Date of Award
Doctor of Philosophy (PhD)
Dr. G. F. Round
Dr. I. A. Feuerstein
The purpose of this investigation is to determine experimentally the fluid dynamic field in models of arterial branching vessels and to identify the flow features which might influence the predominant occurrence of atherosclerotic lesions in such vessels.
Flow conditions in four rigid-walled models representing the aortic bifurcation, iliac bifurcation, mesentric artery branch and renal artery branch are investigated over a Reynolds number range of 1000-4000 and a complete range of flow division between daughter vessels. Qualitative flow streamline patterns and quantitative definition of those flow conditions leading to flow separation are determined primarily at steady flow with a limited set of pulsatile experiments. The flow patterns observed are photographed using high speed cinephotography and a neutrally-buoyant tracer-particle technique. The flow streamline patterns in the four models are complicated and characterized by secondary flow motion. This motion is accentuated with increasing Reynolds number. Flow separation is inducible through alteration of flow division between daughter vessels or by an increase in the flow rate. Each of the four models has distinct combinations of flow rate and flow division ratio which give flow separation at the outside wall of one or both daughter tubes. The separated flows observed here display streamlines forming an open vortex with flow entering and leaving. The site of the separation point in the branching plane is approximately constant with the reattachement points occuring further downstream as Reynolds number increases and as the branch flow rate decreases.
Shear rate distributions at the walls of the four models are measured using an electrochemical technique. This technique is based on an oxidation-reduction reaction at electrodes implanted in the wall. Distribution of wall shear rate of the branching site is very non-uniform, with high shear rate at the leading edge of the flow dividers. The shape of the shear rate curves are functions of the geometry, total flow rate and most importantly the flow division ratio. An unstable pattern of shear is found at the wall where separation is expected to occur. For pulsatile flow, the time-averaged rate of shear is not appreciably changed by frequency and amplitude of pulsation. The biological implication of the results is discussed with specific reference to the sites of atherosclerotic lesions found in man for these geometries.
El Masry, Osama A. A., "Fluid Dynamic Evaluation in Models of Arterial Branches" (1977). Open Access Dissertations and Theses. Paper 749.