Planform structure of turbulent free convection on horizontal surfaces

The planform structure of turbulent free convection over a heated horizontal surface has been visualised and analysed for different boundary conditions at the top and for different aspect ratios, for flux Rayleigh numbers ranging from 10(8) -10(10). The different boundary conditions correspond to Rayleigh-Benard convection, open convection with evaporation at the top and with an imposed external flow on the heated boundary. Without the external flow the planform is one of randomly oriented line plumes. At large Ra, these line plumes seem to align along the diagonal persumably due to a large scale flow along as visualised in the side view. When the external how is imposed the line plumes clearly align in the direction of external how. Flow visualisation reveals that at these Ra the shear tends to break the plumes which otherwise would reach the opposite boundary.