PLUME DISPERSION THROUGH LARGE GROUPS OF OBSTACLES - A FIELD INVESTIGATION

A set of field experiments has been conducted at the Cardington experimental site, in the United Kingdom, to investigate the dispersion of a neutrally buoyant plume released upwind of an array of cubes, each of which measured approximately 2 m x 2 m x 2 m. The plume was released below the height of the obstacle array, and a second control plume was released alongside the array. The behaviour of the plume was recorded using both flow visualisation and measurements of gas concentration. A limited number of velocity measurements was also made. It is found that, relative to the control plume, certain mean concentration statistics no not change materially as the plume passes through the obstacle array. These include the form of the cross-sectional profiles, the decay along the centre line and the lateral growth with downstream distance. However, the mean vertical extent of the plume increases by 40-50%. In addition the r.m.s. fluctuations of concentration within the the plume are reduced. A clipped normal distribution is shown to be an appropriate model for the concentration fluctuations within the array plume.