The aim of the dissertation is to develop a new numerical optimisation technique for the diffuser geometry of a typical turbocharger compressor, using a non-parametric optimisation method (adjoint). This leads to an increase in power and thermal efficiency in real-world drive cycles for passenger car engines.
The geometry and experimental data correspond to the TD025-05T4 compressor from the 1.2-liter Renault Megane passenger car supplied by MTEE. In this study, a set of numerical simulations were conducted along two turbocharger compressor speed lines at 150,000 rpm and 80,000 rpm to analyse and validate the results against experimental data. Three points on each speed line are selected: one point each in regions close to surge and choke and a point in the stable zone of the compressor map.
In addition, this study optimises the diffuser geometry in a passenger vehicle turbocharger compressor using a gradient-based solution approach employing a non-parametrical adjoint shaping optimisation for ideal gas turbulent compressible flow applications. The adjoint solver is a gradient-based optimisation that can automatically generate a series of iterations of a design so that the mesh gradually changes shape to meet a single goal, like the efficiency of the compressor in this case.
The study considers a total of six operating cases on the compressor map to optimise the full and partial load compressor operations, leading to a real-world drive cycle. These cases are the three cases (closer to surge, stable midpoint, and closer to the choke point) on each of the speed lines. A typical result for mid-stable operation on a 150,000 (rpm) speed line shows a gradual increase in efficiency up to a maximum of 2.6% improvement.
While, for choke and surge optimisation, the geometry variation of the optimised diffuser is different, in the stable central area for both speed lines, the geometry change is consistent. Therefore, the diffuser can be made to work best for both half and full load engine operation.
As a result, the optimum diffuser geometry impacts engine efficiency and the overall performance of a typical passenger car for real drive cycles, increasing power and slightly improving thermal efficiency. When a typical car engine is running at full and half-load in real-world operation, the improved compressor efficiency is expected to make a small difference. This will make the engine more powerful and more efficient by about 0.1%.
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
Compressor Flow Phenomenon
Compressor flow behaviour is very complicated, viscous, highly unsteady and transitional. Several flow patterns co-exist, some of them interact with each other. Strong interactions exist in small-sized compressors. Only some of the important flow behaviours will be introduced here, such as the leading-edge vortex, laminar separation bubble, tip leakage flow and others. Looking deep into any single flow phenomenon would take a lot of effort. A comprehensive description is out of the scope of the current work. Therefore, an introductory description is given in this section.
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.
- Quote paper
- Dr Kristaq Hazizi (Author), 2022, Aerodynamic Optimisation of Turbocharger Compressor Diffuser Geometry for Real-World Drive Cycles, Munich, GRIN Verlag, https://www.grin.com/document/1290023
