Characterization of the carborundum used in rough airfoil surface tests and modelling with CFD

摘要

Roughness over the airfoil surface has an impact on the annual energy production of wind turbines. For that reason, its characerization in experiments and computations is needed. In addition, there is not a common method to test rough surfaces in the wind tunnel. The aim of this work is to validate the methodology used to perform wind tunnel experiments on airfoils with surface roughness and the modelling of those experiments with CFD. Rough surfaces are studied using two parameters: the density of covered area with roughness and the shape parameter of the rough elements. These parameters will be analysed in the laboratory using image postprocessing techniques and profilometry in a replication resin. On the other hand, roughness effect over airfoil aerodynamics can be studied using CFD by means of simulating roughness with numerical models. These models account for rough surfaces by a unique parameter (equivalent roughness height h_s) that represents the whole effect of the roughness elements. The h_s value derivation from a rough wind tunnel experiment involves a lot of uncertainty. This methodology will be used to characterize a wind tunnel experiment where roughness is simulated with carborundum grains spread over the airfoil surface. The h_s parameter will be defined to be used in CFD calculations and to make a link with the experiments. This research will be used to create a methodology to be used in the future to characterize real wind turbine blades with rough surfaces and erosion, study them in the laboratory creating a reliable database and analysing it with CFD calculations.