프란시스 수차 캐비테이션 불안정성 인자에 대한 정량적 평가 연구
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Abstract
This paper presents a quantitative evaluation of cavitation-induced instabilities in a Francis hydroturbine. This approach combines a one-dimensional (1D) hydroacoustic model with three-dimensional (3D) CFD analysis. The 1D model incorporates hydraulic inductance, resistance, and draft-tube geometric divergence, as well as cavitation parameters such as wave speed, cavitation compliance, mass-flow gain factor, and bulk viscosity. This enables the prediction of pressure fluctuations, draft-tube cavitation behavior, and transient shutdown characteristics. Complementary 3D CFD simulations using ANSYS CFX yield detailed performance curves of the turbine. The 1D model captures the dynamic hydraulic behavior during guide-vane closure. The combined approach identifies unstable operating regions and characterizes the cavitation compliance, mass-flow gain factor, and wave-speed variation as functions of discharge and cavitation number. It provides a robust framework for evaluating dynamic mechanisms governing cavitation instability in Francis turbines.