PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Aeroacoustic and aerodynamic study of trailing-edge serrated
airfoils in tandem configuration
Xiao Liu1; Syamir Alihan Showkat Ali2; Mahdi Azarpeyvand3; Yannick Mayer412Faculty of Engineering, University of Bristol, United Kingdom

School of Manufacturing Engineering, University Malaysia Perlis, Malaysia
3

Faculty of Engineering, Bristol University, United Kingdom

4

Faculty of Engineering, Bristol University, United Kingdom

ABSTRACTThis paper presents a comprehensive experimental study on the application of trailing-edge serrations as apassive control method for reducing the unsteady aerodynamics loading and noise on airfoils in tandem
configurations. The purpose of this study is to investigate the effectiveness of serrated trailing-edge on
cambered NACA 65-710 airfoil to control and reduce the turbulent flow within the gap area between the two
airfoils. The wake flow characteristics for an isolated cambered NACA 65-710 airfoil with and without thetrailing-edge serration treatment have been carried out using two-dimensional Particle Image Velocimetry(PIV) method. The acoustic signature of the tandem airfoil is also presented for the near- and far-field noise
measurements. Flow experiments were performed using sawtooth serration with different wavelength, forseveral tandem airfoil configurations (different airfoil gap distances). The results show that the use ofserrations can generally lead to a significant reduction in the turbulent kinetic energy within the gap region,
due to the interaction between the flows issued from the tip and root of the serration. The near- and far-field
noise results have shown that a significant noise reduction can be achieved, especially with a sharp sawtoothserration.
Keywords: Passive Flow Control, Serration, Tandem Airfoil

1. INTRODUCTION
As the main component of turbines and compressors, the rotating blades are known to produce
noise due to turbulent flow interactions of the rear-blade (i.e. stator) with the front-blade (i.e. rotor),
which can be broadly categorized into trailing-edge, early separation and stall noise respectively [1].
However, studies of the aerodynamic noise produced by the rotating blades have prevailed as achallenging task over the past decades from both a theoretical perspective and a practical point ofview. The principles of counter-rotating propeller noise were first investigated and analyzed in 1948
by Hubbard [2], which identified the dominant interference mechanisms and their associated noi se
production. Hanson [3] later reproduced and expanded some of Hubbard's findings. Using turbofan
theory, he put forward that the interaction between the tip of the rear-blades and the wake flow resulted
from the front propeller constitutes the major source of noise for the contra -rotating open rotor(CROR) propulsion systems. As such, it was inferred that minimizing wake turbulence intensity of
the front blade could significantly reduce the overall noise signature of CROR systems. A
computational study on the rudimentary effects of the unsteady interference between the airfoils intandem configuration has been performed by Tuncer and Pletzer [4], and it was shown that the relative
motion between the airfoils gave rise to the aerodynamic characteristics of the rear airfoil. In another1

xiao.liu@bristol.ac.uk

2syamir@unimap.edu.my3m.azarpeyvand@bristol.ac.uk
4yannick.mayer@bristol.ac.uk

5367

word, altering the relative position of the tandem airfoils changes the amount of wake turbulence(originating from the front blade) to which the rear airfoil interacts with a nd hence the aerodynamic
noise generation.
In the past decade, reduction of trailing-edge noise through passive methods has been the focus ofmany studies, such as the use of serrated trailing-edge and surface treatment by porous materials andacoustic liners [5-20]. Serrated trailing-edges, in particular, have received significant interest due toits simple yet efficient noise reduction performance. The implementation of sawtooth and slotted sawtooth serrated trailing-edge have shown to be effective in reducing the wake turbulence intensity
and the corresponding noise generation, especially at high angles of attack where maximum
aerodynamic performance is obtained [8, 13, 23]. The ability of serrated trailing-edge to reduce theturbulent energy content within the wake region can be associated with the highly three -dimensional
flow originating from the tip- and root of the serration, making it an attractive solution to mitigate
such wake-airfoil interaction noise for contra-rotating propellers and many other rotor-stator
configurations
Compared to the aeroacoustic studies of a single airfoil, fewer measurements have been reportedon two airfoils aligned in tandem configurations, not to mention airfoils with serrated trailing -edges.
Hence, to better understand the effect of trailing-edge serration and the associated mechanisms ofnoise reduction, an extensive experimental study has been carried out on the aerodynamic andaeroacoustic performance of airfoils in tandem. In what follows, a detailed measurement on the wakedevelopment and near-/far-field noise generation have been undertaken and presented in this paper.

2. EXPERIMENTAL SETUP
2.1 Airfoil and Serration configurations
Figure 1 shows the schematic of the tandem airfoil configuration. The front and rear airfoils both
had a chord length of ܿ ൌ ͳͷͲ݉݉ and a span of ݈ ൌ ͶͷͲ݉݉ . While the front airfoil was
manufactured from aluminum – 7075, the rear airfoil was made from RAKU-TOOL WB-1222
polyurethane board. To install the flat (baseline) and serration inserts at the trailing -edge , the front
airfoil was designed with a ʹǤ͵݉݉blunt trailing-edge and a ͳͷ݉݉ ൈ ͲǤͺ݉݉ slot along the airfoil
span, see Figure 1 (b). In order to have a comprehensive knowledge on the flow interactions, the rear
airfoil was equipped with a total of 34 surface pressure taps on both the pressure an d suction side of
the airfoil, starting from the leading-edge (see Figure 1 (a)). The two airfoils were placed parallel toeach other and rectangular endplates were used to maintain a nearly two -dimensional flow over thetwo airfoils. In the present work, two sawtooth serrations (Figure 2) were chosen based on its ability
to reduce turbulent kinetic energy and noise as documented in [12, 14, 20]. The serration geometricalparameters are summarized in Table 1.

Figure 1 – The tandem airfoil configuration (a) Assembly view of front airfoil (NACA 65-710
with trailing-edge serration) and rear airfoil (NACA 65-710 with pressure taps distribution), (b)NACA 65-710 with and without trailing-edge serration, (c) Side view of the tandem airfoil
arrangement

5368

Table 1 – Serration geometrical parameters
2h
(mm)

ߙ௦
(degree)

λ(mm)Baseline
Wide sawtooth

15
30

22.5

24.8

Sharp sawtooth

30

8.53

9

Figure 2 – Sawtooth serrations
The distance between the front and rear airfoil have been chosen as ܹ ൌ ͲǤͷܿ and ͳǤͲܿ have beenchosen for this study (see Figure 1(c)). The streamwise and vertical distance between the airfoil centrepoints (ܹ௫ and ܹ௬ ) were defined based on the locations where the maximum turbulent kinetic energy
observed from the PIV results obtained for the baseline case of an isolated NACA 65-710 airfoil.
2.2 Experimental setup
In the present study, both the characterization of wake and near-field surface pressure
measurements were carried out in the low turbulence tunnel at University of Bristol. Two -component
Particle-Image Velocimetry was used to determine the wake development and energy contents of an
isolated airfoil with and without the trailing-edge serration. A ͳ݉݉-thick laser sheet was illuminatedby Dantec DualPower ʹͲͲ݉‫ ܬ‬Nd:YAG laser with wavelength of ͷ͵ʹ݊݉ and a repetition rate ofͳͷ‫ݖܪ‬. The time delay between the two consecutive laser pulses was set to ʹ͵ߤ‫ݏ‬, to ensure adequate
particle shifts within the final interrogation window. A mixture of Polyethylene glycol 80 was
atomized to produce seeding with mean particle diameters of ͳߤ݉. For each case, a total of 1600
images pairs, captured by a FlowSense EO 4M CCD camera (ʹͲͶͺ ൈ ʹͲͶͺ‫ ݏ݈݁ݔ݅݌‬ଶ), were analyzed
using DynamicStudio, with a field of view of ͳͶͺ݉݉ ൈ ͳͶͺ݉݉. The iterative process yielded final
correlation windows of ͳ͸‫ ݏ݈݁ݔ݅݌‬ൈ ͳ͸‫ͳ̱( ݏ݈݁ݔ݅݌‬Ǥͳ ൈ ͳǤͳ݉݉ଶ) with an overlap of ͷͲΨ producing
a vector spacing of approximately ͲǤ͸݉݉.
Near-field surface pressure fluctuations were measured using 34 remote Panasonic WM -61A
microphones connected to the brass tubes using plastic tubing with an inner and outer diameter ofͲǤͺ݉݉ and ͵Ǥ͸݉݉ respectively. The calibration of the remote sensing probe was based on theprocedure described in Elsahhar et al. [21]. The unsteady pressure data were acquired by a National
Instruments PX1e-4499 for a period of 16 seconds with a sampling rate of ʹଵ଺ ‫ݖܪ‬.
Far-field noise test was carried out in the University of Bristol’s aeroacoustic facility, which is a
closed-circuit, open-jet anechoic wind tunnel. The experiments in this study were performed at flow
velocities ͵Ͳ݉Ȁ‫ ݏ‬with turbulence intensity levels below ͲǤʹΨ [22]. Signals from an array of ʹ͵
microphones mounted on an arc above the test rig were acquired by PXIe -4499 data acquisition card.
The arc was designed to extend from angles ͶͲι to ͳ͵ͷι in steps of ͷι , and similar to near-fieldmeasurement, the sampling frequency and duration remained as ʹଵ଺ ‫ ݖܪ‬and ͳ͸ seconds, to ensure
data convergence. The power spectral density results for near- and far-field measurements were later
calculated via Welch’s method with a window size of ʹଵସ samples, a Hamming window with ͷͲΨoverlap and normalized with reference pressure of ‫݌‬଴ ൌ ʹͲߤܲܽ.

3. RESULTS AND DISCUSSIONS
3.1 NACA 65-710 Airfoil Wake Measurements
To have a better understanding on the effects of the trailing-edge serrations on the wakedevelopment of the airfoil, PIV measurements of an isolated NACA 65-710 airfoil with the baseline
and two sawtooth serrations (ɉ ൌ ͻ݉݉ and ʹͶǤͺ݉݉) have been carried out at angles of attack, ߙ ൌͲι ǡ ͷι ǡ ͳͲιand ͳͷιfor the flow velocity of ܷ଴ ൌ ͵Ͳ݉Ȁ‫ݏ‬. The fields of view used in our experiments
covered the downstream locations ‫ݔ‬Τܿ ൌ ͲǤʹ to 1, relative to the trailing-edge of the baseline case. Itis crucial to highlight that the turbulence kinetic energy (TKE) maps of the isolated airfoil were thenused to define the location of the rear airfoil (in red circle in Figure 3) for the noise generation studies.
Similar to the experiments reported by Xiao et al. [13], at ߙ ൌ  ͳͲι, implementation of trailing-edge5369

serration significantly modifies the turbulent kinetic energy (TKE) results, for both the wide sawtoothserration (ɉ ൌ ʹͶǤͺ݉݉) in Figure 3(a) and sharp sawtooth serration (ɉ ൌ ͻ݉݉) in Figure 3(b), under
the present investigation. By applying a wide sawtooth serration, the wake TKE result for serration
root shows a strong upward deflection and a thinner wake profile as compared with the baseline case.
This is possibly due to the flow moving over the pressure side of the airfoil through the valley of theserration. Notably different from the root flow, the trend for tip flow is similar to that of the baseline
case with small, and yet noticeable downward deflection. More importantly, when the sharp serration
is applied, a significant TKE reduction (up to approximate 55%) can be observed in the wake TKE
profile (see Figure 3(b)) with the profiles converge rapidly between the tip and the root after ‫ ݔ‬ൌ ͲǤͷܿ.

(a) wide sawtooth serration(b) sharp sawtooth serration
Figure 3 – Wake TKE profiles for isolated NACA65710 airfoil with different serrations at ߙ ൌͳͲι and ܷ଴ ൌ ͵Ͳ݉Ȁ‫ݏ‬. (a) wide sawtooth serration (ߣ ൌ ʹͶǤͺ݉݉) (a) sharp sawtooth serration(ߣ ൌ ͻ݉݉)
3.2 Near- and Far-field acoustic measurements
In order to further investigate the effectiveness of serration treatments for reducing the unsteady
aerodynamic loading on the airfoil and radiated noise, surface pressure fluctuation measurements havebeen performed on the rear airfoil using the remote sensing method. In the tandem airfoil
configurations, the front airfoil was fitted with baseline and different sawtooth serrations while therear airfoils were placed at two different downstream locations, having gap distance of ܹ ൌ ͲǤͷܿ andͳܿ, respectively.
The power spectral density (PSD) of the surface pressure fluctuations acting on the suction side of
the airfoil is shown in Figure 4.With the gap distance of W=0.5c in Figure 4(a), wide sawtoothserration (top row) leads to a considerable increase of the pressure fluctuation energy over a wide
range of frequency, within the leading-edge area of ‫ݔ‬Ȁܿ ൏ ͲǤͳ. It can also be observed that sharp
sawtooth serration (bottom row) resulted in a slightly decreased surface pressure PSD at low
frequencies (݂ܿΤܷ଴ ൏ ͲǤ͹). Furthermore, the surface pressure PSD remains to be noticeably higher
along the root position than those at tip position. Moving downstream to ‫ݔ‬Ȁܿ ൐ ͲǤͳ, the use of trailingedge serrations resulted in a clear reduction (around ͷ݀‫ ܤ‬at ‫ݔ‬Ȁܿ ൌ ͲǤͷ͵͵) of unsteady loading on therear airfoil at frequency range ݂ܿΤܷ଴ ൏ ͲǤ͹ . Unlike the wide sawtooth serration case, a small
reduction of the surface pressure PSD can be observed, which begins immediately from the leading edge and persists beyond ‫ݔ‬Ȁܿ ൌ ͲǤʹ͵͵ . Interestingly, there is not much difference between theserration tip and root positions. Moreover, as observed from the results, trailing-edge serrations do
not particularly benefit in the high frequency region of the pressure spectra. On contrary, an increasein the surface pressure PSD can be clearly seen at the leading-edge region for both serrated cases.
The surface pressure PSD results for the tandem airfoil configuration with the separation gap ofܹ ൌ ͳܿ are presented in Figure 4(b). The result of surface pressure PSD for wide sawtooth serration

5370

shows similar trend to that of smaller separation gap distance, but larger surface pressure PSD
reduction (up to ͹݀‫ )ܤ‬at downstream chordwise locations. For sharp sawtooth serration, it can beobserved that a reduction of the unsteady loading (up to Ͷ݀‫ )ܤ‬on the rear airfoil over almost thewhole suction side of the airfoil at frequency range of ݂ܿΤܷ଴ ൏ ͲǤ͹.
The results observed here is of great interest as the noise radiated from the rear airfoil is directly
related to the unsteady pressure exerted on the airfoil and trailing-edge serrations on the front airfoil
can modify significantly the overall unsteady pressure field experienced by the rear airfoil in thetandem configurations, and therefore the production of airfoil noise.

(a) W=0.5c(b) W=1.0c
Figure 4 – Power spectral density of surface pressure fluctuation on the rear airfoil at ߙ ൌ  ͳͲιand ܷ଴ ൌ ͵Ͳ݉Ȁ‫ݏ‬. (a) airfoil separation distance of W=0.5c (b) airfoil separation distance of
W=1.0cIn order to better illustrate the effect of serrations, Figure 5 shows the contour map of the nearfield coherence between the remote microphone 1 (first microphone on the suction side of the rear
airfoil) and all other microphones at angle of attack ߙ ൌ  ͳͲι and ܷ଴ ൌ ͵Ͳ݉Ȁ‫ ݏ‬with the gap distance
between the front and rear airfoil of ܹ ൌ ͳܿ. The positive ‫ݔ‬Ȁܿ represents the coherence results along
the suction side of the rear airfoil while negative ‫ݔ‬Ȁܿ the pressure side of the rear airfoil.
The coherence map for the baseline case in Figure 5(a) shows a high coherence region in the whole

5371

(a)

(b)

(d)

(c)

(e)

Figure 5 – Contour map of near-field coherence of first microphone on suction side with allother microphones (ܹ ൌ ͳܿ):(a) baseline (b) wide sawtooth – tip (c) wide sawtooth – root(d) sharp sawtooth – tip (e) sharp sawtooth – root
frequency range near leading-edge area (Ͳ ൏ ‫ݔ‬Ȁܿ ൏ ͲǤͲ͵). At low frequency range (݂ ൏ ͵ʹͲ‫)ݖܪ‬, ahigh coherence area can also be found to exist between ͲǤͳ ൏ ‫ݔ‬Ȁܿ ൏ ͲǤʹͷ. While at higher frequency
range, ͷ͸Ͳ‫ ݖܪ‬൏ ݂ ൏ ͵Ǥʹ݇‫ݖܪ‬, high coherence value between first and the rest of the remote sensors
along the suction side of the airfoil can be observed to extend beyond half of the chord length (‫ݔ‬Ȁܿ ൐ͲǤͷ). At a similar frequency range, an elevated region of coherence can also be observed along thepressure side until approximately ‫ݔ‬Ȁܿ ൌ ͲǤʹ.
Figure 5(b) and 5(c) show the contour map of the near-field coherence for wide sawtooth serration
case. At low frequency for both root (Figure 5(b)) and tip (Figure 5(c)) positions, high coherence
value region can be found, similar to that of the baseline case. However, in the high frequency region,
higher coherence, which is present along with the root position (and baseline), becomes noticeably
attenuated. On the other hand, the results for the sharp sawtooth case, show no obvious difference
between the root (Figure 5(d)) and tip position (5(e)) but clear reduction when compared with thebaseline case at high frequency range ( ͷ͸Ͳ‫ ݖܪ‬൏ ݂ ൏ ͵Ǥʹ݇‫) ݖܪ‬. Furthermore, it appears that thecoherence spreads further downstream for the sharp sawtooth serration at low frequency range of ݂ ൏͵ʹͲ‫ݖܪ‬. Results from coherence clearly suggest that the reduction in the unsteady airfoil loading leads
directly to a loss of coherence, and hence possibly better mixing for the near-field flow structures.

5372

(a) W= 0.5c(b) W= 1.0c
Figure 6 – Power spectral density of the far-field noise measurements. (a) airfoil separation
distance of W=0.5c (b) airfoil separation distance of W=1.0c(a) W= 0.5c(b) W=1.0c
Figure 7 – Overall sound-pressure-level directivity patterns. (a) airfoil separation distance of
W=0.5c (b) airfoil separation distance of W=1.0c
Figure 6 shows the far field noise measured at ͵Ͳ݉Ȁ‫ ݏ‬over the tandem airfoil configuration with
two gap distances of ܹ ൌ ͲǤͷܿ (in Figure 6(a)) and ܹ ൌ ͳܿ (in Figure 6(b)). For clarity andreference, the background noise is shown in grey in the figures. In Figure 6(a), when compared withthe baseline case, the far-field PSD demonstrates that trailing-edge serration can lead to a small
decrease in the airfoil noise with frequency lower than ͳǤͷ݇‫ ݖܪ‬for both serration cases, although the
sharp sawtooth produces an additional ͲǤͷ െ ʹ݀‫ ܤ‬reduction than the wide sawtooth. At a higher
frequency range (ͳǤͷ݇‫ ݖܪ‬൏ ݂ ൏ Ͷ݇‫ݖܪ‬ሻ the far-field PSD for the serrated case resulted in a similar
magnitude and trend, as the baseline case. When increase the distance between two airfoils to ܹ ൌͳܿ (see Figure 6(b)), the result for wide sawtooth serration exhibits a small noise reduction, similar
to that observed at ܹ ൌ ͲǤͷܿ gap distance. However, for sharp sawtooth serration, a much moresignificant noise reduction (up to 11 dB) can be identified, which the broadband hump has been
considerably reduced with a frequency range of ͵ͲͲ‫ ݖܪ‬൏ ݂ ൏ ͳǤͷ݇‫ݖܪ‬.
Figure 7 presents the overall sound-pressure-level (OASPL) directivity pattern for the baseline
case and trailing-edge serrated cases for two different gap distances (ܹ ൌ ͲǤͷܿ and ͳܿ ) at ܷ଴ ൌ͵Ͳ݉Ȁ‫ݏ‬. Figure 7(a) shows that both serration geometries slightly reduce the noise levels to that of
the baseline case at all angular locations, with the sharp sawtooth serration outperforming the widesawtooth. In Figure 7(b), as compared with the baseline case, the OASPL results for the wide sawtoothserrated cases remain similar in trend to that of the results in 7(a) across all angular directive range
while the sharp sawtooth serrated case produces an approximately 5 dB reduction.

4. CONCLUSIONSThe present study demonstrates that the use of trailing-edge serration can significantly change thewake flow profiles through enhancing the flow mixing between the pressure and suction side of the
airfoil, which leads to a faster TKE decay. Based on the TKE decay, applying a trailing -edge serration

5373

on the front airfoil in tandem airfoil configurations will reduce the inco ming TKE level for theleading-edge of the rear airfoil. This prone to produce a significant noise decrease (up to 9 dB) at thefrequency lower than 1.5 kHz. The near-field surface pressure measurement and coherence map forserrated cases also show a clear reduction of unsteady aerodynamic loading, and hence airfoil noise,when compared with the unserrated baseline case. A comparison between two serrations shows thatsharp sawtooth configuration produces a more desirable reduction in the near-field loads, whichtranslates into a greater far-field noise reduction.

REFERENCES
1. T. Brooks, D. Pope, M. Marcolini, Airfoil self-noise and prediction, in: NASA-RP-1218, 1989.
2. H. H. Hubbard, Sound from dual-rotating and multiple single-rotating propellers, NACA TN 1654.
3. D. B. Hanson, Noise of counter-rotation propellers, Journal of Aircraft, 22 (7) (1985) 609–617.
4. I. Tuncer, M. Platzer, Analysis of unsteady airfoil interference effects using a zonal navier-stokes solver,in: 33rd Aerospace Sciences Meeting and Exhibit, 1995, p. 307.
5. R. Sandberg, L. Jones, Direct numerical simulations of low reynolds number flow over airfoils withtrailing-edge serrations, Journal of Sound and Vibration 330 (16) (2011) 3818–3831.
6. T. P. Chong, P. F. Joseph, An experimental study of airfoil instability tonal noise with trailing edge
serrations, Journal of Sound and Vibration 332 (24) (2013) 6335–6358.
7. M. Azarpeyvand, M. Gruber, P. Joseph, An analytical investigation of trailing edge noise reduction usingnovel serrations, in: 19th AIAA/CEAS Aeroacoustics Conference, AIAA 2013-2009.
8. M. Gruber, Aerofoil noise reduction by edge treatments, Doctoral thesis, University of Southampton (2012).
9. D. Moreau, L. Brooks, C. Doolan, On the noise reduction mechanism of a flat plate serrated trailing edge
at low-to-moderate reynolds number, in: 18th AIAA/CEAS aeroacoustics conference, AIAA 2012-2186.
10. T. Chong, P. Joseph, M. Gruber, Airfoil self noise reduction by non-flat plate type trailing edge serrations,Applied Acoustics 74 (4) (2013) 607–613.
11. F. Avallone, C. Arce Leon, S. Pr¨obsting, K. P. Lynch, D. Ragni, Tomographic-PIV investigation of theflow over serrated trailing-edges, in: 54th AIAA Aerospace Sciences Meeting, AIAA 2016-1012.
12. L. Ji, W. Qiao, F. Tong, K. Xu, W. Chen, Experimental and numerical study on noise reduction
mechanisms of the airfoil with serrated trailing edge, in: 20th AIAA/CEAS Aeroacoustics Conference,
AIAA 2014-3297.
13. X. Liu, M. Azarpeyvand, R. Theunissen, Aerodynamic and aeroacoustic performance of serrated airfoils,
in: 21st AIAA/CEAS Aeroacoustics Conference, AIAA 2015-2201.
14. S. A. Showkat Ali, X. Liu, M. Azarpeyvand, Bluff body flow and noise control using porous media, in:22nd AIAA/CEAS Aeroacoustics Conference, AIAA 2016-2754.
15. S. A. Showkat Ali, M. Azarpeyvand, C. R. I. da Silva, Trailing-edge flow and noise control using porous
treatments, Journal of Fluid Mechanics, 850 (2018) 83-119.
16. S. A. Showkat Ali, M. Azarpeyvand, M. Szoke, C. R. I. da Silva Boundary layer flow interaction with apermeable wall, Physics of Fluids, 30 (2018) 085-111.
17. S. A. Showkat Ali, M. Azarpeyvand, C. R. I. da Silva, Experimental Study of Porous Treatment for
Aerodynamic and Aeroacoustic Purposes, in: 23rd AIAA/CEAS Aeroacoustics Conference, AIAA 20173358.
18. S. A. Showkat Ali, M. Azarpeyvand, M. Szoke, C. R. I. da Silva, Turbulent Flow Interaction with Porous
Surfaces, in: 24th AIAA/CEAS Aeroacoustics Conference, AIAA 2018-2801.
19. A. Afshari, M. Azarpeyvand, A. A. Dehghan, M. Szoke, Trailing edge noise reduction using novel surface
treatments, in: 22nd AIAA/CEAS Aeroacoustics Conference, AIAA 2016-2384.
20. Q. Ai, M. Azarpeyvand, X. Lachenal, P. M. Weaver, Airfoil noise reduction using morphing trailing edge,in: 21st International Congress on Sound and Vibration, 2014.
21. W. Elsahhar, S. A. Showkat Ali, T. Raf, M. Azarpeyvand, An experimental investigation of the effect of
bluff body bluntness factor on wake-vortex noise generation, in: 24th AIAA/CEAS Aeroacoustics
Conference, AIAA 2018-3288.
22. Y. D. Mayer, H. Kamliya Jawahar, M. Szoke, S. A. Showkat Ali, M. Azarpeyvand, Design andperformance of an aeroacoustic wind tunnel facility at the University of Bristol, Applied Acoustics,
155(2019)358-370.
23. X. Liu, S. A. Showkat Ali, M. Azarpeyvand, On the application of trailingedge serrations for noise control
from tandem airfoil configurations, in: 23rd AIAA/CEAS Aeroacoustics Conference, AIAA 2017-3716.

5374