Application of fast-response pressure sensitive paint to low-speed vortical flow at high angles of attack

  Highly maneuverable aircraft configurations can be subjected to tail buffeting phenomena at moderate subsonic speeds and medium to high angles of attack. Detailed measurement of the aerodynamic surface pressure fluctuations and the corresponding vibrations is of great importance to investigate these buffeting effects. Fast-response pressure sensitive paint (iPSP) was developed at the German Aerospace Center (DLR) to measure unsteady pressure fluctuation effects in a setup with high-speed cameras. The setup allows a high spatio-temporal resolution of the unsteady surface pressures. In the present paper the iPSP method is applied to a mixed-material, flexible aircraft wind tunnel model with double-delta wing and horizontal tail plane in these flow conditions. The low-speed buffeting effects on the configuration are measured using a synchronized system of five connected high-speed cameras to simultaneously record the unsteady surface pressures with iPSP and the dynamic three-dimensional structural deformation. The present application case is particularly challenging due to low levels of pressure fluctuation in the low-speed regime, multi-frequency aeroelastic phenomena on the model, a long distance between the cameras and the model, as well as the combination of synchronized measurement of unsteady surface pressure and structural deformation. Advanced data analysis methods are applied in a post-processing tool chain to cope with these challenges. The focus of the present paper is the setup of the synchronized measurement chain as well as the data analysis tools. First results are evaluated with respect to iPSP unsteady surface pressures. The root-mean square surface pressures show good agreement with high-fidelity CFD results for the flow conditions of interest. Particular focus of the analysis is on the lessons learned regarding the UV illumination setup, the camera arrangement as well as post-processing tools.