DENSITY-MEASUREMENTS OF UNDEREXPANDED FREE JETS OF AIR FROM CIRCULAR AND SQUARE NOZZLES BY MEANS OF MOIRE-SCHLIEREN METHOD

Using the moire-schlieren method for symmetric and asymmetric 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 integrated light deflection across the flow, were converted 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 well with other experimental results, and that those for a square nozzle were much more complex than for a circular nozzle. In spite of the large difference in such profiles, the density variations along the flow axis for both nozzles were very similar to each other.