壅塞空化器的空化机理研究

发布时间：2018-04-03 12:53

本文选题：壅塞空化器　切入点：空化机理　出处：《湖南工业大学》2014年硕士论文

【摘要】：壅塞空化器是一种新型的水力空化发生装置，它充分利用壅塞空化产生的特殊流场有效地加强了水力空化强度，但对产生壅塞空化的机理还有待进一步加深认识。将气液两相临界流的壅塞现象和液体的空化现象结合起来进行研究，针对不同壅塞空化器的结构和尺寸，通过CFD软件数值模拟壅塞空化器的空化流场，利用U型管压差计测量壅塞管壁面沿程静压力的分布，分析壅塞管内沿程压力和空隙率的变化规律，研究空泡生成和气液两相流及其临界流壅塞现象形成的机理；通过水听器测试壅塞空化器产生的空化噪声信号，分析空化噪声的功率谱特性、空化噪声能量比值和溃灭空泡数量和尺寸，并结合壅塞现象的特性研究壅塞空化的空泡溃灭机理，并把数值模拟结果和实验结果进行相互验证。研究结果表明，壅塞管的上游区域形成接近或低于饱和蒸汽压的低压区域，同时管内的含气率迅速升高，管内由单相流动转变为气液两相流，导致壅塞管内两相流的当地音速急剧下降，形成了当地马赫数接近于1的壅塞截面。在壅塞截面的上下游间高达108Pa/m的压力恢复梯度作用下，使得管内有数量多达106级和直径为10-6m级的空泡迅速溃灭，形成了剧烈空化的壅塞空化现象。空化器背压是壅塞空化强度的重要影响因素，在一定的空化器结构和水动力参数下背压存在相应的最佳范围。流量越大越有利于壅塞空化的形成，，大流量下空化器溃灭的空泡数量更多；壅塞环可以在背压和流量不变的条件下影响壅塞截面的位置以及增大壅塞截面处的压力恢复梯度，且背压越低时效果越明显。
[Abstract]:Choking cavitation device is a new type of hydraulic cavitation device. It makes full use of the special flow field produced by choking cavitation to effectively strengthen the intensity of hydraulic cavitation, but the mechanism of producing choking cavitation needs to be further understood.The choking phenomenon of gas-liquid two-phase critical flow is combined with the cavitation phenomenon of liquid. According to the structure and size of different choking cavitation device, the cavitation flow field of choking cavitation device is numerically simulated by CFD software.The distribution of static pressure along the wall of choked pipe is measured by U-tube pressure difference meter. The variation law of pressure and voidage in choked pipe is analyzed, and the formation mechanism of cavitation and gas-liquid two-phase flow and its critical choking phenomenon is studied.The cavitation noise signal produced by choked cavitation device is measured by hydrophone. The power spectrum characteristics of cavitation noise, the ratio of cavitation noise energy and the number and size of cavitation bubble are analyzed.Combined with the characteristics of choking phenomenon, the cavitation collapse mechanism of choked cavitation is studied, and the numerical simulation results and experimental results are verified.The results show that a low pressure region close to or below the saturated vapor pressure is formed in the upstream region of the choked pipe, and the gas holdup in the pipe increases rapidly, and the flow in the pipe changes from a single-phase flow to a gas-liquid two-phase flow.The local sonic speed of the two-phase flow in the choked pipe drops sharply and the local Mach number is close to 1.Under the pressure recovery gradient of up to 108Pa/m between upstream and downstream of the choked section, the number of cavitation bubbles of up to 106m and the diameter of 10-6m are rapidly collapsing, and the phenomenon of choking cavitation is formed.The backpressure of cavitation device is an important factor affecting the choking cavitation intensity. The optimum range of backpressure exists under certain cavitation structure and hydrodynamic parameters.The larger the flow rate is, the more favorable the formation of choking cavitation is, and the more cavitation bubbles are destroyed under the large flow rate, the choking ring can influence the position of the choked section and increase the pressure recovery gradient of the choked section under the condition of constant back pressure and flow rate.And the lower the back pressure, the more obvious the effect is.
【学位授予单位】：湖南工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV131.32;TV136

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