Bird Strike

Aim:

• To simulate a Bird Strike on Aero engine in which the blades of the Aero engine fail as a result of high velocity impact

Case-Setup:

The units system used here is kg-mm-ms.

The cylindrical simple elastic component is assumed as the bird for this simulation.

The model is divided into individual component key files and material,part & sections are included in another key file.

Finally, the boundary conditions and control cards are included in a unique key file.

Renumbering

The node ids, element ids,etc., are all renumbered as follows

Material card

Casing is defined by an elastic card with Youngs modulus of 200 GPa and other properties of steel.

Blades is defined with an aluminium elastic-plastic material card given.

Hub is defined as a rigid material with properties of steel as the results in the Hub component are of the least interest in this simulation.

Bird is defined by an elastic material as follows

Youngs modulus = 2 GPa

Density = `1.5E-6 (kg)/(mm^3)`

Poisson's ratio = 0.47

Boundary conditions

The Casing is constrained at its free edges in all DOFs.

Initial velocity of 0.8 rad/ms (8000 rpm approximately) is given to the Hub and Blades to rotate as a unit.

Bird is given an initial velocity of 150 m/s as the relative velocity between bird and plane would be of that order.

Trials and Debugging

Trial 1 - Blade velocity = 0.5 rad/ms (~5000rpm) & Bird velocity = 6 mm/ms (21.6 km/h)

The bird bounces off of the blades without penerating with such low velocity of the bird.

We can also see the blades penetrating the casing at the end as no contact is defined between them.

Trial 2 - Blade velocity = 0.5 rad/ms (~5000rpm) & Bird velocity = 100 mm/ms (21.6 km/h)

A universal *AUTOMATIC_SINGLE_SURFACE contact is defined to take care of all the unexpected contacts

Large penetrations are seen between the bird and the blades and bird is stuck in the blades. This happened becuse of improper material definition of bird.

The bird's poissons ratio was defined as 0.3 which is usually a case for metals. So it is changed to 0.47

Trial 3 - Blade velocity = 0.5 rad/ms (~5000rpm) ; Bird velocity = 100 mm/ms (21.6 km/h) & Poissons ratio = 0.47 for bird

Now, we can see failure of the blade as a result of contact between both.

Mass scaling

The simulation is run for 3 ms for capturing the collision of bird and failure of blades.

It took 67 seconds to run the simulation without any mass scaling.

Case 1. DT2MS = -5.0E-4

% mass increase = 3.54E-3

Elapsed Time = 36 s

Case 2. DT2MS = -7.0E-4

% mass increase = 6.75E-1

Elapsed Time = 27 s

Case 3. DT2MS = -8.0E-4

% mass increase = 4.64

Elapsed Time = 24 s

The conclusions of mass scaling are as follows

•  We saw that the elapsed time for simulation has decreased with increasing DT2MS parameter
• Also, we notice instabilities when the DT2MS is increased beyond 8.0E-4 which puts our % mass increase limit at around 5%

Results:

Plastic Strain Contour

• We can see that the blade elements fail as they reach a plastic strain of 0.273 rightly as defined in its material card
• The bird does not fail as we did not define failure for it

GLSTAT plot

• The total energy of the system remains conserved at 1160 J which is same as the initial kinetic energy
• The kinetic energy is converted to internal energy as the impact happens
• Hourglass energy is negligible as we employed hourglass control

Contact force plot

• The contact force between bird and blades at the impact is as high as 4.92 kN

Conclusions:

• The Bird strike with Aero engine has been simulated using a cylindrical bird model
• Correct Material card definition is key to every simulation
• Trial and error method is used for the bird and blade velocities to obtain blade failure
• Use of SPH formulation for bird model might give more accurate results