Aerodynamic Optimisation of Turbocharger Compressor Diffuser Geometry for Real-World Drive Cycles

Table of Contents

• Chapter 1 Introduction
• 1.1 Rationale
• 1.2 Aim and Objectives
• 1.3 Research Methodology and Impact
• 1.4 Thesis Structure
• Chapter 2 Literature Review
• 2.1 Research Background
• Drive Cycles
• Types of Drive Cycles
• Emission Test Cycles
• Turbocharger Development History
• Motivation of this Research
• 2.2 Turbocharger Compressor
• Turbocharger Compressor Cycle
• Types of Turbocharger Compressors
• Compressor Performance Characteristics
• Compressor Flow Phenomenon
• Turbocharger Compressor Numerical Simulation
• 2.3 Turbocharger Compressor Diffuser
• Diffuser Performance
• Diffuser Geometry
• 2.4 Centrifugal Compressor Losses
• 2.5 Optimisation Methods
• 2.6 Optimisation Tools for CFD
• Manual Optimisation and Scripting (MOS)
• Design of Experiments (DoE)
• Response Surfaces Results (RSR)
• Goal Driven Optimisation
• RBF‐Morph
• Adjoint Solution
• 2.7 Adjoint Shape Optimisation
• 2.8 Adjoint Method Theory
• 2.9 Adjoint Solver Discrete Versus Continuous
• 2.10 High‐Fidelity CFD‐Based Shape Optimisation
• Shape Optimisation with the ANSYS Adjoint Solver
• High‐fidelity Gradient‐Based Aerodynamic Design Optimisation
• 2.11 OFF‐Design Performance Prediction
• Chapter 3 Research Methods and Strategy
• 3.1 Overall Strategy
• 3.2 Reynolds Averaged Navier‐Stokes equations
• Continuity Equation
• Momentum Equation:
• Energy Equation
• 3.3 Ideal gas equation
• 3.4 Turbulence Models in Turbomachinery
• k‐ε Turbulence Model
• K‐Omega Turbulence Model
• SST K‐Omega turbulence model
• Eddy‐Viscosity Models
• Large Eddy Simulations Navier‐Stokes Equations
• 3.5 General Adjoint Solver Assumptions
• 3.6 Adjoint Method Equations
• 3.7 Combustion Engine Performance Model
• Engine Geometry
• Ideal Four‐Stroke Process
• Exhaust Stroke
• Intake Stroke
• Four‐Stroke Otto Gas Cycle Analysis
• 3.8 CFD Uncertainty Analysis
• Input Uncertainty
• Physical Model Uncertainty
• 3.9 Engine Uncertainty Analysis
• Measurement Uncertainties
• Model Uncertainties
• Uncertainty Analysis Inputs
• Crank Angle and RPM uncertainty
• Chapter 4 Numerical Setup and Validation
• 4.1 Geometry Preparation
• 4.2 Meshing Quality
• 4.3 Numerical Setting
• 4.4 Numerical Model Validation
• Chapter 5 Numerical Analysis
• 5.1 Mesh Refinement
• 5.2 Boundary Conditions and Numerical Results
• 5.3 Predicted Result and Discussion
• Chapter 6 Adjoint Method Optimisation
• 6.1 Baseline Geometry Optimisation
• 6.2 Mesh Refinement Cases Point 24
• 6.3 Baseline Settings and Results Mesh Independency Discussion
• 6.4 Adjoint Solver Settings
• 6.5 Adjoint and Baseline Results Discussion
• 6.6 Post‐Processing Analysis
• Compressor and Diffuser Point 8
• Compressor and Diffuser Point 10
• Compressor and Diffuser Point 13
• Compressor and Diffuser Point 23
• Compressor and Diffuser Point 24
• Compressor and Diffuser Point 27
• 6.7 Optimised Diffuser Proposal for Real‐World Cycle
• 6.8 Engine Performance Impact
• Chapter 7 Conclusion
• 7.1 Summary and Conclusion
• 7.2 Contribution to Knowledge
• 7.3 Recommendations

Objectives and Key Themes

This dissertation aims to develop a novel numerical optimisation technique for the diffuser geometry of a typical turbocharger compressor using a non-parametric optimisation method (adjoint). The goal is to increase power output and improve thermal efficiency in real-world drive cycles for passenger car engines.

• The dissertation investigates the aerodynamic optimisation of turbocharger compressor diffuser geometry for real-world drive cycles.
• It explores the use of a non-parametric optimisation method (adjoint) to improve the efficiency of the turbocharger compressor diffuser.
• It focuses on the impact of the optimised diffuser geometry on engine performance, including power output and thermal efficiency.
• The study considers the practical aspects of implementing the optimised diffuser geometry, including manufacturing adaptability using 3D printing.
• It aims to contribute to the advancement of turbocharger technology and its role in reducing emissions and improving fuel efficiency.

Chapter Summaries

Chapter 1 provides an introduction to the research, outlining the rationale, aim, objectives, and methodology. It also presents the structure of the dissertation.

Chapter 2 delves into the literature review, exploring the research background, turbocharger compressors, diffuser performance, centrifugal compressor losses, and optimisation methods. It focuses on the adjoint method and its application in CFD-based shape optimisation.

Chapter 3 introduces the research methods and strategy, outlining the governing equations, turbulence models, and uncertainty analysis. It also presents the combustion engine performance model used for the study.

Chapter 4 details the numerical setup and validation, including geometry preparation, meshing quality, numerical settings, and the validation of the numerical model against experimental data.

Chapter 5 focuses on the numerical analysis, exploring mesh refinement, boundary conditions, and the discussion of predicted results.

Chapter 6 presents the optimisation of the turbocharger diffuser geometry using the adjoint method, including the optimisation process, results discussion, and post-processing analysis. It also proposes a new optimised diffuser geometry for real-world driving cycles and examines its impact on engine performance.

Chapter 7 concludes the research, summarizing the findings, contributions to knowledge, and recommendations for future work.

Keywords

This dissertation explores the optimization of turbocharger compressor diffuser geometry using CFD simulations and the adjoint method. Key topics and concepts investigated include: turbocharger compressor performance, efficiency, pressure ratio, optimisation, adjoint solver, power output, and thermal efficiency. The study focuses on real-world drive cycles, considering practical manufacturing considerations and aiming to contribute to the development of more efficient and environmentally friendly engines for passenger cars.