Direct numerical simulations (DNS) of flow over triangular and rectangular riblets in a wide range of size and Reynolds number have been carried out. The flow within the grooves is directly resolved by exploiting the immersed-boundary method. It is found that the drag reduction property is primarily associated with the capability of inhibiting vertical velocity fluctuations at the plane of the crests, as in liquid-infused surfaces (LIS) devices. This is mimicked in DNS through artificial suppression of the vertical velocity component, which yields large drag decrease, proportionate to the riblets size. A parametrization of the drag reduction effect in terms of the vertical velocity variance is found to be quite successful in accounting for variation of the controlling parameters. A Moody-like friction diagram is thus introduced which incorporates the effect of slip velocity and a single, geometry-dependent parameter. Reduced drag-reduction efficiency of LIS-like riblets is found as compared to cases with artificially imposed slip velocity. Last, we find that simple wall models of riblets and LIS-like devices are unlikely to provide accurate prediction of the flow phenomenon, and direct resolution of flow within the grooves in necessary.

On the relationship between drag and vertical velocity fluctuations in flow over riblets and liquid infused surfaces / Di Giorgio, S.; Leonardi, S.; Pirozzoli, S.; Orlandi, P.. - In: INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW. - ISSN 0142-727X. - 86:(2020). [10.1016/j.ijheatfluidflow.2020.108663]

On the relationship between drag and vertical velocity fluctuations in flow over riblets and liquid infused surfaces

Di Giorgio S.
Primo
;
Pirozzoli S.;Orlandi P.
Ultimo
2020

Abstract

Direct numerical simulations (DNS) of flow over triangular and rectangular riblets in a wide range of size and Reynolds number have been carried out. The flow within the grooves is directly resolved by exploiting the immersed-boundary method. It is found that the drag reduction property is primarily associated with the capability of inhibiting vertical velocity fluctuations at the plane of the crests, as in liquid-infused surfaces (LIS) devices. This is mimicked in DNS through artificial suppression of the vertical velocity component, which yields large drag decrease, proportionate to the riblets size. A parametrization of the drag reduction effect in terms of the vertical velocity variance is found to be quite successful in accounting for variation of the controlling parameters. A Moody-like friction diagram is thus introduced which incorporates the effect of slip velocity and a single, geometry-dependent parameter. Reduced drag-reduction efficiency of LIS-like riblets is found as compared to cases with artificially imposed slip velocity. Last, we find that simple wall models of riblets and LIS-like devices are unlikely to provide accurate prediction of the flow phenomenon, and direct resolution of flow within the grooves in necessary.
2020
DNS; drag; reduction; riblets; SHS/LIS;
01 Pubblicazione su rivista::01a Articolo in rivista
On the relationship between drag and vertical velocity fluctuations in flow over riblets and liquid infused surfaces / Di Giorgio, S.; Leonardi, S.; Pirozzoli, S.; Orlandi, P.. - In: INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW. - ISSN 0142-727X. - 86:(2020). [10.1016/j.ijheatfluidflow.2020.108663]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1480481
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