High-Resolution LDA Measurements of Reynolds Stress in Boundary Layers and Wakes

The turbulent character of the boundary layer and wake associated with an airfoil has been studied at a Reynolds number of 10(exp 6) and a Mach number of 0.1. To accomplish these measurements, a unique laser Doppler anemometer (LDA) has been developed that is capable of sensing two velocity components from a remote distance of 2.13 m. Using special simultaneity logic and counter-type signal processors, the geometrical features of the LDA have been exploited to provide variable spatial resolution as low as 0.2 mm. By combining the LDA with an on-line computerized data acquisition and display system, it has been possible to measure mean velocity and Reynolds stress tensor distribution at several locations along the upper surface of a 0.9 m chord, flapped airfoil installed in the Ames 7- by 10-Foot Wind Tunnel.