Flow asymmetry genesis in symmetric inlet loop pipe-nozzle systems: A mechanism for uneven power generation in Pelton turbines

Pelton turbines are widely adopted in high-head hydropower systems for their structural simplicity and hydraulic robustness. Despite their geometric symmetry, operational asymmetries are frequently observed. However, the underlying flow mechanisms responsible for such pseudo-symmetric behaviors (apparent symmetry in geometry resulting in measurable asymmetry in flow behavior) remain inadequately understood. In particular, the role of upstream flow structures in influencing jet development and runner performance remains unclear. This study combines high-fidelity numerical simulations with experimental validation to investigate the origin and evolution of asymmetric turbulent flow in a symmetric Pelton turbine system. Results reveal that the flow within the curved inlet loop pipe deflects toward the convex side due to a transverse energy gradient. This deflection results in a discharge imbalance of approximately 0.74 L/s between the left and right outlets. Although the internal nozzle support structure introduces partial straightening, flow asymmetry remains evident. Near the needle tip, jet deflection angles exceed 10°, and high-intensity rotational flow regions with a peak magnitude above 500 s−1 emerge. These asymmetric features in the upstream flow ultimately cause runner-side power and radial force deviations of up to 62.7 W and 7.2 N, respectively. These findings elucidate the multi-stage transmission and amplification of flow asymmetry in Pelton turbines and highlight the critical role of upstream flow conditioning—such as flow control devices or design modifications—in improving hydraulic stability and performance.