A numerical study on the eddy structures of impinging jets excited at the inlet

摘要

Three-dimensional eddy structures arising in plane and round impinging jets excited at the nozzle inlet were investigated numerically by direct numerical simulation and large eddy simulation. Special attention is focused on how spanwise or azimuthal disturbances imposed at the inlet velocity affect the eddy structures in the transition process. In this respect, three spatial wavelength of λ/πD = 1/3, 1/4 and 1/6, where D is the nozzle width or the diameter, were tested in this study. It was found that the round jet showed definite instability at λ/πD = 1/6 while the plane jet showed almost equivalent sensitivity to all modes tested here. As regards the eddy structures in the stagnation region, elongated twin vortices along the impinging plate of the plane jet were reproduced and the number of pairs was found to agree exactly with the span wise wave number imposed at the inlet. In contrast to the plane jet, no organized structures were observed in the stagnation region of the round jet.