Eventos Anais de eventos
CONEM 2022
XI Congresso Nacional de Engenharia Mecânica - CONEM 2022
INFLUENCE OF MESH QUALITY AND TURBULENCE MODEL ON COMPUTATION OF TWO-DIMENSIONAL FLOW ON A BIRADIAL TURBINE VOLUTE
Submission Author:
Luís Morão Cabral Ferro , RN
Co-Authors:
Luís Morão Cabral Ferro, Diogo Neves Ferreira, Luis Gato
Presenter: Luís Morão Cabral Ferro
doi://10.26678/ABCM.CONEM2022.CON22-0478
Abstract
The biradial turbine was proposed to equip wave energy power plants with bidirectional air flows. The turbine is symmetrical to a plane perpendicular to the turbine axis, having one volute upstream and another downstream of the rotor. The upstream volute flow is inwards, whereas the flow through the volute downstream of rotor flow is outwards. The volute has a logarithmic spiral shape. Computational Fluid Dynamics (CFD) can be used to compute the flow through the volute. Velocity and pressure field computation of a turbulent flow by a CFD code requires the generation of a mesh and specification of a turbulent model. The iterative process development and convergence depend on the mesh quality and turbulence model. A two-dimensional geometry was used to analyse mesh and turbulence model influence. The mesh was generated by HEXPRESS™ program of NUMECA software. The initial mesh was generated by specifying cell numbers in radial and tangential directions, using the smaller number for the maximum number of refinements for which HEXPRESS™ was able to generate the mesh. For the viscous layer, a stretching ratio equal to 1.2 was specified. The number of layers was the optimal suggested by the program for a y+ equal to one. Next, the mesh was generated multiplying by 1.5 the initial number of cells in radial and tangential directions of the previous mesh. Eight different meshes were generated. Eight turbulent models were compared. Six linear eddy viscosity models: SARC, Spalart-Allmaras, k-epsilon with extended wall functions (EWF), Realizable k-epsilon without and with EWF and k-omega (SST) and two non-linear eddy viscosity models: the Explicit Algebraic Reynolds Stress Model with and without EWF. The quality of all meshes is analyzed by comparing values of mesh quality parameters. Results are presented for the dependence on mesh discretization of mean radial, tangential velocity components, mean velocity angle at outlet section, total pressure loss coefficient and error extrapolation for the more refined mesh. Residuals of the iterative procedure for continuity, momentum equation, and turbulence quantities for the more refined meshes are also shown. Isolines for radial and tangential velocities components using k-omega are shown. When comparing the evolution of quality parameters with mesh refinement, its quality is always improving. The results show that linear turbulent models are more stable than non-linear ones. The k-omega and Realizable k-epsilon were the only ones in which convergence was achieved for all the meshes. Turbulence model k-omega showed to be the more reliable turbulent model.
Keywords
volute, Turbine, biradial turbine, CFD
