Wind Tunnel Modelling of Aerodynamic Baffle Arrays for Aircraft Exhaust Plume Control

312 Pages·2015·7.67 MB·English

CRANFIELD UNIVERSITY

S VELIKOV

Wind Tunnel Modelling of Aerodynamic Baffle
Arrays for Aircraft Exhaust Plume Control

SCHOOL OF AEROSPACE, TRANSPORT AND MANUFACTURING

PhD THESIS
Academic Year: 2014-2015

Supervisor: K P Garry
April 2015

CRANFIELD UNIVERSITY

S VELIKOV

Wind Tunnel Modelling of Aerodynamic Baffle
Arrays for Aircraft Exhaust Plume Control

SCHOOL OF AEROSPACE, TRANSPORT AND MANUFACTURING

PhD THESIS
Academic Year: 2014-2015

Supervisor: K P Garry
April 2015

CRANFIELD UNIVERSITY

SCHOOL OF AEROSPACE, TRANSPORT AND MANUFACTURING

PhD THESIS

Academic Year: 2014-2015

S VELIKOV

Wind Tunnel Modelling of Aerodynamic Baffle Arrays for Aircraft Exhaust
Plume Control

Supervisor: K P Garry

April 2015

This thesis is submitted in partial fulfilment of the requirements for the degree of
Doctor of Philosophy.

 Cranfield University, 2015. All rights reserved. No part of this publication
may be reproduced without the written permission of the copyright holder.

Abstract

Local air quality is one of the factors constraining the development of airports. In
countries of the European Union where new, stricter regulations for emissions of
nitrogen oxides (NO ) have been introduced since 2010, the limits of mean annual
x
concentrations are already exceeded at certain ground monitoring locations of large
airports. This research project investigates the possibility of practically abating the
aircraft exhaust plume at take-off by placing an array of aerodynamic windbreaks
(‘baffles’) in the runway end safety area close to the aircraft starting position. The thesis
investigates whether an array of baffles in the path of the engine exhaust jet at take-off
enhances the dispersion of the plume and causes it to separate from the ground.

The undertaken experimental investigation comprised sub-scale wind tunnel tests
and full-scale field trials with a BAe 146-301 aircraft, performing take-off and landing
cycles at Cranfield Airport. The initial wind tunnel experiments investigated the effect
of a solid baffle row, placed in the path of a buoyant nozzle jet, on the development of
the plume downstream. Using flow visualisation, the positive effect of the baffle row of
promoting buoyant rise of the plume away from the ground was demonstrated
successfully without the presence of wind tunnel flow. The investigation highlighted the
importance of the distance of the baffles relative to the jet source on their effectiveness.
In the presence of wind tunnel flow, the baffles caused an increased vertical spread of
the plume downstream, but the plume was not observed to separate from the ground.
In preparation of the field trials, the spatial arrangement of the baffle array was
investigated by means of wind tunnel drag measurements, performed with a skin-
friction balance. The experiments focused on key parameters such as the baffle slope
angle and row spacing, favouring a configuration of three rows of baffles of increasing
height. The results were observed to be independent of Reynolds number for Reynolds
numbers above 18000, based on the largest baffle height and the exhaust jet velocity.
Based on the wind tunnel measurements, full-scale baffle prototypes were designed and
manufactured at Cranfield University and were deployed in the field trials.
Lidar and point sampler measurements during the field trials suggested that the
plume had risen away from the ground on one occasion when the aircraft was located
close to the baffles. A positive effect was shown in terms of reduced concentrations
downstream of the baffles. This result was not replicated when the aircraft was further
away from the baffles.

The subsequent wind tunnel experiments focused on replicating the field trials at
1:200 scale in Cranfield’s Atmospheric Boundary Layer Wind Tunnel. The aircraft was
represented at sub scale with a single stationary nozzle while the jet speed and buoyancy
were modelled using similarity parameters such as the Froude number and the ratio of
ambient and jet density. Mean concentration measurements were performed using a
Flame Ionisation Detector method releasing methane as tracer gas. The effect of the
baffles was observed to be mainly local in terms of reduced concentrations close the
ground due to their sheltering effect. A more prolonged effect was found to be the
increase of the plume’s vertical spread resulting in an increase in mean concentrations
away from the ground.

Overall, the results of the sub-scale and full-scale experiments were inconclusive
with regard to the ability of the baffle array to lift-off the plume. It appears that the
parameters, which have a significant effect on the lift-off phenomenon, are the ambient
wind speed and the engine starting position. Additional field trials with a sub-scale
UAV gas turbine have been proposed to investigate further the differences in the
obtained results.
Acknowledgements

It took me quite some time and effort to complete this thesis and I have no doubts
that all this would not have been possible without the support I was offered by so many
people along the way. Although some of them were not directly involved, they have
given me the strength and motivation to carry on until the end.

First and foremost, I would like to thank my academic supervisor Professor Kevin
Garry and Dr Michael Bennett from Manchester Metropolitan University for their
support, invaluable advice and scientific contribution to my work. I very much
appreciate Professor Garry’s understanding and patience with me at times when I was
struggling to find motivation. Of course, this work would not have been possible
without the financial support of EPSRC, for which I will always be grateful.
Thanks also to Jenny Holt, who has always been there to help me with my
experiments and has contributed immensely to my work through countless technical
discussions and advice offered. Additionally, the wind tunnel work would not have been
possible without the assistance of Lynton Banks-Davies, Paul Dancer and John
Thrower. I would also like to thank Dr Simon Christie from Manchester Metropolitan
University and Barry Walker for the preparation of the field trials and for the occasional
friendly conversations, which always raised my spirits and kept me motivated.
I wish to thank my colleagues Klementina Gerova and Apostolos Spanelis for all
the work done together and for the shared ups and downs as doctoral students. Thanks
also to my colleagues at the University’s Sports Department, Roy Chamberlain and
Craig Wilde, for giving me the opportunity to financially support my studies at times
when I was struggling. My deepest gratitude also goes to Sue Richardson, whose
immense efforts and work for the Cranfield Students’ Association have been of great
help to all of us sports enthusiasts running the student clubs on campus.

Of course, this all would not have been possible without the support of my family
back home in Bulgaria, to whom I have never told a single word about my project, but
who never stopped asking me how the work was going. I would like to dedicate this
thesis to my grandpa, who was so proud of me being enrolled as a doctoral student, but
sadly passed away shortly after I started. I promised myself I would finish it one day
and here it is. It’s been a long wait.

At Cranfield, I have met so many people of different background. It is a unique,
very multicultural place where students come and go so fast every year and long-lasting
friendships are difficult to maintain. I was very fortunate to meet a few friends, who
have left such an incredible mark on my life. I wish to thank Diego Lombetti, Lara
Berroth, Giuseppe Trapani and Marta Martínez for being my family in England, Spain
and Germany and for never giving up on me. There are no words to express my
gratitude for all the support they have given me. I would also like to thank Michał
Orłowski and Giacomo Struzziero for being there for me when I needed them and for all
the shared good and bad moments as friends, colleagues and volleyball players on the
court, defending the University colours at home and abroad. I have the privilege of
being able to call all these amazing people my closest friends.
Special thanks goes to Juanjo Giner Sanz for the countless discussions and
training sessions outside in the cold, and for teaching me the true meaning of the words
‘motivation’ and ‘dedication’.
I would also like to thank my house mates and friends Robert Christie, Michele
Vianello and Max Starr, who shared with me the small house we called ‘home’ over the
past few years. Robbie, Maxi and Miki, your support and advice, both personal and
academic, has been invaluable to me and it has been a great pleasure to share a home
with you.

Last but not least, I would like thank Eli, Cristina, and Lourdes from the bottom of
my heart for making me the person who I am today and for teaching me more about life
than they could possibly imagine.

October, 2014
Stefan Velikov