核主泵空化流动对能量转换特性影响的研究

发布时间：2018-04-15 01:41

本文选题：核主泵 + 空化流动　；参考：《兰州理工大学》2017年硕士论文

【摘要】：在整个核电系统中,核主泵被喻为核岛的“心脏”,是核反应堆冷却剂系统的动力设备之一,也是一回路的主要压力边界。核电站中的一回路破口事故和热阱丧失事故均可能导致核主泵发生空化,使其扬程和效率降低,引起反应堆芯过热,空化严重时对核主泵性能和安全运行造成严重影响。本文以一台自主设计的核主泵模型泵为研究对象,通过数值计算,并结合相关试验数据深入研究了核主泵发生空化时其内部空化流动特性。主要研究内容与所得成果如下:1.核主泵空化流动对能量转换的影响。通过流线上压力、速度等的变化规律,结合泵基本方程,对不同空化工况下核主泵叶轮内动、静扬程进行深入研究。结果表明:核主泵内流体的能量主要由叶轮中后段提供,且从前盖板到后盖板,流体获得的能量逐渐减少。空化干扰叶轮内液体的流动,导致空化区域相对速度增大,压力减小,在气泡密集区域,叶片对流体做功极少。同时,随着空化程度加剧,无空化区动扬程增大,静扬程减小,且静扬程减小幅度大于动扬程增大幅度,从而引起泵扬程和效率下降。另外,在空化区域,随着空化程度加剧,动、静扬程突变程度加剧,增大了叶轮内的流动损失,进而导致泵扬程及效率进一步下降。2.空化发展对核主泵性能的影响。选择4种空化工况,通过对比得出核主泵在发生空化时,其性能及内部流场变化规律。结果表明:核主泵发生空化时,其扬程、效率和功率变化对有效空化余量降低的敏感程度不同。随着空化程度加剧,扬程变化率最大,效率次之,功率变化率最小。同时,由空化产生的气泡改变了空化区域流体状态,使流体动力粘度减小,导致空化区域湍流耗散率减小,降低了湍流耗散损失。3.叶片进口边几何形状对核主泵空化流动特性的影响。对4种不同叶片进口边几何形状的模型泵进行空化模拟,得出叶片进口边几何形状对核主泵性能的影响规律。结果表明:叶片进口边减薄,使叶片进口对流体的排挤作用减弱,改善了叶片对进口流动条件改变的适应性,减小叶片进口处的流动损失,使效率升高。另外,增大叶片进口边圆角,进口减薄程度加剧,使进口处过流断面面积增大,流速降低,进而导致压力增大,且低压区逐渐向叶片出口移动,在发生空化时,气泡对叶片进口处流体流动影响逐渐变小。同时,随着叶片进口减薄程度加剧,叶片进口更加接近流线型,液体绕流叶片头部时产生冲击减小,使叶片吸力面靠近进口处的最低压力有所增大。
[Abstract]:In the whole nuclear power system, the nuclear main pump is described as the "heart" of the nuclear island, is one of the power equipment of the nuclear reactor coolant system, and is also the main pressure boundary of the primary circuit.The primary circuit break accident and heat trap loss accident in the nuclear power plant may lead to cavitation of the nuclear main pump, reduce its head and efficiency, cause the reactor core to overheat, and seriously affect the performance and safe operation of the nuclear main pump when the cavitation is serious.In this paper, a self-designed nuclear pump model pump is taken as the research object. The internal cavitation flow characteristics of the nuclear main pump during cavitation are studied by numerical calculation and combined with relevant experimental data.The main contents and results are as follows: 1.The effect of cavitation flow on energy conversion in nuclear main pump.Through the variation of the pressure and velocity in the streamline, combined with the basic equations of the pump, the dynamic and static head of the impeller of the nuclear main pump under different cavitation conditions is studied in depth.The results show that the energy of the fluid in the nuclear main pump is mainly supplied by the middle and back section of the impeller, and the energy obtained by the fluid decreases gradually from the front cover plate to the back cover plate.Cavitation interferes with the flow of liquid in the impeller, resulting in the increase of the relative velocity and the decrease of the pressure in the cavitation region. In the dense bubble area, the blade does little work on the fluid.At the same time, with the increase of cavitation degree, the dynamic head increases and the static head decreases in the no-cavitation area, and the amplitude of the static head is larger than that of the moving head, which leads to the decrease of pump head and efficiency.In addition, in the cavitation area, with the increase of cavitation degree, the sudden change degree of static head and cavitation increase, which increases the flow loss in the impeller, which leads to the further decrease of pump head and efficiency.The effect of cavitation development on the performance of nuclear main pump.Four cavitation conditions were selected and the performance and internal flow field of the nuclear main pump during cavitation were obtained by comparison.The results show that when cavitation occurs in the nuclear main pump, the sensitivity of the head, efficiency and power changes to the reduction of the effective cavitation margin is different.With the increase of cavitation degree, the lift change rate is the largest, the efficiency is the second, and the power change rate is the least.At the same time, the bubble produced by cavitation changes the fluid state in the cavitation region, reduces the dynamic viscosity of the fluid, reduces the turbulent dissipation rate and reduces the turbulent dissipation loss of the cavitation region.Effect of blade inlet geometry on cavitation flow characteristics of nuclear main pump.The cavitation simulation of four kinds of model pumps with different geometry of inlet edge of blade was carried out, and the influence of geometry of inlet edge of blade on the performance of core main pump was obtained.The results show that the thinning of the inlet edge of the blade weakens the extrusion effect of the blade inlet to the fluid, improves the adaptability of the blade to the change of the inlet flow conditions, reduces the flow loss at the inlet of the blade, and increases the efficiency.In addition, increasing the angle of the inlet edge of the blade, increasing the degree of the inlet thinning, increasing the cross section area at the inlet, decreasing the velocity of flow, causing the pressure to increase, and moving gradually to the blade outlet in the low pressure region, when cavitation occurs,The effect of bubble on the fluid flow at the inlet of the blade is gradually reduced.At the same time, with the increase of blade inlet thinning, the blade inlet is closer to the streamline type, and the impact of liquid around the blade head decreases, which increases the minimum pressure near the inlet of the blade suction surface.
【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】：TM623.4

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