A thermographic method to evaluate the local boundary layer separation phenomena on aerodynamic bodies operating at low Reynolds number

Abstract

This study uses infrared thermography to focus on local separation phenomena affecting the laminar boundary layer on aerodynamic bodies operating at low Reynolds numbers, and particularly on the laminar separation bubble that occurs, for instance, in applications such as gliders, microplanes and small windfarm turbines. The work was organized into several stages. First the reliability of the wind tunnel available at the Energetics Department of the “Università Politecnica delle Marche” was tested by comparing the results obtained on an Eppler 387 profile with data provided by other, similar tunnels for the same profile. Then the presence of a laminar bubble was ascertained using classic measuring methods, e.g., the spring balance and pressure distribution analysis. The thermographic apparatus was set up and recordings were made and compared with the trend of the pressure coefficient: coupling the data showed an excellent consistency in the identification of the bubble and confirmed the feasibility of using thermography for the non-invasive measurement of this phenomenon. The final phase of the study involved a preliminary attempt to obtain quantitative information from the thermographic images too: two quantities, L S and B E , were defined for this purpose and enabled a preliminary characterization of the behavior of the laminar bubble according to the angle of attack.