Schlieren Studies of Compressibility Effects on Dynamic Stall of Airfoils in Transient Pitching Motion

Compressibility effects on the flowfield of an airfoil executing rapid transient pitching motion from 0 - 60 degrees over a wide range of Mach numbers and pitching rates were studied using a stroboscopic schlieren flow visualization technique. The studies have led to the first direct experiments] documentation of multiple shocks on the airfoil upper surface flow for certain conditions. Also, at low Mach numbers, additional coherent vortical structures were found to be present along with the dynamic stall vortex, whereas at higher Mach numbers, the flow was dominated by a single vortex. The delineating Mach number for significant compressibility effects was 0.3 and the dynamic stall process was accelerated by increasing the Mach number above that value. Increasing the pitch rate monotonically delayed stall to angles of attack as large as 27 degrees.AFOSR-MIPR-87-0029 and 88-0010NAVAIRAR

An Assessment of the Impact of Compressibility on Dynamic Stall

The effect of compressibility on dynamic stall is assessed, based on a review of past research in this area. A careful discussion of recent research is presented focusing on both model rotor, and 2-D dynamic stall studies where compressibility effects have been quantified. Examples from the various research efforts are discussed, and detailed analysis of the influence of compressibility on the dynamic stall process is presented. Differences between incompressible and compressible dynamic stall physics are identified, and the role of computation in the modeling of the compressible dynamic stall process is discussed.ARO-MIPR-125-93U.S. AFOS