Optimal design process of crossflow Banki turbines: Literature review and novel expeditious equations

The Banki turbine is a crossflow turbine suitable for sites with heads below 200 m and flow rates below 10 m3/s, with maximum efficiency around 80%. Its flexible operation and easy manufacturing make it a suitable hydropower technology for different geographic areas and hydraulic contexts. However, the design procedure proposed in literature is not complete and it is quite fragmented. It lacks of effective equations to select the optimal number of blades, the optimal tip speed ratio, the rotational speed and a preliminary cost estimate. Information on runner material and blade thickness is also fragmented. In this paper, the traditional design procedures are reviewed, and a new and more complete one is proposed to overcome the above-mentioned gaps, providing new expeditious equations and data to be used in practical applications. The new equations are obtained by elaborating and generalizing literature and industrial data, presenting them in a dimensionless form. The current share of Banki turbines and their future developments and opportunities are also discussed.