Study of Supersonic Jet Noise Reduction using LES
Doctoral thesis, 2014
Increases in air traffic and denser population around airports have led to stricter
regulations on aircraft noise. High noise levels from high-speed aircraft can cause
hearing damage in pilots and the airfield personnel. The engine is the main source
of noise of all jet aircraft and is therefore a key component for improvement.
Decreasing jet engine noise can in some cases reduce sonic fatigue and thereby
increase the engine lifetime. In this thesis, the response of the radiated noise from
a supersonic jet emitted from a converging diverging nozzle to steady-state, pulsed
and flapping fluidic injection is studied using Large Eddy Simulation (LES), and
comparisons are made with experimental data. An investigation is also presented
in which actions were taken to reduce the internal shock strength by modifying the
nozzle throat, and thereby reduce the radiated noise. The optimized nozzle nearly
eliminates the internal shock, which reduces the double diamond structure in the
jet plume but increases the strength of the shock at the nozzle exit. It has lower
turbulence levels at the nozzle exit due to a weaker shock interaction with the
shear layer. The optimized nozzle provides equal thrust to the sharp nozzle with
4 % less pressure without any acoustic penalty. The pulsed injection showed that
the radiated noise is sensitive to the pulsation characteristics and the pulsation fre-
quency. It was shown that the noise reduction with pulsed injection can equal the
noise reduction of steady-state injection with a lower net mass flow of the pulsed
injection. However, increased noise was noted at the downstream observers. The
flapping injection cases that were investigated did not show improvements over
the corresponding steady injection cases. These are positive findings, since steady
injection should be simpler and more robust to apply to real jet engines. The
injection was shown to impact the jet thrust, as expected. The net jet thrust in-
creased with increased injection mass flow, whereas the specific thrust decreased.
The momentum thrust was shown to decrease with increased injection mass flow
whereas the pressure thrust increased due to a shock shift at the nozzle exit. The
work presented in this thesis adds to the body of knowledge found in the liter-
ature about supersonic jet noise generation and its noise reduction using fluidic
injection.
G3D
Supersonic Jet
PIV
CD-nozzle
CFD
Compressible flow
CAA
Noise Reduction
LES
Flow Control
Virtual Development Laboratory, VDL, Hörsalsvägen 7a, Johanneberg, Chalmers University of Technology
Opponent: Professor Christophe Bailly, Institut Universitaire de France, Ecole Centrale de Lyon, France