In this study, we analyzed turbulent flows through a phantom (a 180 degrees bend with narrowing) at peak systole and a patient-specific coarctation of the aorta (CoA), with a pulsating flow, using... Show moreIn this study, we analyzed turbulent flows through a phantom (a 180 degrees bend with narrowing) at peak systole and a patient-specific coarctation of the aorta (CoA), with a pulsating flow, using magnetic resonance imaging (MRI) and computational fluid dynamics (CFD). For MRI, a 4D-flow MRI is performed using a 3T scanner. For CFD, the standard k - epsilon, shear stress transport k - omega, and Reynolds stress (RSM) models are applied. A good agreement between measured and simulated velocity is obtained for the phantom, especially for CFD with RSM. The wall shear stress (WSS) shows significant differences between CFD and MRI in absolute values, due to the limited near-wall resolution of MRI. However, normalized WSS shows qualitatively very similar distributions of the local values between MRI and CFD. Finally, a direct comparison between in vivo 4D-flow MRI and CFD with the RSM turbulence model is performed in the CoA. MRI can properly identify regions with locally elevated or suppressed WSS. If the exact values of the WSS are necessary, CFD is the preferred method. For future applications, we recommend the use of the combined MRI/CFD method for analysis and evaluation of the local flow patterns and WSS in the aorta. Show less
In this thesis the molecular emission of species such as CO, HCN and HNC and HCO+ are used to probe and quantify mechanical heating in star-forming galaxies. In the first part of the thesis photo... Show moreIn this thesis the molecular emission of species such as CO, HCN and HNC and HCO+ are used to probe and quantify mechanical heating in star-forming galaxies. In the first part of the thesis photo-dissociation models are used to find a diagnostic of mechanical heating at the level of molecular clouds. It was shown that mechanical heating leaves a strong signature in diagnostics that involve high-J to low-J transitions. In the second part of the thesis , synthetic line emission maps of molecular species are computed for model star-forming galaxies. The emission from these maps are used as input to photo-dissociation models in-order to constrain the physical properties, such as gas density and visual extinction, of star-forming galaxies. It was demonstrated that it is essential to consider mechanical heating in modelling the emission of star-forming galaxies using photo-dominated models. Show less
