The downstream wake response of marine current energy converters operating in shallow tidal flows

This paper presents findings from an experimental study investigating the downstream wake response from marine current energy convertors operating in various degrees of vertical flow constraint. The paper investigates deep vertically unconstrained sites, mid-depth sites and there is a particular emphasis on shallow tidal stream sites. Shallow tidal resources could be utilised for the deployment of first generation farms. The nature of the downstream wake flow will be a critical factor when determining the farm layout and the wake length is heavily influenced by the flow depth or ratio of rotor diameter to flow depth. A porous actuator disk is used to model the marine current energy convertor and an Acoustic Doppler Velocimeter is used to map the downstream wake. Linear scaling of length ratios suggests mid depth sites of 30-50m will produce the shortest wake lengths and for deeper and shallower sites the wake length increases. It is hoped that these relationships between vertical flow constraint and wake length will help with the layout design of tidal stream farms.