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CFD analysis of the flow from an airbag inflator module
Abstract and Figures
The deployment kinematics of an airbag depends significantly on the flow generated by the inflator module. Important design parameters are not only the flow characteristics of the gas generator, but also the geometry of the inflator housing. With the aim of improving understanding of the influence of these parameters on full deployment of the airbag, this study presents a detailed CFD analysis of an idealised inflator housing. The
idealised configuration is used to investigate the deflection of the inflator gas by the airbag retainer ring. In particular, the dependence of jet deflection angle and wall pressure distribution on the relative positioning of the gas jet and retainer ring is quantified. A second focus is on the differences of single- and multi-species
representations of inflator and ambient gases. All simulations are performed with a new Cartesian cut-cell solver based on Adaptive Mesh Refinement (AMR) and dynamic domain decomposition for Massive Parallel Processing (MPP). In a final step, early deployment of the airbag is simulated and analysed incorporating the results of the analysis of the idealised inflator housing.
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... At the beginning of membrane inflation, caused by the high pressure charging gas, the top of membrane uplifts rapidly. Then, both ends of membrane deploy, and form bumps just like the phenomenon appeared in unfolded airbag deployment [12] , lead to uneven deployment. Then, because of none support under membrane, two ends of membrane swing downward, just like the phenomena observed in [13]. ...
Numerical investigation on the fluid structure interaction in the cylindrical membrane inflation is performed by the Euler-Largrangian method. In membrane inflation, the vortex flow and wave system induced by the interaction between compressible jet flow and membrane appeared inside membrane. This phenomenon concentrates the stresses and generates a pair of bumps. The influences of oscillation and bumps on membrane working performance and safety are also investigated.
Safety is a widely spread topic in engineering, from specific producing processes to everyday life. Innovation of passenger cars belongs to the frontline of industrial sector. Higher and higher performance motors, more streamlined vehicle dynamics, more reliable autonomous vehicles, and minor noise and vibration are the most expected developments what customers prefer. However, it is not allowed to forget automotive safety, which effectiveness prevents fatalities to drivers and passengers. A very important part of this safety system are the airbags. Frontal airbags aim at preventing serious injuries from impacts of the driver’s or passenger’s head or upper body against the steering wheel or other parts of the vehicle. Worldwide almost every vehicle produced with frontal or front-seat passenger airbags. Their improvement and investigation of operation is a main role of production. Pressure rise and gas temperature in bladders are significant information related to their operating mechanism. Many investigations can be found in literature which describe the occurring processes during the explosion. Most of them are computational or experimental ones, and others sets up mathematical models. This paper presents options of modelling pressure rise in automotive airbags and inflators. © 2018, Springer International Publishing AG, part of Springer Nature.
Preliminary verification and validation of an efficient Euler solver for adaptively refined Cartesian meshes with embedded boundaries is presented. The parallel, multilevel method makes use of a new on-the-fly parallel domain decomposition strategy based upon the use of space-filling curves, and automatically generates a sequence of coarse meshes for processing by the multigrid smoother. The coarse mesh generation algorithm produces grids which completely cover the computational domain at every level in the mesh hierarchy. A series of examples on realistically complex three-dimensional configurations demonstrate that this new coarsening algorithm reliably achieves mesh coarsening ratios in excess of 7 on adaptively refined meshes. Numerical investigations of the scheme's local truncation error demonstrate an achieved order of accuracy between 1.82 and 1.88. Convergence results for the multigrid scheme are presented for both subsonic and transonic test cases and demonstrate W-cycle multigrid convergence rates between 0.84 and 0.94. Preliminary parallel scalability tests on both simple wing and complex complete aircraft geometries show a computational speedup of 52 using 64 processors with the run-time mesh partitioner. © 1999 by the American Institute of Aeronautics and Astronautics, Inc.
In accordance with National Highway Traffic Safety Administration (NHTSA) regulations and, in particular the Federal Motor Vehicle Safety Standard (FMVSS) 208 for the protection of vehicle occupants from a deploying airbag, the development of frontal restraint systems is driven by new technologies and technical solutions to cover the challenging out-of-position (OoP) load case. Considering the subject of the driver airbags, traditional module technology addressed only the energy absorption capability to protect the driver occupant while in-position for a severe frontal crash load case. The early unfolding characteristics of the deploying airbag and its physical effects on the environment did not therefore form part of the engineering focus at that time. This paper will discuss an advanced driver airbag (DAB) module devised to deploy in an initially less aggressive mode, thereby exposing occupants seated OoP and close to the airbag's effective working area to less risk. The airbag inflation is divided into a primary and a secondary deployment phase by chambering the cushion with internal gas deflection fabric walls. After reaching an internal threshold pressure, these walls fail at a predetermined enervated split line. This leads to full bag deployment to ensure full energy absorption potential for the occupant seated in-position during the crash loading. This sophisticated deployment characteristic is simulated using a numerical approach to represent the actual fluid flow within the airbag to reproduc the airbag's initial unfolding process. Initial simulations recreate a simple physical (pendulum) laboratory test scenario. Further consideration of the OoP performance of the advanced airbag module is provided by replacing the simple pendulum with the more complex digital female frontal dummy positioned in accordance with the FMVSS 208 standard. Finally, the results obtained using the advanced airbag occupant simulation methodology are compared with the results of OoP occupant tests.
The goal conflict in designing occupant restraint systems for cars, namely, on the one hand to protect adult passengers with a hard filled airbag and on the other hand not to injure a child which stands close to the instrument panel is controlled by new legislation, an extension of FMVSS 208. In order to fulfill this law the demands on numerical simulation have increased in describing the airbag system during unfolding with the required accuracy to evaluate the dummy loads in out-of-position situations right from the first airbag contact. The investigation demonstrates, that the currently used simulation method is not appropriate for such analysis. The consideration of the thermo-fluid dynamics inside the airbag is becoming indispensable. The main focus of the study is the description of gas flow inside the airbag. The demands on numerical modelling were analysed for simplified airbag configurations - a flat and a Leporello folded driver airbag. As the airbag simulation proved to be sensitve with regard to the formulation used to describe the inflowing gas, the studies were focused on the determination of these non-stationary boundary conditions for the airbag deployment by modelling combustion and gas dynamics in the gas generator. In a comparison of three characteristic gas generator data sets (from a tank test analysis, a zero-dimensional and a two-dimensional combustion simulation) the differences between the methods are discussed and the effect on the airbag deployment is investigated. Using the three inflator data sets in simulations of a pendulum test, where a spherical impact body is pushed away by a flat and a Leporello folded airbag, shows the same trend in the acceleration curves: The data sets from the tank test analysis and from the zero-dimensional simulation lead to more or less identical pendulum acceleration curves with overestimated maximum values. However, with the data set from the two-dimensional inflator simulation, the lowest maxima and the smallest deviation from test measurements are reached. One exception is the first contact peak value caused by the Leporello folded bag, which is severely overestimated in every case. This behaviour must be investigated in further studies. It has been shown that using two-dimensional gas generator simulation, a further data set can be defined to describe the inflator function in airbag simulation. The mass flow curve characteristic and the small outflow temperature variation over time appear similar to the results of the tank test analysis. However, these two data sets do not show a suitably clear correlation in the airbag simulation results. Therefore additional tests to verify the evaluation methods would be desirable.
Dissertation (Ph.D.)--University of Michigan.
Characterisation of the Performance of an Inflator
- Ch
- K Jung
- Thomas
Ch. Jung and K. Thomas. Characterisation of the Performance of an Inflator. International
Automotive Safety Symposium, Bordeaux, France, 2005.
A Parallel Multilevel Method for Adaptively Refined Cartesian Grids with Embedded Boundaries
- M J Aftosmis
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- G Avodamicus
M. J. Aftosmis, M. J. Berger and G. Avodamicus. A Parallel Multilevel Method for Adaptively
Refined Cartesian Grids with Embedded Boundaries, AIAA paper 2000-0808, Reno, NV., Jan. 2000.
Investigation into the Effectiveness of Advanced Driver Airbag Modules Designed of OoP Injury Mitigation
- J Hoffmann
- M Freisinger
- M Blundell
- M Mahagare
- P Ritmeijer
J. Hoffmann, M.Freisinger, M. Blundell, M. Mahagare, P. Ritmeijer. Investigation into the
Effectiveness of Advanced Driver Airbag Modules Designed of OoP Injury Mitigation. ESV
Conference, Lyon, France, 2007.