THE EVOLUTION OF MATERIAL-SURFACES IN CONVECTION WITH VARIABLE VISCOSITY AS MONITORED BY A CHARACTERISTICS-BASED METHOD

We have studied the evolution of material surfaces in strongly time-de pendent convection for both Newtonian and non-Newtonian temperature- a nd depth-dependent theologies. A spline-characteristic method has been employed. The method of characteristics is second-order in time and f ourth-order in space. Our strategy is to employ a very dense grid for the material surface field with about 50 to 100 times more points than for the temperature field grid. We have detected sharp entrainment of the surrounding material into both the ascending and descending flow structures. We have observed the breakoff process involving the descen ding plume. Mixing takes place very differently for the two theologies . With time, small vortical features are developed inside the Newtonia n plumes, while unmixed islands still persist in the non-Newtonian flo w.