DNS of Turbulent Boundary Layers in the Quasi-Laminarization Process

In this investigation, Direct Numerical Simulations (DNS) of turbulent spatially developing boundary layers (SDBL) with prescribed Very Strong Favorable Pressure Gradients (VSFPG) are performed by means of the Dynamic Multi-scale Approach (DMA) developed by Araya et al. JFM, 670:518–605, 2011 [1]. Although the prescription of an external VSFPG significantly reduces turbulence production, the flow never becomes completely laminar due to the finite value of the streamwise Reynolds normal stress, and thus the flow is quasi-laminar. In this sense, the mean flow carries the footprint of turbulence, particularly in the streamwise direction of the Reynolds stresses. In addition, the vertical transports toward the wall of \(\overline{v'^{2+}}\) and \(\overline{uv'^{+}}\) practically disappear in the inner region and significantly decrease in the outer region of the boundary layer during the quasi-laminarization stage. As a consequence, the “communication” between inner and outer regions is seriously restricted.