p_rgh in OF 1.7

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

 June 14, 2012, 10:12 Hydrostatic Pressure???? #21 Member   Mohammad Fereshtehpour Join Date: Jul 2011 Location: Iran Posts: 61 Rep Power: 7 Dear Friends Hi Here, a lot of discussion about p and p-rgh were done. But I myself couldn't get the final results from the discussions. I want to know, for a multiphase flow, which pressure should be used in order to compare with experimental data? as you know, We can have just hydrostatic pressure in the lab. Is the p-rgh value depended on the origin of the domain?

 August 16, 2012, 15:24 #22 New Member   Christian Fri Join Date: Dec 2009 Posts: 7 Rep Power: 9 I see that since p_rgh is not the dynamic pressure it means that p is not the total pressure (as we could think) and is actually the static pressure. To calculate the total pressure you can use ptot (this will calculate 1/2*rho*U^2 [dynamic pressure] + p [static pressure)]). So, to compare experimental data with the results from OpenFOAM I will use the p file which is the static pressure in OpenFOAM. BlnPhoenix likes this.

November 25, 2012, 04:27
#23
Senior Member

Dongyue Li
Join Date: Jun 2012
Location: Torino, Italy
Posts: 743
Rep Power: 9
Quote:
 Originally Posted by christianfrias I see that since p_rgh is not the dynamic pressure it means that p is not the total pressure (as we could think) and is actually the static pressure. To calculate the total pressure you can use ptot (this will calculate 1/2*rho*U^2 [dynamic pressure] + p [static pressure)]). So, to compare experimental data with the results from OpenFOAM I will use the p file which is the static pressure in OpenFOAM.

so is the p(static pressure) plus 1/2*rho*U^2(dynamic pressure) usually measured in experiment? Why I remember usually in a tube or something ，static pressure is measured in a pressure gauge

May 24, 2013, 10:49
#24
Senior Member

Albrecht vBoetticher
Join Date: Aug 2010
Location: Zürich, Swizerland
Posts: 212
Rep Power: 9
Quote:
 Originally Posted by sharonyue so is the p(static pressure) plus 1/2*rho*U^2(dynamic pressure) usually measured in experiment? Why I remember usually in a tube or something ，static pressure is measured in a pressure gauge
Depending on what you measure. Water pressure level sensors (and piezometers) yust measure the equivalent hydrostatic pressure above the sensor, so they are liquid level sensors and you should compare measurements to p in OF. If you measure the pressure in flow direction to gain drag forces etc. it is more difficult to directly compare measurements and simulation.

July 8, 2013, 07:58
Pressure things ...
#25
New Member

Join Date: Aug 2011
Posts: 1
Rep Power: 0
Hi all,

now i am confused about multiphase pressure. Could anybody put the corresponding qualitative pressure profiles into the file attached?
First figure:
Second figure:
bubble rising to surface; snap shot
Third picture; first contact of a water drop with water surface

Thank you very much!
Attached Images
 pressure.jpg (31.6 KB, 228 views)

 April 6, 2014, 21:51 Cannot find patchField entry for wall? #26 New Member   Limx Join Date: Apr 2014 Posts: 6 Rep Power: 4 We set up the separator model, and stimulates the multiphase flow. After we ran the setFields, the following information occurred: Setting field default values Setting internal values of volScalarField alphaair Setting internal values of volScalarField alphawater --> FOAM FATAL IO ERROR: Cannot find patchField entry for wall file: /home/dell/OpenFOAM/damBreak4phaseFinelmxlmx/0/alphawater.boundaryField from line 34 to line 56. From function GeometricField::GeometricBoundaryField::readField(const DimensionedField&, const dictionary&) in file /home/opencfd/OpenFOAM/OpenFOAM-2.2.2/src/OpenFOAM/lnInclude/GeometricBoundaryField.C at line 206. FOAM exiting -----------------------------------alphawater------------------------------------------- /*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.2.2 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class volScalarField; location "0"; object alphawater; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // dimensions [0 0 0 0 0 0 0]; internalField uniform 1; boundaryField { Wall { type zeroGradient; //value uniform 0; } new_new_out { type fixedValue;//; value uniform 1; } new_out { type fixedValue; value uniform 1; } out { type fixedValue;//outletInlet; value uniform 1; } in { type outletOutlet; outletValue uniform 0; value uniform 0; } } ----------------------------- Maybe the boundary conditions were set incorrectly, but we didn't know how to revise them. Thanks so much for help!

 April 7, 2014, 02:35 #27 Senior Member   Andrea Ferrari Join Date: Dec 2010 Posts: 303 Rep Power: 8 Hi, replace Wall { type zeroGradient; //value uniform 0; } with wall { type zeroGradient; //value uniform 0; } Best, andrea

April 7, 2014, 04:04
#28
Senior Member

Albrecht vBoetticher
Join Date: Aug 2010
Location: Zürich, Swizerland
Posts: 212
Rep Power: 9
Quote:
 Originally Posted by baedmaen Hi all, now i am confused about multiphase pressure. Could anybody put the corresponding qualitative pressure profiles into the file attached? First figure: stationary two phase system (water and air); i think nbadano already posted the answer at December 3, 2010, via this thread Second figure: bubble rising to surface; snap shot Third picture; first contact of a water drop with water surface Thank you very much!
Well, p_rgh depends on your ccordinate system, boundary conditions and eventually a pRefValue and pRefPoint. However, if you have something like an atmosphere pressure = 0 Pa in the air above the surface by specifying an atmosphere boundary condition or a pRefValue = 0 Pa, and your water density and g is specified correctly, you will get a nice triangular hydrostatic pressure starting from zero at the surface for p, but not for p_rgh. The solvers I use work with p_rgh in the Navier-Stokes equations but I use p as result for comparison. I attatched two screenshots of a 3D domain starting at z = 2m at the bottom and reaching z = 3m at the top, with atmospheric pressure 0 Pa, and a bubble at z = 2.25 m and a water drop at z = 2.51 m, both with 0.01 m radius, and the free surface at 2.5 m. The screenshots are taken at T = 0.01 s after simulation start, cell size is 5mm in all directions. Note how the density affects p_rgh, 24680 Pa = 2.51m * g * rho_water
Attached Images
 airBubbleWaterDropAndSurface_p.jpg (14.0 KB, 150 views) airBubbleWaterDropAndSurface_p_rgh.jpg (13.6 KB, 145 views)

Last edited by vonboett; April 7, 2014 at 07:33.

April 7, 2014, 20:28
Thanks so much!
#29
New Member

Limx
Join Date: Apr 2014
Posts: 6
Rep Power: 4
Quote:
 Originally Posted by Andrea_85 Hi, replace Wall { type zeroGradient; //value uniform 0; } with wall { type zeroGradient; //value uniform 0; } Best, andrea
thanks so much!
we have solved this problem. the reason is that we wrote the capital letter W with respect to the word wall.

 March 1, 2016, 12:33 Flow in a straight pipe #30 New Member   John Handel Kennedy Join Date: Feb 2016 Posts: 2 Rep Power: 0 Hi, I am trying to simulate Flow in a Straight Pipe with Heat transfer. I am using the buoyantBoussinesqSimpleFoam solver. I have made g and beta to be zero. The temperature of the wall is 373K and inlet fluid temperature is 293K. The inlet velocity is 1m/s. The diameter of the pipe is 1m and the nu value is 0.01 which makes a Reynolds number to be 100. The laminar Prandtl number is 1.5. I got fully developed flow in simpleFoam i.e. the velocity jumped to 2m/s. However I am not able to get the same velocity profile in buoyantBoussinesqSimpleFoam, The velocity is decreasing towards the outlet. How do we solve this problem? What should I specify in the alpha_t and p_rgh files? Regards John

 Thread Tools Display Modes Linear Mode

 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 On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post nileshjrane OpenFOAM Running, Solving & CFD 20 February 13, 2012 06:54 hcmadhu OpenFOAM Installation 7 August 24, 2010 16:55 MrD OpenFOAM 0 August 11, 2010 15:44 alberto OpenFOAM 12 July 28, 2010 11:59 johnnyb FLUENT 0 August 25, 2003 17:13

All times are GMT -4. The time now is 06:52.