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Three-Dimensional Direct Numerical Simulation of Flow past A Near-Wall Circular Cylinder:Combined Effects of gap ratio and Boundary Layer Thickness on Flow Profiles and Pressure Distribution

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China Ocean Engineering 2023年第6期37卷 948-961页

作者： YING Chao HUA Yang WEI Yu-han JI Chun-ning Zhejiang Institute of Hydraulics&Estuary(Zhejiang Institute of Marine Planning and Design) Hangzhou 310020China Shanghai Investigation Design&Research Institute Co.Ltd.Shanghai 200335China State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin UniversityTianjin 300072China

Three-dimensional direct numerical simulations of the wake flow downstream of a near-wall circular cylinder at different gap ratios and boundary layer thicknesses are carried out by using the iterative immersed boundary *** non-dimensional gap between the cylinder and the wall,G/D=0.2,0.6 and 1.0,the non-dimensional boundary layer thickness,δ/D=0.0,0.7 and 1.6,the Reynolds number,Re=350,and the aspect ratio of the cylinder,L/D=25are ***-resolution visualizations of the complex vortex structures at differentδ/D and G/D are *** transition of the streamwise vortex mode,the combined effects ofδ/D and G/D on the flow statistics,the pressure and shear stress distribution and the hydrodynamic forces are *** show that with decreasing G/D and increasingδ/D,the gap flow and its vortex-shedding are significantly weakened,together with an elongated wake and an enlarged low-velocity area near the wall,leading to the wake mode transition from the two-sided to one-sided *** relative positions of the cylinder regarding the boundary layer alter the flow features of the shear *** an increase inδ/D,the front stagnation point shifts to the upper surface,and the distance between the flow divergence point and the maximum pressure position *** mean drag coefficient and *** of drag and lift coefficients decrease with a decrease in G/D and an increase inδ/D,while the mean lift coefficient increases with decreasing G/D but decreases with increasingδ/D.

关键词： cylinder wake near-wall effect direct numerical simulation boundary layer thickness gap ratio

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The Effect of the gap ratio on the Flow and Heat Transfer over a Bluff Body in Near-Wall Conditions

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Fluid Dynamics & Materials Processing 2022年第1期18卷 109-130页

作者： Shaohua Zhai Guannan Xi School of Mechanical Engineering Nantong UniversityNantong226019China School of Mechanical Engineering Nantong Institute of TechnologyNantong226019China

In order to study the effect of different gap ratios on the thermofluid-dynamic field around a bluff body located in proximity to a heated wall,a series of experiments and numerical simulations have been *** former were carried out using an open circulating water tank experimental platform and a single cylinder and square column as geometrical models(their characteristic length being D).The latter were based on the well-known SIMPLE algorithm for incompressible *** results show that the gap ratio is an important factor affecting the wake characteristics of near-wall bluff *** the gap ratio is small,the influence of the wall on the bluff body wake is *** an increase in the gap extension,periodic vortex shedding is enabled and heat transfer is strengthened accordingly;in addition,the vortex shedding period is larger for the square *** square column displays hysteresis compared with the cylinder at the same gap ratio(the critical gap ratio of cylinder is 0.2~0.4,while that of square column is 0.40.6).

关键词： Transition flow gap ratio near-wall flow characteristic enhanced heat transfer

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Experimental Study of Local Scour Around Four Piles Under Different Attack Angles and gap ratios

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China Ocean Engineering 2024年第4期38卷 612-624页

作者： LIU Ming-ming TANG Guo-qiang JIN Xin GENG Shao-yang School of Architecture and Engineering Liaocheng UniversityLiaocheng 252000China Water-Sediment Regulation and Sand Effective Utilization Special Laboratory of Shandong Provincial Education Department Liaocheng UniversityLiaocheng 252000China State Key Laboratory of Coastal and Offshore Engineering Dalian University of TechnologyDalian 116024China College of Electronic Engineering Chengdu University of Information TechnologyChengdu 610225China College of Energy Chengdu University of TechnologyChengdu 610059China

In an effort to investigate and quantify the patterns of local scour,researchers embarked on an in-depth study using a systematic experimental *** research focused on the effects of local scour around a set of four piles,each subjected to different hydromechanical *** particular,this study aimed to determine how different attack angles—the angles at which the water flow impinges on the piles,and gap ratios—the ratios of the spacing between the piles to their diameters,influence the extent and nature of scour.A comprehensive series of 35 carefully designed experiments were orchestrated,each designed to dissect the nuances in how the gap ratio and attack angle might contribute to changes in the local scour observed at the base of pile *** these experimental trials,a wealth of local scour data were collected to support the *** data included precise topographic profiles of the sediment bed around the pile groups,as well as detailed scour time histories showing the evolution of scour at strategic feature points throughout the test *** analysis of the experimental data provided interesting *** study revealed that the interplay between the gap ratio and the attack angle had a pronounced influence on the scouring dynamics of the pile *** of the key observations was that the initial phases of scour,particularly within the first hour of water flow exposure,were characterized by a sharp increase in the scour depth occurring immediately in front of the *** this initial rapid development,the scour depth transitioned to a more gradual change *** contrast,the scour topography around the piles continuously *** suggests that sediment displacement and the associated sculpting of the seabed around pile foundations are sustained and progressive processes,altering the underwater landscape over *** results of this empirical investigation have significant implications for the design and constructio

关键词： local scour piles gap ratio attack angle

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FORCES ON A NEAR-WALL CIRCULAR CYLINDER

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Journal of Hydrodynamics 2004年第6期16卷 658-664页

作者： ZHANJing-xia WANGJin-jun ZHANGPang-feng FluidMechanicsInstitute BeijingUniversityofAeronauticsandAstronauticsBeijing100083China

The pressure distribution around a near-wall smooth circular cylinder incross-flow was mainly investigated. The experiment was conducted at the sub-critical Reynolds numberranging from 2. 24 · 10~4 to 8. 94 · 10~4, at which the regular vortex separation exists on anisolated circular cylinder. The experimental results indicate that the forces on a circular cylindernear a plane wall are different from those on an isolated circular cylinder. Drag and liftcoefficients of a near-wall circular cylinder strongly depend on gap ratio. The increase of gapratio results in the increase of drag coefficient and the declination of lift coefficient, dragcoefficient ranges from 0. 5 to 1. 0, and lift coefficient from 0. 25 to 0 when gap ratio graduallyincreases from 0 to 1. 0, and then the forces tend to be nearly constant with the increase of gapratio. The attraction between a cylinder and a plane wall, i. e. , downward force, occurs when gapratio lies in certain range. The existence of cylinder changes the pressure gradient on the planewall, and the influence extends to the location where x/D 5. 0 .

关键词： gap ratio static pressure coefficient distribu-tiontlift coefficient dragcoefficient

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Numerical investigation on interaction between regular waves and a fully submerged horizontal cylinder

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Journal of Hydrodynamics 2023年第6期35卷 1101-1118页

作者： Cheng Zeng Yu-die Hu Yu-ran Yin Jie Zhou Ling-ling Wang College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing210098China China Water Resources Bei Fang Investigation Design and Research Co.LtdTianjin300222China College of Mechanics and Materials Hohai UniversityNanjing211100China

This paper presents a 2-D numerical investigation on interaction between regular waves and a fully submerged horizontal cylinder.A mathematical model of numerical wave tank with two-way fluid-solid interactions were developed and *** wave-induced vibrations of a single-degree-of-freedom cylinder were simulated at eleven gap ratios(d/a=8,10,12,14,16,18,20,22,24,28 and 32).Numerical results indicate that significant nonlinear characteristics are introduced into the originally linear waves with the presence of *** on the variation characteristics of cylinder vibration amplitude,the gap ratios can be divided into three ranges,i.e.,the uncertain range(8≤d/a≤14),quasi-linear range(14≤d/a≤20)and linear range(20≤d/a≤32).Under the same wave condition,the gap ratio does not affect the frequencies of vortex shedding and cylinder *** presence of the cylinder complicates the flow field and suppress the vortex shedding around the cylinder.

关键词： Numerical simulation linear wave wave-induced vibration gap ratio flow pattern

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Numerical investigation of windage heating within shrouded rotor-stator cavity system with central inflow

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航空动力学报 2014年第10期29卷 2402-2409页

作者： WANG Qian-shun ZHANG Da LUO Xiang XU Guo-qiang National Key Laboratory of Science and Technology on Aero-Engine Aero-thermodynamics School of Engergy and Power EngineeringBeijing University of Aeronautics and Astronautics

The rotating disk surface temperature rise due to windage heating effect by numerically modeling the turbulent flow within a rotor-stator cavity which is available with a peripheral shroud and imposed through airflow was dealt *** windage heating may be defined as viscous friction heating caused by relative velocity differences across the boundary layers between the fluid and the rotating disk *** kinetic energy dissipation process could transform the rotating shaft power into thermal *** finite volume based solver,ANSYS/CFX was employed to numerically simulate this physical process by using the shear stress transport(SST)turbulence *** results include the rotating disk surface temperature axial distribution and tangential velocity distribution of the fluid *** velocity difference between the result obtained by particle image velocimetry(PIV)experiments and CFD simulation are within 5%.The adiabatic disk temperature rise can be calculated by the tangential velocity of disk and fluid in large gap ratio and turbulent *** temperature distribution results and those estimated via velocity differences are within 10%.

关键词： windage heating rotor-stator cavity system flow structure recovery temperature gap ratio

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Numerical Study of an Oscillating Smaller Cylinder in the Wake of an Upstream Larger Cylinder

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Journal of Ocean University of China 2012年第2期11卷 111-117页

作者： GAO Yangyang YU Dingyong WANG Xikun TAN Soon Keat Maritime Research Centre School of Civil and Environmental EngineeringNanyang Technological University639798Singapore College of Engineering Ocean University of ChinaQingdao 266100P.R.China Nanyang Environmental and Water Research Institute Nanyang Technological University639798Singapore

A numerical study of flow around two tandem cylinders with unequal diameters was carried out. The upstream larger cylinder was fixed and the downstream smaller cylinder was allowed to oscillate in the transverse direction only. Comparisons of the experimental and numerical results were made to investigate the effects of the gap ratio on the maximum vibration amplitude and vortex shedding frequency. The results showed that the vibration response of the smaller cylinder was significantly affected by the presence of the upstream larger cylinder, and resulted in greatly reduced vibration amplitudes. With an increasing gap ratio, the vibration amplitude increased. However, the magnitude was lower than that corresponding to a single cylinder (with the same diameter as that of the downstream smaller cylinder) under the same flow conditions.

关键词： tandem cylinders with unequal diameters numerical simulation gap ratio vibration amplitude

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Effect of Bed Vicinity on Vortex Shedding and Force Coefficients of Fluid Flow on an Offshore Pipeline

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Journal of Marine Science and Application 2017年第1期16卷 81-86页

作者： Fatemeh Namazi-saleh Velluruzhathil John Kurian Zahiraniza Mustaffa Mohammadreza Tahan Dokyun Kim Department of Civil and Environmental Engineering Universiti Teknologi PETRONAS Bandar Seri Iskandar 32610 Perak Darul Ridzuan Malaysia Department of Mechanical Engineering Universiti Teknologi PETRONAS Bandar Seri Iskandar 32610 Perak Darul Ridzuan Malaysia

The effect of rigid bed proximity on flow parameters and hydrodynamic loads in offshore pipelines exposed to turbulent flow is investigated numerically. The Galerkin finite volume method is employed to solve the unsteady incompressible 2D Navier–Stokes equations. The large eddy simulation turbulence model is solved using the artificial compressibility method and dual time-stepping approach. The proposed algorithm is developed for a wide range of turbulent flows with Reynolds numbers of 9500 to 1.5×10^*** of the developed numerical model shows that the proposed technique is capable of properly predicting hydrodynamic forces and simulating the flow pattern. The obtained results show that the lift and drag coefficients are strongly affected by the gap ratio. The mean drag coefficient slightly increases as the gap ratio increases, although the mean lift coefficient rapidly decreases. The vortex shedding suppression happen at the gap ratio of less than 0.2.

关键词： Navier–Stokes equations artificial compressibility method dual time stepping gap ratio flat seabed offshore pipelines vortex shedding

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