Study of moderately underexpanded supersonic moist air jets

Supersonic moist air jet technologies are often applied to powerplants and industrial manufacturing processes, but the major features of supersonic moist air jets are not well known to date, including their qualitative characteristics. An experiment is performed to investigate relative humidity effects on underexpanded supersonic jet structures, such as Mach disk location and diameter, barrel shock wave, and jet boundary locations, etc. It is found that the Mach disk diameter and location are significantly influenced by the relative humidity of moist air. The Mach disk in underexpanded moist air jets is located farther upstream than in dry air jets, and the Mach disk diameter for moist air jets is smaller than that of dry air jets. The Mach disk diameter increases slightly as the relative humidity of moist air increases. Empirical equations are obtained for Mach disk diameter and location, as well as locations of the jet boundary and barrel shock, in underexpanded moist air jets.