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About this book

This thesis offers new insights into the fluid flow behavior of automotive centrifugal compressors operating under near-stall conditions. Firstly it discusses the validation of three-dimensional computational fluid dynamics (CFD) unsteady simulations against acoustic experimental measurements using an original procedure based on plane wave pressure decomposition. It then examines the configuration of the CFD cases, highlighting the key parameters needed for a successful calculation. Moreover, it describes both the compressor mean and unsteady flow field from best-efficiency to near-surge operating points. Lastly, it provides readers with explanations of the various phenomena that arise when the mass flow rate is reduced and the compressor is driven to poor and noisy performance. Written for students, researchers and professionals who want to improve their understanding of the complex fluid flow behavior in centrifugal compressors, the thesis offers valuable practical insights into reducing the acoustic emissions of turbochargers.

Table of Contents

Frontmatter

Chapter 1. Introduction

The use of turbocharging is almost as old as the internal combustion engine itself. Büchi introduced in the first decade of the twentieth century this technology, increasing the rated power of engines through the density rise obtained by a turbocompressor. Turbochargers were first and progressively introduced in aeronautical reciprocating engines, which suffered from a decline in power due to the decrease of the air density when an aircraft would fly at high altitude. Turbocharging was a way to overcome this limitation. Turbocharging was then adopted by large displacement Diesel engines as those used in marine propulsion, locomotives or stationary powerplants. The pairing of Diesel engines and turbocharging technology has been a successful story since then, given that the increase of intake pressure and temperature that the supercharger provides improves the conditions for the development of Diesel combustion. This lead to an increase, not only in power, but also in thermal efficiency.

Roberto Navarro García

Chapter 2. Methodology for Experimental Validation

This book is devoted to the CFD analysis of flow-induced acoustics of turbocharger compressors, as described in Chap. 1. Since this topic has not been covered by many researchers, experimental measurements are used to assess the ability of these simulations to capture compressor noise generation. In this way, the turbocharger test rig should be modeled and experimental probes should be replicated in CFD. However, the existence of long ducts in the rig greatly increases the computational effort [1].

Roberto Navarro García

Chapter 3. Influence of Tip Clearance on Flow Behavior and Noise Generation

In Chap. 2, a CFD model of the centrifugal compressor has been described, which is strongly influenced by the paper of Mendonça et al. [3]. A methodology to compare experimental and numerical spectra has been also developed, showing that the CFD model predicts noise features in agreement with those found in the experiments, for a working point at peak pressure ratio (mass flow rate of 77 g/s at 160 krpm).

Roberto Navarro García

Chapter 4. Sensitivity of Compressor Noise Prediction to Numerical Setup

So far, a CFD model of a centrifugal compressor has been implemented in Star-CCM+ [1], taking as a reference the setup used by Mendonça et al. [2].

Roberto Navarro García

Chapter 5. Compressor Mean Flow Field at Near-Stall Conditions

In Chap. 4 the different setup possibilities have been explored, defining an ultimate numerical configuration that shall be used to study aeroacoustic phenomena at three different working points. However, it seems appropriate to first described mean flow behavior at the studied operating conditions, which range from best efficiency point (BEP) to near surge conditions at 160 krpm (the surge side of this isospeed). To do so, time-averaged values of fluid variables will be displayed in the different regions of the compressor in this chapter. Section A.3.2 explains the approach followed to perform the time-averaging and Sect. A.2 describes the postprocessing surfaces that are used throughout this chapter.

Roberto Navarro García

Chapter 6. Compressor Aerocoustics at Near-Stall Conditions

As stated in Chap. 1, the aim of this book is to contribute to the understanding of turbocharger compressor flow-induced acoustics, particularly regarding whoosh noise phenomenon. To do so, a methodology to compare numerical and experimental spectra has been developed in Chap. 2, which has been used as a tool to evaluate the sensitivity of the noise predicted by the model to parameters such as tip clearance, grid spacing, time-step size, etc. In Chap. 5, using the validated configuration, the main features of the time-averaged flow at three operating conditions have been described.

Roberto Navarro García

Chapter 7. Concluding Remarks

In this chapter, a critical review of the book is performed. Main findings and contributions of this work are included in Sect. 7.2. Section 7.3 is devoted to the enumeration of limitations of the model and the approach followed in this book, which could affect the validity of the aforementioned findings.

Roberto Navarro García

Backmatter

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