PARAMETERS


In order to study the mixing of air and fuel, a mesh has been generated, defining two successive parts : first, the ramjet itself with both air and fuel inlets, then a wide outlet chamber. Only the first part is studied, since the second, largest part is just used to prevent outlet perturbations. The grid is shown on the picture below.

Results will only be analysed in the first part, for the ramjet corresponds to that one. Thus the grid must be extremely refined in this area, as shown on figure below :

Using this mesh, the study can now be carried out. First and foremost, some parameters has to be set before any simulation runs. These parameters are written and listed in different specific files.

 

One of them permits to control boundary conditions, and is called "Melange.asciiBound". The example below explains how to change the velocity inlet. Indeed, red numbers are those which define the velocity inlet.

Grid processing by java moulinette
7 boundary patches.
---------------------------------------------
Patch: 0
Air_inlet
3
107 150 1 1 2 0 0
61.0 0.0 0.0 10000.0 0.0 300.0 50.0
---------------------------------------------
Patch: 1
fuel_up
3
107 150 1 1 2 0 0
0.0 -100.0 0.0 500.0 0.0 300.0 50.0
---------------------------------------------
Patch: 2
fuel_down
3
107 150 1 1 2 0 0
0.0 100.0 0.0 500.0 0.0 300.0 50.0
---------------------------------------------
Patch: 3
Outlet
-3
100 150 1 2 2 0 0
101 300.0 100.0 0.0 0.0 0.0 0.0 0.0
---------------------------------------------
Patch: 4
Inj_wall
1
19 0 0 0 0 0 0
0.0 0.0 0.0 0.0 0.0 0.0 0.0
---------------------------------------------
Patch: 5
Ch_wall
1
19 0 0 0 0 0 0
0.0 0.0 0.0 0.0 0.0 0.0 0.0
---------------------------------------------
Patch: 6
Sil_wall
1
19 0 0 0 0 0 0
0.0 0.0 0.0 0.0 0.0 0.0 0.0

Another file, called "run.dat", permits to set the parameters defining the properties of the iterations. The red sentences are very often used to do computations.

'../../MESHES/MELANGE/Melange.coor' ! Mesh file
'../../MESHES/MELANGE/Melange.conn' ! Connectivity
'../../MESHES/MELANGE/Melange.exBound' ! Boundary 
'../../MESHES/MELANGE/Melange.inBound' ! Interface 
'./Melange.asciiBound' ! Ascii file
'./solut_bnd_file_neqbnd=0' ! Boundary solution file
'./Resu/Solut/Melange.sol_0020000' ! Restart file
'./Resu/Solut/Melange.sol' ! Solutions name

1.0d0 ! Reference length | scales coordinates X by X/reflen 

20000 ! Number of iterations

100 ! Number of elements per group (typically of order 100)
1 ! Initial values: free stream data (0) or restart file (1)
0 ! Ref. velocity: free stream (1) or speed of sound (0) | non-dim. only
1 ! Preprocessor: skip (0), use (1) & write (2) & stop (3)
0 ! PGS convergence acceleration (1) or not (0)
0 ! Peclet: stores artificial visc. fluxes and ratio (1) or not (0) 

1 ! Interactive details of convergence (1) or not (0)
10 ! Prints convergence every x iterations
1 ! Stores solution in separate files (1) or not (0)
1000 ! Stores solution every x iterations

1 ! Euler (0) or Navier-Stokes (1) calculation
0 ! RANS: no RANS (0), k-eps (1) or Spalart-Allmaras model (2)
1 ! Chemistry (>1) or not (0)
11 ! LES (>1) or not (0)
1 ! Artificial viscosity (>1) or not (0)
1 ! Steady state (0) or unsteady (1) calculation

1 0 0 0 0 ! Scheme specification
1 ! Number of Runge-Kutta stages
1.0d0 ! Runge-Kutta coefficients
0.7d0 ! CFL parameter for complete update
0.7d0 ! CFL parameter in second order update
0.01d0 ! 4th order artificial viscosity coeff.
0.3d0 ! 2nd order artificial viscosity coeff.
0.2d0 ! Fourier parameter for viscous time-step

At last, computations are done in batch mode. Therefore, simulations are launched typing this command line "qsub run_sgi" in a terminal. Run_sgi is a file displayed below :

# QSUB -r avme
# QSUB -lt 25000
# QSUB -lM 50mb
# QSUB -eo
# QSUB -s /bin/csh

cd /users/mcip/mcip3/MELANGE/Run1/

mpirun -np 1 ../avbp_SGI_MCIP.e

The last line in red means that the file "avbp_SGI_MCIP.e" is the one to be executed."-np" indicates how many processors are to work on this very simulation : in this case, the value "1" means that only one processor is going to be used for calculations.