Drag decomposition of laminar channel flows developing over convergent–divergent riblets

Guo, Tongbiao; Zhong, Shan; Craft, Tim

doi:10.1016/j.euromechflu.2021.12.006

Cited by 3 publications

(2 citation statements)

References 34 publications

(79 reference statements)

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“…From the physics point of view, Eq. (7) indicates that convection and diffusion of the mean kinetic energy have no influence on its overall integral if the flow assumptions set in this work are considered.…”

Section: Drag Decomposition In a Fully-developed Flow In A Channel Wi...mentioning

confidence: 99%

“…They are a type of spanwise heterogeneous roughness patterns which mimic the surface structures found on sharks' skin 1 and on the secondary flight bird feathers 2 . C-D riblets have received an increasing amount of research attention in recent years [3][4][5][6][7] , and they have been found to be capable of mitigating flow separation 8,9 .…”

Section: Introductionmentioning

confidence: 99%

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Energy-based drag decomposition analyses for a turbulent channel flow developing over convergent–divergent riblets

et al. 2022

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Direct numerical simulations of a turbulent channel flow developing over convergent–divergent (C–D) riblets are performed at a Reynolds number of Reb = 2800, based on the half channel height δ and the bulk velocity. To gain an in-depth understanding of the origin of the drag generated by C–D riblets, a drag decomposition method is derived from kinetic energy principle for a turbulent channel flow with wall roughness. C–D riblets with a wavelength, Λ, ranging from 0.25δ to 1.5δ, are examined to understand the influence of secondary flow motions on the drag. It is found that as Λ increases, the intensity of the secondary flow motion increases first and then decreases, peaking at Λ/δ=1. At Λ/δ≥1, some heterogeneity appears in the spanwise direction for the turbulent kinetic energy (TKE) and vortical structures, with the strongest enhancement occurring around regions of upwelling. All the riblet cases examined here exhibit an increased drag compared to the smooth wall case. From the energy dissipation/production point of view, such a drag increase is dominated by the TKE production and the viscous dissipation wake component. While the drag contribution from the TKE production shear component decreases as Λ increases, the drag contribution from the wake component of both the TKE production and viscous dissipation follows the same trend as the intensity of the secondary flow motion. From the work point of view, the drag increase in the riblet case at Λ/δ=0.25 comes mainly from the work of the Reynolds shear stresses, whereas at Λ/δ≥1, the drag augmentation is dominated by the work of the dispersive stresses. At Λ/δ=0.5, both components play an important role in the increase in the drag, which also exhibits a peak.

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Section: Drag Decomposition In a Fully-developed Flow In A Channel Wi...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Energy-based drag decomposition analyses for a turbulent channel flow developing over convergent–divergent riblets

et al. 2022

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An exhaustive review of studies on bio-inspired convergent–divergent riblets

Mohammadikarachi,

Yousif,

Nugroho

et al. 2024

Ocean Engineering

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Control effect on the divergent and convergent riblets in particle-laden turbulent boundary layer

Yuan,

Sun,

Gao

et al. 2024

Physics of Fluids

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Particle image velocimetry was employed to investigate the impact of convergent–divergent riblets on turbulent boundary layers in both clear water and liquid–solid two-phase flow fields containing 155 μm polystyrene particles. The turbulence statistics such as turbulence intensity and Reynolds stress were investigated. The spatial topology of spanwise vortex head and the development and evolution process of hairpin vortices were explored from Euler and Lagrange perspectives, respectively. Additionally, the particle distribution, concentration, and dispersion within the turbulent boundary layer were statistically analyzed. The results indicated that the boundary layer thickness, friction resistance, integrated turbulence intensity, and Reynolds stress were significantly lower on divergent riblet walls compared to convergent riblet walls. Notably, divergent riblets with a yaw angle of 30° exhibited the best drag reduction effect in both single-phase and two-phase flow fields. The addition of particles resulted in an increase in boundary layer thickness but effectively reduced turbulent fluctuations in the logarithmic region, enhancing drag reduction. This extended the drag reduction range of divergent riblets to a yaw angle of 45°, increasing the maximum drag reduction rate to 26.18%. Through spatial multi-scale local average structure function and finite-time Lyapunov exponent field analysis, it was found that the 30° divergent riblet wall significantly inhibited the development of vortex structures and reduced momentum exchange within the boundary layer. Conversely, the 30° convergent riblet wall had the opposite effect, while the particle phase inhibited the development of all wall turbulent structures. Analysis of particle concentration variations within different regions of the turbulent boundary layer revealed that as the normal height of the boundary layer increased, particle concentration gradually increased, and particle dispersion decreased accordingly. The analysis further showed that particle dispersion was mainly influenced by flow structures, whereas concentration was significantly affected by turbulence intensity. These findings elucidate the effect of the flow field on the particle phase and provide insights into the interaction mechanism between the flow field and particles.

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Drag decomposition of laminar channel flows developing over convergent–divergent riblets

Cited by 3 publications

References 34 publications

Energy-based drag decomposition analyses for a turbulent channel flow developing over convergent–divergent riblets

Energy-based drag decomposition analyses for a turbulent channel flow developing over convergent–divergent riblets

An exhaustive review of studies on bio-inspired convergent–divergent riblets

Control effect on the divergent and convergent riblets in particle-laden turbulent boundary layer

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