Response of turbulent pipeflow to multiple square bar roughness elements at high Reynolds number

Abstract

The response and recovery of turbulent pipeflow over multiple square bar roughness elements with periodic and staggered patterns are examined at a Reynolds number of 1.56 × 105. The square bar roughness elements have a height of h/D = 0.05 and 0.1. Two, three, and four periodically separated bar elements are considered using the smaller height of 0.05, along with one with staggered separation between four tandem elements. An asymptotic trend in response and recovery is observed with three bar roughness elements, after which no substantial variations occur with additional elements. The three elements in the pipe increase the rate of turbulent diffusion compared to cases with a smaller number of elements, which leads to a faster recovery. The separation patterns have negligible effects on the overall recovery or response as long as the elements are positioned outside the recirculation zone formed by the upstream element.