The geometry of a typical adult human carotid bifurcation, complete with the sinus, was establish... more The geometry of a typical adult human carotid bifurcation, complete with the sinus, was established from a study of a large number of angiograms. A rigid model was constructed from glass and investigations were performed under steady flow conditions using flow visualization techniques over a range of upstream Reynolds numbers and flow division ratios through the branches representative of physiologic conditions expected in the human vasculature. The study reveals a complex flow field in which secondary flows play an important role. The separation regions occurring at the outer corners of the branching are also subjected to much higher shear stress. Comparison with pathologic data on localization of atherosclerotic lesions indicates that zones susceptible to disease experience low or oscillatory shear stress while regions subject to higher shear are free of deposits.
The geometry of a typical adult human carotid bifurcation, complete with the sinus, was establish... more The geometry of a typical adult human carotid bifurcation, complete with the sinus, was established from a study of a large number of angiograms. A rigid model was constructed from glass and investigations were performed under steady flow conditions using flow visualization techniques over a range of upstream Reynolds numbers and flow division ratios through the branches representative of physiologic conditions expected in the human vasculature. The study reveals a complex flow field in which secondary flows play an important role. The separation regions occurring at the outer corners of the branching are also subjected to much higher shear stress. Comparison with pathologic data on localization of atherosclerotic lesions indicates that zones susceptible to disease experience low or oscillatory shear stress while regions subject to higher shear are free of deposits.
Arterial branchings are of particular interest in the study of atherogenesis because of the frequ... more Arterial branchings are of particular interest in the study of atherogenesis because of the frequent occurrence of atherosclerotic plaques in these sites. The bifurcation of the common carotid artery into the internal and external branches is an important example due to its frequent involvement with arterial disease and to the fact that transient ischemic episodes and cerebrovascular accidents are often associated with these extracranial lesions. Despite this well-recognized fact, little quantitative information is available concerning the precise distribution of carotid lesions or of their relationship to local hemodynamic factors. Inasmuch as hemodynamic behavior represents a mechanical factor which may create a favorable environment for plaque localization in bifurcations, we have undertaken a study to provide a detailed description of the flow field in the carotid bifurcation and of the distribution of early atherosclerotic lesions in humans. Previously, we have reported on flow visualization in a model of the human carotid bifurcation and on velocity and wall shear stress measurements in the model obtained with laser Doppler anemometry under steady flow conditions [1,2]. Recently, we have harvested human carotid arteries and studied the distribution of atherosclerotic lesions in these vessels.
The distribution of nonstenosing, asymptomatic intimal plaques in 12 adult human carotid bifurcat... more The distribution of nonstenosing, asymptomatic intimal plaques in 12 adult human carotid bifurcations obtained at autopsy was compared with the distribution of flow streamline patterns, flow velocity profiles, and shear stresses in corresponding scale models. The postmortem specimens were fixed while distended to restore normal in vivo length, diameter, and configuration. Angiograms were used to measure branch angles and diameters, and transverse histological sections were studied at five standard sampling levels. Intimal thickness was determined at 15 degrees intervals around the circumference of the vessel sections from contour tracings of images projected onto a digitizing plate. In the models, laser-Doppler anemometry was used to determine flow velocity profiles and shear stresses at levels corresponding to the standard specimen sampling sites under conditions of steady flow at Reynolds numbers of 400, 800, and 1200, and flow patterns were visualized by hydrogen bubble and dye-w...
This paper discusses the development of a process to generate a CFD database for the non-linear l... more This paper discusses the development of a process to generate a CFD database for the non-linear loads process capability for critical loads evaluation at Boeing Long Beach. The CFD simulations were performed for wing/body configurations at high angles of attack and Reynolds numbers with transonic and elastic deflection effects. Convergence criteria had to be tailored for loads applications rather than the usual drag performance. The time-accurate approach was subsequently adopted in order to improve convergence and model possible unsteadiness in the flowfield. In addition, uncertainty issues relating to the turbulence model and grid resolution in areas of high vortical flows were addressed and investigated for one of the cases.
The authors describe an hybrid procedure for computing flow with significant shock/boundary-layer... more The authors describe an hybrid procedure for computing flow with significant shock/boundary-layer interaction or large-scale separation by accounting for viscous effect more accurately than the interactive boundary-layer approach. The inner zone consists of the vortical flow region near the body surface and includes areas of strong viscous effects, shock/boundary-layer interaction, and the downstream wake. Located away from the shock waves and the viscous layer, the outer zone, which surrounds the inner region and extends to the far-field boundary, is assumed to be irrotational. The three-dimensional unsteady Navier-Stokes equations are solved in the inner zone using a semi-implicit time-marching algorithm, and the three- dimensional unsteady full-potential equation is solved in the outer region. The flow-fields in the two regions are tightly coupled to each other at every time step through the exchange of mass and momentum at the zonal interface. Computational results are presented...
The geometry of a typical adult human carotid bifurcation, complete with the sinus, was establish... more The geometry of a typical adult human carotid bifurcation, complete with the sinus, was established from a study of a large number of angiograms. A rigid model was constructed from glass and investigations were performed under steady flow conditions using flow visualization techniques over a range of upstream Reynolds numbers and flow division ratios through the branches representative of physiologic conditions expected in the human vasculature. The study reveals a complex flow field in which secondary flows play an important role. The separation regions occurring at the outer corners of the branching are also subjected to much higher shear stress. Comparison with pathologic data on localization of atherosclerotic lesions indicates that zones susceptible to disease experience low or oscillatory shear stress while regions subject to higher shear are free of deposits.
The geometry of a typical adult human carotid bifurcation, complete with the sinus, was establish... more The geometry of a typical adult human carotid bifurcation, complete with the sinus, was established from a study of a large number of angiograms. A rigid model was constructed from glass and investigations were performed under steady flow conditions using flow visualization techniques over a range of upstream Reynolds numbers and flow division ratios through the branches representative of physiologic conditions expected in the human vasculature. The study reveals a complex flow field in which secondary flows play an important role. The separation regions occurring at the outer corners of the branching are also subjected to much higher shear stress. Comparison with pathologic data on localization of atherosclerotic lesions indicates that zones susceptible to disease experience low or oscillatory shear stress while regions subject to higher shear are free of deposits.
Arterial branchings are of particular interest in the study of atherogenesis because of the frequ... more Arterial branchings are of particular interest in the study of atherogenesis because of the frequent occurrence of atherosclerotic plaques in these sites. The bifurcation of the common carotid artery into the internal and external branches is an important example due to its frequent involvement with arterial disease and to the fact that transient ischemic episodes and cerebrovascular accidents are often associated with these extracranial lesions. Despite this well-recognized fact, little quantitative information is available concerning the precise distribution of carotid lesions or of their relationship to local hemodynamic factors. Inasmuch as hemodynamic behavior represents a mechanical factor which may create a favorable environment for plaque localization in bifurcations, we have undertaken a study to provide a detailed description of the flow field in the carotid bifurcation and of the distribution of early atherosclerotic lesions in humans. Previously, we have reported on flow visualization in a model of the human carotid bifurcation and on velocity and wall shear stress measurements in the model obtained with laser Doppler anemometry under steady flow conditions [1,2]. Recently, we have harvested human carotid arteries and studied the distribution of atherosclerotic lesions in these vessels.
The distribution of nonstenosing, asymptomatic intimal plaques in 12 adult human carotid bifurcat... more The distribution of nonstenosing, asymptomatic intimal plaques in 12 adult human carotid bifurcations obtained at autopsy was compared with the distribution of flow streamline patterns, flow velocity profiles, and shear stresses in corresponding scale models. The postmortem specimens were fixed while distended to restore normal in vivo length, diameter, and configuration. Angiograms were used to measure branch angles and diameters, and transverse histological sections were studied at five standard sampling levels. Intimal thickness was determined at 15 degrees intervals around the circumference of the vessel sections from contour tracings of images projected onto a digitizing plate. In the models, laser-Doppler anemometry was used to determine flow velocity profiles and shear stresses at levels corresponding to the standard specimen sampling sites under conditions of steady flow at Reynolds numbers of 400, 800, and 1200, and flow patterns were visualized by hydrogen bubble and dye-w...
This paper discusses the development of a process to generate a CFD database for the non-linear l... more This paper discusses the development of a process to generate a CFD database for the non-linear loads process capability for critical loads evaluation at Boeing Long Beach. The CFD simulations were performed for wing/body configurations at high angles of attack and Reynolds numbers with transonic and elastic deflection effects. Convergence criteria had to be tailored for loads applications rather than the usual drag performance. The time-accurate approach was subsequently adopted in order to improve convergence and model possible unsteadiness in the flowfield. In addition, uncertainty issues relating to the turbulence model and grid resolution in areas of high vortical flows were addressed and investigated for one of the cases.
The authors describe an hybrid procedure for computing flow with significant shock/boundary-layer... more The authors describe an hybrid procedure for computing flow with significant shock/boundary-layer interaction or large-scale separation by accounting for viscous effect more accurately than the interactive boundary-layer approach. The inner zone consists of the vortical flow region near the body surface and includes areas of strong viscous effects, shock/boundary-layer interaction, and the downstream wake. Located away from the shock waves and the viscous layer, the outer zone, which surrounds the inner region and extends to the far-field boundary, is assumed to be irrotational. The three-dimensional unsteady Navier-Stokes equations are solved in the inner zone using a semi-implicit time-marching algorithm, and the three- dimensional unsteady full-potential equation is solved in the outer region. The flow-fields in the two regions are tightly coupled to each other at every time step through the exchange of mass and momentum at the zonal interface. Computational results are presented...
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Papers by Bala Bharadvaj