Numerical simulations of active stabilization of laminar boundary layers

The use of active wall forcing to modify the evolution of laminar boundary layer flows has potential applications in delaying transition to turbulence and hence in drag reduction. The interaction between the wall motion and the fluid is investigated here in order to gain insight into the physics of the stabilization process, and also to determine the possibilities for stabilization by a passive wall medium. Direct numerical simulations of the time-dependent Navier-Stokes equations in two and three dimensions were performed using spectral numerical methods. The results of these simulations are analyzed to determine the relationship between wall and fluid motion necessary for stabilization and also the energy balance achieved during this process. It is shown that the stabilization procedure used results in a net transfer of energy back into the mean flow and requires that the wall do work on the fluid. This holds true for highly inflectional mean velocity profiles as well as the Blasius profile. These energy fluxes differ significantly from those associated with flow stabilization by a compliant membrane.