The measurement and prediction of sound waves of arbitrary amplitude in practical flow ducts

A study is presented that explores the influence of the peak to mean pressure ratio on the wave action occurring in highly acoustically reactive ducts with significant flow present. Particular practical applications concern predictions of orifice noise emissions from piston engine or compressor intake and exhaust systems, with the effect of acoustic resonances on both excitation and acoustic power transmission. The results indicate that any practical differences between linear and non-linear predictions remain negligibly small when the pressure ratio remains below 1.1, corresponding to 170 dB spl, provided that the influence of all frequency-dependent physical features is included. Above this level of excitation in any lengths of uniform pipe connecting other system components, some new observations demonstrate the extent to which compression wave steepening may be of practical significance in the spectral distribution of the power propagated.