Experimental uncertainty decompositions of aerodynamic coefficients affected by operative condition variations

Abstract

A twofold analysis is performed on an experimental set-up comprising a low-Reynolds wind tunnel, with the aim of quantifying the effect of measurand uncertainties and operative condition variations in the lift and drag curves of a NACA0021 airfoil. The first part of the study focuses on an uncertainty analysis of basic measurands used for calculating standard aerodynamic magnitudes, showing the individual contributions of each of the factors affecting the overall uncertainty ranges. The second part intends to show how those uncertainties are propagated to lift and drag coefficients, and to calculate the effect of varying operative conditions on those curves. It is found that, when changes in operative conditions are left unattended, their influence on derived magnitudes may grow as large as to cause the resultant data to lie outside the estimated uncertainty intervals. Additionally, those variations are shown to depend non-linearly on the operative condition changes that produce them.