Page - 1366 - in Book of Full Papers - Symposium Hydro Engineering

3. PRINCIPLE OF OPERATION - CURVED DRAFT TUBE This special concrete hydropower ejector system in a run off river hydropower layout is equipped with a vertical kaplan turbine and a laterally displaced suction tube (Fig. 1), curved in the plan view. This leads to downstream under a special spillway chute, the so-called ejector ramp. In case of excess water, the ejector ramp is activated by opening an ejector gate at the upper side of the ramp. Downside the ramp the energy of the access flow helps to lower the pressure in area of suction tube outlet and so to increase the useable head for the vertical Kaplan Turbine. The annual energy production can be significantly increased by the use of the hydraulic potential. Fig. 1 Situation of the curved draft tube and the ejector ramp in plan view The goal should therefore be to accelerate the surplus water volume as much as possible in order to achieve a high momentum in the tail race. This increases the suction or creates a lower pressure at the draft tube outlet end and keeps the point of energy conversion as far away as possible from the outlet (Fig. 2), in order to maximize efficient confluence of the two streams. A B C D Fig. 2 Principle and effect of the ejector flow 1366