THE FLOW ANALYSIS OF FLUIDS IN FRACTAL RESERVOIR WITH THE FRACTIONAL DERIVATIVE

1. INTRODUCTION Chang and Yortsos [1 ]presented the theoretical model for infinite fractal reservoir. Acuna et al. [ 2]explained the fractal characteristic of a naturally fractured geothermal field. Acuna [ 3] reviewed the theoretical background of fractal analysis. They alsodemonstrated the application of various diagnostic techniques for fractal pressure transient analysis as developed by Chang and Yortsos [1 ].Tong[4 ? 7]give the analytical solution of various cases for transient flow…     

STUDY OF VORTEX CHARACTERISTICS OF THE FLOW AROUND A HORIZONTAL CIRCULAR CYLINDER AT VARIOUS GAP-RATIOS IN THE CROSS-FLOW

1. INTRODUCTION The flow around a horizontal circular cylinder near a plane boundary (fixed wall) is of great significance in Hydrodynamics. For instance, sewagepipelines in water body of rivers in environmental engineering, conveying pipelines and optica…     

FLOW CHARACTERISTICS OF TURBULENT JETS INJECTED OBLIQUELY IN CROSSFLOW

1 .　INTRODUCTIONThejetinacrossflowisahighlycomplexturbu lentflow ,andwithapplicationsinvariousengineeringfields .Theinjectionofajetintothecrossflowcanaltertheflowfieldandresultinaverycomplexthree di mensionalflowstructure .Numericalsimulationisanimportantmethodtostudythetransversejet cross flow .Chang[1] ,Tamamidis[2 ] ,Lakehal[3] etc .,usedthenormalk εmodelandwallfunctionmethodtosim ulatetheflowfieldoftheturbulentjet .Althoughthenormalk εmodelgivespredictionsofengineeringaccu racyint…     

A MODIFIED SIMPLE ALGORITHM FOR 2-D FLOW IN OPEN CHANNEL

1.　INTRODUCTIONSince the SIMPLE[1 ] algorithm was set up,it has been used to numerically simulateincompressible flow successfully.And later on,the improved algorithms such as SIMPLERalgorithm[2 ] and SIMPLEC algorithm[3] have been presented in succession.For all thealgorithms stated above,only when velocity field varies linearly with water pressure(i.e.,pressure flow) ,owing to the coefficients of the velocity correction formulae beingindependent of pressure,do the velocity corre…     

NUMERICAL MODELLING OF FLOW FIELD IN A TIDAL RIVER AND THE NEAR FIELD OF INTAKE FOR A NUCLEAR POWER PLANT

This Paper concerns with the numerical modelling of flow field in a tidal river and in the vicinity ofintake of a nuclear power plant. The hybrid method of fractional steps presented in [1] was adopted in thismodelling. In order to simulate the local flow field nearby the water intake meticulously, the technique ofthe match of the coarse and fine grids was used. The numerical results are in good agreement with thein-situ measurements of the main current. The detailed data of local flow field nearby the intake providesthe assessment of the sediment transport characteristics in the vicinity of intake of the nuclear powerplant.     

ABRUPT DEFLECTED SUPERCRITICAL WATER FLOW-REVISED THEORY OF SHOCK WAVE

1. INTRODUCTIONIn hydraulic engineering , all the i mpact-typeenergy dissipators[1 ,2], slit-type buckets and thespill way with flaring piers[3]make use of the rapidincrease of flow height caused by the abrupt de-flection of the supercritical flowto formt…     

NUMERICAL SIMULATION OF NONLINEAR WAVE FLOW AROUND COCHLEA CHANNELED STERN SHIPS

A nonlinear method based on Gadd's model [1] [2] is developed to simulate the wave flow around cochlea-channeled stern ships. The subsurface division method is capable of dividing the complicated hull into panels and defining the computer simulated 3-D graphs. Good results are obtained and depicted by computer graphs.     

ENGINEERING APPLICATION OF COMPUTATIONAL FLUID DYNAMICS——THE STATE OF ART

The state of art and future prospects are described for the application of the computational fluid dynamics toengineering purposes.2D and 3D simulations are presented for a flow about a pair of bridges,a flow about a cylin-der in waves,a flow about an airplane and a ship,a flow past a sphere,a two layers flow and a flow in a wallboundary layer,The choice of grid system and of turbulence modei is discussed.     

SYMMETRIC VORTICAL STRUCTURE AND ITS TOPOLOGICAL STABILITY

1.INTRODUCTIONAsymmetric vortices flow over slender bodyhas been a subject of interest to engineers as well asto scientists for a great many years since such avortices series results in great side force and yawingmoment on the body[1-3].For symmetric vortices,fewer attentions are given to it since the side loadsinduced by the symmetric vortex pair is zero.Infact a thorough grasp of the symmetric vorticalstructure is significantly helpful in understandingthe mechanis m for producing asymmet…     

亚临界雷诺数下波浪型圆柱绕流的数值模拟及减阻研究

采用大涡模拟数值方法对亚临界雷诺数Re=3000下波浪型圆柱的绕流现象进行研究分析。研究结果表明,波浪型圆柱的三维尾迹涡结构能得到很好的控制,它在轴向方向呈现周期性正负涡的交替分布特性。随着幅值的增大,波浪型圆柱表面的自由剪切层得以延展,使得旋涡的脱落发生在波浪型圆柱下游较远处,从而达到减阻的目的。波浪型圆柱与普通直圆柱相比,其幅值对平均阻力系数及脉动升力系数的减少及尾迹控制有着更重要的影响,最大减阻可达16%。     

低雷诺数下并列双波浪柱尾迹干扰效应数值模拟

该文针对雷诺数Re=100下不同波长参数(/mλD=2、4、6和8)、不同间距比(1.5/3.5m≤L D≤)的并列双波浪柱后尾迹复杂的三维流动结构及干扰效应进行了数值研究。研究表明:三维并列双波浪柱在较小的间距比/1.5mL D=时,波峰对波谷排列的并列波浪柱后尾迹呈现明显偏置双稳流动结构,而波峰对波峰排列工况下基本呈现单一波浪型钝体后尾迹流动结构(尤其是在大波长/mλD=6和8时);当间距比/3mL D≥时,随着波长/mλD的增大,上下波浪柱各自呈现单波浪柱后尾迹流动结构;较大波长的三维波浪形状更好地组织了后尾迹三维流动结构,减少了并列双波浪柱后尾迹的相互干扰,从而减阻减振明显,最高减阻可达14.5%,脉动升力系数上下游波浪柱均趋于0.1。该研究可为近海工程的多立管结构及悬索桥的拉索振动抑制等提供理论支持。     

FORCE REDUCTION OF FLOW AROUND A SINUSOIDAL WAVY CYLINDER

A large eddy simulation of cross-flow around a sinusoidal wavy cylinder at Re=3000 was performed and the load cell measurement was introduced for the validation test. The mean flow field and the near wake flow structures were presented and compared with those for a circular cylinder at the same Reynolds number. The mean drag coefficient for the wavy cylinder is smaller than that for a corresponding circular cylinder due to the formation of a longer wake vortex generated by the wavy cylinder. The fluctuating lift coefficient of the wavy cylinder is also greatly reduced. This kind of wavy surface leads to the formation of 3-D free shear layers which are more stable than purely 2-D free shear layers. Such free shear layers only roll up into mature vortices at further downstream position and significantly modify the near wake structures and the pressure distributions around the wavy cylinder. Moreover, the simulations in laminar flow condition were also performed to investigate the effect of Reynolds number on force reduction control.     

不同长细比圆柱绕流的大涡模拟

自从人们对层流圆柱绕流现象有了系列研究及清楚的认识后,逐渐把目光投向湍流的圆柱绕流问题,但高雷诺数下的圆柱绕流具有很强的三维特性,因此在数值计算时模型轴向长度的选取是大家关心的问题。该文基于开源软件OpenFOAM运用LES计算了4种不同长细比圆柱的静止圆柱绕流(包括一个二维算例),重点分析和对比了结果中的一些基础参数如St数、平均阻力系数等,与实验结果吻合良好。文中还进一步分析了时均顺流向速度U在流场中沿流向和横向的分布,发现长细比为π的圆柱算例中,计算域的轴向尺度已经能满足圆柱下游靠近圆柱处的流场中的三维结构的发展。     

Flow characteristics of the two tandem wavy cylinders and drag reduction phenomenon

This paper presents an extensive numerical study of 3-D laminar flow around two wavy cylinders in the tandem arrangement for spacing ratios (L/Dm ) ranging from 1.5 to 5.5 at a low Reynolds number of 1...     

近底水平圆柱振荡绕流的三维数值模拟

在Honji和Sarpkaya等人的实验研究中发现，绕圆柱的振荡流并不是简单的二维流动，而是存在复杂的三维流态。本文用有限元方法求解原始变量的Navier-Stokes方程，模拟了Re数为392、Kc数为2时正弦振荡流绕平面附近圆柱的流动。分析了三维流场结构的特点，并分析了平面边界对尾流结构的影响。     

VANISHING OF THREE-DIMENSIONALITY IN THE WAKE BEHIND A ROTATIONALLY OSCILLATING CIRCULAR CYLINDER

The flow behind a three-dimensional rotationally oscillating circular cylinder was studied by a numerical method. The computations were performed at a Reynolds number of 260, which is at a level that the flow wake has developed into a three-dimensional state called Mode-B. The purpose of this paper is to examine the influence of various rotational amplitudes (0.1-0.7) on the wake instability of the flow, while the oscillation frequency is fixed to the value of that measured in the wake of a stationary cylinder. The results show that the rotation with sufficiently high amplitude brings the flow back to its nominal two-dimensional state. Moreover, it is found that the value of the time-averaged drag and the RMS value of the lift are larger than those of a stationary circular cylinder.     

The numerical and experimental investigations of the near wake behind a modified square stay-cable

The near wake structure, the wake-flow characteristics and the drag coefficients behind a modified square stay-cable(MSC) with sinusoidal variations of the cross-section area along the spanwise direction are investigated experimentally and numerically. The Reynolds numbers are chosen as 100 and 500 for the laminar flow and Re= 6 000 and 22 000 for the turbulent flow. The detailed near wake structures, the velocity fields and the force coefficients for the MSC are captured, the effect of the Reynolds number on the flow structure for the MSC is studied. The numerical and experimental investigations show that the free shear layers from the leading edge are widened and prolonged and then roll up into vortices further downstream the MSC, unlike a straight square stay-cable(SSC) under the same flow conditions. As a result, the distinct mean drag reduction and the fluctuating lift suppression are observed for all Reynolds numbers, a drag reduction of at least 15.8% and the rms lift coefficient reduction of up to 95% are observed, as compared with the case of a straight square stay-cable at Re= 500.     

Experimental investigation of flow past a circular cylinder with hydrophobic coating

A series of experiments are performed in a gravitational low-speed water tunnel to investigate the influence of the hydrophobic coating on the flow past a circular cylinder. The mean velocity and turbulence intensity profiles behind the cylinders are measured using the hot-film anemometer while the separation angles are obtained with the flow visualization technology. For the Reynolds number lower than 3 800, the hydrophobic coatings are in the Cassie state, the velocity deficit and the turbulence intensity in the wake of the hydrophobic cylinders are lower than those of the smooth cylinders which implies the drag reduction effect of the hydrophobic coatings. When the Reynolds number becomes higher than 6 600, the hydrophobic coatings turn into the Wenzel state. Through decomposing the velocity data in the turbulent wake into different scales based on the orthogonal wavelet transform, it is found that the total turbulence intensity in the wake of the hydrophobic cylinders becomes almost the same as in the wake of the smooth cylinders while the intensity of the large scales of vortex components in the wake of the hydrophobic cylinders is still lower. Furthermore, the separation angles show the same trend as a function of the Reynolds number but always take smaller values for the hydrophobic cylinders.     

浅水圆柱绕流流动模式探讨

 数值求解了二维浅水方程和RNG k-ε流模型,模拟了不同稳定性系数S和圆柱中心间距G下的单圆柱、两圆柱和三圆柱的尾流流动模式,研究了底部摩擦力对尾流结构的影响。结果表明:随着S增大,尾流在底部摩擦力的作用下趋于稳定,大尺度涡结构逐渐消失。单圆柱尾流区依次出现了涡街（VS）尾流、不稳定漩涡（UB）尾流和稳定漩涡（SB）尾流。多圆柱尾流除了受S数影响外,还与G密切相关。随着G的增大,两圆柱背后依次出现了单钝体绕流、偏转尾流和对称尾流,三圆柱背后则依次出现了单钝体绕流、偏转尾流、对称尾流和非对称尾流。此外,数值结果还表明多圆柱尾流结构不同于单圆柱,多圆柱并排使得尾流更加不稳定。