Abstract: This paper describes a new runner with helical triangular blades that enhances the stability of energy output of vertical axis hydraulic turbines and improves the traditional straight blade H-type runner. In this work, we design four helical triangular blades of different helical warp angles of 15°, 30°, 45° and 60° at mid-span, and examine the influence of warp angles on the hydraulic performance of these blades using computational fluid dynamics analysis. The results reveal that this type of blades increases the power coefficients of the runner and the improvement is most obvious in the condition of large tip speed ratios. And a greater helical warp angle leads to a more stable power output of the runner. A comprehensive comparison shows that a runner with the warp angle of 15° has the best performance, increasing its power coefficients by up to 13.4%; and its stability of energy output is also improved. We compare the vorticity fields between the traditional and modified runners and find out that the helical triangular blade effectively reduces the sizes of the blade wake vortices and the amplitudes of pressure fluctuations on blade surface. All our results indicate that the helical triangular blades help improve the operation stability of vertical axis hydraulic turbines, and that the modified runner, as a tidal energy device, could be adopted to replace the traditional one.

Key words: tidal energy, vertical axis water turbine, helical blade, energy characteristics, pressure fluctuation