Advances in fluid-structure interaction : updated contributions reflecting new findings presented at the ERCOFTAC Symposium on Unsteady Separation in Fluid-Structure Interaction, 17-21 June 2013, St. John Resort, Mykonos, Greece

This book addresses flow separation within the context of fluid-structure interaction phenomena. Here, new findings from two research communities focusing on fluids and structures are brought together, emphasizing the importance of a unified multidisciplinary approach. The book covers the theory, experimental findings, numerical simulations, and modeling in fluid dynamics and structural mechanics for both incompressible and compressible separated unsteady flows. There is a focus on the morphing of lifting structures in order to increase their aerodynamic and/or hydrodynamic performances, to control separation and to reduce noise, as well as to inspire the design of novel structures. The different chapters are based on contributions presented at the ERCOFTAC Symposium on Unsteady Separation in Fluid-Structure Interaction held in Mykonos, Greece, 17-21 June, 2013 and include extended discussions and new highlights. The book is intended for students, researchers and practitioners in the broad field of computational fluid dynamics and computational structural mechanics. It aims at supporting them while dealing with practical issues, such as developing control strategies for unsteady separation and applying smart materials and biomimetic approaches for design and control. Preface 6 Contents 8 Part I Theoretical and Experimental Approaches for the Unsteady Flow Separation in Fluid-Structure Interaction (FSI) 11 Bluff Body Aerodynamics and Aeroelasticity: Nonstationary, Non-Gaussian and Nonlinear Features 12 1 Introduction 12 2 Nonstationarity, Non-Gaussianity and Nonlinearity 13 2.1 Background 13 2.2 Nonstationary/Transient Winds 13 2.3 Non-Gaussianity 15 2.4 Nonlinearity 17 2.5 Role of Turbulence 20 3 Concluding Remarks 21 References 21 Principles of Wake Energy Recovery and Flow Structure in Bodies Undergoing Rapid Shape Change 24 1 Introduction 25 1.1 Overview 25 1.2 Energy Transfer Considerations 27 1.3 Boundary Vorticity Flux 29 2 Experimental Methodology 30 3 Square-Tipped Foil Results 32 4 Streamlined-Tipped Foil Results 35 4.1 Flow Simulation 37 4.2 Circulation Balance Calculations 38 4.3 Circulation Reduction 40 5 Hollow Foil Results 45 6 Discussion 47 7 Conclusions 50 References 51 Experimental Investigation of a Hybrid Morphing NACA4412 Airfoil Via Time-Resolved PIV Measurements 53 1 Introduction 54 2 Actuation Mechanism 55 2.1 Piezoelectric Material Properties 55 2.2 Shape Memory Alloys 56 2.3 Implementation 57 3 Experimental Setup 58 4 Experimental Results 60 5 Conclusion 62 References 64 Naturally Separated Turbulent Flow Around Two Cylinders in Tandem at High Reynolds Number by Time-Resolved PIV 66 1 Introduction 66 2 Experimental Set-Up 68 3 Statistical and Spectral Analysis of the Flow in the Gap Region Between the Two Cylinders 69 3.1 Flow Pattern I 72 3.2 Flow Pattern II 75 4 Conclusions 79 References 80 Inclined Open Channels: The Influence of Bed in Turbulent Characteristics of the Flow 81 1 Introduction 82 2 Experimental Procedure-Measurements 84 3 Analysis of Results 88 4 Conclusions 92 References 93 Part II Instability and Transition in FSI with Unsteady Separation 95 Fluid-Structure Interaction of a Rolling Cylinder with Offset Centre-of-Mass 96 1 Introduction 97 2 Problem Definition 99 3 Methodology 100 3.1 Governing Equations 100 3.2 Non-dimensional Equations 101 3.3 Numerical Formulation 101 3.4 Experimental Setup 102 4 Results 103 4.1 Wake Structure 103 4.2 Body Forces and Velocity 105 5 Conclusions 107 References 108 Transitional Dynamics of Freely Falling Discs 110 1 Introduction 110 2 Mathematical Formulation and Numerical Method 112 3 State Diagram of the Scenario 115 4 Trajectories 116 5 Conclusions 120 References 121 Secondary Instability of the Flow Past Two Side-by-side Cylinders 122 1 Introduction 122 2 The Mathematical Problem 124 2.1 Floquet Analysis 124 3 Numerical Approach 125 4 DNS Results 126 5 Stability Results 129 5.1 Periodic Base Flow 129 5.2 Direct Floquet Mode 131 6 Conclusions 132 References 133 Part III Numerical Approaches for Unsteady Separation in Fluid-Structure Interaction 135 Rotor Computations with Active Gurney Flaps 136 1 Introduction 138 2 Numerical Methods 140 2.1 HMB2 Flow Solver 140 2.2 Proposed Methods for Gurney Flap Modelling 141 3 Implementation of the Gurney Flaps 142 3.1 Gurney Flap Modelled Within the Multi-block Mesh 142 3.2 Gurney Flap Modelled Using Viscous Wall Boundary Condition Across a Block Face 143 3.3 Gurney Flap Modelled Using Blocked Cells Next to a Block Face 143 3.4 Swinging Gurney 149 4 Results for Gurney Flaps in Two Dimensions 151 4.1 Fixed Gurney Flap 152 4.2 Resolving Flow Details Near the Gurney Flap 152 4.3 Comparison Against Thick Gurney Flap 155 5 Results for Gurney Flaps on Wings in Three Dimensions 158 6 Results for Gurney Flaps on Rotors 160 6.1 Mesh and Implementation 160 6.2 UH60A Rotor in Hover and Forward Flight with Two Gurney Flaps 161 7 Conclusions and the Future Work 167 References 168 Fluid Structure Interaction of Multiple Flapping Filaments Using Lattice Boltzmann and Immersed Boundary Methods 170 1 Introduction 170 2 Coupled Lattice Boltzmann---Immersed Boundary Method 171 3 One Single Flapping Filament in an Incoming Fluid Flow 174 4 Multiple Flapping Filaments in an Incoming Fluid Flow 175 5 Concluding Remarks 179 References 180 Lattice-Boltzmann Simulations of an Oscillating NACA0012 Airfoil in Dynamic Stall 182 1 Introduction 182 2 Numerical Method 184 3 Simulation Setup 185 4 Results 186 4.1 2D Static Simulations 186 4.2 2D Dynamic Simulations 187 4.3 3D Dynamic Simulations 188 4.4 Flow Analysis 190 5 Conclusions 192 References 193 Flow and Particles Deposition in Rabit and Rat Airways Under Realistic Inflow Rate 196 1 Introduction 196 2 Methods 198 3 Governing Equation 199 3.1 Airflow Equations 199 3.2 Particle Transport and Deposition Equations 199 4 Results 201 4.1 Model Validation 201 4.2 The Rat Configuration 203 4.3 The Rabbit Configuration 204 5 Conclusions 205 References 206 Part IV LES, Hybrid and Statistical Turbulence Modelling of Unsteady Separated Flows 208 Wall-Modeling in Complex Turbulent Flows 209 1 Introduction 209 2 Equilibrium Wall-Model and Unstructured Meshes 210 2.1 Equations and Implementation 210 2.2 Wall-Model Grid and Coupling to the LES 211 2.3 Sensor-Based Wall-Modeling for Transitional Flows 212 2.4 Application to McDonnell-Douglas 30P/30N airfoil 213 3 Non-equilibrium Formulation 213 4 A Differential Filter-Based Wall Model 217 4.1 Derivation 217 4.2 Application: NACA 4412 Airfoil at Rec = 1.6 times106 218 5 Conclusion and Future Work 220 References 220 Results and Lessons Learned from the EU-Project ATAAC 222 1 Introduction 222 2 The ATAAC Project 223 3 Selected Test Case Results from ATAAC 224 4 Generalized Lessons Learnt for Turbulence Resolving Approaches 229 References 233 Optimising Aspects of BERP-Like Rotors Using Frequency-Domain Methods 235 1 Introduction 236 2 Numerical Methods 238 3 Parameterisation Technique 241 4 Grid and Geometry Generation 243 4.1 Geometry Generation 243 4.2 Tip Anhedral 244 4.3 Mesh Generation 245 5 Flight Conditions 245 6 Hover Results 247 7 Forward Flight Results 249 7.1 Tip Sweep Effects 249 7.2 Effect of Notch Offset 254 7.3 Effect of Notch Gradient 257 7.4 Overall Performance Comparison 257 8 Planform Optimisation 257 9 Summary and Conclusions 263 References 265 A Numerical Study of the Flow Past a Wind Generator 268 1 Introduction 268 2 The Computational Grid 269 3 The Numerical Method 271 4 The Test Case 276 5 Conclusions 280 References 280 Turbulence Near Interfaces---Modelling and Simulations 282 References 290 VMS and OES-Based Hybrid Simulations of Bluff Body Flows 292 1 Introduction 293 2 Methodology 293 3 Flow Past a Circular Cylinder at Re=140,000 (DDES-OES Model) 295 4 Flow Past a Circular Cylinder at Re=1M (RANS/VMS-LES Model) 299 5 RANS-VMS Simulation of Tandem Cylinder at Re=166,000 301 6 DDES-OES Simulation of Tandem Cylinder Re=166,000 302 7 Conclusions 304 References 305 Dynamic Effect of an Active Deformable Flat Plate on Its Turbulent Flow 308 1 Introduction 309 2 Configuration 309 3 Results 311 3.1 3D Simulations of the Static Flat Plate 311 3.2 2D Static Simulations of the Several Deformations 311 3.3 2D Dynamic Simulations 314 4 Conclusions 315 References 315 Part V Control of Unsteady Separated Flows 316 Minimal Modeling for Passive Flow Control via a Poro-elastic Coating 317 1 Introduction 318 2 Limit Cycles and Vortex-Shedding 319 2.1 Characteristics of Limit Cycles 319 2.2 Characteristics of Vortex-Shedding from Aerofoil 319 3 Development of a Minimal Model 320 3.1 Condition for Existence of Limit Cycles 320 3.2 Application to the Case of Vortex-Shedding 321 4 Model Parameters Using the Method of Multiple Scales 322 5 Linear Minimal Model for Coupled Fluid-Structure Interaction: Derivation of Solution 323 6 Results from Computational Model: Brief Overview 325 7 Comparison with Simulation Results 327 7.1 Case of Smooth Aerofoil 327 7.2 Case of Poro-Elastically Coated Aerofoil 328 8 Conclusions 330 References 331 Cylinder Wake Stabilization Using a Minimal Energy Compensator 332 1 Introduction 332 2 Problem Definition 334 2.1 The MCE Compensator 336 2.2 Numerical Methods 338 3 Results 338 3.1 Sensitivity to Sensor Placement and Reynolds Number 340 4 Conclusions 343 References 344 Controlling Unsteady Separation from a Cylinder by Non-Harmonic Perturbations 346 1 Introduction 346 2 Methodology 347 2.1 Numerical Code 347 2.2 Solution Parameters 348 2.3 Post-processing 349 3 Results 350 3.1 Wake States 350 3.2 Damping and Inertia Coefficients 352 3.3 Vortex Dynamics 353 3.4 Streamline Patterns 354 4 Discussion 356 5 Conclusions 358 References 358 Front Matter....Pages i-ix Front Matter....Pages 1-1 Bluff Body Aerodynamics and Aeroelasticity: Nonstationary, Non-Gaussian and Nonlinear Features....Pages 3-14 Principles of Wake Energy Recovery and Flow Structure in Bodies Undergoing Rapid Shape Change....Pages 15-43 Experimental Investigation of a Hybrid Morphing NACA4412 Airfoil Via Time-Resolved PIV Measurements....Pages 45-57 Naturally Separated Turbulent Flow Around Two Cylinders in Tandem at High Reynolds Number by Time-Resolved PIV....Pages 59-73 Inclined Open Channels: The Influence of Bed in Turbulent Characteristics of the Flow....Pages 75-88 Front Matter....Pages 89-89 Fluid-Structure Interaction of a Rolling Cylinder with Offset Centre-of-Mass....Pages 91-104 Transitional Dynamics of Freely Falling Discs....Pages 105-116 Secondary Instability of the Flow Past Two Side-by-side Cylinders....Pages 117-129 Front Matter....Pages 131-131 Rotor Computations with Active Gurney Flaps....Pages 133-166 Fluid Structure Interaction of Multiple Flapping Filaments Using Lattice Boltzmann and Immersed Boundary Methods....Pages 167-178 Lattice-Boltzmann Simulations of an Oscillating NACA0012 Airfoil in Dynamic Stall....Pages 179-192 Flow and Particles Deposition in Rabit and Rat Airways Under Realistic Inflow Rate....Pages 193-204 Front Matter....Pages 205-205 Wall-Modeling in Complex Turbulent Flows....Pages 207-219 Results and Lessons Learned from the EU-Project ATAAC....Pages 221-233 Optimising Aspects of BERP-Like Rotors Using Frequency-Domain Methods....Pages 235-267 A Numerical Study of the Flow Past a Wind Generator....Pages 269-282 Turbulence Near Interfaces—Modelling and Simulations....Pages 283-292 VMS and OES-Based Hybrid Simulations of Bluff Body Flows....Pages 293-308 Dynamic Effect of an Active Deformable Flat Plate on Its Turbulent Flow....Pages 309-316 Front Matter....Pages 317-317 Minimal Modeling for Passive Flow Control via a Poro-elastic Coating....Pages 319-333 Front Matter....Pages 317-317 Cylinder Wake Stabilization Using a Minimal Energy Compensator....Pages 335-348 Controlling Unsteady Separation from a Cylinder by Non-Harmonic Perturbations....Pages 349-361