Bird strike is a serious problem that affects both commercial and military aircrafts. Systematic modeling and simulation of bird strikes are severely lacking, especially for cases involving engine, fan blades, and casings. In the present investigation, explicit 3-D finite element analysis using LS-DYNA is carried out to study the nonlinear transient response of a bird striking a fan system. The bird strike is simulated using Lagrangian blade-bird formulations. The bird is modeled as a fluid jet with a homogenized fluidic constitutive relation, using the Brockman hydrodynamic model, which was found to be the most appropriate. The present simulations are validated using a benchmark test of a bird striking a rigid target that is reported in the literature. Following this validation, a reference case of a bird striking a flexible fan blade was set up and used as the reference case in a series of parametric studies. The effect of bird velocity and its size are examined and attention is given to strikes involving larger birds so as to address the lack of data in this area.

Finite Element Modeling of a Bird Striking an Engine Fan Blade

A comprehensive three-dimensional nonlinear finite element analyses were carried out to examine the effects of the geometry and the incidence angle of canonical 4-lb bird striking a stationary fan blade using LS-DYNA. Three aspects of the work were accordingly examined. The first was concerned with the modeling framework used. The second with the constitutive law that governs the behaviour of the bird. The third was concerned with the influence of the geometry and the angle of incidence of the bird on the integrity of the blade. This article combines and extends the earlier works on both the Lagrangian modeling methodology (Mao et al. AIAA J. Aircr. 44(2), 583–596, 2007) and the bird geometry studies (Meguid et al. 2008) in systematic and integrated manner. Both the bird and the blade were simulated in a Lagrangian framework. Furthermore, the homogenized fluidic constitutive equation of the bird follows the Brockman hydrodynamic model, while the blade is modeled as a viscoplastic material of the Perzyna type. The study focused on the three most-frequently used configurations in the literature; namely, hemispherical-ended cylinder, straight-ended cylinder, and ellipsoid, at various length-to-diameter aspect ratios. The results show that the initial contact area between the bird and target in the early phase of the impact event would have a significant effect on the peak impact force. Normal incidence results in maximum impact forces and plastic strains leading to severe deformation. For the case where 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. The maximum impact force and the resulting plastic strain are not merely governed by the size of the bird but also its density.

/pdf/transient-three-dimensional-finite-element-analysis-of-a-2gixjaaqtf.pdf

Transient three dimensional finite element analysis of a bird striking a fan blade

Damage caused by bird impact on a blade in a rotating fan has been idealized as transverse impact of a fluid jet on a semi-infinite, rigid-plastic beam with a centrifugal force acting parallel to the initial axis of the beam. In this preliminary dynamic analysis, the centrifugal force limits travel of the plastic hinges away from the impact point and decreases the deflection of the beam. A kink forms at the impact point; the amplitude of this kink is related to a moment of the impact force and is inversely proportional to the centrifugal force.

Impact bending of a rotating, rigid-plastic fan blade

The free and forced vibrations of turbine blades are considered. First, various models for the description and the calculation of their dynamical behaviour are presented and methods of solution are discussed. Second, results and parametric studies are considered which show the influence of the most important blade parameters on the vibrations.

Free and Forced Vibrations of Turbine Blades

The free and forced vibrations of turbine blades are considered. First, various models for the descri~tion and the calculation of their dynamical behaviour are presented and methods of solution are disc~ssed. Second~ results and parametric studies are considered which show the influence of the most important blade parameters on the vibrations.

Free and forced vibrations of turbine blades

Structural and dynamic analyses are presented for a shroudless, hollow titanium fan blade proposed for future use in aircraft turbine engines. The blade was modeled and analyzed using the composite blade structural analysis computer program (COBSTRAN); an integrated program consisting of mesh generators, composite mechanics codes, NASTRAN, and pre- and post-processors. Vibration and impact analyses are presented. The vibration analysis was conducted with COBSTRAN. Results show the effect of the centrifugal force field on frequencies, twist, and blade camber. Bird impact analysis was performed with the multi-mode blade impact computer program. This program uses the geometric model and modal analysis from the COBSTRAN vibration analysis to determine the gross impact response of the fan blades to bird strikes. The structural performance of this blade is also compared to a blade of similar design but with composite in-lays on the outer surface. Results show that the composite in-lays can be selected (designed) to substantially modify the mechanical performance of the shroudless, hollow fan blade.

/pdf/structural-dynamics-of-shroudless-hollow-fan-blades-with-1qwyk7nxl9.pdf

Structural dynamics of shroudless, hollow fan blades with composite in-lays

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Structural dynamics of shroudless, hollow fan blades with composite in-lays