Computational Analysis of Gravitational Effects in Low-Density Gas Jets

This study deals with the computational analysis of the near-field flow structure in an isothermal helium jet injected into quiescent ambient air environment. Laminar, axisymmetric, and unsteady flow conditions were considered for the analysis. The transport equations of helium mass fraction coupled with the conservation equations of mixture mass and momentum were solved using a staggered grid finite-volume method. Jet Richardson numbers encompassing both buoyant and inertial jet flow regimes were considered. Buoyancy effects were isolated by initiating computations in Earth gravity and subsequently, reducing the gravity to simulate microgravity conditions in the 2.2 s drop tower. Computed results concur with experimental observations, i.e., a self-excited buoyant jet with periodic flow oscillations in Earth gravity becomes steady in microgravity. In an inertial jet, the flow oscillations occur at the same frequency regardless of the buoyancy, although the oscillation amplitude decreases in microgravity.