Access Type

Open Access Dissertation

Date of Award

January 2012

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical Engineering

First Advisor

Emmanuel Ayorinde

Second Advisor

Trilochan Singh

Abstract

ABSTRACT

NUMERICAL SIMULATION AND EXPERIMENTATION OF PULSATILE FLOWS IN AXISYMMETRIC ARTERIAL MODELS

by

TADESSE GEBREEGZIABHER

December 2011

Co-advisors: 1. Dr. Emmanuel Ayorinde 2. Dr. Trilochan Singh

Major: Mechanical Engineering

Degree: Doctor of Philosophy

The primary motivation for this dissertation is the fluid flow and structural response to unsteady blood flow in the human body. The research work is a synergistic merging of numerical simulation and experimentation. For the experiments, an all-encompassing, highly flexible experimental apparatus was designed and fabricated to facilitate a wide range of operating conditions, the range of which was chosen to accommodate mammalian cardiovascular system for both human and animal species. The parameters that were varied during the course of the experimentation include the frequency of the flow pulsation, tubular materials having various structural properties, and blockages of the tube cross sections to simulate the presence of plaque in arteries. The main outcome of the experimentation was a connection between the amplitude and frequency of the pulsations and the volumetric flow rate of the flowing fluid. Of equal importance is the extent of the response of the wall to the nature of the pulsating flow which was detected, located and characterized using a non-invasive acoustic emission equipment.

The simulations that were performed represent a major advance over prior attempts to simulate pulsating flows in flexible- and rigid-walled tubes. That advance was embodied in the model that was used to characterize the flow. In most of prior studies, a particular flow regime was selected and used throughout the entire solution domain. This selection ignored the fact that flowing fluids passing through variable cross sections undergo changes of flow regime. In particular, a flow initiated in a relatively large upstream cross section may be laminar based on inlet conditions. However, as the fluid travels downstream and enters a constricted cross section, the laminar regime may undergo a transition and subsequently experience turbulence. The capability to accommodate all these flow regimes by a single model was first accomplished in this research. Of special relevance is that the capability to simulate the proper flow regime enabled a more realistic response of the bounding wall of the tube to the imposed pulsations.

Comparisons were made between the experimental results and the predictions of the simulations for two purposes. One was to establish the ranges of applicability of the simulation model. The other established a body of archival-quality information based on confirming experimental and simulated results. Another unique contribution of this research is the determination of the presence of flow-induced acoustic emissions. The motivation for this part of this work is the development of a diagnostic tool to detect, locate, and characterize blockages in arterial models.

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