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Effect of Blade Number on Internal Flow and Performance Characteristics in Low-Head Cross-Flow Turbines

Author

Listed:
  • Ephrem Yohannes Assefa

    (Institute of Energy, Mekelle University, Mekelle P.O Box 231, Ethiopia
    School of Mechanical and Industrial Engineering, Ethiopian Institute of Technology-Mekelle, Mekelle University, Mekelle P.O. Box 231, Ethiopia)

  • Asfafaw Haileselassie Tesfay

    (Institute of Energy, Mekelle University, Mekelle P.O Box 231, Ethiopia
    School of Mechanical and Industrial Engineering, Ethiopian Institute of Technology-Mekelle, Mekelle University, Mekelle P.O. Box 231, Ethiopia
    Department of Civil and Environmental Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway)

Abstract

Cross-flow turbines are widely used in microhydropower systems because of their cost-effectiveness, environmental sustainability, adaptability, and robust design. However, their relatively lower efficiency than other turbine types limit their application in large-scale projects. Previous studies have identified poor flow profiles as a significant factor contributing to inefficiency, with the number of blades playing a critical role in the flow behavior, efficiency, and structural stability. This study employed numerical simulations to analyze how varying the number of blades affects the internal flow characteristics and performance of the turbine at, and off, its best operating points. Configurations with 16, 20, 24, 28, 32, 36, 40, and 44 blades were investigated under constant low-head conditions, fully open valve settings, and varying runner speeds. Simulations were performed using ANSYS CFX, incorporating steady-state conditions, a two-phase flow model with a movable free surface, and a shear stress turbulence model. The results indicate that the 28-blade configuration achieved a maximum hydraulic efficiency of 83%, outperforming the preset 24-blade setup by 6%. Flow profiles were examined using pressure and velocity gradients to identify regions of adverse pressure. Due to the impulse nature of the turbine, the flow profile is more sensitive to changes in the flow speed than to pressure. The flow trajectory showed stability in the first stage but exhibited discrepancies in the second stage, which were attributed to turbulence, recirculation, and shaft flow impingement. The observed performance improvements were linked to reduced hydraulic losses due to flow separation and friction, emphasizing the significance of the number of blades and the regions of optimal efficiency under low-head conditions.

Suggested Citation

  • Ephrem Yohannes Assefa & Asfafaw Haileselassie Tesfay, 2025. "Effect of Blade Number on Internal Flow and Performance Characteristics in Low-Head Cross-Flow Turbines," Energies, MDPI, vol. 18(2), pages 1-32, January.
    • Handle: RePEc:gam:jeners:v:18:y:2025:i:2:p:318-:d:1565711
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    References listed on IDEAS

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    1. Acharya, Nirmal & Kim, Chang-Gu & Thapa, Bhola & Lee, Young-Ho, 2015. "Numerical analysis and performance enhancement of a cross-flow hydro turbine," Renewable Energy, Elsevier, vol. 80(C), pages 819-826.
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    Cited by:

    1. Fengxia Shi & Xuexue Zong & Guangbiao Zhao & Denghui Zhang & Pengcheng Wang & Haonan Zhan, 2025. "Study on the Influence of Split Blades on the Force Characteristics and Fluid–Structure Coupling Characteristics of Pumps as Turbines," Energies, MDPI, vol. 18(7), pages 1-19, March.
    2. Ephrem Yohannes Assefa & Asfafaw Haileselassie Tesfay, 2025. "Effect of Blade Profile on Flow Characteristics and Efficiency of Cross-Flow Turbines," Energies, MDPI, vol. 18(12), pages 1-33, June.

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