IS THE BLOOD FLOW LAMINAR OR TURBULENT AT STENOSED CORONARY ARTERY?

Coronary artery disease (CAD) is the abnormal contraction of heart supply blood vessel. This contraction in the blood vessels limits the flow of oxygenated blood to the heart. Thus, diagnosing its severity helps physicians to select the appropriate treatment plan. Most of the commonly diagnostic methods are qualitative. They depend on the physicians' experience and judgement to specify the severity of the stenoses. Fractional flow reserve is one of the quantitative diagnostic tools used while coronary catheterization is being performed. Fractional flow reserve measures the pressure gradient from the proximal to the distal sides of a coronary artery stenosis; this helps in deciding whether the stenosis limits the oxygenated blood flow. Resent models of vascular hemodynamics consider physiologic blood flow to be laminar. Transition to turbulence is considered as a driving factor for numerous diseases such as stenosis and aneurysm. As the value of Reynolds number does not exceed 2000, the flow is laminar. Several researchers stated that the flow might be turbulent at critical Reynolds number value less than 2000. Hence, the aim of this study is to investigate the most accurate turbulence flow model compared to the available experimental data. It is important to replicate the experimental model. Accordingly, the same non- Newtonian blood flow model and pulsatile flow boundary conditions were used. The stenosed simple geometry with a centered fractional flow reserve guidewire is constructed based on the same dimensions of the experimental setup. The numerical models were simulated with laminar flow and K-epsilon, and large eddy simulation (LES) turbulence modelling. The predicted results are compared with the actual available experimental measurements to investigate the most accurate numerical model of the blood flow in the stenosed coronary artery. Based on the predicted results, pressure drop coefficient (CDP), Pressure recovery coefficient (CPR), and the pressure recovery factor. are investigated in the coronary stenosis with and without fractional flow reserve guidewire. For the severe 89% stenosis, it was found that the error in CDP before and during the guidewire insertion is small. The error in CDP before inserting the guidewire reached -7%, -7%, and -12% for laminar, turbulent K-epsilon, and LES models, respectively and -11%, -11%, and -4% for laminar, turbulent K-epsilon, and LES models, respectively during inserting the guidewire. Accordingly, it can be concluded that the laminar and LES modelling represent better performance in simulating the blood flow rather than the turbulence model.