Control Techniques for Flows with Large Separated Regions: A New Look at Scaling Parameters

Abstract

*† ‡ § Two wind tunnel investigations were conducted with the goals of gaining a better understanding of the mechanisms governing Active Flow Control (AFC) for flows dominated by large separated regions, identifying the proper parameters to use for characterizing the performance of the AFC system under these conditions, and determining the scaling relationships needed to develop AFC systems for large-scale tests and, eventually, for fullscale applications. The first series of tests utilized the ADVINT 5%-scale airfoil model, and the second series of tests utilized the ADVINT pseudoflap model. In both tests, key operational parameters were varied systematically, independently of one another with minimal variations in the model geometry. The parameters that were varied include the free-stream velocity, the AFC amplitude (characterized by the peak jet velocity Uj), the AFC forcing frequency, and most importantly the slot width. On the 5% airfoil model, where AFC primarily affected the flow by controlling circulation, it was found that the key parameter for scaling the AFC effects was the ratio Uj/U∞, and a new parameter, H, incorporating this ratio was proposed. The results of the pseudoflap test indicated that suction was more effective for controlling separation than blowing, and that the optimum locations for suction and blowing were not necessarily the same, indicating that ZMF AFC is not the best choice for controlling flows of this type. Finally, both tests showed that for flows of this type, the AFC effects do not scale with the often used momentum coefficient, Cµ, for ZMF, suction, or blowing AFC methods.