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University of Southampton Research Repository Eprints Soton University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF ENGINEERING, SCIENCE AND MATHEMATICS School of Engineering Sciences A Critical Evaluation and Development of the Operational Utility of Active Rotor Technology by Mark Peter Jones Thesis for the degree of Doctor of Philosophy September 2010 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF ENGINEERING, SCIENCE AND MATHEMATICS SCHOOL OF ENGINEERING SCIENCES Doctor of Philosophy A CRITICAL EVALUATION AND DEVELOPMENT OF THE OPERATIONAL UTILITY OF ACTIVE-ROTOR TECHNOLOGY by Mark Peter Jones Modern manufacturing techniques, materials, and design tools enable the modern helicopter designer to highly optimise the rotor; however the resulting optimum must be a compromise between the demands of axial and forward flight and those arising from conflicting requirements of the advancing and retreating sides of the rotor disc. Active technologies provide the opportunity to alleviate some of this design compromise by adapting the rotor to the specific requirements depending on the blade azimuth, the aircraft’s location within the flight envelope, and the mission upon which it is engaged. Three such active rotor technologies are considered here: air jet vortex generators, trailing edge flaps, and active trailing edges. The performance of each device is assessed through the adaptation of indicial aerodynamics methods within a rotor performance method and associated computer program. The results of these assessments are used to inform a critical evaluation of the operational utility of each technology, and their relative merits and weaknesses are compared. The high-speed performance enhancement capabilities of the air jet vortex generators are confirmed; however when applied to a modern rotor design, which has already been optimised for the delay of retreating blade stall, the performance gains are predicted to be limited. Their overall utility is also found to be restricted in comparison to the other technologies as their unsuitability for higher harmonic control means that they are limited to only the performance enhancement application. In contrast, the adaptability of trailing edge flaps to additional applications can be observed from the literature and is further demonstrated here through the prediction of their ability to reduce helicopter blade sailing. This novel application of the trailing edge flap is investigated using a new dynamics method with results obtained demonstrating promising results for a real case study. Possible drawbacks of the trailing edge flap arise due to the exposure of its hinges, which can cause an increase in drag and also reliability issues in harsh environments. The active trailing edge aims to overcome these problems by eliminating the hinges, but only at the expense of deflection capability. A new model is thus presented which accurately models the active trailing edge and demonstrates that even a restricted deflection capability can be used to provide vibration reduction and performance enhancement capabilities of similar magnitudes to those demonstrated for the trailing edge flap. Table of Contents Table of Contents Table of Contents............................................................................................... i List of Figures................................................................................................... v Declaration of Authorship..............................................................................xiii Acknowledgements......................................................................................... xv Nomenclature................................................................................................ xvii Chapter 1 Introduction................................................................................... 1 1.1 The Helicopter Design Challenge..................................................... 2 1.1.1 Stall Boundaries........................................................................ 3 1.1.2 Rotor Induced Vibration ........................................................... 5 1.2 Passive Design Improvements .......................................................... 7 1.3 Air Jet Vortex Generators ............................................................... 11 1.3.1 Static Vortex Generators......................................................... 12 1.3.2 Steady Air Jet Vortex Generators ........................................... 14 1.3.3 Pulsed Air Jet Vortex Generators ........................................... 18 1.3.4 The Potential Application of Air Jet Vortex Generators ........ 22 1.4 The Trailing Edge Flap and Active Trailing Edge.......................... 23 1.4.1 Numerical Studies................................................................... 25 1.4.2 Practical Implementation and Actuation................................. 38 1.4.3 Active Trailing Edges ............................................................. 46 1.5 Research Aims ................................................................................ 48 Chapter 2 The Modelling of Unsteady Aerodynamics................................ 51 2.1 Introduction..................................................................................... 52 2.2 Unsteady Aerodynamics for Attached Flow................................... 54 2.2.1 Thin Aerofoil Theory for Steady Incompressible Flow.......... 54 2.2.2 Unsteady Effects..................................................................... 57 2.2.3 Modifications for Compressibility.......................................... 62 2.2.4 Attached Flow Modelling in the Third Generation Model ..... 63 2.3 Unsteady Aerodynamics of Separating Flow ................................. 68 2.3.1 Characteristics of Dynamic Stall ............................................ 68 2.3.2 Modelling Flow Separation..................................................... 71 2.4 Chapter Summary........................................................................... 76 Chapter 3 Air Jet Vortex Generators ........................................................... 77 3.1 Overview......................................................................................... 78 3.2 Steady State Modelling of Air Jet Vortex Generators .................... 78 3.2.1 Separation Location Model..................................................... 79 3.2.2 Separation Independent Model............................................... 82 3.2.3 Prediction by Old Model of Effects due to Separation........... 84 3.2.4 New Model for Effects due to Separation............................... 87 3.2.5 Overall Coefficient Prediction ................................................ 90 3.2.6 Static Coefficients with Air Jet Vortex Generators ................ 92 3.3 Unsteady Modelling of Air Jet Vortex Generators......................... 99 3.3.1 Suggested Alterations from University of Glasgow ............... 99 3.3.2 Further Alterations to the Dynamic Stall Model................... 103 3.3.3 Application to the Air Jet Vortex Generator Data ................ 115 3.4 Performance Enhancement of an Advanced Rotor....................... 123 i Table of Contents 3.4.1 Application of the Data......................................................... 124 3.4.2 Analysis of a High Blade Loading Case............................... 126 3.4.3 Analysis of a Low Blade Loading Case................................ 131 3.4.4 Stall and Power Benefits due to Air Jet Vortex Generators.. 133 3.4.5 Operational Benefits due to Air Jet Vortex Generators........ 137 3.5 The Overall Utility of Air Jet Vortex Generators ......................... 141 Chapter 4 Trailing Edge Flaps and their Application to Blade Sailing..... 147 4.1 The Adaptability of Trailing Edge Flaps ...................................... 148 4.2 Helicopter Blade Sailing............................................................... 149 4.2.1 The Dynamic Interface ......................................................... 149 4.2.2 The Blade Sailing Problem ................................................... 150 4.2.3 The Passive Reduction of Blade Sailing............................... 152 4.2.4 The Active Control of Blade Sailing .................................... 154 4.3 The Modelling of Blade Sailing.................................................... 156 4.3.1 Background........................................................................... 156 4.3.2 Stimulus for a New Model.................................................... 159 4.3.3 Flapwise Deflection of a Rotating Beam.............................. 160 4.3.4 Solution of the Blade Equations of Motion .......................... 162 4.3.5 Estimation of the Inertia Terms ...........................................
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