Laminar Flow Past a Circular Cylinder under the Effect of Nonstationary Jet Efflux to the Near‐Wake Region

Changes in a laminar flow past a circular cylinder under the effect of jets blowing out to its rare region have been studied numerically. Jet efflux was caused by a return flow of a part of the incoming flow in the inner channels of the cylinder due to the pressure difference between its front and end stagnation points. The channels connected the inlet window formed in the zone of the front stagnation point with two outlet windows on the backside surface of the cylinder. The influence of the coordinates of the jets issuing through the outlet windows and dimensions of the inlet and outlet windows on variation of the drag and lift coefficient and distribution of the coefficients of pressure and friction on the cylinder surface has been considered. It is shown that under the effect of blowing out the cylinder drag decreased by 4% and the amplitude of buoyancy force oscillations decreased by 40%.     

Capillary Stability in a Tilted Circular Cylinder

The classical capillary stability problem in a vertical circular cylinder is a special case of the more general problem of the stability of liquid above a capillary surface in a circular cylinder with arbitrary orientation of gravity. This problem can, of course, also be viewed as arbitrary cylinder orientation in a steadily accelerating spacecraft. The general (tilted) circular cylinder capillary stability problem is solved numerically by use of the Surface Evolver code for general tilt and general contact angle. Tens of thousands of combinations of contact angle, tilt angle, and Bond number are solved for with a global volunteer computing network running Surface Evolver. The results appear to be symmetric about 90 degree contact angle, as in the previous vertical cylinder studies, and not symmetric about 45 degree tilt.     

非紧致阻抗圆柱气动噪声数值预测与控制方法

为预测非定常流动与非紧致阻抗固体边界相互作用产生的气动噪声,开发一种基于精确格林函数和声模拟理论的气动噪声数值预测方法。非紧致阻抗边界对声波的散射作用计入精确格林函数,远场噪声采用FW-H方程计算。对具有任意几何外形的非紧致阻抗边界,采用边界元方法计算满足声学硬边界或声学阻抗边界条件的精确格林函数。同时,推导了具有阻抗边界条件的二维非紧致圆柱精确格林函数的解析解用以验证数值计算方法。数值计算结果表明数值解与解析解的结果一致,数值解要取得好的网格收敛效果需要在一个波长内布置至少20个网格点。圆柱绕流气动噪声预测结果表明,非紧致边界的阻抗特性对声传播有显著影响,采用合适的阻抗布置方式可以取得有效的噪声控制效果。     

圆柱涡激振动数值模拟研究

基于k-ωSST湍流模型研究典型亚临界状态下(Re=3 900)二维圆柱的涡激振动。通过将圆柱简化为不同刚度的质量弹簧系统,并运用CFX的动网格与CEL功能,研究刚度系数对圆柱涡激振动的影响。研究观察到圆柱涡激振动的自限定现象以及旋涡脱落模态的转变过程,并得到圆柱涡激振动特性随刚度变化的规律。     

两端简支圆柱体的轴对称振动

本文用三维弹性动力学理论研究圆柱体在两端简支约束下的轴对称自由振动问题。给出位移振型和应力振型的解析表达式，求得固有频率的精确解。研究结果表明：在圆柱体的径向还存在着不同的半波数的位移振型，这种性质在初等理论中是无法反映的     

Numerical Study on the Suppression of the Oscillating Wake of a Square Cylinder by a Traveling Wave Wall

Traveling waves generated on the side surfaces of a square cylinder are employed to suppress the oscillating wake for improving the flow behavior around a square cylinder; this method is termed the traveling wave wall (TWW) method. This study aimed to evaluate the influence of the key parameters of TWW on the control of aerodynamic forces and the oscillating wake of the flow around a square cylinder. Unsteady numerical analyses at a low Reynolds number (Re) of 100 were performed using a two-dimensional CFD simulation. First, the grid independence and time step independence tests of the simulation were conducted to verify the rationality of the solving parameter settings, and the validation of flow around the fixed square cylinder at Re =100 was carried out. Subsequently, the lift and drag coefficients and the vortex shedding modes under different combinations of three TWW control parameters, including wave velocity, wave amplitude, and wavenumber, were analyzed in detail. The results show that TWW can remarkably reduce the mean value of drag coefficient and the RMS value of the lift coefficient by more than 12% compared to the method involving a standard square cylinder. Two peaks occur in the lift coefficient spectrum, with the low frequency corresponding to the vortex shedding frequency in the wake of the flow around the square cylinder and the high frequency corresponding to the traveling wave frequency. The vorticity contours show that the alternating vortices in the wake of the square cylinder are not completely suppressed under the selected control parameters.     

On the Visualization of Thermal Counterflow of He II Past a Circular Cylinder

Thermal counterflow of superfluid ⁴He is investigated experimentally in the proximity of a 3 mm diameter cylinder by analyzing the motions of micrometer-sized solid particles, focusing especially on the occurrence of macroscopic vortices. The influence of heating an opaque brass cylinder by the light source is studied, as thermal counterflow is generated from its surface, and compared with the case of a transparent plexiglass cylinder of the same size. Additionally, we report our preliminary investigation of vertical counterflow around the transparent cylinder. We find that care should be taken when applying conventional visualization techniques—particle image velocimetry and particle tracking velocimetry—as spurious vortical structures might be identified in quantum flows displaying two-fluid behavior.     

用快速多极方法预测圆柱绕流的气动噪声

采用声模拟理论预测气动噪声时需要大量的计算时间,快速多极方法将传统点对点计算转变为点集之间的相互作用,可以有效加速计算。基于二维自由空间格林函数的分波展开方式,推导了FW-H方程应用快速多极变换后的积分核函数与计算公式。计算了低马赫数圆柱绕流的非定常流场;并由此预测了气动声源。随后,分别采用传统方法和快速多极方法计算其声场分布。结果表明,基于分波展开方式的快速多极方法能准确计算圆柱绕流气动噪声,在频率较低时能大幅减少声场计算时间,且观测点数越多,加速效果越明显。     

Calculation of Nonstationary Flow Around a Circular Cylinder within the Framework of Multiblock Computational Technologies

A methodological numerical investigation of nonstationary flow of an incompressible viscous fluid around a circular cylinder has been carried out within the framework of the multiblock approach on a set of intersecting rectangular and cylindrical grids.     

Diffraction of Internal Waves by a Submerged Circular Cylinder at Forward Speed in a Two-Layer Fluid

Diffraction of internal waves by a submerged body in a uniform current of a two-layer fluid is considered. The layers are infinitely deep, and the flows are two-dimensional. The linearized potential theory is used for the inviscid and incompressible fluid. The solution for the circular cylinder, which is either below or above the interface, is given in the form of rapidly converging series. This is achieved through the use of certain recursive relations. Numerical results are provided for the exciting forces, wave resistance and lift which may be useful in testing numerical methods used for the study of internal wave diffraction by a submerged body of arbitrary form.     

Torsional Wave Propagation in the Finitely Pre-Stretched Hollow Bi-Material Compound Circular Cylinder

This paper studies the torsional wave dispersion in the hollow bi-material compounded cylinder with finite initial strains. The investigations are carried out within the scope of the piecewise homogeneous body model with the use of the three-dimensional linearized theory of elastic waves in initially stressed bodies. The mechanical relations of the materials of the cylinders are described through the harmonic potential. The numerical results on the influence of the initial stretching or compression of the cylinders along the torsional wave propagation direction are presented and discussed     

Computational Analysis of the Oscillatory Mixed Convection Flow along a Horizontal Circular Cylinder in Thermally Stratified Medium

The present work emphasizes the significance of oscillatory mixed convection stratified fluid and heat transfer characteristics at different stations of non-conducting horizontally circular cylinder in the presence of thermally stratified medium. To remove the difficulties in illustrating the coupled PDE’s, the finite-difference scheme with efficient primitive-variable formulation is proposed to transform dimensionless equations. The numerical simulations of coupled non-dimensional equations are computed in terms velocity of fluid, temperature and magnetic field which are computed to examine the fluctuating components of skin friction, heat transfer and current density for various emerging parameters. The governing parameters namely, thermally stratification parameter     

Possibility of Acoustic Control of Excited Turbulent Jets

The results of experimental investigation of the influence of highfrequency (lowfrequency) acoustic action on a turbulent jet preexcited by sound of low (high) frequency are presented. It is shown that the qualitative character of the action remains the same as that for an unexcited jet. However, the quantitative results here are somewhat different; in particular, the possibilities of suppressing turbulence in the jet in its highfrequency excitation are reduced in this case.     

Pseudosound Pressure Oscillations Caused By the Interaction of a Fluid Flow with the Obstacle in the Form of a Circular Cylinder in a Pipe

Journal of Engineering Physics and Thermophysics - A simulation of the vibroacoustic processes proceeding in a long pipe with an obstacle in the form of a circular cylinder, in which a fluid flows,...