Effects of an air stream on turbulent diffusion of a helium jet from a small nozzle

Abstract

In a round helium jet with a small nozzle, and a Reynolds number of 2.95 × 103, with and without an air stream, mean profiles, instantaneous fluctuations, and correlations of velocity and matter are investigated using the hot-wire technique. The characteristic difference in the behavior of the jet due to the presence of an air stream is extensively studied and summarized as follows: (1) Similarity in mean profiles is not reached at least in terms of r/z and the spreading and decay of the jet follow some slower laws, and (2) lateral turbulent diffusion is reduced while active axial turbulent diffusion is induced in the middle of the distribution of the jet. The correlations between fluctuations are established as a whole, but those between concentration and velocity fluctuations are reduced in the lateral direction. It seems that the turbulent motion of large eddies plays an important role in the transport mechanism of the flow field.