SOUND PROPAGATION IN NARROW CHANNELS WITH ARBITRARY CROSS SECTIONS AND SUPERIMPOSED MEAN FLOW WITH APPLICATION TO CHARGE AIR COOLERS

摘要

Charge air coolers are used on turbo charged IC-engines to enhance the overall gas exchange performance. The cooling of the charged air results in higher density and thus volumetric efficiency. Important for petrol engines is also that the knock margin increases with reduced charge air temperature. A property that is still not very well investigated is the sound transmission through a charge air cooler. The pressure drop in the narrow cooling tubes results in frequency dependent resistive effects on the transmitted sound that is non negligible. As the cross sections of the cooling tubes are neither circular nor rectangular, no analytical solution accounting for a superimposed mean flow exists. The cross dimensions of the connecting tanks, located on each side of the cooling tubes, are large compared to the wavelength for engine breathing noise, here including frequencies up 1.5 kHz, so three dimensional effects are important. In this study an acoustic two-port for sound propagation in narrow tubes, including the effect of viscous and thermal boundary layers, is calculated utilizing a 2D finite element solution scheme. Analytical solutions for circular cross sections are additionally calculated for comparison. The two-port is thereafter combined with 3D acoustic finite element modelling to represent the transmission properties of the charged air when passing the complete air-to-air charge air cooler. From this a linear frequency domain model for the entire charge air cooler is extracted in the form of a two-port. The frequency dependent transmission loss is calculated and compared with corresponding experimental data. Finally, there is a discussion of the results and the potential of using charge air coolers to control the acoustic response of intake systems.