Flow interactions of finite-span synthetic jets and a cross flow

Abstract

The interaction of a finite-span synthetic jet with a cross-flow over a swept-back finite wing was studied experimentally at a Reynolds number of 100,000 and at multiple angles of attack. The focus of the work was to explore the interaction of finite span synthetic jets with a locally attached or separated flow field in the vicinity of the synthetic jet orifice. The effect of blowing ratio and aspect ratio of the jet orifice was discussed in detail. As was shown in previous work for an unswept finite configuration, the time-averaged velocity field exhibits secondary streamwise flow structures that evolve due to the finite span of the synthetic jet orifice. Furthermore, these structures depend upon actuation level of the jet, as well as orifice geometry. Phase-averaged measurements over the swept-back finite configuration showed that in the presence of sweep the flow becomes highly three-dimensional almost immediately downstream of the synthetic jet orifice. It was demonstrated that the baseline flow field that develops over a swept-back configuration (dependent on angle of attack), which is characterized by spanwise and streamwise vorticity components, is responsible for the immediate breakdown of the coherent structures that are introduced by the synthetic jet orifice, and for the formation of the secondary flow structures that were seen in the time-averaged flow field.

The overarching goal of the work was to understand the flow physics associated with a finite-span synthetic jet placed on an aerodynamic configuration. Through experimental investigation, the flow mechanisms of the interaction between a finite span synthetic jet and the flow over a finite span swept back wing was described and successfully understood.

Finally, a simple semi-empirical/theoretical model was developed in order to help depict the flow interactions of the streamwise vortical structures that are generated at the edges of a finite-span synthetic jet orifice in the presence of a cross flow. Using superposition of simple two-dimensional flow fields, the Vortex Dynamics Model was successful in predicting the footprint of finite-span synthetic jets on three-dimensional configurations.

The tip vortex was found to influence the development of the flow structures generated by the synthetic jet; conversely, an investigation on the effect of a finite-span synthetic jet on the development of the tip vortex was also undertaken. The effect of actuation resulted in global changes to the tip vortex by altering its development. Actuation resulted in an overall increase in vorticity magnitude in the core of the vortex with a corresponding decrease in fluctuations of the vortex. Ultimately, the effect of actuation led to both a stronger and more coherent tip vortex.

Furthermore, the effect of jet placement along the span of the wing was studied. A finite-span synthetic jet was placed near the tip of a finite sweptback wing. The focus of that part of the work was to explore the interaction of the synthetic jet with a spatially non-uniform velocity field (due to the presence of a tip vortex), especially the formation and advection of flow structures in the vicinity of the synthetic jet. As was shown, the time-averaged velocity field exhibited streamwise flow structures downstream of the jet.