NUMERICAL STUDIES OF JET-WING DISTRIBUTED PROPULSION FLOW FIELDS

Modern transport aircraft use two or four engines in a Cayley arrangement where the thrust is concentrated just behind each engine. Distributed propulsion is the idea of redistributing the thrust across all or most of the drag producing elements of the vehicle with one major aim of producing a mo re uniform wake and thus higher propulsion efficiency that would lead to lower fuel consumption with an attendant reduction in emissions. Our configuration for distributed propulsion has a modest number of engines with part of the exhaust flow vented from thick trailing edges of the wings to cancel the local profile drag and the rest of the exhaust flow providing thrust to cancel the induced drag and drag of the fuselage and tails. This paper presents the results of CFD studies that were performed on two -di mensional wing sections in transonic, viscous flow to analyze the jetwing distributed propulsion flow fields at a range of flow conditions with different airfoil geometries. The goals of these numerical studies were: (1) to ascertain the effect of jet -wing distributed propulsion on propulsion efficiency, (2) to observe how jet-wing distributed propulsion affects the flow-field (3) to determine design changes that might be implemented for achieving efficient distributed propulsion, and (4) to investigate the effect of the jet-flaps with small jet deflection angles on aerodynamic parameters. Numerical studies were performed using two supercritical airfoils corresponding to the Outboard (11% thick) and Inboard (16% thick) wing sections of a conventional trans port wing. Furthermore, in an attempt to increase the propulsion efficiency, the trailing edge thickness of the Outboard 11% thick airfoil was doubled in size. Jet-wing results were obtained at design Reynolds numbers for all the airfoils and at a low Reynolds number for the Outboard airfoil. The studies show that jet-wing distributed propulsion can be used to obtain propulsive efficiencies on the order of turbofan engine aircraft. If the trailing edge of the Outboard airfoil thickness is expanded, then jet-wing distributed propulsion can give improved propulsive efficiency (7.5% higher). However, expanding the trailing edge must be done with care, as there is a drag penalty. Since the increase in propulsion efficiency could be achieved without expanding the trailing edge and incurring a drag penalty for the Inboard airfoil, this airfoil geometry and other similar transonic wing sections can be thought of as good candidates for the jet-wing application. In addition to the jet-wing studies, some jetflap cases with small jet deflections angles were performed for the Outboard airfoil at the low Reynolds number. The results show that a jet deflected even with a small angle can significantly increase (or decrease, if jet deflection is negative) the lift and pitching moment of a jet-wing vehicle. These results support the idea of using deflected exhaust jets from trailing edges as possible replacement for conventional control surfaces. However, there is also a drag penalty associated with positive jet deflection angles just as with conventional flap deflections.