Peculiarities of the Modelling of the Bird Dynamic Impact on Fan Blades of an Aircraft Turbojet Engine at Operating Modes

The paper considers the problem of adequate mathematical modelling of the impact of flying birds on the fan blades of an aircraft turbojet engine at its normal operating mode. Bird strike with the blades is modelled to evaluate the post-strike deformation and strength state of the blades. Such an evaluation is required for analysing the further serviceability of an aircraft turbojet engine. The suggested approach enables performing such an evaluation using implicit dynamic analysis methods by replacing the flying bird with a special equivalent dynamic load distributed across the strike spot. In contrast to the conventional use of explicit methods for simulating the process of impact of rotating fan wheel blades with a bird flying with a certain speed, such implementation of simulation modelling enables using sufficiently detailed finite-element models. This allows determining the parameters of the stress-strain state of the blades after impact with high accuracy. In this case, the displacements and the deformations of blade points and the stresses therein are suitable for evaluating the wheel serviceability according to airworthiness standards. The problem solution algorithm consists in building computational models for dynamic analysis with detailed account of geometric, physical, mechanical and operating characteristics of the structure. Simulation modelling of the most hazardous variant of bird strike with the fan blades being considered yields the patterns of displacement of blade points, deformations and stresses. The computational model is verified using several error estimation criteria, whereas the approach and results were validated by comparison with test bench experimental data.