Experimental investigation of turbulent flow in a two-pass channel with different U-turn

TL;DR

This study uses TR-PIV to analyze turbulent flow in U-shaped channels with different U-turn geometries, revealing how turning structure influences vortex formation, turbulence, and flow complexity at various Reynolds numbers.

Contribution

It provides detailed experimental insights into flow characteristics in U-shaped channels with different turning sections, highlighting the impact of geometry on turbulence and vortex behavior.

Findings

Flow structure is significantly affected by the shape of the turning section.

Increasing Reynolds number reduces vortex size and number in the corner area.

Flow at the turning section exhibits complex turbulence and wave-like structures.

Abstract

In this paper, the TR-PIV method is used to study the internal flow field characteristics in U-shaped channels. The Reynolds number, based on the square cross section channel hydraulic diameter is 8888,13333 and 17777. Mean flow, Reynolds stress and POD are taken into consideration to investigate the flow characteristic with three different turning sections. Through analysis, a series of important conclusions have been drawn. For the main flow, the structure of turning sections has obvious influence on the characteristics of flow field. The size and number of vortices in the corner area are significantly reduced, because the increase in Reynolds number makes the influx impact stronger. It can be seen from the Reynolds stress distribution which is obviously different in different turning sections that the pulsation caused by the mixing of the main flow and the vortex is obviously stronger than that at the boundary. The flow at the turning section is complex, the distribution of the proportion of turbulent kinetic energy in the low-order mode is relatively gentle, and there is an obvious wavy structure at the turning section of the inner circle and outer circular passage, which matches the velocity field from the POD.