【作者】 王维；

【导师】 姜楠；

【作者基本信息】 天津大学 ， 流体力学， 2010， 硕士

【摘要】 本文对平板层流边界层下的扰动发展演化进行了实验研究。实验模型为三元回流风洞的自由来流背景环境下的平板边界层,平板前缘为椭圆形,流场采用二维平行流假设。实验以自由来流背景中的多频率扰动作为外部扰动源,分析中对扰动波采用空间模式的正则模形式表达。实验中采用热线测量手段,使用单丝热线探针测量边界层流场的流向速度信号,共测量了流向140mm到440mm的流场区域,每个流向位置处沿边界层法向在边界层内测量各点。首先通过速度信号求解出流场边界层速度剖面,由于热线探针不能测量边界层非常靠近壁面的速度分布,文中作者使用最小二乘法对速度数据进行多项式拟合,然后与Blasius标准层流剖面对比。通过与Blasius标准层流剖面的比对发现,实验所测得的流场大部分区域与层流剖面符合的很好,说明流场是层流流场。再次,速度信号出现了准周期的波动,说明有扰动在边界层内产生和发展。来流背景扰动在经过平板前缘的感受性过程之后在边界层内激发了扰动波。通过对速度信号进行傅立叶变换,将流场中的扰动波信号在频域上表达出来。在流向140mm到286mm的流场区域中,检测到了9个频率间隔146.48Hz的扰动波,基波频率是292.97Hz ,最高的频率是1464.84Hz。这些扰动波在流向和法向上的发展趋势类似。法向上扰动的高低幅值在边界层内交替出现。流向上扰动传向下游的过程中幅值逐渐增加。更多还原

【Abstract】 The experimental investigation on the evolution of disturbances in a flat plate laminar boudary layer was executed.The experiment was carried out on a flat plexiglass plate with elliptic leading edge in the environment of wind tunnel freestream.The flow was two-dimensional and parallel.The freestream disturbances were multi-frequency,spatial mode and normal mode.Streamwise velocity measurement was made using single-wire hot-wire probe in the boundary layer region,which is from 140mm to 440mm in the streamwise direction.The velocity were measured on the normal direction at every streamwise location.The mean velocity profiles were obtained from the velocity signal in the first step.Because the probe cannot acquire the velocity signal in the boundary layer close to the wall,the velocity were fitted by the polynomial least-squares method,and then compared with the Blasius velocity profile.Most of the flow field were verified to be laminar by the contrast to the Blasius velocity profile.It’s indicated that the disturbances were reduced and evolved in the boundary layer for the quasi-periodic oscillations in the velocity signals.The initial disturbances were induced by the receptivity of the flat plate’s leading edge to the freestream disturbances.The disturbances in the flow field were illustrated in the frequency-domain by the Fourier transform of velocity signals.There were 9 waves in the flow field from 140mm to 286mm in the streamwise direction,of which the lowest frequency was 292.97Hz,the biggest frequency was 1464.84Hz and the frequency interval was 146.48Hz. These waves had the similar evolutions in both the streamwise and normal direction.Higher and lower amplitude alternately dominated in the boundary layer in the normal direction. The magnitude of amplitude grew with the streamwise direction.更多还原