TY - JOUR

T1 - A large-eddy simulation study of thermal effects on turbulent flow and dispersion in and above a street canyon

AU - Park, Seung Bu

AU - Baik, Jong Jin

AU - Raasch, Siegfried

AU - Letzel, Marcus Oliver

N1 - The authors are grateful to two anonymous reviewers for providing valuable comments on this work. This work was supported by a National Research Foundation of Korea (NRF) grant funded by the South Korean government (MEST) (2011-0017041) and by the Brain Korea 21 Project (through the School of Earth and Environmental Sciences, Seoul National University). This work was also supported by the German Research Foundation under Grant RA 617/15-2.

PY - 2012/5/1

Y1 - 2012/5/1

N2 - 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.Aquadrant 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.

AB - 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.Aquadrant 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.

KW - Fluxes

KW - Heating

KW - Large eddy simulations

KW - Momentum

KW - Turbulence

KW - Urban meteorology

UR - http://www.scopus.com/inward/record.url?scp=84864849506&partnerID=8YFLogxK

U2 - 10.1175/JAMC-D-11-0180.1

DO - 10.1175/JAMC-D-11-0180.1

M3 - Article

AN - SCOPUS:84864849506

VL - 51

SP - 829

EP - 841

JO - Journal of Applied Meteorology and Climatology

JF - Journal of Applied Meteorology and Climatology

SN - 1558-8424

IS - 5

ER -