Visual Observation of an Axisymmetric Impinging Jet

The behavior of flow structure of an axisymmetric impinging jet has been experimentally studied by using the flow-visualization techniques, i.e., the hydrogen bubble technique and the fluorescent dye injection. The Reynolds number based on the nozzle diameter (D=40mm) and the nozzle exit velocity is varied in the range of 4000<Re<11000. The growth of vortex-like structures visualized by the hydrogen-bubble and the dye injection is observed either from the jet axis direction or in the jet cross section. When the jet impinges on the plate, the flow structure is varied by the relation between the location of the plate and the rolling up vortex. When the nozzle-to-plate spacing is less than the nozzle diameter, the frequency of occurance of ring vortices is remarkably effected by the impingement plate. With increasing nozzle-to-plate spacing, the frequency of transport of ring vortices decreases due to the coalescence of vortices and the turbulence in the boundary layer increases.