Steady and Unsteady Excitation of Separated Flow over the NASA Hump Model

Abstract

Separated flow and its control over the NASA hump model were investigated at subsonic speeds. Three-dimensional, unsteady fluid dynamic simulations were supplemented by wind tunnel measurements. Flow control was implemented by means of spatially distributed discrete jets operating in steady and unsteady modes. The effects of excitation amplitude and frequency were studied numerically and experimentally. Several integral parameters were explored as quality metrics. In addition to the existing ones, two new integral parameters, which are slightly modified versions of the normal force and moment coefficients, were introduced. These two parameters together with pressure drag coefficient were found to be well correlated with the flow control and used in the performance evaluation of different flow control methods including, zero net mass flux actuators, steady suction, sweeping jet actuators, and the currently studied steady and unsteady excitations. For the cases tested, it was found that the unsteady excitation is superior to the steady excitation and slightly better than the sweeping jet actuators whereas the steady suction was found to be the most effective. Although the numerical simulations overpredict the separation bubble, these simulations capture the salient features of flow separation control and hence help us to understand the effect of steady/unsteady excitation on the separated flow. splitter plate, and the jet nozzles. Several integral parameters were explored to evaluate different flow configurations. The performance evaluation of different flow control methods including the current and previously tested methods was performed using the integral parameters. low amplitude excitations ( C µ = 0.11%). Results of zero net mass flux (ZNMF) actuators, sweeping jet (SWJ) actuators from previous studies were compared to the currently studied steady and unsteady excitations. Although all AFC methods increased the upstream suction pressure and pressure recovery downstream, the ZNMF actuators were found to be the least effective at this configuration. The ZNMF actuators generated an even higher-pressure drag coefficient although the separation bubble was reported to be reduced. The current unsteady excitation was found to be the most effective AFC method, closely followed by the SWJ actuators. The AFC methods were also compared at slightly higher amplitudes ( C µ = 0.24%).