泵自吸过程两相流瞬变特性及其激励机制研究

Self-priming pump is a critical element in the energy, petrochemical and municipal fields. The stability of self-priming pump is strongly influenced by the complex two-phase flow structures and its excitation during the self-priming process. The main reason is the interference of high-speed flow and low-speed flow in the gas-liquid mixing area. However, the gas-liquid two-phase flow structures in the gas-liquid mixing area are still not fully revealed so far. The transient characteristics of gas-liquid mixed flow in the self-priming process of pump are the starting point of this project. The two-phase flow numerical method-CLSVOF/LES is generated. The experimental and numerical methods are used to investigate the temporal and spatial characteristics of unsteady vortex structures in the shear layer of gas-liquid mixing area in self-priming pump. The evolution progress of multi-scales vortex structures and cavitation flow structures are revealed with analysis of flow field data using the vortex dynamics theory, Proper Orthogonal Decomposition (POD) and spectrum analysis methods. The excitation sources are identified with measurement of pressure pulsation and structural responses signals. Cross-correlation functions are applied to analyze corresponding excitation features from vortices with different scales. Relations between vortex dynamics and structure response are established from the analysis. The outcomes of project provide a new explanatory on temporal and spatial characteristics of flow structures and its excitation mechanism in the self-priming pump and enrich the fundamental theory of self-priming pump. Finally, it can provide a theoretical support for optimizing the self-priming capability and vibration level of self-priming pump.

自吸泵在能源、石化、市政等领域至关重要，自吸过程中复杂的气液两相流动结构及其激励响应严重影响了自吸泵的运行稳定性，其主要原因在于气液混合区内高速流与低速流之间的干涉作用。但目前针对气液混合区内两相流动结构的研究尚不充分。本项目以泵自吸过程中气液流动结构的瞬变特性为出发点，建立高精度的CLSVOF/LES两相流数值计算方法，综合实验和数值计算研究自吸泵气液混合区内剪切层处不稳定涡的时空特性。基于涡动力学理论分析、本征正交分解、频谱分析等流场数据分析，揭示气液混合区内多重尺度涡结构和空泡流形态的演变规律。通过采集压力脉动、结构响应等信号并进行激励源识别，采用互相关函数分析不同尺度涡所对应的激励特性，构建涡动-响应关联关系。项目研究成果将对自吸泵内流动结构的时空特性及其激励特性作出新的诠释，丰富自吸泵基础理论，为自吸泵的自吸性能及振动性能优化提供理论支撑。

本项目以双叶片离心泵自吸过程中气液流动结构的瞬变特性为研究切入点，深入开展了以下几个方面的工作。首先，采用高速摄影技术开展了泵自吸过程气液瞬变特性实验研究，获取了不同自吸阶段泵内气泡体积分数及气泡流型的演变规律，揭示了自吸过程气液混合及气液分离机理；其次，基于自吸过程多尺度气泡流型，提出了考虑气泡大小和相间作用力的两组-双流体模型，开展了自吸过程的数值计算，分析了泵内气液两相相关物理量的时空特征，获取了不同自吸阶段泵内液体体积分数变化分布规律及气相运动规律，定量分析了回流孔位置及大小对自吸性能和水力性能的影响机制，给出了设计准则；再次，采用振动加速度传感器测量了不同自吸阶段的振动响应信号，辨识了结构响应的主要激励频率，揭示了非定常两相流动对振动响应的作用机制。项目研究成果对自吸泵内流动结构的时空特性及其激励特性作出了新的诠释，丰富了自吸式离心泵基础理论，为自吸式离心泵的优化设计提供了理论支撑。