Large Eddy Simulation of a single-started helically ribbed tube with heat transfer

Abstract

This work presents a study of the turbulent flow in a single-started helically ribbed tube with low blockage ratio. The Large Eddy Simulation (LES) approach is used in a wall-resolved periodic configuration. Both an adiabatic and a wall-heated simulations are performed and validated against experiment. Velocity profiles and wall temperatures were measured at the Von Karman Institute (VKI) using Stereoscopic Particle image Velocimetry (S-PIV) and Liquid Crystal Thermography (LCT) by Mayo et al. (2018). Comparisons show that the numerical methodology gives accurate results in terms of mean and fluctuating velocity fields as well as the correct friction drag. The wall temperature profile is also in good agreement with the experiment. The rib induces a large recirculation zone immediately downstream, with a reattachment point occurring a few rib heights farther downstream. The helical shape of the rib also induces a strong swirling motion close to the wall. The pressure drop is found equal to 3.37 Pa/m and is mostly due to the pressure drag. Maximum heat transfer is found just upstream of the reattachment point and on top of the ribs, which is in good agreement with experimentally obtained values. The mean Nusselt number in the ribbed tube is found 2.3 times higher than in a smooth tube confirming the positive impact of such geometry on heat transfer.