# Effect of Impact and Bearing Parameters on Bird Strike with Aero-Engine Fan Blades
## 1 Introduction  
With increasing developments in commercial aviation, the number of bird strikes is also increasing, and the hazards they pose are becoming more severe. According to the report of the Federal Aviation Administration (FAA), bird strikes have resulted in 363 human injuries and fatalities between the years 1990 and 2020. The economic loss due to bird strikes is also drastic. During the year 2020 alone, a USD (United States dollar) 124 million loss was caused by bird strikes directly or indirectly. The aero-space engine is the most frequently damaged component by bird strikes, accounting for 26% of all damaged components [1, 2]. The earliest method of studying bird strikes was the experimental tests, which provided a direct method to assess the bird strike severity [3]. However, it is time-consuming and costly to design and carry-out bird strike experiments [4]. The development of computer technology and improvement of numerical simulation methods after the 2000s haveprovided a new approach for bird strike studies. Combined experimental and numerical approaches can provide feasible and cost-effective outcomes for bird strike studies [5; 6]. Simple geometries such as straight-ended cylinders, spheres, ellipsoids, and hemispherical-ended cylinders are commonly used as bird models in simulations. The noted substitute bird models have been implemented in many studies for many years and have yielded a lot of valuable results [7; 8; 9; 10]. However, as compared to traditional bird models, a realistic bird model provides results that are more consistent with experiments [11; 12; 13; 14]. The Lagrangian, Eulerian, arbitrary Lagrangian-Eulerian (ALE), and smoothed particles hydrodynamics (SPH) methods are the most frequently used techniques to simulate bird strike phenomenon [15; 16; 17]. Due to the large deformation of the bird during a bird strike event and the complexity of the calculations, the SPH method is widely employed in bird strike simulations [18]. Recently, the parametric study of bird strikes has been increasing. Bird impact to rigid plate scenarios are usually implemented to evaluate the efficiency of different bird model geometries [11; 19]. To further understand the influence of the fan structure, the impact target model needs to be changed from a flat plate to a real engine. The impact characteristics of the traditional model on the fan have been obtained [20; 21]. In actual bird strike accidents, the orientation of the bird concerning the engine is random. The same holds for impact location. As a result, the effect of the impact location and bird orientation has been studied numerically [22; 23; 24]. However, due to the limitations of traditional models, such as the sphere model being identical in all orientations, the use of realistic bird models has been increasing recently [19]. The effect of bearing components is also often neglected in fan models impacted by birds. Bird strike impacts can cause transient shocks, and the resulting unbalanced forces can have an impact on the fan [25]. The introduction of bearings into the model is very necessary for accurate bird strike simulation. Furthermore, the mass and flight velocity of the bird also affect the bird strike results [26]. Although many bird strike scenarios have been studied previously, the parametric study of a real bird model striking a rotating fan with bearings has not been investigated before. In this study, numerical simulations are carried out to study the effect of different impact and bearing parameters on the bird striking aero-engine fan blade process. A realistic bird model based on the SPH method as well as a rotary fan with the bearing is constructed through the finite element (FE) method. The influence of six parameters, including bird impact location, bird impact orientation, bird impact velocity, fan rotational speed, damping and stiffness of the bearing on the bird impact process, is investigated.