Numerical Study of the Near-Field of Highly Under-Expanded Turbulent Gas Jets

For safety issues related to the storage of hydrogen under high pressure, it is necessary to deter- mine how the gas is released in the case of failure. In particular, there exist limited quantitative information on the near-field properties of the gas jets, which are important for establishing proper decay laws in the far-field. This paper reports recent CFD results for air and helium obtained in the near-field of the highly under-expanded jets. The gas jets are released from a 30-bar tank with the same opening (orifice). The Reynolds number based on the diameter of the orifice and corre- sponding gas conditions at the exit was well beyond 106. The 3D Compressible Multi-Component Navier-Stokes equations were solved directly without relying on the compressibility-corrected tur- bulence models. The numerical model was initially tested on a one-component (air-air) case, where a few aerospace-driven data sets are available for validation. The shock geometry is characterized through the Mach disk position and diameter. These are compared to the results known from the literature and to the scaling laws developed based on the dimensional analysis. In the second two-component (helium-air) jet scenario, the density field was validated and examined together with other fields, in the attempt to suggest potential initial conditions for the forthcoming far-field simulations.