At present, the oil and energy industry is actively considering alternative structural concepts such as spar type of floating oil platform for deep water oil exploration and production. A spar platform consists of a long, hollow circular cylinder and it is prone to vortex induced vibrations under the combined actions of ocean currents and waves. The present study focuses at a fundamental level on the use of Moving Surface Boundary-Iayer Control (MSBC) as applied to a spar type of cylindrical structure for drag reduction and suppression of vortex induced vibrations. Two small rotating elements are used to inject the momentum into the boundary-layer. Extensive wind tunnel tests yielded information regarding the surface pressure distribution, drag coefficient, Strouhal number and pressure fluctuations in the wake as affected by the rate of momentum injection, location of the rotating elements as well as symmetric and asymmetric momentum injection. The results clearly suggest that the vortex shedding frequency is increased (up to 22%) and the pressure fluctuations associated with the vortex shedding are diminished by as much as 60% in presence of the momentum injection. The drag coefficient is reduced by more than 80%. The investigation was complemented by a comprehensive flow visualization study which clearly demonstrated effectiveness of the momentum injection in disrupting the vortex shedding as well as narrowing of the wake.


Flow past bluff structures have direct engineering significance. Bluff body wakes are complex; they involve the interaction of three shear layers in the same problem, namely a boundary-layer, a separating shear layer, and a wake (Williamson, 1996). A wide variety of structures encountered in wind and ocean engineering practice are fluid dynamically bluff. At present the oil and energy industry is actively considering alternative structural concepts, such as spar type of floating oil platform.

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