Direct computation of perturbed impinging hot jets

The unsteady flow and temperature fields of an impinging hot jet at a Reynolds number of 1000 and a nozzle-to-plate distance of 6 jet diameters have been obtained by direct numerical solution of the compressible time-dependent three-dimensional Navier–Stokes equations using highly accurate numerical methods. Effects of an external perturbation on the flow and heat transfer characteristics of the transitional impinging jet have been examined. Oscillatory behaviour induced by the external perturbation has been observed for the impinging jet. The external perturbation leads to the large-scale vortical structures in the primary jet stream, which subsequently lead to the strong oscillatory behaviour of the impinging jet. The vortical structures lead to flow transitional behaviour that enhances mixing of the hot jet with the ambient fluid. It has been observed that the wall boundary layer of the impinging jet is thin. Both the instantaneous and time-averaged wall shear and normal stresses and Nusselt number are examined. Although the external perturbation strongly affects the flow structures in the primary jet stream, it does not have significant effects on the wall stresses and heat transfer characteristics of the impinging jet due to the re-laminarization effect of the wall.