Bird Strike using LS-DYNA

BIRD STRIKE ANALYSIS

AIM

To perform a bird strike simulation involving a cylindrical shell object which is modeled to reference the bird against an airplane engine whose blades are rotating at subsonic speeds. Hence to study the effect of bird strikes upon engine blades during impact.

INTRODUCTION

Jet engines and aircraft experience bird strikes at regular intervals during flight. However, the engines and windshields of these aircraft are the most vulnerable parts that could lead to severe catastrophes. Hence bird strike analysis is a common procedure followed by most leading aircraft manufacturers to determine the safety and stability of the aircraft system.

This bird strike testing is done either using a computational model of the bird and the engine component and the other way involving shooting out actual physical models of the birds using a so-called 'Chicken gun' at the windshield of the aircraft. Among these, the latter doesn't seem economically feasible. Hence most opt for bird strike analysis done using a computer program that could replicate a real-life scenario based on how the mathematical models of these birds and the aircraft domain system are built upon.

NOTE: Most bird strike analysis performed, involves a clear computational model of the bird using an SPH (Smoothed Particle Hydrodynamics) model. However, in this report the bird is modeled using a simple cylindrical shell part.

KEYWORD SETUP:

1. *INCLUDE

Each part of the whole engine system and the bird component are defined in an individual .k/.dyn (LS-DYNA input file) and referenced to the main file.

This helps in organizing the work-flow and can even help in the debugging process. These methods are universally followed in every industry where a single process follows a hierarchical order.

In this project, the material, and section of each component [Casing, blades, hub, bird] are saved in separate files and compiled onto a main.dyn file using the *INCLUDE_INCLUDE keyword along with other files that reference the termination and output of the simulation.

2. *PART - *MAT & *SECTION

Every component except the hub of the engine is modeled using SECTION_SHELL while the hub using a SECTION_SOLID.

The bird object is modeled using an elastic material [MAT_001] with an elastic modulus of 2000MPa while the casing is modeled using a MAT_RIGID with an elastic modulus of 200GPa.

Since each keyword file of each component are saved under different file names, a numbering system is followed starting from range 1001. Such that each ID of parameters match with the respective component.

3. CONTACT

An AUTOMATIC_SURFACE_TO_SURFACE card is used to define the contact between the blades and the bird upon impact. Here, the bird is referenced as the master segment and the blade is referenced as the slave segment using the SET_SEGM.

In addition, an AUTOMATIC_SINGLE_SURFACE card is used to define self-contact on the blades in case deformation occurs during impact.

4. VELOCITY & PRESCRIBED_MOTION

The INITIAL_VELOCITY keyword is used to define the angular velocity of the blades which rotate about the x-axis defined in the VXR parameter.

The movement of the bird object along the x axis is referenced using a BOUNDARY_PRESCRIBED_MOTION_SET card where the load curve LCID defines the displacement of the bird object with respect to time.

5. OTHER KEYWORDS

The end time of the simulation is set for 10ms using the CONTROL_TERMINATION keyword

The animation file required is accessed using the d3plot which can be selected using the DATABASE_BINARY_D3PLOT card with a time interval of 0.1 ms for each animation frame.

POST-PROCESSING

The main .dyn file which references all the other keyword files is made to run using the LS-DYNA solver and the following results are obtained.

The animation file shows how the blades deformed upon impact. The main reason due to the bird being referenced as a master segment while the blades are referenced as the slave segment.

The above shows the Von-mises stress experienced at the blades where we can clearly see the maximum stress is experienced at the blade where the impact occurs. Hence the above result is feasible.

CONCLUSION:

Hence a bird strike analysis is simulated to determine the effect of bird impact against an aircraft engine.