Acceleration and Injection Effects on Longitudinal Vortices in Concave Wall Boundary Layers

Measurements of longitudinal velocity and wall temperature have been obtained in a wind tunnel with a concave wall, with momentum thickness Görtler numbers from 5 to 10 at the initial station. Vortex generators were used to enhance the vortex structure in flow with zero streamwise pressure gradient. Spanwise variations existed over a limited range which is quantified. It is shown that mild acceleration amplified the vortices and enhanced the regularity of the spanwise variation; strong acceleration, with velocity gradient parameter K near 2 times 10⁻⁶, suppressed them and limited the growth in spanwise-averaged Stanton number. The influence of favourable pressure gradients was confirmed in a curved water channel with similar Görtler numbers. Discrete hole wall jets with varying jet-to-free-stream velocity ratios were used in the water channel to examine the response of longitudinal vortices to a spanwise-periodic disturbance of different wavelengths. The wall temperature characteristic of the jets persisted for a considerable streamwise distance with velocity ratios of 0.4 and unity, while a distribution not dissimilar to that without blowing was found at all stations with a velocity ratio of 1.5.