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Turbulence structure in a diabatically heated forest canopy composed of fractal Pythagoras trees

Schröttle, Josef and Dörnbrack, Andreas (2013) Turbulence structure in a diabatically heated forest canopy composed of fractal Pythagoras trees. Theoretical and Computational Fluid Dynamics, 27, pp. 337-359. Springer. DOI: 10.1007/s00162-012-0284-8 ISSN 0935-4964


Official URL: http://link.springer.com/article/10.1007%2Fs00162-012-0284-8


We investigate the turbulent flow through a heterogeneous forest canopy by high-resolution numerical modeling. For this purpose, a novel approach to model individual trees is implemented in our large-eddy simulation (LES). A group of sixteen fractal Pythagoras trees is placed in the computational domain and the tree elements are numerically treated as immersed boundaries. Our objective is to resolve the multiscale flow response starting at the diameter of individual tree elements up to the depth of the atmospheric surface layer. A reference run, conducted for the forest flow under neutral thermal stratification, produces physically meaningful turbulence statistics. Our numerical results agree quantitatively with data obtained from former field-scale LESs and wind tunnel experiments. Furthermore, the numerical simulations resolve vortex shedding behind individual branches and trunks as well as the integral response of the turbulent flow through the heterogeneous forest canopy. A focus is the investigation of the turbulence structure of the flow under stable thermal stratification and in response to the heating of the fractal tree crowns. For the stratified flows, statistical quantities, e.g. turbulent kinetic energy and vorticity, are presented and the turbulent exchange processes of momentum and heat are considered in detail. The onset and formation of coherent structures such as elevated shear layers above the diabatically heated forest canopy are analyzed. For the stably stratified flow, temperature ramps above the forest canopy were simulated in agreement with previous observations. Thermally driven vortices with a typical diameter of the canopy height were simulated when the tree crowns were diabatically heated. The impact of the coherent flow structures on the heat flux is investigated.

Item URL in elib:https://elib.dlr.de/81315/
Document Type:Article
Title:Turbulence structure in a diabatically heated forest canopy composed of fractal Pythagoras trees
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Dörnbrack, AndreasDLRUNSPECIFIED
Date:15 September 2013
Journal or Publication Title:Theoretical and Computational Fluid Dynamics
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.1007/s00162-012-0284-8
Page Range:pp. 337-359
Series Name:Theoretical and Computational Fluid Dynamics
Keywords:Forest canopy, Fractal trees, Heat, Atmospheric boundary layer, Turbulence
HGF - Research field:Energy
HGF - Program:Renewable Energies
HGF - Program Themes:other
DLR - Research area:Energy
DLR - Program:E SF - Solar research
DLR - Research theme (Project):E - Wind Energy (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Cloud Physics and Traffic Meteorology
Deposited By: Freund, Jana
Deposited On:28 Feb 2013 15:55
Last Modified:06 Sep 2019 15:18

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