| Abstract: |
Presently, air transport has become more common, which resulted inincreased air traffic and thus an increased number of people affected by aircraftnoise, including passengers, crews, and members of communities located nearairports.The development of turbofan engines led to a reduction in jet noise and anincrease in fan and compressor noise. In high-bypass-ratio (HBPR) turbofanengines the fan dominates the inlet-related noise. Aeroengine broadband fannoise is a major contributor to the community noise exposure from aircraft.The purpose of this study is the prediction of the broad band noisegenerated by the fan rotor of a high bypass ratio turbofan engine (similar to GECF6-50). A numerical investigation of the aerodynamics of a fan rotor isdescribed, with emphasis on acoustics.A commercial CFD code (FLUENT 6.3.26) is used to solve the RANSequations. The flow is simulated using a three dimensional, unsteady, viscous,turbulent flow model for intake and fan rotor. Turbulence is modeled using theRNG k-s model. The turbulence model is used with the non-equilibrium wallfunction approach in the near-wall region.The flow field was solved in the fan and its intake using the Navier-Stokesfinite volume solver. The computational domain employed here is a periodicsector through both the fan and its intake bounding an angle of (360/38) wherethe number of fan blades is (38). The intake is a stationary domain while the fanis a rotating one. Rotation of fan rotor is simulated using the sliding gridtechnique.Two flight conditions were considered; take-off and cruise conditions. Fortake-off condition, noise annoys aircrafts’ passengers, crew, and members ofivcommunities located near airports. While for cruise condition, noise annoys onlypassengers and crew.The fan performance map, for the above mentioned flight conditions wasanalyzed considering three rotational speeds; (90%, 100%, and 110% of thedesign speed). Moreover, three case studies were examined; namely, operating(design), chocked, and a near surge points.The basic flow parameters affecting fan rotor’s noise are; flow velocityand relative Mach number, with the flow turbulence as most important.The dominant broad band noise mechanisms are due to, interaction ofturbulence of the incoming flow with the engine casing and nose, interactionbetween the rotating blade and turbulence in the incoming flow (inflow-noise),and interaction between the turbulent boundary layers on the rotor blades andtheir trailing edges (self-noise).Chocked case scored the highest noise level as it has the maximumturbulent kinetic energy levels, maximum mass flow rate and thus maximumrelative Mach number. Near-surge case has the lowest noise level except at thelower part of the suction side ofthe rotor.The main source of broadband noise for the near surge condition is thereverse flow, and separation at the lower part of the suction side of the rotorcausing higher values of turbulence. So, at this region the near surge point has ahigher noise level than the design point. Close to the casing surface, the nearsurge condition has the highest values of turbulent kinetic energy and so thehighest values of noise levels.v
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