Fifth Conference on Urban Environment


High-resolution large-eddy simulation of turbulent flow around buildings including thermal effects


Marcus Oliver Letzel, Institute of Meteorology and Climatology, University of Hannover, Hannover, Germany; and S. Raasch and M. Kanda

The goal of this project is to look into the detailed structure of building-induced turbulence and how it is affected by thermal stratification using high-resolution numerical simulation.

Knowledge about the nature of the turbulent wind field modified by complex buildings is still limited in particular in view of potential dependencies on the thermal stratification, but it is important for issues like the air quality in the vicinity of industrial areas or in streets with heavy traffic. Such building-induced turbulence shall be investigated for different thermal stratification using the high-resolution paralellized large-eddy simulation (LES) model PALM-CITY.

In general the advantage of LES models compared to Reynolds models is that the energy-containing eddies can be resolved even in close vicinity of the building, between buildings or within a street canyon. Thus for the first time a forecast of peak concentrations and maximal wind load will become feasible. PALM-CITY shall be validated using standard resolution LES simulations by Kanda et al. (2004), Rodi et al. (1997) and Shah & Ferziger (1997) as well as experimental wind tunnel data by Kastner-Klein et al. (2001) and Uehara et al. (2000).

The parallel cluster architecture of the new North German supercomputing centre ( now principally allows to simultaneously run two coupled or nested model sets on different computer clusters ('grid computing'). This feature will be added to PALM-CITY within the scope of this project with the aim to extend the scale range of turbulent flow around buildings that is resolvable by LES models by at least an order of magnitude compared with usual models (up to 20003 grid points). This allows to investigate building-induced turbulence not only for neutral stratification (standard in urban CFD models) but also for convective conditions characterized by up- and downdrafts of up to a few hundred meter diameter, while turbulent structures in the vicinity of walls with a size of less than one meter can still be explicitly resolved. This yields new prospects for model validation and the development and testing of turbulence parameterizations.

Modeling aspects of this project involve PALM-CITY code implementations such as the mask method by Briscolini & Santangelo (1989), turbulent inflow and noncyclic boundary conditions, horizontal grid stretching or grid nesting, a dynamic subgrid scale model, thermal building wall boundary conditions, and suitable visualization methods.

This contribution will describe PALM-CITY's modeling technique and give first results of the project.

Session 13, high-resolution (CFD) modeling of flow around buildings and street canyons (parallel with session 12)
Thursday, 26 August 2004, 8:30 AM-12:15 PM

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