Abstract
The crossflow turbines commonly used in small hydropower systems have a single nozzle. We are unaware of any studies of double-nozzle crossflow turbines which could have twice the power output of the single-nozzle design by doubling the flow through the same runner, with a high maximum efficiency. We present a computational analysis of a double-nozzle crossflow turbine, to determine the turbine efficiency and fundamental flow patterns. This work was based on a single-nozzle crossflow turbine with a maximum efficiency of 88%, one of the highest reported in the open literature through extensive experimental measurements. Previous numerical studies on this turbine have shown that the water flow in the runner was confined to less than half the runner periphery, implying that the other half could be used to double the runner power output by employing a second nozzle. We show that adding a second, identical nozzle without making any other changes to the design achieves a doubling of the power output. The dual-nozzle turbine, therefore, has the same efficiency as the original turbine. We also investigate the use of a slider to control the flow at part-load and show that part-load efficiency of the double-nozzle is very similar to that of the original turbine. This demonstrates the feasibility of using two nozzles for crossflow turbines.
Highlights
Crossflow turbines are used in small hydropower systems, mainly in the remote locations in developing countries, due to their inherent simplicity in design and low manufacturing cost
The main purpose of this paper is to evaluate the maximum efficiency of the double-nozzle design at maximum and part-flow operations compared to the single-nozzle case of [5] as studied by Adhikari [10] and Adhikari and Wood [8]
We have presented the first computational analysis of a double-nozzle crossflow turbine based on a single-nozzle 0.53 kW turbine with a maximum efficiency of 88%
Summary
Crossflow turbines are used in small hydropower systems, mainly in the remote locations in developing countries, due to their inherent simplicity in design and low manufacturing cost. Desai [5] and Totapally and Aziz [6] achieved a maximum efficiency ηmax of 88% and 90% respectively for a small-scale 0.53 kW turbine through extensive experimental development, no larger turbines of similar performance have been built and tested. The turbine works on the principle that head is converted into kinetic energy in the nozzle before the flow enters the runner which operates at atmospheric pressure, Adhikari and Wood [7]. This is similar to the operation of Pelton turbines which can achieve more than 90% efficiency and are often designed with multi-jets, Zhang [9]. The major differences between the two are that the flow in crossflow turbines passes twice
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