Copyright © 2012 by ASME 1 INTRODUCTION This work is a collaborative effort between the Biomechanics and Living System Analysis Laboratory (BIOLISYS) in Cyprus and the Biomechanics Laboratory of IACM/FORTH in Greece. Both labs combine interdisciplinary skills from engineering, medicine and biology to provide solutions to clinical problems associated with cardiovascular and other diseases. For this study, numerical flow simulations were performed using: a) open source software VMTK and commercial software ICEM CFD as pre-processors, b) the finite volume based solver Fluent and c) Tecplot 360 (Amtec Inc.) for post- processing. METHODS Solver type and details We used the finite volume solver Fluent v.12.1.4 (Ansys Inc.) for the numerical approximation of the Navier-Stokes equations. For the steady state cases the Coupled scheme was selected for pressure velocity coupling using the pressure-based coupled solver. For the transient solutions the PISO scheme was selected for the pressure velocity coupling using the pressure-based segregated solver. We apply the second order upwind scheme to discretise the convection terms in the momentum equations and a second order pressure interpolation scheme. A first order iterative time advancement scheme is applied for the transient solutions. Gradients are computed using the Green-Gauss node based method. Mesh and boundary conditions We use tools from VMTK to apply cylindrical flow extensions at the inlet (D inlet ~ 0.56 cm) and outlet of the domain so that we prescribe a fully developed flow boundary condition at the inlet and a traction free boundary condition at the outlet. The length of the outflow extension was calculated based on the approximate relation for the entrance length for steady laminar rigid pipe flow: L e /D~0.06Re where L e is the entrance length, D is the tube diameter and Re the Reynolds number [1]. In our case the maximum Re is 649 corresponding to a peak systolic flow rate of 11.42 ml/s. Based on the outlet diameter (0.44 cm) the outflow length using the above relation should be at least 17 cm. An extension of 25 cm was applied. We used ICEM CFD v12.1 (Ansys Inc.) to discretise the computational domain and generate an unstructured mesh. The computational domain (excluding flow extensions) is discretised with ~2.1 10 6 hybrid, linear elements with an average cell center spacing of 0.25 mm. Near-wall layers of prism elements were used throughout the domain for boundary layer refinement with a 10 -2 D inlet distance of the center of the first element from the wall. Triangles were used to discretise the surface of the aneurysm and quads for the extensions. Pyramid and tetrahedral elements were used to fill the core of the computational domain in the aneurysm. The o-grid method was used to generate layers of hexahedral elements in the flow extensions. A parabolic velocity profile was applied at the inlet for the steady flow cases with a mean velocity corresponding to the required flow rate. For the transient flow cases the velocity profiles prescribed at the inlet at each time step were obtain from the Womersley solution (Womersley number~3.5) based on the flow waveform provided (scaled appropriately to generate the desired mean flow rates) . Steady-state flow computations were obtained on a HP Z800 workstation with 4 quadratic Intel Xeon processors in parallel. The total CPU time was around 380 hrs corresponding to total wall clock time of 95 hrs. Time varying solutions were obtained on an Intel Xeon X5355 @ 2.66 GHz processor based Linux cluster requiring a total CPU time of 75 hrs per flow cycle. Grid size and time step independence study We refined our mesh by reducing the mean cell center distance from 0.25 to 0.18 mm thus increasing the number of elements in the aneurysm (excluding the extensions) from ~2.1 10 6 to ~4 10 6 and SBC2012 CFD CHALLENGE: SOLUTIONS USING THE COMMERCIAL FINITE VOLUME SOLVER, FLUENT Nicolas Aristokleous 1 , Mohammad Iman Khozeymeh 1 , Yannis Papaharilaou 2 , Georgios C. Georgiou 3 , Andreas S. Anayiotos 1 Proceedings of the ASME 2012 Summer Bioengineering Conference SBC2012 June 20-23, Fajardo, Puerto Rico SBC2012-80691 1 Department of Mechanical Engineering and Materials Science and Eng., Cyprus University of Technology, Limassol, 3503, Cyprus 2 Institute of Applied and Computational Mathematics, Foundation for Research and Technology – Hellas, Heraklion, Crete, 71110, Greece 3 Department of Mathematics and Statistics, University of Cyprus, Nicosia, 1678, Cyprus