Large-eddy simulation of a planar offset wall-jet with heat transfer: Characterization, turbulent kinetic energy and Reynolds shear stress budgets

Abstract

Planar wall-attaching offset jets can be found in a variety of engineering applications. In the present work, a planar turbulent offset wall-jet, at a Reynolds number of 7500 and an offset-ratio of 5, with heat transfer is numerically studied using large-eddy simulation (LES). First, a grid sensitivity study is performed and the quality of the mesh used is assessed using LES index of quality of resolution and an appropriate mesh is selected. Next, the solver is validated for mean streamwise velocity, streamwise Reynolds normal stress, and the evolution of coefficient of pressure on the wall, using reference experimental data from the literature. Thereafter, the unsteady flow features of the jet, maximum velocity decay and jet-spread, statistical features of flow and temperature, and turbulent kinetic energy (TKE) budgets and in-plane component of Reynolds shear stress are studied. The streamwise evolution of Nusselt number on the wall shows three distinct peaks and the location of these peaks correlates with a change-of-sign of the wall skin-friction coefficient. The domain can be categorized into three distinct regions namely, the recirculation, impingement and wall-jet regions. Distinct flow and thermal characteristics are observed depending on the region of interest. The peak magnitudes of Reynolds normal and shear stresses increase as one moves from the recirculation region to the impingement region and decreases thereafter attaining a lowest value in the wall-jet region. The heat transfer from the wall is observed to be most effective in the recirculation region. The production of TKE is dominant in all the three regions of the flow, whereas the Reynolds shear stress budgets indicate that the production and velocity–pressure-gradient terms are dominant and balance each other in all the three regions of the flow.