Periodic actuation of vortex generators

• Main Author: McEwan, William Thomas
• Published: Queen's University Belfast 2008
• Subjects: 629.13
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485005

The basis of this research is the augmentation of turbulent boundary layer stability. Here stability is referred to as ,the boundary layer's ability to withstand adverse pressure gradient and therefore separation. A practical example of an' issue involving a requirement for greater stability, where separation is a typical and detrimental feature, would be a deployed flap during a critical regime of the flight envelope such as landing. A sub-boundary layer vortex generator (SBVG) is a static flow control device which does not carry the drag penalty of its traditional larger counterparts. It is however less effective. An excited SBVG may be more effective than a static model, in terms of enhancement of stability, with the added benefit of not requiring sophisticated feedback systems to prevent the device from generating detrimental effects during periods other than the flight regime for which it is intended to operate, since the SBVG is embedded within the boundary layer. Here an SBVG was oscillated (or swept) between three inclination ranges at a number of frequencies. The swept inclination ranges were 16° to 24°, 20° to 28° and 24° to 32°. These motions were executed at reduced frequencies of 0.1,0.6, 1.6,3.1,4.7, and 6.3. The data show that dynamic actuation of a sub-boundary layer vortex generator results in a weaker vortex with accelerated decay than is generated by a static vortex generator at equivalent incidence. The strength and persistence of the dynamically generated vortex is closely linked with the reduced frequency, in that increase in frequency results in an increasingly weak vortex with an increasing rate of decay.