Correlation between density and temperature fluctuations of hypersonic turbulent boundary layers at Ma∞=8

The correlation between density and temperature fluctuations (rho ' and T ') of the turbulent boundary layer is significantly affected by wall temperature. Direct numerical simulation databases with the ratio of wall-to-recovery temperature T-w/T-r = 0.8 and 0.15 are considered. A fitting slope method and a two-dimensional correlation method are adopted to visualize the correlated behavior. The results show that an adverse trend and a separated correlated structure are found in the buffer region, which can be treated as the effects of the correlation of rho ' and T '. To reveal the correlation, several statistical analyses are conducted. It indicates that the extreme events in the flow are suppressed with wall cooling; meanwhile, the small-scale fluctuations are enhanced. The behavior of the fluctuations results from the reduced mean swirling strength and the increased radius of the vortical structures.