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February 6, 2023, 07:03 |
BuoyantSimpleFoam pipe flow
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Senior Member
Nico
Join Date: Jan 2022
Location: Germany
Posts: 122
Rep Power: 6 |
Hey guys,
i want to simulate a turbulent flow through a pipe with heat exchange in a pipe. I have made a pure heaxaeder mesh in gmsh and imported in OF. The simulation itself runs and converges. However the results are so far not okay. I want to validate my simulation with the Dittus Boelter equation that give the Nusselt Number as a function of Reynolds and Prandtl Number. The result of the equation is about 100, ym simulation results in 273. I first examined the mesh. The checkMesh utility with additional flags resulted in following: Code:
Mesh stats points: 2251612 faces: 6693073 internal faces: 6633527 cells: 2221100 faces per cell: 6 boundary patches: 4 point zones: 0 face zones: 0 cell zones: 1 Overall number of cells of each type: hexahedra: 2221100 prisms: 0 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 0 polyhedra: 0 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Topological cell zip-up check OK. Face-face connectivity OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology Bounding box inletFluid 3173 3212 ok (non-closed singly connected) (-0.5 -0.5 0) (0.5 0.5 0) outletFluid 3173 3212 ok (non-closed singly connected) (-0.5 -0.5 14) (0.5 0.5 14) wallEntrance 7600 7676 ok (non-closed singly connected) (-0.5 -0.5 0) (0.5 0.5 2) wallDeveloped 45600 45676 ok (non-closed singly connected) (-0.5 -0.5 2) (0.5 0.5 14) Checking geometry... Overall domain bounding box (-0.5 -0.5 0) (0.5 0.5 14) Mesh has 3 geometric (non-empty/wedge) directions (1 1 1) Mesh has 3 solution (non-empty) directions (1 1 1) Boundary openness (3.44459e-17 6.30548e-16 -1.28511e-16) OK. Max cell openness = 3.28417e-16 OK. Max aspect ratio = 7.45032 OK. Minimum face area = 7.69428e-05. Maximum face area = 0.000826506. Face area magnitudes OK. Min volume = 2.53194e-06. Max volume = 7.36883e-06. Total volume = 10.9831. Cell volumes OK. Mesh non-orthogonality Max: 38.9458 average: 6.83294 Non-orthogonality check OK. Face pyramids OK. Max skewness = 1.52765 OK. Coupled point location match (average 0) OK. Face tets OK. Min/max edge length = 0.00384714 0.0413253 OK. All angles in faces OK. Face flatness (1 = flat, 0 = butterfly) : min = 0.999983 average = 1 All face flatness OK. Cell determinant (wellposedness) : minimum: 0.149651 average: 3.62146 Cell determinant check OK. Concave cell check OK. Face interpolation weight : minimum: 0.263644 average: 0.494385 Face interpolation weight check OK. Face volume ratio : minimum: 0.365609 average: 0.971067 Face volume ratio check OK. Mesh OK. End Code:
wallHeatFlux wallHeatFlux1 write: writing object wallHeatFlux min, max, Q [W], q [W/m^2] for patch wallDeveloped = 999.817, 1000.27, 37688.5, 1000 surfaceFieldValue outletTemperature write: areaAverage(outletFluid) of T = 294.348 surfaceFieldValue wallDevelopedTemperature write: areaAverage(wallDeveloped) of T = 299.835 surfaceFieldValue wallEntranceTemperature write: areaAverage(wallEntrance) of T = 298.551 surfaceFieldValue inletTemperature write: areaAverage(inletFluid) of T = 293.15 End Note that the inlet temperature and the wallheatflux are boundary conditions. My calculation of the Nusselt number is done in following way: t_bulk = (t_inlet+t_outlet)*0.5 h = q/(t_wall - t_bulk) with t_wall = areaAverage(wallDeveloped) and q = wallHeatFlux Nu = (h*d_h)/kappa with d_h the hydraulic diameter of my pipe and kappa the thermal conductivity of the fluid at bulk temperature. I have attached a few pictures from my results. I think (pure gut feeling) the the temperature of the outlet is too low and the wall temperature is too high. In my T file the wall heat flux is defined as: Code:
wallEntrance { type externalWallHeatFluxTemperature; mode flux; q uniform 1000; kappaMethod fluidThermo; value uniform 293.15; } wallDeveloped { type externalWallHeatFluxTemperature; mode flux; q uniform 1000; kappaMethod fluidThermo; value uniform 293.15; } Thanks in advance! Image explanation: The first image shows the temperature plot as seen from the outlet; the second from the inlet and the third a clip through the pipe. |
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