DIRECT SIMULATION OF TRANSITION IN AN OSCILLATORY BOUNDARY-LAYER

Numerical simulations of Navier-Stokes equations are performed to stud y the flow originated by an oscillating pressure gradient close to a w all characterized by small imperfections. The scenario of transition f rom the laminar to the turbulent regime is investigated and the result s are interpreted in the light of existing analytical theories. The 'd isturbed-laminar' and the 'intermittently turbulent' regimes detected experimentally are reproduced by the present simulations. Moreover it is found that imperfections of the wall are of fundamental importance in causing the growth of two-dimensional disturbances which in turn tr igger turbulence in the Stokes boundary layer. Finally, in the intermi ttently turbulent regime, a description is given of the temporal devel opment of turbulence characteristics.