סמינר מחלקתי Wygnanski

School of Mechanical Engineering Seminar
Monday, January 19, 2015 at 15:00
Wolfson Building of Mechanical Engineering, Room 206

ACTIVE FLOW CONTROL AS A FLUIDIC FENCE PREVENTING TIP STALL ON SWEPT BACK WINGS

Israel J. Wygnanski

Th is limited by flow separation. Although some principles of active separation control in two-dimensional flow are well known, their application to aircraft has not been realized partly because of wing sweep-back and partly because of the weight and complexity of the systems providing the flow control. Sweeping jet actuators overcame many of the objections stated above because they do not possess moving parts and if used in small numbers they require little mass flow and energy to operate. This is the case on swept back, high aspect ratio wings where the spanwise boundary layer flow has to be reduced in order to avoid tip stall. This observation is rooted in the application of boundary layer theory to yawed airfoils of infinite span. The concept that is commonly referred to as the “Independence Principle” was considered inapplicable to turbulent flows for more than sixty years, and it cannot be rigorously applied to finite, tapered wings. Nevertheless the precept is sufficiently robust to be reduced to practice as it broadly suggests that the spanwise flow contributes to separation although its dominance is not an indicator of stall. Experimental results at multiple scales supporting these observations will be presented and discussed.e size and complexity of an airplane wing is determined by the maximum lift that it can generate, mostly for takeoff and landing purposes, and this