The Modeling of Roughness Effect on the Performance of a Controlled Diffusion Airfoil

The manufacturing and operational roughness of aerodynamic profiles impacts both the laminar and the turbulent boundary layers state, directly affecting the aerodynamic and thermal performance of typical turbomachinery components. By better understanding the underlying physical mechanisms, the present work aims at building a more refined and comprehensive model to take the effects of surface finish into account. The model is implemented into the MIT Multiple Blade Interacting Streamtube Euler Solver (MISES) and is validated against experimental results for different roughness levels, Reynolds number, and Mach number regimes. In the proposed model, the roughness effects on the turbulent boundary layer (BL) state are included through the modification of the turbulent skin friction law, while the roughness level is implemented through a new definition of k_s that accounts for the influence of the roughness skewness. Particular emphasis is placed on the modeling of the transitionally rough regime. Finally, roughness effects on transition are modeled by implementing the Mayle rough-induced onset transition criterion. Results are validated in terms of the total pressure loss coefficient and the outlet flow angle, leading to a marked improvement in terms of agreement with the experimental data.