A demonstration of MEMS-based active turbulence transitioning

At Re = 25000 an active transition to turbulence was demonstrated on a cylinder equipped with flush mounted micro-electro-mechanical-systems (MEMS) shear stress sensor arrays and a thin spanwise slit for internal acoustic perturbations. MEMS hot film sensor arrays measured separation and vortex shedding data which were used to aim and tune acoustic perturbations to the boundary layer; this produced an instability-driven acceleration of the transition process. Perturbations tuned to the instability frequencies (Strouhal number of 2 at Re = 25000) and directed at the separation point achieved dramatically higher root-mean-square (RMS) fluctuation levels, thereby delaying separation and reducing wake velocity delicits of the cylinder. Time histories and spectral analysis map the amplification of the input disturbances by the shear layer instability. (C) 2000 Published by Elsevier Science Inc. All rights reserved.