Numerical Investigation Into the Effects of CoFlow Air on a Self-Excited Helium Jet

A numerical investigation is carried out on a helium jet having Reynolds number 150, and Richardson number 6.11. The effect of air co-flow on a self-excited helium jet is studied in the near field using commercial software ANSYS Fluent V18.1. The co-flow velocity ratio varied in the range of 0.17–0.87. The contours of the helium mole fraction along with the streamlines show the interaction of the toroidal vortex with the jet. The suppression of toroidal vortex is observed as the air co-flow velocity induced to the jet flow. Due to the suppression of vortices, radial spread/diffusion is limited, resulting in large gradients at the shear layer. The flickering frequency increases with the air co-flow. The amplitude of the oscillation at axial locations of higher z/d increases up to a certain co-flow velocity and then drops significantly at high co-flow velocity ratios. However, at upstream (near jet exit plane), oscillation amplitude decrease with increase in air co-flow. The velocity difference in the shear layer to the ambient elucidates the stabilization mechanism of the self-excited helium jet.

Modeling of a reaction control jet interacting with high-speed cross-flow in slip flow regime

Numerical investigation of a sonic reaction control jet interacting with the high-speed cross-flow has been carried out over a generic missile body. Simulations are performed in the early-hypersonic slip flow regime for air, CO2, and helium jet gases. An open source computational fluid dynamics tool, OpenFOAM is used to model the steady state, three-dimensional compressible Navier–Stokes equations with k-ω shear stress transport turbulence model. The conventional computational fluid dynamics solver is extended with additional features, such as transport of species, nonequilibrium boundary conditions for velocity slip and temperature jump, and a heat load calculation utility based on the sliding friction effect. The extended solver is validated with the direct simulation Monte Carlo results for the case of a sonic argon jet injected into hypersonic nitrogen cross-flow. The extended solver is able to accurately capture all the qualitative flow features like separation shock, bow shock, and barrel shock, and it also improves heat load predictions in the slip flow regime. The main objective of the present work is to study the effect of rarefaction and change in jet gas species on the complex flow topology, heat load distribution, and spread of jet gas on the missile body. Heat load predictions are found to be strongly dependent on the slip velocity of molecules in addition to the temperature gradient near the wall. The strength of a bow shock and a barrel shock is higher for helium jet, compared to air and CO2 jets, which spread more along the missile body, and weaker shocks and reduced heat load is generated. The current work is significant from the perspective of the thermal design of spacecraft surfaces and positioning of the optical sensors.