05_Flows Modeling in Automotive

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  • Projekt wspfinansowany ze rodkw Unii Europejskiej w ramach Europejskiego Funduszu Spoecznego

    ROZWJ POTENCJAU I OFERTY DYDAKTYCZNEJ POLITECHNIKI WROCAWSKIEJ

    Wrocaw University of Technology

    Automotive Engineering

    Marcin Tkaczyk

    FLOWS MODELING IN

    AUTOMOTIVE ENGINEERING

    Wrocaw 2011

  • Wrocaw University of Technology

    Automotive Engineering

    Marcin Tkaczyk

    FLOWS MODELING IN

    AUTOMOTIVE ENGINEERING Developing Engine Technology

    Wrocaw 2011

  • Copyright by Wrocaw University of Technology

    Wrocaw 2011

    Reviewer: Jan Kulczyk

    ISBN 978-83-62098-08-8

    Published by PRINTPAP d, www.printpap.pl

  • 3

    Table of contents

    Introduction ................................................................................................................................ 5

    1. Basis .................................................................................................................................... 5

    1.1. Continuity and Momentum Equations ......................................................................... 5

    1.2. Introduction for real flows ........................................................................................... 7

    1.3. Choosing a Turbulence Model .................................................................................... 8

    1.3.1. Transport Equation for the Spalart-Allmaras Model ............................................ 8

    1.3.2. The Standard, RNG, and Realizable k- Models ............................................... 9

    1.3.3. The Standard k- Model ..................................................................................... 9

    1.3.4. Transport Equations for the Standard k- Model ................................................ 9

    1.3.5. The RNG k- Model .......................................................................................... 11

    1.3.6. The Realizable k- Model ................................................................................ 14

    1.3.7. The Standard and SST k- Models ................................................................... 18

    1.3.8. The Standard k- Model ................................................................................... 19

    1.3.9. The Reynolds Stress Transport Equations ......................................................... 25

    1.4. Solution Strategies for Turbulent Flow Simulations ................................................. 25

    1.5. Mesh Generation ........................................................................................................ 26

    1.6. Accuracy .................................................................................................................... 26

    1.7. Convergence .............................................................................................................. 26

    2. Aerodynamice ................................................................................................................... 28

    3. Inlet and outlet in combustion engines ............................................................................. 37

    4. MOVING/DEFORMING MESH ..................................................................................... 51

    4.1. Conservation Equations ............................................................................................. 51

    4.2. Defining Dynamic Mesh Events ................................................................................ 52

    4.2.1. Procedure for Defining Events ........................................................................... 52

    4.3. Using the In-Cylinder Model ..................................................................................... 58

    4.3.1. Overview ............................................................................................................ 58

    4.3.2. Defining Starting Position Mesh for the In-Cylinder Model ............................. 62

    4.3.3. Defining Motion/Geometry Attributes of Mesh Zones ...................................... 63

    4.3.4. Defining Valve Opening and Closure ................................................................ 69

    4.3.5. Defining Events for In-Cylinder Applications ................................................... 69

    5. Injection ............................................................................................................................ 70

    5.1. Point Properties for Single Injections ........................................................................ 71

    5.2. Point Properties for Group Injections ........................................................................ 71

    5.3. Point Properties for Cone Injections .......................................................................... 75

    5.4. Point Properties for Surface Injections ...................................................................... 77

    6. Modeling Engine Ignition ................................................................................................. 79

    6.1. Autoignition Models .................................................................................................. 79

    6.1.1. Overview ............................................................................................................ 79

    6.1.2. Model Limitations .............................................................................................. 79

    6.2. Ignition Model Theory ............................................................................................... 80

    6.3. Transport of Ignition Species .................................................................................... 80

    6.4. Knock Modeling ........................................................................................................ 80

    6.5. Ignition Delay Modeling ........................................................................................... 82

    6.6. Modeling of the Source Term .................................................................................... 82

    6.7. Correlations ............................................................................................................... 82

    6.8. Using the Autoignition Models ................................................................................. 83

    7. Modeling Species Transport and Finite-Rate Chemistry .................................................. 86

    7.1. Theory ........................................................................................................................ 86

  • 7.2. Overview of User Inputs for Modeling Species Transport and Reactions ................ 967.2.1. Enabling Species Transport and Reactions and Choosing the Mixture Material

    987.2.2. Defining Properties for the Mixture and Its Constituent Species ..................... 1007.2.3. Defining Boundary Conditions for Species ..................................................... 113

    7.3. Theory ...................................................................................................................... 1147.4. Species Transport Without Reactions ...................................................................... 1177.5. Modeling Non-Premixed Combustion ..................................................................... 118

    7.5.1. Description of the Equilibrium Mixture Fraction/ PDF Model ........................ 1187.5.2. Benefits and Limitations of the Non-Premixed Approach ............................... 1187.5.3. Details of the Non-Premixed Approach ........................................................... 1197.5.4. Restrictions and Special Cases for the Non-Premixed Model ......................... 1377.5.5. Modeling Approaches for Non-Premixed Equilibrium Chemistry .................. 1417.5.5.1. Single-Mixture-Fraction Approach .............................................................. 141

    7.6. Modeling Liquid Fuel Combustion Using the Non-Premixed Model .................... 1487.6.1. Adding New Species to the prePDF Database ................................................. 148

    4

  • Introduction The aim of this course book is to present the theoretical fundamentals of numerical modeling issues accomplished within Flows Modeling in Automotive Engineering course.

    - First chapter introduces fundamentals of modeling basing on mass conservation law, energy conservation law, principle of conservation of momentum supplemented with a turbulence models,

    The course book follows the course chronology, therefore it was divided into five chapters of which:

    - Second chapter describes the possibilities of modeling issues related with vehicle aerodynamics

    - Third chapter describes modeling of an intake and exhaust systems of a piston combustion engines,

    - Fourth chapter introduces fundamentals of modeling with usage of dynamic mesh, which are indispensable in terms of combustion process modeling within an piston combustion engine,

    - Fifth chapter presents the theoretical deliberation of fuel injection into the cylinders of piston combustion engine,

    - Sixth chapter describes the numerical modeling of an engine ignition system, - Seventh chapter describes numerical models of combustion process within the piston

    combustion engine.

    1. Basis [13] Following chapters describes the fundamentals of finite volume method on which the software used in Flows Modeling in Automotive Engineering is based.

    1.1. Continuity and Momentum Equations

    For all flows, FLUENT solves conservat