Relation Between Cellular Structure of Underexpanded Radial Jet and Curvature Effect of Slit Nozzle

A radial underexpanded jet is a supersonic jet issuing from a small slit between two circular tubes which are placed face to face with each other. The small slit comprised of these two tubes is referred to as a ‘slit nozzle’ in this study. Such flow is a simple model of the wall jet of jets impinging on an object or the flow downstream of pressure reducing valves. In this study, the jet structure and the oscillation phenomena of the radial jet issuing from the slit nozzle was numerically investigated using the symmetric TVD (Total Variation Diminishing) scheme and the frequency of oscillation was analyzed by FFT analysis. Computational results showed that the jet had a shock cell structure. Such structure is well known to be the typical structure of underexpanded rectangular or axisymmetric jet. The most remarkable difference between the radial jet and those jets was the decreasing ratio of the cell size, and the difference becomes conspicuous if the nozzle diameter D is smaller. The oscillation behavior of the radial jet also depends on D because of its curvature effect. The frequency of oscillation decreases gradually as the nozzle diameter increases and suddenly drops at about D/b = 20, where b is the width of the slit between two tubes.