Momentum flux in Rayleigh–Benard convection

The statistical quantities concerning the momentum flux in the Rayleigh–Benard convection are investigated in detail. The transition from soft turbulence to hard turbulence is captured through the momentum flux. The time series of the momentum flux is studied and its power spectrum shows the sign of the transition. The two-time correlation function does not saturate its value in the range of the transition. Except for the transition regime the two-time correlation function for the momentum flux converges to 0 and we estimate the viscosity by the turbulence. We confirm that the viscosity coefficient increases as we increase the temperature difference between the top and bottom plates