The control of flow separation: Study of optimal open loop parameters

Abstract

Effective parameters in active flow control (AFC) have been studied to clarify a perspective of AFC. In particular, NACA0015 airfoil has been chosen for this study. Fluidic devices such as a synthetic jet actuator (SJA) have been considered because these can enforce two main control parameters of AFC, frequency and momentum ratio, but fluidic excitation with complete blowing and suction cycle was applied with the harmonic excitation as the boundary condition. Flows around the NACA0015 airfoil were simulated for a range of operating conditions. Attention was paid to the active open loop control for the flow separation of the airfoil with SJA at different angles of attack and flap angles. A large number of simulations using unsteady Reynolds averaged Navier-Stokes and large eddy simulation models were performed to study the effects of momentum ratio (Cμ) in the range of 0% to 11% and non-dimensional frequency, F+, in the range of 0–2 for the control of flow separation at the various angles of attack. The optimum value of Cμ as well as F+ was evaluated and discussed. The computational model predictions showed good agreement with several experimental data available such as NASA Langley, Texas A&M, and Clarkson University. It was observed that different angles of attack and flap angles have different requirements for the minimum value of the momentum coefficient, Cμ, for the SJA to be effective for control of separation. It was also found that the variation of F+ noticeably affects the lift and drag forces acting on the airfoil. An intuitive analogy was introduced to evaluate the optimum momentum ratio in AFC, and the results of the optimum momentum ratio have been presented in comparison with available literature data.