Interferometric investigations of compressible dynamic stall over a transiently pitching airfoil

The compressible dynamic stall flowfield over a NACA 0012 airfoil transiently pitching from 0 to 60 deg at a constant rate under compressible flow conditions has been studied using real-time interferometry. A quantitative description of the overall flowfield, including the finer details of dynamic stall vortex formation, growth, and the concomitant changes in the airfoil pressure distribution, has been provided by analyzing the interferograms. For Mach numbers above 0.4, small multiple shocks appear near the leading edge and are present through the initial stages of dynamic stall. Dynamic stall was found to occur coincidentally with the bursting of the separation bubble over the airfoil. Compressibility was found to confine the dynamic stall vortical structure closer to the airfoil surface. The measurements show that the peak suction pressure coefficient drops with increasing freestream Mach number, and also it lags the steady flow values at any given angle of attack. As the dynamic stall vortex is shed, an anti-clockwise vortex is induced near the trailing edge, which actively interacts with the post-stall flow.

[1]  Y. Aihara,et al.  Transient Aerodynamic Characteristics of a Two-Dimensional Airfoil During Stepwise Incidence Variation , 1985 .

[2]  Peter F. Lorber,et al.  Airfoil dynamic stall at constant pitch rate and high Reynolds number , 1987 .

[3]  M. S. Chandrasekhara,et al.  A phase-locked high-speed real-time interferometry system for large amplitude unsteady flows , 1995 .

[4]  M. S. Chandrasekhara,et al.  Design and development of a facility for compressible dynamic stall studies of a rapidly pitching airfoil , 1989, International Congress on Instrumentation in Aerospace Simulation Facilitie.

[5]  M. S. Chandrasekhara,et al.  A real time interferometry system for unsteady flow measurements , 1991, ICIASF '91 Record., International Congress on Instrumentation in Aerospace Simulation Facilities.

[6]  M. S. Chandrasekhara,et al.  Flow visualization studies of the Mach number effects on the dynamic stall of an oscillating airfoil , 1990 .

[7]  M. Francis,et al.  Airfoil dynamic stall performance with large-amplitude motions , 1985 .

[8]  M. S. Chandrasekhara,et al.  A Study of Dynamic Stall Using Real Time Interferometry , 1994 .

[9]  M. S. Chandrasekhara,et al.  Design and development of a compressible dynamic stall facility , 1992 .

[10]  M. S. Chandrasekhara,et al.  Schlieren studies of compressibility effects on dynamic stall of transiently pitching airfoils , 1993 .

[11]  Eric J. Jumper,et al.  Lift-curve characteristics for an airfoil pitching at constant rate , 1986 .

[12]  Christopher Kedzie,et al.  Unsteady Aerodynamic Forces at Low Airfoil Pitching Rates , 1988 .

[13]  J. S. Shang,et al.  Assessment of Technology for Aircraft Development , 1995 .

[14]  R. J. Goldstein.  Optical systems for flow measurement: shadowgraph, Schilieren, and interferometric techniques. , 1983 .

[15]  Miguel R. Visbal,et al.  Dynamic stall of a constant-rate pitching airfoil , 1990 .

[16]  J. H. Strickland,et al.  An Experimental Investigation of an Airfoil Undergoing Large-Amplitude Pitching Motions , 1985 .