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pyxbird March 5, 2013 21:14

water levelrise
 
Dear all,
Hi, I am simulating flow in a flume, the inlet boundary is velocity boundary, however every time I begin the simulation, the water level will increase and extend to the outlet boundary and never descend. For example, the fluid elevation I define at the inlet and outlet boundary is 50cm, but after the flow becoming steady the water level keeps 55cm and never change. How can I solve this problem?
1.At the outlet boundary, I have tried continuative, pressure and outflow boundary.
2.I have tried to increase the velocity slowly at the inlet boundary but it doesn't work.
3.I have put an obstacle at the top of the flume to avoid water rising but the simulation will exit anormally.
So who can figure out why?

gdtiaozi March 6, 2013 01:01

Model Setup->General->Interface tracking->Free surface or sharp interface

Model Setup->General->Number of fluids->One fluid

Model Setup->Meshing & Geometry->Initial->Void initial state->Pressure:101325Pa

pyxbird March 6, 2013 02:32

Quote:

Originally Posted by gdtiaozi (Post 411830)
Model Setup->General->Interface tracking->Free surface or sharp interface

Model Setup->General->Number of fluids->One fluid

Model Setup->Meshing & Geometry->Initial->Void initial state->Pressure:101325Pa

Thank you, maybe I should give the pressure of air, I will try it soon.

pyxbird March 6, 2013 03:25

2 Attachment(s)
Quote:

Originally Posted by gdtiaozi (Post 411830)
Model Setup->General->Interface tracking->Free surface or sharp interface

Model Setup->General->Number of fluids->One fluid

Model Setup->Meshing & Geometry->Initial->Void initial state->Pressure:101325Pa

It doesn't work, the level of the water still rises and doesn't dscend.
I will show two pitures below.

Jing_min March 6, 2013 04:35

Quote:

Originally Posted by pyxbird (Post 411813)
Dear all,
Hi, I am simulating flow in a flume, the inlet boundary is velocity boundary, however every time I begin the simulation, the water level will increase and extend to the outlet boundary and never descend. For example, the fluid elevation I define at the inlet and outlet boundary is 50cm, but after the flow becoming steady the water level keeps 55cm and never change. How can I solve this problem?
1.At the outlet boundary, I have tried continuative, pressure and outflow boundary.
2.I have tried to increase the velocity slowly at the inlet boundary but it doesn't work.
3.I have put an obstacle at the top of the flume to avoid water rising but the simulation will exit anormally.
So who can figure out why?


Hi
Please send me the file : "prepin"

pyxbird March 6, 2013 04:52

Quote:

Originally Posted by Jing_min (Post 411863)
Hi
Please send me the file : "prepin"

Title
This is a sample input file
$xput
remark='!! Remarks beginning with "!! " are automatically added and removed by FLOW-3D.',
remark='!! Do not begin any user added remarks with with "!! ". They will be removed',
twfin=250,
itb=1,
ifin=4,
ifvisc=1,
ifvis=4,
ifdynconv=1,
gz=-980,
ipdis=1,
idpth=1,
ifmu=1,
tpltd(1)=0.5,
$end
$limits
$end
$props
units='cgs',
tunits='c',
mu1=0.01,
fluid1='Water at 293 K',
thexf1=0.00018,
cv1=41820000,
tstar=100,
tl1=-0.149999999999977,
ts1=-0.149999999999977,
clht1=3350000000,
cvs1=21000000,
thcs1=221500,
rhofs=0.917,
teut=-273.15,
tmelt=-273.15,
ceut=0,
pcoef=0,
rhof=1.0,
sigma=73,
thc1=59700,
$end
$scalar
$end
&PCAP
/
&BCDATA
remark='!! Boundary condition X Min',
ibct(1)=6,
ubct(1, 1)=44.1,
fbct(1, 1)=1,
flhtbct(1, 1)=50,
remark='!! Boundary condition X Max',
ibct(2)=8,
flhtbct(1, 2)=50,
remark='!! Boundary condition Z Min',
ibct(5)=2,
/
&MESH
ntotal=1000,
nxcelt=2500,
px(1)=0,
px(2)=5000,
nycelt=1,
py(1)=0,
py(2)=1,
nzcelt=70,
pz(1)=0,
pz(2)=70,
/
$obs
remark='!! Component common parameters',
avrck=-3.1,
$end
$fl
nfls=1,
remark='!! Fluid Region 1',
fluidRegionName(1)='Water at 293 K',
fzh(1)=50,
pvoid=1.01325e+05,
iflinittyp=0,
$end
$bf
$end
$temp
$end
$motn
$end
$grafic
anmtyp(1)='dpth',
anmtyp(2)='f',
anmtyp(3)='vel',
$end
&HEADER
project='pre out',
/
$parts
$end
Documentation: general comments, background, expectations, etc.

#start tables:
#fluid1:
#blkmodts
#end blkmodts
#cv1
#end cv1
#cvnc
#end cvnc
#elastmodts
#end elastmodts
#emod1
#end emod1
#fs
#end fs
#mu1sr
#end mu1sr
#mu1t
#end mu1t
#poissonrts
#end poissonrts
#rhof
#end rhof
#shrmodts
#end shrmodts
#sigma
#end sigma
#thc1
#end thc1
#yield1
#end yield1
#end fluid1
#fluid2:
#cv2
#end cv2
#emod2
#end emod2
#mu2sr
#end mu2sr
#mu2t
#end mu2t
#rhof2
#end rhof2
#thc2
#end thc2
#yield2
#end yield2
#end fluid2
#end start tables

pyxbird March 6, 2013 04:55

Quote:

Originally Posted by Jing_min (Post 411863)
Hi
Please send me the file : "prepin"

sorry, some errors emerge when I am uploading the prepin file, can you see it in my reply?

flow_CH March 10, 2013 07:23

Quote:

Originally Posted by pyxbird (Post 411813)
sorry, some errors emerge when I am uploading the prepin file, can you see it in my reply?

send me zip file of prepin.

Flowdy November 7, 2013 16:06

It was happening to me also and I discover that the flow in given was bigger than flow out, then the volume of water will increase for sure… you could check it.


Another problem could be the delta time. When there is instabilities in the delta time or delta x the information of the volume flow will be lost and the volume so... I mean check the Courant-Friedrichs-Lewy condition

afgh October 8, 2014 03:09

It was happening to me and i change the height of mesh with height free surface. and i will change the velocity inlet fluid elevation constant and outflow -pressure and fluid elevation constant. this work similar the ansys cfx.
and i dont know this is wright or wrong?

Allenlin October 9, 2014 01:46

Hi, Pyxbird

The case that you simulated is open channel flow. In flow-3d, the velocity is uniform distribution in velocity inlet boundary, but the velocity profile is parabolic distribution in channel if the flow is fully developed. Hence, they need to increase the flow area to maintain the same flow rate. There is why your result shows higher water level.

hans_ina October 10, 2014 02:31

I do the outlet as outflow and its work, i simulated without obstacle

jason_sjtu November 11, 2014 22:29

Quote:

Originally Posted by pyxbird (Post 411813)
Dear all,
Hi, I am simulating flow in a flume, the inlet boundary is velocity boundary, however every time I begin the simulation, the water level will increase and extend to the outlet boundary and never descend. For example, the fluid elevation I define at the inlet and outlet boundary is 50cm, but after the flow becoming steady the water level keeps 55cm and never change. How can I solve this problem?
1.At the outlet boundary, I have tried continuative, pressure and outflow boundary.
2.I have tried to increase the velocity slowly at the inlet boundary but it doesn't work.
3.I have put an obstacle at the top of the flume to avoid water rising but the simulation will exit anormally.
So who can figure out why?


hi ,perhaps you can try set water depth in initial condition instead of using fluid region.

jason_sjtu November 21, 2014 08:34

hi pyxbird,
the rising water level frustrate me a lot recently, although i tried several changes in the up_stream and down_stream boundary conditions.
Now, have you get the problem solved? if so ,could you please share the solution with me? thank you


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