PLUMES AND WAVES IN CONVECTION: A QUEST FOR HARD-TURBULENT CONVECTION IN AIR

David Yuen, Minnesota Supercomputer Institute and Dept. of Geology and Geophysics, Minneapolis, University of Minnesota

The swirling smoke coming out from a burning cigarette represents very turbulent convection from a point-source. In fact, a simple calculation shows that the local Rayleigh number near one's nose, as one smokes, lies between 1011 and 1012. This number puts it in the hard-turbulent regime. Smoking air and boiling soup belong to the finite Prandtl number regime for which we humans have developed a great deal of empirical intuition from our forefathers. This is in contrast to corn syrup and honey, very viscous fluids, which behave counter intuitively. We will present results from recent high resolution calculations of finite Prandtl number (Pr = 1) convection up into the regime of hard turbulence or Ra around 109. Internal waves are found for Rayleigh number of around 108. These waves are being driven inertially and represent a new mechanism for energy transport in finite Prandtl number convection. Secondary instabilities can be developed within these waves. There are strong interactions between the cold and hot boundary layers via both plumes and waves. These high-resolution calculations show that inertially dominated instabilities, such as waves, begin to take hold at high enough Rayleigh number.