A Comparison of Openflume Turbine Designs with Specific Speeds (Ns) Based on Power and Discharge Functions
Keywords:pico hydro, openflume, specific speed
Openflume turbines have more stability and efficiency than other types of turbines, such as Pelton, Turgo, undershot, breastshot, overshot and cross-flow turbines, because openflume turbines have wider non-dimensional Ns ranges. The design of an openflume turbine blade depends on Ns parameters: power function and discharge function. In this study, two openflume turbines were designed with these parameters to determine which was best. With analytical calculations, two runner geometries, A and B, were designed based on discharge and power functions, respectively, and further developed and tested. The runners had the same numbers of blades but different angles of attack. The calculations predicted that Runner A would produce 735.08 W of power, and runner B would produce 1037.77 W of power. However, in numerical simulations, runner A produced 656.29 W of power, and runner B produced 874.49 W of power. Based on those methods runner B was more efficient than runner A. Based on the analytical designs, runner B was manufactured and tested. The power it produced was 868.69 W. The differences between the experiment and numerical results, in terms of efficiency, were not significant. Thus, the numerical simulation was valid. Consequently, the design of an openflume turbine runner should be based on Ns power functions.