Effect of froude number on three-bladed archimedes screw turbine efficiency

Energy crisis which is globally occured around the world attract researchers to study renewable energy. Experimental study of Archimedes screw turbine that had been applied as microhydro power plant for low head, they are focused on fluid flow. Fluid flow on Archimedes screw turbine is a flow with a free surface. Froude Number is utilized for this free surface flow. Efficiency of screw turbine is influenced by geometric and flow losses. The aim of this experimental study is to recognize flow phenomenon among blades of screw turbine, which have connected to the effect of the Froude Number to efficiency. Observed parameters are varied in inlet flow as a characteristic length (y), inflow velocity (c₀), and the turbine shaft declivity (α). The model of screw turbine is made in laboratory scale with acrylic. The geometric shape of three-bladed have seven screws, number of helix turns are 21, thread angle of 30⁰, the radius ratio of 0.54 with a pitch of 2.4R₀. The Froude Number (Fr) is the ratio index of inertia fluid force (water) in an element by gravitation force. Relative value of measured inertia force is an axial tranport velocity of fluid flow (V_ax). The result of this study is if the Froude Number increase then the vortex is formed among the blades, therefore efficiency decrease. The highest efficiency is 89 %, it occurs in 25⁰ of turbine shaft declivity and 0.15 of Froude Numbers, respectively.