Numerical simulation of powered high-lift jet effects for large transport

Taking C-17 transport engine installation as reference and considering external mixing of engine jet gas streams, a powered high-lift configuration with externally blowing flap (EBF) and the corresponding cruise model were constructed. Based on the structured multi-block grid techniques and Reynolds-averaged Navier-Stokes methods, numerical validations were carried out on a high-lift model and a fan-jet engine nacelle, and then the EBF effects were investigated. For powered high-lift configuration at low speed, most jet flow impinged directly on the lower flap surfaces and then deflected downward, while the rest was sucked and speeded up by the slots, and then blown upon the upper flap surfaces. The two parts of them converged at the flap trailing edge and extended downward. Spanwise lateral flow characteristics existed when the jet flow affected on the flap. Circulations increased significantly not just around the flaps but also on the slat and main wing. Both the available and maximum lift coefficients were larger than 4.0, breaking through the limit of the traditional mechanical high-lift systems. Longitude trim problems may be severer due to larger nose down pitching moment. For the cruise model at high speed, the engine jet flow will obviously affect the pressure distributions on lower wing surface, making the lift decrease and the drag increase significantly. Thus jet effects should be well considered during the clean wing design for powered high-lift configuration.