PIV-Measurements of unsteady flow fields in different wind tunnels

Abstract

For the first time the unsteady flow field above a NACA 0012 airfoil oscillating in pitch has been investigated in a wind tunnel by means of Particle Image Velocimetry. Due to the short measuring time of only few microseconds instantaneous flow fields could be measured. First, the static stall at low Mach numbers and high angles of incidence (Ma &#61 0,25, alpha &#61 5 -25) and at high Mach numbers and low angles of incidence (Ma &#61 0,75, alpha &#61 0 -5) with shocks embedded in the flow field has been investigated in the high speed-blow down wind tunnel of DLr Goettingen. Then the unsteadyflow fields above an airfoil under dynamic stall conditions (oscillation frequence f &#61 6,6 Hz) have been measured in the subsonic wind tunnel of the French German research Institute of Saint Louis (ISL). The results show the strong unsteady behaviour of the flow above the profile, especially in the downstroke raegime and allow a better understanding of the dynamic stall process. The experimental data and the quantities derived from them as vorticity are of such high quality that they allow a comparison with results of numerical calculation.