Principal Investigator Zoltan Spakovszky
Aircraft engine design trends tend towards higher bypass ratio, lower pressure ratio fan designs for improved fuel burn, reduced emissions and noise. Low-pressure ratio fans offer increased propulsive efficiency and, besides enabling thermodynamic cycle changes for improved fuel efficiency, significant acoustic benefits can be achieved. Fan diameters increase as fan pressure ratios (FPR) are reduced, and the design of innovative nacelle concepts becomes critical to limit the impact of larger diameter fans on nacelle weight and drag. The proposed work addresses the uncharted design space of low FPR propulsors and their nacelles and will provide new inlet and nacelle design guidelines to minimize nacelle drag and maximize fuel burn benefits in low FPR propulsors without jeopardizing operability.
Since low-pressure ratio fans and their nacelles are more closely coupled than current turbofan engines, inlet-fan interaction and inlet flow distortion at the fan face are increased. Consequently, a coupled fan-nacelle approach capable of capturing inlet-fan and fanexhaust interactions is required to evaluate the performance of low FPR propulsors. In this work, a fast and reliable body force based approach was developed to assess the performance of innovative nacelle concepts. In this approach, rotor and stator blade rows are replaced by body force fields determined from steady single-passage RANS simulations. Steady full-annulus simulations are carried out to determine the performance of fan stage and nacelle in the presence of non-uniform inflow and back pressure distortion due to pylon and bifurcation. The developed method was demonstrated to capture the coupling of internal and external flows and the distortion transfer through the fan stage and reduces the computational cost by up to two orders of magnitude compared to full 3D unsteady RANS simulations.
The next step is to use the body force based approach to conduct a parametric study of candidate inlet and nacelle geometries with the objective to improve the propulsor performance by reducing nacelle drag and weight.