학술논문
비속도 170급 프란시스 수차: Thoma number 변화에 따른 정격 조건에서의 과도상태 유동특성
Document Type
Academic Journal
Author
Source
에너지공학. 2024-03 33(1):31-43
Subject
Language
Korean
ISSN
1598-7981
2713-7074
2713-7074
Abstract
본 연구에서는 프란시스 수차의 운전 안정성과 캐비테이션 발생 가능성을 예측하는데 주로 사용되는 지표인 Thoma number의 변화에 따른 수차의 수력학적 성능과 유동 특성 분석 연구를 수행하였다. 수치해석을 통하여 캐비테이션 발달을 정밀하게 예측하기 위해 다상 모델 및 Unsteady Reynolds-averaged Navier-Stokes 방정식을 사용하였다. 수치해석의 정확성을 확보하기 위하여 격자 의존성 시험을 수행하였고, 실험 및 수치해석의 결과를 비교함으로써 수치 해석 모델의 유효성을 입증하였다. Thoma number의 변화에 따른 유동 특성 분석을 위해 선정된 두 개의 Thoma number (0.1211 및 0.3633) 조건에서 수력학적 성능은 비슷한 결과를 나타내었다. Thoma number가 낮은 경우 가이드 베인과 러너 사이의 영역에서는 비정상적인 압력 패턴이 더욱 발달하였으나 러너 영역에서는 Thoma number에 상관없이 유사한 유동특성을 보였다. 드래프트 튜브에서의 유동 특성을 비교한 결과, Thoma number에 따른 축 방향 속도 및 원주 방향 속도의 변화가 크지 않음을 확인하였다. 따라서 정격 조건에서의 Thoma number 변화는 러너 및 드래프트 튜브에서의 압력 맥동 및 유동 특성에 큰 영향을 주지 않는 것으로 분석하였다. 이러한 연구 결과는 프란시스 수차의 설계 및 운전에 관한 연구에서 활용될 수 있다.
Francis turbine is efficient at converting hydraulic to mechanical energy, but it faces stability issues and cavitation problems at different outlet pressures. Thoma number ( ) influences cavitation even at rated conditions, leading to erosion and pressure fluctuations, which can cause turbine component failures. In the current study, a 170-class Francis turbine that was operating at rated condition underwent a detailed examination to evaluate its performance and flow behaviour under various Thoma numbers. For accurate flow physics description, we employed the Unsteady Reynolds-averaged Navier-Stokes equation. The two-phase model was used to simulate cavitation, and the Grid Convergence Index was used to guarantee grid accuracy. Our numerical approach dependability was proven by comparison with experimental data. For both (0.1211 and 0.3633), constant hydraulic performance with no appreciable variations was observed. In the vaneless area, abnormal pressure patterns were visible, including the initial blade passing frequency. Except for pressure fluctuations brought on by variations in output pressure, flow properties like meridional velocity and flow angle remained constant in the runner region regardless of . Within the draft tube, the axial and circumferential velocities were identical. Thoma numbers changed the maximum pressure pulsation magnitude, but no discernible differences were seen. In conclusion, the turbine showed no noticeable effects at rated operation with varying Thoma numbers under cavitation-prone situations. Further off-design investigations can be conducted based on the present methodology and compared accurately with the rated condition results.
Francis turbine is efficient at converting hydraulic to mechanical energy, but it faces stability issues and cavitation problems at different outlet pressures. Thoma number ( ) influences cavitation even at rated conditions, leading to erosion and pressure fluctuations, which can cause turbine component failures. In the current study, a 170-class Francis turbine that was operating at rated condition underwent a detailed examination to evaluate its performance and flow behaviour under various Thoma numbers. For accurate flow physics description, we employed the Unsteady Reynolds-averaged Navier-Stokes equation. The two-phase model was used to simulate cavitation, and the Grid Convergence Index was used to guarantee grid accuracy. Our numerical approach dependability was proven by comparison with experimental data. For both (0.1211 and 0.3633), constant hydraulic performance with no appreciable variations was observed. In the vaneless area, abnormal pressure patterns were visible, including the initial blade passing frequency. Except for pressure fluctuations brought on by variations in output pressure, flow properties like meridional velocity and flow angle remained constant in the runner region regardless of . Within the draft tube, the axial and circumferential velocities were identical. Thoma numbers changed the maximum pressure pulsation magnitude, but no discernible differences were seen. In conclusion, the turbine showed no noticeable effects at rated operation with varying Thoma numbers under cavitation-prone situations. Further off-design investigations can be conducted based on the present methodology and compared accurately with the rated condition results.