Analysis on variable nozzle turbine performance influenced by multiple factors under pulsating flow conditions

To improve the matching between the turbine and engine, computational fluid dynamics (CFD) methods were adopted to investigate the unsteady performance of variable nozzle turbine influenced by pulsating flow frequency, pulsating flow amplitude, nozzle vane angle and turbine rotating speed. Results show that the turbine instantaneous minimum mass flow rate under 80 Hz condition is 10.4% higher than that under 40 Hz condition, and the lowest efficiency increases by 4.7%. At high pulsating frequency, the unsteady efficiency apparently lags behind velocity ratio. Under pulsating amplitude of 25 kPa condition, the swallow capacity and efficiency recover rapidly, indicating that it is possible to design turbines by steady flow hypothesis under low amplitude conditon. For nozzle angle of 32 degree, the mass flow difference between pulsating inlet flow condition and steady inlet flow condition is 3.3% more than that of 10 degree, and the efficiency difference is 6.6% more. Higher nozzle angle makes turbine flow field more pulsative and results in mass flow rate and efficiency dropping significantly. Under turbine rotating speed of 47 256 r/min condition, the mass flow rate and efficiency variation caused by pulsating inlet flow is 2.9% and 0.8% more compared to that of 30 000 r/min. The turbine flow field is more sensitive to turbine inlet condition when rotating speed is high, and the mass flow rate, efficiency and attacking angle deviate from equivalent steady values.