scale periodic forcing and turbulence with reversed initial conditions. We show, using the Eddy-Damped Quasi-Normal Markovian closure, that for turbulence in the presence of periodic forcing, a scaling is reproduced ( indicating the Taylor-scale Reynolds number) when the forcing-frequency is adjusted to be of the order of the inverse of the integral time-scale. It is shown that the spectrum can be decomposed into an equilibrium spectrum, governed by Kolmogorov scaling in the inertial range, and a perturbation spectrum, proportional to , k being the wavenumber. For reversed turbulence, a novel procedure is introduced to prescribe initial conditions for the nonlinear transfer. Subsequently a clear transient with a scaling is observed in the dynamics.
{"title":"An EDQNM study of the dissipation rate in isotropic non-equilibrium turbulence","authors":"L. Fang, W. Bos","doi":"10.1080/14685248.2023.2189731","DOIUrl":"https://doi.org/10.1080/14685248.2023.2189731","url":null,"abstract":"The energy cascade from large to small scales is a robust feature of three-dimensional turbulence. In statistically steady turbulence, the average dissipation is in equilibrium with the energy injected in the system. A global quantity measuring the deviations from such a flux equilibrium is the normalised dissipation rate , corresponding to the viscous dissipation, normalised by quantities associated with the largest scales of the system. Recent investigations have pointed out how this normalised dissipation rate varies in unsteady flows. We focus on two test-cases to assess non-equilibrium in isotropic turbulence. These cases are, respectively, turbulence in the presence of a large-scale periodic forcing and turbulence with reversed initial conditions. We show, using the Eddy-Damped Quasi-Normal Markovian closure, that for turbulence in the presence of periodic forcing, a scaling is reproduced ( indicating the Taylor-scale Reynolds number) when the forcing-frequency is adjusted to be of the order of the inverse of the integral time-scale. It is shown that the spectrum can be decomposed into an equilibrium spectrum, governed by Kolmogorov scaling in the inertial range, and a perturbation spectrum, proportional to , k being the wavenumber. For reversed turbulence, a novel procedure is introduced to prescribe initial conditions for the nonlinear transfer. Subsequently a clear transient with a scaling is observed in the dynamics.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44292892","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-07DOI: 10.1080/14685248.2023.2186415
Y. K. İlter, Aras Çetinkaya, U. Ünal
Reducing skin friction has a key role in the efficiency of rail, highway, and airway transport vehicles or naval systems such as ships and underwater vehicles. In recent years, there is a growing interest in investigating turbulent drag-reducing capabilities of dimpled surfaces, which have great potential as a passive solution, while there still exists highly conflicting views and drag reduction rates reported in the literature as well as a lack of information about the drag reduction mechanism. In this study, large-eddy simulations (LES) were performed to investigate the characteristics and physical mechanism of the fluid flow over dimpled surfaces in a fully developed channel flow. The Reynolds number based on the channel height and the mean bulk velocity was nearly 5600 for all cases examined. Within the framework of the study, various dimple depth to diameter ratios as well as different dimple arrangements and geometries were considered. The detailed mean and instantaneous flow fields, turbulent kinetic energy budget and spectral characteristics of the flow are presented. The study revealed the potential of the dimpled surface in reducing skin friction and provided critical information about the flow features affecting the performance of the dimples.
{"title":"Large eddy simulations of the turbulent channel flow over dimpled surfaces","authors":"Y. K. İlter, Aras Çetinkaya, U. Ünal","doi":"10.1080/14685248.2023.2186415","DOIUrl":"https://doi.org/10.1080/14685248.2023.2186415","url":null,"abstract":"Reducing skin friction has a key role in the efficiency of rail, highway, and airway transport vehicles or naval systems such as ships and underwater vehicles. In recent years, there is a growing interest in investigating turbulent drag-reducing capabilities of dimpled surfaces, which have great potential as a passive solution, while there still exists highly conflicting views and drag reduction rates reported in the literature as well as a lack of information about the drag reduction mechanism. In this study, large-eddy simulations (LES) were performed to investigate the characteristics and physical mechanism of the fluid flow over dimpled surfaces in a fully developed channel flow. The Reynolds number based on the channel height and the mean bulk velocity was nearly 5600 for all cases examined. Within the framework of the study, various dimple depth to diameter ratios as well as different dimple arrangements and geometries were considered. The detailed mean and instantaneous flow fields, turbulent kinetic energy budget and spectral characteristics of the flow are presented. The study revealed the potential of the dimpled surface in reducing skin friction and provided critical information about the flow features affecting the performance of the dimples.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45753522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-21DOI: 10.1080/14685248.2023.2182439
MD Kamruzzaman, L. Djenidi, R. Antonia
A Hot-wire anemometry experiment is conducted to investigate how two turbulent fields decaying with different mean velocities interact at their interface. A grid with different mesh sizes and solidities on either side of the grid centerline is used to generate two turbulent fields. It is found that the resulting turbulent shear layer created at the interface of the two fields evolves in a self-preserving manner. Further, the Taylor microscale Reynolds number, increases linearly while and become constants as the distance x downstream of the grids increases. Off the centerline one observes the classical decay of turbulence, e.g. varies like (n is negative) and decreases. It is observed that the transport equation for is dominated by the production and pressure-velocity correlation in the central region of the turbulent shear layer while production, dissipation, and turbulent diffusion of the transport equation for dominate in the central part of the shear layer. The pressure-velocity correlation term for is negligible on the centreline of the shear layer and important on the edges. The measurements of the scale-by-scale (SBS) energy terms on the shear layer centerline reveal that the energy transfer from large to small scales occurs in a non-trivial manner.
{"title":"Experimental study of two side-by-side decaying grid turbulent fields at different mean velocities","authors":"MD Kamruzzaman, L. Djenidi, R. Antonia","doi":"10.1080/14685248.2023.2182439","DOIUrl":"https://doi.org/10.1080/14685248.2023.2182439","url":null,"abstract":"A Hot-wire anemometry experiment is conducted to investigate how two turbulent fields decaying with different mean velocities interact at their interface. A grid with different mesh sizes and solidities on either side of the grid centerline is used to generate two turbulent fields. It is found that the resulting turbulent shear layer created at the interface of the two fields evolves in a self-preserving manner. Further, the Taylor microscale Reynolds number, increases linearly while and become constants as the distance x downstream of the grids increases. Off the centerline one observes the classical decay of turbulence, e.g. varies like (n is negative) and decreases. It is observed that the transport equation for is dominated by the production and pressure-velocity correlation in the central region of the turbulent shear layer while production, dissipation, and turbulent diffusion of the transport equation for dominate in the central part of the shear layer. The pressure-velocity correlation term for is negligible on the centreline of the shear layer and important on the edges. The measurements of the scale-by-scale (SBS) energy terms on the shear layer centerline reveal that the energy transfer from large to small scales occurs in a non-trivial manner.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48622715","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-15DOI: 10.1080/14685248.2023.2178654
J. Riley, M. Couchman, S. M. de Bruyn Kops
The effects of the variation in the Prandtl number on turbulence in a stably-stratified fluid is investigated by direct numerical simulation. The results of simulations are presented of the homogeneous decay of turbulence for a given initial Froude number and three different initial Reynolds numbers of increasing values. For each of these cases results for two different Prandtl numbers, 1 and 7, are shown. Various statistics are put forward, including kinetic and potential energy decay rates, kinetic and potential energy dissipation rates, buoyancy fluxes, energy spectra, and statistics conditioned on the local value of the vertical density gradient. It is found that the effect of increasing the Prandtl number is to increase the kinetic energy dissipation rate, while decreasing the potential energy dissipation rate. There is a notable transfer of potential to kinetic energy for the higher Prandtl number case. Finally there is evidence, based upon the analysis of vertical planes and statistics conditional on the local density gradient, that most irreversible mixing of both density and momentum occurs in regions of stronger static stability.
{"title":"The effect of Prandtl number on decaying stratified turbulence","authors":"J. Riley, M. Couchman, S. M. de Bruyn Kops","doi":"10.1080/14685248.2023.2178654","DOIUrl":"https://doi.org/10.1080/14685248.2023.2178654","url":null,"abstract":"The effects of the variation in the Prandtl number on turbulence in a stably-stratified fluid is investigated by direct numerical simulation. The results of simulations are presented of the homogeneous decay of turbulence for a given initial Froude number and three different initial Reynolds numbers of increasing values. For each of these cases results for two different Prandtl numbers, 1 and 7, are shown. Various statistics are put forward, including kinetic and potential energy decay rates, kinetic and potential energy dissipation rates, buoyancy fluxes, energy spectra, and statistics conditioned on the local value of the vertical density gradient. It is found that the effect of increasing the Prandtl number is to increase the kinetic energy dissipation rate, while decreasing the potential energy dissipation rate. There is a notable transfer of potential to kinetic energy for the higher Prandtl number case. Finally there is evidence, based upon the analysis of vertical planes and statistics conditional on the local density gradient, that most irreversible mixing of both density and momentum occurs in regions of stronger static stability.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46675355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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