Pub Date : 2021-06-03DOI: 10.1080/14685248.2021.1916023
J. Cheng, Jianzhao Wu, Yu-lu Liu, Zhiming Lu
Spontaneous and stochastic reversal of large scale flow structure is an intriguing and crucial phenomenon in turbulent Rayleigh-Bénard type natural convection. This paper proposes a new control approach to eliminate the reversals through stabilising the corner flows using two small sidewall controllers. Based on a series of direct numerical simulations, it is shown that the control can successfully stop the growth of corner vortices and suppress the reversal of large-scale circulation, if the width of sidewall controllers installed within or near the top of corner vortices is large enough. When the controllers are located around the centre, they can easily break up the large-scale structures or even divide the single roll mode into a double-roll mode for very large widths. Moreover, the influence of sidewall controllers on the heat transport is studied. It is shown that the heat transport efficiency can be slightly enhanced or suppressed when the proper location and width are chosen. The present findings provide a new idea to control the large-scale flow structure and reversals in thermally driven convection through sidewall controlling.
{"title":"Sidewall controlling large-scale flow structure and reversal in turbulent Rayleigh-Bénard convection","authors":"J. Cheng, Jianzhao Wu, Yu-lu Liu, Zhiming Lu","doi":"10.1080/14685248.2021.1916023","DOIUrl":"https://doi.org/10.1080/14685248.2021.1916023","url":null,"abstract":"Spontaneous and stochastic reversal of large scale flow structure is an intriguing and crucial phenomenon in turbulent Rayleigh-Bénard type natural convection. This paper proposes a new control approach to eliminate the reversals through stabilising the corner flows using two small sidewall controllers. Based on a series of direct numerical simulations, it is shown that the control can successfully stop the growth of corner vortices and suppress the reversal of large-scale circulation, if the width of sidewall controllers installed within or near the top of corner vortices is large enough. When the controllers are located around the centre, they can easily break up the large-scale structures or even divide the single roll mode into a double-roll mode for very large widths. Moreover, the influence of sidewall controllers on the heat transport is studied. It is shown that the heat transport efficiency can be slightly enhanced or suppressed when the proper location and width are chosen. The present findings provide a new idea to control the large-scale flow structure and reversals in thermally driven convection through sidewall controlling.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"380 - 392"},"PeriodicalIF":1.9,"publicationDate":"2021-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1916023","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48249710","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 : 2021-06-03DOI: 10.1080/14685248.2021.1932947
E. Juntasaro, K. Ngiamsoongnirn, Phongsakorn Thawornsathit, P. Durbin
ABSTRACT The objective of this paper is to propose a new intermittency transport equation that is naturally capable of capturing the effects of free-stream turbulence and pressure gradient on bypass and natural transition without need for any extra parameters/terms to take into account the free-stream turbulence and the pressure gradient. This new intermittency transport equation is obtained by derivation and, in it, only its production term is modeled via two empirical functions in order to detect the onset location of transition and to control the growth rate of transition process. Only one sensing parameter is used to detect the transition onset for both natural and bypass transition. For the purpose of not altering the original form of the base turbulence model, the effective intermittency factor is used to describe the separation-induced transition. The base turbulence model remains unmodified in conjunction with the effective intermittency factor as a regulator to control the net turbulent generation rate. For the evaluation of model performance, the modeled intermittency equation is tested against (1) the transitional boundary layer on a flat plate with zero and non-zero pressure gradients, (2) the transitional flow over a compressor blade with a laminar separation bubble, and (3) the transitional flow over a wind turbine airfoil at various angles of attack. The present results are also compared to those of the transition model of Menter et al. [1] and those of the transition model of Langtry and Menter [2]. The evaluation results reveal that the new intermittency transport equation is capable of predicting the bypass, natural and separation-induced transition.
{"title":"Development of an intermittency transport equation for modeling bypass, natural and separation-induced transition","authors":"E. Juntasaro, K. Ngiamsoongnirn, Phongsakorn Thawornsathit, P. Durbin","doi":"10.1080/14685248.2021.1932947","DOIUrl":"https://doi.org/10.1080/14685248.2021.1932947","url":null,"abstract":"ABSTRACT The objective of this paper is to propose a new intermittency transport equation that is naturally capable of capturing the effects of free-stream turbulence and pressure gradient on bypass and natural transition without need for any extra parameters/terms to take into account the free-stream turbulence and the pressure gradient. This new intermittency transport equation is obtained by derivation and, in it, only its production term is modeled via two empirical functions in order to detect the onset location of transition and to control the growth rate of transition process. Only one sensing parameter is used to detect the transition onset for both natural and bypass transition. For the purpose of not altering the original form of the base turbulence model, the effective intermittency factor is used to describe the separation-induced transition. The base turbulence model remains unmodified in conjunction with the effective intermittency factor as a regulator to control the net turbulent generation rate. For the evaluation of model performance, the modeled intermittency equation is tested against (1) the transitional boundary layer on a flat plate with zero and non-zero pressure gradients, (2) the transitional flow over a compressor blade with a laminar separation bubble, and (3) the transitional flow over a wind turbine airfoil at various angles of attack. The present results are also compared to those of the transition model of Menter et al. [1] and those of the transition model of Langtry and Menter [2]. The evaluation results reveal that the new intermittency transport equation is capable of predicting the bypass, natural and separation-induced transition.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"562 - 595"},"PeriodicalIF":1.9,"publicationDate":"2021-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1932947","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44563240","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 : 2021-05-31DOI: 10.1080/14685248.2021.1932944
L. Thijs, R. Dellaert, S. Tajfirooz, J. Zeegers, J. Kuerten
ABSTRACT We present an experimental and numerical study of the flow downstream of honeycomb flow straighteners for a range of Reynolds numbers, covering both laminar and turbulent flow inside the honeycomb cells. We carried out experiments with planar particle image velocimetry (PIV) in a wind tunnel and performed numerical simulations to perform an in-depth investigation of the three-dimensional flow field. The individual channel profiles downstream of the honeycomb gradually develop into one uniform velocity profile. This development corresponds with an increase in the velocity fluctuations which reach a maximum and then start to decay. The position and magnitude of the turbulence intensity peak depend on the Reynolds number. By means of the turbulence kinetic energy (TKE) budget it is shown that the production of TKE is dominated by the shear layers corresponding to the honeycomb walls. The near-field and far-field decay of the turbulence intensity can be described by power laws where we used the position where the production term of the TKE reaches its maximum as the virtual origin.
{"title":"Honeycomb-generated Reynolds-number-dependent wake turbulence","authors":"L. Thijs, R. Dellaert, S. Tajfirooz, J. Zeegers, J. Kuerten","doi":"10.1080/14685248.2021.1932944","DOIUrl":"https://doi.org/10.1080/14685248.2021.1932944","url":null,"abstract":"ABSTRACT We present an experimental and numerical study of the flow downstream of honeycomb flow straighteners for a range of Reynolds numbers, covering both laminar and turbulent flow inside the honeycomb cells. We carried out experiments with planar particle image velocimetry (PIV) in a wind tunnel and performed numerical simulations to perform an in-depth investigation of the three-dimensional flow field. The individual channel profiles downstream of the honeycomb gradually develop into one uniform velocity profile. This development corresponds with an increase in the velocity fluctuations which reach a maximum and then start to decay. The position and magnitude of the turbulence intensity peak depend on the Reynolds number. By means of the turbulence kinetic energy (TKE) budget it is shown that the production of TKE is dominated by the shear layers corresponding to the honeycomb walls. The near-field and far-field decay of the turbulence intensity can be described by power laws where we used the position where the production term of the TKE reaches its maximum as the virtual origin.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"535 - 561"},"PeriodicalIF":1.9,"publicationDate":"2021-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1932944","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48500723","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 : 2021-05-28DOI: 10.1080/14685248.2021.1932939
K. Chaudhury, Chandranath Banerjee, Swapnil Urankar
ABSTRACT We present a systematic approach to extract the characteristic vortex region that contains the essential features of a complex flow field. The process involves the analysis of the complex eigenvalues of the velocity gradient tensor. In particular, we propose the analysis using the joint and marginal probability distributions of the complex eigenvalues of the velocity gradient tensor that preserves the sufficient swirling strength and the required orbital compactness of the swirling orbits defining the vortex region. We consider three complex flow scenarios for the application and the assessment of the proposed approach: (i) rotating Rayleigh–Benard convection, (ii) turbulent channel flow, (iii) turbulent flow field in a cylindrical cyclonic separator. While problem (i) is considered for the extraction of subsumed cyclonic structure, problems (ii) and (iii) are reminiscent of wall-bounded turbulent flows, relevant for different industrial applications.
{"title":"Estimation of characteristic vortex structures in complex flow","authors":"K. Chaudhury, Chandranath Banerjee, Swapnil Urankar","doi":"10.1080/14685248.2021.1932939","DOIUrl":"https://doi.org/10.1080/14685248.2021.1932939","url":null,"abstract":"ABSTRACT We present a systematic approach to extract the characteristic vortex region that contains the essential features of a complex flow field. The process involves the analysis of the complex eigenvalues of the velocity gradient tensor. In particular, we propose the analysis using the joint and marginal probability distributions of the complex eigenvalues of the velocity gradient tensor that preserves the sufficient swirling strength and the required orbital compactness of the swirling orbits defining the vortex region. We consider three complex flow scenarios for the application and the assessment of the proposed approach: (i) rotating Rayleigh–Benard convection, (ii) turbulent channel flow, (iii) turbulent flow field in a cylindrical cyclonic separator. While problem (i) is considered for the extraction of subsumed cyclonic structure, problems (ii) and (iii) are reminiscent of wall-bounded turbulent flows, relevant for different industrial applications.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"517 - 534"},"PeriodicalIF":1.9,"publicationDate":"2021-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1932939","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45165924","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 : 2021-05-19DOI: 10.1080/14685248.2021.1925125
N. Ali, M. Calaf, R. B. Cal
For complex flow systems like the one of the wind turbine wakes, which include a range of interacting turbulent scales, there is the potential to reduce the high dimensionality of the problem to low-rank approximations. Unsupervised cluster analysis based on the proper orthogonal decomposition is used here to identify the coherent structure and transition dynamics of wind turbine wake. Through the clustering approach, the nonlinear dynamics of the turbine wake is presented in a linear framework. The features of the fluctuating velocity are grouped based on similarity and presented as the centroids of the defining clusters. Determined from probability distribution of the transition, the dynamical system identifies the features of the wakes and the inherent dynamics of the flow.
{"title":"Cluster-based probabilistic structure dynamical model of wind turbine wake","authors":"N. Ali, M. Calaf, R. B. Cal","doi":"10.1080/14685248.2021.1925125","DOIUrl":"https://doi.org/10.1080/14685248.2021.1925125","url":null,"abstract":"For complex flow systems like the one of the wind turbine wakes, which include a range of interacting turbulent scales, there is the potential to reduce the high dimensionality of the problem to low-rank approximations. Unsupervised cluster analysis based on the proper orthogonal decomposition is used here to identify the coherent structure and transition dynamics of wind turbine wake. Through the clustering approach, the nonlinear dynamics of the turbine wake is presented in a linear framework. The features of the fluctuating velocity are grouped based on similarity and presented as the centroids of the defining clusters. Determined from probability distribution of the transition, the dynamical system identifies the features of the wakes and the inherent dynamics of the flow.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"22 1","pages":"497 - 516"},"PeriodicalIF":1.9,"publicationDate":"2021-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/14685248.2021.1925125","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42401322","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 : 2021-05-07DOI: 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":"22 1","pages":"481 - 496"},"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":"22 1","pages":"231 - 231"},"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":"22 1","pages":"461 - 480"},"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":"22 1","pages":"208 - 230"},"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":"23 1","pages":"232 - 264"},"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}
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