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UNIVERSIT DE SHERBROOKEFacult de gnie

Dpartement de gnie mcanique

EXPERIMENTAL CHARACTERIZATIONOF NOISE GENERATION AND

REDUCTION OF AN AIRFOIL ATMODERATE REYNOLDS NUMBER

Title to be defined

SCA 772 Dfinition du projet de recherche au doctorat

Prateek JAISWAL

Jury: Stephane MOREAU (directeur)Martin BROUILLETTEYann PASCO

Douglas NEAL

Sherbrooke (Qubec) Canada Avril 2014


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ABSTRACT

Missing english abstract file.


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iv


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TABLE OF CONTENTS

1 INTRODUCTION 1

2 Literature Review 3

3 Objectives and Methodology 7

4 CONCLUSION 9

A DONNES 11

LIST OF REFERENCES 13

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vi TABLE OF CONTENTS


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LIST OF FIGURES

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viii LIST OF FIGURES


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LIST OF TABLES

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x LIST OF TABLES


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GLOSSARY

Ceci est un exemple de lexique (glossaire).

Terme technique DfinitionActionneur Dfinition du terme actionneurCapteur Dfinition du terme capteurRfrentiel Dfinition du terme rfrentiel

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xii GLOSSARY


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LIST OF SYMBOLS

Ceci est un exemple de liste des symboles.

Symbole Dfinition[ ] Drive premire selon le rfrentiel inertiel

[ ] Drive seconde selon le rfrentiel inertiea Acclrationm Masset Variable temporelle... ...

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xiv LIST OF SYMBOLS


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LIST OF ACRONYMS

Ceci est un exemple de liste des acronymes.

Acronyme DfinitionOIQ Ordre des ingnieurs du QubecUdeS Universit de Sherbrooke... ...

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xvi LIST OF ACRONYMS


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CHAPTER 1

INTRODUCTION

Talk about the airfoil self noise in a quite ambient atmosphere

Noise generated by an airfoil itself in low turbulent ambiance is known as airfoil self noise.

To be more precise it has been defined by [Brookset al., 1989] "total noise produced when

an airfoil encounters smooth non turbulent inflow". The principal way of noise generation

here is due to three different mechanism-

1)If the flow is attached and Turbulent. Noise generated due to vortical disturbances

present in the boundary layer gets amplified due to presence of a geometrical discontinuitydue to Kutta condition. This results in broadband noise and means that different scales

are responsible for this kind of noise generation resulting in presence of multiple frequency

in radiated noise.

2) If the flow is however laminar and attached at most parts of the airfoil(except at the

trailing edge) this leads to the formation of Tonal Noise. This results from a frequency

selection due to some feedback mechanism.

3) Vortex shedding leading to narrow band noise.

Talk about the nuisance caused by the noise thus generated and places where this type of

noise is pertinent

As already stated the type of noise is related to state of boundary layer. In particular

turbulent boundary layer is mostly encountered in moderate to high Reynolds number.

The Broadband part of noise is considered significant, emitted by turbines, high lift devices,

Fan Blades etc. The Tonal component on the other hand can be found in Micro-turbine ,

UAV, ......

talk about the previous works that has been done already in this domain Tonal and

broadband noise have been extensively studied in the past starting from 1970s onward.

The Broadband Noise has been extensively studied in the past. Various experiments were

performed in the year 1970s and 80s. Subsequently several ad hoc models were proposed.

Later some more mature models were in early 2000 and 2010. Hence more refined models

are present as of now.

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2 CHAPTER 1. INTRODUCTION

Limitations-

1) They are limited to low to moderate chambered airfoil, in particular none of them can

take into account effect of high camber.

2) All of them ignore the eff

ect of mean flow on the flow field statistics.Trailing edge noise reduction using serrations was proposed in late 1970s and in early 90s

models were also proposed which could determine the overall noise reduction. However

this model overestimates the total noise reduced, in addition to this model is limited to flat

plate i.e with zero pressure gradient. Also there seems to be huge discrepancy in various

ways many past researchers have proposed how the noise reduction works in general.

On the other hand their seems to be no two study that predict unique mechanism respon-

sible for tonal noise generation. Since the first comprehensive study done by [Paterson

et al., 1973] till this day no two study have converge on the same conclusion. Also thereseems to be a substantial difference in the observations made from one author to another.

Talk about the difficulties faced by studies made in the past

1)The first few studies were made in a normal wind tunnel-no anechoic chamber till early

80s (not sure) ?

2) Intrusive flow measurements by HWA-now we have development of PIV.

3) Non existence of Digital signal processing.

4) Not taking installation effects into account see for example [Moreau et al., 2003]

Define the scope of the present study

The aim of this PhD is therefore to try and find mechanisms responsible. Also on the

other hand propose some simple solutions for noise reduction in each of the cases that

will be investigated. For this an openjet an echoic wind tunnel will be used. Tomo PIV

systems, wall pressure measurements , HWA and phase array study will be done.

Talk about the structure of DPR


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CHAPTER 2

Literature Review

Talk about the noise generation and where it is pertinent i.e context

Mechanism and implications,How it is formed, Past studies, Conclusion on TS formation

studies.

It is known experimentally that at low-moderate Reynolds number (from few 5 104 to

6 105 an airfoil generates intense whistling sound which in general is several DB higher

than the corresponding Broadband noise. A complete study was first done by [Paterson

et al., 1973] but till this day no clear explanation of the phenomenon exists. What is evenworse is the fact that often new studies do not support the results and claims made in

the past. There seems to be a two school of thoughts, first lead by Tam (see [Tam and

Ju, 2012]) and Nash (see [Nash et al., 1999]. They claim that tonal noise at moderate

reynolds number are due to feedback mechanism. The source of energy lies in the wake,

in particular kelvin Helmholtz instability was pointed out by [Tam and Ju, 2012] to be

the primary energy source. They also point out that a single tone is formed if the airfoil

is kept in clean background (no possible feedback from setup). In particular they point

out that multiple tones observed result from feedback from the wind tunnel components

and the airfoil.

Hence it is important to underscore the differences observed. Firstly, we have to look at

the design of these two studies their implications and limitations.

The paper by [Tam and Ju, 2012]

1) The study have been carried out in a NACA 0012 airfoil. This airfoil is chosen to

avoid any separations at the trailing edge which may produce additional sources. More

importantly this airfoil was chosen so that a comparison can be made with past works.

2) The study of Tam is carried out with zero turbulence level. Which has implications on

its own. One of them is that it cannot be repeated experimentally.

3) The study is restricted to zero angle of attack. The Reynolds number number is between

2 104 to 5 105.

Findings The peak scales with patersons empirical formula.

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4 CHAPTER 2. LITERATURE REVIEW

A single peak is observed.

Near wake oscillations are the primary drivers of the feedback mechanism

Secondary mechanism is also identified as one that leads to discrete vortices in the wake.

Paper by [Nash et al., 1999]

1) Experiments conducted in acoustically lined wind tunnel. From105 to2 106.

2)Experiments conducted at a very low Turbulence intensity about 0.05%

The above are two examples of work that has been carried out in past numerically and

experimentally. They have following observations in common

Both have been carried out in a very no or low turbulence levels respectively.

both report a single tone and which is accordance with patersons [Paterson et al., 1973]

empirical formula.

The observation that a single tone is observed is in contrary to the observations made

by [Arbey and Bataille, 1983], [Prbsting et al., 2014], [Desquesnes et al., 2007] , and

others.

Recent experiments and numerical study conclude that these multiple peaks around the

most amplified one are due to amplitude and frequency modulation. And they concluded

it is not because of feedback of the profile with the tunnel itself as hypothesized by [Nash

et al., 1999]

However all these studies confirm presence of feedback mechanism with is responsible

for frequency selection resulting in tonal noise. Also all the experiments in past are in

accord with paterson emperical formula. Also the linear stability analysis shows that the

frequency of most amplitude wave is equal to frequency of tonal noise.

conclusion

There seems to be large discrepancy in the study, observations and conclusion from one

author to other.

Noise generated by BB

Mechanism and implications,How it is formed, Past studies

Models available for prediction of BB noise

Conclusion on BB formation studies.

Reduction techniques

serrations


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5

Howes model

Previous results

Conclusion

Study made in past show discrepancy and contradict each other on how the noise reduction

through serrations in achieved. Also the analytic model proposed by howe over-predictsthe noise reduction observed. Also the model presented by howe works with flat plate only

i.e with zero pressure gradient.

Noise reduction by Blowing at trailing edge

Results and observation

Conclusion

Installation Effects [Moreau et al., 2003]

PIV

HWA

phased array measurements

Wall pressure sensors

Conclusion on Experimental Tools used

Therefore it will be interesting to study the mechanism responsible for generation of tonal

noise. At our disposal are state of the art anechoic open jet wind tunnel, Tomographic PIV

system , microphone array measurements and many other classical tools. In particularanechoic wind tunnel cuts out possibility of having feedback mechanism with wind tunnel

components and airfoil. This has been already noted by [Nash et al., 1999] . Other

advantage of using such a tunnel is that blade passing frequency (BPF) are not present in

the measurements. A regular fan driven wind tunnel produces additional spurious sources

(BPF) hence open jet tunnel are preferred for aeroacoustics study.

Draw similar conlcusion for use of PIV and HWA measurements.


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6 CHAPTER 2. LITERATURE REVIEW


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CHAPTER 3

Objectives and Methodology

Context

a lot of work in the past have been done and this PhD will be a continuation of the work

in past with aim to improve our understanding.

Talk about benefits of using experimental methods and in particular approach (experi-

mental tools such as PIV, HWA, etc) taken for this thesis.

Definition of project and objectives

Approach and methodology

Talk about how we will proceed with the work

1) complete flow field analysis around the airfoil.

2) Aeroacoustics analysis BB noise compare with different models.

3) Aeroacoustics analysis of TS waves on CD airfoil.

4) Study effect of serrations and blowing on the airfoil trailing edge

At each of the above mentioned steps we will compare our results with HAOs work.

Draw a Time line of the project

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8 CHAPTER 3. OBJECTIVES AND METHODOLOGY


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CHAPTER 4

CONCLUSION

Discuss the aim of study

Talk about the structure of the thesis. i.e the way it is organized step by step.

Justify your approach

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10 CHAPTER 4. CONCLUSION


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ANNEX A

DONNES

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12 ANNEX A. DONNES


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LIST OF REFERENCES

Arbey, H. and Bataille, J. (1983). Noise generated by airfoil profiles placed in a uniformlaminar flow. Journal of Mechanics, volume 134, pp. 3347.

Brooks, T., Pope, D. and Marcolini, M. (1989). Airfoil self-noise and prediction(Technicalreport). National Aeronautics and Space Adminstration.

Desquesnes, G., Terracol, M. and Sagaut, P. (2007). Numerical investigation of the tonenoise mechanism. Journal of Mechanics, volume 591, pp. 155182.

Moreau, S., Henner, M., Iaccarino, G., Weng, M. and Roger, M. (2003). Analysis offlow conditions in freejet experiments for studying airfoil self-noise. AIAA, volume 41,number 10, pp. 18951905.

Nash, E., Lowson, M. V. and Mcalpine, A. (1999). Boundary-layer instability noise on

aerofoils.Journal of Mechanics

, volume 382, pp. 2761.Paterson, R., Paul, G., Fink, M. and Munch, C. (1973). Vortex noise of isolated airfoil.

Journal of Aircraft, volume 10, number 5, pp. 296302.

Prbsting, S., Serpieri, J. and Scarano, F. (2014). Experimental investigation of aerofoiltonal noise generation. Journal of Mechanics, volume 747, pp. 656687.

Tam, C. and Ju, H. (2012). Airfoil tones at moderate reynolds number. Journal ofMechanics, volume 690, pp. 536570.

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14 LIST OF REFERENCES

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