Analysis of noise radiation of a strongly pulsating tailpipe exhaust by the method of characteristics

The problem of propagation of a strongly pulsating flow in a tailpipe is discussedby the method of characteristics in this paper. For a strongly pulsating exhaust,flow maychock at the pipe open end at some part of a pulsating period,where the flow pressure exceeds its critical. In this case,one should set the Mach number there equal to 1 as the boundary condition, instead of flow pressure match condition. Moreover, the fluctuation of flowvariables may be much higher than their respective time averages. To treat with the problemwe simulate the exhaust flow out of the open end as a simple source,set its strength to beproportional to the volume acceleration of the flow and put the turbulence noise of the exhaust into consideraion. The results obtained are compared with our early experiment. Finally, we compute the pressure dependence of the noise at a given pipe length, and the pipelength dependence of the noise and mass flux at a given chamber pressure. The latter allowsone to choice a suitable length for a reciprocating internal combustion engine or an aerodynamic noise generator.