The gas generator is the safety-critical core of every airbag system. Within a few milliseconds, it must provide a defined amount of gas with precisely controlled pressure and temperature – reliably, reproducibly, and under extreme conditions. The fluid dynamics processes that occur – compression shocks, expansion waves, heat transfer, and real gas behavior – are highly dynamic and difficult to fully capture with measurement technology. Computational fluid dynamics (CFD) is therefore an indispensable tool in the development and design of modern gas generators.

Simulation of compressible flows in the gas generator

Unlike incompressible flows – such as in classical hydraulic systems – all essential effects of compressible gas dynamics taken into account. Our CFD simulations fully represent these physical phenomena:

• Shock waves – abrupt, discontinuous changes in the flow field with a sudden increase in pressure, density, and temperature; significant for pressure peaks and structural loads in the housing
• Expansion waves Prandtl-Meyer expansion at geometric transitions and nozzle sections, relevant for flow guidance and momentum distribution in the gas stream
• Compression and Expansion – Influence on temperature and pressure development during the transient filling process of the airbag cushion
• Supersonic flows and Mach number distribution – Design of nozzles and outlets for defined flow regimes

Stationary and Transient Simulation – Methodology and Tools

Depending on the question, we use stationary simulations for basic design and parameter studies, or fully transient calculations to map the highly dynamic ignition and filling process. Our simulation workflows are based on proven open-source and commercial CFD solvers and are managed via our software environment InsightCAE efficiently controlled

• Density-based solvers for compressible high-speed flows with shock capturing
• Adaptive Time Stepping for Stable Transient Simulations with CFL Criterion
• Network refinement in shock zones and near-wall regions for precise gradient resolution
• Parametrized model constructions for efficient variant studies of geometry, pressure, and gas specification

Application areas and development goals

CFD simulation of airbag gas generators supports all phases of product development – from conceptual design to virtual validation before crash testing:

• Design and optimization of nozzle and outlet geometries for defined filling behavior
• Evaluation of different generator concepts – pyrotechnic, hybrid, or cold gas – with regard to pressure-time profile and gas temperature
• Thermal protection of airbag fabric by limiting gas outlet temperature
• Functional proof at extreme temperatures according to automotive standards (e.g., -40°C to +85°C ambient temperature)
• Reduction of development costs and testing effort through virtual variant assessment before physical prototyping

Request CFD simulation for your gas generator

Are you developing or optimizing a gas generator for airbag systems or related pyrotechnic or pneumatic applications? Speak to us - we develop a precise simulation model with you that accelerates and secures your development process.