MICHAEL MANGA: Recent Refereed Publications


Manga, M., and D. Weeraratne, Experimental study of non-Boussinesq Rayleigh-Benard convection at high Rayleigh and Prandtl numbers. Physics of Fluids, vol. 11, 2969-2976.

A set of convection experiments were performed in which a layer of fluid is heated from below and cooled from above. The working fluid, corn syrup, has a viscosity that depends strongly on temperature. Viscosity within the fluid layer varies by a factor of 6 to $1.8\times10^3$ in the various experiments. A total of 28 experiments were performed for Rayleigh numbers ($Ra$) between $10^4$ and $10^8$ and Prandtl numbers ($Pr$) sufficiently large, $10^3 < Pr < 10^6$, that the Reynolds number ($Re$) is less than 1; here, values of $Ra$ and $Pr$ are based on material properties at the average of the temperatures at the top and bottom of the fluid layer. As $Ra$ increases, flow changes from steady to time-dependent at $Ra>O(10^5)$. As $Ra$ increases further, large scale flow is gradually replaced by isolated rising and sinking plumes. At $Ra>O(10^7)$, there is no evidence for any large scale circulation, and flow consists only of plumes. Plumes have mushroom-shaped ``heads'' and continuous ``tails'' attached to their respective thermal boundary layers. The characteristic frequency for the formation of these plumes scales with $Ra^{2/3}$. In the experiments at the largest $Ra$, the Nusselt number ($Nu$) is lower than expected, based on an extrapolation of the $Nu-Ra$ relationship determined at lower $Ra$; at the highest $Ra$, $Re \rightarrow 1$, and the lower-than-expected $Nu$ is attributed to inertial effects that reduce plume head speeds.

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