
[Sponsors] 
(Help) CD error simulating laminar steadystate flow over a sphere [OpenFOAM] 

LinkBack  Thread Tools  Search this Thread  Display Modes 
June 13, 2017, 09:36 
(Help) CD error simulating laminar steadystate flow over a sphere [OpenFOAM]

#1 
Member
Join Date: May 2017
Posts: 47
Rep Power: 8 
Hello,
I’m having some trouble simulating laminar steadystate flow over a sphere (OpenFOAM). The solution is converged but I’m having about 15% error on the drag coefficient (CD) for 10 < Re < 100, and about 20% for Re <= 1. Please, see some pictures of my simulation in this website http://imgur.com/a/AxIWE.
Does anyone have any clue what’s wrong, please? Thanks in advance. 

June 13, 2017, 10:16 

#2 
Senior Member
Uwe Pilz
Join Date: Feb 2017
Location: Leipzig, Germany
Posts: 744
Rep Power: 15 
Calculating pressures is one of the harder task in CFD, harder than calculation velocities. The reason: The pressure is calculated in an indirect way (by correction velocities.
The case you simulated is dome by others too. You may compare their results with the experimental findings of Schlichting: Deviations are more normal than absent.
__________________
Uwe Pilz  Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950) 

June 13, 2017, 12:45 

#3 
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,762
Rep Power: 71 
You could check your solution compared to the analytical solution for the flow around a sphere at low Re number...
How do you compute the stress at the wall? 

June 14, 2017, 08:32 

#4 
Member
Join Date: May 2017
Posts: 47
Rep Power: 8 
There's a code that you write in the controlDict file that calculates the viscous ("integral of the shear stress on the area") and pressure drag.


June 21, 2017, 07:39 

#5  
Member
Join Date: May 2017
Posts: 47
Rep Power: 8 
Quote:
u.jpgw.jpg Observations:
Any idea of what could be wrong in the simulation? Thanks 

June 30, 2017, 08:31 

#6 
Member
Join Date: May 2017
Posts: 47
Rep Power: 8 
I found the problem, I was using a first order interpolation scheme for the advection term (Gauss upwind). So I did some research in the OpenFOAM User Guide and chose the Gauss linearUpwind, which is a second order scheme. And that was the problem indeed! After I did that I'm having a 1,3%error for 20 < Re < 200. Unfortunately, for very low Reynolds numbers (Re = 1 and 0.5) the results are still the same.
p+StreamRe80.jpg 

Tags 
drag, laminar, openfoam, sphere, steady 
Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Issues on the simulation of highspeed compressible flow within turbomachinery  dowlee  OpenFOAM Running, Solving & CFD  11  August 6, 2021 06:40 
is it possible to predict how long it takes to reach steady state solution in unstead  Alimohamadi_nasr  CFX  4  November 11, 2013 06:11 
Flow Across Tube Banks  Transient vs Steady State  HeatTransferFan  CFX  11  September 28, 2012 14:21 
convergence problem in 3D steady state, laminar flow in a bath  vajiheh  FLUENT  0  July 10, 2009 12:18 
About the difference between steady and unsteady problems  Lisa  Main CFD Forum  11  July 5, 2000 14:37 