Transitional turbulent flow in a stenosed coronary artery with a physiological pulsatile flow

The turbulence in the blood flow, caused by plaque deposition on the arterial wall, increases by the combined effect of the complex plaque geometries and the pulsatile blood flow. The correlation between the plaque geometry, the pulsatile inlet flow and the induced turbulence in a constricted artery is investigated in this study. Pressure drop, flow velocity and wall shear stress are determined for stenosed coronary artery models with three different degrees of asymmetric stenosis and for different heart working conditions. A Computational Fluid Dynamics model, validated against experimental data published in the literature, was developed to simulate the blood pulsatile flow inside a stenosed coronary artery model. The transitional flow behaviour was quantified by investigation of the changes in the turbulence kinetic energy. It was shown that the separation starts from the side of the asymmetric stenosis and spreads to its opposite side further downstream. The results suggest that there is a high risk of the formation of a secondary stenosis at a downstream distance equal to 10- times of the artery diameter at the side and bottom regions of the first stenosis due to the existence of the recirculation zones and low shear stresses. Finally, a stenosed patient specific coronary artery model was employed to illustrate the applicability of the obtained results for real geometry models. The results of this study provide a good prediction of pressure drop and blood flow rate, which can be applied in the investigation of the heart muscle workout and the required heart power.N. Freidoonimehr, M. Arjomandi, N. Sedaghatizadeh, R. Chin, and A. Zande

Wind farm noises: mechanisms and evidence for their dependency on wind direction

Abstract not availableNima Sedaghatizadeh, Maziar Arjomandi, Benjamin Cazzolato, Richard Kels

Effect of wall confinement on a wind turbine wake

This study investigates the effect of wall confinement on a wind turbine wake as a means to guide future wind-tunnel-based wake studies. Large Eddy Simulation was utilised to simulate the wake region for two cases. The first case simulated the NREL phase VI wind turbine in a wind tunnel with 9% blockage. The reason behind selecting this case is the availability of the experimental data in the literature which enabled us in validating the model. The second case was the same turbine located in an unconfined environment, with the same flow upstream velocity. The results show that the wind tunnel walls significantly affect the wake development and its stability, even with a blockage of less than 10%. Tip vortices in the unconfined environment start to break down closer to the turbine compared to the wall-bounded case, resulting in a shorter wake recovery length for the unconfined flow. Vorticity contours reveal coherent vortical structures in the confined wake up to 20 turbine diameters downstream, while these structures dissipate after 16 diameters in an unconfined environment. The calculated power also showed that the turbine in the wind tunnel generates 5.5% more power than that in the unconfined flow. Collectively, these results provide an insight into the effect of walls on the turbine wake in both numerical and experimental studies, offering guidance on how wind tunnel studies relate to real, unconfined flows.N. Sedaghatizadeh, M. Arjomandi, R. Kelso, B. Cazzolato, M. H. Ghayes

Analytical and numerical evaluation of steady flow of blood through artery

Steady blood flow through a circular artery with rigid walls is studied by COSSERAT Continuum Mechanical Approach. To obtain the additional viscosities coefficients, feed forward multi-layer perceptron (MLP) type of artificial neural networks (ANN) and the results obtained in previous empirical works is used. The governing filed equations are derived and solution to the Hagen-Poiseuilli flow of a COSSERAT fluid in the artery is obtained analytically by Homotopy Perturbation Method (HPM) and numerically using finite difference method. Comparison of analytical results with numerical ones showed excellent agreement. . In addition microrotation and the velocity profile along the radius are obtained by using both numerical and analytical approaches.N. Sedaghatizadeh, A. Barari, Soheil Soleimani, M. Mofid

Analytical and numerical evaluation of steady flow of blood through artery

Steady blood flow through a circular artery with rigid walls is studied by COSSERAT Continuum Mechanical Approach. To obtain the additional viscosities coefficients, feed forward multi-layer perceptron (MLP) type of artificial neural networks (ANN) and the results obtained in previous empirical works is used. The governing filed equations are derived and solution to the Hagen-Poiseuilli flow of a COSSERAT fluid in the artery is obtained analytically by Homotopy Perturbation Method (HPM) and numerically using finite difference method. Comparison of analytical results with numerical ones showed excellent agreement. . In addition microrotation and the velocity profile along the radius are obtained by using both numerical and analytical approaches.N. Sedaghatizadeh, A. Barari, Soheil Soleimani, M. Mofid

Modelling of wind turbine wake using large eddy simulation

In an array of wind turbines, the interaction of the downstream machines with the wakes from the upstream ones results in a reduction in the overall wind farm performance. Turbine wakes are a major source of turbulence which exerts fluctuating loads on the blades of the downstream turbines, resulting in the generation of noise and fatigue of the turbine blades. There are many semi-empirical wind turbine wake models in the literature. This paper, develops a fully numerical model of wind turbine wakes using CFD by means of a Large Eddy Simulation (LES). The new LES model is tested against experimental data, showing very good agreement. The advantages of the LES model compared to the available semi-empirical models in the literature are discussed and it is shown that the LES model is very accurate compared to the conventional semi-empirical wake models usually used in industry. Moreover, the LES model is used as a benchmark to compare the accuracy of these semi-empirical models; it is shown that the model proposed by Jensen can predict the velocity deficit most accurately among the semi-empirical models, while the highest degree of accuracy in the wake expansion is achieved by using the Larsen model.Nima Sedaghatizadeh, Maziar Arjomandi, Richard Kelso, Benjamin Cazzolato, Mergen H. Ghayes

Plasma Focus Device as a Breeder of 14.66 MeV Protons to Produce Short-Lived Radioisotopes

In plasma focus devices filled deuterium gas with low pressure admixture gas, 3He, the deuterium creates high energy protons of 14.66 MeV through the 3He(d, p) 4He(Q = 18.35 MeV) fusion reaction. This reaction takes place due to the thermal and non-thermal (beam-target) mechanisms. The proton yield production for deuterium filling gas is determined by using the beam-target character of the pinched plasma and moving boiler model. If we use a low pressure admixture gas like 11B, these high energy protons in turn, could generate short-lived radioisotopes like 11C (used in positron emission tomography) via the 11B(p, n)11C reaction. Calculations indicate the influence of drive parameter to the final yield for a Mather type device

Approximate solution for blood flow through an artery in Cosserat continuum

This investigation describes steady, laminar, and fully developed blood flow velocity and rotation fields in the rigid femoral artery using Cosserat continuum mechanics approach. The governing filed equations are derived and solution to the Hagen-Poiseuilli flow of a COSSERAT fluid in the artery is obtained analytically by Homotopy Perturbation Method (HPM) and numerically using finite difference method. Comparison of analytic results with numeric ones showed excellent agreement.Abas Ali Fardad, Gholamali Atefi, Nima Sedaghatizadeh, Mohammad Mofid

Fluid structure interaction analysis of a calcified aortic valve

The aim of this paper is to investigate the effect of calcification of the aortic-valve leaflets on the flow pattern and hemodynamic parameters such as transvalvular pressure gradient and valve orifice area based on fluid structure interaction modelling methodology using ANSYS. The geometry has been developed in ANSYS Workbench based on echocardiography images available in the literature. A pulsatile inlet velocity extracted from Doppler velocity measurement data in the literature has been used as an inlet boundary condition. For modelling the turbulent flow downstream of the leaflets, the k- SST turbulence model was used. For comparison, both healthy and calcified aortic valves were modelled and analysed. Results show that the transvalvular pressure gradient increases from 769 Pa for the healthy aortic valve to 2356 Pa for the calcified one. Furthermore, there is a significant decrease in the valve orifice diameter, from 13.5 mm for the healthy aortic valve leaflets to 9.21 mm for the calcified one. It was also shown that the wall shear stress on fibrosa and ventricular layers of the leaflets are significantly changed as a result of change in the thickness and material properties of the leaflets. Averaged wall shear stress on the ventricular surface increases from 16.3 Pa for the healthy case to 23.8 Pa for the calcified aortic valve. For the fibrosa surface, it decreases from 3.42 Pa for the healthy leaflets to 1.53 Pa for the calcified one.A. Rezaei Kivi, N. Sedaghatizadeh, M. Arjomandi, A. Zander, B. Cazzolat