28-08-2017, 12:34 PM
The blood flow in the arteries is dominated by unstable flow phenomena. The cardiovascular system is an internal flow circuit with multiple branches in which a complex liquid circulates. A non-dimensional frequency parameter, the Womersley number, governs the relationship between unstable and viscous forces. The normal arterial flow is laminar with secondary flows generated in curves and branches. Arteries are living organs that can adapt and change with different hemodynamic conditions. Under certain circumstances, unusual hemodynamic conditions create an abnormal biological response. The inclination of the speed profile can create pockets in which the direction of the cutting voltage of the wall oscillates. Atherosclerotic disease tends to be localized in these sites and results in narrowing of the lumen of the artery, a stenosis. Stenosis can cause turbulence and reduce flow through viscous head loss and flow asphyxia. Very high shear stresses near the throat of the stenosis can activate the platelets and thus induce thrombosis, which can totally block blood flow to the heart or brain. The detection and quantification of the stenosis serve as the basis for surgical intervention. In the future, the study of arterial blood flow will lead to the prediction of individual hemodynamic flows in any patient, to the development of diagnostic tools to quantify the disease and to design devices that mimic or alter blood flow. This field is rich in challenging problems in fluid mechanics involving three-dimensional pulsatile flows at the edge of turbulence.