Flow and Heat Transfer in a Turbocharger Radial Turbine Shyang
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Flow and heat transfer in a turbocharger radial turbine by Shyang Maw Lim December 2016 Technical Reports from Royal Institute of Technology KTH Mechanics SE-100 44 Stockholm, Sweden Akademisk avhandling som med tillst˚andav Kungliga Tekniska H¨ogskolan i Stockholm framl¨aggestill offentlig granskning f¨oravl¨aggandeav teknologie licenciatexamen torsdag den 19 januari 2017 kl 13:15 i sal Q2, Osquldasv¨ag10, Kungliga Tekniska H¨ogskolan, Stockholm. TRITA-MEK Technical report 2016:19 ISSN 0348-467X ISRN KTH/MEK/TR-16/19-SE ISBN 978-91-7729-238-8 c Shyang Maw Lim 2016 Universitetsservice US{AB, Stockholm 2016 Shyang Maw Lim 2016, Flow and heat transfer in a turbocharger radial turbine Competence Center for Gas Exchange (CCGEx) and Linn´eFlow Centre, KTH Mechanics, SE-100 44 Stockholm, Sweden. Abstract In the past decades, stricter legislation has been imposed to improve fuel econ- omy and to reduce tail-end emissions of automotive vehicles worldwide. One of the important and effective technologies adopted by the automobile manu- facturers to fulfill legislation requirements is the turbocharger technology. As unavoidable large temperature gradients exists in an automotive turbocharger, heat transfer is prominent. However, the effects of heat loss on the turbocharger turbine performance is unclear, i.e. there is no consensus about its effects among researchers. Therefore, the objective of the licentiate thesis is to inves- tigate the effects of heat transfer on an automotive turbocharger radial turbine performance. Furthermore, the thesis also aims to quantify the heat trans- fer related losses in a turbocharger turbine. Both gas stand (continuous flow) and engine-like (pulsating flow) conditions are considered. By using Detached Eddy Simulation (DES), the flow field of the targeted turbocharger turbine is computed under adiabatic and non-adiabatic conditions. Energy balance and exergy concept are then applied to the simulations data to study the effects of heat loss on performance and to quantify the heat transfer related losses. The main findings of the licentiate thesis are 1) Pressure ratio drop in turbine is less sensitive to heat loss as compared with turbine power, and hence there is a risk of making wrong conclusions about the heat transfer effects on the turbine performance by just comparing the measured pressure ratio under adiabatic and non-adiabatic scenarios; 2) It is possible to quantify heat transfer related losses in a turbocharger turbine. This quantification allows understanding on how well the turbine system utilizes the available energy, and assisting identifi- cation of the system component that is sensitive to heat transfer; 3) Heat loss has insignificant effect on turbine power under the investigated engine-like pul- sating flow condition; and 4) Even under unavoidable non-adiabatic conditions, much of the exergy is discharged to the environment and more effort could be done to recover the wasted exergy as useful work in the current turbine system. The outcomes of the licentiate thesis naturally lead to the main focus of future work, i.e. exploring different exhaust valve strategies to minimize losses and to optimize flow exergy extraction as useful turbine work for better exhaust gas exergy utilization. Descriptors: pulsatile exhaust flow, efficient radial turbine, turbocharger per- formance, Detached Eddy Simulation, level of integration with the Internal Combustion Engine, heat transfer effect iii Shyang Maw Lim 2016, Str¨omningoch v¨arme¨overf¨oringi en turbolad- dare med radialturbin Competence Center for Gas Exchange (CCGEx) and Linn´eFlow Centre , KTH Mekanik , SE - 100 44 Stockholm , Sverige. Sammanfattning Under de senaste decennierna har allt str¨angarelags- tiftning inf¨ortsf¨oratt f¨orb¨attrabr¨ansleekonomin och minska avgasutsl¨appen fr˚anmotorfordon v¨arlden¨over. En av de viktigaste och mest effektiva tekniker som inf¨ortsav biltillverkarna f¨oratt kunna uppfylla lagkraven ¨arturbolad- dartekniken. Eftersom stora temperaturgradienter existerar i en fordonsturbo- laddare, spelar v¨arme¨overf¨oringen framtr¨adanderoll. Emellertid ¨areffekterna av v¨armef¨orlusterp˚aturboturbinprestanda oklar, dvs det finns ingen konsen- sus bland forskare om dess effekter. Syftet med denna licentiatavhandling ¨ar d¨arf¨oratt unders¨oka effekterna av v¨arme¨overf¨oringp˚aprestanda f¨orradial- turbinen i en fordonsturboladdare. Vidare syftar avhandlingen till att kvan- tifiera v¨arme¨overf¨oringsrelateradef¨orlusteri en turboladdares turbin. B˚ade fall med kontinuerligt gas fl¨odeoch motorliknande, pulserande fl¨odebeak- tas. Str¨omningsf˚alteti den utvalda turboladdarens turbin ber¨aknasmed en metod kallad Detached Eddy Simulation (DES) under adiabatiska och icke adiabatiska f¨orh˚allanden.Energi- och exergibalanser f¨orsimuleringsresultaten analyseras sedan f¨oratt studera effekterna av v¨armef¨orlusterp˚aprestanda och kvantifiera v¨arme¨overf¨oringsrelateradef¨orluster. De viktigaste resultaten av licentiatuppsatsen ¨ar1) Tryckf¨orh˚allandet¨over turbinen ¨armindre k¨ansligtf¨or v¨armef¨orlusterj¨amf¨ortmed turbineffekten. D¨armedfinns det en risk f¨oratt felaktiga slutsatser dras betr¨affandeeffekterna av v¨arme¨overf¨oringp˚aturbin- prestanda genom att enbart j¨amf¨oradet uppm¨attatryckf¨orh˚allandetunder adiabatiska och icke adiabatiska f¨orh˚allanden;2) Det ¨arm¨ojligt att kvantifiera v¨arme¨overf¨oringsrelateradef¨orlusteri en turboladdares turbin. Denna kvan- tifiering ger f¨orst˚aelsef¨orhur v¨alturbinsystemet utnyttjar den tillg¨angliga energin, och bist˚armed identifiering av systemkomponenter som ¨ark¨ansliga f¨orv¨arme¨overf¨oring;3) V¨armef¨orlusterhar en obetydlig inverkan p˚aturbin- effekten f¨ordet unders¨oktamotorliknande, pulserande fl¨odesf¨orh˚allandet;och 4) Under oundvikliga, icke-adiabatiska f¨orh˚allanden, sl¨apps¨aven en stor del av exergin ut till omgivningen och det finns utrymme f¨orf¨orb¨attringarg¨allande exergiutnyttjandet i det aktuella turbinsystemet. Baserat p˚aresultaten av li- centiatavhandlingen kommer det fortsatta arbetet att fokusera p˚aatt utforska olika avgasventilstrategier f¨oratt minimera f¨orlusteroch optimera omvandling av fl¨odesexergitill anv¨andbartturbinarbete f¨orb¨attreavgasexergiutnyttjande. Deskriptorer: pulserande avgasfl¨ode,effektiv radialturbin, turboaggregatpre- standa, Detached Eddy Simulation, integrationsniv˚amed f¨orbr¨anningsmotorn, v¨arme¨overf¨oringseffekt iv Preface This licentiate thesis represents an effort to improve the understanding of heat transfer and heat transfer related losses of a turbocharger turbine. The the- sis is a monograph, which consists of a total of seven chapters. Chapter One briefly describes the needs and working principle of turbocharging and defines the research scopes and objectives of the thesis. Chapter Two discusses the implications of heat transfer on turbine performance, reviews current state-of- the-arts and defines the performance metrics used in describing the turbine performance. Descriptions about turbulence models and numerical methods used in this study are summarized in Chapter Three and Four, respectively. In Chapter Five, validation and verification of the computational setup is ad- dressed. Chapter Six reports the main results of the thesis, in which the effects of heat transfer on turbine performance under hot gas stand (continuous flow) and engine-like (pulsating flow) conditions are discussed. Proposed future work can be found in the last chapter of the thesis, i.e. Chapter Seven. I would appre- tiate comments and suggestions from both academia and industry to enhance the study analysis, to deepen the interpretation of the results, and to improve the readability of the thesis. Thank you and I hope that you enjoy reading the thesis. December 2016, Stockholm Shyang Maw Lim v Quality is much better than quantity. One home run is much better than doubles. Steve Jobs (1955{2011) vi Contents Abstract iii Preface v Chapter 1. Introduction 1 1.1. Global standards on fuel economy and emissions 1 1.2. Supercharging and turbocharging 2 1.3. Heat transfer in turbochargers 8 1.4. General effects on performance 10 1.5. Research scopes and objectives 12 Chapter 2. Turbine and turbine performance metrics 15 2.1. Heat transfer implications on turbocharging 15 2.2. Modeling of heat transfer 17 2.3. Turbocharger performance and assessment 20 2.4. Turbine power and torque 26 2.5. Heat transfer rate 27 2.6. Exergy analysis 27 2.7. Bejan number 29 Chapter 3. Turbine flow modeling 30 3.1. Compressible flow governing equations 30 3.2. Reynolds Averaged Navier-Stokes (RANS) modeling 32 3.3. Large Eddy Simulation (LES) modeling 35 3.4. Detached Eddy Simulation (DES) modeling 37 Chapter 4. Numerical methods 39 4.1. Discretization 39 4.2. Boundary conditions 41 vii Chapter 5. Method of validation and verification 44 5.1. Computational domain and grid 44 5.2. Boundary conditions 45 5.3. Methodology 46 5.4. Grid convergence study 47 5.5. Influence of turbine wheel rotation per time-step 54 5.6. Stationary-rotating interface type sensitivity 55 5.7. Influence of turbulence model 64 Chapter 6. Heat transfer effects on the turbine performance 70 6.1. Turbine assessment under continuous flow conditions 70 6.2. Exhaust manifolds and pulsating flow effects 74 Chapter 7. Summary and future work 82 Acknowledgements 84 References 86 viii CHAPTER 1 Introduction Turbocharging has been proposed and invented more than 100 years ago by Alfred B¨uchi in 1905, but extensive development and application of the tech- nology in automotive vehicles have only been started about 30 years ago (see e.g. Ninkovi´c2014;