CFD of F-18 Aircraft at High Alpha (Angle of Attack)
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Between 1987 and 1996, NASA pursued a high alpha (angle of attack) flight research program using a modified F/A-18A jet, which is predominantly used by the US Navy to this day. By modifying the flight control and jet nozzle systems, NASA was able to achieve controlled flights up to 70 degrees of angle of attack with its so called High Alpha Research Vehicle (HARV). We picked the HARV case to put CAEbridge's surface mesh preparation, tetrahedral grid generation and CFD solver capabilities to test in the context of aerospace applications. |
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Unable to identify a good source for the particular aircraft geometry, we ripped a detailed two-seater F/A-18E Super Hornet mesh geometry out of a flight simulator game and scaled the aircraft dimensions to match those of the HARV's. Unsuitable for CFD, the input surface mesh assembly was processed into an optimal water tight form while preserving the part identities. For this several CAEbridge developed mesh manipulation tools were utilized. Finally a tetrahedral grid generator was utilized to output a 1.5million volume element case. |
| CAEbridge F/A-18 Geometry Model | |
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| Water Tight Surface Mesh | Tetrahedral Volume Mesh |
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For the simulation, the aircraft is positioned at 30˚ angle of attack and steady state solution was obtained with an Rng-k-epsilon turbulence model. In comparison with the HARV case for which we have been able to acquire some photos, the strake vortex break-down point is consistently at about 2/3 length down stream of the strake. Note that the CFD model incorporates an extended two-seater canopy, hence it is a misleading reference for the brake down point. |
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CFD Model Strake Vortex |
HARV Strake Vortex |
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| Regions of High Turbulent Kinetic Energy | Centerline Pressure Contours |
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| Surface Pressure | |
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With the availability of extensive information on the specifications and performance characteristics of this aircraft, we envision running advanced unsteady simulations integrating six degrees of freedom motion model for the aircraft motion. |
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