涡轮气动设计对空气涡轮起动机自由运转转速的影响分析

In order to control the air turbine starter free-running operation and reduce the adverse impact of high free running speed on safe operation of the air turbine starter，the influence analysis of the aerodynamic de⁃ sign to the value of free-running speed was carried out. An aerodynamic design method of reducing free running speed by controlling flow incidence angle is proposed and four main factors affecting the incidence angle were identified，which include blade structure angle，degree of reaction，load coefficient and flow coefficient.Results show that the incidence angle has a significant effect on the free-running speed. The negative incidence angle at peak power speed can be effectively improved by selecting appropriate turbine aerodynamic design parameters，and the incidence loss at larger speed can be enhanced，thus reducing turbine free running speed value. Further，the engine test results prove that using the design method proposed in this paper，the peak power speed value of the optimized turbine is reduced by 21.7% on the premise that the peak power is basically unchanged，and the es⁃ timated free-running speed value can be reduced by nearly 20%.