Mechanical Engineering 595

Computational Fluid Dynamics Laboratory #2 Instructions

1. Basic Setup

There are two different programs that you have to run in order to do the second lab. First there is the oblique shock wave calculation which is started by executing the "oblique" command. The second is the program that is used for observing the results, called "Fieldview".

1.1 Getting a copy of the CFD code

If you are reading this, then you can get the assignment off of my web page. You can download the file to your /scratch/<username> directory and then decompress it there, using the command:

zcat 595.tar.Z | tar xvf -

The assignment is also located on the m38 system in my home directory under "/usr/people/dnwillia/595". To copy the assignment for your group:

1. login to m38 
2. Change to your /scratch directory
3. Type "cp -R /usr/people/dnwillia/595/ ."

You now have the necessary files to run the assignment problem in a directory called "595" that should be in your root directory.

2. Running Fieldview

The Fieldview binaries are located in the directory /local/fv/bin. You should add this path to your PATH environment variable, and then type fv to start Fieldview. To add this path to your path environment variable add the following line to your .profile: export PATH=$PATH:/local/fv/bin.

3. Running the Oblique Shock Wave Program

To run the oblique shock wave program, one just edits the startup.txt file which contains the data
that sets up the initial conditions, and controls the program. After editing this file, one just types
oblique to start the calculations. If you do not want to wait around for it to finish, you should type
the following instead:

nohup oblique &

which runs the program in the background, and makes it so that the program will keep running when you log out.

3.1 Input Data Files for the Shock Wave Program

An example startup.txt file is already set up for a Mach 1.5 flow, atmospheric temperature of 22 degrees, atmospheric pressure of 90 kPa, and a 23 degree wedge. This roughly corresponds to the experiment you performed earlier this year. An explanation of this file follows.

startup.txt:

This file contains the input data for the oblique shock wave program. The program reads the data that defines the free stream properties, wedge geometry, and the variables that control the simulation behaviour. An example of this file is as follows:

***** INPUT DATA ********** # Free-Stream Mach number (Nozzle exit mach number) 1.5 # Atmospheric Temperature (degrees C) 22.0 # Atmospheric Pressure (kilopascals, kPa) 90.0 # Wedge or Cone Angle (degrees) 23.0 # Wedge or Cone simulation (1 = Wedge, 2 = Cone) 1 ***** SIMULATION CONTROL DATA ************ # Initial data control ( 0 = uniform, 1 = start with restart file ) 0 # Number of timesteps 10000 # Control for output of Fieldview files (0 = no, 1 = yes) 1 # Interval between Fieldview files 20 # Output control ( 0 = no restart files, 1 = write restart files ) 1 # Interval between output (restart) files (In timesteps) 200 # File name for input restart file (max 80 characters) restart.00200

Figure 3.1: Example "startup.txt" Input Data File

Lines with # signs and the beginning are comments, other lines are input data. Each line of input data can be explained as follows:

1. The free stream Mach number, ahead of the wedge or cone.

2. Atmospheric temperature, which must be in degrees celcius.

3. Atmospheric pressure, which must be in kPa.

4. The angle of deflection of the wedge or cone.

5. Flag controlling whether you want to simulate the flow over a wedge or cone (1,2).

6. Flag that controls the initial startup condition (0,1)

0:  Sets up the simulation with a uniform condition throughout the 
    computational domain.

1:  Start with a restart file.  The name of the restart file is specified
    at the end of the input file.

7. Number of time steps to run

Number of the timesteps that you want to run, range (0 to whatever).
This changes if you use a restart file.  For example, if your restart
file is from time step 200 and you put 100 here, nothing will run.  It
will just read the restart file then exit.  However, if you put
something higher than 200, like say 210.  Then the calculation will
run until timestep 210 starting at timestep 200.

8. Control of output for Fieldview files(0,1)

0: no Fieldview files will be output

1: Fieldview files will be output

9. Interval between Fieldview files

For example, if you want to output every 500th timestep then set this value to 500.

10. Flag for saving restart files or not

If you set this to 0, the program will not save any restart files.
If you set this to 1, the program will save them.  The restart file
names have the following format:

restart.xxxxx where xxxxx is the time step number.

11. Interval between successive restart files.

This number sets the interval between writing restart files.  For example,
if you set this to 200, then the restart files will be written at steps
200, 400, 600, ... etc.