On Extraction Of Ic-Engine Intake Acoustic Source Data From Non-Linear Simulations

Abstract

Non linear 1-D CFD time domain prediction codes are used for calculation of performance of the gas exchange process for IC-engines. These codes give time varying pressures and velocities in the exhaust and intake system. They could therefore in principle be used to predict radiated orifice noise. The accuracy is however not sufficient for using them as a virtual design tool. Using linear three dimensional frequency domain codes, more accurate results might be provided for complicated geometries. Radiated shell noise and frequency dependent damping could also be included in the frequency domain models.  To calculate insertion loss of air-cleaner systems or the level of radiated intake orifice and shell noise, information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range for simulation of dominating engine harmonics is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where the multi-load methods and especially the two-load method are most commonly used. These tests are time consuming, expensive and require physical hardware and can therefore not be used for early predictions. It would therefore be of interest to extract the acoustic source data from existing 1-D CFD gas exchange codes. This paper presents a comparison between results obtained applying the two-load technique to measurements on a six-cylinder personal car petrol engine  and to 1-D simulations of identical intake systems on the same engine. The results show that it is possible to obtain reasonably accurate source strength as well as source impedance estimates for the intake side from 1-D gas exchange simulations.QC 20120124</p