5:15 PM - 7:15 PM
[MIS16-P02] Modification of turbulent Rayleigh-Bénard convection by applying temperature difference along horizontal surface
Keywords:Rayleigh-Bénard convection, Experimental fluid mechanics, Horizontal convection, Heat and momentum transport
We examined responses of turbulent Rayleigh-Bénard convection to adding temperature differences along the horizontal surfaces of a fluid vessel by laboratory experiment. The temperature difference is given by two cupper blocks, whose temperature can be controlled separately by connected thermostatic baths, set on the top and bottom of the vessel with the aspect ratio two. The temperature difference was thus applied with keeping local, vertical temperature difference through the fluid layer. Test fluid is water seeded by micro capsules of thermochromic liquid crystals, which enable the simultaneous measurement of both velocity and temperature fields by particle tracking velocimetry and calibration between exhibiting color of the micro capsules and temperature against incident white light, respectively. Rayleigh number examined in the study ranges from O(108) to O(109) and the corresponding flow conditions seem fully developed thermal turbulence without the horizontal temperature difference.
Flow visualization displayed that adding temperature difference unifies multiple large-scale circulations, which emerge at each moment in the thermal turbulence, into a single circulation despite horizontal temperature differences relatively small to the vertical ones. Quantified velocity fields by the image processing indicated that the circulation is enhanced larger by adding the temperature difference. Bulk Reynolds number, which is defined by spatial root-mean-square values of two components of velocity on a visualized vertical plane as the representative velocity scale, was chosen as the measure of momentum transportation by the convection. Variation of the Reynolds number seems to be organized by confined Rayleigh number, which was newly established in our recent study using simple addition of the vertical and horizontal temperature differences as the representative temperature scale and the height of the fluid layer as the length scale.
Local and instantaneous heat transport were quantified by analyzing temperature profiles beneath the top boundary of the fluid layer. Time averaged distribution of the local heat flux indicated that the horizontal temperature difference enhances the heat transport at the low temperature side, while the transport at the high temperature side is maintained at similar value in the cases without the horizontal temperature gradient. Time variations of the heat transport distributions visualized that the separations of the thermal boundary layer are regularized in time and space by adding the horizontal temperature difference.
Flow visualization displayed that adding temperature difference unifies multiple large-scale circulations, which emerge at each moment in the thermal turbulence, into a single circulation despite horizontal temperature differences relatively small to the vertical ones. Quantified velocity fields by the image processing indicated that the circulation is enhanced larger by adding the temperature difference. Bulk Reynolds number, which is defined by spatial root-mean-square values of two components of velocity on a visualized vertical plane as the representative velocity scale, was chosen as the measure of momentum transportation by the convection. Variation of the Reynolds number seems to be organized by confined Rayleigh number, which was newly established in our recent study using simple addition of the vertical and horizontal temperature differences as the representative temperature scale and the height of the fluid layer as the length scale.
Local and instantaneous heat transport were quantified by analyzing temperature profiles beneath the top boundary of the fluid layer. Time averaged distribution of the local heat flux indicated that the horizontal temperature difference enhances the heat transport at the low temperature side, while the transport at the high temperature side is maintained at similar value in the cases without the horizontal temperature gradient. Time variations of the heat transport distributions visualized that the separations of the thermal boundary layer are regularized in time and space by adding the horizontal temperature difference.