Assessment of the Thin-airfoil Method for Predicting Steady Pressure Distribution on Partially-porous Airfoils

An analytical method for predicting the steady pressure distribution on porous airfoils with a prescribed porosity distribution is assessed through comparison of its lift prediction with experimental data. The method is based on the thin-airfoil formulation. The no-slip boundary condition of the airfoil surface has been replaced by the Darcy’s boundary condition, allowing interaction of the air flow between the suction and the pressure sides. The ‘PARSEC’ airfoil parameterization method is employed to minimize inaccuracies in modelling the airfoil shape. A general match is found between model predictions and measurements of fully- and partially-porous airfoils, given that the airfoil is thin and/or the porous materials used have relatively high air flow resistivities (r). However, a difference between model predictions and measurements occurs for partially porous airfoils with low chordwise porous extent ratios (cpc), or with a relatively low r. The model gives a drop of pressure difference on the solid extent upstream of the porous extent, which is not found in the measurements. This may lead to an underestimation of lift by the model. Apart from that, prediction inaccuracies could also be expected for airfoils with a relatively high surface curvature and/or thickness.
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