The aim of current research is to investigate numerically the fluid dynamics of lobe pumps and typical factors which could impact on performance of the pump including profile of rotor surface, number of lobes, gap size between rotor and casing, and clearance between two rotors, etc. The circular and epicycloidal curves are used to generate profiles for rotor surface, while the complex flow phenomena inside the pump are simulated by dynamic mesh technique. With wide range of investigated speed from 1000 to 5000rpm, the study produces significant information on flow pattern, velocity and pressure fields. The advantage of epicycloidal pumps over circular ones has been demonstrated via characteristic curve which performs pressure head versus rotational speed. Meanwhile the analysis has proved that multilobes, three and four lobes, do not increase performance of the pump but provide more stable output and higher capacity compared with two-lobe pumps. The results confirm great impact of gap size between rotor and casing wall on the pump efficiency. Decrease of the gap from 1.25mm down to 0.5mm produces about 425% increasing of pressure head. In addition, it has been also proved that the clearance between two rotors could be varied from 0.12mm to 0.15mm without much effect on performance of the pump.
Summary. Blood flow rheology is a very complex phenomenon. Hemodynamics owns Newtonian or non-Newtonian characteristic is still debatable. There is no model which represents the viscous property of blood is approved by all researchers. Recently, studies related to blood tend to classify blood as nonNewtonian fluid. In this research, power law, Casson and Carreau which are being the most popular non-Newtonian models are applied to investigate the hemodynamics variables that influence formation of thrombosis and predict damageability to blood cell. The branched arterial system is simplified as Tjunction geometry and the computational fluid dynamics software Fluent 6.2 with finite volume method is utilized to analyze the blood flow rheology in cases of continuous and pulsatile flow. The analysis results are compared with that of Newtonian model and give out very interesting hemodynamics predictions for each model. The size of recirculation zone is different from each model that is observed significantly. The wall shear stress of Carreau model gets the highest value, 14% in case of continuous flow and around 17% in pulsatile case bigger than that of Newtonian model. The results of pulsatile flow show that the Newtonian model is closed to power law model while the Casson model is similar to the Carreau model.
Blood flow rheology is a very complex phenomenon. Hemodynamics owns Newtonian or non-Newtonian characteristic is still debatable. Recently, studies related to blood tend to classify blood as non-Newtonian fluid. In this research, power law, Casson and Carreau which are being the most popular non-Newtonian models are applied to investigate the hemodynamics variables that influence formation of thrombosis and predict damageability to blood cell. The branched arterial system is simplified as T-junction geometry and the computational fluid dynamics software Fluent 6.2 with finite volume method is utilized to analyze the blood flow rheology in cases of continuous and pulsatile flow. The analysis results are compared with that of Newtonian model and give out very interesting hemodynamics predictions for each model. The size of recirculation zone is different from each model that is observed significantly. The wall shear stress of Carreau model gets the highest value, 14% in case of continuous flow and around 17% in pulsatile case bigger than that of Newtonian model. The results of pulsatile flow show that the Newtonian model is closed to power law model while the Casson model is similar to the Carreau model.
Human aortic valve is made of thin collagen type tissue. The three leaflets open and close under fluid forces exerted upon them. To simulate the hemodynamic characteristics of the blood flow, ANSYS CFX10.0 software was utilized to analyze the three-dimensional Reynolds-averaged Navier-Stokes equations. With a quasi-steady analysis model, we predict values of the blood velocity and the wall shear stress both over the valve leaflets and the endothelial lining. In addition, investigation on fluid dynamic of a heart valve supposed suffering prolapsed disease has been also conducted, and compared with normal valve. Analysis results highlight that leaflet opening situation and valve geometry affect the shear stress distribution and vortex flow regime. Maximum shear stress takes place near the center of leaflet trailing edge at the very beginning of systolic phase with value of 7.093N/m 2 . At peak systole, the maximum wall shear stress distributes near the aortic root where jet impingement takes place. Current study also demonstrated the interactive impact between low and high wall shear stress on relation to heart valve disease.
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