Velocity Profile near Free Surface in Circulating Water Channel

Abstract

The boundary layer on the wall surface of the nozzle, the wave suppresser and the channel wall itself affects strongly to the velocity profile of the test section of a circulating water channel. The velocity near the free surface is always smaller than the uniform velocity which is normally determined by the mean value at fairly deep position. In order to obtain the uniform velocity near water surface, the rotor method, a jet-like flow generated by the rotor at the edge of the nozzle accelerates the velocity, is employed here. In this paper, it is shown that at first the two-dimensional wake theory represents the velocity defect near the free surface, and the two-dimensional jet flow theory can be used for representing the flow by the rotor itself. The uniformed velocity profile is obtained by superimposed these two prof les. The optimum rotation number of the rotor is theoretically determined as a function of the uniform velocity.