Comparison of turbulence closures for optimized active control

• Simulation of the flow above a backwards facing step with a synthetic jet actuator.
• Optimization of the actuation parameters with a statistical learning approach.
• Comparison of the results for four turbulence closures.

Active flow control strategies, such as oscillatory blowing/suction, have proved their efficiency to modify flow characteristics for various purposes (e.g. skin friction reduction, separation delay, etc.) in case of rather simple configurations. To extend this approach to industrial cases, the simulation of a large number of devices at real scale and the optimization of parameters are required. In this perspective, numerical simulations based on Reynolds-Averaged Navier–Stokes (RANS) equations seem to be the most appropriate framework, despite the well known limitations of turbulence closures in the context of unsteady separated flows. Thus, the objective of this work is to evaluate the ability of RANS models for the optimization of control devices and compare the results obtained using different turbulence closures. In this perspective, an incompressible RANS solver for unstructured grids is coupled with a surrogate-based global optimizer. The resulting tool is applied to derive an optimal actuation, based on an oscillatory blowing/suction device, for a set of turbulence closures including two-equation eddy-viscosity models and an explicit algebraic Reynolds stress model. As test-case, the reduction of the separation length for a backward facing step is targeted. Results are finally compared and analyzed, in terms of flow characteristics and optimal actuation parameters found.