Large-Scale Circulation in Turbulent Rayleigh-Benard Convection Systems Michelle Fitts and Erik Ackermann

Abstract

In Rayleigh-Benard systems, we explore convection and fluid dynamics in a fluid-filled cell whose top and bottom plates are set at fixed cold and hot temperatures, respectively. In particular, we focus on the onset of large-scale circulation (LSC), which is characterized by colder fluid circulating toward the bottom while warmer fluid circulates to the top in a noisy, but planar motion. Our fluid-filled cylindrical cell has an aspect ratio of 1; aspect ratio is defined as the ratio of the diameter of the cell to the length. The cell is defined by two parameters: Rayleigh number (Ra) which is proportional to the temperature difference and Prandtl number (Pr) which is the ratio between the kinetic viscosity and thermal diffusivity of the fluid. Using Nek5000, a spectral element code, we numerically-simulated fluid flow for Prandtl number of 0.7, and Rayleigh numbers between 5e+6 and 5e+7. We compiled the data for the temperature and velocity of these simulated systems and made animations to observe the behavior and LSC of the fluid in the cell over time. Correlating these plots with measurements of the amplitude and azimuthal angle of the plane of LSC, we were able to determine the location of cessations. In addition, we calculated the area of the sheet-like plumes in the boundary layer. We discovered that the fraction of plumes compared with total cross-sectional area of the cell decreases with increasing Rayleigh numbers.