| Popis: |
This work presents several treatments of the wall boundary conditions for RANS turbulence models. The focus is the investigation of wall functions suitable for non-equilibrium conditions where the standard wall functions derived from the law-of-the-wall are known to fail. Although the thesis focuses on wall treatments, for deeper understanding of the problem, knowledge of turbulence modelling is essential. Therefore some key concepts are outlined through a derivation of the law-of-the-wall. Also, analytical solutions for the k − ε and k − ω SST model for the near-wall regions are given. A property, which defines the treatment of the wall boundary condition, is the asymptotic consistency of turbulence model which is briefly discussed. A general methodology for specifying the wall boundary condition is explained and expressions for each method are presented in detail. Wall treatment for the k − ω SST model based on pressure sensitised law-of-the-wall is derived in detail and leads to a conclusion that including the convective terms in expressions could improve accuracy. The wall treatments are implemented in foam-extend and compared with the standard wall functions on two test cases: flow past the NACA4412 aerofoil and the 6:1 prolate spheroid. A conclusion is reached that certain wall treatments offer an advantage over standard ones imple- mented in foam-extend, although it is emphasised that further investigation on the effects of pressure gradient and convective terms should be conducted. |
