Using the tools of Direct Numerical Simulation (DNS) and Linear Stability Theory (LST) we are studying active concepts to control nonlinear stages of transition. Besides the investigation of the well known wave superposition approach we developed a new method to actively control transitional disturbances. This concept uses the feedback of instantaneous flow data (wall shear stress or spanwise vorticity), obtainable at the wall to drive plain actuators. Avoiding long propagation distances between sensor and actuator this procedure (called ωz-control) results in a very effective damping in linear and nonlinear cases. With some extra improvements like spatial filters between sensor and actuator it is possible to delay transition even in strongly nonlinear scenarios like the K-breakdown scenario (transition due to fundamental resonance). Both methods have been investigated in a Blasius boundary layer. Besides the K-breakdown already mentioned for basic investigations a “linear” scenario was used, consisting of Tollmien-Schlichting waves with different propagation angles.
Active Control of Nonlinear Disturbances in a Blasius Boundary Layer (Keynote)
Gmelin, C, Rist, U, & Wagner, S. "Active Control of Nonlinear Disturbances in a Blasius Boundary Layer (Keynote)." Proceedings of the ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. Volume 1: Fora, Parts A and B. Montreal, Quebec, Canada. July 14–18, 2002. pp. 1357-1362. ASME. https://doi.org/10.1115/FEDSM2002-31044
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