Abstract
A gas-jet momentum force drives the air bag into position during a crash. The magnitude of this force can change as a result of aspiration. To determine the potential magnitude of the effect on the momentum force and mass flow rate in an aspirated system, a series of experiments and simulations of those experiments was conducted. The simulation consists of a two-dimensional unsteady isentropic CFD model with special “infinite boundaries”. One of the difficulties in simulating the gas-jet behavior is determining the mass flow rate. To improve the reliability of the mass flow rate input to the simulation, a sampling procedure involving multiple tests was used, and an average of the tests was adopted.
Highlights
To help protect both the driver and the front seat passenger in a frontal crash, the air bag has been developed as a supplemental restraint system
A current area of research has been the gas jet that issues from the mouth of the air-bag canister and pushes the air bag toward the occupant
The numerical model presented provides computed output in reasonable agreement with measured data for two cases, one with air aspiration and one without. This agreement supports the position that the numerical model may be of considerable value in analysis and design of the dynamic behavior of inflator-canister air-bag systems
Summary
To help protect both the driver and the front seat passenger in a frontal crash, the air bag has been developed as a supplemental restraint system. The pressure inside the inflator was measured and used to calculate the mass flow rate. The gas jet in the experiment issues out of the air-bag canister and strikes the drum The concept is one of extending the characteristics-like lines that exist outside the computational domain (i.e., those beyond the infinite boundary), back in time to the initial undisturbed conditions. The total reaction force is found by integrating over the entire area A of that boundary In both cases the input mass flow rate for the simulation is computed directly from the measured time history of pressure inside the inflator, under the assumption that the flow at the exit of the hole of the inflator is sonic. In as much as the force is dominated by the momentum flux, it is natural that the force follows the pattern of the inflator mass flow
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