Numerical study of momentum and heat transfer in unsteady impinging jets

Direct numerical simulations of an unsteady impinging jet are performed to study momentum and heat transfer characteristics. The unsteady compressible Navier–Stokes equations are solved using a high-order finite difference method with non-reflecting boundary conditions. It is found that the impingement heat transfer is very unsteady and the unsteadiness is caused by the primary vortices emanating from the jet nozzle. These primary vortices dominate the impinging jet flow as they approach the wall. Detailed analysis of the instantaneous flow and temperature fields is performed, showing that the location of primary vortices significantly affects the stagnation Nusselt number. Spatio-temporal behaviour of the heat transfer is analysed, with instantaneous Cf and Nu variations showing the correlation between the local heat transfer and the flow field. Near the secondary vortices, the breakdown of the Reynolds analogy is observed.