Efficiency optimization of twin vertical-axis helical hydrokinetic turbines (VAHHTs) based on Taguchi method

Abstract

In order to improve the utilization rate of kinetic energy of water flow, recent research on hydrokinetic turbine prototypes has changed from the standalone turbine to the twin-turbine system. In this paper, multiple design parameters and their interaction are considered to improve the efficiency of a novel twin vertical-axis helical hydrokinetic turbines (VAHHTs) based on the Taguchi method. An orthogonal array outlining these 5 parameters, e.g. spacing (L/D), rotation direction (RD), phase difference (ϕ), incoming flow angle (β), and blade-tip speed ratio (λ), with 4 different levels per parameter, is constructed. By means of the orthogonal array, the original 1024 numerical cases are reduced to 16 cases, which greatly reduces the computing resources and time. The results show that the degrees of influence of these parameters on turbine efficiency are ordered as follows: λ>β>RD>ϕ>L/D. The L/D is the parameter that has the least influence on the efficiency of twin VAHHTs. Furthermore, an analysis of the signal-to-noise (S/N) ratio suggests that the combination of the five parameters that maximizes the efficiency of the twin VAHHTs is L/D = 1.4, RD = (counterclockwise, clockwise), ϕ = 30°, β = 90°, and λ = 0.9. It turns out that the efficiency of the optimized twin VAHHTs is 14.45% higher than that of the single VAHHT.