Steady and Oscillatory Flow Control Tests for Tilt Rotor Aircraft

Abstract

The purpose of this manuscript is to address one of the many questions plaguing the application of fluidic active flow control for performance enhancement over wings and airplanes. Specifically, what mode of Active Flow Control (AFC) is most effective; steady suction, steady blowing, or a periodic variation of both? The tilt rotor model is chosen because it represents very demanding requirements over a wide range of incidence angles, α, varying from −90°<α<+20° and flap deflections 0°<Δ_f<85° as it transitions from hover to cruise.

Measurements were carried out on a V-22 airfoil that has a simple flap (contrary to the flap being used currently on the airplane) with AFC emanating from a single slot carved in the flap for the purpose of download alleviation. The same slot was used to improve the performance of the airfoil in cruise and determine its dependence on the method of flow control. Levels of momentum input and the frequency of the periodic actuation were investigated as well. Steady and oscillatory suction and pure (zero mass flux) periodic perturbations proved to be very effective at low momentum coefficients while steady blowing required a large threshold value be exceeded before proving its effectiveness. These observations apply in cruise and hover alike. Download measurements were also carried out on a three-dimensional, 1/10^th scale model of the airplane whereupon the two dimensional parametric studies were confirmed. The use of suction reduced the download on the model by 30% while weak periodic excitation reduced it by 16%.