Fundamental Research on Flow and Heat Transfer Characteristrics of Turbulent Duct Flow with Injection

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Numerical analysis was carried out for thurbulent aif flow in a circular tube with uniform injection through the tube wall surface. The analysis was found to be useful for predicting the skin-friction coefficient and the pressure gradient in the self-preserving flow region. The present analysis predicted also qualitatively well the local reduction of turbulence intensity in a region just downstream of the starting point of the injection.An experimental study was made on a fully developed turbulent flow of air at a Reynolds number of 6000, entering a rectangular acrylic duct with uniform fluid injection through the bottom porous wall at two injection rates. 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 both the turbulence production and the redistribution of turbulence. (2)Close to the upper wall, 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.The signals obtained above were also processed by using a quadrant method. It was found that the Reynolds shear stress caused by the ejection in the coherent fluid motion near the porous wall decreases with an increase of the injection rate.Some features of the turbulent duct flow with injection were clarified by the present research. The numerical analysis for predicting quantitatively the relaminarization near the starting point of injection and measurement of turbulence quantities in the self-preserving flow ragion will be proceeded in the near future.