Turbulent Thermal Convection with an Obstructed Sidewall

We present an experimental study of turbulent convection in a cell with staggered fingers on its sidewall using water as the convecting fluid. Our measurements reveal that Nu∼Ra^-0.27, and that the temperature probability density function (PDF) at the cell center is a double-peaked function which can be fitted by the superposition of two Gaussians. Moreover, it is found that the size of the local temperature fluctuations scales with Ra and that the scaled PDFs for different Ra have an invariant form. Visualization studies show that the mean flow pattern in the cell is a twisted asymmetric four-roll circulation, which helped to explain the observed PDF.