Fundamentals of Haemodynamics - Computational Hemodynamics: Theory, Modelling and Applications - page 92

this phenomenon can be explained from the velocity and vectors shown in Fig. 4.23b
and c . As the blood flows over the location of the aneurysm, part of it impinges at
the bottom aneurysmal wall, and its flow direction is reversed along the outer wall,
forming a clockwise-rotating vortex inside the aneurysm. The aortic artery narrows
downstream of abdominal aorta, hence the blood flow velocity is accelerated and
pressure drop consumption increases. The streamlines demonstrate that the aneu-
rysm experiences strong secondary flow due to the flow recirculation, and as a con-
sequence consumes more flow energy and increases the patient's cardiac workload.

4.8 Summary

Fundamentals of haemodynamics were introduced in this chapter. The main proper-
ties of blood that govern its flow behavior are viscosity and density which wield
great influence on our health and well-being. As such clinical implications can be
deduced from measurements of these two properties. During blood flow the blood
experiences shear and pressure forces caused by the variation in flow velocity from
the arterial wall to the artery centre. When it travels at high momentum and/or in
large arteries relative to its viscosity, then its flow behaviour is characterised by
turbulence. At low momentum and/or small arteries the flow is typically laminar.
Since blood flow is enclosed by the arterial walls, it can be classed as a type of
internal pipe flow. The influence of the artery walls give rise to the different bound-
ary layer formation as it develops through the pipe. It was shown that Poiseulle's
Law and Bernoulli's Equation provides useful estimates of pressure drop across the
artery network.
The chapter culminates with specific examples in the carotid bifurcation, aor-
tic arch, and in aneurysms which highlighted fluid dynamics characteristics. These
included flow a stagnation point, flow separation, and secondary flow in the form
of Dean vortices in bifurcating arteries, and curved aortic arch. The presence of an
aneurysm caused localised recirculation and contributed to flow resistance.
The fundamental haemodynamic theory from this chapter has a strong connec-
tion with fluid dynamics. Therefore this chapter provides a solid foundation for
understanding the derivations of the governing equations of fluid and structural
dynamics that is presented in Chap. 5.