| dc.description.abstract | Fluid flow in helically coiled pipes is not fully understood. Although many efforts have been devoted to investigating the complex characteristics of the flow in helically coiled pipes, much is unknown for especially high Reynolds numbers, i.e., turbulence. In this thesis, turbulent flow in helically coiled pipes is numerically investigated. First, direct numerical simulation of turbulent flow in a straight pipe is carried out for numerical validation. Then, we examine turbulent flow in helically coiled pipes using the fully turbulent flow from a straight pipe. An increase in the turbulent kinetic energy is observed at the first curve of helically coiled pipes. However, stabilization of the turbulent flow is observed towards the outlet, which is observed numerically for the first time. Due to the curved path and the centrifugal force, two counter-rotating vortices referred to as Dean vortices are observed. These vortices rapidly intensify the dissipation by creating smaller eddies in the flow and hence contribute to stabilizing the flow. We found that the higher curvature and lower torsion are associated with faster stabilization by modifying the geometry. Lastly, numerical simulations of blood flow in the internal carotid artery (ICA), which shares geometrical characteristics with helically coiled pipes, are conducted with patient-specific geometries. Recent studies proposed the correlation between flow instability and the initiation of cerebral aneurysms in the ICA. Therefore, we aim to contribute to understanding the formation of flow instability in the ICA by applying the gained knowledge from helically coiled pipes. In some of the patients, ’turbulent-like’ flow is found. A patient with stable flow has a higher curvature and lower torsion in the carotid siphon, which agrees with the results of helically coiled pipes. Dean vortices are observed for the first time and may be associated with flow instability in the ICA. | eng |