湍流边界层中马蹄形涡的形成方式

本文使用一种新的流动显示方法——激光片光运动法和几种实验技巧对湍流边界层中的马蹄形涡进行了观测,发现并描述了其形成的四种方式:二次不稳定式、组合式、变形式和突发式。对这四种马蹄形涡的形成及发展进行了研究和比较。实验结果表明,这些马蹄形涡在尺度、运动速度和变形上是有差别的。     

STUDY ON THE FUEL AIR MIXING INDUCED BY A SHOCK WAVE PROPAGATING INTO A H_2-AIR INTERFACE

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Effect of free-stream turbulence on conical vortex dynamics

The influence of Free-Stream Turbulence (FST) on the space–time dynamics of a conical vortex developing along a A-pillar is studied experimentally. Measurements of unsteady wall pressure and velocity by High Speed-Stereo PIV highlight the important effects of turbulence on the mean and instantaneous properties of the vortex. Very significant increases in Reynolds stresses into the vortex region and in wall fluctuating pressure are observed in the presence of FST. In smooth flow, the frequency content of the pressure and velocity fields is very rich with low and high frequency contributions due to the meandering of the vortex and instabilities in the vortex core. Meandering shows, for the different integral length scales and intensities of turbulence tested, a great receptivity to the presence of a FST and we observe a global motion of the vortex structure at low frequency. This frequency is modulated by the value of the integral length scale of the FST. We show that the mean conical structure is a wave guide for the perturbations of the core but that, with FST, the spatio-temporal evolution of the envelope overwhelms the intrinsic instability of the vortex core observed in smooth flow.     

Mathematical Modeling of Flows Inside Rotating Bodies Made of Cellular-Porous Materials

A physicomathematical model is developed, which describes gas flows inside rapidly rotating bodies made of cellular-porous materials. Asymptotic and numerical solutions are obtained for some problems of forced centrifugal convection inside cylindrical cellular-porous bodies. The effect of the governing parameters (drag coefficient and dimensionless length of the cylinder) on characteristics and types of flows is considered. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 78–85, November–December, 2005.     

Analysis of Unsteady Motion with Respect to Noise Sources in a Gas Turbine Combustor: Isothermal Flow Case

In order to evaluate the direct and indirect contributions to the total combustion noise emission, a combustion chamber consisting of a swirl burner and an exit nozzle of Laval-shape, representing a gas turbine combustor, is investigated by means of experiments and large eddy simulation. Focused on the isothermal flow case first and encouraged by a good overall agreement between the LES and the experimental data for the flow field, a first characterisation of the flow with respect to noise sources is performed. To analyse acoustic properties of the flow, time and length scales are evaluated inside the combustor. Furthermore, the evidence for the existence of a precessing vortex core (PVC), typical for configurations with swirl, is revealed. Finally, the effect of the PVC on the flow inside the Laval nozzle is discussed.     

流向强迫振荡圆柱绕流的涡脱落模态分析

通过求解采用ALE方法描述的运动坐标系Navier-Stokes方程组,分析均匀来流下雷诺 数为150的静止和流向振荡的圆柱绕流. 主要研究了强迫振荡频率和较大振幅比 (A/D=0.3-1.2)对圆柱升力、阻力变化特性以及涡脱落模态的影响. 研究表 明,流向振荡圆柱绕流存在多种涡脱落模态,如对称S以及反对称A-I, A-III, A-IV等多种形式;比较研究结果,拓展了各模态下对应的锁定区域,并将其分为5个 子区;A-I模态中圆柱受力较以前所知更复杂;通过分析计算结果,发现最大加速度 比Af_{c}^{2}/Df_{s0}^{2}可能是涡脱落模态(尤其是对称S模态)最有效的控制参数.     

Reynolds数对大攻角细长旋成体绕流滚转角效应影响的数值研究

使用低耗散的Roe格式,数值模拟了Reynolds数(Re)对大攻角细长旋成体绕流滚转角效应的影响.模型头部加了几何小扰动块以引发流场的不对称.在较大的Re数(Re=10 5)下,本文的计算结果与实验是相符的,此时细长体的滚转会导致双稳态、双周期现象,即侧向力随滚转角呈现类似方波形式的双周期变化,方波中侧向力基本保持不变的状态对应于流场的正则态,且两个正则态的侧向力方向相反,方波中侧向力基本保持不变的状态对应于流场的正则态,且两个正则态的侧向力方向相反;而在较小的Re数(Re=4 000)下,如果扰动足够大,细长体的滚转将导致不同的双稳态现象,此时两个正则态的侧向力方向相同,而在较小扰动下双稳态现象不再出现;Re数更小时(Re=1 000),即使在较大的扰动下,双稳态现象也不再出现,侧向力随滚动角仍是连续变化的.本文的计算结果表明,Re数越小,流场对头部扰动的感受性越弱.     

To formulating a nonlinear initial-boundary problem of an unsteady separated flow around an airfoil

A general formulation of a nonlinear initial-boundary problem of an unsteady separated flow around an airfoil by an ideal incompressible fluid is considered. The problem is formulated for a complex velocity. Conditions of shedding of vortex wakes from the airfoil are analyzed in detail. The proposed system of functional relations allows constructing algorithms for solving a wide class of problems of the wing theory. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 2, pp. 48–56, March–April, 2007.     

Model of a strong discontinuity for the equations of spatial long waves propagating in a free-boundary shear flow

The long-wave equations describing three-dimensional shear wave motion of a free-surface ideal fluid are rearranged to a special form and used to describe discontinuous solutions. Relations at the discontinuity front are derived, and stability conditions for the discontinuity are formulated. The problem of determining the flow parameters behind the discontinuity front from known parameters before the front and specified velocity of motion of the front are investigated. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 4, pp. 206–213, July–August, 2008.     

NUMERICAL STUDY OF PARTICLE DISTRIBUTION IN WAKE OF LIQUID-PARTICLE FLOWS PAST A CIRCULAR CYLINDER USING DISCRETE VORTEX METHOD

Particle-laden water flows past a circular cylinder were numerically investigated. The discrete vortex method (DVM) was employed to evaluate the unsteady water flow fields and a Lagrangian approach was applied for tracking individual solid particles. A dispersion function was defined to represent the dispersion scale of the particle. The wake vortex patterns, the distributions and the time series of dispersion functions of particles with different Stokes numbers were obtained. Numerical results show that the particle distribution in the wake of the circular cylinder is closely related to the particle's Stokes number and the structure of wake vortices: (1) the intermediate sized particles with Stokes numbers, St, of 0.25, 1.0 and 4.0 can not enter the vortex cores and concentrate near the peripheries of the vortex structures, (2) in the circular cylinder wake, the dispersion intensity of particles decreases as St is increased from 0.25 to 4.0.