Investigation into Influence of Wall Roughness on the Hydraulic Characteristics of an Axial Flow Pump as Turbine

Kan Kan, Qingying Zhang, Yuan Zheng, Hui Xu, Zhe Xu, Jianwei Zhai and Alexis Muhirwa
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Kan Kan: College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China
Qingying Zhang: College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China
Yuan Zheng: College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China
Hui Xu: College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China
Zhe Xu: College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China
Jianwei Zhai: College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China
Alexis Muhirwa: Department of Renewable Energy, Rwanda Polytechnic—IPRC Tumba, Kigali 6579, Rwanda

Sustainability, 2022, vol. 14, issue 14, 1-20

Abstract: Pump as turbine (PAT) is a factual alternative for electricity generation in rural and remote areas where insufficient or inconsistent water flows pose a threat to local energy demand satisfaction. Recent studies on PAT hydrodynamics have shown that its continuous operations lead to a progressive deterioration of inner surface smoothness, serving the source of near-wall turbulence build-up, which itself depends on the level of roughness. The associated boundary layer flow incites significant friction losses that eventually deteriorate the performance. In order to study the influence of wall roughness on PAT hydraulic performance under different working conditions, CFD simulation of the water flow through an axial-flow PAT has been performed with a RNG k-ε turbulence model. Study results have shown that wall roughness gradually decreases PAT’s head, efficiency, and shaft power. Nevertheless, the least wall roughness effect on PAT hydraulic performance was experienced under best efficiency point conditions. Wall roughness increase resulted in the decrease of axial velocity distribution uniformity and the increase of velocity-weighted average swirl angle. This led to a disorderly distribution of streamlines and backflow zones formation at the conduit outlet. Furthermore, the wall roughness impact on energy losses is due to the static pressure drop on the blade pressure surface and the increase of turbulent kinetic energy near the blade. Further studies on the roughness influence over wider range of PAT operating conditions are recommended, as they will lead to quicker equipment refurbishment.

Keywords: wall roughness; axial flow pump; pump as turbine; hydraulic characteristics (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2022
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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