EFFECTS OF DOMAIN-SIZE ON LARGE-EDDY SIMULATION FOR A FORCED-CONVECTION FLOW IN A PIPE WITH CIRCUMFERENTIALLY-VARYING HEAT FLUX

摘要

We performed large-eddy simulations by using an open source CFD code, OpenFOAM to examine the performance of large-eddy simulations for examining turbulence heat-transfer processes of forced-convection in a pipe with non-homogeneous thermal boundary conditions; an accurate description of such processes is of practical interest of nuclear engineering. Special attention was paid to the domain size in the streamwise direction, which must be closely related to the turbulence processes with super structures. Three domain sizes were used: the size was varied from 5R to 100R, where R is the radius of the pipe. The turbulence intensities of temperature fluctuations near the heated surface strongly depended on the domain size. This was because that the turbulence intensities were closely related to large-scale fluid motions, the scale of which is much larger than 25R, and such large-scale fluid motions interfered in the dynamics of turbulence heat transfer processes near the heated surface. This indicates that the large-eddy simulations for estimating the turbulence heat-transfer rate in the pipe must require the large domain size in the streamwise direction with well resolved grids to capture turbulence eddies near the heated surface.