Bird Strike - Project - 2
Objective:
To simulate the impact of a bird strike on the blades of an aeroplane turbine, using the given Aero and bird FE models.
Model setup
The main file contains the four main parts of the model namely the casing, hub, blade and the bird. They have to be segregated and saved as separate .k files, so that they can be referenced in the main.k include file.
1. Bird
The part representing the bird is defined with shell elements with a thickness of 2.5 mm and ELFORM 2.
2. Blade
The part representing the bird is defined with shell elements with a thickness of 1.2 mm and ELFORM 2.
3. Hub
The part representing the bird is defined with solid elements with ELFORM 4.
4. Casing
The part representing the bird is defined with shell elements with a thickness of 2.0 mm and ELFORM 2.
Material definition (Material.k file)
The casing and hub are defined with elastic steel material with properties as shown below.
The bird is defined with an elastic material with properties shown below.
The blades are defined with a piecewise linear plastic material, whose properties are given in the material file.
Boundary conditions (B_C .k file)
The casing is fixed with SPC on all nodes, constraining motion in all directions.
The blades are given an angular velocity of 0.5 rad/ms, and the velocity of the bird's motion is assumed as 116 mm/ms in the X-direction, as shown below.
Contact definition (Contact . k file)
The following contacts need to be defined in the model.
Contact between
1. Bird and fan blades
2. Fan blades and hub
3. Fan blades (self contact)
4. Blades and casing
The contact between bird and fan blades is defined using a nodes-surface contact as shown below. (Nodes - bird, surface - blades)
A tied Surface-Surface contact is defined between the blades and the hub.
For self-contact of the blades on impact, an automatic single surface contact is used
The contact between the damaged fan blades and casing is defined using an automatic surface - surface contact.
Database and control cards (Control_Database.k file)
The following control cards are defined.
The hourglass energy computation is enabled (HGEN = 2), and the simulation time is 2.0 ms.
The following database cards are defined.
A timestep value of 0.1 ms is given for BINARY_D3PLOT and for the outputs in DATABASE_ASCII.
DATABASE_EXTENT_BINARY card with STRFLG = 1 is used, to compute the strain energy in the model.
Main keyword file (Main.k file)
The main file is the include file containing the references to all the individual input (.k files), and the material, boundary and control files, as shown below.
The nodes, elements and the other parts and materials are renumbered in the main file with an uniform convention for ease of use, as shown below.
Results
The model is now ready for simulation and the results can be viewed.
The results of the stress, strain and energy plots can be seen below.
Von mises stress
Effective Plastic strain
Element values
The maximum von mises stress of 0.113 GPa occurs on element 621371. This is higher than the yield stress of 0.0113 GPa of the blades, therefore element failure occurs.
Effective plastic strain
The highest EPS of 0.272 occurs at element number 508082. Since it is in the plastic region, there is permanent deformation in the material ie EPS value stays constant.
Energy plot
The total energy remains constant throughout the simulation. The internal energy and kinetic energy move towards convergence and the hourglass energy remains low throughout the simulation.
Mass scaling
Though the estimated time was 1 hour, the simulation took around 16 minutes to complete, without mass scaling.
Using mass scaling, the run time can be shortened further.
Trial 1:
TSSFAC:0.9, DT = 2.0e-4
The estimated time to complete is 21 minutes, the simulation is completed in around 5 minutes. The percentage of mass addition is 2.49 %.
Trial 2:
TSSFAC: 0.9, DT = 2.2e-4
The estimated time to complete is 18 minutes, the simulation is completed in around 6 minutes. The percentage of mass addition is 4.33 %.
Trial 3:
TSSFAC: 0.9, DT = 2.5e-4
The estimated time to complete is 20 minutes, the simulation is completed in around 5 minutes. The percentage of mass addition is 8.39 %.
Using a limit of percentage mass increase of 5%, it is seen that the percentage increase with a DT of 2.5e- 4 is much higher. Therefore, the maximum value of DT which helps the percentage increase to stay within the limit of 5% is 2.2e-4, which has a percentage increase of 4.33%.
Conclusion
Thus, the simulation of a bird strike on the aeroplane blade is carried out with and without mass scaling, and the results have been discussed.
The relevant files can be found under the link
https://drive.google.com/drive/folders/1PNnSBpWqMlW8Ueyplzrt_bHn09zUyGdt?usp=sharing