(Georgia Institute of Technology, 2018)
Berguin, Steven H.; Renganathan, Sudharshan Ashwin; Ahuja, Jai; Chen, Mengzhen; Tai, Jimmy C. M.; Mavris, Dimitri N.
A sensitivity analysis is performed to quantify the relative impact of perturbing a set of design variables representing an airplane configuration with Over-Wing Nacelles (OWN), operating at transonic cruise. The goal is to study the impact of perturbing the engine's XYZ position and power setting on installation drag, engine inlet pressure recovery, and lift curve characteristics. High- fidelity Reynolds Averaged Navier-Stokes (RANS) simulations of the Common Research Model (CRM) modified with powered, over-wing nacelles are performed and dominant main effects and interactions are identified. The most dominant effect was by far the engine's X position, but it was also found that podded OWN configurations exhibit statistically significant, aero-propulsive coupling. Specifically, certain engine locations cause changes in the flow-field that deteriorate inlet pressure recovery and, vice
versa, a change in engine boundary conditions can affect installation drag. It is therefore recommended to simulate OWN concepts using a coupled MDA or MDAO approach to capture interdependencies between aerodynamics and propulsion.
(Georgia Institute of Technology, 2018)
Ahuja, Jai; Renganathan, Sudharshan Ashwin; Berguin, Steven; Mavris, Dimitri N.
The Over Wing Nacelle (OWN) concept enables the installation of turbofans with high bypass ratios for improved effciency in commercial transport vehicles, in addition to offering other advantages in the form of (i) mitigation of jet noise, (ii) foreign object damage avoidance and (iii) jet-powered lift. While these benefits can be offset by the large transonic drag rise, aerodynamic shape optimization of the wing and nacelle outer mold lines can help realize the full aerodynamic potential of the OWN concept. However, if coupling between the airframe aerodynamics and the propulsion system is strong, multidisciplinary optimization may need to be conducted. In this paper, the aerodynamics-propulsion coupling in the OWN concept is studied. A high fidelity Reynolds Averaged Navier Stokes (RANS) model along with a low fidelity engine thermodynamic cycle analysis model are
used to represent the aerodynamic and propulsion systems respectively. The necessary coupling variables are identified and the coupled system is solved for disciplinary feasibility using the Fixed Point Iteration technique. The Common Research Model (CRM) wing and nacelle are used as the baseline geometry to carry out the study. The study reveals that for the OWN concept, aerodynamics-propulsion coupling is not significant enough to warrant multi-disciplinary shape optimization. While airframe aerodynamics has a strong effect on the propulsion system, the reverse interaction is weaker.