Hydraulic efficiency of horizontal waterwheels: Laboratory data and CFD study for upgrading a western Himalayan watermill

Traditional waterwheels are widely used in remote areas as a source of mechanical energy for grinding grain. The classical design suffers of a very low hydraulic efficiency. The basic challenge is to increase the power output but not the rpms, with a desirable working regime in the range of 120-160 rpm. We study the hydraulic efficiency of waterwheels with analytical expressions and measured data from two laboratory scale designs in a variety of cases that differ in 1) blade inclination angle, 2) inclination angle of the water conduit, 3) blade geometry and 4) impact point of the waterjet on the blade surface. A waterwheel with blades with a notch in the upper edge does not improve the straight blade results. A very simple curved blade profile may enhance the hydraulic efficiency up to 46%. We analyze the performance of the new designs when applied to a real waterwheel located in the western Himalaya by means of Computational Fluid Dynamics (CFD) simulations. The maximum power delivered by the traditional wooden made waterwheel is 1.97 kW at 120 rpm. The waterwheel having 36 curved iron blades generates a power equal to 3.2 kW also at 120 rpm.