EXPERIMENTAL STUDIES ON FLOW TRANSITION OF A PLANE WALL-JET

Flow transition in the developing region of a plane wall jet is studie d experimentally by means of hot-wire measurements. The Reynolds numbe r, based on the jet exit velocity and nozzle exit height, varies from 3 x 10(2) to 3 x 10(4) in the investigations. The results indicate tha t the most important factor causing wall jet flow to change from the i nitial exit state to the final turbulent state is the rapid increase o f turbulent intensity from the formation of vortical structures and th eir interactions with the wall. Data also shows that the transition pr ocess of the wall jet depends on the Reynolds number in the operating range. When the Reynolds number is greater than 2000, the mean velocit y distribution of the wall jet changes directly from a top-hat profile at the nozzle exit to a turbulent profile in the turbulent developed region. When the Reynolds number is smaller than 2000, Glauert's lamin ar velocity profile is found between the nozzle exit and the turbulent region. It is also found that the transition will be delayed and the transition region prolonged with the decrease of the Reynolds number.