Decomposition of blood flow in a cerebral artery with an aneurysm

Brain aneurysms occur when the wall of a blood vessel weakens and expands. The rupture of a brain aneurysm has devastating effects. However, the precise causes of this disease are still unknown, although it is believed that blood flow plays a key role. The flow within aneurysms is complex, difficult to measure and interpret, with more studies needed. The purpose of the present study is therefore to evaluate the decomposition of blood flow within aneurysms, to improve our understanding and potentially help separate pathological from physiological flow patterns. Direct numerical computational fluid dynamics simulations, using OpenFOAM, are evaluated using spectral proper orthogonal decomposition (SPOD) and triple decomposition, or phase-averaging, techniques. The velocity and the wall shear stress fields are decomposed. Phase-averaging is used to separate the base pulsatile and physiological laminar flow from the turbulent fluctuations, while the SPOD is used to identify the most energetic space–time coherent structures in the flow. The results obtained from the decomposition techniques are promising, in particular with the SPOD identifying a significant frequency peak around 25 Hz in the realistic aneurysm geometry studied here. In addition, two main vortical structures are identified in the mean flow. Decomposition assessments such as the ones performed in this study can have important consequences in the evaluation of aneurysm pathophysiology, considering that vascular walls may be affected differently depending on the flow structure and characteristic frequencies.