一种新的运动激波--非定常边界层相互干扰现象

本文探讨了一种新的激波－非定常边界层相互干扰现象，这种激波－边界层干扰现象既不同于定常激波－边界层干扰现象，又不同于激波在端面反射后与该激波所诱导的边界层之间的干扰现象，而是运动激波与稀疏波和第一激波所诱导的非这常边界层之间的干扰现象，本文对这种现象用微波动力学理论进行分析，并把这种干扰现象看成激波的绕射现象，同时在稀疏波破膜的双驱动激波管中进行实验观察，最后把理论分析与实验观察进行了比较。     

INTERFERENCE OF SHOCK AND BOUNDARY LAYER IN SUPERSONIC FLOW

激波与物面边界层的干扰涉及可压缩流动的稳定性、转捩、分离等问题,直接影响到飞行器的阻力、表面热防护和飞行性能等工程技术问题。首先总结了前人对于激波与边界层的干扰所做的工作,之后重点研究和对比分析了超声速与跨声速流动中,正激波、斜激波以及头部激波对于飞行器层流和湍流边界层的干扰影响。激波强度的不同对边界层干扰作用不同,在强干扰情况下将会引起边界层分离和翼型失速。     

抽吸激波管的性能分析与计算

为了减小由于反射激波和透射激波分叉引起的反射型激波风洞试验气体提前受到污染的现象,本文研究了一种新的具有抽吸的激波管流动,分析了抽吸缝的作用,给出了这种抽吸激波管性能参数的计算方法,同时还给出了反射激波与边界层相互作用引起的激波分叉的形状随抽吸量变化的计算公式。实验证实了边界层抽吸可以有效地减小激波与壁面边界层相互作用所产生的分离现象。计算与测量结果是一致的。     

激波诱导含灰气体边界层中的粒子分布

本文研究当激波沿着一个固体表面等速地穿越含灰气体运动时所诱导的层流边界层特性。考虑了作用在气体边界层中球形粒子的 Saffman 升力,建议了一种计算近壁区中弥散相密度剖面的方法,并给出了数值计算结果。本文结果表明:在激波后方存在着一个弯曲的薄层区域,其中的粒子密度可以比其波前原始值增加许多倍。这种粒子聚集效应对于工业中粉尘爆炸等实际问题具有重要意义。     

The distribution of particles in a shock-induced boundary layer of a dusty gas over a solid surface

The laminar boundary layer behind a constant-speed shock wave moving through a dusty gas along a solid surface is studied. The Saffman lift force acting on a spherical particle in a gas boundary layer is taken into account. A method for calculating the density profile of dispersed phase near the wall is proposed and some numerical results are given. It is shown that behind the shock wave, there exists a curved thin layer where the density of particles is many times higher than the original one. This dust collection effect may be of essential importance to the problem of dust explosion in industry.     

激波与转捩边界层干扰非定常特性数值分析

激波与边界层干扰的非定常问题是高速飞行器气动设计中基础研究内容之一.以往研究主要针对层流和湍流干扰,在分离激波低频振荡及其内在机理方面存在着上游机制和下游机制两类截然不同的理论解释.分析激波与转捩边界层干扰下非定常运动现象有助于进一步加深理解边界层状态以及分离泡结构对低频振荡特性的影响规律,为揭示其产生机理指出新的方向.采用直接数值模拟方法对来流马赫数2.9,24?压缩拐角内激波与转捩边界层干扰下激波的非定常运动特性进行了数值分析.通过在拐角上游平板特定的流向位置添加吹吸扰动激发流动转捩,使得进入拐角的边界层处于转捩初期阶段.在验证了计算程序可靠性的基础上,详细分析了转捩干扰下激波运动的间歇性和振荡特征,着重研究了分离泡展向三维结构对激波振荡特性的影响规律,最后还初步探索了转捩干扰下激波低频振荡产生的物理机制.研究结果表明:分离激波的非定常运动仍存在强间歇性和低频振荡特征,其时间尺度约为上游无干扰区内脉动信号特征尺度的10倍量级;分离泡展向三维结构不会对分离激波的低频振荡特征产生实质影响.依据瞬态脉动流场的低通滤波结果,转捩干扰下激波低频振荡的诱因来源于拐角干扰区下游,与流场中分离泡的收缩/膨胀运动存在一定的关联.     

Investigation on onset of shock-induced separation

A great number of experimental data indicating shock wave/boundary layer interactions in internal or external supersonic flows were reviewed to make clear the mechanism of the interaction and to decide the onset of shock-induced separation. The interesting conclusions were obtained for the considerably wide range of flow geometries that the onset of separation is independent of the flow geometries and the boundary layer Reynolds number. It is found that the pressure rise necessary to separate the boundary layer in supersonic external flows could be applied to such internal flows as overexpanded nozzles or diffusers. This is due to the fact that the separation phenomenon caused by shock wave/boundary layer interactions is processed through a supersonic deceleration. The shock-induced separation in almost all of interacting flow fields is governed by the concept of free interaction, and the onset of shock-induced separation is only a function of the Mach number just upstream of shock wave. However, physical scales of the produced separation are not independent of the downstream flow fields.     

Study of the Interaction of a Streamwise-Oscillating Shock with the Boundary Layer on a Flat Plate

The distinctive features of the flow in the region of interaction between an oscillating shock and a flat-plate boundary layer are studied for the laminar, transitional, and turbulent flow regimes. The flow patterns and the pressure and heat transfer distributions in the interaction region are analyzed at different intensities, frequencies, and amplitudes of the oscillating shock. The results of the interaction of oscillating and steady shocks with the flat-plate boundary layer are compared.     

振动激发对高超声速气动力/热影响

随着飞行马赫数的不断提高,空气的高温气体效应越来越明显,对高超声速飞行器的气动力/热特性产生重要影响.高温气体效应对气动力/热的影响机理复杂,影响参数众多,迄今为止国内外尚未完全研究清楚.发生高温气体效应时,多个非线性物理过程耦合在一起,地面试验和数值模拟无法将这些过程解耦,无法给出关键物理机理.为了解决这一问题,文章提出一种理论分析与数值模拟相结合的两步渐进新方法:先通过牛顿迭代法得到发生振动激发过程的斜激波无黏解;再将该无黏解的结果作为边界条件,求解边界层的黏性解.利用该方法研究了振动激发过程对二维斜劈的气动力/热特性的影响规律.研究结果表明,振动激发过程对斜激波后的温度、密度、马赫数、雷诺数和斜激波角影响较大,而对压力和速度影响较小.斜激波波后的无黏流动与边界层流动是耦合在一起的.发生振动激发后,斜激波波后雷诺数的增大会导致边界层厚度减小,结合多个物理量的变化,如速度增大和温度减小,共同对边界层内的摩擦阻力和气动热产生影响.对比完全气体的结果发现,振动激发使壁面摩阻升高,而使壁面热流降低.分别通过影响激波层和边界层,振动激发对摩阻的影响是弱耦合的,而对热流的影响则是强耦合的.     

FLAT-PLATE BOUNDARY-LAYER FLOWS INDUCED BY DUSTY SHOCK WAVE

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Theoretical investigation on shocklets in compressible boundary layers

By the shock relationships, the wavy characteristics and the forming condi-tions of a shock wave are analyzed. The wavy characteristics of an Euler system are stud-ied theoretically. The present research focuses on the wavy characteristics of Tollmien-Schlichting （T-S） waves, the excitation conditions of shocklets in compressible boundary layers, and the viscous effect on shock. The possibility of existence of shocklets in the compressible boundary layer and the physical mechanism of formation are theoretically interpreted.     

Effect of boundary layer on Mach reflection over a wedge surface

Abstract. In this paper, we consider the phenomenon of unsteady Mach reflection generated by a plane shock wave advancing over a straight wedge surface, with particular attention to the deviation of the flow field from the self-similar nature. We examine the observed change in angle between incident and reflected shocks, which is in contrast to the fact that the angle should remain constant with time in a self-similar flow. The effect of the boundary layer behind the advancing shock wave over the surface of the wedge is considered to cause this, and boundary layer theory is utilized to estimate the thickness of the layer. It is found that the thickness increases as to the time t compared with t by the overall expansion in the self-similar flow. Assuming that the thicker boundary layer is effectively equivalent to a change in wedge angle, the effect of the boundary layer on the flow field should be less in later stages with larger t values in accordance with the observation above. Received 6 March 2000 / Accepted 23 April 2001     

Large-eddy simulation of low-frequency unsteadiness in a turbulent shock-induced separation bubble

The need for better understanding of the low-frequency unsteadiness observed in shock wave/turbulent boundary layer interactions has been driving research in this area for several decades. We present here a large-eddy simulation investigation of the interaction between an impinging oblique shock and a Mach 2.3 turbulent boundary layer. Contrary to past large-eddy simulation investigations on shock/turbulent boundary layer interactions, we have used an inflow technique which does not introduce any energetically significant low frequencies into the domain, hence avoiding possible interference with the shock/boundary layer interaction system. The large-eddy simulation has been run for much longer times than previous computational studies making a Fourier analysis of the low frequency possible. The broadband and energetic low-frequency component found in the interaction is in excellent agreement with the experimental findings. Furthermore, a linear stability analysis of the mean flow was performed and a stationary unstable global mode was found. The long-run large-eddy simulation data were analyzed and a phase change in the wall pressure fluctuations was related to the global-mode structure, leading to a possible driving mechanism for the observed low-frequency motions.      

The flow structure of dilute gas-particle suspensions behind a shock wave moving along a flat surface

The asymptotic and numerical investigations of shock-induced boundary layers in gas-particle mixtures are presented.The Saffman lift force acting on a particle in a shear flow istaken into account.It is shown that particle migration across the boundary layer leads tointersections of particle trajectories.The corresponding modification of dusty gas model isproposed in this paper.The equations of two-phase sidewall boundary layer behind a shock wave moving at aconstant speed are obtained by using the method of matched asymptotic expansions.Themethod of the calculation of particle phase parameters in Lagrangian coordinates isdescribed in detail.Some numerical results for the case of small particle concentration aregiven.     

Aerodynamic heating in the region of shock and turbulent boundary layer interaction induced by a cylinder

Detailed distributions of heat flux in the region of shock wave and turbulent boundary layer interaction induced by a cylinder were measured in the shock tunnel. Oil flow patterns and Schlieren photographs were taken. Empirical relations were given for determining separation shock angle, peaks of heat flux and their locations on both cylinder leading edge and flat plate surface, and other characteristic parameters of the interaction region.     

Shock-unsteadiness model applied to oblique shock wave/turbulent boundary-layer interaction

Reynolds-averaged Navier–Stokes prediction of shock wave/turbulent boundary layer interactions can yield significant error in terms of the size of the separation bubble. In many applications, this can alter the shock structure and the resulting surface properties. Shock-unsteadiness modification of Sinha et al. (Physics of Fluids, Vol.15, No.8, 2003) has shown potential in improving separation bubble prediction in compression corner flows. In this article, the modification is applied to oblique shock wave interacting with a turbulent boundary layer. The challenges involved in the implementation of the shock-unsteadiness correction in the presence of multiple shock waves and expansion fans are addressed in detail. The results show that a robust implementation of the model yields appreciable improvement over standard k–ω turbulence model predictions.     

跨音速翼型上的激波／边界层干扰自适应控制计算

在激波区使用自适应壁对跨音速翼型的激波／边界层的相互作用（干扰）进行控制，可改变机翼的气动性能，这种被动控制可通过在翼型的激波区开一凹腔，其上覆盖一弹性橡胶膜柔壁来，本文给出用Ｎａｖｉｅｒ－Ｓｔｏｋｅｒ方程数值模拟这一自适应控制翼型的跨音速粘性绕流，提出了一个适应于本特殊情况（物面边界局部地区在求解过程中有变化）的处理办法。并探讨了自适应柔壁对当代跨音速翼绕流的影响。     

含灰气体激波管侧壁层流边界层流动特征

水文采用数值方法求解含灰气体激波管中侧壁层流边界层,揭示了这类流动中呈现的三个特征不同的区域.为了研究两相边界层的发展,本文构造了一个包括六点和四点格式的隐式有限差分程序,引进了适当描述气固两相间相互作用的非斯托克斯关系,并分别给出了气体和粒子的速度与温度剖面。此外,文中还讨论了激波管压力比、粒子载荷比和粒子尺寸对侧壁边界层流动特性的影响。     

激波诱导的燃烧粉尘云边界层的结构

足够强的激波扫过铺有可燃粉尘的界面时，波后形成燃烧的粉尘云边界层。为揭示其内部结构，本文对该现象进行了实验和理论两个方面的研究。理论计算表明燃烧粉云边界层可分为三个区域：诱导区、反应区和扩散区，诱导区的粉尘浓度最高，计算获得的粉尘云轮廓和点火延迟与实验结果基本吻合．     

变高度圆柱诱导的激波边界层干扰

采用分区方法及Ｒｏｅ三阶流通量差分分裂格式求解雷诺平均Ｎ－Ｓ方程,湍流附加黏性系数用Ｂａｌｄｗｉｎ－Ｌｏｍａｘ模型计算,数值模拟了高超声速条件下变高度圆柱诱导的激波边界层层干扰,其流场的主要特性均与实验结果一致或规律相同,结果清晰地展示了流场结构以及气动载荷分布随柱高度的变化特征,产说明激波碰撞和旋涡运动都可能导致飞行器表面局部气动载荷的增加。