
[Sponsors] 
November 29, 2004, 14:41 
Pressure based and Density based Solver

#1 
Guest
Posts: n/a

Hello,
what do we mean by Pressure based solver and Density based solver? what are the pros and cons of it? Is there any paper or journal or book to read about these in detail? For Hypersonic Compressible Flows , which solver is useful? Thanks, Xobile 

November 30, 2004, 07:24 
Re: Pressure based and Density based Solver

#2 
Guest
Posts: n/a

I also want to know the difference...will be glad if some one can make it clear.
Although I do know that density based solvers are more accurate for supersonic flows, while pressure based solvers are more accurate for incompressible subsonic flows. So for your application, density based solvers should be used. 

November 30, 2004, 09:46 
Re: Pressure based and Density based Solver

#3 
Guest
Posts: n/a

PL. TELL ME THE RELATIONSHIP BETWEEN THE PRESSURE, HEAD,PIPE DIA & LENGTH OF PIPE. FOR EXAMPLE: INLET WATER PRESSURE TO PIPE IS 10 BAR, PIPE DIA3/4",PIPE LENGTH600MTR, HEAD 2M. HOW MUCH COULD BE THE OUTLET WATER PRSSURE AT THE OTHER END OF PIPE?


July 10, 2009, 05:57 

#4 
New Member
Johnson Emmanuel
Join Date: Jul 2009
Posts: 7
Rep Power: 10 
Historically speaking, the pressurebased approach was developed for lowspeed incompressible flows, while the densitybased approach was mainly used for highspeed compressible flows. However, recently both methods have been extended and reformulated to solve and operate for a wide range of flow conditions beyond their traditional or original intent."
"In both methods the velocity field is obtained from the momentum equations. In the densitybased approach, the continuity equation is used to obtain the density field while the pressure field is determined from the equation of state." "On the other hand, in the pressurebased approach, the pressure field is extracted by solving a pressure or pressure correction equation which is obtained by manipulating continuity and momentum equations." The pressurebased solver traditionally has been used for incompressible and mildly compressible flows. The densitybased approach, on the other hand, was originally designed for highspeed compressible flows. Both approaches are now applicable to a broad range of flows (from incompressible to highly compressible), but the origins of the densitybased formulation may give it an accuracy (i.e. shock resolution) advantage over the pressurebased solver for highspeed compressible flows." refer: http://courses.cit.cornell.edu/fluent/wedge/step4.htm 

July 22, 2009, 08:21 
Highspeed?

#5 
New Member
Join Date: Jun 2009
Posts: 3
Rep Power: 10 
How do you quantify Highspeed?


July 23, 2009, 08:58 

#6 
New Member
Vinayender
Join Date: Jul 2009
Location: India
Posts: 24
Rep Power: 10 
To add to Jhonfriend point's
In incompressible flows, pressure is not a function of density and temperature ( or a weak function of for for very low mach flows). In compressible flows, pressure is a function of both density and temperature and is determined by state equation (as John metioned) and hence the alorithm you use should respect this physics and hence we have a different algorithm for both regioms of flows. Normally for Mach no greater than 0.3 can be taken as the barrior for compressible and incompressible flows.
__________________
Thanks , Vinayender 

August 3, 2012, 12:07 

#7 
New Member
John Mern
Join Date: Jul 2012
Posts: 2
Rep Power: 0 
Coupled pressurebased solvers can be used in compressible flows and can sometimes be more efficient if there is a large region of low Re flow in the domain.


August 3, 2012, 15:42 

#8  
Senior Member
Join Date: Aug 2011
Posts: 271
Rep Power: 9 
Quote:
clear and perfect!!!! I have learned something tonight ! Thanx Johnfriend 

August 3, 2012, 15:58 

#9  
Senior Member
Join Date: Aug 2011
Posts: 271
Rep Power: 9 
Quote:
I guess you are not in the right section to ask for your question.Your post has nothing to do with the original post of Xobile Anyway, first compute the Reynolds number for your problem, then take the Moody's diagram and obtain the pressure loss coefficient lambda for your pipe. If P0 is the pressure at inlet,then the pressure at outlet will be P0 (lamba*L*Rho V²)/(2D) where D is the diameter, L the lenhht of your pipe, Rho the density, V the magnitude of velocity in the pipe. This is a rough result. 

August 16, 2013, 05:35 
2d airfoilsolver settings

#10 
New Member
deepthi
Join Date: Feb 2013
Posts: 7
Rep Power: 6 
For solving the 2d airfoil for various angles of attack which is used pressure or density based solver?Also simple or coupled is used?why?
The operating condition is at sea level and the velocity around 60m/s. thanks in advance 

August 21, 2013, 06:15 

#11 
New Member
TPRPR1
Join Date: Apr 2013
Posts: 13
Rep Power: 6 
@deepthishan
teriyadu poyya! 

October 16, 2013, 06:58 
Inviscid Simulation

#12 
New Member
Jose Marķa Olmos
Join Date: Feb 2013
Posts: 3
Rep Power: 6 
Hi!
I'm trying to chech the validity of the potential flow (Assuming inviscid flow) in subsonic and supersonic case of a slender body. If I use the Pressure based solver in the subsonic case, I get a real good answer. However, if I make the same with supersonic case, the solution doesn't converge. If I use the density based solver i get a fairly good answer. Anybody knows why this is happening? Thank you in advance 

October 25, 2013, 15:43 

#13 
New Member
Debanjan Deep
Join Date: Mar 2009
Posts: 14
Rep Power: 10 
If I want to simulate a high speed air bearing where the rotating surface velocity magnitude is at the range of 100m/s to 250m/s; which solver should I use pressure based or density? I am getting velocity divergence for density based solvers but is working fine with pressure based. Why is it happening do you think?


December 6, 2013, 08:47 

#14 
Senior Member
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,210
Rep Power: 20 
Hi,
although has passed several years but thanks Johnson for helpful text, the link isn't there,what link you or other readers refer for density and pressure based solvers explanations and comparisons? refer: http://courses.cit.cornell.ed...edge/step4.htm
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked. 

December 23, 2013, 09:20 

#15 
New Member
Oscar Ochoa
Join Date: Nov 2013
Posts: 4
Rep Power: 5 
Hi Ehsan
I I found the same information in the next link: http://aerojet.engr.ucdavis.edu/flue...ug/node986.htm You can find more information about the algorithms in the link in the bottom of the page (25.1.1 PressureBased Solver and 25.1.2 DensityBased Solver) Greetings 

December 24, 2013, 02:09 

#16 
Senior Member
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,210
Rep Power: 20 
Thank you very much dear Oscar,that was so helpful.
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked. 

April 8, 2015, 13:16 
low speed

#17 
New Member
muammar
Join Date: Apr 2015
Posts: 1
Rep Power: 0 
Explain the reasons why CFD codes are written in low speed solver and high speed solvers. A student is simulating an object flying at a velocity of 290m/s in the air using FDS6. Can this student obtain acceptable results and why?


April 9, 2015, 16:08 

#18 
Member
nm
Join Date: Mar 2013
Posts: 81
Rep Power: 6 
Pressure based and density based solvers differ in how they couple the three equations. In most modern CFD software both can be used interchangeably according to the problem. However density based solvers might give faster convergence rates for compressible flows as that was the primary intended purpose. But that's not always the case either.
So experiment a bit with both. But if you have a highspeed flow( Mach 0.3 or above) make sure to use a compressible solver. https://www.sharcnet.ca/Software/Flu...ug/node988.htm https://www.sharcnet.ca/Software/Flu...ug/node987.htm 

April 13, 2015, 07:49 
Problem in Trickle Bed reactor

#19 
New Member
Rahul omar
Join Date: Aug 2013
Posts: 12
Rep Power: 6 
Hi,
I've tried to model a Trickle Bed reactor by both options 1) Three phase eulerian 2) 2 phase eulerian with porous media. Both simulations had convergence problem. Problem for Gas & liquid phase is how to define the bubble dia considering gas is continuous phase. For the 3 phase case, I patched solid vol fraction i.e. (1  bed voidage ) in the solution domain, but to my surprise, solid volume fraction keeps on changing and eventually get replaced by the liquid & gas which is not correct. Anybody has any clue? Response will be appreciated. email omar.rahul51@gmail.com 

December 8, 2015, 02:55 
Pressure base or Density base

#20 
New Member
Chotai Nikhil
Join Date: Aug 2015
Posts: 7
Rep Power: 4 
imechanica.org/files/fluent_13.0_lecture05solversettings.pdf


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Using Density Gradient C_R_G(c,t), Pressure Based Solver  Anirudh_Deodhar  Fluent UDF and Scheme Programming  1  October 25, 2013 05:43 
Pressure gradient in UDF for density based solver  matzb  FLUENT  0  February 22, 2010 07:34 
regarding density and pressure based solver  Reddy  CFX  3  October 11, 2007 03:08 
regarding density and pressure based solver  Reddy  FLUENT  0  August 18, 2007 11:11 
Pressure based and Density based Solver  Xobile  Siemens  1  November 30, 2004 22:13 