Abstract
This study explores the problem of optimal spatial placement of microjet actuators for flow control in a canonical bluff body of relevance to the aerodynamics community, namely, the slanted cylinder with a slant angle of . The solution found by a genetic algorithm whose goal function is to reduce aerodynamic drag (achieving 10.6% reduction at ) challenges the intuitive and, to date, most commonly followed de facto standard of using line arrays of steady microjet actuators to control a flow field. This study provides strong evidence that line arrays are not the optimal approach for active flow control of this bluff body wake, since most of the jets in the line array were neutrally, or even negatively, contributing to the goal function of drag reduction. Further observations of the flow physics with surface flow visualization and particle image velocimetry unveil two key mechanisms that were leveraged by this automated approach: First, a shrinkage of the separation bubble at the leading edge of the slanted surface appears to be strongly related to the very strong energization of the boundary layer just upstream of the separation due to microjets in crossflow being applied in tandem. Second, a wavelike perturbation that appears to be related to an increased wandering of the vortex pair formed in the far field of this wake is also observed. Although this study employed steady microjet actuators, the lessons learned can potentially be extended to other actuation mechanisms commonly used for active flow control. The results obtained demonstrate the spatial sensitivity problem is one that, despite its complexity and challenges in physical implementation, is worthwhile considering in active flow control studies.
2 More- Received 23 February 2021
- Accepted 10 August 2021
DOI:https://doi.org/10.1103/PhysRevFluids.6.083903
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