Santa Clara University Scholar Commons Mechanical Engineering Masters Theses Student Scholarship 2012 CFD study on aerodynamic effects of a rear wing/ spoiler on a passenger vehicle Mustafa Cakir Santa Clara University Follow this and additional works at: http://scholarcommons.scu.edu/mech_mstr Part of the Aerodynamics and Fluid Mechanics Commons, and the Mechanical Engineering Commons Recommended Citation Cakir, Mustafa, "CFD study on aerodynamic effects of a rear wing/spoiler on a passenger vehicle" (2012). Mechanical Engineering Masters Theses. Paper 1. This Thesis is brought to you for free and open access by the Student Scholarship at Scholar Commons. It has been accepted for inclusion in Mechanical Engineering Masters Theses by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Department of Mechanical Engineering December 2012 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISOR BY Mustafa Cakir ENTITLED CFD STUDY ON AERODYNAMIC EFFECTS OF A REAR WING/SPOILER ON A PASSENGER VEHICLE BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MECHANICAL ENGINEERING Thesis Advisor Chairman of Department Department of Mechanical Engineering December 2012 Department of Mechanical Engineering December 2012 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISOR BY Mustafa Cakir ENTITLED CFD STUDY ON AERODYNAMIC EFFECTS OF A REAR WING/SPOILER ON A PASSENGER VEHICLE BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MECHANICAL ENGINEERING Thesis Advisor Thesis Reader Chairman of Department Department of Mechanical Engineering December 2012 CFD STUDY ON AERODYNAMIC EFFECTS OF A REAR WING/SPOILER ON A PASSENGER VEHICLE By Mustafa Cakir MASTER THESIS Submitted in Partial Fulfillment of the Requirements For the Degree of Master of Science In Mechanical Engineering In the School of Engineering at Santa Clara University, December 2012 Santa Clara, California TABLE OF CONTENTS LIST OF FIGURES ......................................................................................................... iii LIST OF TABLES ............................................................................................................ v ABSTRACT ...................................................................................................................... vi 1 AUTOMOBILE AERODYNAMICS ........................................................................ 1 1.1 WHAT IS AERODYNAMICS? ....................................................................................... 1 1.2 SCOPE OF AERODYNAMICS ...................................................................................... 2 1.3 EXTERNAL FLOW PHENOMENA OF AUTOMOBILE .......................................... 3 1.4 FACTORS CONTRIBUTING TO FLOW FIELD AROUND VEHICLE ................. 5 1.4.1 BOUNDARY LAYER ................................................................................................ 5 1.4.2 FLOW SEPARATION ................................................................................................ 5 1.4.3 FRICTION DRAG ...................................................................................................... 7 1.4.4 PRESSURE DRAG ..................................................................................................... 7 1.5 FORCES AND MOMENT ON VEHICLE .................................................................... 8 2 CFD (COMPUTATIONAL FLUID DYNAMICS) ................................................ 10 2.1 WHAT IS CFD? .............................................................................................................. 10 2.2 ADVANTAGES OF COMPUTATIONAL FLUID DYNAMICS .............................. 12 2.3 NUMERICAL METHOD .............................................................................................. 13 2.3.1 PRE-PROCESSOR .................................................................................................... 14 2.3.2 NUMERICAL SOLVER ........................................................................................... 16 2.3.3 POST PROCESSOR .................................................................................................. 18 3 VEHICLE AND THE SPOILER ............................................................................ 18 3.1 INTRODUCTION TO SPOILER ................................................................................. 18 3.2 GENERIC MODELS ...................................................................................................... 19 3.2.1 VEHICLE GENERIC MODELS AND DIMENSIONS ........................................... 19 3.2.2 SPOILER GENERIC MODELS AND DIMENSIONS ............................................ 21 4 NUMERICAL SIMULATION ................................................................................ 22 4.1 CAD MODELS ................................................................................................................ 22 4.2 VIRTUAL WIND TUNNEL AND VEHICLE ORIENTATION ............................... 25 4.3 MESH GENERAION ..................................................................................................... 30 i 4.3.1 MESH SIZING AND INFLATION .......................................................................... 30 4.4 VALIDATION PROCEDURE ...................................................................................... 36 4.5 SOLVER SETTINGS ..................................................................................................... 37 5 SIMULATION RESULTS ....................................................................................... 40 5.1 SIMULATION RESULTS OF CASE #1, CASE #2 AND CASE #3 .......................... 40 5.2 SIMULATION RESULTS OF BENCHMARK #1, BENCHMARK #2 AND BENCHMARK #3 .................................................................................................................... 48 5.2.1 BENCMARK #1: EXAMINE GRID CONVERGENCE ......................................... 49 5.2.2 BENCMARK #2: EXAMINE GRID CONVERGENCE ......................................... 52 5.2.3 BENCMARK #3: EXAMINE MODEL UNCERTAINTIES ................................... 55 6 CONCLUSION ......................................................................................................... 58 7 FUTURE WORKS .................................................................................................... 60 LIST OF REFERENCE ................................................................................................. 61 ii LIST OF FIGURES Figure 1.1 Fuel energy usage at urban driving .............................................................. 2 Figure 1.2 Fuel energy usage at highway driving .......................................................... 3 Figure 1.3 Streamline of external flows around a stationary vehicle ........................... 4 Figure 1.4 Flow Separation at the rear of vehicle .......................................................... 6 Figure 1.5 Flow Separation at the rear of vehicle with rear spoiler ............................. 7 Figure 1.6 Forces On Vehicle Body ................................................................................. 8 Figure 2.1 The different disciplines contained within computational fluid dynamics [2] .............................................................................................................................. 11 Figure 2.2 The three basic approaches to solve problems in fluid dynamics and heat transfer. [2] .............................................................................................................. 12 Figure 2.3 The inter-connectivity functions of the three main elements within a CFD analysis framework. [2] .......................................................................................... 14 Figure 2.4 An overview of the solution procedure [2] ................................................. 17 Figure 3.1 Dimensions of the generic vehicle model [side-view] ................................. 20 Figure 3.2 Dimensions of the generic vehicle model [back-view] ............................... 20 Figure 3.3 Generic model and dimensions of first spoiler ........................................... 21 Figure 3.4 Generic model and dimensions of second spoiler ...................................... 22 Figure 4.1 Vehicle 3D CAD model ................................................................................. 23 Figure 4.2 First spoiler 3D CAD model ........................................................................ 23 Figure 4.3 Second spoiler 3D CAD model .................................................................... 24 Figure 4.4 Assembly 3D CAD model of vehicle and first spoiler ................................ 24 Figure 4.5 Assembly 3D CAD model of vehicle and second spoiler ........................... 25 Figure 4.6 Virtual wind tunnel and the vehicle orientation ........................................ 26 Figure 4.7 Virtual wind tunnel surface labeling for automatic appropriate boundary conditions. a) Velocity-inlet, b) Symmetry, c) symmetry-top, d) symmetry-side, e) pressure-outlet, f) wall ........................................................................................ 29 Figure 4.8 Mesh generation with standard settings. .................................................... 30 Figure 4.9 Mesh generation with modified sizing settings. ......................................... 31 Figure 4.10 Mesh generation