Title: Model-based design of wall oscillations for turbulent drag
reduction

Abstract: Flow control represents a viable approach for addressing the
global energy crisis by, for example, designing energy-efficient air
and water vehicles, and high-power wind farms. In spite of
computational and technological advances in flow control design,
optimization of these strategies is often prohibitively expensive and
scaling of the developed designs to larger and faster flows is not
straightforward. This creates a critical demand for development of
control-oriented models that promote systematic design and
optimization. In this talk, we introduce control-oriented models of
transitional and turbulent wall-bounded flows. Perturbation analysis
(in the control amplitude) is used as a basis for designing wall
oscillations that reduce turbulent drag with positive control
efficiency. The effect of control on the second-order statistics of
turbulent fluctuations in the linear time-periodic model is determined
from the solution of the corresponding Lyapunov equation. The optimal
frequency of oscillations and the turbulent flow structures that we
obtain agree well with the results of numerical simulations and
experiments. We conclude by discussing several ongoing research
directions.