Flow Simulation at OffDesign Conditions
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Flow Simulation at OffDesign Conditions
Kennett, D.J., Hoholis, G. and Badcock, K.J.
BAE Systems
Technology Strategy Board (TSB)
Project Background
The ability of computational fluid dynamics to predict the steady and unsteady fluid flow over the SACCON UCAV configuration, with and without control surface deflections, at off design conditions is investigated.
The complex, nonlinear flow, various combinations of control surface deflection and the presence of multiple interacting vortices on the flow histories provides a challenging test for current capability.
A range of static and dynamic test cases have been computed, for both low and high speed flows, for comparison with experimental data, obtained as part of the NATO STO AVT201 Task Group.
The simulations are performed using a multiblock code to solve the ReynoldsAveraged NavierStokes equations; and the control surfaces are modelled with a deformed mesh and blended gaps that simplify the geometry.
These tests will provide an assessment of the ability of computational fluid dynamics to evaluate such flows, and will allow for deficiencies in the state of the art to be identified.
Results show that the flow is quite benign at angle of attack 10 degrees, but becomes very nonlinear at angles of attack 15 degrees and above.
Several vortices are present, which the RANS equations are able to predict, though not necessarily at the correct location or with the correct strength.
The SACCON has a rounded leading edge, and so the flow is very sensitive to the turbulence model used, especially in the separation region.
Results
Click on the following images to enlarge the view.
Pressure coefficient with left inboard flap deflection 20 degrees and right inboard flap deflection +20 degrees at alpha 15 degrees angle of attack.
Pressure coefficient with left outboard flap deflection 20 degrees and right outboard flap deflection +20 degrees at alpha 15 degrees angle of attack.
References
More details can be found in the following publications:
Conference Papers

Kennett, D. J., Hoholis, G., Badcock, K. J., "Numerical Simulation of Control Surface Deflections over a Generic UCAV configuration at Offdesign Flow Conditions," 32nd AIAA Applied Aerodynamics Conference, Atlanta, Georgia, June. 2014.
AIAA Paper 20142134