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

2.1.1 Drive Cycles

2.1.2 Types of Drive Cycles

2.1.3 Emission Test Cycles

2.1.4 Turbocharger Development History

2.1.5 Motivation of this Research

2.2 Turbocharger Compressor

2.2.1 Turbocharger Compressor Cycle

2.2.2 Types of Turbocharger Compressors

2.2.3 Compressor Performance Characteristics

2.2.4 Compressor Flow Phenomenon

2.2.5 Turbocharger Compressor Numerical Simulation

2.3 Turbocharger Compressor Diffuser

2.3.1 Diffuser Performance

2.3.2 Diffuser Geometry

2.4 Centrifugal Compressor Losses

2.5 Optimisation Methods

2.6 Optimisation Tools for CFD

2.6.1 Manual Optimisation and Scripting (MOS)

2.6.2 Design of Experiments (DoE)

2.6.3 Response Surfaces Results (RSR)

2.6.4 Goal Driven Optimisation

2.6.5 RBF-Morph

2.6.6 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

2.10.1 Shape Optimisation with the ANSYS Adjoint Solver

2.10.2 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

3.2.1 Continuity Equation

3.2.2 Momentum Equation:

3.2.3 Energy Equation

3.3 Ideal gas equation

3.4 Turbulence Models in Turbomachinery

3.4.1 k-ε Turbulence Model

3.4.2 K-Omega Turbulence Model

3.4.3 SST K-Omega turbulence model

3.4.4 Eddy-Viscosity Models

3.4.5 Large Eddy Simulations Navier-Stokes Equations

3.5 General Adjoint Solver Assumptions

3.6 Adjoint Method Equations

3.7 Combustion Engine Performance Model

3.7.1 Engine Geometry

3.7.2 Ideal Four-Stroke Process

3.7.3 Exhaust Stroke

3.7.4 Intake Stroke

3.7.5 Four-Stroke Otto Gas Cycle Analysis

3.8 CFD Uncertainty Analysis

3.8.1 Input Uncertainty

3.8.2 Physical Model Uncertainty

3.9 Engine Uncertainty Analysis

3.9.1 Measurement Uncertainties

3.9.2 Model Uncertainties

3.9.3 Uncertainty Analysis Inputs

3.9.4 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

6.6.1 Compressor and Diffuser Point 8

6.6.2 Compressor and Diffuser Point 10

6.6.3 Compressor and Diffuser Point 13

6.6.4 Compressor and Diffuser Point 23

6.6.5 Compressor and Diffuser Point 24

6.6.6 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

Research Objective and Scope

The primary objective of this dissertation is to devise a novel numerical optimisation technique for the diffuser geometry of standard turbocharger compressors, utilizing an adjoint-based, non-parametric approach. This research aims to enhance the power output and thermal efficiency of passenger car internal combustion engines when subjected to real-world driving cycles.

• Numerical simulation and validation of a turbocharger compressor stage.
• Application of the adjoint method for diffuser geometry shape optimisation.
• Analysis of compressor performance characteristics across various operating points (surge, central, and choke).
• Evaluation of the impact of optimised diffuser geometries on overall engine efficiency and performance.

Excerpt from the Book

Summary of Chapters

CHAPTER 1 INTRODUCTION: This chapter introduces the global necessity for improved turbocharger efficiency and defines the research aim, objectives, and questions.

CHAPTER 2 LITERATURE REVIEW: This chapter reviews fundamental literature on turbocharger compressors, drive cycles, existing numerical optimisation methods, and the theory of Adjoint Solver applications.

CHAPTER 3 RESEARCH METHODS AND STRATEGY: This chapter presents the quantitative research strategy, the governing equations for fluid dynamics (Navier-Stokes), turbulence models, and the numerical approach used for uncertainty analysis.

CHAPTER 4 NUMERICAL SETUP AND VALIDATION: This chapter details the initial geometric preparation, mesh generation, and validation of the numerical model against experimental data.

CHAPTER 5 NUMERICAL ANALYSIS: This chapter conducts a thorough analysis of mesh refinement effects to ensure solution independence and presents boundary conditions.

CHAPTER 6 ADJOINT METHOD OPTIMISATION: This chapter documents the application of the Adjoint Solver to optimise diffuser geometry and discusses the resulting efficiency improvements across various operating points.

CHAPTER 7 CONCLUSION: This chapter summarizes the research findings, contributions to the field of turbomachinery design, and provides recommendations for future investigations.

Keywords

Turbocharger compressor, CFD, k-omega SST turbulence model, Compressor performance, Efficiency, pressure-ratio, Optimisation, Adjoint solver, Power output engine, Thermal efficiency

Frequently Asked Questions

What is the core focus of this research?

The research focuses on the aerodynamic optimisation of turbocharger compressor diffuser geometry using a non-parametric adjoint method to improve efficiency and power for real-world driving cycles.

What are the primary thematic areas covered?

The work covers Computational Fluid Dynamics (CFD) simulation, turbulence modelling, diffuser geometry optimisation, and the analysis of engine performance impact in passenger vehicles.

What is the main research question?

The research asks what percentage improvement in compressor efficiency can be achieved via the adjoint method and whether these improvements remain consistent across different real-world driving conditions.

Which scientific methodology is employed?

The study employs a quantitative, deductive approach, utilising finite volume numerical methods for solving Navier-Stokes equations within a meshed fluid domain using ANSYS Fluent software.

What does the main body address?

The main body addresses the validation of baseline models through experimental comparison, followed by iterative shape optimisation using the Adjoint Solver and a subsequent engine performance impact analysis.

What are the characterizing keywords of the work?

Key terms include Turbocharger compressor, CFD, k-omega SST turbulence model, compressor performance, efficiency improvement, and adjoint shape optimisation.

How is the Adjoint Solver specifically applied to the diffuser design?

The Adjoint Solver is applied post-convergence of a traditional flow solution to calculate sensitivity derivatives, which then automatically guide mesh morphing iterations to achieve a more efficient diffuser shape.

What is the conclusion regarding engine efficiency impact?

The study concludes that the optimised diffuser geometry impacts overall performance by providing a measurable, consistent improvement in compressor stage efficiency, leading to a small but significant increase in engine power and thermal efficiency.