CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

How do I interprete the result of steady flow simulation?

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

Like Tree1Likes
  • 1 Post By jsm

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 1, 2021, 15:41
Question How do I interprete the result of steady flow simulation?
  #1
New Member
 
Abhishek
Join Date: Sep 2020
Location: Magdeburg, Germany
Posts: 10
Rep Power: 4
AbhishekShingalaCFD is on a distinguished road
I am running 3D steady multiphase simulation of pump (with one inlet and two outlet), Inlet: Mixture of water and oil
Outlet1 (low pressure): Mostly oil
Outlet2 (high pressure): Mostly water

[1]. These split in outlet leads to a property known as separation efficiency (eta_T)
eta_T=volume fraction of oil at Outlet1/ Volume fraction of oil at Inlet

[2]. Another property of interest is Pressure Head (H_HPO):
H_HPO= depends on pressure, velocity and density at inlet and at Outlet2

[3]. To define stopping criteria, a new property (Volume integral 1) is introduced.
volume integral 1= volume integral of volume fraction of oil in pump.

In general case, when property of interest (i.e., eta_T, H_HPO, volume integral 1) do not change over iterations and residual drops at sufficient level simulation is considered as converged.

Resultant plot of all mentioned properties are attached. Where two times simulation diverged because of k-epsilon turbulent solver error (hit turbulent viscosity limit (1e+6)) and stopped after floating error.

Experimental results: eta_T = 0.99
H_HPO= 0.79 m

To Questions: I am dealing with two problems.
Problems 1 (neglecting simulation divergence): If I would take value of resultant properties at certain iterations for validation it matches with the experimental result. In such case, is the validation reliable?

[Correct under relaxation factor (URF) and convergence tolerance (CT) in AMG linear solver improves the solver performance, result of simulation, saves simulation time as less number of iteration is needed]
Problem 2: Do you think having a correct URF and CT can improve the result of this simulation more (improve validation)?
Attached Images
File Type: png PTJ_07@363063_eta_T Monitor Plot.png (51.9 KB, 11 views)
File Type: png PTJ_07@363063_H_HPO Monitor Plot.png (54.0 KB, 11 views)
File Type: jpg PTJ_07@363063_Residuals.jpg (89.7 KB, 11 views)
File Type: png PTJ_07@363063_Volume Integral Monitor Plot.png (42.1 KB, 9 views)
AbhishekShingalaCFD is offline   Reply With Quote

Old   June 2, 2021, 04:36
Default
  #2
jsm
Senior Member
 
JSM
Join Date: Mar 2009
Location: India
Posts: 192
Rep Power: 18
jsm is on a distinguished road
In general, transient calculation is recommended for multiphase flows because of unsteady flow behavior. By seeing residual monitor, you might achieved the solution convergence by using tight Under Relaxation Factor. But the flow might be transient in nature.

Any way in both cases, add monitor points for the important quantities like volume fraction, pressure head or velocity etc., at critical locations. If monitored quantities are oscillating within acceptable range (preferably smaller range) then solution can be considered as converged steady state solution. If not, you have to solve it in transient solver.
__________________
With regards,
JSM
jsm is offline   Reply With Quote

Reply

Tags
solver convergence, solver crash, steady and unsteady state

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
Intuition for why flow follows convex surfaces lopp Main CFD Forum 47 February 1, 2022 14:14
write bc data and read it for other simulation jdp810 SU2 1 May 8, 2021 18:04
Transient & steady simulation DIVYA P SOMAN ANSYS 0 September 3, 2016 15:09
Can not achieve statistically steady flow in Openfoam jiaodanuma OpenFOAM 0 August 16, 2016 07:49
fluid flow fundas ram Main CFD Forum 5 June 17, 2000 22:31


All times are GMT -4. The time now is 05:50.