Simulations of laminar and transitional cold wall jets

The wall jet studied herein is a fundamental idealization of a refrigerated air curtain. Specifically, two-dimensional and three-dimensional idealized cold wall-jets are studied at a variety of flow conditions (different inflow profiles and Reynolds numbers) to investigate the effect on wall jet thickness and temperature distributions. The objective of the work is to allow an increased understanding of the evolution of temperature distribution within wall jets for laminar and transitional flow conditions, and the corresponding jet thicknesses. The primary simulation technique is direct numerical simulation (DNS) of the full Navier–Stokes equations, possible at modest Reynolds numbers. However, at higher Reynolds numbers a conventional Reynolds-averaged Navier–Stokes approach is also employed. Significant variations in wall jet thickness (both in terms of time-dependent variations and the time-averaged mean) are found as a function of Reynolds number, with a minimum occurring at flow speeds immediately prior to transition. The wall jet evolution (in terms of temperature distribution and jet thickness) is also sensitive to the inflow; whereby a constant gradient profile provides the lowest growth rates. Interestingly, the Reynolds-averaged Navier–Stokes approach yields quantitatively similar results to the 2-D and 3-D DNS approach at a wall-jet Reynolds number of 2000.