Simulative Quantification of the Supersonic Discharge Process of Cold Gas Airbag Inflators

Abstract

A simulative method for quantifying the discharge process of cold gas airbag inflators is presented. The pressure, mass flow and the influences of the flow field are relevant to a robust and predictive airbag deployment. Simulations in this regard are compared and validated with experimental data. It turns out that simulated mean pressures inside the inflator deviate by 5–10% from measured data. A complex and highly turbulent flow field with supersonic and subsonic flow emerges. An influential longitudinal vortex forms in the cold gas inflator, leading to a highly dynamic discharge process. This vortex would not be found with the current state-of-the-art methods, such as the simple tank test or analytical models. It is shown that a simple turbulence model such as the k−ω shear stress transport predicts the flow field with sufficient accuracy in comparison with the large eddy simulation. Real gas effects must be taken into account inside the high-pressure reservoir, leading to a faster discharge compared to the ideal gas, due to faster moving expansion waves in the reservoir. Real gas effects outside the high-pressure reservoir seem to be negligible. A simplified simulation model was developed that uses only part of the whole cold gas inflator model and serves as a good practical approach for airbag deployment simulations, with less computational effort. Thus, the method presented here can provide high-quality inflow data for airbag deployment simulations.