CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > ANSYS > FLUENT

Simple Box - Gravity with Pressure Outlet - Unrealistic Reverse Flow

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Search this Thread Display Modes
Old   July 22, 2020, 12:36
Post Simple Box - Gravity with Pressure Outlet - Unrealistic Reverse Flow
New Member
Join Date: Apr 2020
Posts: 2
Rep Power: 0
pyccknn is on a distinguished road
Hi all

I intend to simulate a tidal turbine in a tidal current. First, I am trying to test the application of gravity/hydrostatic pressure gradients to a simple box of sea water of the same dimensions as my domain so that I can get this right before adding the turbine.

Inlet velocity 0.1m/s, the nearest wall to the right is inlet (flow in +y direction)
Seawater properties: density 1024kg/m3, visocisty 0.00111
the domain is 48x48x80m
Gravity applied with operating density 0
A reference pressure at the origin represents that which would be experienced at 24m depth below sea level (about 340,000Pa)
pressure outlet with 0 gauge pressure
Remaining boundaries are walls
using k-w SST
Coupled method
Coarse mesh for the sake of this experiment

As you can see I am getting a bizarre reverse flow circulating flow pattern, as well an incorrect and inconsistent pressure values along the height of the box. I think the issue is with the pressure outlet: by applying a fixed pressure at outlet and applying gravity to the domain so that fluid with a pressure gradient arrives at the outlet, the velocity at outlet has to vary along the outlet to change pressure to a constant value?
I have selected average pressure specification, I am not sure how else to allow fluent to maintain the
pressure gradient at outlet.
The values of pressure at top and bottom (Z direction) are not as expected and not consistent along the flow path - the upper boundary should see 1atm pressure as if it is sealevel. I believe the pressure contour shows relative/gauge pressure, so max and min should be about +-2.4e5Pa

I have been able to achieve a more realistic result (consistent and correct pressure gradient, max and min pressure expected, relatively smooth flow from inlet to outlet) by applying mass flow inlet and outlet. This is fine for a confined channel but is not applicable to my physical scenario and as such shouldnt be used.

As I say I think this is an issue of the options selected for the pressure outlet, but I am not sure. Any advice is great!
Attached Images
File Type: jpg Capture2.jpg (123.7 KB, 22 views)
File Type: png Capture.PNG (44.2 KB, 11 views)
pyccknn is offline   Reply With Quote

Old   July 23, 2020, 09:02
New Member
Join Date: Apr 2020
Posts: 2
Rep Power: 0
pyccknn is on a distinguished road
For reference, this is what I would like to achieve (attached)

This is by applying gravity along with equal mass flow inlet and outlet
Attached Images
File Type: png Capture3.PNG (174.6 KB, 19 views)
pyccknn is offline   Reply With Quote

Old   December 1, 2021, 17:31
New Member
Join Date: Mar 2021
Posts: 23
Rep Power: 5
cbooks77 is on a distinguished road
I know this is an old post but I have recently encountered a similar problem. I haven't completely solved this issue but what I did do is specify the outlet pressure profile with a UDF to be (rho*g*h) the hydrostatic pressure. There is still a small discontinuity in the pressure gradients of the outlet and interior domain. This significantly reduced the reverse flow but the pressure gradients do not perfectly align hence there is still reverse flow. I'm still working on a solution. I cannot use outflow in my case because I have incompressible flow.

Were you able to find a solution?
cbooks77 is offline   Reply With Quote


gravity, hydrostatic pressure, pressure gradient, pressure outlet, reverse flow

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Wind tunnel Boundary Conditions in Fluent metmet FLUENT 6 October 30, 2019 12:23
Pressure inlet vs outlet position, transient, time dependent pressure and gravity silent2608 FLUENT 0 February 6, 2016 10:19
changing velocity (outlet) BC to pressure outlet majid_kamyab FLUENT 7 October 22, 2014 11:50
simple model, difficult outlet Eric CFX 7 May 23, 2014 08:13
Hydrostatic pressure in 2-phase flow modeling (long) DS & HB Main CFD Forum 0 January 8, 2000 15:00

All times are GMT -4. The time now is 04:06.