Abstract: Hydraulic turbine is the core equipment for hydropower utilization. The traditional lift-type horizontal axis hydraulic turbine needs a certain flow velocity to obtain an established efficiency, and thus is not suitable in the cases of low flow rates. To expand the application scope, we design two new drag-type horizontal axis turbines with different propeller blade angles based on the Archimedes spiral principle, and investigate their hydrodynamic performance and wake characteristics using the computational fluid dynamics method. The results show that these variable angle designs have larger power coefficients in the tip speed ratio range of 0.5 to 2.0, and their peak value is up to 16% larger than that of the fixed angle. And the power coefficients are also larger than those of lift-type horizontal axis turbines reported previously in the literature; the coefficient is increased by at least 60% at the tip speed ratio of 1.5, for instance. Meanwhile, the variable angle turbine has a smaller thrust coefficient in the whole tip speed ratio range, while its performance fluctuation is more obvious than that of the fixed angle. Flow field analysis reveals that annular spiral tip vortices and strip-shaped hub vortices develop behind the two drag-type horizontal axis turbines, and the variable angle designs make the tracks of tip vortices and hub vortices more continuous and extend longer into the downstream. In addition, the wake recovery of the variable angle turbines are much faster than that of the fixed angle. The results reveal the hydrodynamic and wake characteristics of our drag-type horizontal axis hydraulic turbines, which can be referred to in their optimal design and application promotion.

Key words: hydropower, drag-type horizontal axis hydraulic turbine, hydrodynamic performance, wake, computational fluid dynamics