Use of fan rig data for the understanding and prediction of fan broadband noise and noise changes due to a variable area nozzle

Abstract

This thesis presents the results of the research component of this EngD, entitled
Use of fan rig data for the understanding and prediction of fan broadband noise and noise
changes due to a variable area nozzle
As suggested by the title, fan rig noise measurements form an integral part of this thesis. The
analysis of a database of rig noise measurements forms the first section of this thesis, in two
parts. The first part describes the analysis of a set of fan rig noise measurements, including the
variation of fan broadband and tone noise in forward and rearward arcs. The second part
examines a large database of fan rig noise measurements, and attempts to derive correlations
of fan broadband noise and fan performance parameters. Cluster Analysis, Principle
Component Analysis, and Regression Analysis are used to understand and describe the
underlying physics of broadband noise generation and the relationships between these
predictors.

The second section of this thesis uses a cascade broadband noise model to investigate rotorstator
broadband noise. Predictions of the broadband noise from this noise model are
compared to rig measurements, showing good accuracy. The underlying physics of rotorstator
broadband noise generation is investigated by performing two parametric studies using
the broadband noise model. The first parametric study investigates the effect on broadband
noise of simple flow and geometric parameters, namely number of vanes, vane chord, vane
stagger angle, and rotor wake turbulence intensity, turbulent length scale, and flow Mach
number onto the cascade. These results are used to derive scaling power laws for the
prediction of changes in broadband noise due to changes in these parameters. The second
parametric study expands upon this by investigating the effect on broadband noise of the fan
design parameters shaft speed, pressure ratio, and efficiency, at approach, cutback and cruise
conditions. The variation in broadband noise due to these design parameters is explained by
considering the underlying flow and geometric parameters such as number of vanes and Mach
number, and the scaling power laws based on these simple parameters are used to predict the
change in broadband noise between different performance points.
The final section of this thesis investigates the effect of varying exhaust nozzle area on total
engine noise. A new method is presented that allows the transfer of changes in fan rig noise to
Eugene P. Deane EngD Thesis September 2009 2
engine noise predictions, to estimate the change in fan noise due to the pressure ratio changes
brought about by a variable area nozzle. Changes in engine noise are investigated for
approach, cutback, and sideline conditions, and the application of the new method assessed.

As the research displayed in this thesis is closely linked to industry, the foundation of work
presented in several chapters is dependent on data or figures that are commercially sensitive.
It has therefore been necessary to create a confidential appendix (Appendix X) to include
these commercially sensitive items. These additional results and figures in Appendix X are
supplementary in nature, and sufficient results are presented in the public thesis to illustrate
the results of the various chapters. Where supplementary information and results are available,
this is clearly indicated at the pertinent point in the published thesis, along with the section of
Appendix X where the information can be found.

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