摘要
本学位论文分为两部分内容：一部分为空化区掺气泡与空泡相互作用的研究,另一部分为水力空化多孔板空化区紊动空化特性的研究。
高速水流由于其特殊性不能按一般水力学问题进行分析,它涉及到很多方面问题：水流脉动、掺气、空化空蚀、消能防冲、雾化等等。其中,空化空蚀是国内外水力学专家最为关注的重点和难点之一。当水流速度达到一定程度时,水流压强低于相应的饱和蒸汽压强,水流内部形成空穴,这就是空化现象。空化水流由低压区流到较高压力区时,空泡溃灭便会产生空蚀破坏。空化空蚀由于是流体内部随机的复杂现象,因此从微观上弄清机理才能揭示空化空蚀的规律。一方面,空化空蚀对人们有负面影响,比如破坏泄水建筑物表面,损坏水力机械等等；另一方面,空化空蚀对人们有正面影响,比如处理难降解废水,切割钢板等等。因此对于空化空蚀的研究而言,在特定的情况下减免或加强空化空蚀,更能增加研究的完整性。
本文第一部分是以减少空化空蚀的负面影响作用为出发点,对空化区掺气泡与空泡相互作用进行了试验研究。随着我国水利建设中高坝建筑日益增多,高速水流带来的空化空蚀不容忽视。研究表明,为减免高速水流空化产生的空蚀破坏,经济且有效的措施是在低压空化区或在易发生空蚀部位上游设置掺气设施强迫掺气。为了合理地利用掺气抑制空化或减免空蚀破坏,必须掌握掺气减蚀的机理。迄今为止,人们主要对空泡与空泡之间的相互作用进行了研究,而对掺气条件下空化区掺气泡与空泡的相互作用的研究甚少。本文在浙江工业大学水力学实验室的直流式水洞中采用三维粒子测速仪(PIV)、高速摄影机、SINOCERA-YE6263压力数据采集系统等先进的量测仪器,对半圆柱与圆柱突体空化区掺气泡与空泡相互作用进行了试验研究。考虑不同掺气浓度、不同流速对空化区掺气泡与空泡相互作用的影响,研究表明：所拍摄的粒子图像和高速摄影图片与Manage系统处理得到的流场速度矢量图基本一致。高速摄影观察表明流速和掺气浓度对空泡与掺气泡互相作用的影响不是独立的。掺气能缩减空化云的范围,所需要的掺气浓度随着流速的增大而不断递减,并给出了有效掺气浓度与流速的经验公式。
本文第二部分是以利用空化空蚀的正面影响作用为出发点,对水力空化多孔板空化区的紊动空化特性进行了试验研究和数值模拟。随着工业化的发展,含有大量难降解有机物的工业废水逐年增多,对人们的健康构成了严重的威胁。水力空化是近年来发展起来的一种处理难降解废水的新技术,对于解决全球的水污染问题具有重大意义。本文基于计算流体力学软件FLOW-3D,数值模拟了不同孔口形状(矩形、三角形、圆形)多孔板下游的紊动特性,包括紊动能、紊动强度和雷诺应力的变化规律,并考虑不同流速、孔口数量、大小及其布置方式的影响。采用SINOCERA-YE6263压力数据采集系统对每种孔口形状(矩形、三角形、圆形)多孔板下游的压力特性进行了试验研究,分析了孔口数量、大小及其布置方式对多孔板下游压力的时均和频谱特性的影响,对水力空化装置的多孔板进行优化设计并得出了最有利于空化的多孔板。
This thesis has included two main parts:(1) Experimental study on interaction between aeration bubbles and cavitation bubbles of cavitation region;(2) Numerical simulation and experimental study on turbulence cavitation characteristics of hydrodynamic cavitation advice with multi-orifice plates.
High-velocity flow can not be analyzed according to the general hydraulics problems because of its specificity, involving many aspects such as fluctuation of flow, aeration, cavitation, energy dissipation and atomization etc. Cavitation is the focus and difficulty which concerned by hydraulics experts at home and abroad. When the flow velocity reaches a certain value and flow pressure is lower than the relevant saturated vapor pressure, the hole, hollow or cavity will occur inside of the flow, which is the phenomenon of cavitation. Cavitation erosion arises from the cavity flow from low-pressure to higher pressure. It is necessary to reveal the mechanism law of cavitation on microscopic, because of the complexity phenomenon of the fluid internal. On the one hand, cavitation has a negative impact, such as destruction of the surface of the discharge structures, damage of hydraulic machinery, etc. On the other hand, it has a positive impact, such as treating hard-biodegradable pollutants, cutting steel plates, etc. Therefore, it can be enhance the integrity of the research to study to prevent or strengthen the cavitation in particular situation.
In the first part, the relation between aeration bubbles and cavitation bubbles are experimental studied based on reducing cavitation erosion as a starting point. With the development of hydropower and hydraulic, the increase of discharge structure from high dams, the cavitation cause by high-velocity flow can not be ignored. In order to prevent the problem of cavitation damage because of high-velocity flow, an economic and effective measure is to set up aerators for generating forced aeration in the low-pressure cavitation regions or upper locations liable to cavitation erosion. It is necessary to study the mechanism of aeration to prevent the cavitation damage. So far, the research only on the interaction between cavitation bubbles mainly, but there is little study of interactions between aeration bubble and cavitation bubble in the cavitation region on the condition of aeration. The interaction between aeration bubbles and cavitation bubbles of cavitation region of the semi-cylindrical and cylindrical irregularities were observed in details by using three-dimensional Particle Image Velocimetry, high speed photography, and the pressure data acquisition system of Sinocera-YE6263in the Hydraulics Laboratory at Zhe Jiang University of Technology. The effects of interaction between aeration bubbles and cavitation bubbles at different gas concentrations and different flow velocities were considered. The experimental results showed that the particle images and high-speed photographs captured were consistent with velocity vector handling by the manage system. The effects of velocity and gas concentration to the interaction between aeration bubbles and cavitation bubbles were not independent through high-speed photographs. The range of cavitation cloud reduced on aeration. The empirical formula of the effective gas concentration and velocity was given, which shown that the effective gas concentration decreasing with increasing of velocity.
The second part is based on using the positive effects of cavitation as a starting point. Turbulence cavitation characteristics of hydrodynamic cavitation advice with multi-orifice plates were numerical simulated and experimental studied. With the process of industrialization, it is a serious threat to human's health with wastewater which contains large amounts of hard-biodegradable pollutants. Hydrodynamic cavitation is a new method to treat hard-biodegradable pollutants in recent years, which of great significance to solve the global water pollution problem. This paper was based on the hydrodynamic software FLOW-3D, the turbulence characteristics of multi-orifice plates with different shapes (rectangular, triangle, circle) were numerical simulated, such as turbulent kinetic energy, turbulence intensity and Reynolds stress. The effect of different velocities, multi-orifice plates with different size, number and arrangement were considered. The pressure characteristics behind multi-orifice plates were experimental studied by the pressure data acquisition system of SINOCERA-YE6263. The effect of multi-orifice plates with different size, number and arrangement to the time average pressure and frequency spectrum were considered. The multi-orifice plate which is most conducive to cavitation was obtained by optimization.
引文
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