The test entry involved measuring the wing’s pressure distribution using pressure-sensitive paint (PSP), a surface pressure measurement technology already employed in previous campaigns. In addition, the transient wing deformations were measured using two high-speed cameras. For this purpose, fluorescent markers were applied to the wing lower side along the leading and trailing edge. This arrangement enables simultaneous measurement of the unsteady pressure distribution and structural deformation on the same wing.
A special feature of this measurement campaign is the specific excitation of structural eigenmodes of the wind tunnel model in the vicinity as well as in the frequency range of the transonic buffet. The Anti-Vibration System (AVS), a piezo-electric damping system, was used as an excitation source. The AVS is located between the model and the sting and could be used for the active excitation of the wind tunnel model through a software modification.
Prior to the measurement, the wind tunnel model was excited with a linearly varying frequency under constant inflow conditions. The response of the model due to this frequency sweep was analyzed in-situ. The natural frequencies determined during the ground vibration tests change due to the cold temperature in the test section. In addition, the achievable excitation amplitude can vary due to the aerodynamic loads. For these reasons, this step is used to make a final selection of the excitation frequencies. The wind tunnel model was then subject to an imposed vibration at constant frequencies and an unsteady PSP and deformation measurement was carried out.
The pressure and deformation measurements with and without active excitation were carried out in a Reynolds number range between 6.6 M and 12.9 M at a temperature of 180K. For the Mach numbers 0.78, 0.80 and 0.84, a respective angle of attack range was selected that specifically allow the investigation of three-dimensional transonic buffets.
The measurement campaign was successfully completed on the 13th of December 2024. The data obtained on unsteady pressure distributions and wing deformations will enable the detailed analysis of the effects of structural vibrations on the three-dimensional transonic buffet for a transport aircraft configuration at realistic Reynolds numbers. The measurement data also serve to validate simulations that reproduce these effects numerically.
See also: FOR-2895-Young Talent Program-Full Program for Participants!