Turbulent Drag Reduction by Streamwise Traveling Waves of Wall-Normal Forcing

Fukagata, Koji; Iwamoto, Kaoru; Hasegawa, Yosuke

doi:10.1146/annurev-fluid-120720-021445

Cited by 12 publications

(2 citation statements)

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“…This paper explores alternative formulations of the existing integrals and decompositions for flows above smooth surfaces, and extensions of these integrals and decompositions for flows above rough surfaces. Considering the successes of the integral methods thus far (Fukagata, Iwamoto & Hasegawa 2024), extending the existing methods to previously unexplored flow scenarios promises new insights, and such endeavours should need no further motivation. This is particularly true for rough-wall boundary layers, which are common in fluid engineering (Jiménez 2004;Flack & Schultz 2010;Chung et al 2021).…”

Section: Motivationmentioning

confidence: 99%

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Integral methods for friction decomposition and their extensions to rough-wall flows

Zhang,

Yang,

Chen

et al. 2024

J. Fluid Mech.

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A primary objective of integral methods, such as the momentum integral method, is to discern the physical processes contributing to skin friction. These methods encompass the momentum, kinetic energy and angular momentum integrals. This paper reformulates existing integrals based on the double-averaged Navier–Stokes equations, and extends their application to flows over rough walls. Our derivation yields distinct decompositions for the bottom-wall viscous friction coefficient, denoted as $C_S$ , and the roughness element drag coefficient $C_R$ . The decompositions comprise three terms: a viscous term, a turbulent term and a roughness (dispersive) term – regardless of the flow configuration, be it channel or boundary layer. Notably, when these integrals are evaluated for laminar flow scenarios, only the viscous term remains significant. In addition, we elucidate the spatial distributions of the terms within these decompositions. To demonstrate the practicality of our formulations, we apply them to analyse data from direct numerical simulations of turbulent half-channel flows. These flows feature aligned and staggered cubical roughness at various packing densities. Our analyses, based on kinetic-energy-oriented decompositions, reveal that when the surface coverage density $\lambda _p$ is small, the dominant terms within the decompositions are the viscous and turbulent terms. With increasing $\lambda _p$ , the viscous dissipation term decreases, while the turbulent production term increases and then decreases. These variations arise from a subdued near-wall cycle and the development of a shear layer at the height of the cubes.

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Section: Motivationmentioning

confidence: 99%

“…The third criticism concerns the weighting, i.e. (1 − x 3 /δ) and (1 − x 3 /δ) 2 in the integral (Fukagata et al 2024). This weighting is a result of the triple integration.…”

Section: Momentum-based Integralmentioning

confidence: 99%