Ian Carr | The George Washington University (original) (raw)
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Flow separation over a surface-mounted obstacle is prevalent in numerous applications. Previous s... more Flow separation over a surface-mounted obstacle is prevalent in numerous applications. Previous studies of 3D sepa- ration around protuberances have been limited to steady ow. In biological and geophysical ows, pulsatile conditions are fre- quently encountered, yet this situation has not been extensively studied. Primarily motivated by our previous studies of the ow patterns observed in various human vocal fold pathologies such as polyps, our research aimed to ll this gap in the knowledge concerning unsteady 3D ow separation. This is achieved by characterizing velocity elds surrounding the obstacle, focused primarily on the vortical ow structures and dynamics that occur around a hemispheroid in pulsatile ow. As part of this study, two- dimensional, instantaneous and phase-averaged particle image velocimetry data in both steady and pulsatile ows are presented and compared. Coherent vortical ow structures have been identi- ed by their swirling strength. This analysis revealed ow struc- tures with dynamics dependent on the pulsatile forcing function. A mechanism to explain the formation and observed dynamics of these ow structures based on the self-induced velocity of vortex rings interacting with the unsteady ow is proposed.
American Journal of Physiology - Heart and Circulatory Physiology, Sep 1, 2013
While it is intuitively clear that aortic anatomy and embolus size could be important determinant... more While it is intuitively clear that aortic anatomy and embolus size could be important determinants for cardiogenic embolic stroke risk and stroke location, few data exist confirming or characterizing this hypothesis. The objective of this study is to use medical imaging and computational modeling to better understand if aortic anatomy and embolus size influence predilections for cardiogenic embolic transport and right vs. left hemisphere propensity. Anatomically accurate models of the human aorta and branch arteries to the head were reconstructed from computed tomography (CT) angiography of 10 patients. Blood flow was modeled by the Navier-Stokes equations using a well-validated flow solver with physiologic inflow and boundary conditions. Embolic particulate was released from the aortic root and tracked through the common carotid and vertebral arteries for a range of particle sizes. Cardiogenic emboli reaching the carotid and vertebral arteries appeared to have a strong size-destination relationship that varied markedly from expectations based on blood distribution. Observed trends were robust to modeling parameters. A patient's aortic anatomy appeared to significantly influence the probability a cardiogenic particle becomes embolic to the head. Right hemisphere propensity appeared dominant for cardiogenic emboli, which has been confirmed clinically. The predilections discovered through this modeling could represent an important mechanism underlying cardiogenic embolic stroke etiology.
Flow separation over a surface-mounted obstacle is prevalent in numerous applications. Previous s... more Flow separation over a surface-mounted obstacle is prevalent in numerous applications. Previous studies of 3D sepa- ration around protuberances have been limited to steady ow. In biological and geophysical ows, pulsatile conditions are fre- quently encountered, yet this situation has not been extensively studied. Primarily motivated by our previous studies of the ow patterns observed in various human vocal fold pathologies such as polyps, our research aimed to ll this gap in the knowledge concerning unsteady 3D ow separation. This is achieved by characterizing velocity elds surrounding the obstacle, focused primarily on the vortical ow structures and dynamics that occur around a hemispheroid in pulsatile ow. As part of this study, two- dimensional, instantaneous and phase-averaged particle image velocimetry data in both steady and pulsatile ows are presented and compared. Coherent vortical ow structures have been identi- ed by their swirling strength. This analysis revealed ow struc- tures with dynamics dependent on the pulsatile forcing function. A mechanism to explain the formation and observed dynamics of these ow structures based on the self-induced velocity of vortex rings interacting with the unsteady ow is proposed.
American Journal of Physiology - Heart and Circulatory Physiology, Sep 1, 2013
While it is intuitively clear that aortic anatomy and embolus size could be important determinant... more While it is intuitively clear that aortic anatomy and embolus size could be important determinants for cardiogenic embolic stroke risk and stroke location, few data exist confirming or characterizing this hypothesis. The objective of this study is to use medical imaging and computational modeling to better understand if aortic anatomy and embolus size influence predilections for cardiogenic embolic transport and right vs. left hemisphere propensity. Anatomically accurate models of the human aorta and branch arteries to the head were reconstructed from computed tomography (CT) angiography of 10 patients. Blood flow was modeled by the Navier-Stokes equations using a well-validated flow solver with physiologic inflow and boundary conditions. Embolic particulate was released from the aortic root and tracked through the common carotid and vertebral arteries for a range of particle sizes. Cardiogenic emboli reaching the carotid and vertebral arteries appeared to have a strong size-destination relationship that varied markedly from expectations based on blood distribution. Observed trends were robust to modeling parameters. A patient's aortic anatomy appeared to significantly influence the probability a cardiogenic particle becomes embolic to the head. Right hemisphere propensity appeared dominant for cardiogenic emboli, which has been confirmed clinically. The predilections discovered through this modeling could represent an important mechanism underlying cardiogenic embolic stroke etiology.