Hi,

I am working on modeling an air vehicle in Fluent 6.2.16. I will be running plenty of simulations for this model (maybe close to 1,000) and want to create a method to output the forces on the aircraft with as little effort as possible.

I set off by creating a journal file that would read one simulation, and then output the forces. Once I verified that this was working, I copied and pasted the text and just replaced the name of the simulation, thereby creating a really long journal file. This means the force data should be output to the same file, so I can just edit it in Excel, but it didn't work. For example, I created a journal for angles of attack (AOA) from -4 to 5 (starting at -4 and working through to 5), and it does not write the forces to file for -3, 2 and 3 degrees AOA.

I went through with the GUI each step of the journal file, and it gave NO errors when running through AOA -3, and gives the exact GUI transcript as the ones that do work.

I can take the same journal file and delete, everything after -3 degrees AOA and it will write the forces for -3 to file, but as soon as I add -2 after it, it fails to write -3 once again. This is very strange since -4, is the same as -3 and -2, just different file names are used.

Having double and triple checked the journal file for errors, I came to assumption that something else must be wrong because the only item different between each AOA is the file name, which are correct since I can get -3 working if that is all I run. Has anyone else had any similar experiences, or know of another simple method for outputting force data to file.

If anyone would like a copy of the full journal file, let me know and I will e-mail it, but I seriously do not think there is anything wrong with it, because as I said, it gives no errors messages.

Thank you for anyone who can help,

Andrew

P.S. Here is a part of the journal for one complete angle of attack (this is a 2D simulation at present), I just repeated this several times, changing the filename (I did'nt include the extra lines in the real one, it is just easier to read this way):

;ANGLE OF ATTACK NEGATIVE 4

;READ CASE

file read-case-data FV_M10_VG1_AOAN4.cas yes

;SET REFERENCE VALUES

report reference-values area 33.377 length 33.377 depth 1

report reference-values compute pressure-far-field inlet

;LIFT

solve monitors force lift-coefficient yes

front_top_airfoil leading_edge lower_cowl lower_elevon lower_front_cowl

lower_rear_cowl rear_top_airfoil trailing_edge upper_center_engine

upper_elevon upper_front_cowl upper_rear_cowl ()

yes yes "FV_M10_VG1_LIFT.txt" no yes

-0.069756 0.997564

;DRAG

solve monitors force drag-coefficient yes

front_top_airfoil leading_edge lower_cowl lower_elevon lower_front_cowl

lower_rear_cowl rear_top_airfoil trailing_edge upper_center_engine

upper_elevon upper_front_cowl upper_rear_cowl ()

yes yes "FV_M10_VG1_DRAG.txt" no yes

0.997564 -0.0697564

;MOMENT

solve monitors force moment-coefficient yes

front_top_airfoil leading_edge lower_cowl lower_elevon lower_front_cowl

lower_rear_cowl rear_top_airfoil trailing_edge upper_center_engine

upper_elevon upper_front_cowl upper_rear_cowl ()

yes yes "FV_M10_VG1_MOMENT.txt" no yes

16.6885 0

solve iterate 0

Give a diff. file name for lift,drag,moments. use %i/%t if reqd. try to write down case & data at the end. R u initiliasing the solution for every new case or not?

Hi, Thank you for the response Mahesh.

I was hoping I could write them into one file as it would just make life a whole lot easier.

Re: Initialising for every new case: On the ones I am having problems with at the moment, I did initialise for every case, because for each angle of attack, I change the geometry slightly, so I had new msh files for each one. I know one of the simulations I am having problems with took twice as many iterations.

I have also tried this on UNIX and Windows and get the same occurance in both instances, and I have run the following journal sequences to try and spot what the problem might be:

1. Angle of Attack Negative 4 (AOAN4), then AOAN3, then AOAN2 = Didn't write forces for AOAN3

2. AOAN4, then AOAN3 = Works Fine

3. AOAN3, AOAN4, AOAN2 = Didn't write forces for AOAN3

4. AOAN3, AOAN3 = Didn't write forces for first AOAN3

This tends to point to a problem with obtaining forces from AOAN3 in any position other than the end of the journal. At first I thought it might be the fact that it didn't have enough time to write the forces, so instead of running for zero iterations to get the forces, I ran for one iteration, but it still didn't write the forces for AOAN3.

Thank you for your response, that is my plan B, if I cannot get it to write into a single file.

Andrew