Questions from beginners (radiation, aerodynamics, aerodynamic moments)

[tomato143398]

Dear technicians, hello. I recently got into the PICLAS software (beginner) and am also learning and trying out some calculations. At present, there are two problems, the first one: I want to calculate the radiation between gas particles, particles and surfaces (photon tracking), but there is no similar parameter.ini file in the user manual, I have tried some, all failed. I would like to ask you how to learn the relevant knowledge of radiation (photon tracking). If there is a relevant case tutorial, please recommend it to me. Second: I want to calculate the aerodynamic force and torque of the geometric model, but there is no relevant data in the post-processing, and there is no relevant introduction in the user manual. How should I proceed?

[irsbeyer]

We don't have tutorials for radiation modeling yet. However, you can take a look at the regressioncheck-directory where you can find some examples. In "NIG_Radiation" there are cases where local cell emission is simulated (Rad_Emission*) and where radiative transfer is simulated using a black body radiator (RadTrans_Cylinder*). A detailed description of the cases can be found in https://doi.org/10.1016/j.jqsrt.2022.108083. A combined case can be found in "WEK_DSMC_Radiation" and "WEK_Radiation", where first a DSMC simulation is performed and then the radiation and radiative transfer are simulated using the results of the DSMC simulation. This case is based on the 70 degree cone of the tutorials, but the temperatures are increased for higher radiative energy. All parameters should be described in the piclas-documentation, if not, please let us know where you have difficulties so that we can improve it.

For the calculation of aerodynamic forces such as the drag, the result "Total_ForcePerArea" (i.e. pressure) in the considered direction x, y, or z needs to be integrated over the reference area in this direction. When ParaView is used, the filter "IntegrateVariables" can be applied to do this. If symmetries are employed in the simulation (e.g. only a quarter of a satellite is simulated), the result for the drag needs to be adapted correspondingly.

We hope this answers your questions.

[tomato143398]

Thank you for your answer, which provides an idea to solve the radiation calculation. I have come across some problems recently. First, spectral information of molecules and atoms is required for radiation calculation, so only oxygen atom, nitrogen atom and nitrogen molecule spectral information are provided in the "regressioncheck" document. Unfortunately, I need other molecular information such as oxygen. I searched the nist database according to the brief introduction, but I did not find all the information. I was confused by the data structure in the spectral file such as "N2i_NIST". 2: When I perform two-position axisymmetric calculation (it seems necessary to use structural grid), the grid is output cgns file by pointwise, and the corresponding boundary conditions are also set, and the relevant files can be seen in the attachment. The problem is that after the successful output of h5 grid file from the hopr.ini file, the egative determinant of Jacobian in calc_df_inv: Df-determinant 2.8028340899312387E-002 2.1702497631738722E-003 3.4605515035811552E-003 3.2600505634482996E-002 is: -9.2124834649434163E-004 "(see Attachment 1 for relevant documents) or" The calculation will stop at a certain time, but the program does not crash ". Third, there is some confusion about the Settings associated with variable time step calculations, such as Part-VariableTimeStep-Distribution, part-VariableTimeStep-Distribution-Adapt and Part-VariableTimeStep-LinearScaling, Part-VariableTimeStep-ScaleFactor I don't know how to use it. Finally, there is the idea that the radiation calculated in piclas is only for atoms and molecules, and it is not clear whether the algorithm can be applied to ions. Looking forward to your reply！ May joy and health be with you always. May happiness follow you wherever you go！ Sincerely yours！ At 2025-01-28 15:40:56, "irsbeyer" ***@***.***> wrote: We don't have tutorials for radiation modeling yet. However, you can take a look at the regressioncheck-directory where you can find some examples. In "NIG_Radiation" there are cases where local cell emission is simulated (Rad_Emission*) and where radiative transfer is simulated using a black body radiator (RadTrans_Cylinder*). A detailed description of the cases can be found in https://doi.org/10.1016/j.jqsrt.2022.108083. A combined case can be found in "WEK_DSMC_Radiation" and "WEK_Radiation", where first a DSMC simulation is performed and then the radiation and radiative transfer are simulated using the results of the DSMC simulation. This case is based on the 70 degree cone of the tutorials, but the temperatures are increased for higher radiative energy. All parameters should be described in the piclas-documentation, if not, please let us know where you have difficulties so that we can improve it. For the calculation of aerodynamic forces such as the drag, the result "Total_ForcePerArea" (i.e. pressure) in the considered direction x, y, or z needs to be integrated over the reference area in this direction. When ParaView is used, the filter "IntegrateVariables" can be applied to do this. If symmetries are employed in the simulation (e.g. only a quarter of a satellite is simulated), the result for the drag needs to be adapted correspondingly. We hope this answers your questions. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you authored the thread.Message ID: ***@***.***>

[irsbeyer]

1. The input of the radiation data is based on the input of the radiation program PARADE. You can find the data structure in the referring literature. In addition, we will add a small description to the PICLas documentation to make the files a little easier to understand.
2. The grid does not have to be a structured grid, but only one cell in z-direction is allowed, which has to be centered around zero in the z-direction. A exemplary simulation can be found e.g. in the DSMC-cone-2D tutorial (documentation Section 7.5). Unfortunately, you did not attach any data, so we cannot have a look into it. If it still does not work, please reach out again.
3. The variable time step is described in detail in Section 4.13 of the documentation. There are also several regressionchecks that use a variable time step. You can just grep for the variable Part-VariableTimeStep-Distribution for examples.
4. Yes, radiation of atomic and molecular ions can be simulated as well. They are enabled and treated like neutral atoms and molecules (Radiation-bb-atoms, Radiation-bb-molecules), the data files look the same as for neutral atoms and molecules, but with the corresponding energy levels and transition lines/bands.

If you need support with your simulations, you can also contact us directly (boltzplatz GmbH), where we offer exactly this as a service.

[tomato143398]

1. The input of the radiation data is based on the input of the radiation program PARADE. You can find the data structure in the referring literature. In addition, we will add a small description to the PICLas documentation to make the files a little easier to understand.
2. The grid does not have to be a structured grid, but only one cell in z-direction is allowed, which has to be centered around zero in the z-direction. A exemplary simulation can be found e.g. in the DSMC-cone-2D tutorial (documentation Section 7.5). Unfortunately, you did not attach any data, so we cannot have a look into it. If it still does not work, please reach out again.
3. The variable time step is described in detail in Section 4.13 of the documentation. There are also several regressionchecks that use a variable time step. You can just grep for the variable Part-VariableTimeStep-Distribution for examples.
4. Yes, radiation of atomic and molecular ions can be simulated as well. They are enabled and treated like neutral atoms and molecules (Radiation-bb-atoms, Radiation-bb-molecules), the data files look the same as for neutral atoms and molecules, but with the corresponding energy levels and transition lines/bands.

If you need support with your simulations, you can also contact us directly (boltzplatz GmbH), where we offer exactly this as a service.

Thank you for your reply. I want to simulate the radiation of molecules (nitrogen, oxygen, nitric oxide, carbon monoxide), atoms (nitrogen, oxygen) and ions (corresponding ions). The reference file only contains the spectral information of nitrogen, oxygen and nitrogen atoms. PARADE corresponding input information, I looked online without the slightest clue. I hope you can provide the relevant documents or the location of all the spectral information so that I can find it.