Effect of Draft Tube Size on the Performance of a Cross-Flow Turbine

Abstract

This article describes the effect of using different sizes of draft tubes on the performance of a 5-kW cross-flow turbine. An effort is made to arrive at an optimum size for the particular turbine tested, as the existing draft tube (203 mm) had an adverse effect on the performance at higher heads. The study involved variation of different performance parameters such as output, efficiency, runaway speed, and speed ratio for four different cases, viz., without the draft tube and with three different sizes of draft tubes (203, 250, and 300 mm) in the head range 3-9 m. The investigation shows that a properly sized draft tube enhances the efficiency of a cross-flow turbine over the entire space of its operation.