WAVE BOUNDARY-LAYERS IN A CONVERGENT TUNNEL

This work deals with turbulent oscillatory boundary layers in a conver gent-divergent channel with smooth walls. Two kinds of measurements we re conducted: velocity measurements and wall shear-stress measurements . Most of the measurements were conducted for three different values o f the half-angle of divergence beta, namely 0 degrees, 0.5 degrees and 1 degrees. Two other parameters which govern the flow are the Reynold s number, Re, and the parameter a/D where a is the amplitude of water particles at the center of the channel and D is the half-width of the channel. In the tests Re was maintained constant, approximately at Re= 6x106, while a/D as varied over a range from about 20 to 39 in most of the experiments. The results indicate that three exists a constant st reaming near the wall in the direction towards the convergent end of t he channel. The magnitude of this streaming increases with beta and al so with the distance from the divergent end of the channel. The result s further indicate that the friction coefficient increases with beta f or the convergent half period and decreases with it for the divergent half period. Regarding the turbulence, the experiments show that turbu lence is largely suppressed in the convergent half period; this is fel t even in the early stage of the following divergent half period. It r ecovers, however, shortly after and an immense growth in turbulence if observed for the rest of the divergent half period of the flow.