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. Open image in new window Fig. 3.1 Transmitting ways of airborne noise