概率密度函数分析监测发动机气动不稳定征兆

Application of Probability Density Function Analysis in the Monitoring of Engine Aerodynamic Instability Precursor

对某型单轴涡喷发动机节流过程中的喘振故障进行了试验研究。在手工关闭放气带的情况下,该型发动机的共同工作线确定地穿越喘振区域,从最大状态收油门减速将会导致该型发动机进入不稳定工作。数据分析中发现压气机第一级静子机匣壁面静压对节流最为敏感,且静压脉动分量的概率密度函数分布随节流有规律地发生变化。定义了概率密度函数特征值θ来量化这种变化。进一步的数据分析表明,θ可以反映压气机第一级端部的流动分离情况,可以作为试验发动机节流过程中的气动稳定性指标。与直接检测模态扰动和短周期扰动相比,监测θ的变化可以为该型发动机提供较长的失速预警时间。

Experiments were performed to investigate surge problem of a single shaft axial flow turbojet engine during throttling. If the discharge bleed valve of the engine is closed manually, the working line of the engine will traverse the stalling region in a mass flow range, thus throttling from full speed may surely transit the engine into unstable operation. It is observed that the casing wall static pressure of the first compressor stage stator is most sensitive to throttling operation, and that probability density functions of the pulsating components of the static pressure vary accordingly. An eigenvalue,θ,is then introduced to quantify the variation of probability density functions. Further data analysis demonstrates that eigenvalue θ is capable of reflecting some aspects of flow separation in the tip region of the first compressor stage, and that θ may serve as an indicator of imminent aerodynamic instability of the engine, thus long stall warning time of the examined turbojet engine is achievable than that to directly detect modes or spikes.