倒伞曝气机驱动的氧化沟内三相流机理研究

The flow state of air-liquid-solid three-phase mixture in the oxidation ditch directly determines the efficiency and stability of the sewage treatment system. In this project, based on the experiment and numerical simulation, the mechanism of three-phase flow in the oxidation ditch driven by inverted umbrella aerator is to be thoroughly studied.. A multi-parameter measuring method concerning three-phase flow in the oxidation ditch will be developed. The surface boundary of inverted umbrella aerator will be modeled, the searching and tracking method of three-phase liquid surface will be studied, and the IBM-VOF coupling numerical method which is more suitable for the three-phase flow in the oxidation ditch driven by the inverted umbrella aerator will be built. The trajectory of splash and the evolution of entrainment will be captured. The behavior characteristics of air bubble and the motion characteristics and accumulation position of solid particle will be studied. As a result of these, the interaction between liquid, air bubble and solid particle will be revealed. And, the change law of flow structure under three-phase action and its influence on the macroscopic performance will be studied. Then, the aeration mechanism of the inverted umbrella aerator will be explored. A mathematical model for the geometrical parameters of the aerator and the macro performance of the oxidation ditch will be established..The project aims at systematically expounding the mechanism of air-liquid-solid three-phase flow in the oxidation ditch driven by inverse umbrella aerator, and providing experimental data and theoretical basis for the development of multiphase flow in rotating machinery.

氧化沟内气-液-固三相混合流态直接决定了污水处理系统的效率和稳定性。本项目从试验测试和数值计算出发，深入研究倒伞曝气机驱动的氧化沟内三相流机理。. 发展氧化沟内三相流多参数测量技术；实现倒伞曝气机物面重构及模化，建立三相液面捕捉与追踪模型，构建适用于倒伞曝气机驱动的氧化沟内三相流动的IBM-VOF耦合计算模式，实现对含有旋转自由液面、自掺气、多相间相互作用等复杂流动现象的高效、准确预测；掌握水跃运动轨迹及卷吸的演化过程，研究气泡行为特性、颗粒运动特性及积聚位置，揭示液体、气泡、颗粒相间作用机理；研究三相作用下流动结构的变化规律及对宏观性能的影响，揭示倒伞曝气机充氧曝气机理，建立曝气机设计、运行参数与氧化沟宏观性能的数学模型。. 项目旨在系统揭示倒伞曝气机驱动的氧化沟内气-液-固三相流机理，为旋转机械多相流发展提供试验数据和理论基础。

倒伞曝气机驱动的曝气池内部三相流动较为复杂，涉及旋转自由液面、自掺气、水跃、卷吸、气泡聚并破碎、以及污泥颗粒沉降等过程。同时其曝气性能受叶轮转速、叶轮浸没深度、叶片数等参数影响较大，使得在内流分析和曝气性能预测等方面存在很多亟待解决的难题。主要研究内容如下：.1. 搭建了倒伞曝气机三相流和污泥沉降速率测试试验台，测量不同浓度下污泥沉降速率，建立沉降模型，研究倒伞曝气机在不同转速、不同浸没深度和不同污泥浓度下其曝气性能变化规律，测量在倒伞曝气机稳定运行时，曝气池内固定测点流速及污泥浓度。针对倒伞曝气机内存在气泡重叠黏连、反光等现象，无法直接通过高速摄影试验结果准确地提取气泡特征参数的问题，从中值滤波、分水岭分割处理、二值化与特征提取等环节出发，提出一种图像处理方法实现了气泡特征参数的有效提取。.2.综合考虑多相流模型、群体平衡模型、气泡破碎聚并模型和kLa传质方程，并在计算时赋予与试验相同的气泡特征参数，建立了一种能够准确模拟倒伞曝气机驱动下曝气池内部三相流方法，准确揭示了曝气机水跃、卷吸、气泡聚并及破碎、以及污泥颗粒沉降等过程。结果表明：气泡的聚并行为会造成速度损耗，而水跃和卷吸作用会促使环流旋涡形成，受环流漩涡影响卷吸的气体逐渐向底部运动。气体主要分布在浅层水体，同时浅层水体也是气－液－固三相混合区域，氧传质主要发生在混合区域内。污泥在曝气池内部分布都较为均匀，污泥的运动由于重力及污泥颗粒间相互作用力导致的竖直方向的沉降运动以及倒伞曝气机叶轮的离心力作用而导致的水平方向的离心运动两部分叠加。.3 .基于量纲分析法建立了倒伞曝气机曝气性能预测模型，解决了缩比样机无法预测原模型曝气性能的问题。建立一种基于试验设计和响应面的倒伞曝气机充氧性能优化设计方法。以叶片数，幅板倾斜角度，幅板间隙开度三个参数作为设计变量，以标准动力效率最高为目标，构建主要结构参数与目标的多元回归响应面模型。