Flow Simulation at Off-Design Conditions
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, non-linear 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 AVT-201 Task Group.
The simulations are performed using a multiblock code to solve the Reynolds-Averaged Navier-Stokes 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 non-linear 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.
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.
More details can be found in the following publications:
Kennett, D. J., Hoholis, G., Badcock, K. J., "Numerical Simulation of Control Surface Deflections over a Generic UCAV configuration at Off-design Flow Conditions," 32nd AIAA Applied Aerodynamics Conference, Atlanta, Georgia, June. 2014.
AIAA Paper 2014-2134