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Effectiveness of spanwise forcing for turbulent drag reduction at higher Re

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The effectiveness of open-loop spanwise-forcing techniques in reducing turbulent skin-friction drag is studied via an extensive parametric study by direct numerical simulations for increasing values of the Reynolds number Re. We consider in particular the streamwise-traveling waves introduced by Quadrio et al. The main outcome of the study is that the control parameters strongly affect the way drag reduction depends on Re. The set of control parameters yielding the maximum drag reduction changes with Re and regions of the parameter space exist where the Re-sensitivity is low. Here, with respect to what is currently believed, increasing Re has a much less dramatic (or even beneficial) effect from an energetic standpoint, since the power required for the control action may reduce with Re faster than drag reduction.

Author(s):

Davide Gatti    
Center of Smart Interfaces, Technische Universität Darmstadt
Germany

Maurizio Quadrio    
Dept. Aerospace Sciences and Technology, Politecnico di Milano
Italy

Cameron Tropea    
Center of Smart Interfaces, Technische Universität Darmstadt
Germany

Bettina Frohnapfel    
Institute of Fluid Mechanics, Karlsruhe Institute of Technology
Germany