Thermo-fluid characteristics of unsteady turbulent flow in channel with Cascade promoters.

Abstract

The heat transfer problem concering a pipe flow with turbulence promoters on the inside wall has been previously studied from the standpoint of heat transfer augmentation. Little attention has been turned to unsteady flow phenomena in channels with turbulence promoters. In this paper, the periodically fluctuating unsteady turbulent flow in channels with turbulent promoters, which is controlled by Coanda effect due to fluid ejection from the top of promoters is experimentally studied. Firstly, the flow controlling performance by Coanda effect is examined for two different promoters, and the optimum operating condition is determined. Then, variations of mean an fluctuating velocity components with space and time are obtained by the conditional sampling technique. The peaks of turbulent intensity correspond well to the gradients of mean velocity profiles, even in the transient state of the flow fluctuation. The heat transfer coefficient for the unsteady flow is constant along the flow direction, and a little enhanced due to the flow fluctuation.