Vorticity dynamics and scalar transport in separated and reattached flow on a blunt plate

Two‐dimensional calculations are performed for a Reynolds number of 1000 and an effective Prandtl number of unity to study the dynamics of large‐scale spanwise vortices with a passive scalar field in a separation and reattaching flow over a blunt plate. A triple decomposition technique is used to isolate the quasiperiodic fluctuations related to the large‐scale vortices shed from the separated shear layer. Three vortex shedding modes are identified in the reattachment zone, two of which involve partial pairings. The coherent vortices shed from the reattachment zone have a dominating effect on scalar transport, and act as ‘‘large‐scale mixers’’ by entraining wall scalar around their upstream periphery and free‐stream scalar on their lower downstream edge. There is a definite relationship between the phase‐averaged perturbations (due to the presence of coherent vortices) in the wall friction factor and wall scalar transport with their respective time mean maximums. On the other hand, although there does exist an explicit spatial relationship between the instantaneous stagnation point and instantaneous location of maximum wall scalar transport, there is no such relationship in the mean between the two locations, except that both are dependent on the vorticity dynamics in the reattachment region.