Wind tunnel study of gas dispersion from ground source on a single building

Abstract

Experimental investigation of dispersion from ground source on a single building model was performed. The measurements were conducted in boundary layer wind tunnel in Aerospace Research and Test Establishment (VZLU). Simple rectangular building model, gas flow controllers and flame ionization detectors were used for these experiments. Emissions presented non-buoyant and heavy gases emitted out of a ground-level point source. Tracing gas (ethane) was used for the concentration measurements. Effect of changing source concentration and source distance was studied both on windward and leeward side of the model building. Significant differences between these two basic cases were observed. Keywords: Emission dispersion, ground-level source, boundary layer wind tunnel. INTRODUCTIONThere has been significant development in the field of air pollution modelling, even though it is a very challenging task. The emphasis in air pollution modelling is now placed on computer modelling and simulation due to increasing computing power, but experimental measurements in wind tunnels or in situ still have their inevitable place. The so-called physical modelling techniques are mainly used for computer models validation and verification and for model comparison.There are many industrial chemical plants in the world, which use various toxic gases and other chemical substances. These gases present a serious potential threat to the workers and neighbouring community in the case of accident or any other unfortunate event. Non-buoyant and dense gases (e.g. propane) are potentially more dangerous, because they spread and stay near the ground surface, whereas buoyant and light gases (e.g. helium and hydrogen) disperse quickly.Experimental verification of computer simulation results will also be a part of new software, which is developed in VZLU. This software will be used for estimating the progress of gas dispersion in chosen urban areas in Czech Republic under actual meteorological conditions. The software will be based on pre-calculated results of gas dispersion in turbulent boundary layer in urban areas near chosen chemical factories considering 3D terrain model including buildings. In case of accident or terrorist attack, the size of the contaminated area with harmful gases will be estimated using this software. Standard dispersion models are time and computing power consuming, that is why our model uses pre-calculated results for the most significant weather conditions, i.e. wind direction, etc. Such a dispersion model, which would take into account topography, buildings and actual plus forecasted meteorological conditions, does not exist in the Czech Republic. The VZLU dispersion model uses Navier-Stokes equations with k-omega turbulence model and dispersion equations.

Wind tunnel measurement of flow and dispersion over urban area

“…Previous dispersion studies in VZLU dealt with simple dispersion cases, i.e. change in roughness [4], rectangular building [5], terrain wave and slope [6]. Large terrain model in scale 1:1500 was used in [7].…”