Aeropropulsive assessment of engine installation at cruise for UHBPR turbofan with body force fan modelling

Abstract

The overall propulsive performance of an aircraft with podded nacelles depends on the interaction occurring between the wing body and the propulsor. With the tight installation required for Ultra-High Bypass Ratio (UHBPR) turbofans, the engine and airframe flows are more coupled, resulting in a mutual interference that can affect the working condition of the turbomachinery and the wing flow. In the paper, we employ a fully coupled fan stage model based on a body force method to evaluate the performance of an ultra-high bypass ratio turbofan in a nominal and closely-coupled installation position, along the cruise phase of a long-haul flight at Mach number 0.85. By comparing the results obtained with a standard powered-on representation based on one-dimensional static boundary conditions, we assess the effect of the engine/airframe coupling on the aerodynamics and propulsive forces. The major differences occur on the discharge flow, on the internal fan nozzle duct and on the jet/wing interaction, due to the nonuniform fan stage outlet status in the body force simulations. The net vehicle force deviates from 1% to 1.6%, according to the position and the cruise phase. The sensitivity of the propulsive forces to the change of installation position, instead, is in general consistent for the two methods. The discrepancy can be much larger if the 1D boundary conditions are not corrected for true engine operating points arising under installation, exceeding 8% in the tighter assembly for the net vehicle force.