# outputs interpretation

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June 26, 2014, 03:13
outputs interpretation
#1
Member

Hedley
Join Date: May 2014
Posts: 52
Rep Power: 10
The toolchain is now working great under Linux with Intel MPI for parallel . When I run the inv_NACA0012.cfg which takes only 21.6 seconds on my home PC the output in paraview in the flow.VTK has the following . Note solve is at Mach 0.1135 and AOA 5.25 degrees.

Conservative 1
Conservative 2
Conservative 3
Conservative 4
Mach
Pressure
etc

Question - What are these actually showing on the plot eg does conservative 3 show transition point ?? . The scale shown on each plot also dont make sense to a beginner like me . For example how would I see lift distribution over the chord ?
Attached Images
 cons1.jpg (16.0 KB, 16 views) cons2.jpg (15.6 KB, 12 views) cons3.jpg (18.4 KB, 15 views) cons4.jpg (17.4 KB, 9 views)

 July 8, 2014, 20:56 #2 Senior Member   Heather Kline Join Date: Jun 2013 Posts: 309 Rep Power: 12 The conservative variables are the values which are conserved in the equations: conservative_1: density, (conservation of mass) conservative_2: density*x-velocity (conservation of momentum in x) conservative_3: density*y-velocity (conservation of momentum in y) conservative_4: density*e (conservation of energy). So this gives you the density, momentum, and energy distributions of the flow, from which the other variables can be calculated. For the lift you will want to use the surface flow output, which will give you the pressure coefficient (pressure nondimensionalized) on the surface. For a 2-dimensional airfoil this does not give you the "lift" distribution, it gives you the pressure distribution, from which the lift is calculated. A lift distribution describes the distribution of lift over a three-dimensional wing. I highly encourage you to read a book such as Anderson's "Fundamentals of Flight" (or any aerospace textbook, but Anderson happens to be a favorite of many aerospace engineers). The transition point is more complicated. This will become clearer as you read the sections in the book above on boundary layers, turbulence, and viscous flow. In short, an euler simulation is not going to show you that information, and I recommend that you look through the cfd-online wiki as a starting point for finding out more about transition models (if you don't want to buy a textbook).

 July 9, 2014, 01:43 #3 Member   Hedley Join Date: May 2014 Posts: 52 Rep Power: 10 Thank you for this informative reply . I do have Anderson's book and 28 others plus have done Drela's on line courses at MITX. Most books and courses tend to be in English for a few pages after which the content transitions to ' Math on Steriods '. It seems as if lift distribution on 3D wing is a combo of - local lift , downwash , induced lift and hence effective cL , taper ratio , sweep , airfoil section profiles , aspect ratio among others - and then to add variety into the mix if I have some squashed insects on the leading edge of the laminar flow airfoil then early transition at that point , and so on . The end goal remains - To run a solve over my airplane wing www.falcomposite.com - that has been meshed in Pointwise to establish where the stall will start and then to remodel the outboard section - perhaps Hoerner tip - and re run until I have optimized low speed handling to lessen current wing drop at critical AOA

 July 9, 2014, 23:07 #4 Senior Member   Heather Kline Join Date: Jun 2013 Posts: 309 Rep Power: 12 If you have not tried this already, I would suggest trying out the compute_polar.py python script which will help produce a plot of lift vs angle of attack. This script is in the SU2_PY directory.

 July 10, 2014, 15:33 #5 Member   Hedley Join Date: May 2014 Posts: 52 Rep Power: 10 Thanks do you have an example command line input for this compute_polar.py ?

 July 12, 2014, 13:37 #6 Senior Member   Heather Kline Join Date: Jun 2013 Posts: 309 Rep Power: 12 The command line will be: compute_polar.py -f {yourconfigfile} -n {numberofprocessors} -i {iterations} iterations and number of processors/partitions are optional. In order to find out what the options are for any of the python files, simply open the file and look for parser.add.option near the top of the file. By looking at these lines you can find out what the options and defaults are. If you don't want the default range of mach number and aoa you will need to edit the file manually. Python files do not need to be recompiled after editing. The angle and mach number ranges are controlled by np.linspace commands, which you can find out more about from python documentation.

 July 12, 2014, 14:02 #7 Member   Hedley Join Date: May 2014 Posts: 52 Rep Power: 10 Thanks again - perhaps you can write a user guide which I would be happy to pay for . I recently got a book after watching the lecture http://youtu.be/QKCK4lJLQHU which was interesting

 July 14, 2014, 08:58 #8 Member   Hedley Join Date: May 2014 Posts: 52 Rep Power: 10 Thanks for the command - It has been running for 48 hours and is over 300,000 iterations . Do you know how to get it to stop -- besides ctrl-c Do you know what format the polars are in as i only have paraview.

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