Repository: Freie Universität Berlin, Math Department

A large-eddy simulation study of thermal effects on turbulent flow and dispersion in and above a street canyon

Park, S.B. and Baik, J.J. and Raasch, S. and Letzel, M.O. (2012) A large-eddy simulation study of thermal effects on turbulent flow and dispersion in and above a street canyon. J. Appl. Meteor. Climatol., 51 (5). pp. 829-841. ISSN Online: 1558-8432 Print: 1558-8424

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Thermal effects on turbulent flow and dispersion in and above an idealized street canyon with a street aspect ratio of 1 are numerically investigated using the parallelized large-eddy simulation model (“PALM”). Each of upwind building wall, street bottom, and downwind building wall is heated, and passive scalars are emitted from the street bottom. When compared with the neutral (no heating) case, the heating of the upwind building wall or street bottom strengthens a primary vortex in the street canyon and the heating of the downwind building wall induces a shrunken primary vortex and a winding flow between the vortex and the downwind building wall. Heating also induces higher turbulent kinetic energy and stronger turbulent fluxes at the rooftop height. In the neutral case, turbulent eddies generated by shear instability dominate mixing at the rooftop height and appear as band-shaped perturbations in the time–space plots of turbulent momentum and scalar fluxes. In all of the heating cases, buoyancy-generated turbulent eddies as well as shear-generated turbulent eddies contribute to turbulent momentum and scalar fluxes and band-shaped or lump-shaped perturbations appear at the rooftop height. A quadrant analysis shows that at the rooftop height, in the neutral case and in the case with upwind building-wall heating, sweep events are less frequent but contribute more to turbulent momentum flux than do ejection events. By contrast, in the case with street-bottom and downwind building-wall heating, the frequency of sweep events is similar to that of ejection events and the contribution of ejection events to turbulent momentum flux is comparable to that of sweep events.

Item Type:Article
Uncontrolled Keywords:Fluxes, Heating, Momentum, Turbulence, Large eddy simulations, Urban meteorology
Subjects:Mathematical and Computer Sciences > Mathematics > Applied Mathematics
ID Code:1381
Deposited By: Ulrike Eickers
Deposited On:21 Feb 2014 11:34
Last Modified:21 Feb 2014 11:34

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