Download files
Abstract
Synthetic jet, a turbulent shear flow generated from an oscillating train of coalescing vortex rings having a time-averaged zero net mass flow rate, is generally applied in a distributed manner. A distinctive method of applying synthetic jet technology, namely an asymmetrical localised synthetic jet, is developed with the aim of improving the aerodynamic performance and efficiency of three-dimensional bluff and streamlined bodies. Further, the use of an asymmetrical localised synthetic jet will contribute towards the deficiency of three-dimensional flow studies.
Two main characteristics of unsteady three-dimensional fluid-structure interaction that produce drag were investigated: flow separation of the boundary layer and the wake region. A bluff body, an 80 mm side-supported sphere, was tested at a Reynolds number of 5 x 104 in a closed test section wind tunnel in the UNSW Aerodynamics Laboratory. Surface pressure measurements on the sphere showed a delay in flow separation and a reduction in drag due to the synthetic jet. Wake survey data obtained using a five-hole pressure probe were used to formulate a set of guiding criteria resulting in a four step process to determine wake regions with reversal of flow. Pressure and vorticity contour plots showed that the synthetic jet increased the streamwise velocity component and decreased the size of the wake. Further, the wake region was characterised using non-standard definitions of displacement thickness, momentum thickness and shape factor to show that the synthetic jet decreases the energy loss in the wake. A surprising discovery was the ability of the synthetic jet to smooth the flow at the support-sphere junction.
CFD modelling was applied to the bluff and streamlined bodies using an advanced commercial CFD package. The results agreed with the experimentally obtained data. Synthetic jet localisation produces marked differences in the flow field depending on the position of actuation. Interference drag was sensitive to the asymmetry of the synthetic jet with the higher angles decreasing the entrainment into the sphere-support juncture.
The synthetic jet angle of incidence was optimised experimentally using a NACA0012 airfoil with a cut-off wing. The optimal synthetic jet angle of 23o was used on a forward swept wing based on a NACA23012 profile. The localised synthetic jet was able to reduce the drag and wing tip vorticity.
Asymmetrical localised synthetic jet can be used strategically on three-dimensional bluff and streamlined bodies to inhibit flow separation, decrease reversal of flow in the wake region and reduce interference and induced drag.