Asymmetric 75% and 95% area reduction, transparent Sylgard stenotic models were operated under internal carotid artery (ICA) [Womersley parameter, alpha=5.36, Re(mean) =213 and 180, respectively, and Re(peak)=734 and 410, respectively] and left anterior descending coronary artery (LAD) flow wave forms (alpha=2.65, Re(mean)=59 and 57, respectively, and Re(peak)= 137 and 94, respectively) to evaluate the effect of these conditions on particle residence times downstream of the stenoses. Amberlite particles (1.05 g/cm3, 400 microm) were added to the fluid to simulate platelets and their motion through the stenotic region and were traced using a laser light sheet flow visualization method with pseudo-color display. Two-dimensional (2D) particle motions were recorded and particle washout in the stenotic throat and downstream section were computed for all cases. All four model cases demonstrated jetting through the stenosis which followed an arching pattern around a large separation zone downstream. Considerable mixing was observed within these vortex regions during high flow phases. Particle washout profiles showed no clear trend between the degrees of stenosis although particles downstream of the stenoses tended to remain longer for LAD conditions. The critical washout cycle (1% of particles remaining downstream of the stenosis), however, was longer for the 95% stenoses cases under each flow condition due to the larger protected region immediately downstream and maximal for the LAD 95% case. Results of this study suggest that particle residence times downstream of 75% and 95% stenoses (approximately 3-6 s for ICA and approximately 8-10 s for LAD) exceed the minimum time for platelet adhesion (approximately 1 s) for at least 1% of cells and, thus, may be sufficient to initiate thrombus formation under resting conditions.
Current fluid film seal/bearing pressure numerical solutions taking into account both circumferential and axial lubricant flows are not in wide spread use. The most common method is to solve a two dimensional finite element method of Reynolds equation. However, this type of solution often leads to a long computer solution times when employed in an advanced seal/bearing code. A new approximate solution of Reynolds equation for oil seal or bearing flows is proposed in this paper which includes the axial flow modeling. The objective is achieved by means of an axial approximation that can be used to develop a one dimensional centerline circumferential pressure finite element solution to Reynolds equation. Optimization of the parameters associated with the approximate solution parameters is shown. Example seal/bearing pressure and load capacity calculations are presented and the solution verified by comparison with a full finite element 2-D solution. Also, the method of calculating the axial and circumferential lubricant flows as well as axial and circumferential power losses are presented and validated.
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