Secondary motions above a staggered multi-scale rough wall

Viggiano, Bianca; Bossuyt, Juliaan; Ali, Naseem; Meyers, Johan; Cal, Raúl Bayoán

doi:10.1017/jfm.2022.262

Cited by 4 publications

(2 citation statements)

References 28 publications

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“…Other factors also affect the strength of the secondary motions. The impacts of thermal stratification, roughness geometry and roughness arrangements have been investigated by Forooghi, Yang & Abkar (2020), Medjnoun, Vanderwel & Ganapathisubramani (2020) and Viggiano et al (2022), respectively. Nonetheless, the aforementioned studies did not report statistically significant asymmetries in the mean flow, which is the focus of our current investigation.…”

Section: Roughness-induced Large-scale Secondary Flowsmentioning

confidence: 99%

Asymmetric secondary flows above geometrically symmetric surface roughness

Zhang,

Yang,

Zhu

et al. 2023

J. Fluid Mech.

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The mean flow behaviour of a turbulent boundary layer over rough walls is expected to exhibit symmetries that govern the flow dynamics. In particular, when roughness elements are arranged in a spanwise symmetric manner, the mean flow above them should also exhibit spanwise symmetry. This symmetrical consideration has garnered substantial empirical support. We conduct direct numerical simulations (DNS) of flow over aligned cube arrays to test such symmetry considerations further. We vary the surface coverage density from 0.25 % to 6.25 %, and employ an averaging time of about 100 large-eddy turnover times, which is longer than the typical averaging time in prior DNS studies of rough-wall boundary layers. The results suggest the presence of spanwise asymmetry in the mean flow. Specifically, we observe the development of a prominent secondary vortex on one side of the cubical roughness, accompanied by a relatively smaller secondary vortex on the other side. This asymmetry becomes most pronounced when the surface coverage density is approximately 0.59 %, and diminishes as the coverage density approaches either a low or a high value. We also establish that this mean flow asymmetry is robust across variations in the domain size, the initial condition, and the placement of the cubes in the spanwise direction.

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Section: Roughness-induced Large-scale Secondary Flowsmentioning

confidence: 99%

Asymmetric secondary flows above geometrically symmetric surface roughness

Zhang,

Yang,

Zhu

et al. 2023

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

“…They moreover demonstrated that the form-induced dispersive stresses were significant in the outer layer and Townsend's outer-layer similarity hypothesis is not valid in these cases. When the same roughness elements were placed in a staggered arrangement by Viggiano et al (2022), the effect on the global velocity defects in the outer layer was only minimal compared with a smooth wall and there were no large-scale secondary flows. We could roughly view the relationship between these two configurations as a 'roughness equivalent' to the link between the present subject of two-dimensional heterogeneous temperature and the study of temperature variations in the spanwise direction by Bon & Meyers (2022) (compare figures 1a and 1b).…”

Section: Introductionmentioning

confidence: 99%

Secondary flows induced by two-dimensional surface temperature heterogeneity in stably stratified channel flow

Bon,

Broos,

Cal

et al. 2023

J. Fluid Mech.

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The structure and impact of thermally induced secondary motions in stably stratified channel flows with two-dimensional surface temperature inhomogeneities is studied using direct numerical simulation (DNS). Starting from a configuration with only spanwise varying surface temperature, where the streamwise direction is homogeneous (Bon & Meyers, J. Fluid Mech., 2022, pp. 1–38), we study cases where the periodic temperature strip length $l_x/h$ (with $h$ the half-channel height) assumes finite values. The patch width ( $l_y/h =\{{\rm \pi} /4, {\rm \pi}/8$ }) and length are varied at fixed stability and two different Reynolds numbers. Results indicate that for the investigated patch widths, the streamwise development of the secondary flows depends on the patch aspect ratio ( $a=l_x/l_y$ ), while they reach a fully developed state after approximately $25l_y$ . The strength of the secondary motions, and their impact on momentum and heat transfer through the dispersive fluxes, is strongly reduced as the length of the temperature strips decreases, and becomes negligible when $a\lesssim 1$ . We demonstrate that upward dispersive and turbulent heat transport in locally unstably stratified regions above the high-temperature patches lead to reduced overall downward heat transfer. Comparison to local Monin–Obukhov similarity theory (MOST) reveals that scaled velocity and temperature gradients in homogeneous stably stratified channel flow at $Re_\tau =550$ agree reasonably well with empirical correlations obtained from meteorological data. For thermally heterogeneous cases with strips of finite length, the similarity functions only collapse higher above the surface, where dispersive fluxes are negligible. Lastly, we show that mean profiles of all simulations collapse when using outer-layer scaling based on displacement thickness.

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Agrivoltaic system success: A review of parameters that matter

Ali

2024

Journal of Renewable and Sustainable Energy

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Solar energy is a rapidly growing sector, and agrivoltaic farms are playing an increasingly important role in meeting the world's energy needs. However, as the size and complexity of these farms increase, so do the challenges associated with managing them efficiently. This article presents a comprehensive review of the fundamental parameters that underpin agrivoltaic systems. Focusing on the latest research, this review examines the challenges and opportunities intrinsic to the implementation of agrivoltaic energy systems, paying particular attention to the various parameters that contribute to their performance. These parameters encompass a range of factors such as heat islands, shading factors, and surface energy budget. The review underscores the importance of considering a diverse array of parameters when developing agrivoltaic energy systems to optimize their efficiency and effectiveness.

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Secondary motions above a staggered multi-scale rough wall

Cited by 4 publications

References 28 publications

Asymmetric secondary flows above geometrically symmetric surface roughness

Asymmetric secondary flows above geometrically symmetric surface roughness

Secondary flows induced by two-dimensional surface temperature heterogeneity in stably stratified channel flow

Agrivoltaic system success: A review of parameters that matter

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