Effects of incidence angle in bird strike on integrity of aero-engine fan blade

Abstract

The possibilities of blade deformation and even fracture, the need for subsequent containment and reduction in thrust and power supply make bird strikes to aero-engine fan blades very serious events. Due to the different bird-plane flight paths and the different types of turbofan engines, the incidence angle between the bird and the engine fan blade can vary within a wide range. The present explicit non-linear three-dimensional finite-element analyses examine in detail the effect of the incidence angle when a canonical 4-lb bird strikes a typical engine fan blade, using the commercial code LS-DYNA. Both the bird and the blade are simulated in a Lagrangian framework. The homogenised fluidic constitutive equation of the bird follows the Brockman hydrodynamic model, while the blade is modelled as a viscoplastic material of the Perzyna type. It was found that normal incidence results in maximum impact forces and plastic strains leading to severe deformation. For the case in which the incidence angle is equal to or larger than 60 • , the impact forces are significantly reduced, and the blade deformation remains within the elastic range. In addition, this work also provides a theoretical calculation for the bird Hugoniot pressure by assuming it as a high-speed soft-body impactor, thus providing a means for obtaining a quick conservative upper bound solution. Nomenclature (in SI units)A cross = Cross-sectional area of the bird, A cross = π 4 D 2 (m 2 ) C i = Compressive modulus of the bird material (Pa) D = Diameter of the bird (m) E = Young's modulus of the blade material (Pa) F = Impact or contact force between the bird and the target (N) I = Impulse between the bird and the target, I = ∝ 0 F · dt (N s) I ad = Normalised Impulse, I ad = I m·ẇ 0 L = Length of the bird (m) M = Mass of the bird (kg) P = Pressure (Pa) P TH s = Theoretical stagnation pressure, P TH s = 1 2 ρ 0 ·ẇ 2 0 (Pa) P ad = Normalised impact pressure, P ad = F/A cross P TH s T = Normalised time, T = t T 0 = t L/ẇ 0 T 0 = Nominal impact duration, T 0 = L/ẇ 0 (s) c, p = Strain-rate parameters, c = 40.0 s −1 , p = 5.0 d α = Damping coefficient t = Time (s) u, v, w = Displacements in x-, y-and z-direction (m) * Corresponding author. Email: r.mao@tudelft.nlẇ 0 = Initial velocity of the bird (m/s) x, y, z = Cartesian coordinates (m) θ = Incidence angle (degree) σ ij = Stress tensor (Pa) δ ij = Kronecker delta symbol e ij = Strain rate tensor (s −1 ) ρ = Instantaneous mass density of the bird (kg/m 3 ) ρ 0 = Initial mass density of the bird (kg/m 3 ) µ = Mass density change ratio of the bird, µ = ρ ρ 0 − 1 ν = Poisson ratio of the fan blade material IntroductionOf all foreign object damage to aircraft, 90% can be attributed to bird strikes. These bird-strike events place both aircraft and passengers at risk. Bird-strike statistics indicate that over 400 people have been killed worldwide as a result of bird strikes [17]. In the United States, damage due to bird strike costs the aviation industry over US$600 million annually [21]. The alarming frequency of bir...

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Effect of Bird Yaw/Pitch Angles on Soft Impact Damage of a Fan Assembly

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Transient Analysis and Safety Assessment of Turbofan Engine Structures during Bird Ingestion

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