Henri Orbanić, BSH Hišni aparati d.o.o. Nazarje, Slovenia.

1. BSH Home Appliances Group
Bread dough modeling and simulation
by using ANSYS Polyflow
5.7.2018
Henri Orbanić

2. 5.7.2018 Bread dough modeling and simulation by using ANSYS Polyflow
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Content
‒ Short introduction of the company
‒ Previous work on the dough kneading simulation and the requirements
‒ Short presentation of ANSYS Polyflow
‒ Possibilities and limitations of using ANSYS Polyflow for dough kneading simulation
‒ Using ANSYS Polyflow for studying dough flow.
‒ Conclusions and future work.

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Label BrandsLocal Brands
Global Brands
Cooking and Baking
Washing and Drying
Consumer Products
Refrigeration and Freezing
Dishwashing
Home appliances under the BSH brands

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Production 2017:
8.1 mio pcs
Plant Nazarje : Production program
MOTOR APPLIANCES
Production quantity 2017:
6.5 mio pcs
THERMIC APPLIANCES
Production quantity 2017:
1.6 mio pcs*
* Coffee grinder included

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Plant Nazarje: MOTOR APPLIANCES
Production quantity 2017:
6.5 mio pcs

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The simulation of kneading bread dough – an overview of past work
‒ Bread dough – mixture of wheat flour and water plus additives (salt, yeast,
sugar etc).
‒ Depending on the flour-water ratio, the dough can be a dry plastic mass
or a soft sticky mass.
‒ Points of interest:
‒ obtaining load regime on the machine,
‒ studying the kneading process.
‒ Results until now:
‒ Obtaining the rheological properties of the developed dough.
‒ Initial simulations were performed in ANSYS Fluent
‒ Topics which are problematic in performing simulations:
‒ Formation of elastic bulk shape – free surface development and
deformation,
‒ Defining proper viscoelastic material model,
‒ Defining wall slip condition (or “stickiness”).

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Material or rheological properties of viscoelastic materials
‒ Viscosity - a measure of its resistance to gradual
deformation by shear stress or tensile stress.
‒ Viscoelastic materials exhibit behavior somewhere in
between that of purely viscous and purely elastic
materials.
‒ Viscoelasticity is studied using dynamic mechanical
analysis where an oscillatory force (stress) is applied to a
material and the resulting displacement (strain) is
measured.
Ref.:
http://projekt.sik.se/rheology/Undr
e_rheobeginners2.htm
Ref.:
https://en.wikipedia.org/wiki/Visco
sity

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Shear viscosity vs Shear rate – before wall slip occurs
10
3
10
4
10
5
Pa·s
10
-2
10
-1
10
0
10
1
1/s
Shear Rate
.
TAU
Anton Paar GmbH
CSR-testo_mv_1 1
CP25-1-SN38017; d=0.048 mm
Viscosity
CSR-testo_mv_2 1
CP25-1-SN38017; d=0.048 mm
Viscosity
CSR-testo_mv_3 1
CP25-1-SN38017; d=0.048 mm
Viscosity
CSR-testo_sv_1 1
CP25-1-SN38017; d=0.048 mm
Viscosity
CSR-testo_sv_2 1
CP25-1-SN38017; d=0.048 mm
Viscosity
CSR-testo_sv_3 1
CP25-1-SN38017; d=0.048 mm
Viscosity
CSR-testo_vv_3 1
CP25-1-SN38017; d=0.048 mm
Viscosity
CSR-testo_vv_1 2
CP25-1-SN38017; d=0.048 mm
Viscosity
CSR-testo_vv_1 1
CP25-1-SN38017; d=0.048 mm
Viscosity
OCF-testo_vv3 1
CP25-1-SN38017; d=0.048 mm
Viscosity
500g flour/ 250g water
500g flour/ 285g water
500g flour/ 300g water
10
0



n
c
n
K
K








Herschel-Bulkey fluid model use in Fluent
K – consistency index
n – flow index
c – critical or limiting shear rate
K = 4100 kg/ms, n = 0.48, 0 = 500 Pa, c = 0.0001

9. 5.7.2018
‒ Shear modulus is represented by the
complex modulus G*.
‒ It can be divided into the storage
modulus G’ which describes the elastic
properties, and G”, the loss modulus
which describes the viscous properties.
‒ The storage and loss modulus in
viscoelastic materials measure the
stored energy, representing the elastic
portion, and the energy dissipated as
heat, representing the viscous portion.
Bread dough modeling and simulation by using ANSYS Polyflow
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Storage G’ and loss G’’ modulus vs. shear rate
10
1
10
2
10
3
10
4
10
5
Pa
G'
G''
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
%
Strain
TAU
Anton Paar GmbH
OCF-testo_vv1 1
CP25-1-SN38017; d=0.048 mm
G' Storage Modulus
G'' Loss Modulus
OCF-testo_vv2 1
CP25-1-SN38017; d=0.048 mm
G' Storage Modulus
G'' Loss Modulus
OCF-testo_vv3 1
CP25-1-SN38017; d=0.048 mm
G' Storage Modulus
G'' Loss Modulus
G’ – storage modulus
G’’ – loss modulus
Behaves more like
elastic body
Behaves more like
fluid body

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Simulation performed in ANSYS Fluent and
the results
‒ VOF two-phase simulation, laminar flow
‒ Complex kinematics was solved by the remeshing method
‒ Convergence was problematic because of free surface
(viscosity difference, surface tension)
‒ Results: flow field, free surface formation, loads on the hook
and container (used for potential comparison with
measurements )

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Findings about using Fluent
‒ Currently not possible to simulate viscoleastic effects in Finte Volume Mehods
‒ Difficult to simulate complex free surfaces where phases have very different viscosities - simulation takes a
lot of time because of slow solving (VOF, dynamic meshing, poor convergence)
‒ Difficult to simulate wall slip effect (experimental data is difficult to obtain).
‒ A different simulation tool is needed to model the flow of viscoelastic materials.

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Simulation of dough kneading by using ANSYS Polyflow
‒ ANSYS Polyflow is a finite-element computational fluid dynamics (CFD)
program designed primarily for simulating applications where viscous and
viscoelastic flows play an important role.
‒ It is used in a wide variety of applications, including polymer and rubber
processing, food rheology, glassworks furnaces, and many other problems
involving the flow of non-Newtonian fluids.
‒ Typical applications: extrusion, blow molding
‒ The flow phenomena observed with polymeric fluids, for example, cannot be
predicted by the classical Navier-Stokes equations.
‒ Non-Newtonian behavior has many facets. Among them are the shear-rate
dependence of the shear viscosity, the presence of normal stresses in
viscometric flows (Weissenberg effect or „climbing“ of the fluid), high resistance
to elongational deformation, and memory effects associated with the elasticity
of the fluid.
‒ ANSYS Polyflow offers a wide variety of constitutive models for both non-
Newtonian inelastic and viscoelastic fluids.
‒ WORKFLOW – Workbench geometry – meshing – solver setup – solving –
CFD-Post
http://www.digitaleng.news/de/speed-the-design-and-
production-of-extrusion-dies/
http://www.technet-alliance.com/software/software-
product/ansys-polyflow/

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Possibilities and limitations when using viscoleastic material models in Polyflow
‒ Flows with internal moving parts – Mesh Superposition technique or Sliding Mesh technique. Both
techniques are not available for viscoleastic fluids.
‒ Remeshing techniques are available. They are necessary when free surfaces or moving interfaces are
present.
‒ Free surfaces - When solving an extrusion problem it is possible that two free surfaces will come into contact.
But it is not possible to define fluid-fluid contact onto the same surface.
‒ Volume of Fluid (VOF) simulation is available – used for injection and filling - faster than remeshing
techniques.
‒ Convergence issues – mesh preparation, solver setup, problematic are non-linearities.
Rigid rotation - single phaseSwirling flow 2.5D axisymmetric
+ free surface + remeshing
VOF viscoelastic flow -
swelling

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Additional rheological measurements of bread dough in order to better define the
viscoelastic model
‒ Special interest is to measure rheological properties in high shear and strain mode where non-linear effects
appear.
‒ Thus besides shear viscosity, complex modulus, 1st normal stress difference and elongational viscosity are
good to have.
‒ The problem at higher shear strains is the appearance of material wall slip – disrupts the measurement.
‒ Special measurement equipment for elongation is needed for polymer like materials – clamping difficulties.

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ANSYS Polymat
‒ The chosen material constitutive model for dough was Phan Thien-Tanner
(PPT) differential viscoelastic model
‒ Relaxation time - characteristic time required for the polymer coil to relax
from a deformed state to its equilibrium configuration. It is a key parameter
for characterizing a viscoelastic fluid.
‒ Viscoelastic models ca include single relaxation time or they can be multi
mode models with multiple relaxation times – better fitting.
 increases from
0.001 to 1000 s
 increases from 0 to
1000 s

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Validation of viscoelastic flow - Couette flow
‒ A whole range of shear rates can be tested in order to
check if the proper shear stress is achieved.
‒ A 2D flow between two parallel walls is used where bottom
wall velocity is 0 while the upper wall velocity is v ≠ 0.
‒ The inlet and outlet are defined as symmetry boundary
conditions.
symmetrysymmetry v1 = 0
v2 > 0
v2/h = const. h

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First simulation trials
‒ Steady state simulation,
‒ Evolution of the relaxation time parameter from 0 to 1 s.,
‒ Rigid rotation:  = 2* rad.
‒ No-slip condition on the walls.
‒ Figures: Velocity in Z direction depending on the material relaxation time.

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Conclusions and future work
‒ It is possible to simulate flow of viscoelastic materials like bread dough but for simple kinematics and low
local shear rates.
‒ Higher local shear rates cause non-linear effects which lead to problems with convergence.
‒ Also it is difficult or not possible to simulate complex free surfaces, fracturing, tearing and joining of material.
‒ Again different tool is required.
‒ Possibilities:
‒ ANSYS Explicit
‒ Smoothed-particle hydrodynamics (SPH) – a meshfree Lagrangian method.

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THANK YOU!