Optimization of Kaplan Hydroturbine at Very Low Head with Rim-Driven Generator

The objective of the paper is to study the design and optimization of Kaplan hydroturbines for a very low head (less than 3 m), with a particular emphasis on the use of rim-drive electrical generators. The work is based on an experimental setup and computational fluid dynamics (CFD) analysis of various design parameters for maximum output power and efficiency. Two designs are presented in this paper. One is a 90-cm (35-in.) diameter vertical-oriented Kaplan hydroturbine system as an intended product capable of generating over 50 kW. The other is a smaller, 7.6-cm (3-in.) diameter horizontal-oriented system for prototyping and laboratory verification. Both are analyzed through CFD based on large eddy simulation (LES) of transient turbulence. Specific design for the runner and the stator, intake tube shape, as well as guide vanes upstream of the turbine was studied to get the most from the available head. The intent is to use 3D-printing manufacturing techniques, which may offer original design opportunities as well as the possibility of turbine and water conduit design customization as a function of the head and flow available from a specific site. Based on the CFD analysis, the 7.6-cm diameter system achieved the highest power output and the maximum efficiency at the rotational speed range of 1500-2000 rpm, while for the experimental testing, the optimum rotational speed range was 1000-1500 rpm. Because of the mismatch between CFD and experimental results, the CFD results were correlated due to the presence of air and friction; moreover, error and uncertainty analysis were presented for both methods. For the 90-cm case, the optimum performance was found at a rotational speed around 350 rpm according to the CFD results. Finally, investigating the shape of the intake tube of the hydroturbine setup can significantly increase the power output and the efficiency of the system.