Dynamics of shear-coaxial cryogenic nitrogen jets with acoustic excitation under supercritical conditions

A comprehensive numerical investigation has been conducted into the flow dynamics of a shear coaxial injector and its response to transverse acoustic excitations under supercritical conditions. The model accommodates full conservation laws and real-fluid thermodynamics and transport phenomena, and is numerically implemented on a distributed computing facility using a multi-block domain decomposition technique. As a specific case, the injection of liquid nitrogen through the inner tube at a lower velocity and gaseous nitrogen through the outer annulus at a higher velocity was explored. The near-field flow evolution is characterized by the three mixing layers originating from the rims of the two concentric tubes. The characteristic frequency of the recirculating wake flow downstream of the inner tube match the dominant vertex shedding frequency in the shear layers. A larger velocity ratio of the outer-to-inner jets enhances entrainment of the outer stream into inner region and consequently, results in a shorter inner potential core and a larger spreading angle of the outer shear layer. A higher chamber pressure results in a shorter inner potential core and a smaller spreading angle. The phenomena can be attributed to the momentum flux ratio and density ratio effects. The effect of acoustic excitation on the jet flow evolution is apparent even at a small amplitude of acoustic pressure oscillation at 0.3% of the mean chamber pressure. The jet exhibits sinuous-like structures in the slices perpendicular to the acoustic velocity direction.