Computational and experimental studies of compressible dynamic stall

Recent efforts in the numerical analysis of massively stalled aerodynamic flows have concentrated on solving the full Navier-Stokes equations. While most of the literature of the past decade has considered only the incompressible approximation, compressible solutions are now realizable. An understanding of the effects of compressibility on the stall phenomenon will lead toimproved computational algorithms and experimental procedures. If compressibility effects are limited to certain ranges of aircraft motions and of Reynolds and Mach numbers, then the incompressible approximation may be used more reliably. Studies undertaken at the United Technologies Research Center have attempted,through computational and experimental procedures, to characterize dynamic stall at freestream Mach numbers between 0·2 and 0·4. Two computational procedures, one solving the compressible Navier-Stokes equations and the other the incompressible Navier-Stokes equations, have been used to analyse two-dimensional flows which exhibit deep, prolonged stall. Comparisons of the computational results with the experimental data base are encouraging. The generation and subsequent convection of the stall vortex are well modeled and events such as an increased lift curve slope coinciding with this vortex generation are accurately characterized. This computational and experimental investigation provides detailed aerodynamicinformation at Reynolds and Mach numbers representative both of helicopter rotor retreating blades in forward flight and of combat aircraft performing low-speed maneuvers. Motions considered are nonperiodic, constant pitch rate ramps. Airfoil angles of attack begin near the zero lift value and increase well past all dynamic stall events.