Effects of Pressure Gradient on Higher Order Statistics in Turbulent Boundary Layers

This paper investigates the effect and influence of pressure gradient on the skewness and flatness in turbulent boundary layers, which are subjected to adverse, zero and favourable pressure gradients. The large scale features are found to increase the skewness in the near wall-region for adverse pressure gradients in a manner similar to the effect of changing Reynolds number as documented by Metzger & Klewicki [1] for zero pressure gradient flows. The skewness is expanded by decomposing the fluctuating velocities into small and large-scale components, u+ = u+L + u+S, and the individual terms are compared. The large-scale term, u+3L/(u2)3/2, and the cross product term, 3u+L u+2S/(u2)3/2, are found to be the major contributors for the skewness factors and change drastically with pressure gradient. Further, it is found that the cross product term could replace the amplitude modulation method proposed by Mathis et al (2009) [2] in turbulence boundary layer flows with pressure gradient.