Large eddy simulation of a round jet into a counterflow

Abstract

A round jet into a counterflow under different jet-to-current velocity ratios was investigated using large eddy simulation. The results agree well with experimental measurements from laser-Doppler anemometry and laser-induced fluorescence that include velocity and mean concentrations along the centerline and radial direction. Vortex rings appear in the region near the jet exit and large-scale vortex structures still occur near the stagnation point. The flow becomes more chaotic and three-dimensional with the presence of these structures. In particular, their presence near the stagnation point results in large velocity fluctuations that enhance the mixing process and dilution. These fluctuations are described by probability density functions that deviate from Gaussian distribution. The three-dimensional streamlines indicate that the jet not only oscillates in three directions but also rotates about the jet axis and around the vortex. The second and third moments of the velocity or scalar fluctuations identify that the mixing processes are greater in the region before the stagnation point.