有叶扩压器进口蒸汽喷射的扩稳机理研究

Due to the high pressure recovery ability, vaned diffuser is widely used in centrifugal compressor especially for fields having strict requirements on efficiency and compactness. However, it always shows poor performance at off design conditions and as the key component controlling the stability from practical experiences. In open literature, however, there are few reports about the influences of vaned diffuser on system stability. Therefore, current project chooses a centrifugal compressor of a small gas turbine with total pressure ratio of 4.2 as the research object and focuses on instability mechanisms. With potential application in combined cooling, heating and power system (CCHP) of small gas turbines, the applicant plans to utilize steam injection to increase the compressor stable operation range. Depending upon steam quality (superheated/saturated), nozzle parameter (position/angle), and other factors, steam injection will bring at least following things: a. it has an effect on the properties of the flow, specially in changes to the gas constant, and gamma; b. depending upon the temperature difference between the steam and the air, the heat transfer effect between the two fluids changes the diffuser incidence angle; c. different non-uniform temperature in both axial and circumferential direction. These factors together will alter the performance of both diffuser and impeller. The applicant will start research from the above metioned directions and use both numerical and experimental methods.The innovation lies in not only understanding mutual influencing mechanisms of steam injection on diffuser inlet flow filed, performance and system stability, but also extending the operation range using engineering applicable methods.

有叶扩压器在扩压方面的优势，使其在效率和尺寸要求较高的场合得到广泛应用，但其变工况性能不好，且常是决定离心压缩机稳定裕度的关键部件。然而文献中对其在稳定性方面的研究较少，本项目以某小型燃气轮机用离心压缩机（总压比4.2）为研究对象，以冷热电三联供（CCHP）系统的热电比调节为应用背景，申请者拟研究其失稳路径、失稳机理并通过扩压器进口的喷射蒸汽实现扩稳。蒸汽喷射将至少有如下效果：影响扩压器进口的流场特性；改变工质气体常数、比热比等物理参数；引起蒸汽与空气的换热；改变扩压器进口温度场分布。取决于蒸汽特征（过热/饱和、压力）、喷嘴参数（位置、角度等）等参量，上述几种因素共同影响扩压器和叶轮的工作特性，进而改变机组稳定性。项目将主要从以上角度展开研究，研究手段以实验为主，数值和理论分析为辅。创新点在于澄清蒸汽喷射对部件特性与机组稳定性的作用规律，并在理解规律的情况下形成具有应用前景的扩稳手段。

有叶扩压器在扩压方面的优势，使其在效率和尺寸要求较高的场合得到广泛应用，但其变工况性能不好，且常是决定离心压缩机稳定裕度的关键部件。然而文献中对其在稳定性方面的研究较少，本项目以某小型燃气轮机用离心压缩机（总压比4.2）为研究对象，以冷热电三联供（CCHP）系统的热电比调节为应用背景，申请者对某燃气轮机用离心压气机进行了0.5的缩尺，分别进行了叶轮+无叶扩压器、叶轮+有叶扩压器的性能实验、叶轮进口放气、扩压器进口注蒸汽的扩稳试验。除了常规的性能测试仪表外，在叶轮进口、叶轮出口、有叶扩压器通道内、扩压器下游的排气集流器内都布置了动态和稳态数据传感器。.通过分析数据，从多个角度交叉确认了有叶扩压器为该机组的控稳部件，而这其中扩压器进口的半无叶空间的流动状态为决定性因素，在设计时，可以通过调整喉部面积，达到调整该区域流动的目的。扩压器在不同转速下，失稳的形态也不一致，在80%转速下为模态波型失速，在90%转速失速为脉冲型失速，本文首次发现了外界因素对失速形式的变化，即80%转速下，失速波由正向传播变成了后向传播、而90%转速甚至由脉冲失速变为模态波失速。进一步的研究表明在不同转速下，均存在上限值，超过该值，甚至会提前触发失稳，触发机理与轴流压缩机的脉冲型失速机理类似。研究最后还研究了工质类型、温度、喷嘴数目、位置对扩稳效果的影响并与其它工业内常用的放气、打回流等进行了对比，结果表明蒸汽扩稳的机理可以从经典的流动角和抑制失稳模态的角度得到殊途同归的解释、扩稳效果受制于注入介质的速度而非动量，不同温度的介质通过与主流的换热通过引起主流气体膨胀或收缩，影响着扩压器内部的流动、喷嘴周向均布且均位于相邻叶片中间的布局扩稳效果最佳、喷嘴数目增加和非对称的布局降低了扩稳的效果、蒸汽喷射的扩稳效果比常规喉部放气和与扩压器进口回流两种方法要好。