Experimental and Computational Studies on Dynamic Stall in Low Speed Flows
In the present. studies dynamic stall phenomena have been experimentally and computationally investigated. In the computational studies two numerical methods are developed for capturing dynamic stall characteristics. One is based on discrete vortex method and the other is based on viscous calculations. In the calculations by a discrete vortex method combined with a panel method the separation point is predicted by boundary layer calculation based on integral method. Separated flows around pitching airfoils are simulated for various conditions. Various hysteresis curves of lift of airfoils at dynamic stall are obtained. The results suggest that the method has a excellent capability of simulating vortical flows with excellent small computation cost. in the calculations by viscous flow calculations incompressible Navier-Stokes equations have been solved by a third-order upwind scheme. The unsteady flow fields around a pitching airfoil are calculated by moving a grid system relative to the freestream. Remarkable characteristics of dynamic stall are obtained. Also the hysteresis curve of aerodynamic characteristics of C L and C M are obtained. In the experiments a wing section of NACA00I2, whose aspect ratio is 5, is oscillated in pitch in low-speed flow. Flow visualization by smoke-wire technique has been conducted in order to observe the flow physics. Quite different flow patterns in pitch-up and pitch-down processes are observed.
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