Dept. of Mech. Eng. and Appl. Mech., Univ. of Michigan, Ann Arbor, MI 48109-2125
An extensive amount of literature is available on the performance of automotive silencers subject to linear acoustic disturbances and no-mean or steady-mean flow conditions. The flow through the automotive exhaust system exhibits, however, a number of nonlinear phenomena including high sound pressure levels reaching 180 dB and varying mean flow, as well as spatially and temporally changing temperatures. These nonlinearities are difficult to treat with the linearized acoustic theory approach in the frequency domain. The present study provides experimental results as well as numerical predictions for a production vehicle full exhaust system (Ford 1.9L Escort engine) and investigates the nonlinearities. The study implements a time-domain finite-difference approach to predict the acoustic performance based on the work of Chapman et al. [Winter Annual Meeting of ASME (1982)], which solves the one-dimensional, variable cross-sectional area, nonlinear balance equations of mass, momentum, and internal energy coupled with the equation of state for compressible flows. Nonlinearities are discussed in view of the experimental data and by comparing the terms of the momentum balance from computational results.