Energy Conversion and Management: X (Apr 2025)
Verification of a very low-head axial turbine design using multiphase flow model for energy resource utilization from open canal: A case at Tana Beles sugar irrigation system, Ethiopia
Abstract
The Tana Beles dual-purpose project comprises an upstream hydropower plant and a downstream sugar irrigation system, serving as a pilot study site. This research aims to verify an existing Very Low-Head Axial Turbine (VLHT) design through unsteady free surface (UFS) simulations using the Ansys CFX Multiphase Flow Homogeneous Model. The existing design utilized steady single-phase (SSP) and unsteady single-phase (USP) simulations with a free-slip wall at the canal’s top, employing the Reynolds-averaged Navier-Stokes equation. Both the existing and current CFD simulations employ hexahedral meshes, an inflation technique near walls, and the Shear Stress Turbulence (SST) model. The VLHT is intended to provide power for rural communities near the canal.The UFS simulation predicted flow depth and free surface location in all canals without significant air entrainment except at the energy dissipator. It helped determine side wall heights to prevent overflow at the VLHT design point. Key metrics like mechanical power, hydraulic efficiency, head losses, energy grade line, VLHT discharge, and spillover flow were quantified.Due to the canal’s low-speed flow (1–2 m/s) and the VLHT runner’s low rotational speed (40 rpm), the performance parameters obtained from SSP/USP and UFS simulation produced nearly similar results. As such, SSP/USP simulation is considered adequate for such low-speed applications. However, the UFS simulation revealed significant flow features unconsidered in the SSP/USP approach, such as the distinct air–water interface, the location of air entrainment, and hydraulic jumping. These flow characteristics could significantly affect VLHT performance and must be examined for reliable evaluation in high-speed flow turbine design.
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