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Numerical Simulation and Design of Aspirated Inflator in Airbag
The aspirated inflator in airbag basically uses the principle of Coanda effect in an interior flow field. The high-pressure gas flowing through the primary nozzle speeds up and lowers its pressure to entrain air from the environment. Then the gas flows through a diffuser that increases the static pressure of the gas so as to open the airbag. The aspirated inflator can lower the use of bursting charge, and may provide a safer means as well as less environmental pollution. The mixed gas will decrease the danger of burn.
Numerical analysis uses a computational fluid dynamic (CFD) package Fluent. The simulations are focused on the axisymmetric EXAIR and 2D symmetric inflators. The flow fields are unsteady with the assumption of ideal gas. The Standard k —εmodel is employed to solve the continuity and Navier-Stokes equations. Simulations results show that aspirated inflator can continue entrain environmental air. Discuss of the flow characteristics ranges from the aspiration ratio to the Coanda effect, shock wave and dimension of the inflator.
In this study, the environmental effects, including surrounding temperature, the high-pressure inlet temperature and pressure, on the aspirating process and aspiration ratio of the inflator are further examined. It is found that the effects due to the inlet temperature and pressure agree well with the predictions of one-dimensional theorem with a difference below 5 % except for the pressure variation. Consequently, the one-dimensional theorem is valuable to some extend for estimating the aspiration ratio of two-dimensional inflator.
This study addresses the suggestion of revising the axisymmetric EXAIR and 2D symmetric inflators. For the revised inflators, reversed flow is eliminated and therefore the aspiration capability is enhanced. This simulation analysis provides useful information for experiments and design of the aspirated inflator.
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