Parameters governing the turbulent wall jet in an external stream

Mean velocity distributions in a plane, turbulent, and fully developed wall jet embedded in a uniform stream were measured for a variety of initial velocity ratios and Reynolds numbers. It was determined that the bulk of the flow is self-similar, provided the maximum velocity in the jet is twice as large as the freestream velocity. The normalized velocity profile depends on two velocity scales and on two length scales that, in turn, depend on the momentum flux at the nozzle, the viscosity, and the initial velocity ratio between the jet and the freestream defined by R ≡ (U_j - U_∞)/(U_j + U_∞). The width of the nozzle that was commonly used to reduce these data has no part in the similarity considerations. The approximate self-similarity may be used to estimate the skin friction that is otherwise determined with considerable difficulty.