Oscillating Airfoil Velocity Field During Large Amplitude Dynamic Stall

The leading edge flow field of an airfoil executing a. sinusoidal oscillatory motion and experiencing dynamic stall under compressibility conditions has been studied using a two component LDV system. Phase averaged mean velocity measurements and some flow quantities derived from it are presented and discussed. The results indicate extremely large accelerations of the flow are present around the leading edge with mean velocity values 60% higher than and instantaneous velocities as large as 1. 75 times the free stream velocity. The velocity profiles at certain locations over the airfoil resemble that of a wake

Analysis of Compressible Light Dynamic Stall Flow at Transitional Reynolds Numbers

The article of record as published may be found at http://dx.doi.org/10.2514/3.13248Numerical and experimental results of steady and light dynamic stall flow over an oscillating NACA 0012 airfoil at a freestream Mach number of 0.3 and Reynolds number of 0.54 x 10⁶ are compared. The experimental observation that dynamic stall is induced from the bursting of a laminar separation bubble points to the role of transition in influencing the flow development. Its modeling, including the changes in transition onset location and transition length with increase in airfoil angle of attack, is critical for computing the dynamic stall flow properly. In this study, the transition onset point is specified suitably and a simple transition length model is incorporated to determine the extent of the laminar separation bubble. The thin-layer approximations of compressible, Reynolds-averaged, Navier-Stokes equations are used for the numerical solution, with an implicit, upwind-biased, third-order-accurate scheme for the numerical integration. Remarkably good agreement with experiments is obtained in steady flow for the pressure and velocity distributions near the leading edge. Oscillatory airfoil flow results compare favorably on the upstroke, but on the downstroke, the computations do not predict the light stall and vorticity shedding that were observed experimentally.U.S. Naval Air Warfare Center, Weapons Division, China Lake, CAU.S. Army Research Office, Durham, NC, ARO-MIPR-125-93U.S. Naval Air Warfare Center, Weapons Division, China Lake, CAU.S. Army Research Office, Durham, NC, ARO-MIPR-125-9