两级对置式离心压气机湿压缩研究

Wet Compression Effects on an Opposed-Setting-Two-StageCentrifugal Compressor

关键词:  湿压缩  两级离心压气机  喷水量  水滴粒径  数值模拟

Key words:  Wet compression  Two-stage centrifugal compressor  Water spraying rate  Water droplet diameter  Numerical simulation

摘要:

本文以两级对置式离心压气机为对象，采用数值模拟方法研究了湿压缩对压气机特性和内部流场的影响。数值计算借助ANSYS CFX软件，采用欧拉-拉格朗日法耦合计算连续流场和离散粒子项，基于k-ε湍流模型、变比热拟合公式计算焓熵值，利用安托万方程求解饱和蒸汽压力并加入液滴破碎CAB模型和撞壁模型。在压气机进口采用干空气和不同喷水量与粒径组合共计7个工况条件下，对比分析了压气机总体性能变化、部件性能变化及水滴的运动轨迹。结果表明，湿压缩使得整机压比和效率均有所提高，但效果越好裕度越小。低压级内湿压缩效果明显，水滴蒸发使得出口温度降低；高压级湿压缩降温增益不明显，但受上一级冷却效果影响，压比和温比都增加。水滴在叶轮中主要积聚在叶片压力面根部。扩压器和回流器中产生了较大的尾迹损失，扩压器前缘受水滴破碎和掺混作用，产生较大熵增。

Abstract:

The effects of wet compression on the performance and internal flow field of an opposed-setting-two-stage centrifugal compressor are studied by utilizing a numerical simulation method. The ANSYS CFX software is adopted, which is based on Eulerian-Lagrangian method to calculate the continuous flow field and discrete particle terms, k-ε turbulence model, variable specific heat fitting formula to solve the enthalpy and entropy, Antoine equation to solve the saturated vapor pressure, CAB droplet breakup model and collision model. At 7 inlet conditions with dry air and different combinations of water spraying rate and particle size, the variation of compressor total performance, component performance and the trajectory of water droplets are analyzed and compared. The results show that wet compression can improve the pressure ratio and efficiency of the whole machine, but the higher the pressure ratio and efficiency are, the less the stall margin is. In the low-pressure stage, liquid evaporation decreases the outlet temperature. The high-pressure stage benefits from the cooling effects of the former stage so that both pressure ratio and temperature ratio increase, but the enhancement by wet compression is less obvious. Droplets mainly accumulate at the root of the pressure side of the impeller blades. Large losses occur near the trailing edge in both the diffusers and the return channel. The leading edge of the diffuser vane is attacked by the water droplets, and there will be a large entropy generation due to droplet breakup and mixing.