QUICK-START FOR FLUENT FOR MAE 3241
Open Cygwin
At prompt, type startxwin.bat
After a moment, this will open another window (notice the icon is an ‘X’ in
the upper left corner of the window). Commands will now be typed in this
window.
At the prompt of the ‘X’ window, type xhost +
This will allow you to see all the windows needed by Fluent.
Login to olin.fit.edu
ssh –Y –l tracks_username olin.fit.edu
If you are asked whether you are sure you want to connect, type yes.
Enter your password.
Move to your working directory.
cd directory
At the prompt, type fluent 2d
If you get an error at this point, try the following:
In Windows: START MENU PROGRAMS ACCESSORIES COMMAND PROMPT
Type IPCONFIG
Record the IP Address
In the ‘X’ Window type setenv DISPLAY ipaddress:0.0
whereipaddressis the IP Address you just recorded.
Type fluent 2d again. If this doesn’t resolve the problem, see me.
From this point on, you will be guided through the menus of Fluent to perform various tasks. The procedures below will help you set up your first case for zero-angle-of-attack. From there, repeat the relevant procedures to change the angle of attack and run the various cases.
FILE READ CASE…
Select the naca0007.msh file from your working directory.
GRID CHECK
This verifies your grid. It should produce no errors.
DEFINE MODELS SOLVER…
Select “Coupled”. Use all other default settings.
DEFINE MODELS ENERGY…
Turn on the energy equation.
DEFINE MODELS VISCOUS…
Select the Spalart-Allmaras model. Use the default settings.
DEFINE MATERIALS…
Make sure that “air” is selected as the default Fluent Fluid Material.
Change the “Density” option to “Ideal Gas.”
Change the “Viscosity” option to “Sutherland.” Use default settings.
Press “Change/Create” followed by “Close.”
DEFINE OPERATING CONDITIONS…
Set Pressure to zero. All calculated pressures are now “gauged” to this pressure.
DEFINE BOUNDARY CONDITIONS…
Select the “freestream” boundary on the left column and “pressure-far-field” type on the right column. If it asks you to verify the change, press “yes.” Press “Set…” if the pressure far-field window does not appear. Change the values as follows:
P = 101325 (Gauge Pressure)
M = 0.2
T = 300
X = 1.0
Y = 0.0
Select Turbulent Viscosity Ratio from the drop-down menu next to “Turbulent Specification Method” and makesure its value is set to 10.
Note that the X and Y values are used to determine the angle of attack.
X = cos
Y = sin
When you have set the freestream boundary conditions, press OK. Select the
“outflow” boundary on the left column and the “pressure-outlet” on the right
column. Verify the change, if necessary. Press “Set…” if the pressure-outlet window does not open by itself. Set the pressure, temperature, and turbulent viscosityratio values as above.
Press OK when done, and exit the Boundary Conditions window.
(If you check, you will see that the wall boundaries are already set to the “wall”
boundary condition type.)
SOLVE CONTROLS SOLUTION…
Modified Turbulent Viscosity Ratio = 0.9
Turbulent Viscosity = 1.0
Solid = 1.0
These values aid in the convergence of your solution.
Courant Number = 5
This value essentially controls the speed at which you will reach a steady solution.
Under “Discretization,” set both options to “Second Order Upwind.”
Press ‘OK’ to exit.
SOLVE INITIALIZE INITIALIZE…
Select “freestream” from drop-down menu and press “Init” then “Close.”
SOLVE MONITORS RESIDUAL…
Under “Options,” change “Print” to “Plot”
Change the “Convergence Criterion” for “nut” from 0.001 to 1.0e-06.
(“nut” corresponds to the turbulent viscosity.)
Press “OK.”
SOLVE MONITORS FORCE…
Here you will set options so you can watch the progress of your solution.
Select the “Plot” option.
Highlight wall-3 and wall-4.
Ensure “Drag” is selected from the “Coefficient” drop-down menu.
Plot Window should have a value of 1.
Set X = 1.0, Y = 0.0. (These values should match your velocity components you
set for boundary conditions above.)
Press “Apply.”
Select “Lift” as the coefficient.
Select “Plot” and again highlight wall-3 and wall-4.
Change the “Plot Window” number to 2.
Reverse your values for X and Y. (Be careful. This may be done for you automatically.)
Press “Apply.”
Select “Moment” as the coefficient.
Again, select “Plot” and highlight the two walls.
Plot Window = 3
Since you want the moment center to be at the quarter-chord point, enter
X = 0.0508, Y = 0.0
Press “Apply” and “Close.”
REPORT REFERENCE VALUES…
Select “freestream” from the dropdown menu.
Change the “Area” and “Length” values to 0.2032, which corresponds to your chord length.
Press “OK”
SOLVE ITERATE…
Set the number of iterations to 100 and press “Iterate.”
Four windows will open showing you the residuals and the coefficients.
The first 100 iterations are done to start your solution and smooth out any abrupt
changes to the flow field. You will now change the Courant number to speed up
your solution and then iterate to a steady state.
SOLVE CONTROLS SOLUTION…
(If the program seems to freeze-up, close the various plot windows first.)
Courant Number = 20
Press “OK”
SOLVE ITERATE…
Set the number of iterations to at least 500. (As you approach the stall AOA, you will need to increase the number of iterations upwards of 1000.)
Press “Iterate.”
After your solution has converged…
REPORT FORCES…
Select “Forces” option.
Make sure wall-3 and wall-4 are highlighted.
The “Force Vector” is the direction of the force you are looking for. For example,
is in the same direction as your freestream velocity vector. Lift is normal
to drag.
For the case here, set X and Y as you did for your boundary conditions.
This will give you the drag coefficient.
Press “Print.”
In the Fluent console window, you’ll see a bunch of numbers representing the
various factors going into the drag coefficient calculation. Scroll all the way to
the right and record the “net” “total coefficient” value. This is your drag
coefficient.
Return the FORCES window. Reverse your values of X and Y. Press “Print.”
This time, the net total coefficient will represent your lift.
Again, return to FORCES window. Select the “Moments” option. Again, you
want moments about the quarter-chord, so X = 0.0508 and Y = 0.0. Press
“Print.” The net total coefficient now is your moment coefficient about the
quarter-chord.
Repeat this process starting with DEFINE BOUNDARY CONDITIONS, changing the values of the velocity vector in the “Boundary Conditions” window for each angle of attack.
When you are done, FILE EXIT. Then type exit in all open Cygwin windows until they close.