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Seminar: Fluid Mechanics

Dolphin-Inspired Drag Reduction for Marine Vehicles

Speaker: Lars-Uve Schrader
Organization: HSVA
Time: 2018-05-24 10:30
Place: Teknikringen 8

Abstract

Dolphins are able to sustain an underwater speed of about 9 m/s across long distances. This fascinating endurance stimulated the hypothesis that the thick, pliable dolphin skin keeps a large portion of the boundary layer laminar via a delay of transition to turbulence, thus acting as a drag-reducing passive flow-control device. This talk presents an effort to transfer the dolphin's control strategy to the flow conditions around the bow of a small ship. To this end, polymeric compliant coatings in analogy with dolphin skin were developed, manufactured and tested in a water tunnel, using a 1:3.2 scale model of the ship. In preparation of the experiments, RANS-based flow simulations and laminar boundary-layer computations were carried out to devise a suitable baseflow, subjected to spatial Orr-Sommerfeld stability calculations both over rigid and compliant surfaces. Wall compliance was included in the stability analysis via boundary conditions deriving from a spring-damper backed membrane model of the compliant coating. With this procedure, coating properties such as thickness, Young's modulus and damping coefficient were "optimised" so as to obtain a significant downstream shift of the transition location according to the e^N criterion. Polymeric materials for "artificial dolphin skins" were selected based on the calculated coating properties. These skins were indeed able to reduce the drag of the ship model in the water tunnel.