Dynamics of Supercritical-pressure Coaxial Jets Submitted to Transverse Acoustic Modulations.

摘要

Large-Eddy Simulation of transcritical turbulent mixing is investigated in this report. This analysis is motivated by rocket propulsion applications where cryogenic oxygen is injected at low temperature, below the critical value, in a high pressure environment where the pressure is above critical. This situation is here envisaged by analyzing the behavior of a nitrogen jet delivered by a shear coaxial injector comprising an inner stream injected at temperatures close to the critical temperature and a coaxial flow at a higher temperature. Real gas Large Eddy Simulations are carried out for selected experiments previously performed at AFRL, Edwards Air Force Base (USA). Two geometrical configurations associated with two sets of mass flow rates have been studied at AFRL (LarThin and SarThick). They lead to different jet dynamics and subsequently different responses to acoustic modulation. Calculations retrieve what is observed experimentally both in the absence of an external modulation and under transverse acoustic field. It is shown in particular that in the LarThin case the acoustic forcing produces large scale transverse oscillations of the inner stream and promotes the formation of counter rotating vortices in the wake of the high density jet. These coherent structures stretch the inner jet, increasing the mass exchange surface between the two streams and the mixing efficiency. In the SarThick situation, a large scale back flow is established around the inner jet, which limit its downstream penetration promoting recirculation of cold fluid behind the thick lip. The acoustic modulation has a limited effect on the jet geometry in this case, probably because of the presence of this dynamic back flow region. The inner jet length is nevertheless reduced in a significant way. and the injection temperature is below the critical value for at least one of the propellants.