The turbulent boundary layer with foreign gas injection—I. Measurements in zero pressure gradient

Abstract

The results of an experimental investigation are reported of the development of the turbulent boundary layer with surface mass injection. Two injectants were employed, air and freon, with normalized injection rates up to 0.8 per cent of the free-stream mass flux. For air injection the present data are in very close agreement with the measurements of Simpson et al. [3] exhibiting a weaker effect of injection on the local skin friction coefficient than the other investigations of this flow. With Freon injection, even though density variations occur between the wall and the free stream as high as 4:1, the measured velocity profiles are little different from those obtained with the same rate of air injection. Both mean velocity and concentration profiles become self-preserving after a short initial development region. Comparison of mixing-length and turbulent-Schmidt-number distributions also show no discernible difference from those obtained in uniform density flows.