Bird Strike - Project - 2

LS DYNA – Bird Strike

By Enos Leslie

Mechanical Engineer

09th  August 2024

Bird Strike in Aero Engine

This is a classic nonlinear transient dynamics problem similar to car crash and mobile drop. While accurate modelling of the problem requires advanced techniques such as SPH, this problem can be solved using generic explicit solver. Here are the informations required to model the phenomenon.

The blades should rotate at a constant velocity but the casing should remain stationary. The cylindrical bird model should travel along its own axis and hit the blades. Use elastic material for the bird(2000MPa) and the casing(200GPa). The material model for the blades is attached. The velocity of the engine blades and the birds can be chosen so that blade failure can be seen within a short span of time.

A few extra requirements for this project: 

- Follow a consistent numbering approach 100000+ for nodes, 500000+ for elements, and 1000+ for the parts. All other keywords should be numbered within 10000-19999 while following a range for each one. This guideline that the student is following should be included in the final submission

- The bird, casing, and the blades should be in different input files and there should be one main file referencing all the input files. The main file should contain only references. Control cards and boundary conditions should be there in another separate file. The reference include path should be such that the folder can be copied anywhere and it is able to correctly reference all the file and run the simulation.

These two requirements are must in a professional setting when dealing with large models and multiple people working with the same model simultaneously. 

OBJECTIVE

My objective for this project is to simulate non-linear transient Birds-Strike simulation where the bird tries to hit the gas turbine blade by using Ls-Dyna. 

PROCEDURE

Due to the nature of the problem, The input geometry is divided into four parts and saved into .k file to be called up later.

Files are :

• BirdStrike_Bird_P.k
• BirdStrike_Blade_P.k
  
• BirdStrike_Casing_P.k
  
• BirdStrike_Hub_P.k
  

MATERIALS

There are four materials cards established in this project.

• 001 -ELASTIC (Bird_Material)

Density = 2x E-06 Kg/mm3 ||  Young Modules = 2 Gpa  ||   Poisson ratio = 0.33 ||

Density = 7.8x E-06 Kg/mm3 ||  Young Modules = 200 Gpa  ||   Poisson ratio = 0.33 ||

• 024 - PIECEWISE_LINEAR_PLASTICITY (Blade_Material)

Density = 2.713x E-06 Kg/mm3 ||  Young Modules = 68.94 Gpa  ||   Poisson ratio = 0.33 ||

LCSS =1 . LCSS calls the defined curve refernce 1 which has the stress / strain nonlinear curve input

• 024 - PIECEWISE_LINEAR_PLASTICITY (Hub_Material)

Density = 8.2x E-06 Kg/mm3 ||  Young Modules = 145 Gpa  ||   Poisson ratio = 0.33 ||

SECTION 

Three shell sections were defined with one solid section

SHELL_Bird_Section || ELFORM =-16 ||  T = 3mm || 

SHELL_Casing_Section || ELFORM =2 || T = 6mm || 

SHELL_Blade_Section ||  ELFORM =-16 ||  T = 3mm || 

SOLID_Hub_Section || ELFORM =10 || 

The materials is saved as a keyword  as : BirdStrike_MATERIALS.k

BOUNDARY CONDITIONS

• PRESCRIBED_MOTION_SET

Constant motion of the hub is created with DOF = 5 || VAD = 0 || LCID = 2 ||

LCID curve is define for the velocity with time graph which is seen below:

Angular_Velocity_Hub ( 1 rad/ms)              for                  0 to 10ms

• SPC_SET 

Casing_fixed : Spc is defined for the casing and it is fixed in all DOF

Hub_fixed : SPc is defined for the hub and it is fixed in DOFX

• INITIAL_VELOCITY_GENERATION

PART = 1001(BLADE) ||  OMEGA = 1 rad/ms  

PART = 1003(BIRD) ||  VX = 25 mm/ms  

The Boundary is saved as a keyword  as : BirdStrike_Boundary_conditions.k

CONTACT

Four contacts have been defined

• Automatic_nodes_to_surface  || Blade(slave) to Casing(masters)
• Automatic_nodes_to_surface  || Bird (slave) to Blade (masters)
• Automatic_single_surface         || Self_Contact_Blade
• Tied_surface_to_surface           || Hub_to_Blade

The Contacts card is saved as a keyword  as : BirdStrike_CONTACTS.k

CONTROL

Energy : HGEN = 2 || RWEN = 2  ||  SLNTEN = 2 || RYLEN = 2 ||

CONTROL_TERMINATION : ENDTIME = 10ms ||

TIMESTEP :  TSSFAC = 0.9 || 

The Control card is saved as a keyword  as : BirdStrike_CONTROL.k

INCLUDE 

All the separate .k files are called into a main file to run the Birdstrike analysis. The nodes and elements are renumbered.

RESULTS

The Bird crashes the blade and the blades are plastically deformed with an effective plastic 2.718e-01 mm and von mises stress of 0.9701 Gpa.

GRAPHS

The kinetic energy of the blade increased gradually with a slight dip at 1ms which is the point when the bird impacts the blade. Shortly after the bird falls off and the blade continues to rotate to a maximum energy of 280 kg*mm2/ms2

From the chat above, it can be seen that the blade received a maximum X-force of 1.45kg mm/ms^2 from the bird impact thus causing deformation to the blades. Also the force impact was at 1ms which was the exact moment the bird struck the blades and later went 0 because the bird fell off.

CONCLUSION

The results clearly demonstrate that the birdstrike event caused irreversible damage to the turbine blade, emphasizing the importance of robust design and material selection to mitigate such impacts. The observed plastic deformation and high stress levels underline the necessity for further improvements in blade design, potentially incorporating materials with higher toughness and impact resistance to prevent catastrophic failure.

This report serves as a critical assessment of the structural integrity of turbine blades under birdstrike conditions. It highlights the impact forces involved and the resulting material responses, including plastic deformation and stress distribution. The findings underscore the need for enhanced design considerations in turbine blade engineering to withstand unexpected impacts, ensuring safety and operational reliability in aerospace and other relevant industries. The analysis provides valuable insights for future improvements in blade design, contributing to the overall safety and durability of turbine systems.