Experimental Investigation of the Effects of Synthetic Jet Actuation on the Kármán Vortex Formation and Shedding in the Turbulent Wake of a Cantilevered Triangular Prism
Date
2023-07
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Abstract
The effects of synthetic jet actuation on the Kármán vortex formation in the three-dimensional turbulent wake of a cantilevered triangular prism of aspect ratio 4 protruding a thin turbulent boundary layer is investigated experimentally at a Reynolds number of 12000. Results are reported for surface pressure measurement on the leeward face and wake of the obstacle and particle image velocimetry for selected planes in the wake. Synthetic jet is used to excite the flow through two slits spanning the obstacle height along the edges of the leeward face. The mean-field characteristics for the baseflow and actuated flows are characterized and the coherent structures of the flow are identified. It is found that the actuation generally increases the total kinetic energy of turbulent fluctuations (TKE) and the amplitude of the fluctuations due to Kármán shedding. It is shown that the process of vortex formation for the baseflow and actuated flows is qualitatively similar and the cause of shedding frequency shift due to actuation is explained. A self-regulating mechanism is identified in the wake which links the circulation flux in the wake to the streamline curvature and the base pressure. Flow recirculation is shown to have a key role in explaining the wake response to the actuation. It accounts for the increased transfer rate of circulation downstream of the
bluff body and affects the base pressure. Forming vortices are observed to reach a saturation level before the shedding in a behavior similar to formation process of vortex rings and vortex lines. A non-dimensional parameter including the effective formation parameters at the moment of shedding is introduced. Similarities between the results observed for the wake of the triangular prism and other geometries suggest a broader relevance of the argument.
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Keywords
Kármán Vortex Formation and Shedding, Bluff Body Wake, Flow Actuation
Citation
Abbaspour, M. (2023). Experimental investigation of the effects of synthetic jet actuation on the Kármán vortex formation and shedding in the turbulent wake of a cantilevered triangular prism (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.