Numerical Studies of Jet-Wing Distributed Propulsion and a Simplified Noise Metric Method

Abstract

<P> In recent years, the aircraft industry has begun to focus its research capabilities on reducing emissions and noise produced by aircraft. Modern aircraft use two to four engines arranged on the wing or behind to produce thrust that is concentrated directly behind the engine. Kuchemann suggested a way to improve the propulsive efficiency by changing the normal configuration of engine and aircraft. This concept is the jet-wing distributed propulsion idea, which redistributes the thrust across the span of the wings. Distributed propulsion is accomplished by using many smaller engines spread across the wings or several large engines to duct the exhaust flow in a jet-wing. The jet-wing concept can be used to reduce noise and also as a replacement for flaps and slats by deflecting the jet. Since the distributed propulsion concept is also a method to reduce noise, it's important to have a simplified method of calculating the trailing edge noise of a wing. <P> One of the purposes of this paper was to study the effect of adding jet-wing distributed propulsion to a thick "inboard" airfoil. The two-dimensional jet-wing model was analyzed by parametric computational fluid dynamic (CFD) studies using the Reynolds-averaged, finite-volume, Navier-Stokes code GASP. The model was set up to be self-propelled by applying velocity and density boundary conditions to the blunt edge of the airfoil. A thick "inboard" airfoil from a realistic transonic wing was needed for the study and so the span station of the EET Wing was chosen. This airfoil was thick with a thickness to chord ratio of 16%. In adding distributed propulsion to this thick airfoil, it was found that there was an increase in the propulsive efficiency as compared to typical modern high-bypass-ratio turbofan engines with no negative aerodynamic consequences. <P> The other purpose of this study was to create and assess a simplified method to calculate the trailing edge noise metric value produced by an airfoil. Existing methods use RANS CFD, which is computationally expensive and so it seemed important to find a less expensive method. A method was formed using the Virginia Tech Boundary Layer Java Codes which calculated the characteristic turbulent velocity and characteristic turbulent length scale. A supercritical airfoil, SC(2)-0714, was used to assess the simplified method as compared to the more computationally expensive GASP runs. The results showed that this method has trends that follow those of the GASP results with the method compare well up to modest lift coefficients.