Investigating the Impact of Ship Superstructure Aerodynamics on Maritime Helicopter Operations

256 Pages·2013·13.04 MB·English

Investigating the Impact of Ship
Superstructure Aerodynamics on Maritime
Helicopter Operations

Thesis submitted in accordance with the requirements of the
University of Liverpool for the degree of Doctor in Philosophy
by
Christopher Henry Kääriä
School of Engineering
The University of Liverpool
August 2012
Abstract

The work reported in this thesis has investigated the impact of ship superstructure
geometry on helicopter operations to the flight decks of naval warships. Ship-Helicopter
operating limits for military frigates and destroyers are often restricted in difficult weather
conditions because of excessive pilot workload caused by the unsteady ship airwake.
Experiments have been conducted in a water tunnel using a specially designed Airwake
Dynamometer (AirDyn) to characterise the steady and unsteady aerodynamic loading of a
helicopter immersed in the airwake of a generic ship that has been called the Shortened
Research Frigate (SRF). The AirDyn is a 1:54 model-scale helicopter, mounted on a six-
component force block; it has a simplified spinning main rotor and fuselage based on a
Merlin AW-101. The AirDyn has been shown to be an effective tool for characterising
the steady and unsteady aerodynamic loading of a helicopter model in a ship’s airwake
and the aerodynamic loads measured by the AirDyn were found to correlate with at-sea
and simulation flying experience for a range of Wind-Over-Deck (WOD) conditions and
ship geometry configurations. The airwakes of the SRF without the presence of a
helicopter model have also been investigated using unsteady Computational Fluid
Dynamics (CFD). A Detached-Eddy Simulation (DES) approach was used for the
turbulence modelling as it has been shown to be capable of capturing the bluff-body type
flow features typical of ship airwakes. Analysis of the CFD data revealed the underlying
aerodynamic causes of the observed loading characteristics of the AirDyn. A range of
ship geometry modifications were made to the SRF to determine the feasibility of
mitigating the adverse effects of the airwake by modifying existing ships or by improving
the designs of future ships. A range of modifications to the windward hangar side-face of
the SRF were tested using the AirDyn and were found to reduce the severity of unsteady
loads by up to 55% for oblique WOD angles (Green 30°-45°) at important locations
through the flight path of a standard Royal Navy deck-landing manoeuvre. Unsteady CFD
analysis showed that the modifications controlled the flow separation from the top edge
of the windward hangar side-face in such a way as to reduce the height and the angle of
the separated flow and thus the severity of the unsteady flow structures being drawn into
the main rotor of the AirDyn. The unsteady CFD data computed for the baseline and
modified SRF ship geometries was also integrated into the University of Liverpool’s
motion-base flight simulator and piloted flight simulation trials were conducted to
determine the impact of the ship modifications on pilot workload. The results of the
simulation flight trials confirmed the usefulness of the AirDyn as a tool for predicting
pilot experience and showed that it is feasible to modify ship superstructures to the extent
that tangible reductions in pilot workload are achieved.
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Acknowledgements
I would like to thank Professor Ieuan Owen for giving me the opportunity to work on
such a great project and to collaborate with such a wide range of fantastic researchers. His
guidance and support has been invaluable to my work and by allowing me to use my own
initiative I have developed as a researcher more quickly than I could have hoped for. My
time as a PhD student has been hugely rewarding and enjoyable.
This thesis would not have been possible without the work of Dr. Yaxing Wang and John
Curran who developed the AirDyn instrument, under the guidance of Professor Ieuan
Owen and Professor Gareth Padfield. Their hard work laid the foundations for my PhD
for which I am very grateful.
I owe a huge debt of gratitude to Dr. James Forrest who taught me all about ship
airwakes, CFD and much else besides. His openness to sharing knowledge and the
encouragement he has given to me and my research, even from the other side of the
world, has driven me to achieve much more than I could have otherwise.
Thanks also to Dr. Phillip Perfect and Dr. Mark White of the Flight Science and
Technology for their help setting up and running the simulator flight trials and for many
interesting and stimulating discussions in various establishments. Thanks also to test pilot
Andy Berryman for taking part in the trials, his knowledge and experience helped shape
the path of the project.
Thanks to the ladies in the Student Support Office who have guided me through my seven
years at Liverpool as an undergraduate and postgraduate and without whom I would not
have got anywhere!
Thanks to everyone who shared the Fluids Research Office over my 4 years as a PhD
student; James Forrest, Yazdi Harmin (Abercromby Square Pocket Tanks Masters!!!);
Sean Malkeson, Adam Yuile, Mohit Katragadda, Azuraien ‘Yin’ Jaafar, Ellie Tsioli,
Dimitris Tsovolos, Sian Tedds, and Yaxing Wang. Awesome guys!
The biggest thanks go to the Kääriä family, Granny Kate, Aunty Bub, Nanny & Grandad
Caldow; but especially to Mum, Dad, Brother and Sister - Susan, Karl, David and Joanne.
This is for you.
Thank You.

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Contents

Abstract i
Acknowledgements ii
Nomenclature ix
Glossary xi

1. Introduction and Literature Review 1
1.1 Introduction .................................................................................................................... 1
1.1.1 Challenges at the Ship-Helicopter Dynamic Interface ........................................... 1
1.1.2 The Ship Airwake .................................................................................................. 2
1.1.3 Ship-Helicopter Operating Limits .......................................................................... 3
1.1.4 Motivation for Current Study ................................................................................. 4
1.2 Literature Review ........................................................................................................... 6
1.2.1 Highlighting the Challenges at the Dynamic Interface .......................................... 6
1.2.2 Characterising Ship Airwake Aerodynamics ......................................................... 9
1.2.2.1 Experimental Studies ............................................................................... 10
1.2.2.2 Computational Fluid Dynamics ............................................................... 13
1.2.3 Pilot Experience Predictive Tools ........................................................................ 23
1.2.3.1 High-Fidelity Flight Simulation .............................................................. 23
1.2.3.2 Experimental Prediction of At-Sea pilot Experience .............................. 27
1.2.4 Ship Design for Helicopter Operations ................................................................ 31
1.2.5 Literature Review Summary ................................................................................ 34
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1.3 Project Aims and Objectives ....................................................................................... 35
1.3.1 Project Aims ......................................................................................................... 35
1.3.2 Project Objectives ................................................................................................ 36
1.3.3 Resources ............................................................................................................. 37
1.3.4 Publications .......................................................................................................... 38
1.3.4.1 Conference Proceedings .......................................................................... 38
1.3.4.2 Journal Publications ................................................................................. 39
2. Experimental Procedure and Computational Methods 40
2.1 Experimental Procedure .............................................................................................. 40
2.1.1 The Airwake Dynamometer (AirDyn) ................................................................. 41
2.1.1.1 Water Tunnel Facility .............................................................................. 43
2.1.1.2 Dynamic Force Balance Design .............................................................. 44
2.1.1.3 Semi-Conductor Strain Gauges ............................................................... 47
2.1.1.4 AirDyn Fuselage Model .......................................................................... 48
2.1.1.5 Dynamic Main Rotor Design ................................................................... 48
2.1.1.6 Calibration ............................................................................................... 49
2.1.1.7 AirDyn Frequency Response ................................................................... 51
2.1.1.8 Rotor Frequency Scaling ......................................................................... 52
2.1.2 Shortened Research Frigate.................................................................................. 53
2.1.3 Experimental Details and Data Collection ........................................................... 55
2.1.4 Quantifying Unsteady Aerodynamic Loading ..................................................... 56
2.1.5 Aims of the AirDyn Experiment .......................................................................... 61
2.2 Computational Fluid Dynamics .................................................................................. 62
2.2.1 ANSYS Fluent Solver .......................................................................................... 63
2.2.2 Turbulence Modelling Approach ......................................................................... 63
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2.2.3 Detached-Eddy Simulation .................................................................................. 65
2.2.4 Unstructured Mesh Generation ............................................................................ 65
2.2.5 Boundary Conditions ........................................................................................... 67
2.2.6 Time-Step ............................................................................................................. 67
2.2.7 High Performance Computing Resources ............................................................ 67
2.2.8 General Solution Strategy .................................................................................... 68
2.3 Piloted Flight Simulation ............................................................................................. 68
2.3.1 HELIFLIGHT-R Simulator .................................................................................. 70
2.3.2 FLIGHTLAB Simulation Environment ............................................................... 70
2.3.3 Sikorsky SH-60B Helicopter Model .................................................................... 71
2.3.4 Airwake Data Integration ..................................................................................... 73
2.3.5 Airwake Data-Scaling .......................................................................................... 74
2.3.7 Visual Environment and Ship Motion.................................................................. 74
2.3.8 Flight Simulation Test Pilot ................................................................................. 75
2.3.9 Flight Trial Helicopter Manoeuvres ..................................................................... 75
2.3.10 Pilot Workload Assessment ............................................................................... 75
2.3.10.1 Deck Interface Pilot Effort Scale ........................................................... 76
2.3.10.2 Bedford Workload Rating Scale ............................................................ 76
2.4 Chapter Summary ........................................................................................................ 78

3. Steady and Unsteady Aerodynamic Loading Characteristics of the
AirDyn in a Ship’s Airwake 79
3.1 Steady Aerodynamic Loading Characteristics .......................................................... 80
3.1.1 Headwind Thrust Deficit ...................................................................................... 81
3.1.2 Headwind Pitch Down Effect............................................................................... 86
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3.1.3 G45 Pressure Wall................................................................................................ 87
3.1.4 G30 Pressure Wall................................................................................................ 89
3.2 Unsteady Aerodynamic Loading Characteristics ..................................................... 90
3.2.1 Headwind ............................................................................................................. 90
3.2.2. G45 ...................................................................................................................... 93
3.2.3 G30 ....................................................................................................................... 94
3.2.4 Unsteady Aerodynamic Loading at Different Rotor Heights .............................. 98
3.3 Effect of Large Scale SRF Geometry Modifications in a Headwind ..................... 103
3.3.1 Steady Aerodynamic Loading ............................................................................ 103
3.3.2 Unsteady Aerodynamic Loading........................................................................ 104
3.4 Static and Dynamic Rotor Comparison ................................................................... 113
3.5 Chapter Summary ...................................................................................................... 116

4. Development of Ship Modifications to Reduce Unsteady Aerodynamic
Loading of the Helicopters 119
4.1 Targeted WOD Angles ............................................................................................... 119
4.1.1 Dominant Flow Features in Oblique WOD Angles ........................................... 120
4.1.1.1 Hangar Side-Face Separation ................................................................ 120
4.1.1.2 Vertical Hangar-Edge Shear Layer Separation ..................................... 122
4.1.1.3 Deck-Edge Separation ........................................................................... 123
4.2 Hangar Side-Face Modifications .............................................................................. 123
4.2.1 Green 45° WOD angle ....................................................................................... 126
4.2.1.1 150% HH Lateral Translation ................................................................ 126
4.2.1.2 125% HH Lateral Translation Rotor Height .......................................... 130
4.2.1.3 110% HH Lateral Translation Rotor Height .......................................... 133
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4.2.1.4 175% HH Lateral Translation Rotor Height .......................................... 138
4.2.1.5 Summary of Hangar Side-Face Modifications for G45 ......................... 139
4.2.2 Green 30° WOD angle ....................................................................................... 141
4.2.2.1 150% HH Lateral Translation ................................................................ 141
4.2.2.2 125% HH Lateral Translation ................................................................ 146
4.2.2.3 110% HH Lateral Translation ................................................................ 146
4.2.2.4 Vertical Traverse over Landing Spot ..................................................... 147
4.2.2.5 Summary of Hangar Side-Face Modifications for G30 ......................... 148
4.3 Windward Vertical Hangar Edge Modifications .................................................... 150
4.3.1 G30 WOD Condition ......................................................................................... 150
4.3.1.1 150% HH Lateral Translation ................................................................ 151
4.3.1.2 125%HH Lateral Translation ................................................................. 152
4.3.1.3 110% HH Lateral Translation ................................................................ 156
4.3.1.4 Vertical Traverse over Landing Spot ..................................................... 156
4.4 Notch Modification in Headwind Condition ............................................................ 157
4.5 Chapter Summary ...................................................................................................... 159

5. CFD Analysis and Piloted Flight Simulation Trials 161
5.1 CFD Airwake Analysis .............................................................................................. 161
5.1.1 Hangar Side-Face Modifications - G45 WOD ................................................... 161
5.1.1.1 150% HH Vertical Turbulence Intensity ............................................... 163
5.1.1.2 175% HH Vertical Turbulence Intensity ............................................... 163
5.1.1.4 75% HH Vertical Turbulence Intensity ................................................. 164
5.1.1.5 Effect of Modifications on Hangar Side-Face Flow Separation ............ 168
5.1.2 G30 WOD Condition ......................................................................................... 172
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5.1.2.1 Effect of Modifications on Hangar Side-Face Flow Separation ............ 172
5.1.2.2 Effect of Modifications on Hangar-Edge Shear Layer Separation ........ 177
5.2 Piloted Flight Simulation Trials ................................................................................ 178
5.2.1 G45 SRF Geometry Modification Flight Trial Results ...................................... 179
5.2.1.1 Full Deck-Landing Manoeuvre Task ..................................................... 179
5.2.1.2 30-Second Hover over the Flight Deck Task ........................................ 183
5.2.2 Headwind Mast and Lead-Flap Flight Trial Results .......................................... 184
5.2.2.1 30-Second Hover over the Flight Deck Task ........................................ 185
5.2.2.2 Baseline-SRF Headwind and G45 Comparison .................................... 186
5.3 Chapter Summary ...................................................................................................... 188

6. Conclusions and Recommendations 190
6.1 Summary ..................................................................................................................... 190
6.2 Conclusions ................................................................................................................. 192
6.3 Recommendations ...................................................................................................... 196

References 200
Appendix A: Published Papers 209

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Nomenclature

Roman Notation

A Swept area of rotor disc (m2)
b Ship beam at aft end of flight deck (m)
C DES length-scale constant
DES
f Frequency (Hz)
I Turbulence intensity in i'th direction (%)
i
k Turbulent kinetic energy per unit mass (m2/s2)
L Turbulent length scale (m)
t
l Characteristic length scale (m)
l Ship length (m)
R Radius of rotor disc (m)
t Time (s)
u Longitudinal velocity (m/s)
U Free-stream velocity magnitude (m/s)
∞
u Instantaneous velocity component in the i’th dimension (m/s)
i
v Lateral velocity (m/s)
V Velocity magnitude (m/s)
mag
V Voltage Outputs from Sensing Elements (V)
outputs
w Vertical velocity (m/s)
x Longitudinal distance (m)
y Lateral distance (m)
z Vertical distance (m)

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