Pub Date : 2021-05-07DOI: 10.1080/14685248.2021.1918700
Zecong Qin, A. Naso, W. Bos
In purely axisymmetric turbulence sustained by a linear forcing mechanism, a stable, entirely poloidal flow is observed when the toroidal component of the forcing is below a threshold. We investigate using numerical simulations whether this state persists when toroidal variations of the flow are continuously reintroduced and the forcing is purely poloidal. It is shown how the pressure–strain correlation allows the redistribution of the energy towards the toroidal component. A simple statistical model allows to capture the main physical effects on the level of the global energy balance. This model is then used to investigate the stability of the poloidal state for various toroidal-to-poloidal forcing strengths and different degrees of axisymmetry.
{"title":"Transition from axisymmetric to three-dimensional turbulence","authors":"Zecong Qin, A. Naso, W. Bos","doi":"10.1080/14685248.2021.1918700","DOIUrl":"https://doi.org/10.1080/14685248.2021.1918700","url":null,"abstract":"In purely axisymmetric turbulence sustained by a linear forcing mechanism, a stable, entirely poloidal flow is observed when the toroidal component of the forcing is below a threshold. We investigate using numerical simulations whether this state persists when toroidal variations of the flow are continuously reintroduced and the forcing is purely poloidal. It is shown how the pressure–strain correlation allows the redistribution of the energy towards the toroidal component. A simple statistical model allows to capture the main physical effects on the level of the global energy balance. This model is then used to investigate the stability of the poloidal state for various toroidal-to-poloidal forcing strengths and different degrees of axisymmetry.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1918700","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48269310","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 : 2021-05-04DOI: 10.1080/14685248.2021.1899365
Chao Sun
Rotating Turbulence has attracted extensive research efforts over the last decades due to its fundamental interests and relevance to a variety of natural and engineering processes. The present special issue on Rotating Turbulence collects five contributions from renowned researchers to showcase the variety of physical phenomena and recent advances in this exciting area. This Special Issue is opened by a review paper by L. Biferale, who presents an insightful discussion of Rotating Turbulence with varying degrees of complexity and provides a great introduction to the papers on the special issue. Besides, the paper gives thought-provoking future prospects in this area. The paper of G. Boffetta and coworkers reports a study of freely decaying rotating turbulent flows confined in domains with variable heights using laboratory experiments and numerical simulations. The authors show that vertical confinement has important effects on the formation of large-scale columnar vortices and in particular delays the development of the cyclone–anticyclone asymmetry. This effect is observed both in experiments and in numerical simulations which have structural differences in the boundary conditions, demonstrating the robustness of their findings. The paper by Z. Xia, S. Chen and coworker presents a numerical investigation of the hysteresis behaviour in a spanwise rotating plane Couette flow. By performing two groups of direct numerical simulations where Ro varies in steps along two opposite directions, they demonstrate the existence of hysteresis behaviour in the large-scale realisations at the highest Reynolds number considered, which is also manifested in the turbulent statistics. The paper of R. P. J. Kunnen presents an overview of our current knowledge of the geostrophic regime of turbulent rotating Rayleigh–Bénard convection. The phase diagram of the geostrophic regime of rotating convection is described in detail, with a discussion of the subranges characterised by different flow structures and heat transfer scaling. Complications in the laboratory studies of geostrophic convection are discussed, such as domain size, effects of centrifugal buoyancy, confinement and wall modes, non-Oberbeck–Boussinesq effects and inertial wave resonance. In the paper by S. Horn and J. M. Aurnou, the effects of centrifugal buoyancy on the formation of tornado-like vortices are studied computationally based on the Coriolis-centrifugal convection system. They show that centrifugal buoyancy is relevant for naturally occurring tornadoes and a rich variety of tornado morphologies are produced in the quasi-cyclostrophic regime of Coriolis-centrifugal convection. The Editorial Board thanks the authors for their contributions to the special issue and hopes that this special issue will stimulate further progress and interest in the area.
在过去的几十年里，由于旋转湍流的基本利益和与各种自然和工程过程的相关性，它吸引了广泛的研究努力。本期关于旋转湍流的特刊收集了来自知名研究人员的五篇文章，以展示这个令人兴奋的领域的各种物理现象和最新进展。本特刊由L. Biferale的一篇综述论文开篇，他对不同复杂程度的旋转湍流进行了深刻的讨论，并对特刊上的论文进行了很好的介绍。并对该领域的发展前景进行了展望。G. Boffetta及其同事的论文报告了一项使用实验室实验和数值模拟的研究，该研究限制在可变高度域中的自由衰减旋转湍流。作者认为，垂直约束对大尺度柱状涡的形成有重要影响，特别是延缓了气旋-反气旋不对称的发展。这种效应在边界条件有结构差异的实验和数值模拟中都观察到了，证明了他们的发现的稳健性。夏忠、陈思和同事的论文对沿展向旋转平面Couette流的滞回特性进行了数值研究。通过进行两组直接数值模拟，其中Ro沿两个相反方向的步长变化，他们证明了在考虑的最高雷诺数的大规模实现中存在滞后行为，这也体现在湍流统计中。R. P. J. Kunnen的论文概述了我们目前对湍流旋转瑞利-巴萨姆德对流地转体制的认识。详细描述了旋转对流地转状态的相图，并讨论了以不同流动结构和传热尺度为特征的子范围。讨论了地转对流实验研究中的复杂问题，如区域大小、离心浮力的影响、约束和壁面模式、非奥伯贝克-布西内斯克效应和惯性波共振。S. Horn和J. M. Aurnou基于科里奥利-离心对流系统，计算研究了离心浮力对类龙卷风涡形成的影响。他们表明，离心浮力与自然发生的龙卷风有关，在科里奥利-离心对流的准旋转状态下产生了丰富多样的龙卷风形态。编辑委员会感谢作者为本期特刊所作的贡献，并希望本期特刊将促进该领域的进一步发展和兴趣。
{"title":"Special issue on rotating turbulence","authors":"Chao Sun","doi":"10.1080/14685248.2021.1899365","DOIUrl":"https://doi.org/10.1080/14685248.2021.1899365","url":null,"abstract":"Rotating Turbulence has attracted extensive research efforts over the last decades due to its fundamental interests and relevance to a variety of natural and engineering processes. The present special issue on Rotating Turbulence collects five contributions from renowned researchers to showcase the variety of physical phenomena and recent advances in this exciting area. This Special Issue is opened by a review paper by L. Biferale, who presents an insightful discussion of Rotating Turbulence with varying degrees of complexity and provides a great introduction to the papers on the special issue. Besides, the paper gives thought-provoking future prospects in this area. The paper of G. Boffetta and coworkers reports a study of freely decaying rotating turbulent flows confined in domains with variable heights using laboratory experiments and numerical simulations. The authors show that vertical confinement has important effects on the formation of large-scale columnar vortices and in particular delays the development of the cyclone–anticyclone asymmetry. This effect is observed both in experiments and in numerical simulations which have structural differences in the boundary conditions, demonstrating the robustness of their findings. The paper by Z. Xia, S. Chen and coworker presents a numerical investigation of the hysteresis behaviour in a spanwise rotating plane Couette flow. By performing two groups of direct numerical simulations where Ro varies in steps along two opposite directions, they demonstrate the existence of hysteresis behaviour in the large-scale realisations at the highest Reynolds number considered, which is also manifested in the turbulent statistics. The paper of R. P. J. Kunnen presents an overview of our current knowledge of the geostrophic regime of turbulent rotating Rayleigh–Bénard convection. The phase diagram of the geostrophic regime of rotating convection is described in detail, with a discussion of the subranges characterised by different flow structures and heat transfer scaling. Complications in the laboratory studies of geostrophic convection are discussed, such as domain size, effects of centrifugal buoyancy, confinement and wall modes, non-Oberbeck–Boussinesq effects and inertial wave resonance. In the paper by S. Horn and J. M. Aurnou, the effects of centrifugal buoyancy on the formation of tornado-like vortices are studied computationally based on the Coriolis-centrifugal convection system. They show that centrifugal buoyancy is relevant for naturally occurring tornadoes and a rich variety of tornado morphologies are produced in the quasi-cyclostrophic regime of Coriolis-centrifugal convection. The Editorial Board thanks the authors for their contributions to the special issue and hopes that this special issue will stimulate further progress and interest in the area.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1899365","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45921915","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}
Non-premixed impinging jet flames with different coflow conditions are performed using PIV technology combined with numerical simulation to investigate flame instability in the vicinity of wall. Results indicate that the increase of coflow velocity results in a more chaotic flow field and higher fuel efficiency, and the increase of coflow temperature leads to ignition advance and the increase of NO concentration. These can be attributed to the coupling effect of Kelvin-Helmholtz instability, convective instability and Rayleigh-Taylor instability. High coflow velocity is more likely to induce Kelvin-Helmholtz instability and convective instability, and the increase of coflow temperature enhances Rayleigh-Taylor instability and convective instability. Due to the impact effect in the vicinity of wall, the flame instability is more likely to be induced at high coflow velocity. Meanwhile, the increase of coflow temperature can inhibit flame wrinkles. The flame dynamics is affected by turbulent mixing, head-on collision, shear and convective behaviors in non-premixed flames.
{"title":"A study of the influence of coflow on flame dynamics in impinging jet diffusion flames","authors":"Hongxu Li, Jieyu Jiang, Meng Sun, Yongzhe Yu, Chunjie Sui, Bin Zhang","doi":"10.1080/14685248.2021.1917769","DOIUrl":"https://doi.org/10.1080/14685248.2021.1917769","url":null,"abstract":"Non-premixed impinging jet flames with different coflow conditions are performed using PIV technology combined with numerical simulation to investigate flame instability in the vicinity of wall. Results indicate that the increase of coflow velocity results in a more chaotic flow field and higher fuel efficiency, and the increase of coflow temperature leads to ignition advance and the increase of NO concentration. These can be attributed to the coupling effect of Kelvin-Helmholtz instability, convective instability and Rayleigh-Taylor instability. High coflow velocity is more likely to induce Kelvin-Helmholtz instability and convective instability, and the increase of coflow temperature enhances Rayleigh-Taylor instability and convective instability. Due to the impact effect in the vicinity of wall, the flame instability is more likely to be induced at high coflow velocity. Meanwhile, the increase of coflow temperature can inhibit flame wrinkles. The flame dynamics is affected by turbulent mixing, head-on collision, shear and convective behaviors in non-premixed flames.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1917769","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48920253","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 : 2021-03-04DOI: 10.1080/14685248.2020.1864388
Z. Tang, Xingyu Ma, N. Jiang, Xiaotong Cui, Xiaobo Zheng
An experimental investigation of near-wall scale interactions in the presence of a deterministic forcing input is presented in this work. The external forcing input was generated by a wall-mounted piezoelectric (PZT) actuator, which directly introduces a dynamic perturbation into the near-wall cycle of turbulent boundary layer flow. The spectra of velocity fluctuations indicated that the fundamental forcing mode can be observed in all the perturbed cases and that the occurrence of high-order harmonics is dependent on the PZT perturbation amplitude. Under the strong forcing input, the fundamental forcing mode is influenced by large-scale structures through a high-degree amplitude modulation (AM) effect. More importantly, the phase-switching process was found for the high-order harmonics and small-scale turbulence, both of which are in phase with the forcing mode in and are switched to be out of phase in . It was demonstrated that the forcing mode rearranges both the harmonics and small-scale turbulence in the near-wall region, as evidenced by the AM effect and phase relationship. In addition, the near-wall scale rearrangements were confirmed by the skewness cross-term distribution.
{"title":"Local dynamic perturbation effects on the scale interactions in wall turbulence","authors":"Z. Tang, Xingyu Ma, N. Jiang, Xiaotong Cui, Xiaobo Zheng","doi":"10.1080/14685248.2020.1864388","DOIUrl":"https://doi.org/10.1080/14685248.2020.1864388","url":null,"abstract":"An experimental investigation of near-wall scale interactions in the presence of a deterministic forcing input is presented in this work. The external forcing input was generated by a wall-mounted piezoelectric (PZT) actuator, which directly introduces a dynamic perturbation into the near-wall cycle of turbulent boundary layer flow. The spectra of velocity fluctuations indicated that the fundamental forcing mode can be observed in all the perturbed cases and that the occurrence of high-order harmonics is dependent on the PZT perturbation amplitude. Under the strong forcing input, the fundamental forcing mode is influenced by large-scale structures through a high-degree amplitude modulation (AM) effect. More importantly, the phase-switching process was found for the high-order harmonics and small-scale turbulence, both of which are in phase with the forcing mode in and are switched to be out of phase in . It was demonstrated that the forcing mode rearranges both the harmonics and small-scale turbulence in the near-wall region, as evidenced by the AM effect and phase relationship. In addition, the near-wall scale rearrangements were confirmed by the skewness cross-term distribution.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2020.1864388","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44388776","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 : 2021-03-01DOI: 10.1080/14685248.2022.2060508
M. Momenifar, Enmao Diao, V. Tarokh, A. Bragg
Analysing large-scale data from simulations of turbulent flows is memory intensive, requiring significant resources. This major challenge highlights the need for data compression techniques. In this study, we apply a physics-informed Deep Learning technique based on vector quantisation to generate a discrete, low-dimensional representation of data from simulations of three-dimensional turbulent flows. The deep learning framework is composed of convolutional layers and incorporates physical constraints on the flow, such as preserving incompressibility and global statistical characteristics of the velocity gradients. The accuracy of the model is assessed using statistical, comparison-based similarity and physics-based metrics. The training data set is produced from Direct Numerical Simulation of an incompressible, statistically stationary, isotropic turbulent flow. The performance of this lossy data compression scheme is evaluated not only with unseen data from the stationary, isotropic turbulent flow, but also with data from decaying isotropic turbulence, a Taylor–Green vortex flow, and a turbulent channel flow. Defining the compression ratio (CR) as the ratio of original data size to the compressed one, the results show that our model based on vector quantisation can offer CR with a mean square error (MSE) of , and predictions that faithfully reproduce the statistics of the flow, except at the very smallest scales where there is some loss. Compared to the recent study of Glaws. et al. [Deep learning for in situ data compression of large turbulent flow simulations. Phys Rev Fluids. 2020;5(11):114602], which was based on a conventional autoencoder (where compression is performed in a continuous space), our model improves the CR by more than 30%, and reduces the MSE by an order of magnitude. Our compression model is an attractive solution for situations where fast, high quality and low-overhead encoding and decoding of large data are required.
{"title":"Dimension reduced turbulent flow data from deep vector quantisers","authors":"M. Momenifar, Enmao Diao, V. Tarokh, A. Bragg","doi":"10.1080/14685248.2022.2060508","DOIUrl":"https://doi.org/10.1080/14685248.2022.2060508","url":null,"abstract":"Analysing large-scale data from simulations of turbulent flows is memory intensive, requiring significant resources. This major challenge highlights the need for data compression techniques. In this study, we apply a physics-informed Deep Learning technique based on vector quantisation to generate a discrete, low-dimensional representation of data from simulations of three-dimensional turbulent flows. The deep learning framework is composed of convolutional layers and incorporates physical constraints on the flow, such as preserving incompressibility and global statistical characteristics of the velocity gradients. The accuracy of the model is assessed using statistical, comparison-based similarity and physics-based metrics. The training data set is produced from Direct Numerical Simulation of an incompressible, statistically stationary, isotropic turbulent flow. The performance of this lossy data compression scheme is evaluated not only with unseen data from the stationary, isotropic turbulent flow, but also with data from decaying isotropic turbulence, a Taylor–Green vortex flow, and a turbulent channel flow. Defining the compression ratio (CR) as the ratio of original data size to the compressed one, the results show that our model based on vector quantisation can offer CR with a mean square error (MSE) of , and predictions that faithfully reproduce the statistics of the flow, except at the very smallest scales where there is some loss. Compared to the recent study of Glaws. et al. [Deep learning for in situ data compression of large turbulent flow simulations. Phys Rev Fluids. 2020;5(11):114602], which was based on a conventional autoencoder (where compression is performed in a continuous space), our model improves the CR by more than 30%, and reduces the MSE by an order of magnitude. Our compression model is an attractive solution for situations where fast, high quality and low-overhead encoding and decoding of large data are required.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44211592","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 : 2021-03-01DOI: 10.1080/14685248.2021.1898624
S. Horn, J. Aurnou
Coriolis-centrifugal convection ( ) in a cylindrical domain constitutes an idealised model of tornadic storms, where the rotating cylinder represents the mesocyclone of a supercell thunderstorm. We present a suite of direct numerical simulations, analysing the influence of centrifugal buoyancy on the formation of tornado-like vortices (TLVs). TLVs are self-consistently generated provided the flow is within the quasi-cyclostrophic (QC) regime in which the dominant dynamical balance is between pressure gradient and centrifugal buoyancy forces. This requires the Froude number to be greater than the radius-to-height aspect ratio, . We show that the TLVs that develop in our simulations share many similar features with realistic tornadoes, such as azimuthal velocity profiles, intensification of the vortex strength, and helicity characteristics. Further, we analyse the influence of the mechanical bottom boundary conditions on the formation of TLVs, finding that a rotating fluid column above a stationary surface does not generate TLVs if centrifugal buoyancy is absent. In contrast, TLVs are generated in the QC regime with any bottom boundary conditions when centrifugal buoyancy is present. Our simulations bring forth insights into natural supercell thunderstorm systems by identifying properties that determine whether a mesocyclone becomes tornadic or remains non-tornadic. For tornadoes to exist, a vertical temperature difference must be present that is capable of driving strong convection. Additionally, our predictions dimensionally imply a critical mesocyclone angular rotation rate of . Taking a typical mesocyclone height of , this translates to for centrifugal buoyancy-dominated, quasi-cyclostrophic tornadogenesis. The formation of the simulated TLVs happens at all heights on the centrifugal buoyancy time scale . This implies a roughly 1 minute, height-invariant formation for natural tornadoes, consistent with recent observational estimates.
{"title":"Tornado-like vortices in the quasi-cyclostrophic regime of Coriolis-centrifugal convection","authors":"S. Horn, J. Aurnou","doi":"10.1080/14685248.2021.1898624","DOIUrl":"https://doi.org/10.1080/14685248.2021.1898624","url":null,"abstract":"Coriolis-centrifugal convection ( ) in a cylindrical domain constitutes an idealised model of tornadic storms, where the rotating cylinder represents the mesocyclone of a supercell thunderstorm. We present a suite of direct numerical simulations, analysing the influence of centrifugal buoyancy on the formation of tornado-like vortices (TLVs). TLVs are self-consistently generated provided the flow is within the quasi-cyclostrophic (QC) regime in which the dominant dynamical balance is between pressure gradient and centrifugal buoyancy forces. This requires the Froude number to be greater than the radius-to-height aspect ratio, . We show that the TLVs that develop in our simulations share many similar features with realistic tornadoes, such as azimuthal velocity profiles, intensification of the vortex strength, and helicity characteristics. Further, we analyse the influence of the mechanical bottom boundary conditions on the formation of TLVs, finding that a rotating fluid column above a stationary surface does not generate TLVs if centrifugal buoyancy is absent. In contrast, TLVs are generated in the QC regime with any bottom boundary conditions when centrifugal buoyancy is present. Our simulations bring forth insights into natural supercell thunderstorm systems by identifying properties that determine whether a mesocyclone becomes tornadic or remains non-tornadic. For tornadoes to exist, a vertical temperature difference must be present that is capable of driving strong convection. Additionally, our predictions dimensionally imply a critical mesocyclone angular rotation rate of . Taking a typical mesocyclone height of , this translates to for centrifugal buoyancy-dominated, quasi-cyclostrophic tornadogenesis. The formation of the simulated TLVs happens at all heights on the centrifugal buoyancy time scale . This implies a roughly 1 minute, height-invariant formation for natural tornadoes, consistent with recent observational estimates.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1898624","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47486937","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 : 2021-02-16DOI: 10.1080/14685248.2021.1885676
S. Pargal, J. Yuan, G. Brereton
ABSTRACT This paper explores the use of a small-span direct numerical simulation for a transient, smooth-wall turbulent channel flow and then applies the small-span simulation to a transient channel flow with riblets. A flow configuration similar to that of S. He and M. Seddighi (J Fluid Mech. 2013;715:60–102) is used to study the impulse response of a half-height channel flow to an abrupt increase in bulk velocity (with a friction Reynolds number increasing from 180 to 418). A minimal domain span sufficient to include the near-wall quasi-streamwise vortices in the ‘healthy turbulence’ region is used. The turbulent flow undergoes reverse transition toward a quasi-laminar state, followed by a retransition phase to the new equilibrium state. On a smooth wall, detailed comparisons with a full-span case show that the small-span test case captures satisfactorily the essential dynamics during the entire transition process, although it yields a slight delay in recovery to the new equilibrium. This difference is attributed to a slower streak transient growth due to an underestimation of near-wall spanwise fluctuations. This underestimation is associated with the missing large attached eddies that are not contained in the small span of the simulation domain. These comparisons justify the use of small-span simulations for identifying the main flow physics in a non-equilibrium accelerating wall turbulence. The application to the riblet flow shows that riblets do not fundamentally affect the flow dynamics, but delay the retransition as a result of significantly milder streak meandering. The streak-stabilisation effect of riblets is still active in a strongly accelerating turbulence and tends to prolong the flow recovery.
{"title":"Impulse response of turbulent flow in smooth and riblet-walled channels to a sudden velocity increase","authors":"S. Pargal, J. Yuan, G. Brereton","doi":"10.1080/14685248.2021.1885676","DOIUrl":"https://doi.org/10.1080/14685248.2021.1885676","url":null,"abstract":"ABSTRACT This paper explores the use of a small-span direct numerical simulation for a transient, smooth-wall turbulent channel flow and then applies the small-span simulation to a transient channel flow with riblets. A flow configuration similar to that of S. He and M. Seddighi (J Fluid Mech. 2013;715:60–102) is used to study the impulse response of a half-height channel flow to an abrupt increase in bulk velocity (with a friction Reynolds number increasing from 180 to 418). A minimal domain span sufficient to include the near-wall quasi-streamwise vortices in the ‘healthy turbulence’ region is used. The turbulent flow undergoes reverse transition toward a quasi-laminar state, followed by a retransition phase to the new equilibrium state. On a smooth wall, detailed comparisons with a full-span case show that the small-span test case captures satisfactorily the essential dynamics during the entire transition process, although it yields a slight delay in recovery to the new equilibrium. This difference is attributed to a slower streak transient growth due to an underestimation of near-wall spanwise fluctuations. This underestimation is associated with the missing large attached eddies that are not contained in the small span of the simulation domain. These comparisons justify the use of small-span simulations for identifying the main flow physics in a non-equilibrium accelerating wall turbulence. The application to the riblet flow shows that riblets do not fundamentally affect the flow dynamics, but delay the retransition as a result of significantly milder streak meandering. The streak-stabilisation effect of riblets is still active in a strongly accelerating turbulence and tends to prolong the flow recovery.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1885676","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48306553","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 : 2021-02-01DOI: 10.1080/14685248.2020.1849712
Xiaole Wang, B. Cui, Zuoli Xiao
ABSTRACT The performance of ultra-high-lift (UHL) low-pressure turbine (LPT) is subject to complex flow phenomena (e.g. separation, transition and reattachment) which require advanced modelling for accurate numerical predictions. The feasibility and fidelity of three widely used transition-based turbulence models are evaluated in the Reynolds-Averaged Navier-Stokes (RANS) prediction of low-Reynolds number flows in linear UHL LPT cascade (T106C). All three transition models prove to capture the tendency that the size of separation bubble decreases with the increase of Reynolds number or inlet turbulence intensity. It turns out that intermittency factor-transition momentum thickness Reynolds number based shear stress transport turbulence model is the most accurate among the three models, expect for the clean inlet case at an isentropic outlet Reynolds number of . It is suggested that different viscosity ratios should be prescribed at the inlet for various models to mimic the effect of turbulence intensities precisely. In order to take into account the periodic wakes in computation, a moving cylindrical bar is added to the cascade inlet. The assessment of the capability of three models in predicting unsteady wake induced transition is carried out for selected Reynolds numbers. Some practical suggestions are given for the use of transition models based on RANS equations in simulation of the ultra-high-lift LPT cascade flows at low Reynolds numbers.
{"title":"Numerical investigation on ultra-high-lift low-pressure turbine cascade aerodynamics at low Reynolds numbers using transition-based turbulence models","authors":"Xiaole Wang, B. Cui, Zuoli Xiao","doi":"10.1080/14685248.2020.1849712","DOIUrl":"https://doi.org/10.1080/14685248.2020.1849712","url":null,"abstract":"ABSTRACT The performance of ultra-high-lift (UHL) low-pressure turbine (LPT) is subject to complex flow phenomena (e.g. separation, transition and reattachment) which require advanced modelling for accurate numerical predictions. The feasibility and fidelity of three widely used transition-based turbulence models are evaluated in the Reynolds-Averaged Navier-Stokes (RANS) prediction of low-Reynolds number flows in linear UHL LPT cascade (T106C). All three transition models prove to capture the tendency that the size of separation bubble decreases with the increase of Reynolds number or inlet turbulence intensity. It turns out that intermittency factor-transition momentum thickness Reynolds number based shear stress transport turbulence model is the most accurate among the three models, expect for the clean inlet case at an isentropic outlet Reynolds number of . It is suggested that different viscosity ratios should be prescribed at the inlet for various models to mimic the effect of turbulence intensities precisely. In order to take into account the periodic wakes in computation, a moving cylindrical bar is added to the cascade inlet. The assessment of the capability of three models in predicting unsteady wake induced transition is carried out for selected Reynolds numbers. Some practical suggestions are given for the use of transition models based on RANS equations in simulation of the ultra-high-lift LPT cascade flows at low Reynolds numbers.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2020.1849712","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44071133","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 : 2021-01-26DOI: 10.1080/14685248.2021.1876877
R. Kunnen
Rotating Rayleigh–Bénard convection is a simple model system used to study the interplay of buoyant forcing and rotation. Many recent studies have focused on the geostrophic regime of turbulent rotating convection where the principal balance of forces is between the Coriolis force and the pressure gradient. This regime is believed to be representative of conditions in geophysical and astrophysical flows. We hope to be able to extrapolate findings from laboratory experiments and numerical simulations towards these large-scale natural flows. In this paper I sketch the phase diagram of the geostrophic regime of rotating convection, put experimental and numerical studies in their place in these diagrams and discuss the partitioning into subranges characterised by different flow structures and heat transfer scaling. I also discuss some complications faced by experimentalists, such as constraints on the dimensions of the convection cell, wall modes near the sidewall and centrifugal buoyancy.
{"title":"The geostrophic regime of rapidly rotating turbulent convection","authors":"R. Kunnen","doi":"10.1080/14685248.2021.1876877","DOIUrl":"https://doi.org/10.1080/14685248.2021.1876877","url":null,"abstract":"Rotating Rayleigh–Bénard convection is a simple model system used to study the interplay of buoyant forcing and rotation. Many recent studies have focused on the geostrophic regime of turbulent rotating convection where the principal balance of forces is between the Coriolis force and the pressure gradient. This regime is believed to be representative of conditions in geophysical and astrophysical flows. We hope to be able to extrapolate findings from laboratory experiments and numerical simulations towards these large-scale natural flows. In this paper I sketch the phase diagram of the geostrophic regime of rotating convection, put experimental and numerical studies in their place in these diagrams and discuss the partitioning into subranges characterised by different flow structures and heat transfer scaling. I also discuss some complications faced by experimentalists, such as constraints on the dimensions of the convection cell, wall modes near the sidewall and centrifugal buoyancy.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2021-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1876877","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47009077","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 : 2020-12-29DOI: 10.1080/14685248.2020.1863416
M. Ajmi, N. Hnaien, Saloua Marzouk, Lioua Kolsi, Kaouther Ghachem, H. B. Aissia
ABSTRACT The present numerical study aims to numerically investigate the dynamic and turbulent characteristics of a two-dimensional and turbulent offset jet. Three different parameters were investigated: The Reynolds numbers (Re) which was varied from 10000 to 30000, wall inclination angle (α) that was from −20° to +20° and finally the offset ratio (OR) which extends from 3.25–13. Ansys Fluent was numerical CFD solver used in this present investigation. The simultaneous effects of the OR, Re and α were investigated in details. The velocity and pressure contours showed that these three parameters do not contribute equally in the development of such a flow. Also, the turbulent characteristics, such as the turbulence intensities and energies depicted how each parameter influences, separately, the turbulent flow production. Furthermore, different of tripled parameters correlations were developed. These correlations may be of help to more understand certain offset jet flow features more accurately and to predict their exact values.
{"title":"Numerical investigation and triple-parameters correlations development on the dynamic characteristics of a turbulent offset jet","authors":"M. Ajmi, N. Hnaien, Saloua Marzouk, Lioua Kolsi, Kaouther Ghachem, H. B. Aissia","doi":"10.1080/14685248.2020.1863416","DOIUrl":"https://doi.org/10.1080/14685248.2020.1863416","url":null,"abstract":"ABSTRACT The present numerical study aims to numerically investigate the dynamic and turbulent characteristics of a two-dimensional and turbulent offset jet. Three different parameters were investigated: The Reynolds numbers (Re) which was varied from 10000 to 30000, wall inclination angle (α) that was from −20° to +20° and finally the offset ratio (OR) which extends from 3.25–13. Ansys Fluent was numerical CFD solver used in this present investigation. The simultaneous effects of the OR, Re and α were investigated in details. The velocity and pressure contours showed that these three parameters do not contribute equally in the development of such a flow. Also, the turbulent characteristics, such as the turbulence intensities and energies depicted how each parameter influences, separately, the turbulent flow production. Furthermore, different of tripled parameters correlations were developed. These correlations may be of help to more understand certain offset jet flow features more accurately and to predict their exact values.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2020-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2020.1863416","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41424438","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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