Jump to content


  • Content Count

  • Joined

  • Last visited

  • Days Won


Everything posted by cfdguru

  1. Hi @Nadzrin, The advancing front vs. Delaunay triangulation discussion actually refers to the surface meshing. AcuSolve doesn't have much of a preference either way when it comes to surface meshing. The runtime argument I made is in reference to the volume meshing (AcuConsole's octree vs HW-CFD's approach). In this case, the linear solver *should* perform better with the mesh from HW-CFD. Note that the performance won't be radically different between the two approaches, but according to our linear solver experts on the AcuSolve team, the more random mesh is beneficial. Would be an interesting test for someone to run. and report the results!
  2. Right. AcuConsole's mesher will create octree patterns in large open regions. That mesher works as follows: 1.) Create surface mesh using the delaunay triangulation approach 2.) Extrude boundary layers from the surface into the volume regions 3.) Build octree mesh in volume regions 4.) Connect the surface/boundary layer mesh to the octree regions using delaunay or advancing front technique. However, the question is what you feel is superior about the octree approach. The structured nature of an octree mesh is not beneficial to AcuSolve. The randomness of the nodal positions in the HW-CFD mesh tends to make the linear algebra less stiff and can actually lead to faster run times on meshes of similar node count. Additionally, the 2:1 size jumps that are present in the octree mesh can cause a stiff linear system in AcuSolve as well. Overall, you should see that the HW-CFD mesh performs better in the solver, and is also faster to generate due to the more effective use of mult-threading. I'd be interested to hear if your experience is not consistent with these expectations.
  3. Here's a bit more detail on why the two meshes are different. HW-CFD uses an advancing front meshing technique which will cause the mesh patterns to radially grow away from the edges. AcuConsole is using a Delaunay triangulation approach. So, you won't see the radial patterns in the mesh. Also, your original comment about volume meshing caught my attention. What is it about the AcuConsole volume mesh that you feel is superior to the HW-CFD volume mesh?
  4. This is actually a ParaView bug. The Ensight reader doesn't properly handle the displace coordinates option. There are a couple work arounds available. The easiest is to write the data out using CGNS format instead of Ensight. The other option would be to continue using Ensight format, but deactivate the "Mesh Motion" option in AcuOut (alternatively, you can just comment out the corresponding line in the .case file and not re-run the conversion). Then, you'll be able to displace the coordinates in ParaView manually by adding the mesh_displacement vector to the coordinates vector at each time step. This can be done using the Calculator filter by enabling the "Coordinate Results" option.
  5. This error generally means that you are using different versions of the code on the machine that generated the input and the machine on which you are trying to run the mesher. Make sure you are using consistent versions on both machines.
  6. To model an adiabatic wall, you need to set all mechanisms of heat transfer to zero. AcuSolve allows you to model various different heat transfer mechanisms on a given surface. So, let's discuss the two that you are referring to separately. The first mechanism is the heat transfer from the conduction and convection of the material adjacent to the wall that you are assigning boundary conditions to. To zero this mechanism of heat transfer, you need to set temperature_type=flux, and heat_flux = 0.0. The second mechanism of heat transfer that AcuSolve supports on the surface is heat flux to the surroundings that are not present in the model. Let's consider an insulated wall that is adjacent to a large room with a constant temperature. In this case, it may be desirable to model the convection of the wall to the surroundings. This can be accomplished by setting a convective heat flux coefficient and reference temperature. The default setting of convective_heat_coefficient=0.0 ensures that this mechanism of heat transfer is disabled. So in your case, if you want the wall to be truly adiabatic, you will need to set heat_flux=0.0, and convective_heat_coefficient=0.0. Note that when convective_heat_coefficient=0.0, the value specified for reference temperature is irrelevant.
  7. AcuSolve solves for the static pressure as a nodal value. So, what you are seeing in AcuFieldView is static pressure. You can easily compute dynamic pressure using the function calculator if you are interested in seeing contours of that.
  8. The error message indicates that you don't have the AcuSolve feature enabled in your license file. Have you checked the license file to see if that is indeed the case?
  9. This type of error generally appears due to some non-English characters being present in the AcuConsole database. Can you check for these in your surface/volume group names as well as the script that you wrote for the initial conditions?
  10. I think that explains it then. If the input file was written in V13.0, it won't run in V12.0. However, if it is written in V12.0, it will run in V13.0.
  11. What we need to see is the top of the .Log file where it tells what version of AcuPrep is running. It should look something like this: acuPrep: Date = Tue Nov 11 07:40:07 2014 acuPrep: Problem = channel acuPrep: Run = 1 acuPrep: Hostname = sacandaga acuPrep: Platform = Linux 3.11.10-21-desktop x86_64 acuPrep: Machine = linux64 acuPrep: Release = 13.0 acuPrep: Release date = Jun 6 2014 acuPrep: Number of subdomains = 1 acuPrep: Number of threads = 1 acuPrep: Working directory = ACUSIM.DIR acuPrep: ------------------------------------------------------------------ ...
  12. Could you upload your .Log file and .inp file? That will tell us exactly what is going on.
  13. This option should appear under the SIMPLE_BOUNDARY_CONDITION command. It looks like that is where you have it based on the error message. So, it may be that you are just using the wrong version of the code. The wall_function_heat_flux factor was introduced in V13.0, so make sure that is the version you are using.
  14. Density is available if you have DERIVED_QUANTITY _OUTPUT turned on in the AcuSolve input file.
  15. Hi Prashant, There are three steps required to perform a restart: 1.) Ensure that you have the RESTART_OUTPUT enabled in your first run. You will only be able to restart from the time steps for which this type of output is available on disk. 2.) Create a new input file that contains the RESTART{} command and the commands that you want to change. For example, you could create a file called myRestart.inp that contains the following: RESTART{} DENSITY_MODEL("Air"){ type = ideal_gas } RUN{} Note that you only need to issue the commands/parameters that you want to change in the restart file. 3.) Restart the simulation using the new input file: acuRun -inp myRestart.inp Check out the RESTART command in the AcuSolve Command Reference Manual for some more information. You can also search this forum. There have been some other posts regarding restart of simulations.
  16. Correct. Both of the settings described above should produce identical results.
  17. For a simulation like this, you essentially want to model an open atmosphere. So, there are a few options. You could make a huge bounding box around the vehicle and set all of the walls to slip. The assumption here is that the walls are so far away from the exhaust pipe that they won't impact the flow behavior. The other option is that you can set all of your walls to outflow, and let the flow enter and exit as it desires. You will need to make sure you turn on backflow conditions to bound the eddy viscosity as it re-enters the domain, however.
  18. File-->Open Restart-->Formula, then select the .frm file that you have. That will read the file, generate all of the formulas that are contained within it, then make them available as scalar values for display.
  19. It is possible that HyperView is interpolating the solution to the cell centers to produce this contour. AcuFieldView, however, does not do that.
  20. The velocity magnitude at a no-slip wall is zero. You can certianly plot it in AcuFieldView, but the results won't be that interesting. Since AcuSolve is finite element based, the nodes on the wall satisfy this constraint identically, and hence your results are zero. Finite volume codes tend to plot the velocity magnitude at the cell center of the first element off the wall. However, this is NOT the velocity at the wall.
  21. Spalart-Allmaras is an excellent all-purpose model that works well for external aerodynamics. If your flow has a lot of separation and you are interested in the transient behavior, then DES should be used. The default value of relaxation factor in AcuSolve is 0.0 (meaning no relaxation applied). For steady cases, you can increase it as needed up to around .7 or so. For transient cases, it should always be zero.
  22. AcuConsole requires various inputs in order to automatically compute the turbulence parameters. One of those inputs is a velocity scale. So, the velocity that you enter is the one that is used as the velocity scale. For the case of a simple, constant velocity inlet, the velocity scale should be equal to the average velocity at the inlet. Here is a good reference: http://www.cfd-online.com/Wiki/Turbulence_free-stream_boundary_conditions
  23. Yes, you can use AcuProbe.
  24. Cl and Cd can be computed based on the surface output values for traction. The traction represents the force on the airfoil. Knowing the force and angle of attack, you can easily compute the lift and drag coefficients. This can be done using acuProbe, or you can convert the data to table format and use your favorite spreadsheet or plotting program.
  25. cfdguru

    Pipe Flow

    Prithvi, If you use the SST model to perform your simulation, you will have access to the turbulent kinetic energy.
  • Create New...