Numerical Simulations of the Wing Wake and Tip Vortex for Air-to-Air Refuelling

168 Pages·2013·9.74 MB·English

CRANFIELD UNIVERSITY

Alice Miranda

Numerical Simulations of the Wing Wake and Tip Vortex
for Air-to-Air Refuelling

School of Engineering
MSc by Research

MSc by Research Thesis
Academic Year: 2011-2012

Supervisor: Dr. David MacManus
October 2012

CRANFIELD UNIVERSITY

Alice Miranda

Numerical Simulations of the Wing Wake and Tip Vortex
for Air-to-Air Refuelling

School of Engineering
MSc by Research

MSc by Research Thesis
Academic Year: 2011-2012

Supervisor: Dr. David MacManus
October 2012

This thesis is submitted in fulfilment of the requirements
for the degree of Master of Science by Research
© Cranfield University 2012. All rights reserved. No part of this publication may
be reproduced without the written permission of the copyright owner

Abstract
Abstract

The present research was carried out in the framework of the ASTRAEA II
project, in collaboration with Cobham Mission Equipment. One part of the
overall ASTRAEA II project is to design an autonomous air-refuelling system
based on a wake model computed in real-time, which allows the flow field to be
visualised in a Synthetic Environment. In a previous part of the ASTRAEA
project a MATLAB® code was developed based on the extended lifting line
method (referred to as the ELL code) which provides a refuelling tanker wake
model. The aim of this project is to understand the tanker wake, to provide
more detailed flow field predictions and to compare the results with the results
from the ELL code to validate this reduced fidelity method.
The understanding of the tanker wake and tip vortices was carried out
through the use of computational fluid dynamics (CFD) methods. CFD
simulations of three geometries were carried out and post-processed: the DLR-
F6 aircraft geometry, the CRM aircraft geometry (both similar to the A330) and
the NACA0015 swept wing model of Gerontakos and Lee. The latter was used as
a validation test case for the CFD modelling of the wake and the tip vortex. The
CFD simulations were performed using a geometry definition compatible with
the idealised model scale aircraft definitions used in the wind tunnel
experiments. Finally comparisons between the available CFD results and the
ELL code were carried out.
The ELL code computes a qualitatively similar wake and tip vortex flow field,
but only when the code is run with a different set-up which requires more
computing resources. The addition of the simple fuselage model to the ELL code
has provided an improvement in the results compared with the CFD solutions.
The ELL code does not model the vortex roll up and there are notable
differences in the near-field region in particular. Although the flow field
structure is similar between the ELL and the CFD results, there are notable
differences in the local disturbance flow field. In particular, for some
configurations, the tip vortex strength is underpredicted by up to a factor of
three relative to the CFD results.

Acknowledgments
Acknowledgements

I would like to express my deepest gratitude to my supervisor, Dr David
MacManus, for all the lessons, help and guidance he provided during this
research project year. Moreover, I would like to thank him for giving me the
opportunity to work on this project and have this unforgettable experience at
Cranfield University.
I would also like to acknowledge Cobham Mission Equipment and Dr. James
Whidborne for their extremely useful collaboration.
I must thank Robert, Grant, Kishor and Tom, the PhD students that provided
very useful advice for my research. A big thanks to Antonio, a colleague who
worked on a different aspect of the same project.
I am deeply thankful to my life partner Adi for supporting me throughout this
intense year. Without him I would not be where I am.
Moreover, I would like to thank my friend Sophie, with whom I shared a lot of
lunches at Cranfield, for having encouraged me in the hard times and a big
thanks also to all the office colleagues, in particular Mohammed and Suleiman.
Thanks to them the long working days have been funnier.
Last but not least, I must thank my friends back in Italy, in particular Lorenzo,
Simone and Nicoletta, who despite the distance, stayed next to me and never
stopped giving me their help and support.

Table of Contents
Table of Contents

Abstract ....................................................................................................................... v
Acknowledgements .................................................................................................. vii
Table of Contents ...................................................................................................... ix
List of Figures ........................................................................................................... xii
List of Tables ............................................................................................................. xx
Nomenclature ........................................................................................................... xxi
1 Introduction .............................................................................................................. 1
1.1 Introduction to work ........................................................................................ 1
1.2 Project rationale ............................................................................................... 1
1.3 Scope of the project ......................................................................................... 2
1.4 Aim and objectives .......................................................................................... 2
1.5 Project roadmap .............................................................................................. 3
1.6 Thesis outline .................................................................................................. 4
2 Literature review ...................................................................................................... 7
2.1 Air-refuelling .................................................................................................... 7
2.2 Wake flow field and tip vortices ..................................................................... 9
2.3 Experimental studies ..................................................................................... 12
2.3.1 “Gerontakos swept wing” ...................................................................... 13
2.4 Numerical studies .......................................................................................... 15
2.5 Low fidelity model (ELL code) ...................................................................... 18
2.5.1 Prandtl’s classical lifting line theory ..................................................... 18
2.5.2 Weissinger’s extended lifting line theory ............................................ 20
2.5.3 ELL code summary ............................................................................... 21
3 Project overview and methodology ....................................................................... 23
3.1 Introduction .................................................................................................. 23
3.2 Numerical codes ........................................................................................... 23
3.2.1 ANSYS Fluent code ............................................................................... 23
3.2.2 ANSYS CFX code .................................................................................. 26
3.3 Identification of the test cases ...................................................................... 28
3.4 DLR-F6 geometry ......................................................................................... 32
3.4.1 Introduction.......................................................................................... 32
Table of Contents
3.4.2 Experimental data available ................................................................. 33
3.4.3 CFD simulations domain and boundary conditions ............................ 34
3.4.4 Grids ..................................................................................................... 35
3.5 Common Research Model (CRM) ................................................................. 36
3.5.1 Introduction .......................................................................................... 36
3.5.2 Experimental data available for the CRM ............................................ 37
3.5.3 CFD simulations domain and boundary conditions ............................ 39
3.5.4 Grids ..................................................................................................... 42
3.6 CFD models of the Gerontakos swept wing test case ................................... 44
3.6.1 Introduction .......................................................................................... 44
3.6.2 Experimental data available ................................................................. 45
3.6.3 CFD simulations domain and boundary conditions ............................ 45
3.6.4 Grids ..................................................................................................... 47
3.7 Convergence criteria ..................................................................................... 50
3.7.1 ANSYS Fluent criteria ........................................................................... 50
3.7.2 ANSYS CFX criteria .............................................................................. 52
3.8 Post-processing ............................................................................................. 54
3.8.1 Tecplot .................................................................................................. 54
3.8.2 Vortex core and circulation .................................................................. 55
4 DLR-F6 results and analysis ................................................................................. 59
4.1 Introduction .................................................................................................. 59
4.2 DLR-F6 Results............................................................................................. 59
5 CRM at wind tunnel scale ...................................................................................... 69
5.1 Introduction .................................................................................................. 69
5.2 Wing-body CRM geometry at wind tunnel scale results .............................. 69
6 Validation test case results .................................................................................... 79
6.1 Introduction .................................................................................................. 79
6.2 “Gerontakos swept wing” simulations .......................................................... 79
6.3 Comparison with the experimental data ...................................................... 83
7 Results from the ELL method ............................................................................... 93
7.1 Introduction ................................................................................................... 93
7.2 ELL code study .............................................................................................. 94
7.3 ELL code with fuselage of the CRM at wind tunnel scale ............................ 96
7.4 ELL code of the CRM full-scale geometry under air-refuelling conditions 111