Understanding the behaviour of synthetic jets in a boundary layer for flow separation control

• Main Author: Jabbal, Mark
• Published: University of Manchester 2008
• Subjects: 629.13
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504739

Forecasts in air traffic growth, coupled with increases in output of atmospheric carbon pollution, have placed greater demands on the aircraft manufacturing industry to pursue design optimisations that will minimise operating costs and improve aircraft efficiency. Internationally agreed goals, such as the European Vision for 2020 have been set to help alleviate the environmental impact of future aircraft. The development of active flow control technologies, consisting of dynamic actuators with the ability to respond to changes in now conditions at full-scale night, as opposed to the static nature of passive flow control, is believed to be one of the key measures towards the realisation of these goals. Synthetic jet actuators (SJAs) are a promising form of active flow control technology, with a proven capability of demonstrating flow separation control at laboratory scale (Amitay et ai, 1998; Seifert and Pack 1999; Glezer and Amitay, 2002). These devices produce zero-net-mass-flux jets that negate the need for bleed air supply and complex piping. Therefore, SJAs open up possibilities for the efficient, low-energy input control of separated nows on aircraft with the potential for significant improvements in performance, leading to reduced fuel consumption and reductions in the release of environmentally deleterious emissions. Despite the potential of SJAs, little is still known about the detailed flow physical processes of interaction between a SJA and a boundary layer. For practical flow control purposes, the typical vortical structures formed by the interaction of synthetic jets with a boundary layer, their impact near the wall and their relative effectiveness for flow separation control must be considered. The aims of the present research were directed towards furthering understanding in these areas. PlY measurements of circular synthetic jets in quiescent air were undertaken. Firstly, the innuence of the jet now parameters was investigated. The Reynolds number and stroke length influenced the strength and spacing of the ensuing vortex rings respectively. The results were also found to support a performance prediction model for SJAs. Secondly, the influence of SJA geometry for vortex circulation enhancement was investigated. The now behaviour in the orifice duct due to varying orifice depth and the onset of Helmholtz resonance in the cavity due to varymg cavity height were mechanisms responsible for circulation enhancement.