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Über dieses Buch

Aero and Vibroacoustics of Automotive Turbochargers is a topic involving aspects from the working fields of thermodynamics of turbomachinery, aerodynamics, rotordynamics, and noise propagation computation.

In this broadly interdisciplinary subject, thermodynamics of turbomachinery is used to design the turbocharger and to determine its operating conditions. Aerodynamics is needed to study the compressor flow dynamics and flow instabilities of rotating stall and surge, which can produce growling and whining-type noises. Rotordynamics is necessary to study rotor unbalance and self-excited oil-whirl instabilities, which lead to whistling and constant tone-type noises in rotating floating oil-film type bearings. For the special case of turbochargers using ball bearings, some high-order harmonic and wear noises also manifest in the rotor operating range. Lastly, noise propagation computation, based on Lighthill’s analogy, is required to investigate airborne noises produced by turbochargers in passenger vehicles.

The content of this book is intended for advanced undergraduates, graduates in mechanical engineering, research scientists and practicing engineers who want to better understand the interactions between these working fields and the resulting impact on the interesting topic of Aero and Vibroacoustics of Automotive Turbochargers.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction to Turbocharging

Abstract
Downsized engines, reducing the number of cylinders or volumetric size of cylinders, combined with the use of exhaust turbochargers, are being applied more and more in the automotive industry in order to comply with the recently enacted emission laws for CO2 and NOx reduction in automotive vehicles.
Hung Nguyen-Schäfer

Chapter 2. Induced Noise Types

Abstract
Noises induced in automotive turbochargers are normally classified into the following different types of noises.
Hung Nguyen-Schäfer

Chapter 3. Acoustic Propagation Theory

Abstract
Aerodynamic noise types such as pulsation, rotational, growling, and whining noise are generated from airflows in the compressor of turbocharger. Rotordynamic noises are noise types like unbalance whistle, constant tone, crackling noise, and high-order harmonic noise. The unbalance whistle is caused by rotor unbalance; the constant tone is induced by the inner oil whirl occurring in the oil-film radial bearings due to self-excitation instability. Additionally, the high-order harmonic noise and possible wear noise mostly occur in the rolling element bearings. Induced noise is transmitted through the bearing oil films, bearing center housing, compressor housing, air filter system, charge-air intercoolers, exhaust-gas manifold, exhaust-gas system (catalytic converter, particle diesel filter (DPF), and muffler), and car frame to the cabin, as shown in Fig. 3.1. The induced noise excites the bearing center housing and periphery components near the turbocharger, such as air filter, charge-air intercoolers, and exhaust-gas system of catalyzer, DPF, and muffler. The excited vibration responses emit airborne noise into the turbocharger’s environment. Such airborne noise is uncomfortable and undesirable for the vehicle occupants, and should be reduced as much as possible in passenger-type vehicles.
Hung Nguyen-Schäfer

Chapter 4. Analyzing Root Causes of Noise

Abstract
The induced noise types of automotive turbochargers in passenger vehicles have been already displayed in Chap.​ 2. Aerodynamic noise types, such as pulsation, rotational, growling, and whining noise, are generated from airflows in compressors of turbochargers by interactions between the fluid (charge air), solid surface (turbocharger), and fluid (ambient air) at their interfaces. Rotordynamic noise types like unbalance whistle, constant tone, high-order harmonic noise, and wear noise are created from rotordynamics of turbochargers by interactions between the fluid (oil), solid surface (turbocharger), and fluid (ambient air) at their interfaces.
Hung Nguyen-Schäfer

Chapter 5. Computational Nonlinear Rotordynamics of Turbochargers

Abstract
Figure 5.1 displays the rotor of an automotive turbocharger in the center housing and rotating assembly (CHRA) including the rotor shaft, compressor and turbine wheels, rotating floating ring bearings (RFRBs), seal rings, and thrust rings. All rotor components must be taken into account in the rotor dynamic computation to study the rotor vibration response, such as the frequency components in the Waterfall plot, rotor orbits in the phase plane, and response amplitudes in the time domain diagram.
Hung Nguyen-Schäfer

Chapter 6. Subsynchronous Constant Tone

Abstract
Constant tone is induced by the inner oil whirl in hydrodynamic radial bearings. The inner oil whirl frequency order in the rotating floating ring bearings reduces from 0.4X to about 0.3X at increasing rotor speeds, at which the inner oil film temperature increases, leading to reduced oil viscosity. Therefore, the inner oil whirl frequency varies in a narrow frequency band from 600 to 1,000 Hz of the human audible range. This frequency is usually considered in automotive turbochargers as quasi-constant compared to the rotor frequency; hence, its noise is called constant tone. The constant tone occurs at the engine speed range between 1,500 and 3,500 rpm in second to fifth gears with middle to high loads.
Hung Nguyen-Schäfer

Chapter 7. Eigenfrequency Modifications to Reduce Constant Tone Level

Abstract
Constant tone induced by the inner oil whirl is transmitted through the oil films and periphery components neighboring the turbocharger, such as bearing center housing, compressor housing, air filter, charge-air intercooler, exhaust-gas system, and car frame to the vehicle cabin.
Hung Nguyen-Schäfer

Backmatter

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