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- Al Sam, Ali, et al.
(author)
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The effect of moving waves on neutral marine atmospheric boundary layer
- 2014
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In: First Symposium on OpenFOAM® in Wind Energy. - : EDP Sciences. ; 2:01003
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Conference paper (peer-reviewed)abstract
- Large eddy simulations are performed to study the effects of wind-wave direction misalignment of the neutral marine atmospheric boundary layer over a wavy wall. The results show that the wind-wave misalignment has a significant effect on the velocity profiles and the pressure fluctuation over the wave surface. These effects are not confined to the near wave surface region but extend over the whole atmospheric surface layer.
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- Cesur, Alper, et al.
(author)
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Analysis of the wake dynamics of stiff and flexible cantilever beams using POD and DMD
- 2014
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In: Computers and Fluids. - : Elsevier BV. - 0045-7930. ; 101, s. 27-41
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Journal article (peer-reviewed)abstract
- The wake flow behind a cantilever beam of quadratic cross-section at a Reynolds number of 50,000 is investigated using detailed simulations. Two cases are considered, the first one using a stiff beam and the second one with a beam allowing for elastic deformation due to the hydrodynamic forces. The flow is simulated using an implicit large eddy simulation (ILES) approach in OpenFOAM and the structural deformation of the beam is found from a non-linear finite element approach using OOFEM. The motion of the fluid mesh due to the structural deformation is handled by an ALE method. The wake structures are investigated using proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) of the flow field. The results show that apart from the wake structures originating from the vortex shedding there is also a low frequency mode, which is an oscillatory motion in the stream-wise direction, present.
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- Evegren, Philip, et al.
(author)
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On the secondary flow through bifurcating pipes
- 2010
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In: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 22:10
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Journal article (peer-reviewed)abstract
- The secondary motion induced by flow through curves and bifurcations has been subject to investigation over long time due to its importance in physiological and technological applications. In contrast to the flow in a straight pipe, curvature leads to the formation of secondary flow which is often unsteady. Streamline curvature occurs also in bifurcating pipes leading to some corresponding secondary, unsteady flow. This paper presents a detailed description of the unsteady flow in the daughter branch after a 90 degrees bifurcation. A range of Reynolds and Womersley numbers are investigated. The results show the presence of Dean vortices and additional vortical patterns not reported in the literature. Both the streamwise (axial) and the secondary velocity components change character at larger Womersley numbers, leading to less complex secondary flow. Also, at larger Reynolds numbers, flow instabilities are observed. The secondary flow may lead to the formation of unsteady separation bubbles. This in turn yields peaks in the wall shear stress components. Such wall shear stress variations have often been related in the literature to the development process of atherosclerosis. (C) 2010 American Institute of Physics.
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- Evegren, Philip, et al.
(author)
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Pulsating flow and mass transfer in an asymmetric system of bifurcations
- 2011
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In: Computers & Fluids. - : Elsevier BV. - 0045-7930 .- 1879-0747. ; 49:1, s. 46-61
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Journal article (peer-reviewed)abstract
- Pulsating flow through bifurcations are of general interest. In the human body such flows are also very common; for example in blood vessels and the respiratory tract. The characteristics of the flow in arteries have been related to the process of atherogenesis, based on the observation that the initial manifestation of the process is observed at certain common locations, i.e., near bifurcations in vessels of certain size. Inspite of these observations there is no direct understanding between the flow itself and the pathological process. In fact, the flow itself is rather complex since it is unsteady and transitional. The paper considers both unsteady- and steady-flow through a three generation system of (non-symmetric) bifurcations. The geometry consists of a 90 degrees. bifurcation followed by two sets of consecutive symmetric bifurcations. The aim of the paper is to investigate the effects of the bifurcations on the flow and mass transport in such a geometrical configuration that is often found in physiological situations. Additionally, the effects of different inlet velocity conditions have been considered. The different inlet conditions are aimed at studying the sensitivity to variations of inflow conditions; variations found under normal physiological conditions. The results show that the geometrical asymmetry affects the velocity distribution even after a second bifurcation downstream. Two generations down this asymmetry does not have a significant effect any-more. The different inlet conditions affect the flow to the next generation of branches during parts of the cycle. At peak flow and further downstream in the system the effects are negligible. It is also found that over a cycle the mass flow distribution through the outlets can be affected by the inlet velocity conditions. The distribution of a passive scalar is not uniform but depends on the inlet conditions and the Schmidt number (i.e., molecular diffusion).
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- Evegren, Philip, et al.
(author)
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Wall shear stress variations in a 90-degree bifurcation in 3D pulsating flows
- 2010
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In: Medical Engineering and Physics. - : Elsevier BV. - 1350-4533 .- 1873-4030. ; 32:2, s. 189-202
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Journal article (peer-reviewed)abstract
- The exact role of fluid mechanics in the patho-physiological process of atherosclerosis has been a research topic over many years, yet without clear conclusive result. One has observed that morphological manifestations of the disease are found at some well-defined locations: certain vessel bifurcations and in curvatures. The flow in these regions is characterized by unsteadiness and often separation. Currently there are no complete theories that can explain the process since the different components in the process are not fully understood. Here we carry out detailed computations of the unsteady flow in an arterial segment typical to location of early appearance of arterial lesions. We study the wall shear stress (WSS) field variations near a junction with the purpose of identifying fluid-mechanical parameters that can be related to sites of atheroslcerosis. The results show that regions associated with atherosclerosis experience highly elevated temporal- and spatial-derivatives of the WSS, also at less commonly known locations. Thus, large derivatives in time and space do not seem unique for the most common areas of atherosclerosis. Differences in WSS character between these locations are identified as differences in the time period of back flow as well as differences in the magnitude of the WSS derivatives. The data is presented in a way that facilitates understanding of the variations in WSS.
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