Laser-Doppler- and laser-dual-focus measurements in laminar and fully turbulent boundary layers

Optical techniques were applied to boundary layer measurements on a flat plate with natural transition. At freestream velocities of approximately 41 m/s (Re sub L = 10 to the 6th) and turbulence intensity of 1.6 percent, the laminar boundary layer was investigated using a laser-dual-focus velocimeter, whereas the characteristics of the turbulent boundary layer were determined with a laser-Doppler-anemometer. Off-line calculations of the flow and integral parameters of the laminar and turbulent boundary layers were carried out on a minicomputer. Utilizing the stored data of the boundary layer velocity profiles, the shear stress, boundary layer thickness, and turbulence intensity distribution are calculated. The comparison with Pitot-tube measurements, hot wire measurements, and available analytical solutions shows excellent agreement.