基于径向基函数的叶片进口边对离心泵空化性能的影响预测

发布时间：2018-05-13 08:06

本文选题：离心泵 + 空化性能　；参考：《兰州理工大学》2017年硕士论文

【摘要】：随着科学技术的不断发展,流体力学、计算流体力学、流体机械测试技术等学科的理论与应用得以有较大进步,从而使得离心泵内部流动问题的研究也得到迅速发展。目前离心泵的应用越来越广泛,对离心泵在各个领域的安全、稳定运行也提出越来越高的要求。但是,作为水力机械中的一大难题—空化,一直制约着离心泵的发展,其不仅对离心泵的稳定运行产生影响,还对离心泵的过流部件造成较大的破坏。影响其内部空化发生的因素有很多,本文以离心泵叶片进口边为研究对象,采用数值计算与理论分析相结合的方法对叶片进口边形状及位置对离心泵空化性能的影响进行研究及分析。具体的研究内容有以下几个方面:1.通过对不同离心泵叶片进口边形状进行对比分析,发现圆锥型叶片进口边的离心泵具有更优秀的空化性能,该叶片在进口部分更符合流线形规律,可改善流体在该处的入流状态,减少叶片进口边对流体的冲击作用。2.保持叶轮轴面截线形状不变,通过改变轴面截线上叶片进口边在前、后盖板处的位置,得到具有不同前、后掠角度的叶片进口边,经过数值计算得到不同叶片样本的空化性能曲线,并对离心泵内部空泡分布情况进行分析,可总结出当叶片进口边在前盖板处位置改变时对空化性能有较大影响,而叶片进口边在后盖板处位置改变时对空化性能影响较小。3.分析了不同叶片样本的叶片载荷分布情况,叶片进口边在前盖板处前掠时具有较好的空化性能,其与原型叶片相比在叶片进口部分具有较小的载荷分布,叶片工作面压力较低,叶片背面压力较高。从而当离心泵进口压力降低时,该叶片与原型叶片相比其背面压力更难降低到该温度下液体的汽化压力,从而在叶片背面进口边附近更难以产生空泡,因此具有较好的空化性能。而叶片进口边沿着后盖板前掠使得进入叶轮的小部分流体受到叶片由后盖板向前盖板方向的作用力,并且叶片背面后盖板处提前受到液流的冲击使该处压力比原型更高,这两个因素阻止了在进口边前盖板处产生的气泡向后盖板扩散,从而可以避免气泡对叶片流道的堵塞,因此这种离心泵样本在内部空化有一定程度之后扬程下降速率更慢。4.对具有不同叶片样本的离心泵蜗壳内部非定常压力脉动情况进行了分析,具有较好空化性能的叶片样本,在相同NPSHa时其叶轮内部空化区域更小,从而对内部流域的流动影响较小。而空化性能较差的叶片样本,叶轮内部较大的空化区域导致叶轮内部流动的紊乱,产生较多的漩涡,从而直接影响到蜗壳内部压力脉动的程度。5.提出了基于径向基函数(RBF)的叶片进口边位置对离心泵空化性能的影响预测,将叶片进口边前盖板处扭掠角度和后盖板处扭掠角度作为两个设计变量,将离心泵的必需空化余量NPSHr值作为预测值,利用RBF方法建立了不同叶片进口边位置对离心泵空化性能影响的预测模型,取得了较为准确的预测结果。
[Abstract]:With the continuous development of science and technology, the theory and application of fluid mechanics, computational fluid mechanics, fluid mechanical testing technology and other disciplines have been made great progress, which makes the research on the internal flow of centrifugal pumps developed rapidly. At present, the application of centrifugal pumps is becoming more and more extensive, and the safety and stability of centrifugal pumps in various fields are running steadily. However, as a big problem in the hydraulic machinery, cavitation has been restricting the development of centrifugal pumps, which not only affects the stable operation of centrifugal pumps, but also causes great damage to the overflow parts of centrifugal pumps. There are many factors affecting the cavitation of the centrifugal pump. This paper is based on the inlet edge of the centrifugal pump blade. The influence of the shape and position of the inlet edge of the blade on the cavitation performance of the centrifugal pump is studied and analyzed by the combination of numerical calculation and theoretical analysis. The specific research contents are as follows: 1. through the comparison and analysis of the shape of the inlet edge of the blade of different centrifugal pumps, the inlet edge of the conical blade is found. The centrifugal pump has more excellent cavitation performance. The blade is more consistent with the streamline shape in the inlet part. It can improve the flow status of the fluid in the area, reduce the impact of the inlet of the blade on the fluid, and keep the axial plane of the impeller to keep the shape of the interception of the impeller. By changing the position of the inlet edge of the blade at the front and the rear cover, the position of the blade at the front and the rear cover is obtained by changing the position of the blade inlet on the axis of the axis. The cavitation performance curves of different blade samples are obtained by numerical calculation, and the distribution of cavitation in the centrifugal pump is analyzed by numerical calculation. It is concluded that when the position of the blade inlet is changed at the front cover, the cavitation performance is greatly influenced, while the inlet side of the blade is changed at the back plate position. The cavitation performance is less affected by the.3. analysis of the blade load distribution of different blade samples. The blade inlet side has better cavitation performance at the front of the front cover plate. Compared with the prototype blade, it has a smaller load distribution in the inlet part of the blade, the pressure of the blade working face is lower, and the back pressure of the blade is higher. When the pressure is reduced, the back pressure of the blade is more difficult to reduce to the vaporization pressure of the liquid at this temperature, so it is more difficult to produce vacuoles near the inlet side of the blade. Therefore, it has better cavitation performance. The blade inlet border along the back cover makes the small part of the fluid entering the impeller from the rear cover. The force in the direction of the plate forward and the rear cover plate at the back of the blade causes the pressure to be higher than the prototype at the back of the rear cover. These two factors prevent the diffusion of the bubble back at the front cover plate at the inlet side, thus avoiding the plugging of the air bubble on the blade runner, so the centrifugal pump sample is cavitating inside. The unsteady pressure fluctuation in the centrifugal pump volute with different blade samples is analyzed by.4. to a certain extent. The blade samples with better cavitation performance have smaller cavitation area at the same NPSHa, which has less influence on the flow field in the internal flow field, and the cavitation performance is poor. The blade sample, the larger cavitation area inside the impeller leads to the disturbance of the flow inside the impeller and produces more whirlpools, which directly affects the degree of pressure pulsation in the inner shell of the worm.5.. The influence of the inlet position of the blade on the cavitation performance of the centrifugal pump is predicted based on the radial basis function (RBF), and the swept angle of the front cover plate at the inlet of the blade is made. As two design variables, the NPSHr value of the necessary cavitation allowance of the centrifugal pump is taken as the predictive value, and the prediction model of the influence of the inlet position of different blades on the cavitation performance of the centrifugal pump is established by RBF method, and a more accurate prediction result has been obtained.

【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH311

【参考文献】