# Before and after the case¶

## or: Comparing solvers without any claim for correctness¶

### Wien, 2014-06-16¶

"The lesser the people know about how sausages and laws are made, the better they sleep in the night"

Otto v. Bismarck

Who is this Bismarck anyway?

# Overview¶

The aim of this presentation is to demonstrate two new features of PyFoam

• Semi-automatic case setup
• Working with IPython-notebooks

## Structure of the presentation¶

• What is PyFoam
• Our "project"
• Setting up the case
• Getting the results

# And who is PyFoam?¶

• PyFoam is a Python-library
• Aimed at working with OpenFOAM
• Manipulates case files
• Starts runs and analyzes their output
• There are utilities implemented with this library
• This is the part that people usually call "PyFoam"
• Most parts of PyFoam written by the speaker
• Which doesn't mean that he knows how to use it properly

Are usually announced:

• On the Wiki-page
• On the MessageBoard

# The case¶

## p-U-coupled solver¶

• The next version of foam-extend has a p-U-coupled solver pUCoupledFoam
• Sets up one big matrix with pressure and all three velocity components
• Solves them all at the same time
• I never worked with it before
• But people who did are quite excited
• Supposedly it converges faster and is more stable

## The case¶

• There are tutorial-cases that come with pUCoupledFoam
• Never trust tutorials provided with the solver: Their purpose is to make the solver look good
• Instead a well-known case is used that also comes with (Open)FOAM
• pitzDaily: a backward facing step for which measurment data by Pitz and Daily exists
In [6]:
Image(filename="pitzDailyOverview.png")

Out[6]:

# What we're comparing with¶

We like both types of music: we like Country and Western

Jake & Elwood Blues

• There are currently two major forks of the code originally called Foam
• OpenFOAM by ESI-OpenCFD
• Foam-extend by Hrvoje Jasak (Wikki Ltd) and community contributors
• Foam-extend has block-coupled matrixes for some time now
• Until now the examples were conjugate heat transfer and coupled transport equations
• OpenFOAM has a similar facility for approximately a year
• There is now an option to solve the U-Eqn in regular solvers coupled
• According to release notes current versions have improved numerics

We're going to compare:

• coupled31 : pUCoupledFoam from foam-extend-3.1
• segregated31: simpleFoam from foam-extend-3.1
• segregated23: simpleFoam from OpenFOAM-2.3
• coupled23: simpleFoam from OpenFOAM-2.3 with the coupled option for the U-Eqn

# What we're comparing¶

• The base case will be the pitzDaily from foam-extend-3.1
• For OpenFOAM-2.3 the fvSchemes from OF-2.3 will be used
• Because this is what is probably the best there
• For pUCoupledFoam the fvSolution from the tutorial case was used

## Numbers that are compared

• Residuals
• Are calculated the same way. So they should be comparable
• Pressure drop between inlet and outlet
• Detachment point of the circulation behind the step
• The place on the lower wall where the flow changes direction
• Profiles defined on specific locations
• Experimental data is measured from the original paper

# Detachment point¶

In [3]:
Image(filename='pitzDailyDetachmentPoint.png')

Out[3]:

# The measured profiles¶

In [7]:
Image(filename="pitzDailyMeasurments.png")

Out[7]: