Bird Strike Simulation Using ANSYS LSDYNA

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Bird Strike Simulation Using ANSYS LS/DYNA
Carlos Shultz Jim Peters
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Introduction
Bird Ingestion (Bird Strike) Simulation

• Common type of analysis performed to support
  aircraft engine certification
• Quick simulation of a bird strike which captures
  all of the necessary physics to accurately
  predict how a fan will react to a bird ingestion
• Reduces the analysis time to less than 2 days per
  iteration analysis can be part of the regular
  design process

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Finite Element Modeling
Preparing Ansys Models (.db)

• Shell163 elements, Belytschko-Tsay formulation
  for the airfoils, thickness at each node is
  defined appropriately for a smooth mesh
  transition
• Hub mesh is created as rigid Solid164 elements.
  The hub mesh shares nodes with the blade mesh at
  the root of the airfoils

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Finite Element Modeling
Preparing Ansys Models (.db)

• Bird material is simulated with an Euler mesh, a
  stationary mesh which transports the bird
  material within it
• When an element from the airfoils sweeps through
  a brick element of the air that has a volume
  fraction greater than a threshold value, an
  additional set of calculations is triggered which
  transfers momentum between the bird material and
  the airfoils.

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Finite Element Modeling
Preparing Ansys Models (.db)

• Meshing must be done with care to minimize effort
  in subsequent steps, a model with several hundred
  PARTS is typical because each element in the
  airfoil has a different real constant set of
  thicknesses.
• Part numbers are normally assigned to the mesh
  from lowest to highest node/element number. One
  way to assign parts in the proper order is to use
  the EDPART command on selected parts of the model
  in the following manner.
• Select elements to be Part 1, EDPART, create will
  create Part 1
• Also select elements to be Part 2, EDPART, update
  will create Part 2 without changing Part 1 even
  if the numbering of the nodes/elements of Part 1
  are greater than Part 2

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DYNA Input Prepartion
Preparing DYNA Models (.k)

• MAT_PIECEWISE_LINEAR_PLASTICITY used for the
  airfoils and shroud
• MAT_NULL and EOS_TABULATED used for the bird
  material
• CONTROL_HOURGLASS or HOURGLASS using viscous
  control is recommended for high velocity
  deformations
• DAMPING_RELATIVE to stabilize the blades during
  ramp-up and ramp-down, this card provides blade
  damping proportional to the relative velocity of
  the blades and the hub
• SECTION_SOLID_ALE option 12 for the Euler mesh,
  INITIAL_VOID_PART for the mesh initially without
  bird material
• CONTROL_ALE with a currently undocumented
  advection control
• CONSTRAINED_LAGRANGE_IN_SOLID controls the
  interaction between the Euler mesh and the
  Lagrangian mesh

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DYNA Solving
Solving DYNA MODELS (.k)
Plot of Volume Fraction at Time0

• LS/DYNA (9.60) must be run from the command line
  since some of the features used are not yet
  implemented in ANSYS

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DYNA Post Processing
Post Processing Models (d3plot)
Plot of Volume Fraction at Time0.038s

• Both birds are in motion at this time

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DYNA Post Processing
Post Processing Models (d3plot)
Plot of Volume Fraction at Time0.059s

• Impact occurs as a blade hits the 1st bird
• Significant plastic strain occurs in the airfoil

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DYNA Post Processing
Post Processing Models (d3plot)
Plot of Volume Fraction at Time0.085s

• Additional impact occurs as a blade hits the 2nd
  bird
• Additional plastic strain occurs (note that 7
  blades are significantly damaged at this time)

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DYNA Post Processing
Post Processing Models (d3plot)
Plot of Plastic Strain at Time0.085s

• Peak equivalent plastic strain in the model is
  0.485
• Some plastic strain at the root

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ANSYS Post Processing
Post Processing Models (ANSYS)
Pldisp,2 after spin-down

• Coordinates after spin down are exported from
  LSPOST
• Displacements read into ANSYS put into results
  using DNSOL

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ANSYS Post Processing
Post Processing Models (ANSYS)
Plnsol,u,sum after spin-down

• Deformed mesh can be used to calculate various
  pass/fail criteria

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Conclusion
Bird Ingestion (Bird Strike) Simulation

• Simulations predicting the plastic strains
  resulting from a bird ingestion simulation (bird
  strike) of aircraft engine fans can be performed
  fast enough such that the results can be
  incorporated into the normal design iteration
  process

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References

• Olovsson, Lars Souli, Mhamed Do, Ian, LS-DYNA
  ALE Capabilities (Arbitrary-Lagrangian-Eulerian)
  Fluid-Structure Iteration Modeling, LSTC, 2002
• Iannucci, L, Bird-Strike impact modeling, ImechE
  (1998), S531/002/98
• Budgey, Richard, The Development of a Substitute
  Artificial Bird by the International Birdstrike
  Research Group for use in Aircraft Component
  Testing, IBSC25/WP-IE3, April 2000