For a correct comparison between numerical and experimental aerodynamic simulations the use of the same boundary conditions is important. This includes also a knowledge of the position and deformation of the wind tunnel model. Even in low speed wind tunnels a wind tunnel model deformation can be observed, especially for high lift configurations, where higher aerodynamic loads are applied to the wing.
Within the DLR project ForMEx, a model deformation measurement was performed in the low speed wind tunnel NWB (Braunschweig) of DNW by means of the Image Pattern Correlation Technique (IPCT). The deformation of the F11 half model with a span width of 1.4 m was measured in its landing configuration, so that the deformation measurement includes not only the determination of the bend and the twist of the main wing, but also the measurement of the gap variation between the main wing and the slat or the flap. The wind tunnel runs were performed at Mach 0.2 at several angles of attack α, especially in the region of the maximum lift coefficient.
Comparison between experimental and numerical results at α = 15°: (a) bend, (b) twist
The results of the measurement showed that also for low speed wind tunnel tests the deformation of the model is not negligible. At the wing tip a bend of up to 13 mm and a twist of up to 0.4° were obtained. The surface measurement technique IPCT enabled the detection of some details in the deformation which arose due to the complexity of the wind tunnel model. A comparison of the IPCT measurement with numerical calculations using fluid–structure interaction showed a generally good agreement.
