2024
Zhang, Chenying; Wang, Wenjie; Pavesi, Giorgio; Yuan, Shouqi; Pei, Ji
Research on the mechanism of severe unsteadiness of PAT braking condition during the power failure Journal Article
In: Renewable Energy, vol. 232, 2024, ISSN: 18790682.
Abstract | Links | BibTeX | Tags: Braking conditions, CFD numerical simulation, Energy loss, Pump as Turbine, Transient characteristics, Unsteady Flow Evolution
@article{Zhang2024,
title = {Research on the mechanism of severe unsteadiness of PAT braking condition during the power failure},
author = {Chenying Zhang and Wenjie Wang and Giorgio Pavesi and Shouqi Yuan and Ji Pei},
doi = {10.1016/j.renene.2024.121019},
issn = {18790682},
year = {2024},
date = {2024-01-01},
journal = {Renewable Energy},
volume = {232},
publisher = {Elsevier Ltd},
abstract = {The Pump-As-Turbine (PAT) technology has become popular in micro hydropower stations due to its simple installation and cost-effectiveness. Nevertheless, power failures present a substantial risk to the secure and steady functioning of PAT's braking system. The commercial CFD code (ANSYSCFX) is improved by incorporating a secondary development to model the power-off transition using Fortran accurately. This enhancement allows for real-time iterative calculations of angular momentum equations for mixed-flow PAT at different speeds. Meanwhile, the time–frequency domain analysis is utilized to analyze pressure pulsation signals and the evolution of the internal flow field in mixed-flow PAT. An investigation was conducted to have a deeper understanding of braking circumstances. The results revealed that the main frequency of the pressure pulsation aligns with the blade frequency at various flow rates, and there is a sudden change in pressure amplitude during the braking phase. The impeller experienced the majority of energy losses, with the draft tube being the subsequent area of concern. In addition, a thorough examination and comparison of the changes in the internal flow field during braking were carried out. This analysis revealed a distinct double helix structure within the draft tube, with a slower inner helix and a faster outer helix. Furthermore, it was observed that there is a strong correlation between wall shear stresses and hydraulic losses on the blade surface. This research enhanced understanding of the flow characteristics of mixed-flow PAT can help improve system safety and provide valuable guidance for future optimization efforts.},
keywords = {Braking conditions, CFD numerical simulation, Energy loss, Pump as Turbine, Transient characteristics, Unsteady Flow Evolution},
pubstate = {published},
tppubtype = {article}
}
The Pump-As-Turbine (PAT) technology has become popular in micro hydropower stations due to its simple installation and cost-effectiveness. Nevertheless, power failures present a substantial risk to the secure and steady functioning of PAT's braking system. The commercial CFD code (ANSYSCFX) is improved by incorporating a secondary development to model the power-off transition using Fortran accurately. This enhancement allows for real-time iterative calculations of angular momentum equations for mixed-flow PAT at different speeds. Meanwhile, the time–frequency domain analysis is utilized to analyze pressure pulsation signals and the evolution of the internal flow field in mixed-flow PAT. An investigation was conducted to have a deeper understanding of braking circumstances. The results revealed that the main frequency of the pressure pulsation aligns with the blade frequency at various flow rates, and there is a sudden change in pressure amplitude during the braking phase. The impeller experienced the majority of energy losses, with the draft tube being the subsequent area of concern. In addition, a thorough examination and comparison of the changes in the internal flow field during braking were carried out. This analysis revealed a distinct double helix structure within the draft tube, with a slower inner helix and a faster outer helix. Furthermore, it was observed that there is a strong correlation between wall shear stresses and hydraulic losses on the blade surface. This research enhanced understanding of the flow characteristics of mixed-flow PAT can help improve system safety and provide valuable guidance for future optimization efforts.
2021
Yin, Tingyun; Pavesi, Giorgio; Pei, Ji; Yuan, Shouqi
Numerical analysis of unsteady cloud cavitating flow around a 3D Clark-Y hydrofoil considering end-wall effects Journal Article
In: Ocean Engineering, vol. 219, iss. April 2020, pp. 103506, 2021, ISSN: 00298018.
Abstract | Links | BibTeX | Tags: Three-dimensional Hydrofoil, Transient characteristics, Unsteady Cloud Cavitation
@article{Yin2021b,
title = {Numerical analysis of unsteady cloud cavitating flow around a 3D Clark-Y hydrofoil considering end-wall effects},
author = {Tingyun Yin and Giorgio Pavesi and Ji Pei and Shouqi Yuan},
url = {https://www.sciencedirect.com/science/article/pii/S0029801820312762?utm_campaign=STMJ_AUTH_SERV_PUBLISHED&utm_medium=email&utm_acid=30163317&SIS_ID=&dgcid=STMJ_AUTH_SERV_PUBLISHED&CMX_ID=&utm_in=DM110556&utm_source=AC_ https://www.sciencedirect.com/scienc},
doi = {10.1016/j.oceaneng.2020.108369},
issn = {00298018},
year = {2021},
date = {2021-01-01},
journal = {Ocean Engineering},
volume = {219},
issue = {April 2020},
pages = {103506},
publisher = {Elsevier Ltd},
abstract = {This study employs an incompressible homogeneous flow framework with a transport equation based cavitation model and density corrected Shear Stress Transport (SST) k-ω turbulence model to successfully reproduce the unsteady cavitating flow around a 3D Clark-Y hydrofoil with an end wall. Cavity growth, development, and break-off during the periodic shedding process are adequately reproduced and match experimental observations. The predicted shedding frequency is very close to the experimental value of 43.48 Hz. The existence of an end wall brings about the generation and convection of wall-side cavity. Moreover, large horse-type cavity structure is captured, which agrees with experimental results. Cavities at the closure region easily detach from the main pocket part resulting in a secondary vortical structure. Differences between numerical and experimental lift are observed, however, similar to our previous findings, the experimental lift coefficient appears to correlate with the inverse of the second derivative of the total cavity volume. Based on the analysis of vorticity transportation, compressibility source occupies the highest contribution of vorticity transportation and is significantly higher than other two terms, which serves the promotion effect at the trailing region of growing attached cavity while inhibits the development of vorticity within the leading area.},
keywords = {Three-dimensional Hydrofoil, Transient characteristics, Unsteady Cloud Cavitation},
pubstate = {published},
tppubtype = {article}
}
This study employs an incompressible homogeneous flow framework with a transport equation based cavitation model and density corrected Shear Stress Transport (SST) k-ω turbulence model to successfully reproduce the unsteady cavitating flow around a 3D Clark-Y hydrofoil with an end wall. Cavity growth, development, and break-off during the periodic shedding process are adequately reproduced and match experimental observations. The predicted shedding frequency is very close to the experimental value of 43.48 Hz. The existence of an end wall brings about the generation and convection of wall-side cavity. Moreover, large horse-type cavity structure is captured, which agrees with experimental results. Cavities at the closure region easily detach from the main pocket part resulting in a secondary vortical structure. Differences between numerical and experimental lift are observed, however, similar to our previous findings, the experimental lift coefficient appears to correlate with the inverse of the second derivative of the total cavity volume. Based on the analysis of vorticity transportation, compressibility source occupies the highest contribution of vorticity transportation and is significantly higher than other two terms, which serves the promotion effect at the trailing region of growing attached cavity while inhibits the development of vorticity within the leading area.
