The effect of nonequilibrium condensation on hysteresis phenomenon of under-expanded jets

Abstract

Under-expanded jets which are discharged from an orifice or a nozzle have long been subject of researches for aeronautical and mechanical applications. Provided that the jet pressure ratio and nozzle configuration are known, the major features of the steady jet are now well known. However, the jet pressure ratio is often varied even during the process in many practical applications. Many questions remain unanswered with regard to how the supersonic jet responds to the transient process of the pressure ratio and whether the steady jet data for a specific pressure ratio can still bear the same during the transient process of pressure ratio. In the present study, the hysteric phenomenon of under-expanded jets has been investigated with the help of computational fluid dynamics methods. The under-expanded jets of both dry and moist air have been employed to investigate the transient processes of the pressure ratio. The effects of nonequilibrium condensation occurring in the under-expanded moist air jets are explored on the hysteresis phenomenon. It is known that under-expanded air jet produced during the startup transient of jet behaves differently from the shutdown transient process, leading to the hysteric phenomenon of under-expanded jet. It is also known that the moist air jet reduces the hysteric phenomenon, compared with the dry air jet, and that non-equilibrium condensation which occurs in the underexpanded moist air jet is responsible for these findings.

Free underexpanded jets in a quiescent medium: A review

“…Eventually, some numerical studies seem to underline an hysteresis in this position in function of the pressure ratio [41,130,21,115].…”

Exhaust of Underexpanded Jets from Finite Reservoirs

“…The critical pressure for Mach to regular reflection transition was found to depend on the flow history, and a hysteresis loop was calculated [17]. The damping effect of nonequilibrium condensation on hysteresis was examined by Kim et al [19]. Pressure ratios of 3.0 to 6.2 were examined in increments of 0.1 in simulations and experiments.…”

Experimental study on hysteresis phenomena of shock wave structure in an over-expanded axisymmetric jet

“…As in most of the engineering applications of supersonics jets, the working gas is usually steam or moist air and the moist air jets are qualitatively similar to dry air, but non-equilibrium condensation in moist air jet affects the shock configuration, reported by Baek et al [9] and Otobe et al [10]. Meanwhile, Kim et al [11] and Otobe et al [12] have investigated the effect of non-equilibrium condensation on the hysteresis phenomenon of under-expanded supersonic jets and reported that the moist air jet reduced the hysteretic phenomenon compared with the dry air jet, and the non-equilibrium condensation that occurs in the under-expanded moist air jet is responsible for these findings. However, only a few works have, to date, been devoted to the hysteresis phenomena for the reflection type of shock wave and for instance, the transitional pressure ratio between the regular reflection (RR) and…”