Role of Synthetic Jet Frequency & Orientation in Dynamic Stall Vorticity Creation

Abstract

Vorticity creation and its evolution play an important role in the formation of large dynamic stall vortices which cause large excursions in lift, drag and pitching moment on rapidly pitching and oscillating airfoils. While synthetic jets have shown potential in controlling dynamic stall vortices by sustaining lift increases without corresponding drag and pitching moment, their effect on the vorticity creation remains unknown. To address this, high fidelity computational fluid dynamics simulations were conducted to investigate how synthetic jet frequency and orientation alter the dynamic stall leading-edge boundary vorticity flux. Changes in baseline boundary vorticity flux were related to corresponding flow fields to delineate the role of synthetic jets in vorticity creation. Slot orientation was found to play a greater role in altering the amount of vorticity diffused into the flow than actuation frequency. Dynamic stall vortex sizes were found to be directly proportional to the vorticity diffused from the leading-edge and could therefore be effectively manipulated using synthetic jets. The study provides a better understanding of the dynamic stall vorticity creation process and its control using synthetic jets. Nomenclature ‫ܣ‬= synthetic jet amplitude, ‫ݏ݉‬ ିଵ = acceleration ‫ܥ‬ ఓ = synthetic jet momentum coefficient, ሺ݀ ܿ ⁄ ሻ൫ܷ ,௫ ܷ ஶ ⁄ ൯ ଶ ܿ = chord length ݀ = slot width = body force ݂ = airfoil oscillation frequency, ‫ݖܪ‬ ݂ = jet actuation frequency, ‫ݖܪ‬ ݂ ା = non-dimensional actuation frequency, ݂ ‫ݔ‬ ்ா ܷ ஶ ⁄ = unit normal vector pointing out of the flow ܲ = pressure ܴ݁ = chord Reynolds Number, ߩܷ ஶ ܿ ߤ ⁄ ‫ݏ‬ = distance along surface ‫ݐ‬ = time ܷ ,௫ = maximum jet velocity during blowing phase, ‫ݏ݉‬ ିଵ ܷ ஶ = freestream velocity ‫ݔ‬ ்ா = distance from synthetic jet to trailing-edge ߛ = slot orientation ߢ = reduced airfoil oscillation frequency, ߱ܿ 2ܷ ஶ ⁄ ߤ = dynamic viscosity ߩ = density = boundary vorticity flux, ‫ݏ݉‬ ିଶ ࣓ = vorticity ߱ = airfoil angular frequency, 2ߨ݂ ߱ = jet angular frequency, 2ߨ݂

Wind-tunnel tests of synthetic jet control effects on airfoil flow separation

“…Overall, a variety of numerical and experimental investigations had already been carried out to explore the mechanisms of a synthetic jet on improving the maximum lift of airfoil as well as the stall angle [23][24][25][26] . There were some consensuses regarding the parametric analyses of jet parameters, such as the influences from jet momentum coefficient, location of jet and excitation frequency.…”

Design and Manufacture of a Planetary Gearbox Rig

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