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Old   May 8, 2014, 05:39
Default Interpreting the output of SU2
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Hedley
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1. As the solver runs the output line shows CLift ( Total ) and CDrag( total ) BUT I dont know where these are written to for viewing in Paraview ?

2. The paraview plot shows Pressure with a range BUT what is the actual pressure or is it a non dimensional number that I can Scale and get a plot of pressure distribution across the Chord / Half Span ?

3. The AOA is set in the .cfg file - Can a range be specified so that one could get an animated visualization of Pressure difference with AOA.

4. Is the AOA the effective AOA for the wing and does the solver automatically deduct the induced AOA based on flowfield conditions and downwash ?

5. Is the a method to visualize the flow field ie in the Trefftz plane

This is my strangest question but - is there a dummies guide to using SU2 ? - I am trying to investigate tip stall / wing drop and a sequence of steps would be of much help
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Old   May 15, 2014, 15:59
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Sean R. Copeland
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Hello Hedley,

Thanks for your interest in SU2, I'll try to hit your questions:

1. As the solver runs the output line shows CLift ( Total ) and CDrag( total ) BUT I dont know where these are written to for viewing in Paraview ?
A) All scalar performance quantities (lift, drag, moment, efficiency, etc.) are saved to the history file. You can track the convergence of each of these quantities here, and to get the converged value, simply take the last entry.

2. The paraview plot shows Pressure with a range BUT what is the actual pressure or is it a non dimensional number that I can Scale and get a plot of pressure distribution across the Chord / Half Span ?
A) All the solution files are nondimensionalized with the reference values specified in your configuration file. If you want to look at the dimensionalized pressure, you can either multiply your solution files by your reference pressure, or you can run a dimensional simulation with all reference values set to 1. If you want to plot the pressure distribution a particular chord wise station along your wing, you can do that using the settings in the GEOMETRY EVALUATION PARAMETERS section of the configuration file (in the newest version of SU2). Set the number, marker, orientation, and location of the cuts using the parameters here and set the GEO_PLOT_SECTIONS= YES to output these cuts just like the rest of the SU2 output files.

3. The AOA is set in the .cfg file - Can a range be specified so that one could get an animated visualization of Pressure difference with AOA.
A) Once upon a time we had a python script to evaluate at a range of angles of attack to calculate a drag polar. The particular script is 'compute_polar.py' located in the SU2_PY directory. I can't guarantee that this script still works, but it's easy enough to try it. If not, you can use this file as a baseline to write your own script to sweep the angle of attack.

4. Is the AOA the effective AOA for the wing and does the solver automatically deduct the induced AOA based on flowfield conditions and downwash ?
A) The specified angle of attack in the configuration file rotates the incoming free stream by the specified angle -- it doesn't account for any downwash effects at the wing.

5. Is the a method to visualize the flow field ie in the Trefftz plane
A) Not in a pre-packaged way. You can take your volume solution and just extract the data in the Trefftz plane using a post processing tool like Tecplot, or you can do it manually.

This is my strangest question but - is there a dummies guide to using SU2 ? - I am trying to investigate tip stall / wing drop and a sequence of steps would be of much help
A) Unfortunately the only public resources that are available currently for SU2 are those in the documentation on the website (su2.stanford.edu). We have discussed writing such a book -- but it's just a long-term goal at this point.


Hope that helps,
Sean
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Old   May 16, 2014, 00:23
Default Output interpretation
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Hedley
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Thank you for the clarification . I am currently using a trial version of pointwise which expires in 10 days . Is there an open source mesh generation package that you can recommend as whilst pointwise is really excellent I can not justify the expense as an had hoc user for a few models of my airplane.

My main goal is to try and visualise tip stall , modify outboard wing section and rinse and repeat until I have a spanwise loading that reduces tip stall . Initially I thought I could model a stall strip near the root and then visualise streamlines showing stall progression to establish optimal location if stall strip . This use case is typical for GA pilots or airplane builders and I think would make a wonderful tutorial - if it can be done at all - . I would be happy to pay one of the clever people to send me a step by step method to do this . Hedley@cynaps.co.za
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Old   June 5, 2014, 02:44
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Heather Kline
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I am not sure of any open source mesh generation for the .su2 format, however many use the more common cgns format.
SU2 will need to be compiled with cgns support.
See http://adl-public.stanford.edu/docs/...RED/Mesh+files for more details on how to do this.
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Old   June 5, 2014, 04:31
Default SU2 - holding pattern
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Hedley
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Thanks for reply ,

I have given up on SU2 for the time being until I can find an example or tutorial that makes sense for a low speed wing 3D . It would be great to run such a wing at +- .2 Mach and then see expected lift and drag for the wing and at various stations to get an idea of span distribution of lift across the platform to analyse stall conditions .

One could then change the geometry to have different wing twist and see the effect .

Until now all I have seen is high speed tutorials and I have never been able to get a Cl and Cd number that is anywhere what is expected . Either I dont know what I am doing - Or the solver is not tested at low speed - Or the mesh is wrong - Or a combination of all three .
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