Experimental uncertainty decompositions of aerodynamic coefficients affected by operative condition variations.

• A breakdown of the uncertainty analysis of measurands providing individual contributions. • Operative condition variations take aerodynamic coefficients outside uncertainty intervals. • Temperature variations due to wind tunnel operation constitute the critical factor. • The effect of operative condition variations on aerodynamic coefficients is non-linear. • An analysis of the operative conditions is to be performed regardless of the experimental set-up. 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. [ABSTRACT FROM AUTHOR]