Experimental manipulation of wall turbulence: A systems approach

We review recent progress, based on the approach introduced by McKeon and Sharma [J. Fluid Mech. 658, 336-382 (2010)], in understanding and controlling wall turbulence. The origins of this analysis partly lie in nonlinear robust control theory, but a differentiating feature is the connection with, and prediction of, state-of-the-art understanding of velocity statistics and coherent structures observed in real, high Reynolds number flows. A key component of this line of work is an experimental demonstration of the excitation of velocity response modes predicted by the theory using non-ideal, but practical, actuation at the wall. Limitations of the approach and promising directions for future development are outlined. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793444]