Direct numerical simulation of stenotic flows. Part 1. Steady flow (original) (raw)
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"Physiological pulsatile flow in a 3D model of arterial stenosis is investigated by using large eddy simulation (LES) technique. The computational domain chosen is a simple channel with a biological type stenosis formed eccentrically on the top wall. The physiological pulsation is generated at the inlet using the first harmonic of the Fourier series of pressure pulse. In LES, the large scale flows are resolved fully while the unresolved subgrid scale (SGS) motions are modelled using a localized dynamic model. Due to the narrowing of artery the pulsatile flow becomes transition-to-turbulent in the downstream region of the stenosis, where a high level of turbulent fluctuations is achieved, and some detailed information about the nature of these fluctuations are revealed through the investigation of the turbulent energy spectra. Transition-to-turbulent of the pulsatileflowin the post stenosis is examined through the various numerical results such as velocity, streamlines, velocity vectors, vortices, wall pressure and shear stresses, turbulent kinetic energy, and pressure gradient. A comparison of the LES results with the coarse DNS are given for the Reynolds number of 2000 in terms of the mean pressure, wall shear stress as well as the turbulent characteristics. The results show that the shear stress at the upper wall is low just prior to the centre of the stenosis, while it is maximum in the throat of the stenosis. But, at the immediate post stenotic region, the wall shear stress takes the oscillating form which is quite harmful to the blood cells and vessels. In addition, the pressure drops at the throat of the stenosis where the re-circulated flow region is created due to the adverse pressure gradient. The maximum turbulent kinetic energy is located at the post stenosis with the presence of the inertial sub-range region of slope 5/3."
LES of additive and non-additive pulsatile flows in a model arterial stenosis
Transition of additive and non-additive pulsatile flows through a simple 3D model of arterial stenosis is investigated by using a large eddy simulation (LES) technique. We find in both the pulsatile cases that the interaction of the two shear layers, one of which separates from the nose of the stenosis and the another one from its opposite wall, causes recirculation in the flow downstream of the stenosis where the nature of the transient flow becomes turbulent. The strength of this recirculation is found to be quite high from the non-additive pulsations when the flow Reynolds numbers, Re $ 1500, for which both the pressure and shearing stresses take on an oscillating form at the post-stenotic region. Potential medical consequences of these results are discussed in the paper. In addition, some comparisons of the non-additive pulsatile results are given with those of both the additive pulsatile and steady flows. The capability of using LES to simulate the pulsatile transitional flow is also assessed, and the present results show that the smaller (subgrid) scales (SGS) contributes about 78% energy dissipation to the flow when the Reynolds number is taken as 2000. The level of SGS dissipation decreases as the Reynolds number is decreased. The numerical results are validated with the experimental data available in literature where a quite good agreement is found.
Series on Biomechanics, 2019
Numerical simulations have been done for a statistical analysis to investigate the effect of stenotic shapes and spiral flows on wall shear stress in the three-dimensional idealized stenotic arteries. Non-Newtonian flow has been taken for the simulations. The wall of the vessel is considered to be rigid. Physiological, parabolic and spiral velocity profile has been imposed for inlet boundary condition. Moreover, the time-dependent pressure profile has been taken for outlet boundary condition. Reynolds number at the inlet has been ranged approximately from 86 to 966 for the investigation. Low Reynolds number k-w model has been used as governing equation. 120 simulations have been performed for getting the numerical results. However, the numerical results of wall shear stress have been taken for the statistical analysis. The simulations and the statistical analysis have been performed by using ANSYS-18.1 and SPSS respectively. The statistical analyses are significant as p-value in all cases are zero. The eccentricity is the most influencing factor for WSS max. The WSS min has been influenced only by the flow spirality. The stenotic length has an influence only on the WSS max whereas the stenotic severity has an influence on the WSS max and WSS ave .
Laminar Blood Flow through a Model of Arterial Stenosis with Oscillating Wall
In this research, a numerical investigation of the physics of laminar blood flow through a two-dimensional (2D) pipe with an idealized stenosis with oscillating wall has been studied using the finite volume method. The governing Navier– Stokes equations are modified using the time dependent Cartesian curvilinear coordinates to handle the complex geometry, such as, arterial stenosis. The arterial wall is considered as moving sinusoidally in a radial direction. The computations for this case were carried out for a range of Reynolds number and amplitude of the wall oscillation. The flow is characterized by the Reynolds number, ranging from 100 to 300. The numerical results are presented in terms of the velocity, pressure distribution, wall shear stress as well as the vorticity, streamlines and vector plot indicating the recirculation zones at the post stenotic region. Due to the higher Reynolds number pressure drop is higher after the throat location of stenosis and wall shear stress is maximal at the center of the stenosis.