可压缩平板边界层流动的湍流/非湍流界面层空间分布的统计特性

Statistical characteristics of spatial position of turbulent/non-turbulent interface layer in compressible flat-plate boundary layer flow

为揭示可压缩湍流边界层中湍流/非湍流界面层(TNTI)空间分布的演化规律,对马赫数Ma为2.9的空间发展平板湍流边界层流动进行直接数值模拟研究。通过湍流体积分数确定涡量阈值,从而获得TNTI的外边界,并以此为基准统计发现条件平均的涡量和法向速度在TNTI处骤降。根据TNTI的统计结果发现,在湍流段平均界面层,平均TNTI高度和边界层名义厚度保持线性关系。TNTI高度的概率密度函数满足正态分布。在湍流段,界面层高度的均方根(RMS)与平均界面层高度之比呈线性减小的趋势,界面层高度和瞬时摩擦力系数的相关性系数近似为0。随着湍流边界层发展,界面层高度的RMS逐渐趋于常数。

In order to reveal the development law of the spatial position of the turbulent/non-turbulent interface(TNTI)in compressible turbulent boundary layer,a direct numerical simulation is carried out for turbulent boundary layer flow of spatially evolving compressible flat-plate with Ma of 2.9.The vorticity threshold is determined by the volume fraction of the turbulent region to obtain the outer boundary of TNTI.Based on this,it is statistically found that the conditional mean vorticity and normal velocity drop sharply at TNTI.Statistical results of the TNTI show that the mean TNTI height in the turbulent flow section mean interface has a linear relationship with the boundary layer thickness.The probability density function of the TNTI height satisfies the normal distribution.In the turbulent section,the ratio of the root mean square(RMS)of the interface layer height to the average interface layer height decreases linearly,and the correlation coefficient between the TNTI height and the instantaneous friction coefficient is nearly 0.With the development of the turbulent boundary layer,the RMS of the TNTI height gradually tends to a constant.