The situation for the 45° case is more interesting (Fig. 9). Here the release is in an intersection and the flow is oblique. In this snapshot, at z=0.23 H the whole plume is blown into the canyon region between the cubes in the y-direction and none in the x-direction. Note that the flow is constantly changing and that this is literally a snapshot. In a different snapshot this might of course be different and on average the plume would be equally likely to be blown into the gap in the x-direction. A little further up, at z=0.52 H, we see that much of the material is now caught in the wake region. A little still comes from the horizontal location of the original source. Higher still, at z=0.80 H, most of the material is concentrated in the region between the cubes. Nothing comes from the horizontal location of the original source. The highest concentration is around the centre of the gap, but somewhat away from the mean location of the core of the recirculation behind the upstream cube. This indicates the possible release of material trapped further down in the recirculation. These visualisations suggest the idea that transfer from the original source location to the wake occurs predominantly at low levels, whereas the re-release of material occurs mainly at higher levels. It would be of interest to test this hypothesis quantitatively in future studies. Above the array, material appears to be coming from the wake region, which therefore acts as a ‘secondary source’.
case
45°
°
z
0.23 H
H
0.52 H
H
0.80 H
H