File: sessions.txt

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    Typical XFOIL session keyboard inputs.
    All commands can be in lowercase.
    Blank lines below are only for easier reading -- they are not Return's!
    A command with its argument(s) ommitted will result in an input prompt.
    Some files in ./runs are used here.

    Note: The Eppler 387 coordinates are not smooth, so the Cp plots will 
          appear "noisy".  Xfoil's results will not be affected noticably 
          by such cosmetic defects, unless they are very severe.


LOAD e387.dat   ( or:  NACA 4410

GDES              (enter GDES menu)        |
CADD              (add points at corners)  |  These commands are optional,
<return>          (accept default input)   |  and are recommended only for
<return>          (accept default input)   |  Eppler and Selig airfoils   
<return>          (accept default input)   |  to give smoother LE shapes  
<return>          (return to Top Level)    |

PANEL           (regenerate paneling since better panel node spacing is needed)

OPER            (enter OPER menu)
ALFA 5.0
ASEQ 0.0 6.0 2.0

VISC 1.0e5      (set viscous mode, with argument anticipating Re prompt)
CL 0.78
CREF
CPX
BL              (plot boundary layer profiles)
cp_100_040.387
CREF

INIT            (force initialization of viscous solution for big alpha change)
ALFA -2.5
!               (keep iterating on this difficult case)

PACC            (set up for new polar 1)
<return>        (decline writing to polar save file)
<return>        (decline writing to polar dump file)
ASEQ -2.5 -2.0 0.05    (small steps when bottom transition is moving fast)
ASEQ -1.5  8.0 0.5     (bigger steps OK over most of polar)
ASEQ  8.2  9.0 0.2     (small steps when close to stall is more reliable)
PPLOT
PACC            (turn off polar 1 accumulation)

PPAX
<return>        (default alpha axis OK)
<return>        (default CL axis OK)
0.0 0.04 0.02   (better  CD axis)
<return>        (default CM axis OK)
PPLOT

RGET polref_100.387    (read in experimental polar data)
PPLOT

VPAR            (enter viscous parameter menu)
N 11.0          (set new lower turbulence level)
<return>        (back to OPER)

INIT
ALFA -2.5
PACC            (set up for new polar 2)
<return>        (decline writing to polar save file)
<return>        (decline writing to polar dump file)
ASEQ -2.5 -2.0 0.05    (small steps when bottom transition is moving fast)
ASEQ -1.5  8.0 0.5     (bigger steps OK over most of polar)
ASEQ  8.2  9.0 0.2     (small steps when close to stall is more reliable)
PPLOT           (both polars compared to experimental polar)
PACC
VISC

PWRT 1          (write polar 1 to save file)
e387_09.100     (filename indicates Eppler 387, Ncrit=9, Re=100K)

ALFA 4.0        (set inviscid solution for MDES design operations)
<return>        (exit OPER)

MDES
AQ 0.0 4.0 8.0
RESE
BLOW            (zoom in on region of interest, undo with RESE)
MODI            (modify some segment of one of the q(s) curves with cursor)
MODI            (repeat if necessary to modify further...)
MODI
.
.
EXEC
<return>
PANEL
OPER
CL 0.5
  etc....
<return>
GDES
GSET
CAMB
INPC
0.0 0.0
0.5 0.03
1.0 0.0
ADD
<return>
PLOT
TCPL            (turn off camber/thickness plotting activated in CAMB)
FLAP 0.70 0.04 -5.0
PLOT
EXEC
<return>
OPER
ALFA 5.0
  etc....



=========================================================================

  Typical XFOIL session to generate and plot two polars.
  All commands can be in lowercase.
  Blank lines below are only for easier reading -- they are not Return's!
  A command with its argument(s) ommitted will result in an input prompt.


LOAD  airfoil_file.dat
                                         
GDES              (enter GDES menu)        |
CADD              (add points at corners)  |  These commands are optional,
<return>          (accept default input)   |  and are recommended only for
<return>          (accept default input)   |  Eppler and Selig airfoils   
<return>          (accept default input)   |  to give smoother LE shapes  
<return>          (return to Top Level)    |

PANE            (optional: use if input airfoil_file.dat has inadequate points)

OPER            (enter OPER menu)
VISC 2e5        (toggle viscous mode, with Re = 200000)
TYPE 2          (optional: use if constant-lift polars are to be used)

ALFA -2         (specify minimum alpha (must give CL>0 for Type 2 polar))
PACC            (toggle auto accumulation on for new polar 1)
polar1_file     (choose polar save filename, or <return> for no file writing)
<return>        (decline dump file writing)
ASEQ -2  8 0.2  (compute alpha sequence to generate polar)
PPLO            (optional: plot the polar we have so far)
ASEQ 8.2 9 0.2  (compute additional points if needed)
PPLO
PACC            (toggle auto accumulation off)

RE 1.5e5        (set new Re = 150k, still using Type 2 CL dependence)
INIT            (current alpha=9, so re-initialize for very different alpha)

ALFA -2
PACC            (toggle auto accumulation on for new polar 2)
polar2_file     (choose polar save filename, or <return> for no file writing)
<return>        (decline dump file writing)
ASEQ -2  9 0.2  (compute alpha sequence to generate polar)
PACC            (toggle auto accumulation off)

PPLO              (plot all two polars currently stored)
PGET polar3_file  (optional: read previously-generated polar save file)
PPLO              (plot all three polars currently stored)
HARD              (make Postscript file of current polar plot)

<return>
QUIT



Notes:

1) Sometimes you may not want to automatically write the polar to a file.
In this case the PACC command is followed by a <return> rather than a filename:

PACC
<return>

You can later use PWRT if you decide to write out the polar after all:

PWRT           (will display all stored polars available for writing)
2              (choose polar 2 for writing)
polar2_file    (specify output filename)

This approach is "dangerous" in that if XFOIL crashes, the stored polars 
are lost.  This may or may not be a big deal, depending on how many polar
points you have.  XFOIL doesn't crash very easily, but it can happen.
A common cause is accidental specification of a silly flow condition, e.g.

ALFA 90

In viscous mode this will produce all sorts of numerical fireworks,
and possibly an arithmetic fault.


2) Saved polar files can be plotted with the separate PPLOT program.
Or you can use XFOIL itself, by reading in each polar file via PGET,
and then plotting them via PPLO.  PDEL, PSUM, etc. can also be used
to set up a list of polars that you want to plot.  PPAX can be used 
to change the polar plot axis limits.


3) It is sometimes necessary to change the airfoil name in the polar save file.
This can be easily done with a text editor.  But do not change the other
information headers, since this might confuse the polar file read routine.