EFFECTS OF LID-DRIVEN CAVITY SHAPE ON THE FLOW ESTABLISHMENT PHASE

Experiments are carried out to study the flow establishment phase inside closed cavities submitted to the impulsive translation from rest, of one of their walls at a Reynolds number of 1000. Three standard industrially machined or molded cylindrical cavity shapes are studied and are compared with respect to the efficiency of mixing process: square, rectangular and semi-circular of length-to-width ratio of 2:1. The flow structures in the mid-cross-section are analysed by means of fine topological and kinematic visualization series using two complementary techniques: continuous dye filament and discrete solid tracers both coupled with a laser sheet illumination. Particular attention is given to vorticity propagation and primary/secondary eddy formations. Although a roughly similar vortex generation is observed in all examined cavities, important differences appear with time. The semi-circular cavity flow results in a much more homogeneous and uniform recirculation with no secondary flow recirculation zone. On the contrary, the square and rectangular cavity flows develop a better flow mass dispersion and, respectively, one and two secondary eddies. At the final time of observation (t^*=12), both semi-circular and rectangular cavity flows seem to reach their steady state whereas the square one continues to evolve. Comparisons with 2-D computational results of other authors illustrate the three-dimensional flow aspect present in experiments.