14th International Symposium on Particle Image Velocimetry – ISPIV 2021
August 1–5, 2021

Investigation of Large Scale Motions in Zero and
Adverse Pressure Gradient Turbulent Boundary

Layers Using High-Spatial-Resolution PIV
D. Jovic1,∗, M. Shehzad1, B. Sun1, Y. Ostovan2, C. Cuvier2, J.M. Foucaut2, C.

Willert3, C. Atkinson1, J. Soria1

1 Laboratory for Turbulence Research in Aerospace & Combustion (LTRAC), Department of Mechanical
and Aerospace Engineering, Monash University, Clayton, 3800, Victoria, Australia

2 Univ. Lille, CNRS, ONERA, Arts et Metiers Institute of Technology, Centrale Lille, UMR 9014 - LMFL
- Laboratoire de Mécanique des Fluides de Lille - Kampé de Fériet, Lille, F-59000, France

3 Institute of Propulsion Technology, German Aerospace Center (DLR), Cologne, Germany
∗ daniel.jovic@monash.edu

Abstract
Particle image velocimetry (PIV) has been used to capture the high-spatial-resolution (HSR) two-component,
two-dimensional (2C-2D) velocity fields of a zero-pressure-gradient (ZPG) turbulent boundary layer (TBL)
and of an adverse-pressure-gradient (APG) TBL. Proper Orthogonal Decomposition (POD) is performed
on the measured velocity fields to characterize the velocity fields as large or small scale motions (LSMs or
SSMs), with further characterisation of the LSMs into high and low momentum events. This paper reports
the findings of the PIV experiment and the subsequent analysis of the high Reynolds number ZPG and APG
TBLs.

1 Introduction
The investigation of LSMs in TBL flows is essential in order to identify and characterize the dominant coher-
ent structures in these flows. LSMs are coherent patterns of alternating regions of high and low momentum,
such as the velocity streaks of the buffer layer. Proper Orthogonal Decomposition (POD) is performed on
the velocity field to study the coherent structures in turbulent flow. This allows the investigation of distri-
bution of turbulent kinetic energy (TKE) as a function of scale in the TBL flows that are inhomogeneous in
the streamwise direction Liu et al. (2001). POD allows for LSMs to be characterized as structures whose
contribution to the domination spatial mode is above a threshold, with further characterization into high and
low momentum events based on the temporal coefficient.

2 Experimental Methodology
High-spatial resolution (HSR) 2C-2D single-exposed PIV images were taken in the x−y plane of the turbu-
lent boundary layers in the LMFL High-Reynolds-Number Boundary Layer Wind Tunnel at Laboratoire de
Mécaniquedes Fluides de Lille (LMFL), Lille, France. This facility has a 2m wide, 1m high and 20.6m long
test section with the ZPG, favourable-pressure-gradient (FPG) and APG sections, as shown in Figure 1.

ZPG FPG APG

FOV

FOV

3.5m
2.2mUe = 9m/ s

x

y

-5 deg
x = 6.8m

s = 5.6m

Figure 1: Schematic of the test section in the LML Wind Tunnel. Figure adapted from Cuvier et al. (2017).



The FOVs shown in Figure 1 were illuminated using a dual-cavity BMI Nd:YAG laser with a wavelength
of 532nm and an output energy of up to 200mJ. This enabled an Imperx Bobcat B6640 29MP camera to
image the seeding with a mean diameter of 1µm produced by a seeder using a water-glycol mixture. Over
10,000 single-exposed image pairs were captured, which were subsequently analysed using an in-house
multigrid/multipass cross-correlation PIV algorithm written by Soria (1996). Due to the physical sensor
array size of the camera, dewarping was used to correct for lens distortion, as done in Sun et al. (2021).

3 Results and Discussion

Figure 2: Mean streamwise velocity profile (U+) with high
momentum LSMs (U+

h ) and low momentum LSMs (U+
l ).

The results obtained from this experimental
campaign are in good agreement with the Eu-
HIT results from Cuvier et al. (2017) which
were collected in the same facility under iden-
tical operating conditions. The EuHIT re-
sults were captured with more cameras than
the current experiment, which allowed mea-
surement of a longer domain at significantly
less spatial resolution. The analysis is per-
formed using the snapshot POD method, and
the results allow for the velocity fields used in
the POD to be characterized as LSMs that are
high or low-momentum events, which aide in
the investigation of the effect of LSMs on the
turbulent statistics. Figure 2 shows that the
results for the mean streamwise velocity pro-
file of the ZPG-TBL, which shows that the
high momentum LSMs have a higher mean
streamwise velocity than the original ensemble and that the low momentum LSMs have a lower mean
streamwise velocity than the original ensemble. Similar results were observed for the APG-TBL, which
along with the effect of these events on the second-order turbulent statistics, will be presented. Further
details are available in Shehzad et al. (2021).

4 Acknowledgements
The authors would like to acknowledge the support of the Australian Government on this research through
an Australian Research Council Discovery grant. Daniel Jovic and Bihai Sun gratefully acknowledge the
support through an Australian Government Research Training Program (RTP) Scholarship. Callum Atkin-
son was supported by an ARC Discovery Early Career Researcher Award (DECRA) fellowship. The authors
also acknowledge the computational resources provided via a NCMAS grant and an ARC LIEF grant.

References
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Shehzad M, Sun B, Jovic D, Ostovan Y, Cuvier C, Foucaut JM, Willert C, Atkinson C, and Soria J (2021)
Investigation of large scale motions in zero and adverse pressure gradient turbulent boundary layers using
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Sun B, Shehzad M, Jovic D, Cuvier C, Willert C, Ostovan Y, Foucaut JM, Atkinson C, and Soria J (2021)
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	Introduction
	Experimental Methodology
	Results and Discussion
	Acknowledgements