Dynamic Characterization of Flow Separation on the Suction Side of a Pelton Turbine Bucket

Abstract

Antoine Leveaux, Master of Science in Energy Engineering/ Title: Dynamic Characterization of Flow Separation on the Suction Side of a Pelton Turbine Bucket/ Supervisors: Hillewaert Koen & Gervais Nicolas/

This master's thesis presents an in-depth experimental investigation into suction side flow separation in Pelton turbine buckets. Building on previous static studies, it introduces a dynamic setup using 2D extruded profiles from two Pelton runner geometries. The objective is to better understand flow detachment mechanisms and provide high-quality data to support CFD model development.

Six 2D profiles are tested under various hydraulic heads, speed ratios, and jet diameters. Mounted on a rotating wheel, the profiles interact dynamically with the water jet. High-speed imaging and precise measurements quantify separation characteristics, including detachment location and flow direction.

Results show hydraulic head as the most influential parameter, enhancing inertial effects and reducing viscous and surface tension forces. Speed ratio also affects separation behavior, especially at higher heads. Flow rate has limited impact on separation angle but increases separation length. Only three profiles (F1, F2, and S1) exhibited measurable separation, highlighting the role of geometry.

Dynamic testing captures realistic flow behavior but introduces challenges such as motion blur and increased measurement dispersion. These are mitigated through calibration and repeated measurements. Static testing offers clearer imaging but oversimplifies flow dynamics.

The Asphodel CFD tool, using Smoothed Particle Hydrodynamics (SPH), qualitatively reproduces some experimental trends but tends to over-predict separation onset and intensity. These discrepancies are largely due to the neglect of viscous and surface tension effects under low-head conditions.

Despite limitations of the 2D approach, the study provides valuable insights into flow separation mechanisms. Dimensionless numbers (Reynolds, Weber, cavitation) and velocity triangle analysis help interpret the influence of operating conditions.

In conclusion, this work contributes to a deeper understanding of flow separation in Pelton buckets and lays the groundwork for future research, including improved experimental techniques, refined CFD models, and 3D flow visualization.