Análise dos efeitos do gradiente de pressão adverso na camada limite turbulenta de um aerofólio NACA0012 em altos ângulos de ataque

Author(s)

Leandro Júnio de Oliveira Silva

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica
• Defense date: 2024-08-22

Examining board members

William Roberto Wolf; Livia Souza Freire Grion; Luiz Augusto Camargo Aranha Schiavo

• Advisor: William Roberto Wolf

Abstract

An investigation of turbulent boundary layers (TBLs) is presented for a NACA0012 airfoil at angles of attack 9 and 12 deg. Wall-resolved large eddy simulations (LES) are conducted for a freestream Mach number M = 0.2 and chord-based Reynolds number Re = 400,000. The boundary layers are tripped near the airfoil leading edge on the suction side. For the angles of attack analyzed, mild, moderate and strong adverse pressure gradients (APGs) develop over the airfoil. Despite the strong APGs, the mean flow remains attached along the entire airfoil suction side. Similarly to other APG-TBLs investigated in the literature, a secondary peak appears in the Reynolds stress and turbulence production profiles. This secondary peak arises in the outer layer and, for strong APGs, it may overcome the first peak typically observed in the inner layer. The analysis of the turbulence production shows that other components of the production tensor become important in the outer layer besides the shear term. For moderate and strong APGs, the mean velocity profiles depict three inflection points, the third being unstable under inviscid stability criteria. In this context, an embedded shear layer develops along the outer region of the TBL leading to the formation of two-dimensional rollers typical of a Kelvin-Helmholtz instability which are captured by a spectral proper orthogonal decomposition (SPOD) analysis. The most energetic SPOD spatial modes of the tangential velocity show that streaks form along the airfoil suction side and, as the APG becomes stronger, they grow along the spanwise and wall-normal directions, having a spatial support along the entire boundary layer. Results of a quadrant analysis for the Reynolds shear-stress distribution show that sweeps are predominant near the wall, while ejections dominate in the outer region. The former are the main contributor to the inner peak of turbulence production. Due to the strong APG, a secondary peak of production arises in the outer layer, and the combination of both sweeps and ejections contribute to such peak. A backflow characterization is also performed, demonstrating that as the APG increases, the magnitude of the friction coefficient decreases, leading to a higher probability of such events near the trailing edge (AU)

• FAPESP's process: 22/00256-4 - Statistics of turbulent boundary layers developing under different pressure gradients
• Grantee: Leandro Júnio de Oliveira Silva
• Support Opportunities: Scholarships in Brazil - Master