Effect of Initial Turbulence of Main Jet on the Characteristics of Reattached Jet

Abstract

In a few recent studies, it has been shown that the initial turbulence of the jet changes the jet structure significantly. However, the effect of this initial turbulence on the characteristics of the fluidic devices has never been made clear.
In this paper, therefore, effects of the initial turbulence of main jet on the static behaviour and the switching of a reattached jet are investigated. In order to increase the initial turbulence level of main jet, small high-velocity air jets are injected perpendicular to the main flow through the subjet pipe installed in the main jet duct. The results can be summarized as follows: 1. Increase of turbulence level leads to a greater loss of the jet centerline velocity and a greater spreading of the jet, and consequently caused a shorter reattachment distance and a smaller bubble region. 2. Effect of initial turbulence on the switching of a reattached jet could be explained by the decrease of reattachment distance and the increase of the jet width caused by the increase of turbulence level. 3. Effect of initial turbulence on the jet structure could be characterized by the velocity loss. By taking this velocity loss into the previous theoretical analysis, effects of turbulence on the static behaviour of a reattached jet could be predicted well.