Pub Date : 2022-07-14DOI: 10.1080/14685248.2022.2094936
J. Yao, C. J. Teo
We have investigated the effects of rib surface curvature of a superhydrophobic wall in both laminar and turbulent channel flows. Direct numerical simulation is performed for laminar flows and large eddy simulation is performed for turbulent flows. The parametric study shows that a convex rib surface leads to a lower flow ratethan a flat rib for all Reynolds numbers. A concave rib surface firstly increases and then decreases the flow rate as the curvature angle becomes larger, where an optimal curvature angle exists to maximise flow rate. The value of the optimal curvature angle varies with the Reynolds number. A curved rib surface can modify the distribution of the mean velocity and turbulent statistics near the SH wall. Analysis shows that the overall effect of a curved rib surface on the flow rate is the combination of the wetted area augmentation and the change to the spanwise flow interaction, which depends on the curvature angle and the Reynolds number. The SH wall does not change the fundamental structures of near-wall vortices in turbulent flows. The ridge-groove pattern formed by the curved rib surface can provide additional drag reduction similar to that arising from the surface riblets.
{"title":"Drag reduction by a superhydrophobic surface with longitudinal grooves: the effects of the rib surface curvature","authors":"J. Yao, C. J. Teo","doi":"10.1080/14685248.2022.2094936","DOIUrl":"https://doi.org/10.1080/14685248.2022.2094936","url":null,"abstract":"We have investigated the effects of rib surface curvature of a superhydrophobic wall in both laminar and turbulent channel flows. Direct numerical simulation is performed for laminar flows and large eddy simulation is performed for turbulent flows. The parametric study shows that a convex rib surface leads to a lower flow ratethan a flat rib for all Reynolds numbers. A concave rib surface firstly increases and then decreases the flow rate as the curvature angle becomes larger, where an optimal curvature angle exists to maximise flow rate. The value of the optimal curvature angle varies with the Reynolds number. A curved rib surface can modify the distribution of the mean velocity and turbulent statistics near the SH wall. Analysis shows that the overall effect of a curved rib surface on the flow rate is the combination of the wetted area augmentation and the change to the spanwise flow interaction, which depends on the curvature angle and the Reynolds number. The SH wall does not change the fundamental structures of near-wall vortices in turbulent flows. The ridge-groove pattern formed by the curved rib surface can provide additional drag reduction similar to that arising from the surface riblets.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"405 - 432"},"PeriodicalIF":1.9,"publicationDate":"2022-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47650088","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 : 2022-07-03DOI: 10.1080/14685248.2022.2081293
Ugo Piomelli, O. Métais
It is with great regret that we announce the death of Marcel Lesieur, who passed away on March 22, 2022, at the age of seventy-six. Professor Lesieur was a world leader in the field of turbulence, and the founding editor of this journal. Marcel Lesieur graduated from the École Polytechnique and obtained a Ph.D. from the University of Nice. After a period at the Centre National de la Recherche Scientifique (CNRS), he became a professor of fluid mechanics at the Institut Polytechnique de Grenoble. He retired in 2007, and, at the time of his death was Professor Emeritus. At the Laboratoire des écoulements géophysiques et industriels (LEGI) of Grenoble, he established a research group that carried out ground-breaking research on turbulent flows. Members of his research team occupy prestigious positions at Universities, in industry, and in research centres worldwide. His studies focussed on the simulation and modelling of turbulent flows. They spanned theoretical developments, applications to canonical flows and to more realistic configurations. Using the Eddy-Damped Quasi-Normal Markovian theory he developed advanced subgrid-scale models that were later extended to complex geometries. He carried out novel direct and large-eddy simulations of turbulent flows in a variety of configurations relevant to mechanical, environmental, and aerospace engineering, oceanography and meteorology. Among them are stratified and rotating flows, transitional and turbulent boundary layers, and transport of passive scalars. He authored two books; the first one, “Turbulence in Fluids: Stochastic and Numerical Modelling” (1987) was the first treatise on the subject since those by Townsend (1956) and Hinze (1959); it is now on its fourth edition. The second, “Large-Eddy Simulations of Turbulence”, with O. Métais and P. Comte (2005), was probably the first book to be published on this subject. In recognition of his work, Professor Lesieur received several prizes, including the CNRS bronze medal, the Seymour Cray-France prize and the Marcel Dassault Grand Prize from the Académie des Sciences. He was also elected to the Académie des Sciences in 2003. In the editorial sphere, Marcel Lesieur had the vision to predict the potential of onlineonly journals. This vision was realized in 2000, with the first issue of this journal, which he founded. At the time, the possibility of including colour figures and animations in a journal
我们怀着极大的遗憾宣布马塞尔·勒西厄去世，他于2022年3月22日去世，享年76岁。Lesieur教授是湍流领域的世界领导者，也是本刊的创刊编辑。Marcel Lesieur毕业于École巴黎综合理工学院，并获得尼斯大学博士学位。在法国国家科学研究中心(CNRS)工作一段时间后，他成为法国格勒诺布尔理工学院流体力学教授。他于2007年退休，去世时是名誉教授。他在格勒诺布尔大学的“身体与工业实验室”(LEGI)建立了一个研究小组，对湍流进行了开创性的研究。他的研究团队成员在世界各地的大学、工业和研究中心担任着重要职位。他的研究重点是湍流的模拟和建模。它们跨越了理论发展、规范流的应用和更现实的配置。利用涡流阻尼拟正态马尔可夫理论，他发展了先进的亚网格尺度模型，后来扩展到复杂的几何形状。他在与机械、环境、航空航天工程、海洋学和气象学相关的各种配置中进行了新颖的直接和大涡湍流模拟。其中包括层状和旋转流动、过渡和湍流边界层以及被动标量的输运。他写了两本书;第一部《流体中的湍流:随机和数值模拟》(1987年)是继汤森(1956年)和欣泽(1959年)之后关于这一主题的第一篇论文;现在已经是第四版了。第二本书，《湍流的大涡模拟》，由O. m . m . samtais和P. Comte合著(2005)，可能是关于这个主题的第一本出版的书。为了表彰他的工作，莱西厄教授获得了多个奖项，包括法国国家科学研究院铜奖、西摩·克雷-弗朗斯奖和法国科学院颁发的马塞尔·达索大奖。他还于2003年当选为法国科学院院士。在编辑领域，Marcel Lesieur有远见地预测了纯在线期刊的潜力。这一愿景在2000年通过他创办的《华尔街日报》创刊号得以实现。当时，在日记中加入彩色人物和动画的可能性很小
{"title":"In memoriam, Marcel Lesieur (1945-2022)","authors":"Ugo Piomelli, O. Métais","doi":"10.1080/14685248.2022.2081293","DOIUrl":"https://doi.org/10.1080/14685248.2022.2081293","url":null,"abstract":"It is with great regret that we announce the death of Marcel Lesieur, who passed away on March 22, 2022, at the age of seventy-six. Professor Lesieur was a world leader in the field of turbulence, and the founding editor of this journal. Marcel Lesieur graduated from the École Polytechnique and obtained a Ph.D. from the University of Nice. After a period at the Centre National de la Recherche Scientifique (CNRS), he became a professor of fluid mechanics at the Institut Polytechnique de Grenoble. He retired in 2007, and, at the time of his death was Professor Emeritus. At the Laboratoire des écoulements géophysiques et industriels (LEGI) of Grenoble, he established a research group that carried out ground-breaking research on turbulent flows. Members of his research team occupy prestigious positions at Universities, in industry, and in research centres worldwide. His studies focussed on the simulation and modelling of turbulent flows. They spanned theoretical developments, applications to canonical flows and to more realistic configurations. Using the Eddy-Damped Quasi-Normal Markovian theory he developed advanced subgrid-scale models that were later extended to complex geometries. He carried out novel direct and large-eddy simulations of turbulent flows in a variety of configurations relevant to mechanical, environmental, and aerospace engineering, oceanography and meteorology. Among them are stratified and rotating flows, transitional and turbulent boundary layers, and transport of passive scalars. He authored two books; the first one, “Turbulence in Fluids: Stochastic and Numerical Modelling” (1987) was the first treatise on the subject since those by Townsend (1956) and Hinze (1959); it is now on its fourth edition. The second, “Large-Eddy Simulations of Turbulence”, with O. Métais and P. Comte (2005), was probably the first book to be published on this subject. In recognition of his work, Professor Lesieur received several prizes, including the CNRS bronze medal, the Seymour Cray-France prize and the Marcel Dassault Grand Prize from the Académie des Sciences. He was also elected to the Académie des Sciences in 2003. In the editorial sphere, Marcel Lesieur had the vision to predict the potential of onlineonly journals. This vision was realized in 2000, with the first issue of this journal, which he founded. At the time, the possibility of including colour figures and animations in a journal","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"325 - 326"},"PeriodicalIF":1.9,"publicationDate":"2022-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42586926","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 : 2022-07-03DOI: 10.1080/14685248.2022.2092121
F. Durst, M. Breuer, B. Ünsal, K. Haddad
The literature stresses the inherent stability of laminar pipe flows with parabolic velocity profiles and this paper refers to the relevant publications summarizing this work. To cause such flows to turn into their turbulent state requires laminar pipe flows to be triggered externally. Ring-type, wall-mounted obstacles can be used for this purpose, and investigations in this area are of particular interest to the authors’ work, summarized in this paper. In the investigations presented here, however, a special triggering technique was employed that allowed laminar pipe flows to be exposed to obstacle disturbances for only about 30 ms. Individual puffs and slugs could be produced in this way. Comparisons with fixed wall-mounted obstacles showed that the properties of both types of turbulent slugs were the same. Theoretical derivations are described to provide the required obstacle height as a function of the Reynolds number, to trigger fully developed laminar pipe flows to turn into their turbulent state. Corresponding experimental investigations were also performed as described. Very good agreement between the theoretical and experimental results was obtained. All this demonstrates that a relatively simple ‘ad hoc theory’ can derive the required height of ring-type, wall-inserted obstacles to trigger laminar pipe flows with parabolic velocity profiles to turn turbulent. Other ways to trigger laminar pipe flows to turn turbulent were also investigated by employing blowers and plenum chambers and varying the lengths and diameters of pipes. It is demonstrated, in a somewhat qualitative way, that the maintenance of laminar pipe flows requires all components of a test rig to be matched to each other to maintain pipe flows laminar.
{"title":"Laminar-to-Turbulent Transition of Pipe Flows Triggered by Wall-Mounted, Ring-Type Obstacles","authors":"F. Durst, M. Breuer, B. Ünsal, K. Haddad","doi":"10.1080/14685248.2022.2092121","DOIUrl":"https://doi.org/10.1080/14685248.2022.2092121","url":null,"abstract":"The literature stresses the inherent stability of laminar pipe flows with parabolic velocity profiles and this paper refers to the relevant publications summarizing this work. To cause such flows to turn into their turbulent state requires laminar pipe flows to be triggered externally. Ring-type, wall-mounted obstacles can be used for this purpose, and investigations in this area are of particular interest to the authors’ work, summarized in this paper. In the investigations presented here, however, a special triggering technique was employed that allowed laminar pipe flows to be exposed to obstacle disturbances for only about 30 ms. Individual puffs and slugs could be produced in this way. Comparisons with fixed wall-mounted obstacles showed that the properties of both types of turbulent slugs were the same. Theoretical derivations are described to provide the required obstacle height as a function of the Reynolds number, to trigger fully developed laminar pipe flows to turn into their turbulent state. Corresponding experimental investigations were also performed as described. Very good agreement between the theoretical and experimental results was obtained. All this demonstrates that a relatively simple ‘ad hoc theory’ can derive the required height of ring-type, wall-inserted obstacles to trigger laminar pipe flows with parabolic velocity profiles to turn turbulent. Other ways to trigger laminar pipe flows to turn turbulent were also investigated by employing blowers and plenum chambers and varying the lengths and diameters of pipes. It is demonstrated, in a somewhat qualitative way, that the maintenance of laminar pipe flows requires all components of a test rig to be matched to each other to maintain pipe flows laminar.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"382 - 404"},"PeriodicalIF":1.9,"publicationDate":"2022-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45450959","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 : 2022-06-06DOI: 10.1080/14685248.2022.2083626
G. Tian, Zuoli Xiao
Compressible flow past a heated circular cylinder at subcritical Reynolds number of 3900 is numerically investigated by using the large-eddy simulation method. Rigorous validations of the numerical model are carefully performed under isothermal conditions on the basis of available experimental data. The calculated mean flow and Reynolds stresses show good agreement with the published experimental data. The effects of temperature difference between the cylinder surface and the freestream on the flow statistics and thermal characteristics are further studied in detail by setting two kinds of wall temperature boundary conditions. It is manifested that increasing the wall temperature leads to the augmentation of skin friction drag, suppression of turbulent intensity, enhancement of flow mixing and extension of recirculation zone. In addition, it is found that the variations of thermo-physical properties pose a slight effect on the wall heat flux before the boundary layer separates from the cylinder surface. It is worth noting that the recirculation bubble length can be used as a distance scaling parameter to weaken the temperature dependence of the flow and thermal statistics. These results provide a more detailed insight into the statistical difference in the wake region of cylinder when the temperature effect is taken into account.
{"title":"Non-isothermal flow past a heated circular cylinder in subcritical regime: a numerical investigation based on large-eddy simulation","authors":"G. Tian, Zuoli Xiao","doi":"10.1080/14685248.2022.2083626","DOIUrl":"https://doi.org/10.1080/14685248.2022.2083626","url":null,"abstract":"Compressible flow past a heated circular cylinder at subcritical Reynolds number of 3900 is numerically investigated by using the large-eddy simulation method. Rigorous validations of the numerical model are carefully performed under isothermal conditions on the basis of available experimental data. The calculated mean flow and Reynolds stresses show good agreement with the published experimental data. The effects of temperature difference between the cylinder surface and the freestream on the flow statistics and thermal characteristics are further studied in detail by setting two kinds of wall temperature boundary conditions. It is manifested that increasing the wall temperature leads to the augmentation of skin friction drag, suppression of turbulent intensity, enhancement of flow mixing and extension of recirculation zone. In addition, it is found that the variations of thermo-physical properties pose a slight effect on the wall heat flux before the boundary layer separates from the cylinder surface. It is worth noting that the recirculation bubble length can be used as a distance scaling parameter to weaken the temperature dependence of the flow and thermal statistics. These results provide a more detailed insight into the statistical difference in the wake region of cylinder when the temperature effect is taken into account.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"352 - 381"},"PeriodicalIF":1.9,"publicationDate":"2022-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41570673","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 : 2022-05-31DOI: 10.1080/14685248.2022.2071431
Z. Dong, Jianli Tong, Zhou Huang
A combined fishway containing notched weir, central orifice and vertical slot with an identical layout was designed, and its turbulence characteristics were experimentally studied. An acoustic Doppler velocimetry (ADV) was used to measure three-dimensional velocity. Flow regime, average velocity, turbulence intensity, Reynolds stress, power frequency-spectrum, correlation function, turbulence scale were analysed. The experimental results showed the combined fishway was of remarkable three-dimensional flow structures. Longitudinal velocity exhibited obvious extreme value region on the horizontal plane. Extreme values of longitudinal turbulence intensity were concentrated mainly on the mixing region between weir flow and orifice jet, as well as the vertical slot wall jet region, extreme value region of transverse turbulence intensity occurred on the central plane of orifice jet, and extreme values of vertical turbulence intensity were scattered. Reynolds stress extreme value occurred mainly in the convergent zone of multiple jets. Dominant frequency of power frequency-spectrum was highest for notched weir and lowest for vertical slot. Longitudinal velocity fluctuation exhibited a correlation with time, which was characterised by dominant frequency. Turbulence scales showed eddy structures were related to flow zones.
{"title":"Turbulence characteristics in a weir-orifice-slot combined fishway with an identical layout","authors":"Z. Dong, Jianli Tong, Zhou Huang","doi":"10.1080/14685248.2022.2071431","DOIUrl":"https://doi.org/10.1080/14685248.2022.2071431","url":null,"abstract":"A combined fishway containing notched weir, central orifice and vertical slot with an identical layout was designed, and its turbulence characteristics were experimentally studied. An acoustic Doppler velocimetry (ADV) was used to measure three-dimensional velocity. Flow regime, average velocity, turbulence intensity, Reynolds stress, power frequency-spectrum, correlation function, turbulence scale were analysed. The experimental results showed the combined fishway was of remarkable three-dimensional flow structures. Longitudinal velocity exhibited obvious extreme value region on the horizontal plane. Extreme values of longitudinal turbulence intensity were concentrated mainly on the mixing region between weir flow and orifice jet, as well as the vertical slot wall jet region, extreme value region of transverse turbulence intensity occurred on the central plane of orifice jet, and extreme values of vertical turbulence intensity were scattered. Reynolds stress extreme value occurred mainly in the convergent zone of multiple jets. Dominant frequency of power frequency-spectrum was highest for notched weir and lowest for vertical slot. Longitudinal velocity fluctuation exhibited a correlation with time, which was characterised by dominant frequency. Turbulence scales showed eddy structures were related to flow zones.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"327 - 351"},"PeriodicalIF":1.9,"publicationDate":"2022-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49080984","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 : 2022-05-24DOI: 10.1080/14685248.2022.2071429
Ziye Fan, Z. Tang, Xingyu Ma, N. Jiang
Experiments of particle image velocimetry (PIV) in the turbulent boundary layer at have been conducted to investigate the convection characteristic of turbulent structure and the validity of Taylor’s hypothesis. Views of ( , the boundary layer thickness) were captured by four streamwise-arranged cameras. Distributions of streamwise turbulent kinetic energy on a streamwise scale were investigated by continuous-wave transform, and scales were found where the portion of streamwise turbulent kinetic energy approaches maximum. Fluctuating velocities (instant velocity minus average velocity on time dimension) were divided into large-scale motion (LSM) and small-scale motion (SSM) portions, bounded by . Convection velocities of LSM and SSM are determined by the spatiotemporal correlation method, and they are larger than local average velocities in near-wall regions, but smaller than local average velocities in wake regions. Statistical characteristics between velocity fields reconstructed by Taylor’s hypothesis and original fields were compared by the autocorrelation method, and the reconstructed field’s patterns are longer than original field’s patterns, while their heights do not have clear distinction. The correlation of original velocity fields and reconstructed fields shows that LSM can hold on over and SSM over in streamwise convection separation for regions of , given a threshold value (correlation coefficient C = 0.6).
{"title":"Convection of multi-scale motions in turbulent boundary layer by temporal resolution particle image velocimetry","authors":"Ziye Fan, Z. Tang, Xingyu Ma, N. Jiang","doi":"10.1080/14685248.2022.2071429","DOIUrl":"https://doi.org/10.1080/14685248.2022.2071429","url":null,"abstract":"Experiments of particle image velocimetry (PIV) in the turbulent boundary layer at have been conducted to investigate the convection characteristic of turbulent structure and the validity of Taylor’s hypothesis. Views of ( , the boundary layer thickness) were captured by four streamwise-arranged cameras. Distributions of streamwise turbulent kinetic energy on a streamwise scale were investigated by continuous-wave transform, and scales were found where the portion of streamwise turbulent kinetic energy approaches maximum. Fluctuating velocities (instant velocity minus average velocity on time dimension) were divided into large-scale motion (LSM) and small-scale motion (SSM) portions, bounded by . Convection velocities of LSM and SSM are determined by the spatiotemporal correlation method, and they are larger than local average velocities in near-wall regions, but smaller than local average velocities in wake regions. Statistical characteristics between velocity fields reconstructed by Taylor’s hypothesis and original fields were compared by the autocorrelation method, and the reconstructed field’s patterns are longer than original field’s patterns, while their heights do not have clear distinction. The correlation of original velocity fields and reconstructed fields shows that LSM can hold on over and SSM over in streamwise convection separation for regions of , given a threshold value (correlation coefficient C = 0.6).","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"305 - 323"},"PeriodicalIF":1.9,"publicationDate":"2022-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45733741","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 : 2022-05-06DOI: 10.1080/14685248.2022.2070174
Sarvesh Kumar, Amitesh Kumar
In this paper, the three-dimensional turbulent wall jet flow is investigated for three different developing initial velocity profiles. The developing initial velocity profiles at the nozzle exit are generated by three different lengths ( , 50 and 90) of the square nozzle . The velocity profiles at the nozzle exit are measured with the single probe hot-wire anemometer. The Reynolds number based on the bulk mean velocity and nozzle height is 25,000 for all the cases. The measured velocity profiles at the nozzle exit are used as the inlet conditions for the numerical simulations. The results show that the initial velocity profile affects the flow field of the wall jet in near and far-field regions. It is found that the contours of streamwise velocity and turbulent kinetic energy exhibit the effect of initial conditions in the near field. The Reynolds shear stress component dominates in the vertical jet centreline plane, and it increases with a decrease in the nozzle length. The Reynolds shear stress component dominates in the lateral plane, and also exhibit the dependency on initial conditions.
{"title":"Dependence of wall jet phenomenology on inlet conditions and near-field flow development","authors":"Sarvesh Kumar, Amitesh Kumar","doi":"10.1080/14685248.2022.2070174","DOIUrl":"https://doi.org/10.1080/14685248.2022.2070174","url":null,"abstract":"In this paper, the three-dimensional turbulent wall jet flow is investigated for three different developing initial velocity profiles. The developing initial velocity profiles at the nozzle exit are generated by three different lengths ( , 50 and 90) of the square nozzle . The velocity profiles at the nozzle exit are measured with the single probe hot-wire anemometer. The Reynolds number based on the bulk mean velocity and nozzle height is 25,000 for all the cases. The measured velocity profiles at the nozzle exit are used as the inlet conditions for the numerical simulations. The results show that the initial velocity profile affects the flow field of the wall jet in near and far-field regions. It is found that the contours of streamwise velocity and turbulent kinetic energy exhibit the effect of initial conditions in the near field. The Reynolds shear stress component dominates in the vertical jet centreline plane, and it increases with a decrease in the nozzle length. The Reynolds shear stress component dominates in the lateral plane, and also exhibit the dependency on initial conditions.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"276 - 304"},"PeriodicalIF":1.9,"publicationDate":"2022-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43182181","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 : 2022-04-01DOI: 10.1080/14685248.2022.2051531
G. K. Balajee, N. Panchapakesan
We present results from three large eddy simulations (LES). The first two were those of a single jet at a Reynolds number of 11000 with different cell density distributions. The simulation results are validated with earlier experimental and computational studies at the same Reynolds number and almost the same boundary conditions. We establish the repeatability and reproducibility of the characterisation of a single axisymmetric jet. Additionally, we performed an LES of five round jets using the same discretisation schemes and boundary conditions. The five jets were placed in a cross or plus configuration, with a central jet surrounded by four outer jets. The mass flux, momentum flux and the Reynolds number of the five jet configuration were set to be equal to those of the single jet. Further, we analyse the near-field development of the multiple jets, along with entrainment and symmetry characteristics as the jet evolves. LES's ability to provide information about large-scale motions was used to compute conditional statistics. We, then, present details of an initial attempt to characterise the turbulent non-turbulent interface boundary and the coherent structures in the core of the jet in a unified manner using helicity density as the detector variable.
{"title":"Large eddy simulations of single and multiple turbulent round jets","authors":"G. K. Balajee, N. Panchapakesan","doi":"10.1080/14685248.2022.2051531","DOIUrl":"https://doi.org/10.1080/14685248.2022.2051531","url":null,"abstract":"We present results from three large eddy simulations (LES). The first two were those of a single jet at a Reynolds number of 11000 with different cell density distributions. The simulation results are validated with earlier experimental and computational studies at the same Reynolds number and almost the same boundary conditions. We establish the repeatability and reproducibility of the characterisation of a single axisymmetric jet. Additionally, we performed an LES of five round jets using the same discretisation schemes and boundary conditions. The five jets were placed in a cross or plus configuration, with a central jet surrounded by four outer jets. The mass flux, momentum flux and the Reynolds number of the five jet configuration were set to be equal to those of the single jet. Further, we analyse the near-field development of the multiple jets, along with entrainment and symmetry characteristics as the jet evolves. LES's ability to provide information about large-scale motions was used to compute conditional statistics. We, then, present details of an initial attempt to characterise the turbulent non-turbulent interface boundary and the coherent structures in the core of the jet in a unified manner using helicity density as the detector variable.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"173 - 213"},"PeriodicalIF":1.9,"publicationDate":"2022-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41548644","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 : 2022-03-29DOI: 10.1080/14685248.2022.2053143
L. Thamri, T. Naffouti
In the present investigation, the evolution of homogeneous and stratified turbulence under a horizontal and a vertical shear is deliberate by coupled second-order model SSG-SL. This model is a result of a combination between the Speziale, Sarkar and Gatski model (SSG) and the Shih and Lumley model (SL). Horizontal shear and vertical shear are related to the angle between the shear and the vertical gradient of stratification; θ = π/2 and θ = 0, respectively. This study is performed for different values of Froude number Fr ranging from 0.35–1.11. The SSG-SL model confirms the asymptotic equilibrium states for various physical parameters governing the problem (b12, b11, ε/KS, , K/E and Kρ/E) for two shear orientations (θ = π/2 and θ = 0). A comparison between findings using the present coupled model of SSG-SL and those by Direct Numerical Simulation of Jacobitz (DNSJ) [Jacobitz F, Sarkar S. A direct numerical study of transport and anisotropy in a stably stratified turbulent flow with uniform horizontal shear. Flow Turbul Combust. 2000;63:343–360.; Jacobitz F. A comparison of the turbulence evolution in a stratified fluid with vertical or horizontal shear. J Turbul. 2002;3:1–18.] is carried out. For the horizontal shear related to θ = π/2, an excellent agreement between predictions by the SSG-SL model and the results of DNSJ [Jacobitz, Sarkar;Jacobitz] is detected for turbulent thermal and dynamic fields.
{"title":"Effect of the Froude number on a stratified turbulence under two shear orientations using coupled SSG and SL models","authors":"L. Thamri, T. Naffouti","doi":"10.1080/14685248.2022.2053143","DOIUrl":"https://doi.org/10.1080/14685248.2022.2053143","url":null,"abstract":"In the present investigation, the evolution of homogeneous and stratified turbulence under a horizontal and a vertical shear is deliberate by coupled second-order model SSG-SL. This model is a result of a combination between the Speziale, Sarkar and Gatski model (SSG) and the Shih and Lumley model (SL). Horizontal shear and vertical shear are related to the angle between the shear and the vertical gradient of stratification; θ = π/2 and θ = 0, respectively. This study is performed for different values of Froude number Fr ranging from 0.35–1.11. The SSG-SL model confirms the asymptotic equilibrium states for various physical parameters governing the problem (b12, b11, ε/KS, , K/E and Kρ/E) for two shear orientations (θ = π/2 and θ = 0). A comparison between findings using the present coupled model of SSG-SL and those by Direct Numerical Simulation of Jacobitz (DNSJ) [Jacobitz F, Sarkar S. A direct numerical study of transport and anisotropy in a stably stratified turbulent flow with uniform horizontal shear. Flow Turbul Combust. 2000;63:343–360.; Jacobitz F. A comparison of the turbulence evolution in a stratified fluid with vertical or horizontal shear. J Turbul. 2002;3:1–18.] is carried out. For the horizontal shear related to θ = π/2, an excellent agreement between predictions by the SSG-SL model and the results of DNSJ [Jacobitz, Sarkar;Jacobitz] is detected for turbulent thermal and dynamic fields.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"214 - 231"},"PeriodicalIF":1.9,"publicationDate":"2022-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48488718","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 : 2022-03-04DOI: 10.1080/14685248.2022.2046762
T. Ohta, Fumiya Osaka, Yuta Kitagawa
Modulation of turbulent flow by cavitation in fluid machinery can cause vibrations, noise, and erosion. In this study, we confirm the cavitation phenomenon and observe its characteristics to predict the flow and control it accordingly. We perform a direct numerical simulation of the turbulent Couette flow of water with vortex cavitation using a cavitation model to predict phase change based on pressure distribution. In this simulation, we investigate the characteristics of the local interaction between turbulence vortices and cavitation and the global modulation of the turbulent flow, i.e. mean velocity and wall friction coefficient. We observe that a cavity is generated where a low-pressure region is created in the centre of the turbulence vortex; the growth of the cavity weakens the vortex and reduces the intensity of the turbulence. Further, the vortex becomes stronger as the cavity contracts; this phenomenon occurs repeatedly in a turbulent flow field with vortex cavitation. In a turbulent flow field with vortex cavitation, mechanical oscillations can occur spontaneously. In addition, we found that the turbulence vortex weakened by cavitation regenerates around the cavity. The unsteady phenomenon of the turbulence vortex cavitation repeatedly grows and decays monotonically; however, it does not necessarily repeat these spatially in the same manner. The spatial characteristics of the turbulence structure are different from those observed in single-phase turbulent flow.
{"title":"Modulation of turbulent Couette flow with vortex cavitation in a minimal flow unit","authors":"T. Ohta, Fumiya Osaka, Yuta Kitagawa","doi":"10.1080/14685248.2022.2046762","DOIUrl":"https://doi.org/10.1080/14685248.2022.2046762","url":null,"abstract":"Modulation of turbulent flow by cavitation in fluid machinery can cause vibrations, noise, and erosion. In this study, we confirm the cavitation phenomenon and observe its characteristics to predict the flow and control it accordingly. We perform a direct numerical simulation of the turbulent Couette flow of water with vortex cavitation using a cavitation model to predict phase change based on pressure distribution. In this simulation, we investigate the characteristics of the local interaction between turbulence vortices and cavitation and the global modulation of the turbulent flow, i.e. mean velocity and wall friction coefficient. We observe that a cavity is generated where a low-pressure region is created in the centre of the turbulence vortex; the growth of the cavity weakens the vortex and reduces the intensity of the turbulence. Further, the vortex becomes stronger as the cavity contracts; this phenomenon occurs repeatedly in a turbulent flow field with vortex cavitation. In a turbulent flow field with vortex cavitation, mechanical oscillations can occur spontaneously. In addition, we found that the turbulence vortex weakened by cavitation regenerates around the cavity. The unsteady phenomenon of the turbulence vortex cavitation repeatedly grows and decays monotonically; however, it does not necessarily repeat these spatially in the same manner. The spatial characteristics of the turbulence structure are different from those observed in single-phase turbulent flow.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":"23 1","pages":"152 - 172"},"PeriodicalIF":1.9,"publicationDate":"2022-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43773089","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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