Comparison of LES of Steady Transitional Flow in an Idealized Stenosed Axisymmetric Artery Model With a RANS Transitional Model

Abstract

In this study, two different turbulence methodologies are investigated to predict transitional flow in a 75% stenosed axisymmetric experimental arterial model and in a slightly modified version of the model with an eccentric stenosis. Large eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) methods were applied; in the LES simulations eddy viscosity subgrid-scale models were employed (basic and dynamic Smagorinsky) while the RANS method involved the correlation-based transitional version of the hybrid k-ε/k-ω flow model. The RANS simulations used 410,000 and 820,000 element meshes for the axisymmetric and eccentric stenoses, respectively, with y(+) less than 2 viscous wall units for the boundary elements, while the LES used 1,200,000 elements with y(+) less than 1. Implicit filtering was used for LES, giving an overlap between the resolved and modeled eddies, ensuring accurate treatment of near wall turbulence structures. Flow analysis was carried out in terms of vorticity and eddy viscosity magnitudes, velocity, and turbulence intensity profiles and the results were compared both with established experimental data and with available direct numerical simulations (DNSs) from the literature. The simulation results demonstrated that the dynamic Smagorinsky LES and RANS transitional model predicted fairly comparable velocity and turbulence intensity profiles with the experimental data, although the dynamic Smagorinsky model gave the best overall agreement. The present study demonstrated the power of LES methods, although they were computationally more costly, and added further evidence of the promise of the RANS transition model used here, previously tested in pulsatile flow on a similar model. Both dynamic Smagorinsky LES and the RANS model captured the complex transition phenomena under physiological Reynolds numbers in steady flow, including separation and reattachment. In this respect, LES with dynamic Smagorinsky appeared more successful than DNS in replicating the axisymmetric experimental results, although inflow conditions, which are subject to caveats, may have differed. For the eccentric stenosis, LES with Smagorinsky coefficient of 0.13 gave the closest agreement with DNS despite the known shortcomings of fixed coefficients. The relaminarization as the flow escaped the influence of the stenosis was amply demonstrated in the simulations, graphically so in the case of LES.

Large Eddy Simulation of Transitional Flow in an Idealized Stenotic Blood Vessel: Evaluation of Subgrid Scale Models

“…The study reported the inability of these models to accurately capture the transition to turbulence in the poststenotic region. Similar conclusions were drawn by Tan et al [13] who performed steady inflow simulations in stenosis models using RANS methodology.…”

“…The velocity profiles at the other vessel bisecting plane (xz-plane) are in poor agreement with DNS from x=D % 5 to x=D % 8, with peak velocity values been overpredicted in this region. Similar observations were made by Tan et al [13] and Varghese et al [12] who evaluated dynamic Smagorinsky model for this problem.…”

“…In the previous studies, Varghese et al [12] and Tan et al [13] performed LES of eccentric stenotic flows from the standpoint of validating against the DNS results. While Varghese et al [12] showed that LES with a dynamic Smagorinsky model within FLUENT was not capable of predicting the onset of transition correctly, Tan et al [13] showed that LES with a constant coefficient Smagorinsky model within OpenFOAM gave a closer agreement with DNS than the dynamic Smagorinsky model, although the differences with the DNS solution was quite significant.…”

“…Mean flow predictions, although showing an improvement over RANS based models were in poor agreement with DNS. More recently, Tan et al [13] performed LES of stenotic flows under steady inlet conditions and reported a turbulent flow field for the axisymmetric model at a Reynolds number of 1000, unlike DNS which predicted a laminar flow-field throughout the domain. For the eccentric model, an early transition to turbulence was predicted and the constant coefficient Smagorinsky model predicted the mean quantities more accurately than its dynamic version when compared with the DNS results.…”

A computational study on spiral blood flow in stenosed arteries with and without an upstream curved section

“…see Ghalichi et al [6], Varghese and Frankel [7], Lee et al [8,9] and Li et al [10]) to study the axisymmetric stenotic flow. In the context of LES applications, most recent studies include Varghese et al [11], Paul et al [12,13,14,15], Tan et al [16], Gårdhagen et al [17] and Barber and Simmons [18].…”