Large Eddy Simulation Study of Atmospheric Boundary Layer Flow over an Abrupt Rough-to-Smooth Surface Roughness Transition

Ghaisas, Niranjan S (2023) Large Eddy Simulation Study of Atmospheric Boundary Layer Flow over an Abrupt Rough-to-Smooth Surface Roughness Transition. Boundary-Layer Meteorology, 188 (2). pp. 229-257. ISSN 0006-8314

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Abstract

The atmospheric boundary layer flow downstream of an abrupt rough-to-smooth surface roughness transition is studied using large eddy simulations (LES) for a range of surface roughness ratios. Standard wall models assume horizontal homogeneity and are inapplicable for heterogeneous surfaces. Two heterogeneous-surface wall models are evaluated, one based on a local application of similarity theory using a twice-filtered velocity field (BZ model) and another based on a local friction-velocity obtained by blending the upstream and downstream profiles (APA model). The wall shear stress and the turbulence intensity (TI) are sensitive to the wall model while the mean streamwise velocity and the total shear stress (TSS) are less sensitive. The APA model is more accurate than the BZ model on comparison to previous experiments. The wall shear stress obtained using the APA wall model is sensitive to the ratio of the equilibrium and the internal boundary layer (IBL) heights, while other statistics are not. The IBL height is insensitive to the turbulent quantity (TSS or TI) on which it is based. Several analytical relations for the IBL height are evaluated using the LES data. Two models are found to be accurate for different roughness ratios while one model is reasonable over the full range investigated. A phenomenological model is developed for the TI downstream of the roughness jump using a weighted average of the upstream and far-downstream profiles. The model yields reasonable predictions for all roughness ratios investigated.

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IITH Creators:

IITH Creators	ORCiD
Ghaisas, Niranjan S	http://www.orcid.org/0000-0002-1189-0024

Item Type:

Article

Uncontrolled Keywords:

Atmospheric boundary layer; Internal boundary layer; Large eddy simulation; Surface heterogeneity; Turbulence intensity; Atmospheric movements; Atmospheric thermodynamics; Blending; Boundary layer flow; Shear flow; Shear stress; Surface roughness; Turbulence; Atmospheric boundary layer flows; Boundary layer heights; Down-stream; Internal Boundary layer; Large-eddy simulations; Roughness ratio; Smooth surface; Surface heterogeneities; Turbulence intensity; Wall model; flow velocity; heterogeneity; homogeneity; large eddy simulation; shear stress; surface roughness; turbulent boundary layerl;

Subjects:

Physics > Mechanical and aerospace
Physics > Mechanical and aerospace > Transportation Science & Technology

Divisions:

Department of Mechanical & Aerospace Engineering

Depositing User:

Mr Nigam Prasad Bisoyi

Date Deposited:

28 Sep 2023 15:01

Last Modified:

28 Sep 2023 15:01

URI:

http://raiithold.iith.ac.in/id/eprint/11726