Preliminary experimental study on multi-stage gravitational water vortex turbine in a conical basin

Gravitational water vortex turbine (GWVT) is an ultra-low head turbine that extracts energy from an artificially induced gravitational water vortex in the basin of cylindrical or conical configuration. The latter type of basin helps in the re-construction of vortex once it is distorted after passing through a runner and thus, provide an additional potential for power extraction at different heights along the basin. In the absence of a detailed experimental study on multi-staging of GWVT in a conical basin, a preliminary investigation has been carried out using runners of Savonius type blades and producing power independently because of telescopic shafts arrangement. The effects of crucial design parameters such as rotor diameter to basin diameter ratio (RB), vortex-blade interaction, the position of the various stages and the offset distance between the neighboring stages, on the performance of GWVT are reported. In addition, the performance parameters which include rotational speed, torque and power are investigated under various rotor submergence conditions; thus, revealing maximum performance for a brimming vortex-blade interaction. One of the key findings of the study is the complex transfer of energy between the two neighboring stages through the vortex flow without the physical contact of rotors. Moreover, multi-staging provides more power than single-stage GWVT by strengthening the vortex in the vicinity of each other through rigid body rotation of the neighboring runners. The outcomes of the present study make it a potential benchmark for the future generations of GWVT technology.