Unsteady Aerodynamics and Aeroacoustics of a High-Bypass Ratio Fan Stage

Abstract

A numerical investigation of the unsteady aerodynamics of a fan stage comprised of a transonic rotor, swept fan exit guide vane (FEGV), and low-pressure compressor inlet guide vane (IGV) is described, with emphasis on acoustics. It is shown that the effects of the two downstream stator rows on the time-mean blade flow field are negligible, permitting its investigation using isolated rotor calculations. Simulations of this type are carried out along the engine operating line to quantify the acoustic sources associated with the upstream shock field and wake turbulence-stator interaction. The shock noise achieves its maximum value near the flyover acoustic certification condition, while the wake turbulence is least at this condition owing to its proximity to the design point. The behavior of these noise sources is explained physically by carrying out a detailed examination of the rotor flow field. The unsteady interaction between the rotor and stator rows at a high-power setting is investigated next. It is shown that the time-mean IGV flow is significantly affected by this interaction. Moreover, the unsteady loading on the IGV is found to be large. The behavior of the upstream-propagating acoustic field generated by rotor-IGV interaction is examined. The interaction between the rotor and FEGV is found to be linear in nature. The FEGV surface unsteady pressure and far-field acoustic field behavior are investigated.