Novel Diagnostic Techniques and Actuator Technology for Turbulent Shear Flows

摘要

A new approach to the manipulation and control of shear flows using novel fluidictechnology based on synthetic jets has been developed. These jets have the unique property of being zero-mass-flux in nature; i.e., they are synthesized from the working fluid in the flow system in which they are embedded. Although there is no net mass injection into the overall system, the jets allow momentum transfer into the embedding flow. The interaction of synthetic jets and an embedding flow near the flow boundary leads to the formation of closed recirculation regions and thus an apparent modification of the flow boundary. These features enable synthetic jets to effect significant global modifications in embedding flows on scales that are one to two orders of magnitude larger than the characteristic length scale of the jets themselves. This actuation technology was applied to the vectoring of a high aspect ratio rectangular jet (7 rn/sec, 7.62 x 1.27 cm) using co-flowing, millimeter-scale synthetic control jets. The control jets have an orifice width of 0.5 mm span the entire width of the primary jet nozzle and are placed along each of the long sides and near the exit plane of the primary jet. The ratio of the momentum flux in the cross-stream plane between each control jet and the primary jet is 1:35. The present experiments have demonstrated that each control jet can vector the primary jet at angles exceeding +300 without an appreciable increase in the cross-stream spreading of the primary jet. A unique feature of the synthetic jet actuators is that vectoring can be directed either towards or away from the actuator. Thus, when the two control are operated in concert, the primary jet is vectored at angles exceeding +%8Oo. Strong instabilities of the jet column are excited when the control jets are amplitude-modulated resulting in substantial increase in small scale motions a.