Category: CFD Applications

Urban Flow and Dispersion

CFD Large Eddy Simulation을 이용한 실제 도시 스케일의 유동 및 확산 특성에 대한 연구

Turbulent flow and dispersion characteristics over a real urban street canyon are investigated by large-eddy simulation model. Two kinds of sub-grid scale (SGS) model, which are the constant coefficient Smagorinsky model and Vreman model, are assessed to evaluate SGS model performance. Turbulent statistics, particularly turbulent stresses, and wake patterns are compared between the two SGS models for three different wind directions. We found that while the role of the SGS model is small in average sense, local or instantaneous contribution to total stress near the surface or edge of the buildings is not negligible. Yielding smaller eddy viscosity near the walls than the Smagorinsky model, the Vreman model appears to be more appropriate for the simulation of a flow in a complex urban street canyon. In the following investigation of a flow field over a real urban street canyon, we found that depending on wind direction relative to the street canyon, wind fields, turbulence statistics, and dispersion patterns show very different characteristics. Particularly, tall buildings near the street canyon predominantly generate turbulence, leading to homogenization of the mean flow inside the street canyon. Furthermore, the release position of pollutants sensitively determines subsequent dispersion characteristics.

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Human-Induced Contaminant Transports in Indoor Environments

실내환경내에 보행자의 출입과정에서 유발되는 오염물질의 이동에 대한 수치 연구를 기반으로 생화학 무기 공격 혹은 독성물질의 누출, 병원 내 전염 통제등을 위한 연구를 하고자 한다.

A large eddy simulation is used to investigate contaminant transport due to complex human and door motions and vent-system activity in room compartments where a contaminated and clean room are connected by a vestibule. Human and door motions are simulated with an immersed boundary procedure. We demonstrate details of contaminant transport due to human- and door-motion induced wake development during a short-duration event involving the movement of a person (or persons) from a contaminated room, through a vestibule, into a clean room. Parametric studies that capture the effects of human walking pattern, door operation, over-pressure level, and vestibule size are systematically conducted. A faster walking speed results in less mass transport from the contaminated room into the clean room. The net effect of increasing the volume of the vestibule is to reduce the contaminant transport. The results show that swinging-door motion is the dominant transport mechanism and that human-induced wake motion enhances compartment-to-compartment transport.

Choi & Edwards (2008) Indoor Air ; Choi & Edwards (2011) Indoor Air

Snapshots of vorticity iso-surfaces colored by SF6 mass concentration for person walking event; Contour plots of concentration in (b) vertical plane view; at (c) z=1.0 and (d) z=1.5m in horizontal plane view.

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