为了研究沙粒粒径与含沙量对离心泵空化特性的影响,对含沙条件下与清水介质下离心泵内部空化流场进行数值计算.所采用沙粒粒径分别为0.005、0.010、0.015 mm,含沙量分别为0.5%、1.0%、1.5%.通过对清水介质外特性与平头圆柱空化流动进行数值计算并与试验结果相对比,验证算法的可靠性.计算结果表明:含沙量为1.0%时,随粒径逐渐增大,沙粒对空化的影响表现为先促进、后抑制;沙粒粒径为0.010 mm时,随含沙量不断增多,沙粒对空化的影响表现为先促进、后抑制.高压条件下,清水介质中无空化泡产生,含沙水流中均有少量空化泡产生.空化充分发展时,与清水介质相比,含沙水中空化泡分布表现为先增大、后接近、再变小.在沙粒磨蚀与空蚀的共同作用下,含沙水流条件下的扬程均低于清水介质下的扬程,且分别随粒径、含沙量的增加,逐渐减小.%To study the effects of sand particles on the cavitation flow in the centrifugal pump, the method of computational fluid dynamics (CFD) was employed to study the internal cavitation flow field of the centrifugal pump in the pure water and sand water respectively. Based on Fluent 15.0, Mixture model, RNGk-ε(renormalization groupk-ε) turbulence model and Schnerr-Sauercavitation model were used to research the cavitation flow. For the cavitation flow in the sand water, sand mean diameters selected were 0.005, 0.010 and 0.015 mm and sand concentrations were 0.5%, 1.0% and 1.5% respectively. Unstructured grids constructed by ANSYS-ICEM(Integrated Computer Engineering and Manufacturing), were applied to disperse the computational domain. Accuracy of numerical calculation was improved by grids independence check and the total number used was 2817398. Numerical results of pure water performance of the centrifugal pump and cavitation flow around the flat-nosed cylinder were compared with the experimental results to verify the reasonableness of the algorithm used in the simulations. Numerical results revealed that the algorithm designed was appropriate to simulate cavitation flow. To lower the turbulent viscosity in cavitation region, RNGk-ε turbulence model was modified. Cavitation performance curves were built, the vapor had the volume fraction of 0.1 in different cavitation periods, and the effect of sand particles on the cavitation flow was investigated. To study the effect of sand mean diameter, sand concentration was 1.0% and sand mean diameter was increased from 0.005 to 0.015 mm gradually. When the outlet pressure was 6.0×105Pa, cavitation did not occur in the pure water of the centrifugal pump and vapor did not exist in the pure water. In the sand water, a few cavitation bubbles appeared. For the critical net positive suction head (NPSHc) which was the NPSH when the head was reduced by 3.0%. In the pure water, it was 3.7214 m and in the sand water with sand mean diameter of 0.005, 0.010 and 0.015 mm, it was 4.952, 3.7479 and 3.638 m respectively, and when cavitation developed fully, theNPSH was 3.436, 3.541, 3.438 and 3.337 m respectively for the pure water and the sand water with 3 different sand mean diameters, indicating that the effects of sand particles on the cavitation flow were accelerative at first, and then inhibited. When sand mean diameter was 0.010 mm, in the critical cavitation stage and cavitation full development stage, NPSH in the pure water and sand water had inconspicuous difference. Compared with cavitation occurring in the pure water, when sand mean diameter was 0.010 mm, sand particles had little effect on the development of cavitation in the sand water. To study the effect of sand concentration, sand mean diameter was 0.010 mm and sand concentration increased from 0.5% to 1.5% gradually. Under outlet pressure of 6.0×105Pa, cavitation did not occur in the pure water of the centrifugal pump and vapor did not appear in the pure water too. And a few cavitation bubbles existed in the sand water, stating clearly that sand particles had a close relation with the formation of cavitation bubbles. In the critical cavitation period, NPSHc was 3.7214, 4.7801, 3.7479 and 3.4906 m respectively for the pure water and the sand water with 3 different sand concentrations of 0.5%, 1.0% and 1.5%, and in the cavitation full development period, NPSHwas 3.436, 3.841, 3.438 and 2.9604 m separately, explaining that effects of sand concentration on the cavitation flow were accelerative at first, and then inhibited too. When sand concentration was 1.0%, in the critical cavitation period and cavitation full development period, NPSH in the pure water and sand water had little difference, illustrating that compared with cavitation occurring in the pure water, sand particles had little effect on the development of cavitation under the 1.0% sand concentration. When sand particles promoted the development of cavitation, volume of vapor with volume fraction of 0.1 in sand water was larger than that in the pure water. During sand particles inhibiting the development of cavitation, the volume was smaller than that in the pure water. For sand particles had little effect on the evolution of cavitation, the distribution was similar. During cavitation fully evolving, interaction of abrasion and cavitation erosion made the head in sand water less than that in the pure water. With sand concentration being invariant, when sand mean diameter increased and with sand mean diameter being constant, when volume fraction increased gradually, head in sand water decreased continuously. Number of cavitation nuclei, virtual mass force, slip velocity, and so on had a close connection with sand particles promoting the development of cavitation. Viscosity, abrasion effect, and so on had a close relationship with sand particles inhibiting the evolution of cavitation.
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