Sound radiation of the exhaust gas turbocharger as a function of the compressor inflow

摘要

The use of exhaust gas turbochargers in modern engine concepts is essential to achieve high efficiencies, low fuel consumption, and low emissions. However, the high rotational speed, a wide range of compression ratios, and dynamic acceleration and deceleration processes cause both tonal and broadband sound radiation. Due to packaging constraints, the intake cycle is often characterized by deflections and cross-section jumps. That leads to a strong secondary flow at the inflow of the compressor. Therefore, in this study, we intensively investigated the influence of disturbed inflow conditions on the sound radiation of the exhaust gas turbocharger. As a result, we found that the flow caused by a 105 degrees-bend in front of the compressor leads to an increase in broadband flow noise up to 5.5dB(A). The decisive factor here is the amount of pre-whirl at the outer radius of the pipe. A high velocity gradient additionally shifts the surge line towards lower flow coefficients and mass flows, respectively. That indirectly reduces the sound radiation due to the greater distance of the operating points to the surge line. However, pre-whirl can counteract this effect. The surge line shifts to larger mass flows due to the decrease of the relative flow angle. In contrast, low turbulence levels and homogeneous compressor inflow lead to reduced flow separation and thus lower broadband sound radiation. The reduction of the secondary flow in the intake of the compressor, e.g. due to pre-guidance devices, therefore represents a promising way of reducing the noise emission of the exhaust gas turbocharger in a passenger car. (C) 2021 Elsevier Ltd. All rights reserved.