Abstract: This paper presents an experimental study of a dual-motor driven contra-rotating full tubular pump for tidal power generation. The first and secondary impellers of this pump adopt the same structural form, and the speed ratio of their rotators in pumping mode is examined. The results show that at the same rotational speed of the two-stage impellers, the overall head of the second stage is higher than that of the first stage, but the latter has lower shaft power and higher efficiency. At different rotational speeds of the two impellers, no hump occurs in the lift head curve of low flow conditions; the pump efficiency is improved significantly with its high hydraulic efficiency zone shifted towards the design flow point. The lift head and power of the pump are linearly related to the rotational speed of its secondary impeller; its shaft power is mainly related to the corresponding flow rate and rotational speed. A variable rotational speed can be applied to the secondary impeller to achieve an operating power equal to that of the first-stage so as to avoid the overload of its motor. The results are of great theoretical and practical significance to the hydraulic performance and the safe and stable operation of full tubular pumps.

Key words: tidal power generation, full tubular pump, pumping conditions, counter-rotating impeller, speed matching