Noise Prediction of a NACA 0015 Airfoil with Gurney Flap

154 Pages·2015·15.71 MB·English

by  Xueqing Zhang

Master of Science Thesis
Noise Prediction of a NACA 0015
Airfoil with Gurney Flap
A study based on Time-Resolved Particle Image Velocimetry
Xueqing Zhang
December 22, 2015
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Noise Prediction of a NACA 0015
Airfoil with Gurney Flap
A study based on Time-Resolved Particle Image Velocimetry
Master of Science Thesis
For obtaining the degree of Master of Science in Aerospace
Engineering at Delft University of Technology
Xueqing Zhang
December 22, 2015
Faculty of Aerospace Engineering · Delft University of Technology
Delft University of Technology
Copyright (cid:13)c Aerospace Engineering, Delft University of Technology
All rights reserved.
DELFT UNIVERSITY OF TECHNOLOGY
DEPARTMENT OF AERODYNAMICS
The undersigned hereby certify that they have read and recommend to the Faculty
of Aerospace Engineering for acceptance the thesis entitled “Noise Prediction of a
NACA 0015 Airfoil with Gurney Flap” by Xueqing Zhang in fulfillment of the
requirements for the degree of Master of Science.
Dated: December 22, 2015
Supervisors:
Dr. ir. Andrea Sciacchitano
Prof. dr.-Ing. Fulvio Scarano
Dr. ir. Daniele Ragni
Dr. ir. Bas W. van Oudheusden

Preface
This thesis is dedicated to my family, whose unconditional love is never absent to back
me up, and whose own sedulous pursuits of professional excellence always encourage me
to move on. In memory of my grandfather, who set the paragon of a qualified aerospace
engineer for me to follow. I am grateful to Teng Wang, for his help in digital signal
processing and for every moment we have spent together.
Many gratitudes to Dr.Andrea Sciacchitano, for offering me the opportunity to work on
aeroacoustics and for being an excellent mentor throughout the process. It has been an
honour to work under his supervision. Si me lo permite, quisiera darle mis m´as sinceras
felicitaciones y mis mejores deseos para esta nueva etapa en su vida, ¡un b´eb´e!
Furthermore, I would like to thank Dr.Stefan Pr¨obsting, for the patient guidance
and discussions in aeroacoustics, as well as for sharing the perceptions he harbours
for this world that offered me a viewpoint I could otherwise ignore with my eastern
cultural background. I would also like to thank all the technicians in the aerodynamics
department for their friendly help and icecreams.
To all who shared this journey, thank you! Special mentions are due to Ilke and Zhenni,
without whom my journey at TU Delft would never have begun; to Alberto, Ananth,
Bo, Bowei, Jiale, Jiggar, Koen, Linfeng, Mudit, Remco, Shengling, Shruthi, Teng, Yifei,
Ziyuan and many others with whom I had the pleasure of crossing our paths; to Xin
Liao and Xing Meng, who are far away but always near.
Xueqing Zhang (Caddie)
张 雪晴
Delft, December 2015
MSc. Thesis XueqingZhang
vi Preface
People who design machines and airplanes, no matter how much they be-
lieve that what they do is good, the winds of time eventually turn them into tools
of industrial civilization. They’re cursed dreams. Beautiful yet cursed dreams.
— Hayao Miyazaki
“设计飞机和机械的人，无论他们的意图是多么善良，时代之风会把它转
化为机械文明的工具，从来都不是无害的，都是被诅咒的梦想。”
— 宫崎 骏
XueqingZhang M.Sc. Thesis
Abstract
Air traffic noise, especially during the aircraft take-off and landing, has been uni-
versallyacknowledgedasanuisance,forwhichreason,theInternationalCivilAvia-
tion Organization(ICAO) has ratified articles and established specifications aiming
at the attenuation of air traffic noise, such as the Annex 16. The implementation
of large bypass ratio turbo-fan engines on civil aircrafts and the application of de-
signs such as engine nacelle and chevron nozzle have shifted the attention of noise
control to the deployment of high-lift devices during take-off and landing. Source
control is proved to be effective in the reduction of aeronautical noise. Traditional
aeroacoustic assessments rely mainly on microphone (array) measurements and
instantaneous flow fields obtained from CFD. However, the former fails in provid-
ing the mechanism of sound generation and the latter becomes prohibitive in the
operating Reynolds number range of real aircrafts.
Previous investigations have validated the causality between the unsteady trans-
verse velocity in the wake of the high-lift devices and the far-field pressure fluctua-
tion. This thesis is a continuation of the previous study, focusing on investigating
the feasibility of noise prediction of high-lift devices based on experimental data
obtained by time-resolved PIV . A model of NACA 0015 airfoil with Gurney flap
of the height of 6% the chord length has been investigated by means of 2D time-
resolved PIV in combination with simultaneous microphone measurements. The
Gurney flap is a simplified model of the high-lift devices with more complex struc-
ture in real application. The experimental parameters were selected such that the
source of sound can be treated as compact and consequentially guaranteed the
MSc. Thesis XueqingZhang
viii Abstract
applicability of both the distributed and the lumped formulation of the Curle’s
aeroacoustic analogy.
In the first step, the time evolving pressure field was deduced from the velocity
field measured by 2D TR-PIV, by the Poisson-based solver for quasi-2D incom-
pressible flows. Pressure on the surfaces of the airfoil then constitutes the source
terms of the distributed formulation of Curle’s analogy and the corresponding far-
field noise was evaluated. In the second step, the aerodynamic loads of the airfoil
were evaluated from the velocity field by means of momentum balance, which were
then used in the lumped formulation for noise prediction. The spanwise coherence
length evaluated from the cross-plane flow visualizations was applied for the cor-
rection of 3D effect.
Both formulations of the Curle’s analogy yield noise evaluation of fair agreement
with the simultaneous microphone measurements. All the calculated far-field noise
power spectra reproduce the peak at Ka´rm´an vortex shedding frequency, which
agrees well with the microphone measurements. The pressure fluctuations yielded
by distributed formulation of the Curle’s analogy are somehow damped due to
the Gaussian smoothing applied to the velocity fields in the process of pressure
reconstruction for the elimination of spurious spatial derivatives. Such damping
effect can be circumvented by the lumped formulation, since the pressure is only
evaluated on control volume boundaries in the locating in the far-wake, where 3D
motions are weaker than in the region in direct proximity of the airfoil trailing
edge. The high frequency components in the computed acoustic spectra are the
most affected by the experimental and numerical errors. The coherence length
correction reduce the over-estimation of the predicted noise levels with respect to
the microphone measured ones. However, there still exists room for improvement
in the procedure of coherence length correction.
Concludingly, this thesis proved TR-PIV an effective approach in the noise pre-
diction of airfoil with Gurney flap and stepped out the first step in PIV-based
aeroacousitic investigations of the high-lift devices. Application of the approach
on high-lift devices with more complex configurations would be a prospective con-
tinuation of the current study.
XueqingZhang M.Sc. Thesis