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Numerical and Experimental Investigation of Thermally Driven Exchange Flow and Wind set up in Canopy Steep Area

Davari, Andisheh | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42105 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jamali, Mirmosaddegh
  7. Abstract:
  8. Solar heating in aqautic systems, causes tempreture increasing.This temperature difference will promote an exchange flow between the vegetation and open water. The exchange flow generated by the differential heating and cooling associated with depth variation has also been studied through laboratory experiment and modelling. Differential solar heating can result from shading by rooted emergent aquatic plants, producing a temperature difference between vegetated and unvegetated regions of a surface water body. Horizontal density difference between shaded and open water regions drives currents that carry fluxes between biologically and chemically distinct regions of an aquatic system. Such buoyancy driven exchange flows play an important role in the transport of dissolved and suspended nutrients, contaminants, oxygen, and other chemicals, and thus can have a significant effect on the aquatic system chemistry and ecology and acounts major mixing process in calm waters. In this thesis, laboratory experiments describe the exchange flow driven by uniform solar radiation and wind flow above vegetation canopies and surface cooling in canopy areas. Effect of radiation intensity and vegetation density on thermally driven exchange velocity is investigated using Particle Imaging Velocimetry (PIV) to quantify the velocity field. Extinction coefficient in the water depth due to light absorption by water molecules and radiation intensity are calculated using a laboratory technique. Flow velocity profile in the water depth and intrusion depth as a function of light intensity, vegetation density, and light penetration is discussed. The impact of emergent canopy on a slope on flow characteristics is invertigated numerically and experimentally. Experimental results have been compared with the numerical model to calibrate the model in thermally driven flow; the results predicted by the model were compared with measured data for several vegetation densities and two different slopes. The intrusion velocity decreases with increasing density of vegetation. Wind is an important factor for scalar fluxes (heat, water vapor, carbon dioxide, etc.) and movements of spores, pollen and particles within a vegetation canopy. In this research we have used the experimental method to observe the water current cauesed by wind surface cooling. In summary the tempureture difference cuased by the water and ice reservoir, made surface layer to be unstable and make a water flow due to depth. According to results, increasing the boundary layer accured by negative thermally flux on water surface.

  9. Keywords:
  10. Exchange Flow ; Image Processing ; Solar Heating ; Canopy Areas with Slope ; Wind Blowing

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