A Roots pump often exhibits the typical characteristics of high gas pressure in the exhaust port, low pressure at a basic volume and large airflow pulsation at the outlet as a result of gas reflux. In light of this, this study employed Pumplinx software for the numerical calculation of the entire flow field of a two-bladed Roots pump. The effects of the rectangular and curved reflux groove structures on the internal flow field of a Roots pump, especially on the outlet pressure pulsation and flow rate, were unveiled separately. The rectangular reflux groove controlled the angle and thickness, while the curved reflux groove regulated the coordinates of the key points on the Bezier curve. It is worth recognizing that different reflux groove structures were not noticeable in enhancing the inlet measurement flow pattern; reduce the exhaust pressure pulsation, flow pulsation and exhaust section vortex. Interestingly, the rectangular return groove far outweighed the curved groove when optimizing the pressure and flow pulsation when registering the higher flow loss compared to the curved return groove. The merits and demerits of the Q criterion and omega criterion in characterizing the vortex structure of the flow field in the Roots pump were compared by Tecplot software. The omega criterion looked more robust, clear and continuous in revealing the strong and weak vortices in the Roots pump. The outcome of this research work could provide a reference for the study of Roots pump airflow pulsation, vortex analysis and casing structure design optimization.
为提高1D水锤模型对有压管道瞬变流预测精度,在传统1D恒定摩阻模型中引入额外的瞬时附加摩阻项,建立了改进的非恒定摩阻模型.利用2个模型分别对3种不同初始流速工况的水库-管道-阀门系统压力瞬变特性进行数值模拟,并对比了不同模型的预测精度.结果表明:恒定摩阻模型和非恒定摩阻模型的压力波在第1个周期内的压力变化预测值均与试验值较为接近.而在第1个压力波周期以后,二者在低流速工况预测的压力峰值与试验值误差分别为10.3％和4.7％,改进的非恒定摩阻模型预测精度大幅提高.对压力波传播特性的研究表明,压力波在系统内不同位置处的传播和反射特性存在明显不同:在1个水锤波周期内,压力波在水箱处受到压强差作用产生全负反射,而在阀门处由于微流段的速度变化为0,仅改变了方向.研究结果能够为有压管道的安全稳定运行和优化设计提供一定的参考.
The optimal design of centrifugal compressor blade under multiple working conditions faces the problems of large design space and insufficient flexibility, thus causing redundant blind search and reducing the optimization efficiency. In order to improve the above problems, the FFD-based parameterization method of centrifugal compressor blade with complex surface was proposed, for which a mapping model of local geometric region and mesh control body was established, the influence law of diffe-rent basis functions on blade geometry configuration was explored, and the fine optimization of blade geometry shape was carried out by combining multi-objective evolutionary algorithm and CFD technology. The results show that the optimized flow field structure is further improved, the isentropic efficiency of rated and common conditions are increased by 0.48% and 0.40%, respectively, and their surge margins are as well increased by 1.6% and 1.8%, respectively, which achieves an efficient and flexible fine design of centrifugal compressor blade with complex curved surface by using less design variables.
为深入分析水质对人工复配土壤入渗特性的影响,采用室内土柱模拟试验,分析了天然积水和地下水2种不同化学性质的供水情况下,水质对砒砂岩与沙土 7种不同体积比下(1∶0,5∶1,2∶1,1∶1,1∶2,1∶5,0∶1)复配后人工复配土壤入渗特征的影响.结果表明:在人工复配土壤质地为粉壤土和砂壤土时(砒砂岩与沙复配比例为1∶0,5∶1,2∶1,1∶1,1∶2),天然积水的入渗时间显著高于地下水的入渗时间;在人工复配土壤质地为壤砂土和砂土时(砒砂岩与沙复配比例为1∶5,0∶1),天然积水和地下水的入渗时间无明显差异;相同水质情况下,不同复配土的入渗时间由长到短按复配比排序为1∶0,5∶1,2∶1,1∶1,1∶2,1∶5,0∶1;同一砒砂岩与沙复配比例下,天然积水处理下的累积入渗量大于地下水处理,且在砒砂岩与沙比例为2∶1处理中,水质间的累积入渗量差异最大,累积入渗量与时间的拟合关系符合对数入渗模型;湿润锋推进距离变化规律与累积入渗量的变化规律一致.结果显示,水质显著影响复配土壤入渗性能,影响的程度与复配土壤质地类型密切相关.
为了研究反应堆一回路对核主泵(RCP)叶轮入流特性的影响,将蒸汽发生器(SG)、入口弯管、冷热段管道、核反应堆及RCP进行联合简化建模.基于CFD方法对其一回路进行流场计算分析,对比分析均匀入流条件下RCP数值计算结果与试验结果,可以发现,由数值模拟得到的扬程和效率误差均在5％以内,验证了数值计算方法的正确性.在反应堆一回路中采用多孔介质模型,通过泵特性曲线与管路特性曲线的动态匹配,使得闭式系统RCP流量与额定工况值相差0.998％,扬程相差3.76％,二者误差较小,从而实现了管路阻力的动静态调节.研究结果表明:入口弯管内流动的周向对称性被破坏,其压力和速度分布呈现不均匀分布,受弯管曲率的影响,在离心力作用下产生二次流动;与均匀入流工况相比,非均匀入流工况下RCP入口处形成了 一对回旋方向相反的旋涡,速度和压力的对称分布特性被破坏,且沿周向和径向的轴向速度变化均大于平均速度的80％.因此,本研究建立的数值预测方法可以为研究反应堆一回路对RCP叶轮入流特性的影响提供理论依据.
