Simulation of Comanche Tail-Buffet
Investigator: R. Meakin, Army AFDD (AMCOM)
Application Overview
For certain flow conditions involving the Comanche Helicopter in level forward flight, a tail-buffet phenomenon has been observed in test-flights and in scale-model tunnel tests. For the tunnel tests, the phenomenon has been observed with and without the main rotor. OVERFLOW-D is applied to this problem to identify the unsteady aerodynamic mechanism of the phenomenon and to collect computational statistics for software development purposes.
Methodology
Overset structured grids are used to discretize the Comanche geometry. The approach is well suited to analysis of such applications. Grid components conform to the shape of the Comanche, facilitating resolution of the viscous boundary layer and important off body aerodynamics. The near-body portion of the Comanche geometry is decomposed into 110 components and approximately 2.2 million points. The default off-body grid system includes 233 components and 5.1 million points, for a total of 343 components at 7.3 million points in all. The baseline simulation is carried out on 22-nodes of the IBM-SP (osprey) at the DoD MSRC located at CEWES. The simulation is repeated for a subset of the case temporal domain using 1, 12, 18, 24, and 30 processors to evaluate scalability. The scaleup computations are repeated on an SGI Origin 2000 machine for comparative purposes. Results of the simulations are available in AIAA Paper 99-3302-CP.
Results
Simulation of the Comanche tail-buffet phenomenon is carried out on the near-body and default off-body grid system. Solution adaption within the off-body domain was not initiated because all of the significant flow features were contained in the near-body and default level-1 off-body grids. Of course, adaption would have extended the level-1 grid to resolve the wake system downstream of the aircraft. However, since the wake has little, if any, effect on the source of the tail buffet, adaption is never initiated in the simulation.
Picture 1Selected surfaces from near-body grid system
Picture 2
Close-up of near-body grid (top front part of canopy) overlapping level-1 off-body grid
Picture 3
Boundaries of default level-1 off-body grid components at y=0 plane
Picture 4
Visualization of vortex shedding from rotor hub (top view) (click on picture for animation)
Picture 5
Visualization of vortex shedding from rotor hub (side view) (click on picture for animation)
Picture 6
Instantaneous Mach field at y=0 plane (side view)
Significance
This effort has dual objectives that
involve evaluation of project software and the aerodynamic performance of Comanche systems
during missile launch. The Army Aeroflightdynamics Directorate will use project software
and the compute resources of the CEWES MSRC for these simulations. The specific missile
and launch conditions will be determined later in the CHSSI project life so that final
computational statistics can be gathered from near final versions of OVERFLOW-D2 and solve
a specific problem of immediate interest to the Army at that time.
References
1. Meakin, R., ``Unsteady Aerodynamic Simulation of Static and Moving
Bodies Using Scalable Computers,'' AIAA-99-3302-CP, pp. 469-483, 14th AIAA
Computational Fluid Dynamics Conference, Norfolk, VA, June 1999.
2. Meakin, R., ``On Adaptive Refinement and Overset Structured Grids,''
AIAA-97-1858-CP,
pp. 236-249, 13th AIAA Computational Fluid Dynamics Conference, Snowmass, CO, June 1997.
3. Meakin, R., ``Unsteady
Simulation of the Viscous Flow About a V-22 Rotor and Wing in Hover,''
AIAA-95-3463-CP, pp. 332-344, AIAA Atmospheric Flight Mechanics Conference, Baltimore,
MD, August 1995.
Wanna see another adaptive
application?
Selected surfaces from near-body grid system
Close-up of near-body grid (top front part of canopy) overlapping level-1 off-body grid
Boundaries of default level-1 off-body grid components at y=0 plane
Visualization of vortex shedding from rotor hub (top view)
(click on picture for animation, 7.06 MB)
Visualization of vortex shedding from rotor hub (side view)
(click on picture for animation, 7.16 MB)
Unsteady flow over an isolated Comanche helicopter fuselage. Particles released from base of rotor hub.
Instantaneous Mach field on y=0 plane. (Side View)
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