【作者】 闫溟；

【导师】 罗纪生；

【作者基本信息】 天津大学 ， 流体力学， 2006， 硕士

【摘要】 边界层流动稳定性的研究在理论和工程技术领域都有着重要的意义,而边界层感受性研究在流动稳定性的研究过程当中占据着非常重要的地位。本文通过数值模拟的方法,研究了超音速边界层对自由流中局部扰动的感受性问题。文章系统研究了自由流中空间局部的周期扰动在边界层当中激发出的不稳定波的特性;讨论了自由流中局部扰动的频率、空间尺度对边界层感受性的影响;并研究了自由流中扰动在边界层中激发出不稳定波的作用机理。本文主要得到以下结论:1.在边界层外的流场中引入空间局部的周期变化的体积力后,在施加体积力的位置附近会产生扰动速度散度正负交替的周期变化,这相当于在流场中添加了沿马赫波运动的周期变化的体积源。当体积源向壁面传播与边界层作用,会在边界层内产生局部振动。2.边界层内产生局部振动会引起边界层中向下游传播的扰动波,当体积源的频率与边界层中不稳定波的频率相同时,就可以激发出边界层内的不稳定波。对于小幅值扰动,激发的扰动波幅值的演化与线性稳定性理论分析结果一致。3.对于给定的扰动频率,边界层内激发出的扰动波的强度与施加的空间局部的周期体积力扰动的空间尺度有关,有一个最佳的空间尺度可以激发最强的扰动波。更多还原

【Abstract】 The study for the stability of boundary-layer is of significant importance for both theoretical research and engineering applications,while the receptivity is one of the important parts of boundary-layer stability.The supersonic boundary-layer receptivity to local disturbance in freestream is studied by DNS.The mode of the instabile wave which is excited in boundary is studied in this paper,the affections to instabilities by the frequency and range of local desturbance is discussed,the excition mechanism is also studied.The main conclutions are listed below :1. When introduces a periodic local force to the free-stream, the disturb velocity divergence changes periodicly near the force.This is equal to add sources in the flow. The sources interacte with the boundary and produce local disturbance in the boundary.2. The local disturbance can induce wave that propagates downstream, when the frequency of the force is equal to the frequency of the instable wave, the instable wave can be induced. If the amplitude of the force is small, the propagatation of the instable wave accord with the linear stability theory.3. Under a fixed frequency, the engery of the instable wave relates to the size of the force, there is a optimal size that can induce strongest instable wave.更多还原