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Fan Blade Bird Strike Analysis Using Lagrangian,

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Bird strike analysis
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  6th European LS-DYNA Users’ Conference 2.3.3 2.79 Fan Blade Bird Strike Analysis Using Lagrangian, SPH and ALE Approaches Authors: Alexander A. Ryabov, Vladimir I. Romanov, Sergey S. Kukanov Sarov Engineering Center Yuriy N. Shmotin, Pavel V. Chupin  NPO Saturn Correspondence: Alexander A. Ryabov Sarov Engineering Center Phone +7 83130 37306 Email Alex.Ryabov@saec.ru ABSTRACT: Fan blade bird resistance is one of the most important certification requirements for modern jet engines. The development test to meet the requirement is difficult and costly experiment. The expenses can be significantly reduced by using the numerical simulation of fan blade bird strike problem in the design of jet engine. The common technique for such simulations is modeling of bird as a solid cylinder or ellipsoid with material properties similar to water. The paper presents some results of fan blade bird strike analysis using LS-DYNA ®  Lagrangian, SPH and ALE approaches to model the bird. The main objectives of the investigations are to compare the results obtained by means of different approaches and to find out the advantages and disadvantages of every approach. KEYWORDS: Turbojet engine, fan blade, bird strike, numerical simulation.   6th European LS-DYNA Users’ Conference 2.80 2.3.3 INTRODUCTION One of the main problems in the bird strike analysis is choosing of a shape, material  properties and a simulation approach for an object, which model the bird. The common technique is modeling of the bird as a solid ellipsoid, cylinder or hemispherical ended cylinder [1-7]. The material properties are usually chosen to be similar to the properties of water. The simulation approach can be chosen among Lagrangian, SPH or ALE approaches, realized in LS-DYNA ®  [8]. The paper presents comparison of the fan blade bird strike analysis results, obtained using Lagrangian, SPH and ALE approaches. The parameters to compare are the contact force of interaction of the bird’s model and blades, visual bird’s deformation behavior during the process and total CPU time, required to complete solution. In frames of Lagrangian approach, different contact algorithms of interaction of the bird and blades are also investigated. STATEMENT OF THE PROBLEM AND DESCRIPTION OF COMPUTER MODELS A computer model of the fan blades and three computer models of the bird were created for the numerical simulations. A view of the blades and the bird models prepared for ALE approach is represented in Figure 1. Solid finite elements and material model *MAT_RIGID are used for the blades’ model. The model consists of about 440,000 finite elements. Rigid material is used in order to decrease calculation time and exclude possible influence of blades’ deformation process on the total CPU time, required to complete solution. It is assumed that the blades are rotated with constant angular velocity. For all approaches the bird is modeled as a solid ellipsoid with the properties similar to water. At the start of the calculations, the bird model is given an initial velocity towards the fan blades. Lagrangian model of the bird consists of 90,000 solid finite elements, SPH model consists of 100,000 particles. ALE mesh consists of 720,000 finite elements and the bird is initially defined in ~25,000 ALE cells. This mesh is chosen as a result of preliminary calculations and consultations with LS-DYNA ®  developers. In our opinion, this number of ALE elements is close to the minimum, required to obtain relatively adequate results.  6th European LS-DYNA Users’ Conference 2.3.3 2.81 Figure 1: Computer model (ALE approach) RESULTS OF LAGRANGIAN CALCULATIONS In frames of Lagrangian approach, different contact algorithms of the interaction of the  bird and blades are investigated: Calculation Lagr1 – CONTACT_NODES_TO_SURFACE; Calculation Lagr2 – CONTACT_ERODING_SURFACE_TO_SURFACE; Calculation Lagr3 – a combination of CONTACT_NODES_TO_SURFACE and CONTACT_ERODING_SURFACE_TO_SURFACE. RESULTS OF CALCULATION LAGR1 In this calculation the contact between the bird and blades is modeled using  NODES_TO_SURFACE contact algorithm. All the nodes of the bird model are used as the slave set and all the external segments of the blades – as the master set. This technique is allowed nodes to be active in contact even after surrounding elements fail. The total CPU time for calculation Lagr1 is 3 hours. The results of the calculation are  presented in Figures 2, 3. Figure 2 shows dimensionless forces of the contact interaction of the bird and blades. Figure 3 shows the deformed shape of the bird during the interaction with one of the blades. As it can be seen from the picture, the forward edge   6th European LS-DYNA Users’ Conference 2.82 2.3.3 of the blade penetrates into the bird’s material. This situation appears because the bird is modeled in the contact by nodes, but not by segments. This allows the blade to penetrate through the middles of bird’s elements. Figure 2: Forces of the contact interaction of the bird and blades (Lagr1) Figure 3: Interaction of the bird with one of the blades (Lagr1) RESULTS OF CALCULATION LAGR2 In this case the contact between the bird and blades is modeled using ERODING_SURFACE_TO_SURFACE contact algorithm. All the external segments of the bird model are used as the slave set and all the external segments of the blades – as the master set. This technique helps to avoid penetration of the blades into the bird’s material. The total CPU time for calculation Lagr2 is 3 hours. Figure 4 shows dimensionless forces of the contact interaction of the bird and blades. As it can be seen from the  picture, all the forces are much less then ones in calculation Lagr1. The cause of this is that eroding nodes are not active in the contact after surrounding elements fail. This leads to underestimation of the contact forces. RESULTS OF CALCULATION LAGR3 In this calculation the contact between bird and blades is modeled using the combination of ERODING_SURFACE_TO_SURFACE and NODES_TO_SURFACE contact algorithms. The forces of the contact interaction are determined using FORCE_TRANSDUCER_PENALTY algorithm. This technique is both allowed nodes to be active in the contact even after surrounding elements fail and helps to avoid  penetration of the blades into the bird’s material.

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Jul 23, 2017
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