유연화 운전 범위에서의 프란시스 수차 축소 및 실물 모형 구조안정성 연구
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Abstract
Hydraulic turbines, essential for making accurate predictions of structural behavior under varying hydraulic loads, are increasingly operated under flexible conditions to support modern electricity grids. This study presents a comparative fluid-structure interaction (FSI) analysis of scaled-down and full-scale prototype Francis turbine models over a wide range of unit discharges representative of flexible operation. High-fidelity computational fluid dynamics (CFD) simulations capture the evolution of internal flow structures from part-load vortex-rope behavior to overload trailing-edge separation, whereas mapped transient pressure fields enable the structural evaluation of equivalent stress and total deformation. The results showed that the hydraulic performance improved toward the best efficiency point, whereas part-load conditions exhibited a strong vortex region and eddies in the blade passage. The prototype experienced significantly higher stress (100–120 MPa) and deformation (0.44–0.50 mm) than the scale-down model (<20 MPa, <0.01 mm). Based on the normalized results, the similarity between the scaled-down and prototype runners was most consistent with hydraulic performance, whereas pronounced deviations occurred in the structural analysis. This behavior demonstrates that scaled-down model predictions cannot be directly extrapolated to full-scale without accounting for scale-dependent structural effects, thereby emphasizing the importance of an integrated FSI analysis in evaluating runner stability across flexible operating regimes.