Re: [sparta-users] Help - 1D Fourier Flow

[Steve P. <sj...@gm...>]

It looks like you have 100 particles and 100 grid cells?
You are probably getting temp=0 in grid cells with no particles.

Try at least 20 particles/cell and check you are getting
many gas/gas collisions.  Without collisions there is no way for
the gas to convect heat.  Also you will need to time average
your results for a lot more samples/steps to get good stats.

Steve

On Tue, Jun 11, 2024 at 2:07 AM Pradyumnan R ae22b009 <
ae2...@sm...> wrote:

> I am trying to simulate 1D heat transfer that obeys Fourier law using
> SPARTA. The left wall is at a temperature 100 K and the right wall is at
> 500 K. I have written the following code, but the temp.grid file that gets
> dumped has rubbish answers with 0 temperature at several points.
>
> Here's the input script :
>
>
> ################################################################################
> # 1D Fourier Flow
> #
> # Note:
> #  - The "comm/sort” option to the “global” command is used to match MPI
> runs.
> #  - The “twopass” option is used to match Kokkos runs.
> # The "comm/sort" and "twopass" options should not be used for production
> runs.
>
> ################################################################################
>
>
> ################################################################################
> # Variables
>
> ################################################################################
>
> variable x_min equal -1
> variable x_max equal 1
> variable y_min equal -0.1
> variable y_max equal 0.1
> variable z_min equal -0.5
> variable z_max equal 0.5
> variable x_grid internal 0
> variable y_grid internal 0
>
> variable x_cells equal "100"
> variable y_cells equal "1"
> variable z_cells equal 1
> variable Fnum equal 1.0e20
> variable tstep equal 0.1
> variable steps equal 500
> variable time equal "(v_steps * v_tstep)"
> variable n_particles equal "100"
> variable n_every equal 1
> variable n_repeat equal 3
> variable n_freq equal 10
>
> variable temp_left equal 100.0
> variable temp_right equal 500.0
> variable mean_temp equal "(v_temp_left + v_temp_right) / 2"
> variable Vx equal "1 * exp(- 0.1 * v_x_grid ^ 2)"
> variable Vy equal "0.1 * exp(- 0.01 * v_y_grid ^ 2)"
>
>
> #################################################################################
> # Printing Variables to the log file
>
> #################################################################################
>
> print " ---------------- "
> print " x-min = ${x_min} "
> print " ---------------- "
> print " x-max = ${x_max} "
> print " ---------------- "
> print " y-min = ${y_min} "
> print " ---------------- "
> print " y-max = ${y_max} "
> print " ---------------- "
> print " z-min = ${z_min} "
> print " ---------------- "
> print " z-max = ${z_max} "
> print " ---------------- "
> print " x-cells = ${x_cells} "
> print " ---------------- "
> print " y-cells = ${y_cells} "
> print " ---------------- "
> print " z-cells = ${z_cells} "
> print " ---------------- "
> print " Number of Particles = ${n_particles} "
> print " ---------------- "
> print " Simulation Ratio = ${Fnum} "
> print " ---------------- "
> print " Timestep = ${tstep} "
> print " ---------------- "
> print " Number of steps in the simulation = ${steps} "
> print " ---------------- "
> print " Total time of the simulation = ${time} "
> print " ---------------- "
> print " Considering readings every _____ ${n_every} _____ steps "
> print " ---------------- "
> print " Considering the last _____ ${n_repeat} _____ readings separated by
> _____ ${n_every} _____ steps for averaging "
> print " ---------------- "
> print " Computing values every _____ ${n_freq} _____ steps "
> print " ---------------- "
> print " Temperature at the left end = ${temp_left} K"
> print " ---------------- "
> print " Tempearture at the right end = ${temp_right} K"
> print " ---------------- "
>
>
> #################################################################################
> # Initialisation
>
> #################################################################################
>
> dimension 2
> #package kokkos comm threaded gpu/aware yes
> seed 5838959
> units si
>
>
> ################################################################################
> # Problem Definition
>
> ################################################################################
>
> boundary ss r p
> create_box ${x_min} ${x_max} ${y_min} ${y_max} ${z_min} ${z_max}
> create_grid ${x_cells} ${y_cells} ${z_cells}
> balance_grid proc
>
> species air.species N2
> mixture air N2 frac 0.5
>
> create_particles &
> air n ${n_particles} &
> temperature temp_left NULL NULL NULL &
> velocity Vx Vy NULL x_grid y_grid NULL
>
>
> ###############################################################################
> # Settings
>
> ###############################################################################
>
> surf_collide left_wall diffuse ${temp_left} 1.0
> surf_collide right_wall diffuse ${temp_right} 1.0
> bound_modify xlo collide left_wall
> bound_modify xhi collide right_wall
>
> collide vss air air.vss relax constant
> collide_modify vremax 20 yes remain yes nearcp yes 2 vibrate smooth
>
> global fnum ${Fnum} temp ${temp_left}
> timestep ${tstep}
>
> compute temp1 grid all air temp
> fix temp1 ave/grid all ${n_every} ${n_repeat} ${n_freq} c_temp1[*]
>
>
> ##############################################################################
> # Output
>
> ##############################################################################
>
>
> dump temp1 grid all ${n_freq} temp.grid f_temp1[*]
>
> stats_style step cpu wall np nbound ncoll nattempt
> stats_modify flush no
> stats ${n_freq}
>
> run ${steps}
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