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COMPUTATIONAL AERODYNAMICS OFA PARATROOPER SEPARATING

FROM AN AIRCRAFT

V. Udoewa, R. Keedy, T. Tezduyar and E. AkinTeam for Advanced Flow Simulation and Modeling

Mechanical Engineering and Materials ScienceRice University, Houston, Texas

T. NonoshitaNEPON Inc., Japan

K. Stein and R. BenneyNatick Soldier Center

A. JohnsonNetwork Computing Services

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Objectives• To accurately model the aerodynamic

interaction between an aircraft and a paratrooper or cargo

• To investigate the possible crossing of paratrooper paths

• To design methods which can be applied to other problems requiring advanced mesh moving techniques

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Governing Equations

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Deforming-Spatial-Domain/Stabilized Space-Time (DSD/SST)

Formulation

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Deforming-Spatial-Domain/Stabilized Space-Time (DSD/SST)

Formulation

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New Computational Methods and Technologies

• An Advanced Flow Solver based on Parallel Computing

• Mesh Management Methods– Aerodynamic Interaction Between Cargo

Aircraft and Paratrooper or Cargo– Mesh Generation and Update Methods

• Mesh Distortion• When to Remesh• Remeshing Techniques• Methods for Projection after Remesh

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Plane and Paratrooper Surface Mesh with Remeshing Box

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Paratrooper Cabin and Remeshing Box: Side View

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Paratrooper Jump

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Aircraft—New Model

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Paratrooper—Earlier Model

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Paratrooper—New Model

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Simulation Parameters

• Surface Model/Mesh– paratrooper

• nodes 32,643• elements 65,423

• Volume Mesh– paratrooper

• nodes 106,264• elements

602,061

• Near-Term Goal: 1-1.5 million elements

• Dt = 8.1E-10 (Dt*U/L)

– cargo• nodes 69,030• elements

138,126

– cargo• nodes 289,838• elements

1,697,658

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Air Pressure Distribution on Aircraft

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Air Pressure and Streamlines forParatrooper

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What once was treated like a sphere...

…is now recognized as having an inertia tensor

Mechanics Correction…

• Earlier computations had an over-simplified moment of inertia model in calculation of angular velocities

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Paratrooper Path

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Paratrooper Path (I-mtx)

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X-Force

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Y-Force

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Z-Force

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X-Force (Inertia Matrix)

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Y-Force (Inertia Matrix)

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Z-Force (Inertia Matrix)

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Spoiler Door…

• Due to restrictions with refinement values and mesh generation software, we had to compromise for the shape without the holes (may be represented later by changing boundary conditions of individual nodes)

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Reasoning for No Holes...

• For refinement values too low, our surface mesh generator would create unrealistic diamond holes and ugly elements

• In order to get shapely holes, mesh needed too much refinement, and unexplained patches of ugliness appeared

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Cause of Problems…

• A necessary evil of our surface modeler is that faces must be defined by no more than four edges, making an already complicated geometry become even more unwieldy

• Removing the holes makes the problem much more manageable

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Creating a Full Surface Model…

• The surface modeler needed the added capability of completing the generated half of a symmetric surface model to create a full one

• Fortran 90 was used to write a program which mirrors the cargo plane across the symmetry plane and synthesizes the model together

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Adding the Cargo Door…

• Using the skeleton of the F90 program used to mirror the plane, more functions were added to complete repetitive tasks (e.g. copying lines) while creating the rear cargo door

• Both the lower and upper doors were modeled to better approximate the actual geometry

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Modeling the Cargo

• First, we studied the video of an arbitrary cargo drop for reference

• An initial cargo model was rendered to reflect the shape and proportion of the real cargo

• Changes were made in the organization (but not shape) of model for simplicity

• To accurately portray the motion of the cargo, our dynamics solver was changed to simulate the cargo sliding down the floor and tipping off of the edge

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Cargo Simulation

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Cargo Pre-Tipping

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Cargo Tipping Stage

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Aircraft Model with Higher Refinement…

• Double refinement boundary layer test case

• Working to find the “right” refinement

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Costs/Challenges

• Flow Solver• Mesh Moving

– Newton’s Laws– Navier-Stokes Equations

• Remeshing• Projection

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What’s Next?

• Spoiler door• Add wind effects• Better boundary layer

resolution• Modifications to

aircraft geometry

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Acknowledgments

• US Army Natick Soldier Center• NASA Johnson Space Center• National Science Foundation: Alliances

for Graduate Education and the Professoriate

Slide Number 1ObjectivesGoverning EquationsDeforming-Spatial-Domain/�Stabilized Space-Time (DSD/SST)�FormulationSlide Number 5New Computational Methods and TechnologiesPlane and Paratrooper Surface Mesh with Remeshing BoxParatrooper Cabin and Remeshing Box: Side ViewParatrooper JumpAircraft—New ModelSlide Number 11Paratrooper—Earlier ModelParatrooper—New ModelSlide Number 14Slide Number 15Simulation ParametersSlide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Air Pressure Distribution on �AircraftAir Pressure and Streamlines for�ParatrooperMechanics Correction…Paratrooper PathParatrooper Path (I-mtx)X-ForceY-ForceZ-ForceX-Force (Inertia Matrix)Y-Force (Inertia Matrix)Z-Force (Inertia Matrix)Spoiler Door…Reasoning for No Holes...Cause of Problems… Creating a Full Surface �Model…Adding the Cargo Door…Modeling the �CargoCargo SimulationSlide Number 40Slide Number 41Cargo Pre-TippingCargo Tipping StageAircraft Model with Higher �Refinement…Slide Number 45Costs/ChallengesWhat’s Next?Slide Number 48