Pulsatile flow analysis in a bend square channel by modal decomposition

Abstract

Abstract. The article analyzes the results of numerical simulations of pulsatile flow in a square channel with a 90• bend using Proper Orthogonal Decomposition (POD). The simulations of laminar steady and unsteady flow obtained by ANSYS Fluent commercial system were used as input for modal decomposition. Several regimes for different values of individual parameters (stationary flow component, ) were simulated. Not only energy-related modes but also modes significant from the viewpoint of energy dissipation. Other evaluated modes are the modes corresponding to the pulsatile flow frequency and the modes reflecting the flow separation at the bend. AimThe aim of the paper was to analyze the results of numerical simulation of unsteady pulsatile flow in the square cross-section channel with a 90• bend in the middle of its length using the Proper Orthogonal Decomposition (POD) method. ModelThe geometric model of channel for numerical simulation was created within the Designer program, which is part of the ANSYS Workbench v14. The channel model had a constant square cross-section over the whole length with an edge length of 5 mm. The channel was, in its whole length of 1000 mm, divided into several independent, consecutive sections. The lengths of the sections at the inlet and outlet from the computational area were 250 mm and they could be described as input (section 1) / output (section 5), or stabilizing sections. The remaining internal sections were considered to be the sections suitable for flow parameters evaluation. The middle section (3) -out of 5 sections -had dimensions of a cube with a 5 mm edge. Such dimensionally designed channel allowed the use of the same geometry even for data verification in a straight channel. The remaining two, yet unspecified sections, namely section 2 and 4, were divided proportionally. All the aforementioned divisions and constructions were based on [1]. Numerical simulation Computational meshFor the created channel a structured mesh containing only elements of six-wall type was defined. A non-uniform mesh a e-mail: lukas.manoch@fs.cvut.cz b e-mail: jan.matecha@fs.cvut.cz c e-mail: hana.netrebska@fs.cvut.cz d e-mail: josef.adamec@fs.cvut.cz was considered and created for all 3 axis of Cartesian coordinate system, in which the geometry was created. It was the thickening of the mesh towards the wall and corners of the channel model. The density of the mesh elements was increased further in the longitudinal direction, i.e. downstream. This thickening was kept exactly to the middle of the central element (figure 1). The scheme of mesh generation was subsequently mirrored according to one of its plane, perpendicular to the flow direction. The total number of the mesh elements was around 4M. The areas for definition of boundary conditions were also defined within the mesh generation. These were mainly the interface between particular sections. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distri...