An exploration of the wake of an in-stream water wheel

Research on low-impact, low capital-cost hydropower is increasing as efforts to decarbonise energy systems accelerate. The in-stream water wheel can potentially aid in this decarbonisation effort, but there is little research into the fluid environment around these turbines. This is despite the potential impact that the fluid environment can have on turbine power characteristics and hydrography of the local stream. This paper provides a qualitative analysis of the wake of an in-stream water wheel using dye injection and analysis, supported by quantitative analysis of the near-wake using particle image velocimetry. The results demonstrate that the wake of an in-stream water wheel is primarily characterised by large periodic vortices generated by the shedding of the leading edge vortex as the blade rotates through the fluid, with smaller counter-rotating vortices shed as the local flow angle reverses near the blade entry and exit. The wake maintains a coherent structure three diameters downstream of the turbine, which could potentially impact the power generation of downstream turbines. This wake coherence is largely consistent across different numbers of turbine blades and blade depth ratios.