Open Source Software Course: Assignment 1

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1 Open Source Software Course: Assignment 1 Mengmeng Zhang Aeronautical and Vehicle Engineering, Royal Insistute of Technology (KTH), Stockholm, Sweden Mengmeng Zhang Open Source Software Course / 15

2 Solvers Three solvers icofoam: incompressible flow solver interfoam: two-phrase incompressible flow solver simplefoam: an implementation for steady incompressible flow using the SIMPLE algorithm SIMP LE algorithm in OpenF OAM Mengmeng Zhang Open Source Software Course / 15

3 icofoam icofoam: cavity, cavityfine Pressue for cavity original mesh Pressure for cavity fine (doubled) mesh The mesh is refined by increasing the number of cells in each direction, in blockmeshdict file. The mesh is generated by blockmesh. One can see that the coarse mesh results mapping on the fine mesh by mapfields. Mengmeng Zhang Open Source Software Course / 15

4 icofoam icofoam: cavity, cavityfine, cavitygrade Velocity magnitude for cavity coarse mesh Velocity magnitude for cavity fine mesh Velocity magnitude for cavity grade mesh The grading mesh is obtained by changing the gradient (or mesh growth rate) in each direction from 1 to 2, in blockmeshdict under the folder /constant/polymesh. The fine mesh result are mappling onto the grade mesh by mapfields. The case is solved by running icofoam. Mengmeng Zhang Open Source Software Course / 15

5 icofoam icofoam: cavity, cavityclipped, cavityfine Velocity vector for cavity original mesh Velocity vector for cavity clipped mesh Velocity vector for cavity fine mesh The cavity mesh and the fine mesh results are all mapped from the coarse (original) mesh results. Figures above show the velocity vector by filtering cell centers and then using Glyphs in ParaView c. Mengmeng Zhang Open Source Software Course / 15

6 icofoam icofoam: cavity, cavityhighre - I Velocity magnitude for cavity with R e = 10 Velocity magnitude for cavity with R e = 100 The Reynolds number is increased 10 times in the latter case by decreasing the kinematic viscosity by factor of 10 in transportproperties dictionary. Mengmeng Zhang Open Source Software Course / 15

7 icofoam icofoam: cavity, cavityhighre - II Streamline for cavity with R e = 10 Streamline for cavity with R e = 100 The streamline can be visualized by selecting Stream Tracer with line source and the same number of the lines for both cases. All the cases for icofoam can be run by Allrun. Mengmeng Zhang Open Source Software Course / 15

8 interfoam interfoam: dambreak, dambreakfine - I Velocity magnitude on coarse mesh, t=1s Velocity magnitude on fine mesh, t=1s Refine the mesh in blockmeshdict (same as in icofoam solver). Use the setfields utility to update the fields. Mengmeng Zhang Open Source Software Course / 15

9 interfoam interfoam: dambreak, dambreakfine - II Water (blue) and air (red) on coarse mesh, t=1s Water (blue) and air (red) on fine mesh, t=1s We can see that the mesh size effects the results quite a lot. Mengmeng Zhang Open Source Software Course / 15

10 simplefoam simplefoam: pitzdaily - I In this case it calculates a steady turbulent flow over a backward-facing step. The flow goes from inlet (left) to outlet (right). At the inlet we have strong uniform flow in the x direction and, as it passes over the step, it generates shear on the fluid below, generating a vortex in the bottom half of the domain. The regions of high shear will therefore be close to the centreline of the domain and close to the walls. The mesh is defined in blockmeshdict and generated by blockmesh. In controldict, the time step deltat is set to 1 since in steady state cases such as this is effectively an iteration counter. With benefit of hindsight we know that the solution requires 1000 iterations reach reasonable convergence, hence endtime is set to Mengmeng Zhang Open Source Software Course / 15

11 simplefoam simplefoam: pitzdaily - II Turbulent kinetic energy, 100 iteration. Turbulent kinetic energy, 1000 iteration (steady state) The case is convergeced after 765 iterations. Mengmeng Zhang Open Source Software Course / 15

12 Utilities : utilities used, to be contid:: blockmesh: a multi-block mesh generator (every case); checkmesh: checks validity of a mesh (every case); refinemesh: refines cells in multiple directions (0,1,2 direction) (can be used in cavityfine instead of using mapfields); Mengmeng Zhang Open Source Software Course / 15

13 Utilities : utilities used, to be contid:: mapfields: maps volume fields from one mesh to another, reading and interpolating all fields present in the time directory of both cases. Parallel and non-parallel cases are handled without the need to reconstruct them first (cavityfine, cavityclipped); setfields: set values on a selected set of cells/patchfaces through a dictionary (dambreakfine); decomposepar: makes a domain decomposition for parallel computations (can be used for large cases); Mengmeng Zhang Open Source Software Course / 15

14 Utilities : utilities used The usages for all the utilities can be found if we type: utility -help For example, if we would like to find out the usage of utility blockmesh, we type: blockmesh -help in the command window. All of the utilities must be run under the case folder we want to run. Mengmeng Zhang Open Source Software Course / 15

15 Post-processing and visualization : parafoam Once the case is done, a temporary.openfoam file is generated when parafoam is opened. It can be saved to VTK file for next time opening in Paraview directly. In parafoam (or Paraview) the case can be visualized in many aspects, for different time steps and so on. Different filters help to visualize different solutions, such as velocity, pressure, kinetic energy, transportation and so on. The mesh can be visualized by selecting edge. Vectors can be visualized by selecting Glyphs, streamline Stream Tracer, and contours Contour. The case can be cut by Clip and also sliced by Slice. The filtered/processed results can be saved as.csv file which data are stored in columns that can be post-processed in other plotting tools. To open multiple cases in parafoam one needs to generate additional case by hand using touch command. Mengmeng Zhang Open Source Software Course / 15