High Reynolds Number Unsteady Thermal Convection in a Shallow Layer.

A two-dimensional mean circulation was set up along with turbulent thermal convection in a slightly inclined layer of water, heated from below and insulated at top and sides. Mean flow and turbulent moments were measured with an LDV to compare with previous studies of convection in horizontal layers and to examine the effect of the mean flow on the turbulence. The inclined angles ranged from 0.16 to 5.5 degrees. The observed mean flow, which was embedded in a highly turbulent environment, had a symmetric profile about the center, similar to the flow pattern of inclined laminar convection; however, its intensity did not decrease following a sine relation. The joint moments of turbulent temperature, perpendicular and longitudinal velocity were presented and compared with previous work. There was fractional contribution to the heat flux by mean temperature advection. A relatively high Reynolds stress generated by the perpendicular transfer of longitudinal momentum in thermals was also observed. Implications with regard to the mean flow were discussed. Turbulent moment data were also applied to a second order closure model which included the transport mechanism by buoyancy. Finally, power spectra and spectral evolution within the convective layer were also analyzed, including a model study of a noise process due to the finite data rate in LDV measurements. Comparison with spectra obtained from the atmospheric boundary layer experiments were satisfactory.