Aerodynamic Investigations of an Advanced Over-the-Wing Nacelle Transport Aircraft Configuration

The transonic aerodynamic characteristics of an advanced, Over-the-Wing Nacelle (OWN), subsonic transport configuration are assessed using both inviscid Euler and viscous Navier-Stokes CFD. Results of the assessments are compared to a similar configuration with a more traditional Under-the-Wing Nacelle (UWN) installation and a similar reference Wing-Body (WB). The engine installation and inboard wing section of the OWN are designed to create a channel between the nacelle and fuselage that accelerates the upper surface wing flow, increases leading edge suction, and subsequently reduces the overall drag. CFD results were used to examine the span loadings of the three configurations and allow normalization of their wing twist distributions. Qualitative observations and quantitative drag computations are performed for the three configurations at a cruise Mach number of 0.78, an approximate altitude of 35,000 ft, and a CL of 0.44. It was found that the OWN’s inboard wing channel section is effective in producing favorable leading edge suction but that the overall drag, compared to the UWN, is higher by 32 counts. Although the source of this drag excess could not be precisely identified, it was isolated in the nacelle region. CFD solutions were obtained for several transonic Mach numbers to assess the drag rise characteristics of the three configurations. Inviscid Euler results showed similar trends to previous studies where the OWN is higher in drag at lower Mach numbers but enjoys a much milder drag rise than the UWN or WB and has lower drag at higher Mach numbers. Viscous Navier-Stokes results however showed that the effect of shock-induced flow separation significantly increases the drag rise but that the OWN still likely experiences it less severely than the UWN. Overall, the results of this study indicate that the Over-theWing Nacelle concept under consideration appears to be an aerodynamically competitive engine installation to the more traditional Under-the-Wing pylon installation.