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Simulations of the Transient Flow Generated from a Started flat plate

Chinese Journal of Mechanical Engineering 2012年第6期25卷 1190-1197页

作者： WANG Leqin MA Xudan LI Zhifeng WU Peng WU Dazhuan Institute of Process Equipment Zhejiang UniversityHangzhou 310027China Engineering Research Center of High Pressure Process Equipment and Safety Ministry of EducationHangzhou 310027China

Transient operations are commonly founded in fluid machineries such as the starting, stopping, and variations of rotor speeds, etc. Flow generated from a started fiat plate is of fundamental importance. Experiments have been done to observe the flow evolution in current researches. And in order to explore the flow in more detailed scale, some vortex methods with high resolution and other numerical methods were developed to solve various related problems by some researchers. But the promotion of vortex method to engineering application is rare due to its complexity and difficulty in specifying the boundary conditions. In order to build up a method of numerical study for such problems, a simplified model is built up with a flat plate. The development of two-dimensional viscous incompressible flow generated from an impulsively started and uniformly accelerated infinitesimally thin flat plate is simulated numerically. A dynamic mesh（DM） method based on the spring analogue and local remeshing is applied to realize the mesh motion caused by the started plate. Researches show that the mesh quality will decline under large grid shear force during the updating process. To conquer this problem, a region near the plate is separated to guarantee the mesh quality at location of interest which is the innovation of the present paper. All computations at least cover a period during which the plate translates 6 times its length. The simulated instantaneous velocity profiles, flow structures and drag coefficients under several Reynolds numbers （20 ≤ Re ≤ 126） and accelerations （20 m/s2≤ a ≤ 152 m/s2） are presented and compared with existing results in literatures. Comparisons are found to be satisfactory, confirming the validity of the current proposed method（region separated DM）. The proposed DM method is firstly used to study the transient flow generated from a started flat plate and can be used in further study of transient characteristics during transient operations of turbo machineries.

关键词： numerical simulation flat plate start transient flow region separated dynamic mesh

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A numerical flat plate friction line and its application

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Journal of Hydrodynamics 2015年第3期27卷 383-393页

作者：王展智熊鹰时立攀刘志华 Department of Naval Architecture Naval University of Engineering

This paper studies the regression of a numerical two-dimensional flat plate friction line using the RANS method with the SST k - co turbulence model. Numerical simulations with different inlet turbulence kinetic energies are first conducted. Comparing with the experimental data, the finest grid and the appropriate inlet turbulence kinetic energy are selected to compute the fiat plate friction resistance at 14 Reynolds numbers. Two numerical friction lines are obtained by the least squares root fitting method and one similar to that of the ITTC-1957 line and the cubic polynomials in logarithmic scales, and the results are compared to the friction line proposals available in the open literature. Finally, the full scale viscous resistance predictions of DTMB5415, KVLCC2, SUBOFF are compared between the numerical friction line and the friction line proposals available in the open literature based on the form factor approach. It is shown that the form factor keeps relatively constant via the numerical friction line for the bare hull, but the form factor concept in extrapolating the model test results is not appropriate for appended hulls. It is suggested that for computing a form factor numerically, it is best to use a numerical friction line.

关键词： friction line form factor flat plate RANS uncertainty analysis

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Effects of aspect ratio and inclination angle on aerodynamic loads of a flat plate

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Advances in Aerodynamics 2020年第1期2卷 278-300页

作者： Mehrdad Shademan Arash Naghib-Lahouti Institute for Aerospace Studies University of TorontoM3H5T6TorontoOntarioCanada

Large Eddy Simulations are carried out to analyze flow past flat plate in different configurations and inclinations.A thin flat plate is considered at three inclination angles(α=30°,60°and 90°)and three aspect ratios(AR=0.5,2 and 5).The Reynolds number based on the free stream velocity and chord length of the plate at different inclination angles varies between 75,000 to 150,000.An increase in the inclination angle while the aspect ratio(span to chord)is constant results in higher drag and lower lift on the plate.Increasing the aspect ratio at a constant inclination angle increases the mean aerodynamic loading except for theα=30°and AR=0.5 case where the mean forces are larger than the other aspect ratios for this specific inclination angle.The small aspect ratio suppresses and blocks the separation of the flow from the top and bottom edges causing larger aerodynamic forces relative to AR=2,5.Visualization of the flow structures shows the tip vortices have a significant role in controlling the shedding vortices from the top and bottom edges.Atα=30°and AR=0.5,the two tip vortcies control and suppress the flow separation from the top and bottom edges.A stable wake was found for this case with no fluctuation.As the aspect ratio increases,the influence of the tip vortices on flow separation from the top and bottom edges reduces.As a result,larger fluctuations were found for cases with higher aspect ratios.

关键词： flat plate Aspect ratio Inclination angle CFD OpenFOAM Aerodynamic loads

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A NUMERIGAL EXPLORATION OF SECONDARY STARTING FLOW AROUND A flat plate BY THE DISCRETE VORTEX MODEL

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Acta Mechanica Sinica 1988年第4期 311-318页

作者： P.W.Bearman J.M.R.Graham London SW7 2BY Department of Aeronautics Imperial College of Science and Technology

In the present work,a further numerical simulation of the starting flow around a flatplate normal to the direction of motion in a uniform fluid has been made by means of the discretevortex method.The secondary separation occurring at rear surface of the plate is explored,andpredicted approximately using Thwait’s method.The calculated results show that in the early stages ofthe flow secondary separation does occur.The evolution of flow field,the vortex growing process andthe characteristics of secondary vortices have been described.The time dependent drag coefficients,the vorticity shed from the edges and rear surface,and the separation positions are calculated as well asthe distributions of velocity and pressure on the plate.In the case of flow normal to the plate,thecalculated secondary vortices are weak.Their existence will change the local velocity distributions andaffect pressure distributions.However,the effect on drag coefficient is negligible.

关键词： starting flow flat plate secondary separation discrete vortex model numerical exploration

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AN APPROXIMATE METHOD FOR DETERMING THE VELOCITY PROFILE IN A LAMINAR BOUNDARY-LAYER ON flat plate

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Applied Mathematics and Mechanics(English Edition) 1999年第4期20卷 112-117页

作者：袁镒吾刘又文

In this paper, using the integration method, it is sought to solve the problem for the laminar boundary_layer on a flat plate. At first, a trial function of the velocity profile which satisfies the basical boundary conditions is selected. The coefficients in the trial function awaiting decision are decided by using some numerical results of the boundary_layer differential equations. It is similar to the method proposed by Peng Yichuan, but the former is simpler. According to the method proposed by Peng, when the awaiting decision coefficients of the trial function are decided, it is sought to solve a third power algebraic equation. On the other hand, in this paper, there is only need for solving a linear algebraic equation. Moreover, the accuracy of the results of this paper is higher than that of Peng.

关键词： flat plate laminar flow boundary_layer velocity profile method of weighted residuals (MWR)

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Influence of sub boundary layer vortex generator height and attack angle on cross-flows in the hub region of compressors

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Chinese Journal of Aeronautics 2022年第8期35卷 30-44页

作者： Hao FU Ling ZHOU Lucheng JI School of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China Institute for Aero Engine Tsinghua UniversityBeijing 100084China

It has been recently shown that Sub Boundary layer Vortex Generator(SBVG,abbreviated as VG hereafter)can suppress the Cross-Flow(CF),and therefore,can eliminate corner separation and increase aerodynamic loading when installed on the end wall inside middle-load compressor passages.However,when VGs are applied in high-load compressors,it is difficult to achieve ideal results.This is because the definition of the VG attack angle in the presence of CF in existing research is confusing,and the stronger CF in high-load compressors worsens the problem and results in an improper design and optimization range of VG attack angle.Therefore,this paper clarifies the definition of the VG attack angle in the presence of CF and reveals the CF controlling mechanism of VG on a flat plate.The differences in the flow phenomena around a VG both with and without CF are also studied.The numerical results show that a larger height or attack angle of the VG generates a greater CF suppression effect.However,the cross velocity increases when surmounting the primary vortex induced by the VG,except that this enhanced CF is less conspicuous for larger VG heights.Compared to the cases without CF,the VG suffers an additional loss because of the stronger separation and primary vortex loss caused by the CF.

关键词： Compressors Corner separation Cross-flow flat plate Vortex generator

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Effects of adverse pressure gradient on Reynolds stresses inturbulent boundary layers

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航空动力学报 2017年第2期32卷 463-469页

作者： LUO Xiao-tian ZHANG Ce MA Wei TENG Jin-fang School of Aeronautics and Astronautics Shanghai Jiao Tong University

The effects of adverse pressure gradient(APG)on Reynolds stresses in turbulent boundary layers(TBLs)with APG were analyzed.The difficulty of this work was attributable to the Reynolds stresses in TBLs with APG under two combined effects,i.e.:effect of upstream flow and effect of APG.The effect of upstream flow is an inherent effect no matter pressure gradient exists or not.The individual effect was analyzed from absolute developments of Reynolds stresses in TBLs with zero pressure gradient(ZPG)firstly.Effect of APG was then analyzed from absolute developments of Reynolds stresses in TBLs with APG.Result showed that,for absolute development of mean streamwise Reynolds stresses,APG accelerated its development in TBL with ZPG;for absolute development of mean normal or shear Reynolds stresses,APG increased their magnitude in the outer part,and decreased their extent of large value region.

关键词： turbulent boundary layer adverse pressure gradient zero pressure gradient Reynolds stresses flat plate

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A preliminary analysis and discussion of the condominium building collapse in surfside,Florida,US,June 24,2021

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Frontiers of Structural and Civil Engineering 2021年第5期15卷 1097-1110页

作者： Xinzheng LU Hong GUAN Hailin SUN Yi LI Zhe ZHENG Yifan FEI Zhi YANG Lingxiao ZUO Key Laboratory of Civil Engineering Safety and Durability of Ministry of Education Tsinghua UniversityBeijing 100084China School of Engineering and Built Environment Griffith University Gold Coast CampusQueensland 4222Australia China Architecture Design&Research Group Co. LtdBeijing 100044China Beijing Key Laboratory of Earthquake Engineering and Structural Retrofit Beijing University of TechnologyBeijing 100124China

On June 24,2021,a 40-year-old reinforced concrete flat plate structure building in Miami suffered a sudden partial collapse.This study analyzed the overall performance and key components of the collapsed building based on the building design codes(ACI-318 and GB 50010).Punching shear and post-punching performances of typical slabcolumn joints are also studied through the refined finite element analysis.The collapse process was simulated and visualized using a physics engine.By way of these analyses,weak design points of the collapsed building are highlighted.The differences between the reinforcement detailing of the collapsed building and the requirements of the current Chinese code are discussed,together with a comparison of the punching shear and post-punching performances.The simulated collapse procedure and debris distribution are compared with the actual collapse scenes.

关键词： progressive collapse flat plate simulation punching

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Unified analysis of pressure melting of ice around horizontal columns

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Progress in Natural Science:Materials International 2007年第3期17卷 371-374页

作者： LIU Feng, CHEN Wenzhen, MENG Bin and GONG Miao (College of Power and Shipping, Naval University of Engineering, Wuhan 430033, China) College of Power and Shipping Naval University of Engineering Wuhan 430033 China

The contact melting processes of ice, caused by pressure under the two-dimension axisymmetric horizontal columns, are generally studied. The unified mathematical expressions of the characteristic parameters for the pressure contact melting processes are obtained. Applying these expressions to the analysis of the pressure contact melting of ice around the horizontal cylinder, elliptical cylinder and flat plate, the related results in the published literatures are obtained, which prove the correctness and validity of the expressions. In addition, the expressions for the pressure contact melting of ice around the wedge-shaped object are also derived.

关键词： pressure melting contact melting horizontal columns flat plate wedge-shaped object

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NUMERICAL INVESTIGATIONS INTO THE FRICTION REDUCTION BY MICROBUBBLES FOR flat plateS

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Journal of Hydrodynamics 2003年第3期15卷 82-88页

作者： Zhan De-xin, Wang Jia-mei, Lin Li-ming School of Transportation, Wuhan University of Technology, Wuhan 430063, China, Sch. of Transp. Wuhan Univ. of Technol. Wuhan 430063 China

The two-dimensional flow on the flat plate with injected microbubbles issimulated using the software, PHOENICS (V3. 2), usually used in the CFD (Computational FluidDynamics). A set of formulas for K-ε turbulence model modified with the presence of microbubbles,is employed. With considering the effect of gravity, interfacial lift, inter-phase friction, virtualmass force and interfacial pressure on the flow with microbubbles, numerical calculations for theinfluence of variable air volume fracton as well as distribution, injecting speed, microbubblediameter and position of introducing microbubbles on the friction reduction are presented. Resultsshow that the friction reduction increases with increasing volume fraction and microbubble diameterwithin the range of 100μm, and that the velocity in the boundary layer with microbubbles is greaterthan that without microbubbles. The order of magnitude and trends of the experimental skin-frictionare reproduced well. The uniform free-stream speed in all cases is 4m/s, giving Reynolds number ofup to 20 million.

关键词： flat plate friction reduction by microbubbles modified K-ε turbulencemodel numerical simulation

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