Experiments were conducted in a lid-driven cavity with a stable vertical temperature stratification to study flow and thermal structures. Flows are driven by the top lid, which slides in its own plane at a constant speed. The top wall is maintained at a higher temperature than the bottom wall. The end walls and side walls are thermally insulated. Flow visualization was accomplished by the PIV technique. Results are obtained over a wide range of physical parameters, i.e. 400≤Re≤6000, $5 × 10^{6}≤Gr≤1 × 10^{7}$, aspect ratio (A=H/L)\approx & 1. The Prandtl number is fixed at 6.0(water). Systematical evaluations of the results are carried out to ascertain the relative importance of natural and forced convections. When Gr/$Re^{2} ≪ 1$, the effect of the vertical temperature gradient is minor and the flow structures are similar to those of the non-stratified fluid flows in a convectional lid-driven cavity flow. Fluids in the primary vortex are well mixed and the temperature is fairly uniform in the main circulating region. When Gr/$Re^{2} ≫ 1$, the temperature stratification tends to suppress the vertical fluid motion. Much of the fluid motion takes place in the vicinity of the top sliding lid and the bulk of the middle and bottom portions of the cavity interior are nearly stagnant. In these regions, vertically linear temperature distributions are seen.
