Abstract
Efficiency is a critical consideration in the design of hydro turbines. The crossflow turbine is the cheapest and easiest hydro turbine to manufacture and so is commonly used in remote power systems for developing countries. A longstanding problem for practical crossflow turbines is their lower maximum efficiency compared to their more advanced counterparts, such as Pelton and Francis turbines. This paper reviews the experimental and computational studies relevant to the design of high efficiency crossflow turbines. We concentrate on the studies that have contributed to designs with efficiencies in the range of 88–90%. Many recent studies have been conducted on turbines of low maximum efficiency, which we believe is due to misunderstanding of design principles for achieving high efficiencies. We synthesize the key results of experimental and computational fluid dynamics studies to highlight the key fundamental design principles for achieving efficiencies of about 90%, as well as future research and development areas to further improve the maximum efficiency. The main finding of this review is that the total conversion of head into kinetic energy in the nozzle and the matching of nozzle and runner designs are the two main design requirements for the design of high efficiency turbines.
Highlights
The turbine is the core component of hydropower systems and improving its efficiency, defined as the ratio of power extracted from the water to the product of the mass flow rate, gravity, and available head at the turbine
The review revealed that crossflow turbines can achieve 90% efficiency
A systematic computational study for matching the nozzle and runner designs, which is an important criterion not investigated in detail in the literature, has been performed in [5]
Summary
The turbine is the core component of hydropower systems and improving its efficiency, defined as the ratio of power extracted from the water to the product of the mass flow rate, gravity, and available head at the turbine. Β 1 = tan−1 uθ − ωR1 where subscript “r” indicates a radial, and “θ” a tangential component, and it is assumed that the runner entry velocities are uniform This is Equation (10) of Adhikari and Wood [2]. By matching kinetic energy at the runner entry to the product of runner torque and ω, and assuming that no angular momentum exits the second stage, Equation (14) of Adhikari and Wood [2] gives the optimum ω, ωmax , for nozzle velocity U0 according to h20. Adhikari [5] characterized the main flow features of 8–90% efficient turbines, and applied these to improve the efficiency of a turbine measured at 67–91% We anticipate that these results provide fundamental design principles for further improvement of ηmax.
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