Abstract:
A new developed pilot helmet is destroyed in an ejection process in wind tunnel test. In this helmet, there is a big cavity between the outer helmet and the inner helmet. The initial analyses show that, when a high speed outer flow crushes into the cavity from the gap between the blinker and the oxygen mask, a great impact load may be induced on the helmet. For this characteristcs, a simulation method is proposed. First, the gap is closed, and the outer flow is simulated by solving the steady Navier-Stocks equations. Then, the gap is opened, the unsteady impact process of the outer flow crushed into the cavity is simulated by solving unsteady Navier-Stockes equations. The influence of free stream velocity, the flight altitude and the angle of attack on the impacting process is studied. The unsteady aerodynamic load on the inner helmet and the outer helmet are analyzed. The study shows that the difference between the pressure on the internal surface and that on the outside surface of the outer helmet is about 0.6atm under the impact of the air stream. The distribution of the pressure is asymmetrical in the impact process, which may lead to the dilacerations of the helmet.