Abstract: The pulsating exhaust in turbocompound technology significantly exerts effects on the performance of the two-stage turbine. The effects of exhaust pulse frequency and amplitude were investigated to reveal the unsteady characteristic of the two-stage turbine under pulsating flow conditions on the base of a threedimensional unsteady flow simulation model. In the model, the flows in the high-pressure turbine were modeled using full stage passage, which could consider the asymmetric flows caused by the volute. The flows in the lowpressure turbine were modelled using single passage to improve the calculation efficiency. The results show that as the frequency increases from 40 to 120 Hz, the peak instantaneous power of high-pressure stage turbine increases significantly by 15.4%, while the peak instantaneous power of low-pressure stage turbine changes within 1%. With the increase of pulse amplitude, the efficiency of low-pressure stage turbine decreases more greatly than that of high-pressure stage turbine. When the coefficient of the pulse amplitude is 1.6, the rotor efficiencies of the high- and low-pressure stage drop down 3.66% and 8.09%, respectively. The incidence angle of low-pressure turbine rotor from the middle to the tip of the blade varies significantly during the pulse period, resulting in significant flow loss at the leading edge of the blade.

Key words: internal combustion engine ,  turbomachinery , two-stage turbine ,  pulsating flow ,  unsteady characteristic , flow mechanism