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MEASURED AND NUMERICALLY SIMULATED BURSTING FREQUENCY OF FLOW WITHIN AND ABOVE A SUCCESSIVELY THINNED FOREST

Steven Edburg
Mechanical Engineering, Washington State University PO BOX 642920, Pullman, Washington, 99164, USA

David Stock
Mechanical Engineering, Washington State University PO BOX 642920, Pullman, Washington, 99164, USA

Brian Lamb
Civil and Environmental Engineering, Washington State University PO BOX 642910, Pullman, Washington, 99164, USA

Harold W. Thistle
Forest Health Technology Enterprise Team USDA Forest Service 180 Canfield St., Morgantown, West Virginia, 26505, USA

Abstrakt

Intermittent coherent structures play a key role in the transport of momentum and scalars between a forest canopy and the atmosphere. Two features of coherent structures are bursts and sweeps. Transport of high speed momentum towards the canopy is defined as a sweep, wheras, transport of low speed momentum away from the canopy is defined as a burst. Capturing the time frequency of bursts is important in describing the exchange of scalars and momentum between a forest canopy and the atmosphere. We applied a single point burst detection algorithm to measured and simulated flow through a successively thinned loblolly pine canopy. Measurements were conducted in four canopies with varying leaf area density and basal area. A large-eddy simulation was used to simulate the flow within and above the two of the four canopies. Source terms were added to the momentum and sub-grid turbulent kinetic energy transport equations to represent the effect of the forest canopy. Results from a dense and an open canopy are presented. The LES under predicts the turbulent kinetic energy and time between bursts for the open canopy. This may be attributed to the sub-grid scale turbulent kinetic energy source term and the domain size.