DNSを用いた開花噴流の混合特性評価

抄録

A wide variety of applications of jets enhancing mixing, diffusing, heating and cooling efficiency have been studied. For example, jets are used in the industrial processes such as combustion, ventilation and so on, and their improvement of mixing and diffusion is demanded. It is well known that the characteristics such as mixing and diffusion of the jet are markedly dependent on the large-scale vortex structures being formed near the nozzles. Therefore, as giving appropriate inflow conditions at a nozzle, it is capable of controlling the large vortex structures near field around nozzle and is expected to improve the mixing performance. In particular, blooming jets occur with superimposition of axial and helical excitations on the inlet velocity profile. Blooming jets are characterized by vortex rings moving along branches of separate streams. In previous studies, it is observed that blooming jets change the number of branches with specific frequency ratio of axial to helical. The present study evaluates the mixing performance of blooming jet using direct numerical simulation (DNS) varying the frequency ratio. It reveals that the statistical entropy and entrainment rate are obviously greater than that of unexcited jet as well as the momentum transfer of blooming jet is significantly enhanced.