Merging of sheet plumes in turbulent convection

The predominant coherent structures near the hot or cold wall in turbulent convection are sheet plumes. We present results from a visualization experiment in turbulent free convection in water over a horizontal heated surface at moderately high Rayleigh number (Ra=105 to 109). We observe the random initiation of sheet plumes very close to the heated surface at regular intervals. These sheet plumes move horizontally in the direction of the bulk flow and merge with the neighbouring plumes. Two merging plumes are being often found to be parallel. We study the merging dynamics of two parallel sheet plumes by measuring the lateral velocities at different times of their merging, at different heat flux.