Download Assessing The Impact of Dynamic Mesh Approach within a Heart

Assessing The Impact of Dynamic Mesh
Approach within a Heart Pump Using
STAR-CCM+
Mohammed G. Al-Azawy, A. Turan and A. Revell
School of Mechanical, Aerospace and Civil Engineering, The
University of Manchester, Manchester, England, UK
08/03/2016- Prague
1
Overview
 Background about the ventricle assist device
 Computational model of pulsatile LVAD design
 Modelling of the valves and pusher plate moving
 Computational model of continuous blood pump design
 Results and discussion
08/03/2016- Prague
2
The Human Heart and the heart as a pump
 Two upper chambers; atria
(transferring)
 Two
lower
chambers;
ventricles (pumping)
 Four valves
Outlet port
Inlet port
Aortic
valve
Mitral
valve
 Two types of heart assist device:
• Total artificial hearts (TAHs)
• Ventricular
assist
devices
(VADs): LVAD or RVAD
08/03/2016- Prague
50cc Penn State (LVAD)
(V2 design)
Pusher
plate
3
Categorization of Ventricular Assist Devices
According to the development of VADs, we can rate the VADs into
three generation as shown below:
 1st generation: pulsatile pump
08/03/2016- Prague
 2nd and 3rd generation: Rotary continuous flow
4
Dynamic modelling of valves and pusher
plate
 All the simulations were
solves via STAR-CCM+®
v10.02 to solve the
conservation of mass and
momentum equations.
 The meshes were created
for the 3-D simulations
using both Pointwise and
STAR-CCM+.
 An overset mesh algorithm is used for
each instance of mesh motion, and a zerogap technique was employed to ensure full
valve closure.
08/03/2016- Prague
Overset
region
(b)
Background
region
(a)
Inactive cells in
the small gap
(c)
5
 The Elliptic Blending Reynolds Stress Model (EB-RSM) is used here to capture the effects
of turbulence.
 Two common models for Non-Newtonian blood flow (Carreau and Cross) are compared
to the Newtonian model to investigate their impact on predicted levels of shear rate and
1
wall shear stress.
0.9
0.4
The0.8 forth cycle has been chosen to
extract the data from the
0.7
simulation
0.6
0.3
0.2
0.1
0.5
0
Velocity (m/s)
X-velocity (m/s)
Spatial resolution
• Five different
meshes were
created.
• The mesh M4
(2,541,665) is
selected for the
following
simulation.
08/03/2016- Prague
-0.1
-0.2
M1
M2
M3
M4
M5
-0.3
-0.4
-0.5
-0.03
-0.02
-0.01
0
0.01
Position(m)
0.02
0.4
0.3
0.2
0.1
0.03
0
1
2
3
4
5
Cycle
6
Results and discussion
(a)
Comparison of mean flow field
 The current numerical simulations are validated against the instantaneous flow fields from
the in-vitro tests of the same device. The comparisons consist of traces of instantaneous
velocity magnitude
at 0.2extraction
points
in the chamber for all models.
V1
0
0.4
0.6
0.8
0
0.9
0.7
0.6
0.5
0.4
0.3
08/03/2016- Prague
0.5
0.4
0.3
0.2
0.1
0.1
0
0.1
0.2
0.3
0.4
t/T
0.5
0.6
0.7
0.8
0.9
0.8
0.6
0.2
0
0.6
Experimental
EB-RSM : Newtonian
EB-RSM : Carreau
EB-RSM : Cross
k-epsilon : Newtonian
0.8
Velocity (m/s)
Velocity (m/s)
0.7
0.4
0.9
Experimental
EB-RSM : Newtonian
EB-RSM : Carreau
EB-RSM : Cross
k-epsilon : Newtonian
0.8
0.2
1
0
0
0.1
0.2
0.3
0.4
0.5
t/T
0.6
0.7
0.8
0.9
1
7
Examination of non-Newtonian blood rheologies
Newtonian
 The valve position in the inlet and outlet
ports gives rise to complexity of the flow
behaviour inside the chamber throughout
the cycle.
 For the sake of clarity the streamlines in
the figure are divided into two groups( 1st
group: lines 1 and 2, 2nd group: lines 3 and 4)
at t/T = 0.3.
 It can be observed that the re-circulation
regions are enlarged in the non-Newtonian
models, especially in the cross model (see
lines 2 and 4). This observation is significant
in implying that the identification of
regions of flow stagnation.
08/03/2016- Prague
Carreau
Cross
Inlet port
1
2
3
4
8
Sensitivity of x-velocity profile of lines
within the domain
Diastolic phase
0.35
x-velocity (m/s)
0.35
0.3
Line a
0.3
Carreau
Newtonian
0.25
0.25
0.2
0.2
0.15
0.15
0.1
0.1
0.05
0.05
0.1
Line b
Line c
Carreau
Newtonian
0.05
Carreau
Newtonian
Line a
Line b
0
-0.05
-0.1
-0.15
Line c
-0.2
-0.25
0
0
-0.05
-0.05
-0.3
-0.1
0.6
0.8
1
1.2
1.4
-0.1
-0.35
0.6
0.8
1
1.2
1.4
-0.4
-0.4
-0.2
x/Dm
x/Dm
0
0.2
0.4
x/Dch
Systolic phase
x-velocity (m/s)
0.1
Line e
0.1
Line c
Carreau
Newtonian
0.05
0
0
-0.1
-0.1
-0.2
-0.2
-0.1
-0.3
-0.3
-0.15
-0.4
-0.4
0
Line d
Line e
-0.05
Line c
-0.2
-0.25
Carreau
Newtonian
-0.5
-0.5
-0.7
-1.4
-1.2
x/Da
-1
-0.8
-0.6
-0.7
-0.3
Carreau
Newtonian
-0.6
-0.6
08/03/2016- Prague
0.1
Line d
-1.4
-1.2
x/Da
-0.35
-1
-0.8
-0.6
-0.4
-0.4
-0.2
0
0.2
0.4
x/Dch
9
08/03/2016- Prague
10
08/03/2016- Prague
11
Clinical issues of shear stress
•
•
•
Potential
blood
clot
damage
models
concerning shear stress
and exposure time.
Flow
patterns
that
contribute
to
the
haemolysis
potential
include areas of raised
shear stress around the
valves, which contribute
to platelet activation.
This was investigated by
plotting
contours
of
viscous shear stress at
three planes as shown in
the figure for Newtonian
model.
08/03/2016- Prague
1.0e+03
1.0e+02
10.0
1.00
0.1
t/T=0.0028
t/T=0.007
t/T=0.62
t/T=0.63
t/T=0.3
t/T=0.6
t/T=0.613
t/T=0.992
t/T=0.998
1.0e-02
1.0e-03
Viscous shear
stress (Pa)
t/T=0.8
12
 The figure illustrates contour of wall
shear stress (WSS).
 Results are displayed for the Newtonian
and Carreau models. Snapshots of WSS
are plotted over the surface of the
chamber and the mitral zone at early/peak
of diastolic phase and over the aortic zone
and chamber at peak/late of systole. From
the figure, it can be seen that the
differences between the models are
relatively low, particularly in the mitral
and aortic zones.
(a) Newtonian
Wall shear stress (N/m2)
(b) Carreau
(c) Valve
position
t/T=0.0043
08/03/2016- Prague
t/T=0.3
t/T=0.8
t/T=0.997
13
Centrifugal blood pump
outlet
 The centrifugal blood pump proposed by
FDA (Food and Drug Administration)
(CBP-FDA) is a simple centrifugal type,
which is composed of impeller (rotor),
pump housing, inlet and outlet tube as
shown in the figure.
08/03/2016- Prague
Housing
Rotor
(Impeller)
Inlet
14
 Meshes were built with
Pointwise (V16.04R4)
and
STAR-CCM+
(V10.02), as shown in
the figure.
 From this figure, it can
be observed that the
mesh of inlet and
outlet ports are created
using structured mesh
by
Pointwise
and
Polyhedral mesh for
other parts of the pump
using STAR-CCM+.
08/03/2016- Prague
15
Dynamic modelling of rotor (impeller) and
spatial resolution
 The multiple-reference frame (MRF)
approach
or
steady-state
moving
reference model must be used to study the
behaviour of blood flow as steady-state
simulation within the CBP-FDA.
 The sliding mesh technique or transient
rigid body motion model for unsteady.
 3-D, turbulent flow using EB-RSM model.
 Six different cases were employed to
operate the CBP-FDA.
 Five different meshes were used to
investigate the spatial mesh required.
Mesh
Total mesh cells
08/03/2016- Prague
Simulation
cases
Volume Flow
Rate (L/min)
Pump speed
(RPM)
Case 1
2.5
2500
Case 2
2.5
3500
Case 3
4.5
3500
Case 4
6.0
2500
Case 5
6.0
3500
Case 6
7.0
3500
MC1
MC2
MC3
MC4
MC5
794,490
1,758,441
3,699,425
5,691,749
7,554,649
16
Results
Velocity magnitude within the blade
passage and outlet
Case 1
Case 1
Case 2
Case 2
Case 3
Case 3
Case 4
Case 5
Case 4
Case 6
Case 5
0.00 0.44 0.89 1.33 1.78 2.22 2.67 3.11 3.56 4.00 4.44 4.89 5.33 5.78 6.22 6.67 7.11 7.56 8.00
Velocity magnitude (m/s)
Case 6
08/03/2016- Prague
17
Case 1
Shear rate to investigate the non-Newtonian
effect
Case 2
Case 1
Case 2
Case 3
Case 3
Case 4
Case 5
Case 4
Case 6
Case 5
0.00
28
56
83
111
139
167
194
222
250
Shear rate (1/s)
08/03/2016- Prague
278
306
333
361
389
417 444
472 500
Case 6
18
08/03/2016- Prague
19
Publications
 Mohammed G Al-azawy, A. Turan, and A. Revell (2016) “Assessment of turbulence models
for pulsatile flow inside a heart pump”. Computer Methods in Biomechanics and
Biomedical Engineering, 19:3, 271-285, DOI: 10.1080/10255842.2015.1015527.
 Mohammed G Al-azawy, A. Turan, and A. Revell, (2015( “Investigating the Use of Turbulence
Models for Flow Investigations in a Positive Displacement Ventricular Assist Device. 6th
European Conference of the International Federation for Medical and Biological
Engineering, 45:395-398, DOI:10.1007/978-3-319-11128-5_255.
 Mohammed G Al-azawy, A. Turan, and A. Revell (2016( “Investigating the impact of nonNewtonian blood models within a heart pump” International Journal for numerical
methods in biomedical engineering . (DOI: 10.1002/cnm.2780).
 Mohammed G Al-azawy, A. Turan, and A. Revell (2016 ( “An overset mesh approach for
valve closure: an LVAD application”, 9th International Joint Conference on Biomedical
Engineering Systems and Technologies (BIOSTEC 2016), Rome, Italy, February 2016.
08/03/2016- Prague
20
Thanks for your listening
Questions ??
08/03/2016- Prague
21