Multi Stage Turbine for wave energy plant

Abstract

A wave energy plant based on the patended Seawave Slot-Cone Generator (SSG) is under development by the Norwegian company WAVEenergy AS. The concept is based on the principle that the incoming waves will run uphill on a structure slope and on their return downhill they will flow into multiple reservoirs at different levels. A turbine with multiple stages is being designed to handle the conversion of the potential energy from the different reservoirs. One critical design element of the so-called Multi Stage Turbine (MST) is the choice of labyrinth seals. The labyrinth seals need to be designed in a way that prevents air from leaking into the suction side of the turbine stages. The company Mechanica AS has suggested a design where the labyrinth seals are pressurized by leading water from above the turbine through orifices to the lower labyrinth seal. A model has been made and the labyrinth seal has been tested. The model does not include the turbine, but only the labyrinth seal with appropriate pressure conditions. Additionally, a CFD model of the seal was made, and the calculated results were compared with the test results. Seing that the CFD results showed relatively good correlation with the test results, the CFD model was used to make some further simulations of the labyrinth seal performance. The most important conclusion of both model and CFD results is that the orifices appear to sufficiently pressurize the labyrinth seal. It is not known if this will still be the case when the seal is implemented in the turbine. And although the labyrinth seal should meet the requirement to prevent air leakage, it may still reduce the efficiency of the turbine by causing disturbances in the turbine flow. This must be considered when deciding upon the final MST design, where eventually manufacture practicality and cost are the main regulators.