基于CFD分析的文丘里流量计设计优化

质量流量是核电站热功率核算的关键参数之一，核电站一般采用文丘里流量计和孔板流量计同时测量，然而在低流量区文丘里流量计呈现出明显波动，其参数不稳定严重影响核电站的正常运行。本文基于理论分析结合数值分析，发现脉动流动是导致文丘里流量计测量波动的主要原因。基于分析结果，对文丘里流量计提出了优化设计方案，通过在文丘里管上游集成流量调整装置，从而减小脉动流，有效提升文丘里流量计的稳定性。此外，开展了集成不同类型流量调整装置的文丘里流量计压损特性数值研究，结果表明K-Lab型流量调整装置阻力较小。本文提出的方案可有效提升文丘里流量计测量精度。

Optimal Design of Venturi Flowmeter Based on CFD Analysis

In the second loop of the nuclear power plants, the coolant mass flow is one of the critical parameters for calculating thermal power and also determining the control of the steam generator. Generally, Venturi flowmeter is used to measure the main feedwater flow in nuclear power plants for its high accuracy, wide application, simple construction, and reliability. However, when measuring the low mass flow, the Venturi flowmeter shows an obvious fluctuation, which would result in a significant measurement error, and serious influence on the normal operation control of nuclear power plants. In order to satisfy the need of high accuracy in measuring the coolant mass flow under a wider mass flow range, it is essential to figure out the possible reasons for the measurement error and propose an accurate manufacturing technology to improve the measurement accuracy of Venturi flowmeter. In this paper, through modling the full-size Venturi flowmeter and its upstream and downstream pipelines, the measurement results of the Venturi flowmeter and orifice flowmeter were compared based on the theoretical analysis and numerical analysis. It is found that the measurement results of Venturi flowmeter fluctuate significantly in the low mass flow stage. Based on the measurement principle of differential pressure flowmeter, it is deduced through theoretical analysis that the main reason for the error of Venturi flowmeter in turbulent pulsating flow is that the derivative term in the flow equation is omitted when the differential pressure data is converted into flow output. Based on the analysis of the flow field in the Venturi flowmeter, the vortex distribution in the upstream venturi is significantly improved, and the stability of the Venturi flowmeter is effectively reduced. Through computational fluid dynamics (CFD) numerical simulation, a detailed comparative analysis was carried out to investigate the characteristics of flow stability and resistance before and after optimization. The comparison results of the measured mass flow show that the flow adjustment equipment can improve the stability in mass flow measurement. The feasibility of the optimized design scheme is demonstrated. In addition, the numerical study was carried out to investigate the pressure loss characteristics of Venturi flowmeter integrating different typical types of flow adjustment equipment, including Gallagher, K-Lab, NEL (Spearman), and Zanker. The numerical results show that the resistance of K-Lab flow adjustment equipment is minor. The scheme proposed in this paper can effectively improve the measurement accuracy of Venturi flowmeter and guide the performance improvement of Venturi flowmeter in engineering applications.