Case Studies of the Human Cardiovascular System - Computational Hemodynamics: Theory, Modelling and Applications - page 214

Table 7.7 Fluid properties
used in numerical simulation

Parameters Value Units

Dynamic viscosity 3.5 × 10 −3 Pa

Density 1050 kgm −3

Entrance velocity 0.04377-8.088 cms −1

Exit velocity 0-8.33 cms −1

Pressure 0-100 Pa

Fig. 7.25 Plot of pressure
versus time

ues for Reynolds number in the cerebral artery has a range of 100-300, and is less
than 30 within the aneurysm (Kim et al. 2010b). To model the unsteady nature of the
flow field, transient CFD using ANSYS CFX was performed. A rigid wall condition
is assumed.
Flow in the vessel is simulated from the early-systole state to end diastolic
state of the cardiac cycle T based on an idealistic physiological waveform (refer to
Fig. 7.25 ). The model is simulated for one cardiac cycle T from 0 to 1. The pressure
starts from zero, and the peak pressure and flow rate occurs at t/T = 0.15. The pres-
sure then reduces to zero again at t/T = 0.3 and then continues at zero pressure till
t/T = 1. This pressure variation is repeated in the subsequent cycles.

7.4.4 Aneurysmal Flow Results

Streamline tracing is used to deduce the path of the blood flow. A clearly defined
large-scale vortex is present in the aneurysm sac as shown in Fig. 7.26 . The results
show that an aneurysmal vortex reduces in strength after stenting at time steps
t/T = 0.2, 0.5 and 0.6. Figure 7.27 presents the counter-clockwise vortices in the
aneurysm sac using vorticity and velocity vector fields. In the non-stented artery, a
large-scale vortex exists in the aneurysm sac. When stented, the vortex decreases
as demonstrated by its lower vorticity values. The pressure gradient Δ P and shear
strain rate γ is characterised by using a monitor point at the centre of the aneu-
rysmal sac (indicated by a crosshair in the flow field plots). The pressure gradient
and shear strain rate fields can give a quantifiable indication of the vortex differ-