Author(s): Magali Rodriguez; Gerald Muller

Linked Author(s):

Keywords: Ultralow-head hydropower; Irrigation canal; Supercritical flow; Stream wheel; Power generation

Abstract: Irrigation constitutes an important aspect of agriculture; around 20% of the world’s agricultural land is irrigated producing 40% of the total food production. As water is becoming scarcer, water-saving irrigation methods such as drip or sprinkler irrigation are becoming more popular. However, these systems require power to pressurize water. Electricity is usually not available on agricultural lands, and e.g. petrol or diesel powered pumps become very expensive. At the same time, in many irrigation systems, a significant amount of ultralow-head hydropower is available either in ramps, drop structures or in supercritical flow channels. For instance, in the irrigation system near Llíria (Spain), there is a 300 m long supercritical flow channel section with a velocity of 5.5 m/s, a slope of 0.03, a width of 1.6 m, with a water depth of 0.16 m at a Froude number of Fr = 4.4. The total available hydraulic energy of the flow is 124 kW; the kinetic energy of the flow is 21 kW. This hydropower could be used to drive pumps directly. Supercritical flow channels are here of particular interest because of the high energy density of the flow. A waterwheel would be the simplest way to extract power from this flow. It is a simple machine, there is no alteration of the channel required, and the wheel would sit on the sidewalls of the canal. Debris and sediment can pass through the wheel. Tests of such wheels have been reported in the literature, but most of the reported tests were conducted in situations with a near-horizontal bed, and no consistent theoretical model was described. At Southampton University, a research programme was initiated to develop such a supercritical flow wheel as hydropower converter for this specific application. 1:5 scale model tests were conducted for Fr = 2.6 to 3.5 and efficiencies ranged from 49% to 72% for tip speed ratios of 0.39 and 0.27 respectively. Based on the observations from the model, a theory for the s/c wheel in a sloped bed was developed. It was found that the hydraulic conditions obtained with a sloped bed are different from those of artificially induced supercritical flows in a near-horizontal bed as described in the literature. The theory showed good agreement with the model tests. It indicates that the efficiency increases with increasing Froude number. Combined with model test results and observations, the theory allows to develop solutions for different real world scenarios. The results from the work so far indicate that the supercritical wheel offers a simple, robust and cost-effective solution for power generation in fast flowing irrigation canals.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022807

Year: 2022