ANALYSIS OF THE FLOW IN STENOSED CAROTID-ARTERY BIFURCATION MODELS - HYDROGEN-BUBBLE VISUALIZATION

This paper deals with the effect of geometric changes of mild stenoses on large-scale flow disturbances in the carotid artery bifurcation. H ydrogen-bubble visualisation experiments have been performed in Plexig las models of a non-stenosed and a 25% stenosed carotid artery bifurca tion. The flow conditions approximate physiological flow. The experime nts show that shortly after the onset of the diastolic phase vortex fo rmation occurs in the plane of symmetry. This vortex formation is foun d in a shear layer, which is formed in the carotid sinus. The shear la yer is located between a region with low shear rates at the non-divide r wall and a region with high shear rates at the divider wall. In orde r to gain insight into the parameters that are important with respect to the stability of the shear layer, experiments have been performed i n which the influence of the shape of the Bow pulse, the Reynolds numb er (Re), the Womersley parameter (alpha) and the flow division ratio ( gamma) on the flow phenomena is studied. From these experiments it app ears that the flow phenomena in the carotid artery bifurcation are sig nificantly influenced by Re, alpha the systolic acceleration (sa) and deceleration (sd) and the duration of the peak-systolic flow (T-max). With these results a simplified Bow pulse is chosen, with which the ex periments in the non-stenosed and the 25% stenosed bifurcation are per formed. Comparison of the hydrogen-bubble profiles in the 0 and 25% st enosed models with similar flow conditions shows that the geometric ch ange of the 25% stenosis only slightly influences the flow phenomena. The most striking influences are found in the stability of the shear l ayer. Quantitative experiments by means of laser Doppler anemometry me asurements and numerical computations are needed to analyse the influe nce of the stenosis of the flow field more accurately.