A three-dimensional and pulsatile blood flow in a human aortic arch and its three major branches has been studied numerically for a peak Reynolds number of 2500 and a frequency (or Womersley) parameter of 10. The simulation geometry was derived from the three-dimensional reconstruction of a series of two-dimensional slices obtained in vivo using CAT scan imaging on a human aorta. The numerical simulations were obtained using a projection method, and a finite-volume formulation of the Navier-Stokes equations was used on a system of overset grids. Our results demonstrate that the primary flow velocity is skewed towards the inner aortic wall in the ascending aorta, but this skewness shifts to the outer wall in the descending thoracic aorta. Within the arch branches, the flow velocities were skewed to the distal walls with flow reversal along the proximal walls. Extensive secondary flow motion was observed in the aorta, and the structure of these secondary flows was influenced considerably by the presence of the branches. Within the aorta, wall shear stresses were highly dynamic, but were generally high along the outer wall in the vicinity of the branches and low along the inner wall, particularly in the descending thoracic aorta. Within the branches, the shear stresses were considerably higher along the distal walls than along the proximal walls. Wall pressure was low along the inner aortic wall and high around the branches and along the outer wall in the ascending thoracic aorta. Comparison of our numerical results with the localization of early atherosclerotic lesions broadly suggests preferential development of these lesions in regions of extrema (either maxima or minima) in wall shear stress and pressure.

An incompressible viscous fluid flow with heat transfer over a spherical object inside a pipe is considered. The flow is made three-dimensional by an eccentric positioning of the sphere inside the pipe. The governing equations are solved by a numerical method which uses a finite volume formulation in a generalized body fitted coordinate system. An overset (Chimera) grid scheme is used to resolve the two geometries of the pipe and sphere. The results are compared to those of an external flow over a sphere, and the code is validated using such results in the intermediate Reynolds number range. The blockage effects are analyzed through evaluation of lift, drag, and heat transfer rate over the sphere. Also the change in the shear stress pattern is examined through evaluation of the local friction factor on a pipe wall and sphere surface.

Flow and unsteady heat transfer around a moving and rotating sphere is considered as it passes through the thermal entrance region of a heated pipe. The flow is incompressible and viscous with constant properties, and the heated pipe wall is kept at a constant temperature. Two Peclet numbers of 25 and 100 are considered along with two sphere-to-pipe-diameter ratios of 0.2 and 0.4. The flow is made three dimensional by an eccentric positioning of the sphere inside the pipe. The governing equations are solved by a validated numerical method which uses a finite volume formulation in a generalized body-fitted coordinate system. An overset (Chimera) grid scheme is used to resolve the two geometries of the pipe and sphere. The results are presented in terms of the steady pressure and viscous lift and drag forces on the sphere. In addition the unsteady heat transfer characteristics of the flow are presented in terms of the local and overall Nusselt number evolution around the sphere as it passes through the thermal entrance region of the pipe. Sphere heat-up is also given as the lumped mass sphere temperature as a function of distance from the thermal entrance. [S0022-1481(00)02402-6]

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