# pressure inlet in incompressible flow

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

 June 22, 2005, 09:31 pressure inlet in incompressible flow #1 dirk Guest   Posts: n/a Hello, I have a simple 2D geometry with one inlet and one outlet, the flow is incompressible. I defined the inlet as a "pressure inlet" and the outlet as "outflow". I specified my operating pressure (around 100kPa) at the inlet and calculated the total pressure for the desired velocity with Bernoullis equation. So I had around 13Pa as (relative) total pressure and set the initial gauge pressure to zero. The velocity should have been around 4.7 m/s, but it became almost zero during calculation. Anyone knows, why this happens ? Thanks, Dirk

 June 22, 2005, 12:57 Re: pressure inlet in incompressible flow #2 Jason Guest   Posts: n/a From the fluent manual: Note that outflow boundaries cannot be used in the following cases: if a problem includes pressure inlet boundaries; use pressure outlet boundary conditions (see Section 7.8) instead if you are modeling compressible flow if you are modeling unsteady flows with varying density, even if the flow is incompressible For an overview of flow boundaries, see Section 7.2. So you can't combine pressure inlet and outflow BC. If you want to continue using outflow BC, switch the inlet to a velocity inlet with the 4.7m/s you described. Also, the outflow is a sensitive BC. It assumes the diffusion flux for all variables is 0 (i.e. fully developed flow). The only place I've seen it used successfully is in pipe flow, several diameters downstream of any disturbance so that the fully developed flow assumption is valid. Just becareful where you use it. Hope this helps, and good luck, Jason

 June 22, 2005, 13:27 Re: pressure inlet in incompressible flow #3 dirk Guest   Posts: n/a Thanks Jason, I should have read this passage of the manual. I used velocity inlet before, but wanted to test other boundary conditions. When I did unsteady calculations I set a sinusoidal inlet velocity and got oscillating static and total pressure at the inlet. But I would like to have a constant total pressure. So I will have to use pressure inlet and pressure outlet, I guess. Dirk

 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 OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Wijaya FLUENT 15 May 18, 2016 10:08 frmap1 Main CFD Forum 0 April 15, 2010 10:32 Ben FLUENT 0 November 21, 2004 01:47 Denis Tschumperle FLUENT 7 August 9, 2000 02:19 ram Main CFD Forum 5 June 17, 2000 21:31

All times are GMT -4. The time now is 13:49.