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

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