Unsteady Characteristics of Shock Waves in the Variable Nozzle Turbine of a Turbocharger

Variable nozzle turbine can enhance the transient response of engine through the regulation of nozzle opening. Under the operating condition characterized by high expansion ratio and small nozzle opening, strong unsteady shock waves tend to develop at the trailing edge of the nozzle blades. These shock waves introduce significant periodic loadings, which can result in high-cycle fatigue and eventual fracture of the rotor blades. This study investigates the unsteady flow characteristics within a representative variable nozzle turbine, with particular focus on the temporal and spatial evolutions of shock waves and their dynamic coupling with the rotor-stator system. It is found that both the intensity and the spatial structure of the shock waves exhibit periodic variation in response to rotor-induced disturbances. The pressure disturbance with a frequency of 10 kHz induces significant blade loading at 50% span of the rotor blade leading edge, whose maximum root mean square (RMS) amplitude is 17.45 kPa. It substantially increases the probability of high-cycle fatigue for the rotor blade leading edge. These findings can offer meaningful guidance for optimizing and controlling shock waves in variable nozzle turbines.