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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. Keywords: Aortic Arch, Biofluid Mechanics, Scientific Computing, Direct Simulation, Atherosclerosis

Highly unsteady three-dimensional flows in curved pipes with significant variation of flow geometry and flow parameters are studied. Using improvements in computational efficiency, detailed knowledge concerning flow structures is obtained. The numerical solutions of the Navier-Stokes equations have been obtained with a variation of the projection method, and the numerical method was enhanced by new algorithms derived from the physics of the flow. These enhancements include a prediction of the flow unsteady pressure gradient based on fluid acceleration and global pressure field corrections based on mass flow. This new method yields an order of magnitude improvement in the calculation's efficiency, allowing the study of complex flow problems. Numerical flow simulations for oscillating flow cycles show that the curved pipe flows have a significant inviscid-like nature at high values of the frequency parameter. The shape of the velocity profiles is strongly influenced by the frequency parameter, whereas the influence of variations on the pipe cross-sectional area is shown to be rather weak. For large values of the frequency parameter the flow history strongly influences the low mass flow part of the cycle leading to highly unusual velocity profiles. The wall shear stress is studied for all the flows calculated. Our results show that wall shear stress is sensitive to area constrictions, the frequency parameter, as well as the shape of the entrance profile. [DOI: 10.1115/1.1400748]

A study was conducted to analyze an incompressible viscous fluid flow supporting heat transfer over a spherical object in a pipe. The sphere was located off center to generate three-dimensional effects. The method of solution was characterized by a finite volume formulation of the incompressible continuity equations. Results indicated that the asymmetry of flow promotes a lifting force on the sphere. In addition, there were changes in the local shear stress levels on the pipe.

A finite difference time-domain solver for Maxwell's equations accurately predicts the radar cross sections of three-dimensional objects, through the simulation of electromagnetic scattering. The algorithm utilizes body-fitted grids and Lax-Wendroff scheme to solve the Maxwell's equations. The method is more effective, than the traditional finite difference time domain method. The method helps in determining the appropriate shape design for achieving aerodynamic efficiency and low observability. Results demonstrating the effectiveness of the method are presented.

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 results are presented in terms of the study of pressure and vicious lift and drag forces on the sphere.

Suction feeding is the most commonly used mechanism of prey capture in fishes and other aquatic vertebrates, but little is known about the temporal or spatial patterns of water flow generated outside the fish's head during suction feeding or how this flow influences prey capture performance. Using computational fluid dynamics techniques, we developed a three-dimensional computer model of suction feeding that we used to explore (1) the spatial distribution of flow velocity in front of the mouth, (2) the nature of the bow wave that is created in front of a forward swimming predator, and (3) the relative importance of drag and acceleration reaction in generating the forces that prey experience as a result of these flows. The velocity of water toward the mouth of a suction feeding fish diminishes greatly within a very short distance from the mouth of the fish, approximately proportional to the inverse of distance to the third power. This distance increased by only modest amounts when the fish greatly increased the suction velocity at its mouth opening. Forward body movement creates water movement away from the mouth of the fish (a bow wave) that must be overcome by suction in order to yield a net movement of water toward the mouth of the fish. We propose a new function for jaw protrusion: it ameliorates this effect of the bow wave on prey capture by moving the mouth opening (the suction source) out of the influence of the bow wave. During suction feeding, acceleration reaction force may dominate the total forces exerted on prey (depending on flow conditions and the size of the prey), suggesting that both water velocity and acceleration are important determinants of suction feeding performance.

Examines the three-dimensional simulation of pulsatile blood flow in the human aortic arch. Implication of the arch branches for the secondary blood flows; Deviation of the primary flow velocity in the ascending aorta; Presence of wall shear stresses in the aorta.