Turbulent thermal convection over rough surfaces with varying roughness size

Abstract eng:
We present experimental study of turbulent thermal convection over rough surfaces with varying roughness size. It is found that the local temperature fluctuations measured at the cell center and near the sidewall change significantly with the increase of the roughness parameter λ, which is defined as the ratio of the height of the pyramid-shaped roughness element over the width of its base. The change of the local temperature fluctuations occur concomitantly with the change of the global heat transport law of the system, i.e. the Rayleigh number Ra dependence of the non-dimensional heat flux Nusselt number N u. Detailed examinations of the local temperature time series indicate that the changes are brought into by the changes of plume dynamics which is supported by the observation that the dissipative power Q increases with the increase of λ.

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