الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Presently, air transport has become more common, which resulted in
increased air traffic and thus an increased number of people affected by aircraft
noise, including passengers, crews, and members of communities located near
airports.
The development of turbofan engines led to a reduction in jet noise and an
increase in fan and compressor noise. In high-bypass-ratio (HBPR) turbofan
engines the fan dominates the inlet-related noise. Aeroengine broadband fan
noise is a major contributor to the community noise exposure from aircraft.
The purpose of this study is the prediction of the broad band noise
generated by the fan rotor of a high bypass ratio turbofan engine (similar to GE
CF6-50). A numerical investigation of the aerodynamics of a fan rotor is
described, with emphasis on acoustics.
A commercial CFD code (FLUENT 6.3.26) is used to solve the RANS
equations. The flow is simulated using a three dimensional, unsteady, viscous,
turbulent flow model for intake and fan rotor. Turbulence is modeled using the
RNG k-s model. The turbulence model is used with the non-equilibrium wall
function approach in the near-wall region.
The flow field was solved in the fan and its intake using the Navier-Stokes
finite volume solver. The computational domain employed here is a periodic
sector through both the fan and its intake bounding an angle of (360/38) where
the number of fan blades is (38). The intake is a stationary domain while the fan
is a rotating one. Rotation of fan rotor is simulated using the sliding grid
technique.
Two flight conditions were considered; take-off and cruise conditions. For
take-off condition, noise annoys aircrafts’ passengers, crew, and members of
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communities located near airports. While for cruise condition, noise annoys only
passengers and crew.
The fan performance map, for the above mentioned flight conditions was
analyzed considering three rotational speeds; (90%, 100%, and 110% of the
design 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 velocity
and relative Mach number, with the flow turbulence as most important.
The dominant broad band noise mechanisms are due to, interaction of
turbulence of the incoming flow with the engine casing and nose, interaction
between the rotating blade and turbulence in the incoming flow (inflow-noise),
and interaction between the turbulent boundary layers on the rotor blades and
their trailing edges (self-noise).
Chocked case scored the highest noise level as it has the maximum
turbulent kinetic energy levels, maximum mass flow rate and thus maximum
relative Mach number. Near-surge case has the lowest noise level except at the
lower part of the suction side ofthe rotor.
The main source of broadband noise for the near surge condition is the
reverse flow, and separation at the lower part of the suction side of the rotor
causing higher values of turbulence. So, at this region the near surge point has a
higher noise level than the design point. Close to the casing surface, the near
surge condition has the highest values of turbulent kinetic energy and so the
highest values of noise levels.
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