engleski

Experimental flow studies in an elastic Y-model

To determine the causes and history of atherosclerosis it is necessary to understand the hemodynamic parameters of blood circulation. Hemodynamic parameters play an important role in the formation of atherosclerotic plaques, especially near bends and bifurcations where the flow separates from the wall. Here the flow is laminar and non-axial with eddies, secondary flow, flow separation and stagnation points. Stenoses are found predominantly in flow separation areas. Therefore, it is important to study separately the following flow parameters: steady and pulsatile flow, wall elasticity and non-Newtonian flow behaviour of blood. An elastic simplified silicone Y-model simulating the human carotid artery was used for the analysis of these parameters. Flow was visualized at steady flow using dyes and at pulsatile flow with a photoelastic apparatus and a birefringent solution. The local axial velocity at steady and pulsatile flow was determined with a one component laser-Doppler-anemometer (LDA). Pulsatile flow was generated by a piston membrane pump. A glycerine-water solution was used to simulate the Newtonian flow behaviour of blood. A DMSO-Separan water solution was used to simulate the non-Newtonian flow behaviour. Pulsatile flow creates higher and lower shear rates compared to steady flow depending on the velocity amplitude. The non-Newtonian fluid showed markedly different flow behaviour than the Newtonian fluid especially in areas of flow separation. Shear gradients were calculated from these velocity measurements. Shear stresses were calculated from these velocity shear gradients using a bicubic spline interpolation and the viscosity of the non-Newtonian fluid at these shear gradients. At special areas, high shear stresses >10 Pa were found. The elasticity of the model wall also influences the flow behaviour. The measurements showed that the characteristics of pulsatile flow and the elasticity of the model wall should be observed concomitantly. This paper presents the steady and pulsatile flow with a Newtonian and non-Newtonian fluid in an elastic model.

Laser-Doppler-anemometer; Newtonian fluids; Non-newtonian fluids

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