Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
A comparative study of a transition model with a full turbulence model on the aerodynamic analysis of a wind turbine airfoil
Submission Author:
Anderson de Moura Ribeiro , MG
Co-Authors:
Anderson de Moura Ribeiro, Felipe Loureiro, Patricia Habib Hallak, Afonso Celso de Castro Lemonge
Presenter: Anderson de Moura Ribeiro
doi://10.26678/ABCM.COBEM2023.COB2023-0751
Abstract
Wind energy is rapidly becoming an economically viable energy source as significant improvements in the performance of modern wind turbines are being achieved, which are also due to better understanding and CFD modelling of the flow field. Laminar boundary layers generate relatively low friction forces, whereas turbulent boundary layers result in relatively large friction forces, making the laminar flow more desirable over the body as much as possible, as a means of reducing drag. The lift is obtained only as long as the boundary layer can withstand the lift producing pressure gradients about the airfoil. However, the laminar boundary layer can withstand only negligible adverse pressure gradients without separation, which makes the transition to turbulent flow desired to occur before the major adverse gradients are encountered, otherwise it would be reached a definite laminar separation and stall, producing drag through both friction and pressure forces with loss of lift. On the transition, boundary layers then undergo a laminar separation and reattach as a turbulent boundary layer. The fully turbulent flow computation does not capture this phenomenon, which may significantly overpredict the friction drag. So it is of concern the transition to turbulent boundary layer so, mainly, drag can be evaluated properly. A CFD analysis of an air flow with a Re = 3.0 * 10^6 around the wind turbine airfoil NACA 63-215 was conducted under the finite volume method formulation in the OpenFOAM framework using a local correlation-based transition model (LCTM), gamma-ReTheta, based on two new transport equations, in addition to the SST k-omega equations; one for intermittency, gamma, and another one for a transition onset criterion, ReTheta. The transport equations do not attempt to model the physics of the transition process itself, but implement transition correlations which account for transition due to freestream turbulence intensity, pressure gradients, and separation. Finally, the analysis was also carried out under the fully turbulent model Spalart-Allmaras for comparison purposes with both the transition model results and experimental data. It was concluded that the fully turbulent model overpredicts the drag coefficient before the stall, mainly due to the friction drag, while the LCTM leads to a better drag coefficient curve when compared to the experimental data. This shows that accounting for the transition on the flow field modelling of this wind turbine airfoil has lead to better results.
Keywords
Laminar-turbulent transition, CFD, OpenFOAM, Wind turbine airfoil
