S0510304 DNSを用いたノズル回転制御下における衝突噴流の熱流動解析

Abstract

In order to develop a new heat transfer procedure of impinging jet, we conduct a DNS (direct numerical simulation) of controlled impinging jet. As a proposed procedure, a nozzle is rotated around a given axis normal to the impinging wall. To realize the high accurate computation, the discretization in space is performed with hybrid scheme in which sine or cosine series and 6th order compact scheme are used. For the surrounding boundary condition, in order to reduce the artificial noise due to the occurrence of vortex at the outflow boundary, a fringe technique is newly developed and introduced at the surroundings of computational volume. As a control parameters, a rotating frequency is varied. From view of instantaneous velocity magnitude and instantaneous vortex structures, it is found that jet circumferentially rotates depend on the rotating frequency in the free jet region, and that the jet diffuses largely compared to the case of the uncontrolled jet. Furthermore, in order to investigate dominant flow structures, DMD (dynamic mode decomposition) method is applied. Using DMD, for controlled case, the large-scale structures spiral flow are extracted. The local Nusselt number distribution is calculated too to estimate the heat transfer performance. For the controlled case, the heat transfer performance around the impinging position markedly decreases compared to the uncontrolled one, however it is found that a homogeneous heat transfer appears around the impinging position under a specific frequency of rotation.