Experimental Studies on Laminarization of Turbulent Flow in a Duct with Injection

Abstract

An experimental study was made on a fully developed turbulent flow of air at a Reynolds number of 6000, entering a rectangular duct with an aspect ratio of 6 with uniform fluid injection through the bottom porous wall at two injection rates : 0.01 and 0.004. Measurements were made of the streamwise and transverse velocity distributions by means of a Laser Doppler Velocimeter. The following conclusions were drawn : (1) Close to the porous wall, the absolute value of <uv>^^- decreases rather sharply around the starting point of injection, and the flow tends to be locally laminar. This is caused by the change of mechanisms of both the turbulent production and the redistribution of turbulence. (2) Close to the upper wall, the absolute value of <uv>^^- decreases gradually as the flow moves downstream, and the flow also tends to be laminar. The tendency is caused by the flow acceleration and by the change of the redistribution mechanism of turbulence.