Powered Lift CFD Predictions of a Transonic Cruising STOL Military Transport

§A key enabler for the efficient design of powered lift systems for future STOL (Short TakeOff and Landing) aircraft is the ability to perform accurate CFD (Computational Fluid Dynamics) predictions of highly complicated geometries which contain both internal and external flow paths. In the case of an aircraft employing powered lift, the prediction of CLmax, stall, and pitch break is tightly coupled to the correct simulation of the propulsion losses through the internal flow paths and the behavior of the blown jet across the aerodynamic surfaces. CFD standards and practices for simulating powered lift have recently been validated as part of the Air Force’s “Speed Agile” research into a future transonic, STOL transport. This paper highlights comparisons of CFD simulations to wind tunnel testing of a transport employing hybrid powered lift that was recently tested at 23% scale in the Air Force Arnold Engineering Development (AEDC) Center National Full-scale Aerodynamics Complex (NFAC) in 2011. The model utilizes a hybrid powered lift system consisting of vectored thrust from two Williams FJ-44 engines combined with a blown circulation control flap that is fed air from a fan offtake duct. The CFD modeled both the internal and external geometry up to the engine fan and turbine faces, which were modeled with boundary conditions. Details such as the fan air offtake duct, the engine fan/core daisy lobe mixer, the vectored thrust flaps, circulation control plenum and air exit slot, and the blown flaps were all modeled along with the external aircraft geometry and the wind tunnel test section. Results show excellent correlation between CFD and test data over a range of engine thrust and blown flap settings, validating the use of these tools for design of future hybrid powered lift aircraft.