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Analysis of Boundary Layers Through Computational Fluid Dynamics and Experimental Analysis

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Analysis of Boundary Layers Through Computational Fluid Dynamics and Experimental Analysis Analysis of Boundary Layers through Computational Fluid Dynamics and Experimental analysis By Eugene O’Reilly, B.Eng This thesis is submitted as the fulfilment of the requirement for the award of degree of Master of Engineering Supervisors Dr Joseph Stokes and Dr Brian Corcoran School of Mechanical and Manufacturing Engineering, Dublin City University, Ireland. October 2006 DECLARATION I hereby certify that this material, which I now submit for assessment on the programme of study leading to the award of Degree of Master of Engineering is entirely my own work and has not been taken from the work of others save and to the extent that such work has been cited and acknowledged within the text of my own work Signed ID Number 99604434 Date 2&j \Oj 2QOG I ACKNOWLEDGEMENTS I would like to thank Dr Joseph Stokes and Dr Brian Corcoran of the School of Mechanical and Manufacturing Engineering, Dublin City University, for their advice and guidance through this work Their helpful discussions and availability to discuss any problems I was having has been the cornerstone of this research Thanks also, to Mr Michael May of the School of Mechanical and Manufacturing Engineering for his invaluable help and guidance in the design and construction of the experimental equipment To Mr Cian Meme and Mr Eoin Tuohy of the workshop for their technical advice and excellent work in the production of the required parts and to Mr Keith Hickey for his help with all my software queries and computer issues Thanks also to Mr Ben Austin and Mr David Cunningham of the School of Biotechnology DCU for their support, they always made themselves available to meet me and allowed me unrestricted use of their School’s equipment whenever I asked I am grateful to the Insh Research Council for Science and Engineering Technology (IRCSET), without whose funding this project would not have been made possible Thanks to my parents, Eugene (Gene) and Nancy, they are truly responsible for every step of my education, they have encouraged me continually to do my best and always provided me with the means to achieve this Also to my sisters Orlagh and Elva for their friendship and offers to help in any way they could with my work I must mention my housemates Robbie, Peter, Susan, Cathenne and Rosemary, they have been a constant source of friendship for the past few years and have quite literally adopted me into their family and I am very happy to be an 4honorary-Flanagan’ Finally, Mary, who has stood by me through it all, she has been there to listen to me, advise me and always encouraged me when I was feeling low Your love and support are truly appreciated II Analysis of Boundary Layers through Computational Fluid Dynamics and Experimental analysis Eugene O’Reilly Dublin City University, Dublin, Ireland ABSTRACT Boundary layers, although unnoticeable to the naked eye, are a characteristic found where the velocity of a fluid relative to a solid surface is zero, hence in the vicinity of this surface a region of velocity increases rapidly from zero up to main stream velocity This has the undesirable effect of causing turbulent flow over long surfaces, which reduce the performance of moving solids (examples being cyclists, automobiles, aircrafts) by introducing frictional drag forces It has been noted that skin-fnction drag is strongly enhanced by the onset of turbulence, however, in turn this turbulence is also greatly enhanced by the separation of the airflow In combination this laminar flow separation and skin-fnction drag decrease lift effects and/or increase pressure drag on aerodynamic surfaces, resulting in decreased efficiency, that is, increased fuel consumption This research aims to examine the development of the boundary layer Specifically the study will look at the effects of separation within the boundary layer and on its impact on the development of the boundary layer and other aspects of the fluid flow Computational Fluid Dynamics or CFD is the analysis of systems involving such phenomena as fluid flow, by means of computer-based simulation This technique is very powerful and spans a wide range of applications CFD has lagged behind other simulation techniques due to the complexity of fluid flow behaviour However, the availability of affordable high performance computational hardware and the introduction of user friendly interfaces, have led to a recent upsurge of interest in the development of CFD simulation packages such as FLUENT Using CFD a computational model is built to represent a system or device that is under investigation The advantages of using CFD are to substantially reduce lead times and costs of new designs, also it is a means of predicting certain outcomes before manufacture To conduct the experimental stages of this research a wind tunnel facility was designed and constructed in- house In conjunction with this, 2D CFD models of the wind tunnel test section were developed The wind tunnel facility was then used to validate the readings obtained from the CFD models A number of blunt plate test pieces were placed in the wind tunnel and the resulting boundary layer development across the test pieces was measured A 2D CFD model was also constructed and the results were consistent with experimental findings Experimental results revealed a reattachment of the flow, with the surface of the test pieces, at a point of x/d = 4 444 from the leading edge of the test piece III TABLE OF CONTENTS Page Declaration I Acknowledgements II Abstract III Table of Contents IV Table of Figures VII List of Tables X Nomenclature XI CHAPTER 1 INTRODUCTION 1 CHAPTER 2 LITERATURE SURVEY 3 2 1 INTRODUCTION 3 2 2 FLUID MECHANICS 3 2 2 1 Compressible and Incompressible flow 4 2 2 2 Fluid Flow Analysis 5 2 2 3 Laminar and Turbulent Flow 5 2 2 4 Bernoulli’s Equation 5 2 3 AERODYNAMICS 7 2 2 1 Lift 7 2 2 2 Pressure and Lift 8 2 2 3 Drag 9 2 2 4 Aero factors 11 2 2 5 Performance 12 2 2 6 Stability 14 2 2 7 Cooling 15 2 2 8 Visibility 15 2 2 9 Comfort 16 2 4 BOUNDARY LAYERS 17 2 5 FLAT PLATE SEPARATION AND BOUNDARY LAYER CONTROL 24 2 6 BLUNT PLATE SEPARATION AND REATTACHMENT 27 2 7 CFD AND BOUNDARY LAYER ANALYSIS 28 2 8 PRESENT RESEARCH OBJECTIVES 29 CHAPTER 3 COMPUTATIONAL FLUID DYNAMICS 30 3 1 WHY USE CFD'? 31 3 2 DEVELOPMENT OF CFD 32 3 3 GOVERNING EQUATIONS OF CFD 33 3 3 1 Finite Control Volume 33 3 3 2 The Continuity Equation 33 IV 3 3 3 The Momentum Equation 34 3 4 CFD PROCEDURE 35 3 5 TURBULENCE MODELS 37 3 6 CFD SOLVERS 38 3 6 1 Meshmg of the geometry withm Gambit 38 CHAPTER 4 DESIGN OF EXPERIMENTAL EQUIPMENT 40 4 1 DESIGN BRIEF 40 4 2 PRODUCT DESIGN SPECIFICATION 40 4 3 RESEARCH INTO THE AVAILABILITY AND COST OF ‘OFF THE SHELF5 WIND TUNNELS 42 4 4 INVESTIGATION OF POSSIBLE SOLUTIONS TO THE DESIGN PROBLEM 43 4 5 WIND TUNNEL DESIGN 45 4 5 1 Possible Wind Tunnel Designs 45 4 5 2 Open or Closed Test Section 46 4 5 3 Test Section Size 46 4 6 WIND TUNNEL CONCEPTUAL DESIGNS 48 4 6 1 Concept 1 48 4 6 2 Concept 2 49 4 6 3 Concept 3 50 4 7 CONCEPT ANALYSIS 52 4 7 1 Concept Evaluation 53 4 8 THE OPEN RETURN WIND TUNNEL 55 4 8 1 Weighted Decision Matrix 56 4 9 DETAILED DESIGN 58 4 9 1 Final Design 58 4 9 2 Development of the Design 58 4 10 FLOW MEASUREMENT INSTRUMENTATION 68 4 10 1 Pressure 68 4 10 2 Velocity 69 4 10 3 Development of the Instrumentation Equipment 71 4 11 EXPERIMENTAL PROCEDURE 74 4 1 1 1 Specification of Test Pieces 74 4 112 Design of Experimental Procedure 74 4 113 Analysis of Leading Edge Region 76 CHAPTER 5 RESULTS AND DISCUSSION 77 5 1 EXPERIMENTAL RESULTS 77 5 1 1 Comparison of Air Velocities 77 5 1 2 Boundary Layer Development Results - Part 1 79 5 1 3 Boundary Layer Development Results - Part 2 84 5 1 4 Separated Flow at Leading Edge 86 5 2 COMPUTATIONAL FLUID DYNAMICS RESULTS 88 V 5 2 1 Generation of the model within Gambit 88 5 2 2 Import of the model into FLUENT 89 5 2 3 Boundary Layer Development Profiles - Part 1 91 5 2 4 Boundary Layer Development Profiles - Part 2 98 5 3 COMPARISON OF RESULTS 102 5 3 1 Boundary Layer Development 1 02 5 3 2 Separation and Re-attachment of the flow 104 CHAPTER 6 CONCLUSIONS AND FUTURE WORK 105 6 1 CONCLUSIONS 105 6 2 FUTURE WORK 106 6 3 PUBLICATIONS AND PRESENTATIONS 107 REFERENCES 108 APPENDICES 114 Appendix A A1 Appendix B A2 Appendix C A3 Appendix D A10 Appendix E A15 Appendix F Al 8 VI TABLE OF FIGURES CHAPTER 2. LITERATURE SURVEY................................................................Pages 3-29 Figure 2.1: Variation of velocity with distance from a solid boundary....................................4 Figure 2.2: Lift is generated when the airfoil is inclined to the direction of flow. The direction of the resultant force due to the pressure creates this lift.................................8 Figure 2.3: Pressure distribution around an airfoil......................................................................8 Figure 2.4: Values of drag coefficient, Cd, for various body shapes.......................................9 Figure 2.5: Contribution of aerodynamics to vehicle performance and design...................12 Figure 2.6: The influence of drag on max speed of a car.........................................................13 Figure 2.7: The influence of drag on acceleration of a car.....................................................
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