Direct Numerical Simulation of Active-Controlled Impinging Jets

In order to improve the heat transfer on the wall, impinging jets are used in various industrial applications, and have been investigated experimentally and numerically so far. However, it is not enough to make clear the detail of vortical structure contributing to the heat transfer. In the present paper, direct numerical simulations (DNS) of the impinging jet are conducted through the control of vortical structure in order to investigate the heat transfer. The discretization in space is performed with a hybrid scheme in which Fourier spectral and 6th order compact scheme are adopted. As the control parameter, two cases of perturbations are superposed on the inflow boundary conditions. These excitations contribute to the generation of coherent vortical structures, resulting in the enhancement of mixing away from the impinging wall. However, the heat transfer at the wall is not vitalized in comparison to the no excitation case. The reason why no enhancement of the heat transfer occurs are considered, based on both the balance of the heat flux and the snapshot of flow. It is found that the excitation strengthens the upward flow, which disturbs the heat transfer, and that the upward lifting of coherent vortical structures make the inactive state in the vicinity of the impinging wall.