Case Studies of the Human Cardiovascular System - Computational Hemodynamics: Theory, Modelling and Applications - page 188

Fig. 7.7 Measured and
predicted velocity distribu-
tion at the centre-plane of a
stenosed carotid bifurcation.
The longitudinal sectioning
of the carotid bifurcation is
performed to compare the
measured and predicted flow
fields. The PIV and CFD
results show good agreement,
which highlights the credibil-
ity of the numerical simula-
tion in flow modelling of the
patient specific anatomy
quantifiable amount. The laser beam was expanded to a 2 mm thick plane verti-
cal light sheet that was directed through the replicated model. Measurements were
taken in 3 mm slices in sagittal planes from left to right. The field of view of the
CCD camera was 165 mm × 132 mm using 1280 × 1024 pixels of a CCD array.
Figure 7.7 presents the comparison between predicted and measured stream-
wise flow patterns at the center-plane of the stenosed carotid artery. In general, both
measured and predicted stream-wise flow patterns are in satisfactory agreement.
Flow separation and re-circulation regions due to the abrupt cross-sectional area
expansion at the sinus region 1 are successfully captured by the CFD simulation,
including the highly skewed velocities caused by curvature and irregularity of both
ICA and ECA. Nevertheless, stream-wise velocities in both ECA and ICA are found
to be over-predicted by the CFD model.
Figure 7.8 shows the quantitative comparison of the measured axial velocity
profiles at the centre-plane with the numerical simulation results at four different
axial locations. Axial velocities are plotted against the dimensionless radial
locations and are normalized by the total length of each cross-section lines. Overall,
the predicted velocity profiles at all cross-section lines are in satisfactory agreement
with measurements. In particular, the velocity profiles along the ICA that are
depicted in Fig. 7.8b , c compared reasonably well with the experimental data. Axial
velocities are over-predicted around 30-55 % in comparison to the measurements
though the main trends are captured rather well for the ECA. Such error can be at-
tributed to the probable onset of transitional turbulent flow in which laminar flow
calculations that have been assumed are invalid. Without an appropriate transitional
model or resolution of all turbulent scales (DNS), the CFD simulation underesti-
mates the strength of turbulence being induced through the secondary flows which
consequentially over-predicts the axial velocity magnitude. Nonetheless, it can be
1 The carotid sinus region is at the bifurcation point of the carotid artery at the origin of the internal
carotid artery (ICA). It exhibits a region of dilation in its cross-sectional area.