UNIVERSITÀ DEGLI STUDI DI PARMA DIPARTIMENTO DI INGEGNERIA INDUSTRIALE Corso di Laurea Magistrale in Ingegneria Meccanica THREE DIMENSIONAL CFD SIMULATION OF A TURBOCHARGER TURBINE FOR MOTORSPORT APPLICATIONS SVILUPPO DI UN MODELLO DI SIMULAZIONE 3D CON UN CODICE DI CALCOLO CFD DI UNA TURBINA PER SOVRALIMENTAZIONE DESTINATA AD APPLICAZIONI MOTORSPORT Company Advisor: Academic Advisor: Ing. M. CHIODI (FKFS Stuttgart) Prof. Ing. A. GAMBAROTTA Ing. P. ROBERTI (FKFS Stuttgart) Candidate: CRISTIAN CAPILUPPI Anno Accademico 2011-2012 Index 1 Introduction ......................................................................................................................... 1 2 CFD tools: brief outlines ..................................................................................................... 2 3 Turbocharging fundamentals .............................................................................................. 5 3.1 Why turbocharging .......................................................................................................... 5 3.2 Supercharging technology and strategies ........................................................................ 6 3.2.1 Mechanical supercharger versus turbocharger .................................................................. 6 3.2.2 Layouts: the twincharger ................................................................................................... 10 3.2.3 Layouts: two stages twin turbocharger ............................................................................. 12 3.2.4 Layouts: the hybrid turbocharger...................................................................................... 14 3.3 Characteristics ............................................................................................................... 15 3.3.1 The turbine map ................................................................................................................ 15 4 Model description ............................................................................................................. 17 4.1 Geometry design ........................................................................................................... 17 4.1.1 Tomography results ........................................................................................................... 19 4.1.2 Previous CAD resetting ...................................................................................................... 21 4.2 Mesh design ................................................................................................................... 23 4.2.1 Preparing the surface ........................................................................................................ 23 4.2.2 Surface mesh setting ......................................................................................................... 24 4.2.3 Creating the volume mesh ................................................................................................ 28 4.3 The regions layout ......................................................................................................... 31 4.3.1 Interfaces creation between the parts .............................................................................. 32 4.3.2 Regions .............................................................................................................................. 33 4.3.3 Rotating motion specification ........................................................................................... 35 4.3.3.1 MRF Approach ............................................................................................................... 35 4.3.3.2 RBM Approach ............................................................................................................... 38 4.4 The boundaries definition .............................................................................................. 40 4.4.1 Mass flow inlet boundary .................................................................................................. 40 4.4.2 Pressure inlet boundary .................................................................................................... 43 4.5 Boundary and initial fluid conditions ............................................................................ 44 4.5.1 The GT-Power working point ............................................................................................. 44 I 4.5.2 The fluid initial conditions ................................................................................................. 46 4.6 Physics definition .......................................................................................................... 47 4.6.1 Gas model .......................................................................................................................... 48 4.6.2 The continuum fluid domain ............................................................................................. 50 5 Simulations results ............................................................................................................ 54 5.1 Mesh size influence ....................................................................................................... 55 5.2 Inlet boundary type influence ........................................................................................ 57 5.3 Inlet geometry influence ................................................................................................ 59 5.4 Pressure and Temperature gradients through the blades ............................................... 61 5.5 Gas composition influence ............................................................................................ 65 5.6 Virtual test bench .......................................................................................................... 68 5.6.1 Outlet duct flow analysis ................................................................................................... 68 5.6.2 Building the turbine characteristic .................................................................................... 75 5.6.3 Choking mass flow rate refinement .................................................................................. 84 5.6.4 Ultimate turbine characteristic ......................................................................................... 86 5.7 Time calculation of the flow crossing the blades .......................................................... 93 6 Industrial CT analysis ....................................................................................................... 98 6.1 Technological signs ....................................................................................................... 98 7 Conclusions ..................................................................................................................... 100 8 References ....................................................................................................................... 102 9 Symbols and Abbreviations ............................................................................................ 103 II Introduction 1 Introduction This master thesis work has been conducted at the research institute for automotive engineering and engine technology Stuttgart (FKFS), with the virtual engine development team. Its main purpose is to give the customers of projects and advanced analysis solutions, through 3D-CFD tools. Nowadays, the computational fluid dynamic applied to the optimisation of engines have arose a leading role in the thermal design of powertrain systems, to compare different layout solutions with reduced prototyping costs. These kinds of simulations are in facts very required, since they can interact with the testing and prototyping steps and sustain them. To complete the versatility of these tools, the 3D-CFD codes can interact with other simulation approaches. For example, it’s possible to set a complex and detailed three dimensional flow simulation with quite reliable data resulting from a real time or 1D-CFD analysis. These last mentioned models are for sure more flexible in time calculation, but they only provide signals or the mean values of thermal parameters in one spatial coordinate of the system volume. This work aim was to insert in this scenario the basis for the three dimensional fluid dynamic simulation of a turbocharger for motorsport application, starting from the turbine component. Several steps in building the model are normally required, nevertheless bringing to its most reliable behaviour aligned to the calibration values. The work abstracts are exposed along the following chapters in a structured and methodical way, towards the most understanding and precise improvement explanation, as well as inspire further development steps. 1 CFD tools: brief outlines 2 CFD tools: brief outlines Computational fluid dynamics, usually abbreviated as ‘CFD’, defines a branch of fluid mechanics that uses numerical methods and algorithms to predict physical fluid flows and heat transfer. Nowadays, the on-going research yields software achieving the accuracy and speed of complex simulation scenarios (turbulent and unsteady flows): hence, CFD tools can be used to calculate design mass-flow rates, pressure drops, heat transfer fluxes and fluid dynamic forces. Once the fluid and its thermodynamic working properties are defined, CFD software can simulate the interaction of liquids and gases with surfaces defined by boundary conditions: