Street canyon

Predicting solid particle transport in the lowest parts of the atmosphere is a major issue for man-made obstacles in semi-arid regions.
Here, we investigate the effects on solid particle saltation, of square obstacles on the ground with different spacings.
The aerodynamic field is determined by large eddy simulations coupled with an immersed boundary method for the obstacles.
Solid particles are tracked by a Lagrangian approach.
Take-off and rebound models are introduced for the interaction of particles with the wall.
Without particles, fluid velocity profiles are first compared with experiments showing good agreement.
Special focus is put on the recirculation zone that plays an important role in solid particle entrapment.

Particle concentration fields are presented. Accumulation zones are studied regarding the different obstacle spacings as an extension of the aerodynamic scheme by One (1988) to solid particle transport. A deposition peak appears before the first obstacle. When the spacing between the two obstacles is large enough, some particles are trapped within the recirculation and a second deposition peak arises. The streamwise evolution of the horizontal saltation flux shows that the lowest flux downstream of the obstacles is obtained for the highest separation. The deposition rate or the streamwise saltation flux are estimated globally as a function of obstacle spacing. These results illustrate how the numerical tool developed here can be used for assessing air quality in terms of solid particle concentration.