Bird strike analysis : AN ANALYTICAL APPROACH

Abstract: Airplanes have a risk of encounter birds while flying, taking off or landing and to ensure a safe flight the engines have to sustain functionality after one or several bird strikes; one vital part in the engine is the first stage rotor and hence it has to withstand bird strikes. Commercial finite element codes with explicit time marching techniques are commonly used today but they can be time-consuming and therefore a faster analytical method is sought. An analytical method is suitable for comparison of rotor blades in an early design process. The force during the bird strike was divided into two parts in accordance with a paper by Sinha et al. [1], a slicing force and a travelling force. Once the force was obtained it was transformed to a pressure over an area. The pressure and area was then used to perform a transient analysis in ANSYS. The analytical based results are then compared to results obtained in a simulation done in LS-DYNA. The force exerted on a rotor blade, analytical and in LS-DYNA, shows good agreement with respect to maximum force. Comparing the displacement of the rotor blade in ANSYS and LS-DYNA shows that the magnitude agrees well but the phase does not agree as well. It is possible to make automated scripts with a minimum of input data required to perform the analysis. The slicing force shows a good estimate of the maximum force exerted on a single blade during a bird strike. The impulse of the slicing force can also be seen as a lower limit of the total impulse felt by a single blade. The travelling force based on the paper by Sinha et al. was found to have some insufficiency and the recommendation is therefore to exclude the travelling force, in current state, from the analysis.