Joint Seminar: Scalar and momentum transport over complex surfaces

In urban areas, ​built structures in the atmospheric boundary layer can induce complex flow patterns and influence the transport of heat and mass.  Large-eddy simulation (LES) is a useful tool of computational fluid dynamics to study the turbulent momentum and scalars. However, the quality and reliability of LES for turbulent boundary layer flow need to be a assessed critically. This is especially pertinent for the case of flow and transport over rough elements at high Reynolds numbers. Given that very few studies have addressed this problem at high Reynolds numbers, we conducted detailed comparisons with both wind-tunnel experiments and field observations. T​he results give confidence in using LES as a numerical tool to study the problem of interest. Numerical experiments are then ​conducted to study the similarities and differences ​of momentum and passive scalar exchanges over t​hree-dimensional idealized urban surfaces in a turbulent channel fl​ow. We show that the spatial heterogeneity introduces significant dispersive fluxes, which mainly contribute to the differences in momentum and scalar exchanges. Increasing the ​frontal density induces a general transition in the  f​low from a rough boundary layer type to a mixed-layer-like type. This transition results in an increase in the efficiency​ of turbulent momentum transport, but different behavior​ occurs for scalars due to reduced contributions of large scale motions in the roughness sublayer. The results can guide interpretation of field measurements in a heterogeneous canopy and inform model development to account for the differences in momentum and scalar dispersive fluxes. 

Date

19.10.2016

Time

13:30 h

Place

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

Speaker

Qi Li, Department of Civil & Environmental Engineering, Princeton University, USA

Organizers

Juan Pedro Mellado

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