圆形冲击射流混合过程的LIF研究-边界条件效应

We consider the effects of the mixing conditions at the nozzle, on the mixing in a circular impinging jet. Two situations are considered: the completely premixed tracer or a locally injected tracer. The local instantaneous concentration field is determined by using Planar Laser-Induced Fluorescence (PLIF) technique. The premixed injection variant reveals the mixing effects of the outer shear layer, while the local mixing approach helps in understanding how to utilize the local injection for controlling the mixing of a scalar in an impinging jet. The concentration statistics and the mixing properties indicated by concentration probability density function (PDF) with the two injection methods are presented. The results show the well-known structural features in the turbulent impinging jet, the nature of mixing varies significantly in different regions of the jet. In the jet core region and the impingement region, the mixing is dominated mainly by the large-scale coherent structure, while in the mixing layer and wall jet region, both the large-scale structure and small scale turbulence control the mixing.