Investigation of the Effect of Inlet Turbulence and Reynolds Number on Developing Duct Flow

Abstract

This study investigates experimentally the effects of upstream flow conditions and Reynolds number on a developing duct flow. Particle image velocimetry (PIV) and hot-wire (HW) anemometry are employed to explore the flow dynamics in a rectangular duct with an aspect ratio of 2 and a length of 40 hydraulic diameters (Dh). Experiments are employed for two Reynolds numbers, ReDh = 17,750 and 35,500 where the inlet turbulence intensity is controlled using different turbulence grids. The results show that the inlet turbulence intensity and Reynolds number have a substantial effect on the flow evolution, the onset of shear layer interaction zone, and the subsequent relaxation to the fully developed flow. The main effect is linked to the development of the boundary layer, as the turbulence intensity decays rapidly in the core flow. The detailed analysis indicates that transition to turbulence advances upstream as the inlet turbulence intensity is increased, leading to an earlier onset of shear layer interaction and the decrease in entrance length. A similar upstream advancement of laminar-to-turbulent transition is induced as the Reynolds number is increased. However, a delay in the onset of shear layer interaction regime is observed at higher Reynolds number due to lower overall boundary layer growth rate. Thus, the focus of the analysis characterization of the boundary layer development and quantification of the associated changes in the duct flow development.