Turbulent Structure in a Pipe Flow with Inclined Cascade Turbulent Promoters

Abstract

Turbulent flow structure in a pipe with inclined cascade turbulent promoters to the pipe axis is studied experimentally as the first step to enhancement of forced convective heat transfer. Many works about the flow in a pipe having axisymmetric turbulent promoters have been reported. In a pipe flow with inclined cascade turbulent promoters, a secondary flow is induced which largely affects heat transfer. The time mean and fluctuating velocities of three directions are measured by a two-color three-beam laser Doppler velocimeter with a Bragg cell. It is found that the velocity component of the secondary flow is over 40 % of the space mean streamwise velocity. The mechanism of secondary flow generation is discussed on the basis of the experimental results for various Reynolds numbers. The pressure loss is also compared with that of the flow in the pipe with axisymmetric ribs.