The effect of large-scale turbulent structures on a simple 2-D canyon-typeflow

This paper is concerned with a preliminary experimental investigation of th e interaction between large turbulent structures, generated in the wake of a circular cylinder, and the rough-wall turbulent boundary layer separated flow immediately downstream of a simple street canyon type geometry represe nted by backward-facing step. The motivation for the work was to provide so me initial data for the validation of a 3-D k-epsilon turbulence model used for the prediction of flows and pollutant dispersion within the urban cano py. The aim has been to assess the extent of the perturbation of a simulate d street canyon caused by regular large-scale eddies generated upstream. Th e research has involved the use of thermal anemometry to determine mean vel ocity and turbulence characteristics both upstream and downstream of the st ep, together with the mean reattachment length for the recirculating flow. The results indicate that the presence of the cylinder in the flow reduces the reattachment length. In addition, the periodic structures generated in the cylinder wake are rapidly mixed with the turbulence in the step shear l ayer such that no periodicity is detected at the reattachment zone.