Pub Date : 2022-10-11DOI: 10.1080/14685248.2022.2131799
S. C. Mangavelli, J. Yuan
Wall roughness induces form-induced (or dispersive) velocity and pressure perturbations inside the roughness sublayer of a wall-bounded turbulent flow. This work discusses the role played by the form-induced velocity in influencing turbulence statistics and structure, using existing direct numerical simulation data of transient half channels in response to an impulse acceleration (Mangavelli et al. Effects of surface roughness topography in transient channel flows. J Turbul 2021;22:434–460). Focuses are given to (i) reshaping of turbulent coherent motions by the rate-of-strain of the mean velocity, and (ii) contributions of different velocity sources to turbulent pressure fluctuations. Half-channel flows in both fully-developed and non-equilibrium, transient states are discussed. Results show that form-induced velocity gradients not only form an important source of turbulent pressure in an equilibrium flow, but also lead to turbulence production and potentially direct structural change of turbulent eddies in a non-equilibrium flow under acceleration.
壁面粗糙度在壁面有界湍流的粗糙度亚层内引起形式诱导的(或色散的)速度和压力扰动。这项工作讨论了形式诱导速度在影响湍流统计和结构方面所起的作用，利用响应脉冲加速度的瞬态半通道的现有直接数值模拟数据(Mangavelli et al.)。瞬态沟道流动中表面粗糙度形貌的影响。[J]中国生物医学工程学报，2021;22:434-460。重点是(i)通过平均速度的应变率重塑湍流相干运动，以及(ii)不同速度源对湍流压力波动的贡献。讨论了完全发育和非平衡状态下的半通道流动。结果表明，形式诱导的速度梯度不仅是平衡流动中湍流压力的重要来源，而且在非平衡流动中加速作用下导致湍流的产生并可能直接导致湍流涡流的结构变化。
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Pub Date : 2022-10-03DOI: 10.1080/14685248.2022.2134571
E. Turgut, Uğurcan Yardımcı
In this study, experiments were conducted to investigate the effects of semicircular strip turbulators placed in the inner tube of a concentric heat exchanger on its exergy loss rate (E*) and effectiveness (e). The Reynolds number (Re), pitch (p), diameter (d), thickness (t) and arrangement style (a) were the design parameters for the study. The changes in these parameters had significant effects on exergy loss rate and effectiveness compared to the results found with the smooth empty tube. The results of the study are given graphically as the change in the exergy loss rate and the change in effectiveness with the number of transfer units (NTU). The largest exergy loss rate and effectiveness values were found to be 0.263 and 0.556, respectively. It was concluded that the effectiveness of the heat exchanger increased with increasing NTU, while the exergy loss rate is decreased. Since the increase in effectiveness will mean an increase in heat transfer, it can also cause an increase in irreversibility. For this reason, multi-performance characteristics have been determined since evaluating the effectiveness together with the exergy loss rate caused by irreversibility will provide more realistic results. Thus, the optimum parameter combination was found, where the maximum effectiveness and the smallest exergy loss rate values were obtained. Finally, the artificial neural network (ANN) model of the study was created and the hyperparameters of the model were determined by the Bayesian optimisation method. In the created ANN model, MSE and R values of effectiveness and exergy loss rate were found as 5.3238e-04, 2.18177e-06 and 0.963, 0.998, respectively. According to these results, it has been confirmed that the proposed ANN model can be used successfully in the modelling of the heat exchanger.
{"title":"Detailed evaluation of a heat exchanger in terms of effectiveness and second law","authors":"E. Turgut, Uğurcan Yardımcı","doi":"10.1080/14685248.2022.2134571","DOIUrl":"https://doi.org/10.1080/14685248.2022.2134571","url":null,"abstract":"In this study, experiments were conducted to investigate the effects of semicircular strip turbulators placed in the inner tube of a concentric heat exchanger on its exergy loss rate (E*) and effectiveness (e). The Reynolds number (Re), pitch (p), diameter (d), thickness (t) and arrangement style (a) were the design parameters for the study. The changes in these parameters had significant effects on exergy loss rate and effectiveness compared to the results found with the smooth empty tube. The results of the study are given graphically as the change in the exergy loss rate and the change in effectiveness with the number of transfer units (NTU). The largest exergy loss rate and effectiveness values were found to be 0.263 and 0.556, respectively. It was concluded that the effectiveness of the heat exchanger increased with increasing NTU, while the exergy loss rate is decreased. Since the increase in effectiveness will mean an increase in heat transfer, it can also cause an increase in irreversibility. For this reason, multi-performance characteristics have been determined since evaluating the effectiveness together with the exergy loss rate caused by irreversibility will provide more realistic results. Thus, the optimum parameter combination was found, where the maximum effectiveness and the smallest exergy loss rate values were obtained. Finally, the artificial neural network (ANN) model of the study was created and the hyperparameters of the model were determined by the Bayesian optimisation method. In the created ANN model, MSE and R values of effectiveness and exergy loss rate were found as 5.3238e-04, 2.18177e-06 and 0.963, 0.998, respectively. According to these results, it has been confirmed that the proposed ANN model can be used successfully in the modelling of the heat exchanger.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45447587","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 : 2022-09-30DOI: 10.1080/14685248.2022.2128360
Maojing Huang, Xiaozhou He
We report a direct numerical simulation (DNS) study of the heat transport and temperature profiles of the plume ejecting and impacting regions in the two-dimensional turbulent Rayleigh–Bénard (RB) convection with slippery plates and horizontally periodic boundary conditions. The numerical study is conducted in the parameter range of Rayleigh number from to and the slip length b from 0 (NS) to ∞ (FS) for the top and bottom plates. Two distinct flow patterns can be seen depending on b, namely convection roll state and zonal flow, which affect the Nusselt number and the Reynolds number . We show that the zonal flow occurs when the normalised slip length , where is the thermal boundary layer thickness for the no-slip (NS) plates. and increase with increasing , and can reach the optimum before the generation of the zonal flow. It is observed that with the effective scaling exponent for the convection roll state, and for the zonal flow. Furthermore, for the convection roll state, the power-law scaling of the local heat flux is in the plume ejecting region, while in the plume impacting region, for varying slip length . The DNS data with different slippery plates for both plume ejecting and impacting regions agree well with the predicted temperature profiles by Huang et al. (J Fluid Mech. 2022;943:A2).
本文采用直接数值模拟(DNS)方法研究了光滑板和水平周期边界条件下二维湍流rayleigh - b纳德(RB)对流中羽流喷射和冲击区的热输运和温度分布。对顶板和底板在瑞利数为、滑移长度b为0 (NS)到∞(FS)的参数范围内进行了数值研究。根据b可以看到两种不同的流动模式，即对流滚转状态和纬向流动，它们影响努塞尔数和雷诺数。我们表明，当归一化滑移长度(其中为无滑移(NS)板的热边界层厚度)时，纬向流动发生。且随增大而增大，在纬向流产生前达到最优。观察到对流滚转状态和纬向流动的有效标度指数。对流滚转状态下，随着滑差长度的变化，局部热通量的幂律标度分别出现在羽流喷射区和羽流冲击区。不同滑板对羽流喷射和冲击区域的DNS数据与Huang et al. (J Fluid Mech. 2022;943:A2)预测的温度剖面吻合较好。
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Pub Date : 2022-08-06DOI: 10.1080/14685248.2022.2109653
O. Khawar, M. F. Baig, S. Sanghi
Direct numerical simulation of Taylor–Couette flow subject to opposition control is investigated at Reynolds number (Re) of 3000. The idea is to impose exact opposite velocities of the detection plane at the walls to counteract near-wall stream-wise vortices. In this study, various velocity control strategies, namely wall-normal, axial, combined and blowing only, have been investigated from the viewpoint of skin-friction drag reduction. Further, the effects of skipping spatial points in azimuthal and axial directions and in time have been investigated from a drag reduction point of view. Based on the emergence of a virtual wall that hinders the vertical transport of momentum (i.e. on reduction of Reynolds shear stress production as well as sweep ejection events), flow physics has been explained via statistical analysis of fluctuations, Reynolds shear stresses, and near-wall coherent structures. The spatial density of near-wall vortical structures shows a marked reduction, followed by quadrant contribution analysis of Reynolds shear stresses reveals a decrease in ejection and sweep events, leading to reduced production of Reynolds shear stresses and skin-friction drag.
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Pub Date : 2022-08-03DOI: 10.1080/14685248.2022.2096223
Jie Shen, Cheng Peng, Jianzhao Wu, K. Chong, Zhiming Lu, Lian-Ping Wang
In this paper, the influence of particle-fluid density ratio and particle diameter on the turbulence modulation by finite-size particles in forced homogeneous isotropic turbulence is investigated. Results show that the presence of finite-size particles always attenuate the turbulence, and the attenuation is larger for particles with larger density when the particle diameter is fixed. But the attenuation is smaller for particles with larger diameter if the density is fixed, and the weaker attenuation is due to the wake fluctuation when the particle Reynolds number is large enough. The turbulence kinetic energy is attenuated at the large scales and augmented at the small scales. The radial dissipation profiles show that the region affected by the particles with same diameter is identical, but the dissipation near the particle surface is larger if the density is larger due to larger slip velocity and particle Reynolds number. For particles with same density, smaller particles have smaller dissipation near the particle surface but the influence region is larger, and the combined effect leads to the result that the contribution of dissipation in the influence region of smaller particles to the total dissipation is larger. The influence region mainly depends on the particle diameter.
{"title":"Turbulence modulation by finite-size particles of different diameters and particle–fluid density ratios in homogeneous isotropic turbulence","authors":"Jie Shen, Cheng Peng, Jianzhao Wu, K. Chong, Zhiming Lu, Lian-Ping Wang","doi":"10.1080/14685248.2022.2096223","DOIUrl":"https://doi.org/10.1080/14685248.2022.2096223","url":null,"abstract":"In this paper, the influence of particle-fluid density ratio and particle diameter on the turbulence modulation by finite-size particles in forced homogeneous isotropic turbulence is investigated. Results show that the presence of finite-size particles always attenuate the turbulence, and the attenuation is larger for particles with larger density when the particle diameter is fixed. But the attenuation is smaller for particles with larger diameter if the density is fixed, and the weaker attenuation is due to the wake fluctuation when the particle Reynolds number is large enough. The turbulence kinetic energy is attenuated at the large scales and augmented at the small scales. The radial dissipation profiles show that the region affected by the particles with same diameter is identical, but the dissipation near the particle surface is larger if the density is larger due to larger slip velocity and particle Reynolds number. For particles with same density, smaller particles have smaller dissipation near the particle surface but the influence region is larger, and the combined effect leads to the result that the contribution of dissipation in the influence region of smaller particles to the total dissipation is larger. The influence region mainly depends on the particle diameter.","PeriodicalId":49967,"journal":{"name":"Journal of Turbulence","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2022-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44379033","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 : 2022-07-14DOI: 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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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}
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