| Turbocharging technology can improve the fuel economy of engine and reduce pollutant emissions of cars,which is the main technology to optimize the piston-type internal combustion engine.At present,research on adjustable nozzle mixed-flow turbo is a heated discussion topic in the turbo technology area.Mixed flow turbo has two advantages.One is that due to the blade inlet of mixed-flow tilted,which can increase the flow of the turbo inlet area,the flow capacity is enhanced greatly and thus enhance the work capacity of the turbo.Another is that the turbo can get higher efficiency at high rotation speed.The turbo with the adjustable nozzle ring can easily keep turbo stage at the same pressure ratio in different gas mass flow even in small gas mass flow.Most of researchers have stated that comparing to place the nozzle ring blades vertically in the meridional plane,the efficiency of the turbo stage is higher by placing the nozzle ring blades obliquely along the inlet direction of the mixed-flow turbine.In order to reduce the flow loss of the adjustable nozzle ring and improve the efficiency of the adjustable mixed flow turbo,this paper researchs the performance of the adjustable mixed flow turbine nozzle ring and its internal flow through the way of numerical calculation.Through changing the blade shape of the nozzle ring to explore the efficiency of the turbo stage and to analyze the reasons.Finally,the more suitable nozzle blade for the mixed flow turbo can be pointed out.Based on HP50 mixed flow turbo,two projects of nozzle ring blade are designed to compare.Because JK50 radical turbo nozzle ring blade is adaptable for the experiment conditions in this study and own successful practice experience,therefore the first blade project is modified based on JK50.Then,the second project is to change the thinner JK50 radical turbo nozzle blade leading edge to another short and thick shape.The computation result of the fourth chapter shows that under the almost same mass flow,the efficiency of the second project is slightly better than the first one.By comparing and analyzing the factors of the channel Mach number,the static pressure difference value of pressure surface and suction surface,the situation of leakage flow,the entropy of nozzle blade outlet area and the entropy of the downstream rotor channels,it is found that the clearance leakage flow is the main factor why these two projects show different efficiency.At the same time,this paper explores the characteristics of the nozzle ring blade wake.Specifically,this paper explains the forming reason of the trail and its process of the development and the transportation,and the mutual effect with the leakage flow.At the same time,the reason of pressure fluctuations of the nozzle ring blade trailing edge and the rotor blade leading edge are analyzed.In order to reduce the effect of leakage flow for the turbine efficiency,on the basis of the second project,a rotating blade in pressure side is designed innovatively in this paper.With the same size blade,parts of the guide blade are fixed to reduce clearance leakage flow and it is expected to reach the higher turbo efficiency.The numerical result shows that the initial state of the new blade turbo efficiency is higher than the original blade turbo efficiency under the same working conditions.However,the efficiency of the new blade turbos,with 20% and 40% opening degree respectively,are lower than the efficiency of the original blade.Although the new blade reduces clearance leakage flow,in order to achieve the purpose of being adjustable flow,higher entropy in triangle cavity between the small blade and fixed part decrease the efficiency of turbo. |
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