Characteristics of secondary circulations over an inhomogeneous surface simulated with large-eddy simulation |
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| Authors: | Thara V Prabha Anandakumar Karipot Michael W Binford |
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| Institution: | (1) Department of Biological and Agricultural Engineering, The University of Georgia, 1109 Experiment st., Griffin, GA 30223, USA;(2) Lab for Environmental Physics, The University of Georgia, 1109 Experiment st., Griffin, GA 30223, USA;(3) Department of Geography, University of Florida, Gainsville, FL 32611, USA |
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| Abstract: | Large-eddy simulation is used to study secondary circulations in the convective boundary layer modulated as a result of horizontally
varying surface properties and surface heat fluxes over flat terrain. The presence of heat flux heterogeneity and its alignment
with respect to geostrophic wind influences the formation, strength and orientation of organized thermals. Results show boundary-attached
roll formation along heat flux maxima in the streamwise direction. The streamwise organization of the updrafts and downdrafts
formed downwind of heterogeneities leads to counter-rotating secondary circulations in the crosswind plane. The distribution
of resolved-scale pressure deviations shows large pressure gradients in the crosswind plane. Spanwise and vertical velocity
variances and heat flux profiles depict considerable spatial variability compared to a homogeneous forest simulation. Secondary
circulations are observed for various ambient wind scenarios parallel and perpendicular to heterogeneities. In the presence
of increased wind speed, thermals emerging from the heat flux heterogeneity are elongated, and organize along and downwind
of large-scale heterogeneity in the streamwise direction. Simulation with a reduced heat flux shows a shallower circulation
with a lower aspect ratio. Point measurements of heat flux inside the roll circulation could be overestimated by up to 15–25%
compared to a homogeneous case. |
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| Keywords: | Convective boundary layer Eddy covariance Large-eddy simulation Rolls Secondary circulation Surface heterogeneity |
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