Supersonic discharge of cold gas inflators into rectangular ducts

Abstract

We discuss the supersonic discharge of cold gas inflators into confined ducts typical of curtain airbag inflation. The medium discharged from the cold gas inflators is helium. For this purpose, two different generic duct geometries are chosen to obtain one case without and one with wall interaction of the underexpanded jet. In the latter case, a so-called shock train develops, which dominates the flow topology. To quantify the flow field, time-resolved pressure transducers measure the static pressure at the duct walls and time-resolved particle image velocimetry measures the velocity in the far field of the underexpanded jet. Schlieren images illustrate the topology of the flow field. A simplified numerical model is then created that drastically reduces the required resources. The numerical model is verified against the experimental data and provides deeper insight into the outflow process. In particular, the interaction of the underexpanded jet with the duct walls and thus the resulting shock train are found to be sensitive. The numerical model can reconstruct the flow topology, pressure and velocity within acceptable limits. The experimental data and numerical results may serve as a basis for subsequent studies on airbag inflation or physically similar processes, especially for the validation of numerical methods.