Physics-guided diagnostic framework for hydro-abrasive erosion and efficiency degradation in Francis turbines

Hydro-abrasive erosion in sediment-laden rivers reduces Francis turbine life and hydraulic efficiency. Although Eulerian–Lagrangian simulations can predict particle trajectories, impacts, and erosion patterns, their computational cost limits routine prototype-scale application. This study presents a physics-guided framework using single-phase clear-water hydrodynamics to identify erosion-prone regions and track efficiency loss under steady and quasi-steady conditions. A prototype HLJF1809-LJ-108 Francis turbine operating under severe sediment exposure was investigated. After 24 months, inspections showed irregular leading-edge recession, localized material loss of 3–5 mm, and non-uniform deterioration over 40%–60% of the suction-side surface. Efficiency declined from 92% to 85%–88%, equivalent to a cumulative loss of 4-7 percentage points. A precursor criterion based on the 90th percentile of turbulent kinetic energy (TKE) was developed. High-TKE regions covered 38%–44% of the runner-blade wetted surface, closely matching observed erosion and DPM-predicted impact zones. A reduced-order feedback model described how early roughness increases near-wall turbulence and accelerates localized material loss before hydrodynamic saturation. Integrating the TKE-based susceptibility index produced an erosion-exposure indicator correlated with measured efficiency degradation. The framework distinguishes cumulative efficiency deficit, ( Δ η cum ), from exposure-dependent incremental loss, ( Δ η E ), supporting rapid hotspot screening, maintenance planning, and erosion-risk assessment, although site-specific recalibration remains necessary.