Joint Assessment of Hydraulic Instabilities and Pressure-Fluctuation Signatures in a Pump as Turbine (PAT) Using Transient Computational Fluid Dynamics and Signal Processing

Miranda Lope J.C.; Navarro Ylachoque D.E.; Ocola Ticona E.H.; Bustamante Flores K.C.; Diaz Arapa C.A. · International Journal of Heat and Technology (2026) · DOI: 10.18280/ijht.440333

Resumen

Pump as Turbine (PAT) systems are a sustainable and cost-effective alternative for small-scale hydropower generation through the repurposing of conventional centrifugal pumps. However, off-design operation can induce hydraulic instabilities, vortex formation, pressure pulsations, and conditions favorable to cavitation, thereby affecting system performance and reliability. This study presents a transient Computational Fluid Dynamics (CFD) analysis of a centrifugal pump operating in turbine mode using ANSYS CFX. The numerical model employed the Scale-Adaptive Simulation Shear Stress Transport (SAS-SST) turbulence model together with the Schnerr-Sauer cavitation model to investigate hydraulic instabilities and cavitation susceptibility under transient operating conditions. Hydraulic performance was evaluated for different mass flow rates, identifying the most favorable operating condition at approximately 5 kg/s. Flow behavior was characterized using turbulent kinetic energy (TKE) contours and Q-criterion vortex identification, revealing intense vortex activity near the blade trailing edges and strong rotor-stator interaction in the volute tongue region. Pressure fluctuation signals extracted at critical locations were analyzed using the Fast Fourier Transform (FFT) and the Short-Time Fourier Transform (STFT). A dominant spectral peak was identified at approximately 94.45 Hz, close to the second rotational harmonic of the impeller shaft frequency, indicating that the impeller region is the primary source of dynamic excitation. The results demonstrate a strong relationship between off-design operation, vortex activity, low-pressure regions, and increased pressure fluctuations. Finally, an operational map was proposed to classify stable, transient, and instability-prone operating regions, providing practical guidance for the safe operation of PAT systems in small-scale hydropower applications.

Instituciones: Universidad Nacional de San Agustín de Arequipa