FAN AND INTAKE COUPLED AERODYNAMIC DESIGN OPTIMIZATION FOR UHBR AERO-ENGINES WITH LOW-PRESSURE RATIO FANS

Kurzfassung

To reduce fuel consumption as well as noise and CO2 emissions, the overall trend in civil aviation is to decrease exhaust velocities associated with an increase of the fan diameter, implying more weight and more drag because of the larger nacelle size. To compensate for the introduced weight increase, the concept of nacelles with short inlet, for which the interaction between the nacelle and the fan is higher than for current engines, is often considered. This paper proposes to design a short inlet geometry with a length over diameter ratio of l/D�0.35 that provides better or equal aerodynamic performances, predominantly for the fan, than conventional long inlet configurations with typical ratios of l/D�0.65. To obtain such a design, an optimization process with a flow field covering the entire fan, intake and nacelle system is used. The first step is to define the parameterization of the nacelle which finally contains the nacelle and the intake contour as basics parameters. The next step is to establish a robust and automatic meshing procedure of the entire calculation domain (far field, nacelle, intake and fan), which guarantees a high mesh quality independent of the parameter selected. AutoOpti, which is an optimization tool developed at DLR, is applied, providing an optimization framework based on an evolutionary algorithm with heavy surrogate model enhancements. For the calculations, which are realized with the DLR in-house solver TRACE, three operating conditions are considered: static take-off (OP1), take-off (OP2) and cruise (OP3). The classification of the results is based on the assessment of the fan aerodynamic performances, considering fan total pressure ratio for OP1 and OP2 with the aim to increase the fan stability limit and on the isentropic efficiency for OP3. Among the Paretofront, the best individual is selected and analyzed qualitatively and quantitatively, explaining the performance gain and corresponding geometric modifications of the intake and lip section. A new optimization process is realized to minimize the pressure peak observed at static take-off condition on the nacelle’s leading edge. Then, a full annulus nacelle geometry is created in order to study the influence of some asymmetric parameters such as the angle of the nacelle inlet face (droop angle), the thickness in circumferential direction and the inflow angle