ROUND JET IN AMBIENT COUNTERFLOWING STREAM

We investigate the penetration and spreading of a round jet into an ambient counterflow using the planar laser-induced fluorescence (LIF) technique. The LIF images enable us to obtain the instantaneous concentration field of the penetrating jet effluent. Large-scale wandering of jet penetration is observed and leads to significant temporal and spatial fluctuations in the location of the dividing interface between jet effluent and ambient fluid. The penetration distance and the lateral spreading width of the jet exhibit fluctuations with covering ranges as large as their corresponding time-averaged values. The degree of fluctuations in these penetration and spreading parameters increases with the jet-to-current velocity ratio, but essentially scales with the mean penetration distance. We also attempt to predict the mean penetration distance by considering the decay of centerline jet velocity under a hypothesis that the counterflow affects the jet via a simple compression of the axial coordinates of jet flow.