Measurements of neutral and dense gas dispersion in a boundary layer wind tunnel with different surface roughness were performed. Neutral or dense gas was emitted from a small "quasi-point" source located in the wind tunnel floor. This "quasi-point" source represents leakages of gases from small industrial plants in the urban area. The tunnel surface was either covered with uniform roughness or with a smooth surface in order to create a significant difference in the boundary layer mean velocity profile and turbulence intensity. Also influence of plume momentum on vertical and horizontal distribution of tracer gas concentration above the source was studied. Both neutral and dense gases were marked with tracer gas (ethane) and concentrations were measured with a comb probe connected to four flame ionization detectors (FID). Results have shown that plume momentum significantly affects plume shape. Boundary layer turbulence intensity also affected plume behavior, but to a lesser degree than plume momentum.

The stereo PIV measurement were performed behind a wing in the plane perpendicular to the flow to study the vortical structures oriented in the streamwise direction, which take place both in suction and pressure sides of the wing. The Reynolds numbers during the experiments in the 3 m wind tunnel range from 0.5 million up to 1.5 million.

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.

Abstract. Measurements of flow and dispersion over urban area model were conducted in the boundary layer wind tunnel in VZLU. Scale model of an industrial area with its residential neighborhood was equipped with ground-level emission source and the flow and dispersion of emissions was measured. Flow field was studied using hot wire anemometer and concentration field was studied using flame ionization detector. These measurements were used for the verification of a new computational model of emission flow and dispersion, which was developed in VZLU.

Abstract. Measurements of gas dispersion from ground source were performed in a boundary layer wind tunnel in VZLU Prague. The measurements include non-buoyant gas dispersion behind a ground level source on a flat plane, on a simple rectangular building model and behind a model hill and rectangular barrier. These measurements will serve for verification of a new gas dispersion software being developed in VZLU. The dispersion model is intended for use by firemen and ambulance services in the case of an accident for immediate estimation of the area with dangerous gas concentration. The dispersion model will use precalculated results for chosen areas in the Czech Republic with industrial plants and residential building in the neighborhood. The size of contaminated area will be estimated using actual meteorological situation, i.e. wind speed and direction etc. and precalculated data of flow and dispersion in the chosen location.

The stereo PIV measurement were performed behind a wing in the plane perpendicular to the flow to study the vortical structures oriented in the streamwise direction, which take place both in suction and pressure sides of the wing. The Reynolds numbers during the experiments in the 3 m wind tunnel range from 0.5 million up to 1.5 million.

Abstract. Experimental investigation of gas dispersion in a critical infrastructure area was performed using a boundary layer wind tunnel. The dispersion of gases is evaluated from the point of view on required function of security systems in case of critical infrastructure accident involving airplane attack. Physical model of the critical infrastructure installed in the wind tunnel is subjected to measurement of gas concentration with flame ionisation detectors.

Wind tunnel studies of gas dispersion over complex terrain model were performed in VZLU Prague. The terrain model with a ground-level emission source was mounted in a boundary layer wind tunnel. Flow and concentration field behind the source was measured. The model presented an area of the Liberec city, 9.0 × 2.4 km in full scale. The emission source was mounted at the position of a heating plant in the model centre and concentration field was measured using flame ionisation detectors. The experimental results will be used for validation and verification of a new computational dispersion model intended for use in case of accidents with dangerous gas leakages in selected areas in Czech Republic.