超临界二氧化碳压缩机特性数值模拟

以某小流量超临界二氧化碳(SCO_2)离心压缩机为例,开展了近临界点SCO_2压缩机多工况数值模拟。研究发现:物性表格的分辨率对流场的计算结果影响较大,尤其是在冷凝区域,同时,物性的剧烈变化导致流场高梯度、强非线性使得近临界点SCO_2压缩机数值模拟存在极易发散的问题。通过精细调节物性表格分辨率以及库朗数等数值参数获得了多工况范围内的收敛解,与实验数据对比的结果表明:5×10~4 r/min转速下设计点进口工况最大相对误差为9.1%。设计了某5MW级热功率SCO_2布雷顿循环主压缩机并完成三维数值模拟。在保证效率基本不变的前提下,通过调整后弯角并与其他几何参数匹配,实现了压缩机压比及喘振裕度增加,并抑制了吸力面冷凝区域的发展。

Numerical simulation of supercritical CO2 compressors characteristics

Based on the numerical simulation of a low-flow centrifugal compressor operating with supercritical carbon dioxide (SCO2), the compressor performance with working conditions slightly above the critical point was studied. It was found that the resolution of carbon dioxide (CO2) property tables had a great influence on calculation results, especially in areas with condensation. Due to the sharp change of CO2 property near critical point, areas of high gradient and strong nonlinearity led to poor convergence. The problem was solved by adjusting parameters like courant number, resolution of CO2 property table and so on. Maximum relative error of calculation and test results was 9.1% under rotating speed of 5×104r/min. Based on the numerical simulation above, a main compressor of one 5MW supercritical CO2 Brayton cycle was designed and three-dimensional numerical simulations were completed. Under the premise of ensuring basically the same efficiency, by adjusting the back sweep angle and matching with other geometric parameters, the compressor pressure ratio and surge margin increased, and the volume of condensation zone on the suction side was reduced.