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-   -   Pressure based and Density based Solver (http://www.cfd-online.com/Forums/main/8398-pressure-based-density-based-solver.html)

 Xobile November 29, 2004 14:41

Pressure based and Density based Solver

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

 sun November 30, 2004 07:24

Re: Pressure based and Density based Solver

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.

 G.Ravanan November 30, 2004 09:46

Re: Pressure based and Density based Solver

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 DIA-3/4",PIPE LENGTH-600MTR, HEAD 2M. HOW MUCH COULD BE THE OUTLET WATER PRSSURE AT THE OTHER END OF PIPE?

 johnfriend July 10, 2009 05:57

Historically speaking, the pressure-based approach was developed for low-speed incompressible flows, while the density-based approach was mainly used for high-speed 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 density-based 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 pressure-based approach, the pressure field is extracted by solving a pressure or pressure correction equation which is obtained by manipulating continuity and momentum equations."
The pressure-based solver traditionally has been used for incompressible and mildly compressible flows. The density-based approach, on the other hand, was originally designed for high-speed compressible flows. Both approaches are now applicable to a broad range of flows (from incompressible to highly compressible), but the origins of the density-based formulation may give it an accuracy (i.e. shock resolution) advantage over the pressure-based solver for high-speed compressible flows."

refer: http://courses.cit.cornell.edu/fluent/wedge/step4.htm

 RRD July 22, 2009 08:21

Highspeed?

How do you quantify Highspeed?

 vinayender July 23, 2009 08:58

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.

 JMern August 3, 2012 12:07

Coupled pressure-based 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.

 leflix August 3, 2012 15:42

Quote:
 Originally Posted by johnfriend (Post 222221) Historically speaking, the pressure-based approach was developed for low-speed incompressible flows, while the density-based approach was mainly used for high-speed 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 density-based 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 pressure-based approach, the pressure field is extracted by solving a pressure or pressure correction equation which is obtained by manipulating continuity and momentum equations." The pressure-based solver traditionally has been used for incompressible and mildly compressible flows. The density-based approach, on the other hand, was originally designed for high-speed compressible flows. Both approaches are now applicable to a broad range of flows (from incompressible to highly compressible), but the origins of the density-based formulation may give it an accuracy (i.e. shock resolution) advantage over the pressure-based solver for high-speed compressible flows." refer: http://courses.cit.cornell.edu/fluent/wedge/step4.htm

clear and perfect!!!! I have learned something tonight !
Thanx Johnfriend

 leflix August 3, 2012 15:58

Quote:
 Originally Posted by G.Ravanan ;31764 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 DIA-3/4",PIPE LENGTH-600MTR, HEAD 2M. HOW MUCH COULD BE THE OUTLET WATER PRSSURE AT THE OTHER END OF PIPE?

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 Vē)/(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.

 deepthishan August 16, 2013 05:35

2d airfoil-solver settings

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.

 tprpr1 August 21, 2013 06:15

@deepthishan

 joolpre October 16, 2013 06:58

Inviscid Simulation

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?

 skyblue_mech October 25, 2013 15:43

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?

 immortality December 6, 2013 08:47

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

 Gatoscar December 23, 2013 09:20

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 Pressure-Based Solver and 25.1.2 Density-Based Solver)

Greetings

 immortality December 24, 2013 02:09

Thank you very much dear Oscar,that was so helpful.

 morey April 8, 2015 13:16

low speed

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?

 nvarma April 9, 2015 16:08

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

 omar.rahul April 13, 2015 07:49

Problem in Trickle Bed reactor

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

 nikhilchotai@gmil.com December 8, 2015 02:55

Pressure base or Density base

imechanica.org/files/fluent_13.0_lecture05-solver-settings.pdf

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