Momentum Coefficient Governing Discrete Jet Actuation for Separation Control

Amplitude scaling laws for active control of boundary layer separation using discrete jet forcing are not fully established. Momentum coefficient is the most widely accepted scaling parameter, but accurate measurement and assessment of the employed assumptions are often not documented or even attempted. This work discusses various methods for experimentally determining the momentum coefficient produced by fluidic oscillators. Complementary simulations of the actuator are performed using delayed detached eddy simulations to validate the methods and offer explanations for shortcomings in the experiments. Scaling methods are applied to the experimental study of separation control on the suction side of a type II Glauert airfoil, otherwise known as the NASA hump model. An array of fluidic oscillators is located at x∕c 0.68 and used to control separation over a range of Reynolds numbers (Re 3.36 × 10⁵ to 1.36 × 10⁶) for various actuator sizes 1∕4 A; A; 4A and spacings Δz∕c 2.27; 4.55; 6.82; and 9.09%. Integrated surface pressure measurements are used to determine the suitability of various momentum coefficient definitions for scaling the flow control efficacy. It is found that the momentum coefficients obtained using direct measurements of actuator plenum or throat pressure govern scaling with respect to both Reynolds number and actuator size. This is independent of the sweeping frequency in the range surveyed.