Design And Performance Analysis Of Three Dimensional Twisted Blade For Variable Nozzle Mixed-flow Turbocharger

Turbocharging technology has become a major technology to promote the efficiency of an internal combustion engine nowadays,which can effectively uprate an internal combustion engine,raise output per litre,reduce fuel consumption and improve the quality of exhaust emissions.As the hotspot of turbocharging,mixed flow turbine keeps high efficiency under high speed ratio and the point of peak efficiency appears under lower speed ratio compared to traditional radial flow turbine.Relevant research shows that the application of variable nozzle ring and altering traditional two dimensional arrangement to spherical nozzle ring can efficiently improve turbine performance and flow behavior inside turbine stage.In this article,to match variable nozzle ring mixed-flow turbine and raise stage efficiency by improving flow loss and spanwise distribution of outlet flow,three different kinds of 3-D twisted vanes for spherical nozzle ring are designed based on JK50 nozzle vane and 3-D twisted vane theory,taking into account nonuniformity of spanwise outlet air flow angle and the effect of inlet inclination of mixed flow turbine.The calculation result indicates that the efficiency of 3-D twisted vanes designed is higher in comparison with original vane under the same operating status and the efficiency curve is also flatter in large opening region.According to the analysis of inlet velocity triangle of rotor,Mach number and static pressure distribution in flow passage of nozzle ring,clearance flow,outlet pitot loss and entropy distribution,downstream entropy and wake loss of rotor,etc.,it is found that the change in pressure field distribution due to 3-D twisted vane can visibly reduce passage vortex and clearance vortex loss and improve inlet attacking angle distribution of rotor along spanwise direction.Meanwhile,the application of backward-inclined design with uniform spanwise profile decreases the opening from vane tip to vane root gradually and shrinks the flow area as well,therefore,at the same vane root opening the flow rate of 3-D twisted vane is smaller than original,which will adversely affects the flow capacity.Since the nozzle ring vane does not perfectly match the downstream rotor due to arc stacking line,downstream flow loss near the hub will relatively increase and the efficiency promotion because of loss reduction will become less obvious.