局部抽吸对边界层流动稳定性的影响和控制研究

在边界层壁面上,设计局部抽吸结构,采用直接数值模拟的方法,获得稳定的三维基本流.在此基础上,研究稳定及最不稳定的二维扰动T-S波的时、空演化机制;进一步探讨了局部抽吸的形式、强度大小及分布结构对二维T-S波的非线性演化影响及其对增长率的贡献大小.结果表明,局部抽吸结构诱导产生的三维基本流是扰动波得以快速增长的一个关键性因素,这是由于平均流剖面的改变及展向速度的出现,增强了流体运动中的不稳定性、扩大了中性曲线的不稳定区域范围.在最不稳定的二维扰动T-S波的非线性演化过程中,由于非线性作用的不断增强,逐渐激发产生出三维扰动波及高次谐波,其三维扰动波的流向波数和频率与二维扰动波的流向波数和频率相同;同时展向速度的大小对二维扰动波的增长、流动的失稳、流向涡的形成等方面都起着激励的作用.随着时、空的不断发展和非线性作用的迅速加强,正、负相间的流向涡逐渐形成,强度逐渐增大,流向涡的影响区域也在不断扩大,涡的形状逐渐拉伸变长,并出现强的剪切层,流动开始失稳等其它机制;这些结论与文献4、5]的结果相吻合.

Study on control and effect of local suction upon hydrodynamic stability of a boundary layer

In this paper,the numerical solutions of a three-dimensional(3-D) base flow are obtained by local suctions designed on the solid surface of a boundary layer.Based on the numerical solutions,the processes of stable and the most instable nonlinear evolution of 2-D disturbance Tollmien-Schlichting wave(T-S wave) are studied.The effect of the form of local suctions,the intensity of those,and the distribution structure of those on the nonlinear evolution of 2-D T-S wave and the growth rate is discussed.The results show that,the basic flow induced by local suctions is a key factor that causes the fast growth of the disturbance wave.Due to the changing of the average flow profile and the appearance of the spanwise velocity,local suctions enhance the hydrodynamic instability,as a result the instable region of neutral curve is amplified,and the maximal growth rate of the 2-D T-S wave is increased.In the process of the nonlinear evolution of 2-D disturbance T-S wave,with the increasing of the nonlinear interaction,the most instable 2-D disturbance wave is triggered to come into being the 3-D disturbance wave and high-frequency harmonics.Its streamwise wave number and frequency are the same as those of 2-D disturbance waves.The spanwise velocity plays an exciting role in the growth of 2-D disturbance wave,the instability of 2-D wave,the formation of the streamwise vortex,and the generation of 3-D disturbance wave.The results of the numerical simulations agrees well with the theoretical and experimental results in literature .