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6.2. Downforce Mechanism on a Diffuser

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6.2. Downforce Mechanism on a Diffuser Aerodynamic Study of a Formula 3 diffuser. Pág. 1 Review The diffuser of a racing car is responsible for collecting all the air flowing under the car and drive it to the outside through the rear part of it. It is a characteristic element that, despite it is true that at first glance it maintains certain similarities in all automobile modalities, it becomes a very particular piece according to the nature of each competition. Any slight modification or variation of the design parameters can make what was considered a simple car a race winner and it is for this reason that this report lays out a very instructional strategy that an aerodynamics engineer could perfectly follow when trying to accomplish the goal of ensuring that the air stays stuck to the bottom of the car and never detaches, which is one of the key components to build a successful diffuser. We are used to focus on which are the problems and what the final solutions to this problems are, but it will be worth it to see and navigate through all the steps that we have to take to go over a path that might seem simple at first. The report that follows is based on one hand on theoretical aerodynamic definitions, concepts and principles to introduce the reader in the field and help him get a full understanding of the work. On the other hand it advances to the detail of the iterative methodology and computer programming used to study the aerodynamic behavior of the diffuser. To contextualize, Formula 3 competition has been chosen. There are a lot of racing car competitions where a diffuser is used but F3 will allow us to see the more important characteristics of this part of a vehicle and at the same time will make the study feasible as its design won’t be as complicated as the one we would require for an F1 car for example letting us focus on the basic but most important settings of a diffuser. Pág. 2 Memory Summary REVIEW _____________________________________________________ 1 SUMMARY ___________________________________________________ 2 1. GLOSSARY ______________________________________________ 5 2. PREFACE ________________________________________________ 7 2.1. Motivation ....................................................................................................... 7 3. INTRODUCTION ___________________________________________ 9 3.1. Goals of the project........................................................................................ 9 3.2. Scope of the project ..................................................................................... 10 4. AERODYNAMICS _________________________________________ 11 4.1. History of aerodynamics .............................................................................. 11 4.2. Introduction to aerodynamics ...................................................................... 14 4.3. Aerodynamics most important principles and equations ............................. 15 4.3.1. Continuity equation ..........................................................................................16 4.3.2. Bernoulli’s equation .........................................................................................16 4.3.3. Venturi effect ...................................................................................................18 4.3.4. Coanda Effect ..................................................................................................19 4.4. Boundary layer ............................................................................................. 20 4.4.1. Boundary layer separation ...............................................................................23 4.5. Vortex ........................................................................................................... 25 4.6. Aerodynamic forces ..................................................................................... 26 4.6.1. Downforce........................................................................................................27 4.6.2. Drag force ........................................................................................................29 5. FORMULA 3 INTRODUCTION _______________________________ 32 6. DIFFUSER ______________________________________________ 33 6.1. Performance parameters of a diffuser: ........................................................ 35 6.2. Downforce mechanism on a diffuser ........................................................... 35 7. FLOW SIMULATION PROGRAM _____________________________ 38 7.1. ANSYS – Computational Fluid Dynamics ................................................... 38 7.2. CFX – Software ........................................................................................... 39 7.3. CFX process ................................................................................................ 41 7.3.1. Creating the Geometry/Mesh...........................................................................41 Aerodynamic Study of a Formula 3 diffuser. Pág. 3 7.3.2. Defining the Physics of the Model................................................................... 43 7.3.3. Solving the CFD Problem ............................................................................... 44 7.3.4. Visualizing the Results in the Post-processor ................................................. 45 8. CFX SIMULATION – FLOW ANALYSIS OF THE DIFFUSER _______ 46 8.1. First Analysis ................................................................................................ 46 8.1.1. Geometry ........................................................................................................ 46 8.1.2. CFX Analysis .................................................................................................. 47 8.1.2.1. Geometry ............................................................................................. 47 8.1.2.2. Mesh .................................................................................................... 47 8.1.2.3. Boundary conditions ............................................................................. 48 8.1.2.4. Run ...................................................................................................... 49 8.1.2.5. Results ................................................................................................. 50 8.2. Second Analysis ........................................................................................... 52 8.2.1. Geometry ........................................................................................................ 52 8.2.2. Mesh, boundary conditions and run. ............................................................... 53 8.2.3. Results ............................................................................................................ 53 8.3. Third Analysis ............................................................................................... 55 8.3.1. Geometry ........................................................................................................ 55 8.3.2. Results ............................................................................................................ 55 8.4. Fourth Analysis ............................................................................................. 58 8.4.1. Geometry ........................................................................................................ 58 8.4.2. Results ............................................................................................................ 58 8.5. Fifth Analysis ................................................................................................ 61 8.5.1. Geometry ........................................................................................................ 61 8.5.2. Results ............................................................................................................ 61 8.6. Possible ways to further improve on the design of this diffuser. .................. 62 8.7. The importance of the mesh and Turbulence Model. .................................. 63 8.7.1. Mesh importance ............................................................................................ 63 8.7.2. Turbulence models ......................................................................................... 64 8.8. Comparative analysis and numerical conclusions ....................................... 67 9. ENVIRONMENTAL IMPACT ________________________________ 69 10. BUDGET OF THE PROJECT ________________________________ 71 11. PROJECT PLANNING _____________________________________ 74 CONCLUSIONS ______________________________________________ 75 Pág. 4 Memory ACKNOWLEDGEMENTS _______________________________________ 77 BIBLIOGRAPHY ______________________________________________ 78 Bibliographic References ...................................................................................... 78 Complementary bibliography ................................................................................ 78 Aerodynamic Study of a Formula 3 diffuser. Pág. 5 1. Glossary Viscosity: Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid. A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion. Compressibility: A measure of how easily a gas can be forced into a smaller volume. Turbulent flow: type of fluid flow
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