不同雷诺数下方柱绕流的数值模拟

在不同雷诺数条件下,对流体绕经方形柱体的流动进行了数值模拟,计算雷诺数分别为100,1×103,1×104和2.2×104.当Re=100时,直接采用N-S方程进行计算;当Re=1×103,1×104和2.2×104时,则引入k-ε湍流模型进行计算.应用Galerkin有限元法对控制方程进行离散和求解,利用分离时间步长法处理控制方程中的非线性项.模拟计算得出了在不同雷诺数下的卡门涡街脱落形态.方柱后尾涡的形态会随雷诺数的变化而产生一定的变化.当雷诺数较低时,尾涡会拖得比较长,随着雷诺数的增加,尾涡长度会随之缩短.计算得到了方柱的受力系数和Strouhal数.将计算结果与文献上的实验和计算结果进行了比较,两者吻合较好.     

Numerical simulation of buoyant drops suspended in Poiseuille flow at nonzero Reynolds numbers

Suspensions of two-dimensional buoyant drops in Poiseuille flow are studied at nonzero Reynolds numbers by numerical simulations. The flow is studied as a function of the Froude number, the Reynolds number, the Capillary number and the density ratio. First, the lateral migration of a drop is studied. Results agree with two-dimensional simulations of solid circular cylinders by Feng et al. (J Fluid Mech 261:95–134, 1994; J Fluid Mech 277:271–301, 1994) qualitatively. At a relatively large Reynolds number (120) and a moderate Froude number (43), a drop shows oscillations across the channel and does not obtain a stable equilibrium position. Simulations are also performed at low and moderate area fractions (0.22, 0.44). It is found that the effective viscosity strongly depends on the Froude number for heavy drops (α > 1). The effective viscosity changes with the Froude number for light drops as well (α < 1), but to a lower extent. The distribution and the fluctuation energy of drops across the channel are non-uniform for buoyant drops that depend on the Froude number. The density ratio also affects the distribution and fluctuation energy of drops across the channel. The effect of the Reynolds number on the effective viscosity of the suspension is also investigated.     

Numerical simulation of planar shear flow passing a rotating cylinder at low Reynolds numbers

Two-dimensional shear flow over a rotating circular cylinder is investigated using lattice Boltzmann method. Simulations are performed at a fixed blockage ratio (B = 0.1) while the Reynolds number, nondimensional shear rate (K) and absolute rotational speed range as 80 ≤ Re ≤ 180, 0 ≤ K ≤ 0.2 and −2 ≤ β ≤ 2, respectively. To verify the simulation, the results are compared to previous experimental and numerical data. Quantitative information about the flow variables such as drag and lift coefficients, pressure coefficient and vorticity distributions on the cylinders is highlighted. It is found that, generally, with the increment in |β|, the absolute value of time average lift coefficient increases and time average drag coefficient decreases, and beyond a certain magnitude of β, the vortex shedding vanishes. It is also revealed that the drag coefficient decreases as the Reynolds number increases while the effect of the Reynolds number on lift is almost negligible. At the end, correlations for drag and lift coefficients ([`(C<sub>D</sub> )] ,[`(C_L )]){(\overline {C_D } ,\overline {C_L })} are extracted from the numerical data.     

Motion of the solid phase of an aerosol at large Reynolds numbers

Improved singly linked expressions are presented for the drag coefficient of the carrying agent and the solution of the equations of motion of the solid phase of an aerosol at large Reynolds numbers.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 3, pp. 405–411, September, 1977.     

The 1999 James Lighthill Memorial Paper: Scaling laws for turbulent wall-bounded shear flows at very large Reynolds numbers

Deep ideas of Sir James Lighthill concerning turbulent flows are discussed in the beginning. The scaling laws for large-Reynolds-number flows are presented in their historical development. The underlying hypotheses are discussed and compared with experiments. Special attention is given to non-universal Reynolds-number-dependent scaling laws that reveal the incomplete similarity of the flows. Recent results concerning scaling laws for boundary layers are presented in more detail and discussed.     

Mathematical simulation of heat- and mass-transfer processes in separated flows with a laminar mixing region at low reynolds numbers

The lower limit of applicability of the mathematical model of heat and mass transfer constructed by Batchelor and Lavrent'ev for separated flow past a bottom trench is extended.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 5, pp. 847–855, May, 1977.     

不同雷诺数条件下静止管道车环状缝隙流场数值模拟

为了探究雷诺数对于静边界环状缝隙流场的影响,采用Fluent软件对雷诺数为115 513、154 018、192 522三种工况下静止管道车环状缝隙流场进行了数值模拟,并通过物理试验进行验证,结果表明:同一雷诺数条件下,在环状缝隙入口处流速最大,之后沿管道车车身方向,环状缝隙流流速呈现先减小后增大的变化趋势,且环状缝隙流流速大于管道内水流的平均流速;各横断面环状缝隙流场均以管道中心呈同心圆分布,即半径相同的各点环状缝隙流流速值大致相同,且从管道车壁面到管壁面方向环状缝隙流流速呈现二次抛物线的变化形式;不同雷诺数条件下,管道内压强值沿程变化趋势大致相同,管道车上游位置处压强沿程呈现逐渐降低的变化趋势,环状缝隙内部和管道车下游位置处的压强值沿程呈现先升高后降低的变化趋势;随着雷诺数的增加,环状缝隙流流速值与压强值和涡量值均呈现出逐渐增大的变化趋势;数值模拟结果同试验结果基本吻合,两者所得环状缝隙流流速最大相对误差不超过7%,表明通过数值模拟来研究管道车环状缝隙流场的方法是可行的。     

Numerical simulation of separated boundary-layer flow

The numerical simulation of time-dependent, 2-D compressible boundary-layer flow containing a region of separation is studied. The separation is generated by the introduction of an adverse pressure gradient along the freestream boundary. In order to validate the numerical method, a low Mach-number laminar separation bubble flow is considered, which enables an extensive comparison with incompressible results. The generation of an adverse pressure gradient along the freestream boundary can be realized in various ways. An imposed decelerating flow boundary is compared with a suction technique. The effects of the strength of the pressure gradient and the presence of small upstream perturbations on the separation bubble are also investigated. The time-averaged characteristics of the flow are in good quantitative agreement with incompressible approximate theories predicting the condition for separation. The appearance of self-excited vortex shedding in unperturbed flows under a sufficiently strong adverse pressure gradient is consistent with incompressible flow simulations reported in the literature. The satisfactory result achieved in the calculation of the low-Mach-number flow encourages the application of the numerical method to flows with strong compressibility effects.     

Flows at small Reynolds and Froude numbers

This study investigates the flows of fluids whose material parameters depend analytically on the pressure and temperature at small Reynolds and Froude numbers. Two different approximations are found and the effects of variable viscosity on laminar flows in a horizontal channel are studied both in the absence and in the presence of frictional heating.     

Wake attenuation in large Reynolds number dispersed two-phase flows

The dynamics of high Reynolds number-dispersed two-phase flow strongly depends on the wakes generated behind the moving bodies that constitute the dispersed phase. The length of these wakes is considerably reduced compared with those developing behind isolated bodies. In this paper, this wake attenuation is studied from several complementary experimental investigations with the aim of determining how it depends on the body Reynolds number and the volume fraction alpha. It is first shown that the wakes inside a homogeneous swarm of rising bubbles decay exponentially with a characteristic length that scales as the ratio of the bubble diameter d to the drag coefficient Cd, and surprisingly does not depend on alpha for 10(-2)相似文献   

Numerical simulation of gas-particle flows behind a backward-facing step using an improved stochastic separated flow model

An improved stochastic separated flow (ISSF) model developed by the present authors is tested in gas-particle flows behind a backward-facing step, in this paper. The gas phase of air and the particle phase of 150 μm glass and 70 μm copper spheres are numerically simulated using the k–ɛ model and the ISSF model, respectively. The predicted mean streamwise velocities as well as streamwise and transverse fluctuating velocities of both phases agree well with experimental data reported by Fessler. The reattachment length of 7.6H matches well with the experimental value of 7.4H. Distributions of particle number density are also given and found to be in good agreement with the experiment. The sensitivity of the predicted results to the number of calculation particles is studied and the improved model is shown to require much less calculation particles and less computing time for obtaining reasonable results as compared with the traditional stochastic separated flow model. It is concluded that the ISSF model can be used successfully in the prediction of backward-facing step gas-particle flows, which is characterised by having recirculating regions and anisotropic fluctuating velocities. Received 20 June 2000     

Relaminarization in supersonic microjets at low Reynolds numbers

Results of measuring the length of the supersonic portion of the air jets that flow out of axisymmetric sonic nozzles 10.4 μm-1 mm in diameter are presented. The measurements are carried out in a range of degree of jet noncalculation of 1–30 and in a wide Reynolds number range, including the laminar and turbulent flow modes. It is shown that the Reynolds number calculated from the nozzle diameter and the outlet parameters of gas is the parameter that governs jet flow. It is found that, for a laminar jet mixing layer, the length of the supersonic portion sharply increases. When the jet mixing layer becomes turbulent, the length of the supersonic portion decreases. The effect of increasing the length of the supersonic portion after its decrease due to the turbulization of flow in a jet and a growth in the Reynolds number is first discovered.     

Numerical simulation of dispersed gas-liquid flows

This paper reviews the available information on numerical simulation of dispersed gas-liquid flows. Emphasis is on informing the reader about various aspects of constructing simulation models rather than giving an exhaustive literature review. The information is organised in a way so as to provide answers to the following questions: how to formulate model equations? how to select suitable algorithms and numerical techniques to solve these model equations? how to translate these into workable computer codes? how to use such codes for simulating flows in industrial equipment? Though greater emphasis is given to dispersed gas-liquid flows, the methodology can be applied to any multi-phase problem. Special features of multi-phase flow simulation over single-phase simulation are highlighted. A case of gas-liquid flow in a bubble column is presented as an illustration for the general methodology. The simulated mean flow field agrees reasonably with the experimental data. Properly validatedcfd codes thus can serve as a useful tool for design engineers of multi-phase systems. Some of the common pitfalls in using simulation codes for design are also discussed. This review is expected to give an overall idea about the present state-of-art of two-phase simulation in industrial equipment.     

Estimation of the thermohydraulic efficiency of swirlers at small Reynolds numbers

To estimate the thermohydraulic efficiency of different types of swirlers of heat exchange in pipes, we have generalized the experimental data, which has made it possible to determine the optimal range of Reynolds numbers and the optimal geometric sizes of swirlers. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 23–30, January–February, 2009.     

Numerical simulations of Coriolis flow meters for low Reynolds number flows

In process industries Coriolis mass flow meters (CMFs) are widely employed for measuring mass flows. Quite often, especially in the oil and gas (O&G) industry, owing to fluids with high viscosities, flow measurements may lie in low Reynolds number regions. At low Reynolds numbers (Re), a CMF reading may deviate under the influence of fluid-dynamic forces. With the help of extensive Fluid-Structure-Interaction simulations (FSI), a detailed insight into physical mechanisms leading to this deviation is provided. The main finding is that this deviation is a function of the Reynolds number and the effect can be explained by a periodic shear mechanism which interacts with the oscillatory Coriolis force and reduces the tube deflection. Experimental results with and without a correction for this effect are shown and compared with corresponding numerical results. If the low Reynolds number effect were ignored, it would lead to errors as large as 0.5% to 1% at Re = 800, however by measuring the Re and making corrections, the effect is reduced to < 0.2%.     

不同雷诺数下圆柱绕流气动噪声数值模拟

基于大涡模拟和声类比相结合的混合方法对不同雷诺数下二维圆柱绕流的远场气动噪声进行预测.预测值与试验数据吻合良好.根据预测结果分析圆柱绕流气动噪声的声场特性,研究流场振荡规律对远场噪声的影响和圆柱绕流气动噪声的辐射特性,并寻找降低圆柱绕流气动噪声的途径.结果表明:随着雷诺数的增加,远场各测量点的总声压级增大;声场的最大声...     

Numerical simulation of confined unsteady aerodynamical flows

A system of algorithms is presented for the computer simulation of confined unsteady flows of a compressible fluid. The methods are valid for a wide range of time scales and are applied to simulate wind tunnel acoustics, flow over a ramp and flow past aircraft cavities.     

Steady flow past an oblate spheroid at small Reynolds numbers

The problem of uniform steady viscous flow over an oblate spheroid is solved in the low-Reynolds-number range 0.1 Re 1.0. The full Navier-Stokes equations are written in the stream function-vorticity form and solved numerically by means of the series-truncation method. Spheroids having axis ratio ranging from 0.245 to 0.905 are considered. The obtained drag coefficients are compared with previous analytical formulae which were based on the solution of the linearized Stokes equations. As expected, the deviation between the present results and the analytical formulae is small for low-Re flows, however, it increases with the increase of Re. The present results provide a measure for establishing the range of validity of the analytical solutions.     

Numerical modeling of complex viscous fluid vortical flows

The influence of the turbulence model, numerical diffusion, and methods of formulating the boundary conditions on a solid wall on computation results is analyzed in an example of a finite-difference simulation of viscous fluid vortical flows in a broad range of Mach and Reynolds number variation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 5, pp. 758–765, November, 1987.