Resistance coefficient in a smooth concentric annular pipe

Abstract

This paper reports an experimental study aimed at determining turbulence and resistance coefficient characteristics of the flowfield in smooth concentric annular conduits. The measurements of velocity field were performed with a laser Doppler anemometer system in the flow region between the inner wall and the radius of maximum velocity (inner region).Velocity profiles along a vertical line normal to the walls are represented in terms of law of the wall. The maximum mean local velocity occurs at positions in agreement with literature formulae. For different distances from the inner wall micro and integral scales of turbulence were calculated. The results show that in flows with high Reynolds numbers small eddies tend to assume greater frequencies and that the time interval over which fluctuating velocity is correlated with itself becomes smaller. A statistical description of turbulence is also reported. The expression of the inner resistance coefficient was obtained by integrating the velocity law. The calculated resistance coefficients are in fair agreement with the experimental ones. Both are always greater than the corresponding values for circular conduits.