Mixing of a Turbulent Wall-Jet into a Free Stream

The turbulent diffusion of a two-dimensional, plane wall-jet into a moving, uniform free-stream with a pressure gradient of zero at various ratios of jet to free-stream velocities is investigated. In order to check similarity conditions far downstream, the investigation was conducted to include 465 slot widths downstream of the slot. A method is given for reducing the results of this investigation to those of previous investigators who studied the mixing of a wall-jet in a stationary free-stream. M. B. Glauert's prediction that a simple similarity rule may not apply too far downstream of the slot is verified. In addition, Glauert's idea of dividing the flow into an inner part and an outer part with slightly different similarity rules is supported by the results of this investigation. For distances of from 20 to 400 slot widths downstream of the slot, it was found that overall similarity in the decay of the velocity excess and the growth of a characteristic jet width is possible for all ratios of jet to free-stream velocities. At high ratios of jet to free-stream velocities, the similarity parameters of the no-free-stream case are approached. Measurements of wall shear stress verify that Blasius' frictional law applies to the wall portion of the flow. The nondimensional, turbulent shear stresses are found to agree with Forthmann's values which were computed from momentum considerations.