Boundary-layer-tripping studies of compressible dynamic stall flow

The challenging task of properly tripping the boundary layer of a leading-edge-stalling airfoil experiencing compressible dynamic stall at Reynolds numbers between 3.6 X 10 5 and 8.1 X 10 5 has been addressed. Real-time interferometry data of the flow over an oscillating airfoil have been obtained at freestream Mach numbers of 0.3 and 0.45. The airfoil was tripped by separately placing five different trips of varying lengths near the leading edge. The trip heights ranged from 40 to 175 μm. The resulting flow and airfoil performance were evaluated using the criteria of elimination of the laminar separation bubble that otherwise forms, delay of dynamic stall onset to higher angles of attack, and production of consistently higher suction peaks. Quantitative analysis of the interferograms showed that the laminar separation bubble was still present with the smallest trip and premature dynamic stall occurred with the largest trip. The right trip was determined to be a distributed roughness element extending from 0.5 to 3% chord. Its height was found to compare reasonably with the airfoil boundary-layer thickness at the dynamic stall vortex formation angle of attack, at a location slightly upstream of the vortex origin in the adverse pressure gradient region.

[1]  S. S. Davis,et al.  Measurements of discrete vortex noise in a closed-throat wind tunnel , 1975 .

[2]  Miguel Visbal.  Effect of compressibility on dynamic stall of a pitching airfoil , 1988 .

[3]  M. S. Chandrasekhara,et al.  Flow visualization studies of the Mach number effects on the dynamic stall of an oscillating airfoil , 1989 .

[4]  J. H. Preston.  The minimum Reynolds number for a turbulent boundary layer and the selection of a transition device , 1958 .

[5]  Peter F. Lorber,et al.  Unsteady Stall Penetration Experiments at High Reynolds Number , 1987 .

[6]  D. G. Mabey,et al.  A review of scale effects in unsteady aerodynamics , 1991 .

[7]  M. S. Chandrasekhara,et al.  Quantitative study of unsteady compressible flow on an oscillating airfoil , 1994 .

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

[9]  M. S. Chandrasekhara,et al.  Interferometric investigations of compressible dynamic stall over a transiently pitching airfoil , 1994 .

[10]  Yasuharu Nakamura,et al.  The effects of surface roughness on the flow past circular cylinders at high Reynolds numbers , 1982, Journal of Fluid Mechanics.

[11]  M. S. Chandrasekhara,et al.  Schlieren studies of compressibility effects on dynamic stall of airfoils in transient pitching motion , 1990 .

[12]  L. Carr,et al.  Compressibility effects on dynamic stall , 1996 .

[13]  O. Lambert,et al.  Dynamic Stall on Advanced Airfoil Sections , 1981 .

[14]  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.

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

[16]  M. S. Chandrasekhara,et al.  An Assessment of the Effect of Compressibility on Dynamic Stall , 1995 .

[17]  M. S. Chandrasekhara,et al.  Transition effects on compressible dynamic stall of transiently pitching airfoils , 1993 .

[18]  Gregory J. Walker,et al.  Effects of Free-Stream Turbulence and Adverse Pressure Gradients on Boundary Layer Transition , 1992 .

[19]  J. Hoffmann,et al.  Effects of freestream turbulence on the performance characteristics of an airfoil , 1991 .

[20]  Rand N. Conger,et al.  Pressure measurements on a pitching airfoil in a water channel , 1993 .

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

[22]  John A. Ekaterinaris.  Compressible studies on dynamic stall , 1989 .