Research On The Technology Of Seat/occupant Protection For Windblast At High Speed

Along with unceasing increase of flight speed, occupant injuries suffered from windblast during high speed ejection are on the increase. To enlarge the performance envelope of seat/occupant systems, the technologies of protection for windblast during high speed need be studied. With extensive emplyment of computational fluid dynamics(CFD) method, and a characteristic of providing sufficient parameters in the flow fields, CFD method has become an efficient means of analyzing the issue of protection for windblast on abroad. Numerical simulation of protection for windblast during high speed is still at the initial stage in China. The principles of protection for windblast during high speed are studied by numerical methods in this thesis. The protective characteristics of several protection devices are analyzed.The main researches in this thesis are as follows: 1) The governing equations and numerical methods which were used in the thesis were discussed, and an N-S equation solution was developed. The unsteady three-dimensional compressible Reynolds-Averaged Navier-Stokes equations were used as governing equations. The central difference scheme of Jameson's finite volume method was used for spatial discretization with an adaptive dissipation model. The dual time-stepping scheme was used for temporal discretization. The local time step method was used for speeding convergence. Non-slipping and non-reflecting conditions were used as boundary conditions. The Detached-Eddy Simulation (DES) method based on Spalart-Allmaras (SA) one-equation turbulence model was applied to simulate the detached viscous flow behind seat/occupant systems. The low speed preconditioning method was used to solve low speed incompressible flowfields. Parallel computation was based on domain decomposition method by calling METIS software and the Message Passing Interface (MPI) standard library applied to communicate. 2) Several complicated three-dimensional geometric seat/occupant models with and without protection devices were drawn by using Solidworks software. The high quality hybrid grids were generated in the fields by applying ICEM pre-processing software. The drag characteristics of some seat/occupant system were calculated by the solution, and the computational results are in good accordance with experimental results. DES method was applicable for simulating the large detached viscous flow fields behind seat/occupant systems by calculating the example. The low speed preconditioning method and parallel computation method were validated to speed convergence. 3) The aerodynamic characteristics of seat/occupant without any protection devices were obtained in steady status. The aerodynamic forces acting on occupant's body and the reason for injuries suffered from windblast were analyzed during high speed, and the principles of protection were discussed. The aerodynamic characteristics of occupant's limbs in steady status were analyzed. The trends of aerodynamic coefficients in different attack angles predicted are in agreement with experiment. 4) The aerodynamic characteristics of seat/occupant systems and occupant's limbs with protection devices were predicted in steady status at various flow conditions and seat/occupant orientations. The pressure distribution on the surface of occupant was analyzed, and the general principles of protecton for windblast during high speed were validated. The protective effect of different protection devices on occupant's limbs and chest and abdomen were analyzed thoroughly. 5) The forces acting on seat/occupant system during free flight after ejection were analyzed. The six-degree-of-freedom(6DOF) equations were set up. The aerodynamic forces acting on seat/occupant system with and without protection devices in unsteady status were calculated by coupling 6DOF equations to N-S equations and generating unstructured dynamic grids by using spring analogy methods and local remeshing methods. The differences between steady and unsteady results were compared. The protective effects of leg lifters and windblast deflector on seat/occupant systems in unsteady status were compared. The effects of protection devices on aerodynamic forces in unsteady status were agreement with that results based on static meshes. 6) Five kinds of seat/occupant models with new size windblast deflector were drawn. The aerodynamic characteristics of corresponding seat/occupant system based on static meshes were calculated. The results show that the effects of changing the size of windblast deflector on the aerodynamic forces acting on seat/occupant systems are less than on the aerodynamic forces acting on occupant's head and neck and on pressure distribution on the surface of head. The drag and lift forces acting on the head and neck and the pressure on the surface of head are decreased by changing the size of windblast deflector. Occupant's head and neck are protected efficiently by using these windblast deflectors.