Numerical Investigation of Internal–External Flow Coupling and Spillage Characteristics of a High-Bypass-Ratio Turbofan Nacelle Using a Body-Force Model

To investigate the coupled internal–external flow and spillage characteristics of high-bypass-ratio turbofan nacelles, an improved compressor body-force model is developed. Starting from the three-dimensional Navier–Stokes equations, circumferentially averaged body-force source terms are extracted from baseline single-passage simulations. The body-force distribution is then normalized, concentrated circumferentially within blade regions using blade geometric data, and corrected radially using five-hole-probe measurements at the rotor inlet and outlet. By correlating the body force with two local aerodynamic parameters, namely the flow following angle and the axial velocity, the model responds to variations in the intake mass-flow rate and inflow angle. The model is first validated for NASA Rotor 67: the predicted characteristic curves agree with the single-passage RANS results within 0.5% over the entire operating range, and the spanwise distributions of total pressure, total temperature, and relative flow angle deviate by less than 1.5% over the 10–90% blade span, with larger deviations confined to the hub and tip regions. Coupled nacelle–fan simulations are then performed, and a powered nacelle spillage-drag test is conducted in a 2.4 m transonic wind tunnel. At Ma = 0.75, the numerical and experimental spillage-drag results show good agreement, and the predicted spillage-drag coefficient is approximately 0.026, with the nacelle frontal area as the reference area.