Turbulent pipe flow with scalar ON is diverging

[Madhurjya814]

The default input file (input_DNS_Re5300.i3d) with less grid resolution is getting scalar diverged. What may be the possible reason? I have not done any modification in the code. Thanks.

! -- mode: f90 --

!===================
&BasicParam
!===================

! Flow type (1=Lock-exchange, 2=TGV, 3=Channel, 4=Periodic hill, 5=Cylinder, 6=dbg-schemes)
itype = 14

! Domain decomposition
p_row=0 ! Row partition
p_col=0 ! Column partition

! Mesh
nx=128 ! X-direction nodes
ny=81 ! Y-direction nodes
nz=81 ! Z-direction nodes
istret = 0 ! y mesh refinement (0:no, 1:center, 2:both sides, 3:bottom)
beta = 0.0 ! Refinement parameter (beta)

! Domain
xlx = 12.5 ! Lx (Size of the box in x-direction)
yly = 1.6 ! Ly (Size of the box in y-direction)
zlz = 1.6 ! Lz (Size of the box in z-direction)

! Flow parameters
re = 5300. ! nu=1/re (Kinematic Viscosity)

! Time stepping
dt = 0.0005 ! Time step
ifirst = 1 ! First iteration
ilast = 750000 ! Last iteration

! Enable modelling tools
ilesmod=0 ! if 0 then DNS
numscalar = 1
iscalar = 1 ! How many scalars? (Set to zero to disable scalars)
iibm=2 ! Flag for immersed boundary method

! Boundary and initial conditions
iin = 1 ! Inflow conditions (1: classic, 2: turbinit, 4: SEM)
u1 = 1. ! u1 (max velocity) (for inflow condition)
u2 = 1. ! u2 (min velocity) (for inflow condition)
init_noise = 3.0 ! Turbulence intensity (1=100%) !! Initial condition
inflow_noise = 0.0 ! Turbulence intensity (1=100%) !! Inflow condition

nclx1 = 0
nclxn = 0
ncly1 = 0
nclyn = 0
nclz1 = 0
nclzn = 0

/End

!====================
&NumOptions
!====================

! Spatial derivatives
ifirstder = 4 ! (1->2nd central, 2->4th central, 3->4th compact, 4-> 6th compact)
isecondder = 4 ! (1->2nd central, 2->4th central, 3->4th compact, 4-> 6th compact, 5->hyperviscous 6th)
ipinter = 2 ! interpolation scheme (1: classic, 2: optimized, 3: optimized agressive)

! Time scheme
itimescheme = 3 ! Time integration scheme (1->Euler,2->AB2, 3->AB3, 4->AB4,5->RK3,6->RK4, 7-->CN2+AB3)

! Dissipation control
nu0nu = 3.0 ! Ratio between hyperviscosity/viscosity at nu
cnu = 0.44 ! Ratio between hypervisvosity at k_m=2/3pi and k_c= pi

/End

!=================
&InOutParam
!=================

! Basic I/O
irestart = 0 ! Read initial flow field ?
icheckpoint = 10000 ! Frequency for writing backup file
ioutput = 500 ! Frequency for visualization
ilist = 25 ! Frequency for writing to screen
nvisu = 1 ! Size for visualisation collection

/End

!=================
&Statistics
!=================

wrotation = 0.12 ! rotation speed to trigger turbulence
spinup_time = 5000 ! number of time steps with a rotation to trigger turbulence
nstat = 1 ! Size arrays for statistic collection
initstat = 100001 ! Time steps after which statistics are collected

/End

!########################
! OPTIONAL PARAMETERS
!#######################

!================
&ibmstuff
!================

rai=0.50 ! when simulating a pipe, inner radius
rao=0.70 ! when simulating a pipe, outer radius (defines wall thickness)
nraf=1000 !level of refinement for iibm==2 to find the surface of the immersed object
nobjmax=2 !number of immersed objects (DO NOT USE ZERO OBJECTS)
iforces=0

/End

!================
&ScalarParam
!================

Sc(1) = 0.71 ! Schmidt number

nclxS1 = 0
nclxSn = 0
nclyS1 = 0
nclySn = 0
nclzS1 = 0
nclzSn = 0

/End

!================
&LESModel
!================

iles = 0 ! LES Model (1: Phys Smag, 2: Phys WALE, 3: Phys dyn. Smag, 4: iSVV, 5: dyn SEV)
smagcst = 0.14 ! Smagorinsky constant
SmagWallDamp = 0 ! 1: Mason and Thomson Damping function, otherwise OFF
walecst = 0.5 ! WALES Model Coefficient
iconserv = 0 ! Formulation SGS divergence (0: non conservative, 1: conservative)

/End

&CASE
/End

With this input file i got after 250 iterations:
Time step = 250/ 750000, Time unit = 0.1250
Velocity:
Bulk velocity before 0.99952649556979689
Bulk velocity after 1.0000000000000029
Scalar: # 1
Bulk phi before 1.0001134246511765
Bulk phi after 0.99999999999999845
DIV U* max mean= 30.130075770636857 0.21163536489272319
DIV U max mean= 1.2254870947990140 1.9839005244451820E-002
U,V,W min= -4.05600834 -3.18796492 -3.14936066
U,V,W max= 6.93458271 3.58505130 3.34031224
CFL_x : 0.03550506
CFL_y : 0.09074661
CFL_z : 0.08455165
Phi1 min max= -236.656555 206.361954
Scalar diverged! SIMULATION IS STOPPED!

[mathrack]

Hello,

You have changed the resolution from 640x320x320 to 128x81x81 without changing the time step and the viscous operator. This could explain the divergence.

As a side remark, you should not use a number of nodes such as 81 in a periodic direction. Powers of 2 or 3 are usually more efficient for the FFT part of the code.