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FLOW INSTABILITIES IN A GRAFT ANASTOMOSIS: FLOW REYNOLDS NUMBER 350

Colin J. Bates
Cardiff School of Engineering Cardiff University, PO Box 685 Cardiff CF24 3TA, UK

Andrew Grand
Cardiff School of Engineering Cardiff University, PO Box 685 Cardiff CF24 3TA, UK

Joanna L. Bates
Department of Radiology Hull Royal Infirmary, Anlaby Road, Hull East Yorkshire, HU3 2JZ, UK

Abstract

The major cause of arterial bypass graft failure is intimal hyperplasia. Low and fluctuating wall shear stresses in the graft, which are associated with disturbed flow, are believed to be an important factor in the development and localisation of intimal hyperplasia.
This study presents details of the flow structure inside a 30° Y-junction, various fillet radii at the intersection between the graft and the host artery have been investigated. Reynolds numbers, based upon water as the working fluid, and pulsatile frequencies (shown in brackets) of 125(0.7 Hz), 230(0.85 Hz) and 350(1 Hz) have been studied together with various Distal Outlet Segment to Proximal Outlet Segment (DOS:POS) flow ratios. The measurements confirm the presence of all the anticipated flow features normally associated with low Reynolds number pulsatile flow through a bifurcation, such as:
(a) the flow impacting the floor of the host artery, as it flows through the junction.
(b) the position where the inlet flow impacted the junction floor was governed by the DOS:POS flow ratio, the fillet radius and the mean Reynolds number.
(c) fluctuating wall shear stresses in the toe, heel and the base of the host artery of the graft.
(d) the existence and longevity of single, double and triple vortices at various phases of each individual pulsatile cycle.