January 30, 2013, ESB 2001

Notwithstanding the computational and technological advances in flow control design, optimization of these strategies is often prohibitively expensive and scaling of the developed designs for implementation at higher Reynolds numbers is not straightforward. This creates a critical demand for development of control-oriented models that promote systematic design and optimization. In the first part of this talk, we introduce a control-oriented model of turbulent channel flows and utilize it for simulation-free design of drag reducing wall oscillations. The optimal frequency of oscillations and the turbulent flow structures that we obtain agree well with direct numerical simulations and experiments at low Reynolds numbers. In the second part of the talk, we study the Reynolds number scaling of the rank-1 approximation to the uncontrolled turbulent channel. We reveal the self-similarities of the streamwise energy density for the model subject to broadband forcing, and show that the energy density can be shaped to predict the streamwise energy intensity at technologically relevant Reynolds numbers (Re_tau ~ 10^3 - 10^10). The two parts of the talk will be integrated to predict the effect of wall oscillations on high-Reynolds number turbulent channels.

Rashad Moarref received his PhD Degree in Electrical Engineering from the University of Minnesota in January 2012. He is currently a Postdoctoral Scholar at the Graduate Aerospace Laboratories of the California Institute of Technology (GALCIT). His research interests are in the broad area of flow control design and include developing model-based approaches for preventing/suppressing turbulence in wall-bounded shear flows.