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In most of the emergency circumstances,the aircrew leaves the aircraft under unsatisfied conditions,such as too high relative velocity to the ambient air or low partial oxygen pressure.The aircrew must pass through this area as quickly as possible before opening the parachute safely,viz.,free-fall.Numerical simulations are conducted in this paper to explore the major characteris-tics of the aircrew free-fall process by using a commercial computational fluid dynamic(CFD) software,FLUENT.Coupled with the classical pressure-altitude and temperature-altitude relations,Navier-Stokes(N-S) equations for compressible flow are solved by using finite volume method.The body velocity and the attitude are predicted with six-degree of freedom(6DOF) module.The evolution of velocities,including horizontal,vertical components and angular velocity,is obtained.It is also analyzed further according to the particle kinetic theories.It is validated that the theories can predict the process qualitatively well with a modi-fied drag effect,which mainly stems from the velocity pressure.An empirical modification factor is proposed according to the fitting results.
In most of the emergency circumstances, the aircrew leaves the aircraft under unsatisfied conditions, such as as too high relative velocity to the ambient air or low partial oxygen pressure. The aircrew must pass through this area as quickly as possible before opening the parachute safely, viz ., free-fall. Numerical simulations are conducted in this paper to explore the major characteris-tics of the aircrew free-fall process by using a commercial computational fluid dynamic (CFD) software, FLUENT. Coupled with the classical pressure-altitude and temperature -altitude relations, Navier-Stokes (NS) equations for compressible flow are solved by using finite volume method. body velocity and the attitude are predicted with six-degree of freedom (6DOF) module. evolution of velocities, including horizontal, vertical components and angular velocity, is obtained. It is also analyzed further according to the particle kinetic theories. It is validated that the theories can predict the process qualitatively wel l with a modi-fied drag effect, which major stems from the velocity pressure. An empirical modification factor is proposed according to the fitting result.