脉冲进气条件下可变喷嘴涡轮性能影响因素分析

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

为了改善涡轮和发动机的匹配,采用计算流体动力学(CFD)方法研究了脉冲进气条件下脉冲频率、脉冲振幅、喷嘴角度以及涡轮转速对可变喷嘴涡轮非定常性能的影响.研究结果表明:脉冲频率为80Hz时涡轮瞬态最低流量比40Hz时提高了10.4%,瞬态最低效率增加了4.7%,效率滞后现象更加明显;低脉冲振幅为25kPa时涡轮通流能力和效率迅速恢复,并且指出在低脉冲振幅时采用稳态设计是可行的;喷嘴角度为32°时,涡轮脉冲进气与稳态进气两种情况下的流量差异比喷嘴角度为10°时增加了3.3%,效率差异则增加了6.6%.涡轮内部脉动强烈,涡轮通流能力和效率下降明显;涡轮转速为47 256r/min时脉冲进气造成的流量和效率变化分别比30000r/min时相应值高了2.9%和0.8%,高转速时涡轮内部流场易受到进口条件影响,涡轮流量、效率以及攻角与稳态情况偏离大.

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 80Hz condition is 10.4%higher than that under 40Hz 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 25kPa 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 32degree,the mass flow difference between pulsating inlet flow condition and steady inlet flow condition is 3.3% more than that of 10degree,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 256r/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 30000r/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.