Effect of tangential absolute velocity at outlet on open flume turbine performance

To address the electricity crisis in Indonesia, the use of open flume pico hydro turbines is a potential solution because Indonesia has 19 GW of hydropower resources at mini, medium, and pico scales. There are two concepts for the design of an open flume pico hydro turbine runner: Euler and Nechleba. Euler's concept recommends that the absolute tangential velocity at the outlet of the blade be zero to optimise power absorption. By contrast, Nechleba explains that to reduce flow separation at the outlet of the blade (separation can reduce efficiency), tangential absolute velocity at the outlet of the blade must not be zero. Accordingly, this study compares the performance of blades designed with these two concepts using a computational fluid dynamics method. The results showed that the maximum efficiency of the blade using the Euler concept was 70.08%, while the blade using the Nechleba concept was 74.39%. Based on the results, a runner design concept that assumes a non-zero tangential absolute velocity at the outlet of the blade is recommended for use in designing an open flume pico hydro turbine runner.