离心泵空化余量分析研究

许多泵长期运行处在临界空化工况与初生空化工况之间,会造成叶片表面出现坑蚀和穿孔等破坏,从而使泵因空化而达不到预期寿命。由此选用一种单级单吸离心泵为研究对象,基于湍流模型k-ε和空化模型Zwart,进行非定常空化数值计算结果分析。对于初生空化的判定,以σ≥1.0时叶片表面刚刚发生空化,产生的汽泡对外特性无影响,且以汽体体积分率为变量,其空化区域的汽体体积分数以10%为基础,作为初生空化的判定依据。其研究结果表明:初生空化余量随流量的增大,先缓慢降低,在额定流量工况下,初生空化点所对应的空化余量最小,随着流量的进一步增大,初生空化余量又缓慢增大。通过分析提出在布置泵吸入系统时使其NPSHa大于初生空化余量NPSHR,即NPSHa>NPSHR,并在初生空化余量NPSHR上加上安全余量值,使得泵完全处在无空化工况运行,进而就可以使泵不因空化而缩短预期寿命。

Analysis and research on cavitation allowance of centrifugal pump

Many pumps run between the critical cavitation condition and the initial cavitation condition for a long period of time,which will cause damage such as pitting erosion and perforation on the blade surface,thus making the pump unable to reach the expected life due to cavitation.In this paper,a single-stage single-suction centrifugal pump was selected as the research object,and unsteady cavitation was calculated numerically based on k-ε turbulence model and Z_(wart) cavitation model.The determination of initial cavitation was based on the cavitation just occurred on the blade surface,and no influence of the bubble produced on the external characteristics.Moreover,the volume fraction of the vapor body was taken as a variable,and the volume fraction of the vapor body in the cavitation region was based on 10%,which was used as the determination basis of initial cavitation.The results show that the initial cavitation allowance first decreases slowly with the increase of flow rate,and the cavitation allowance corresponding to the initial cavitation point is the smallest under the rated flow rate condition,and then increases slowly with the further increase of flow rate.Through analysis,it was put forward to arrange a pump suction system to make its NPSH_a greater than the initial cavitation allowance (NPSH_R),namely the NPSH_a>NPSH_R,and plus safety margin based on initial cavitation allowance value (NPSH_R) make the pump run under the working condition of completely no cavitation,and further make the pump does not shorten its life expectancy due to cavitation.