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Tunable Porous and Patterned Surfaces for Turbulence Control
Research supported by this grant targeted the development of passive control techniques for wall-bounded turbulent flows. Advances in additive manufacturing technology have opened a vast new design space in the development of multi-functional surfaces and materials that can passively control turbulent flows. However, the design and optimization of substrate microstructure to yield a desired response in the overlying turbulent flow remains a challenge. To address this challenge, reduced-complexity models were developed to predict how specific surface treatments modify the near-wall flow field with minimal computation. These models were grounded in the resolvent formalism, which leverages a gain-based decomposition to identify key features of the turbulent flow field. Model predictions showed that the drag reduction performance of so-called riblet surfaces (which have successfully demonstrated drag reduction in prior laboratory experiments and flight tests) correlates well with the amplification or suppression of a single near-wall flow structure. The development of this efficient surrogate model enabled optimization of 2D riblet geometry, preliminary consideration of 3D riblets, as well as the model-guided development of anisotropic porous materials for passive friction reduction in turbulent flows. Model predictions were used to guide the design and fabrication (via 3D printing) of anisotropic porous materials for preliminary laboratory experiments.
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