Density Measurements of Underexpanded Free Jets of Air from Circular and Square Nozzles by Means of Moire-Schlieren Method

Abstract

By using the moire-schlieren method for symmetrical and asymmetrical flow fields, density distributions of underexpanded free jets of air from circular and square nozzles have been measured. Experimental moire image data of the flows, which show the integrated light deflection across the flow, were inverted to an internal density distribution by the numerical inverting method. The experiment was performed systematically by changing the pressure ratio across the nozzles from 4 to 13. It was found that the density profiles measured in the expanded free jets from a circular nozzle agreed with other experimental results on the whole, and that the results for a square nozzle showed complex flow configurations caused by the nozzle figure, nevertheless, the density distribution on the flow axis was very similar to that for a circular nozzle.