小尺寸无静叶对转风扇/压气机气动设计与变工况性能分析研究

Small size vaneless counter-rotating fan/compressor aerodynamic design and performance analysis of variable condition property

关键词:  涡扇发动机  无静叶对转  风扇/压气机  气动设计  变工况特性

Key words:  Turbofan engine  Vaneless counter-rotating  Fan/compressor  Aerodynamic design  Variable condition property

摘要:

无静叶对转风扇/压气机能有效减小发动机陀螺力矩，在轴向长度方面具有优势。然而，无静叶往往导致下游叶片攻角变化较大，变工况性能难以保证，且这一特点随叶尖切线速度的增大而恶化。本文利用小尺寸涡扇发动机风扇叶片根部周向速度较低的特点，尝试对其进行风扇与压气机无静叶对转方案设计。通过速度三角形分析了无静叶对转风扇/压气机的性能特点，开发了无静叶对转风扇/压气机一维设计程序进行参数方案的筛选优化，设计得到小尺寸无静叶对转风扇/压气机构型方案，设计点效率为85.1%，压比为3.16。结果表明，对转压气机的下排叶片相对进口气流角的变化范围较常规转叶+静叶相对进口气流角范围更小，而对转下排叶片的进口速度却将增大1.5~3倍，因此，需要合理选择对转风扇/压气机的轮毂比及转速比，才能保证对转风扇/压气机变转速工况下的设计点效率及失速裕度。减小对转风扇/压气机转速比有利于提高设计点效率和裕度，但本文受发动机总体指标限制，对转速比选择进行了折中。

Abstract:

The vaneless counter-rotating fan/compressor can effectively reduce the axial length and gyro torque of the engine. However， the absence of the stators can lead to a frequently changing attack angle at the downstream， which deteriorates the variable condition performance. Moreover， this characteristic deteriorates with the increase of the tangential velocity of the blade tip. In this paper， taking advantage of the low circumferential speed at the root of the fan blade of the small-sized turbofan engine， the fan and compressor were designed as a counter-rotation scheme without a stator. Firstly， the performance of the vaneless counter-rotating fan/compressor are analyzed through the speed triangle. Then， a one-dimensional design program for the vaneless counter-rotating fan/compressor is developed to optimize the design parameters. Finally， a small size vaneless counter-rotating fan/compressor is designed with its design point efficiency of 85.1% and pressure ratio of 3.16. Results show that the relative inlet flow angle towards the downstream rotors varies less than that in conventional compressors with rotors and stators while the flow velocity incoming those vaneless counter-rotating rotors would increase by 1.5 to 3 times compared to conventional ones. Thus， the hub ratio and speed ratio of a counter-rotating fan/compressor should be set for guarantee of its design point efficiency and stall margin under variable speed conditions. Moreover， reduction in speed ratio could benefit counter-rotating fan/compressor’s design point efficiency and stall margin， the speed ratio was set as a compromise solution under restrictions of engine overall design.