WINDTUNNEL

Task

The Institute of Fluid Mechanics at the Technical University of Braunschweig is engaged in a research project studiyng high Iift wing profiles for aviation. The aerodynamics are visualized using particle image velocimetry. The mechanical deformations of the carbon fiber profile due to the aerodynamic forces need alsotobe measured. The measurement method of choice should not influence the air flow within the windtunnel.

Procedure

Video photogrammetry requires only 0.1 mm thin retroreflective, circular markers that do not interfere with the flow, making it ideal for the task. The number of markers is unlimited, so that a large number of deformation values can be acquired across the width and length of the profile. The cameras and lighting were placed outside the wind tunnel to avoid obstructing the airflow. The calibration object was shown to the cameras from the within the wind tunnel to compensate for the refraction error caused by the Observation window. Figure 1 shows the flow conditions in the wind tunnel, figure 2 visualizes the green Iaser light of the Particle Image Velocimetry, figure 3 depicts the cameras mounted above the wind tunnel, figure 4 is a schematic representation of the overall structure and figure 5 gives an insight into the interior with the targets on the wing profiles.

Result

Figures 6 and 7 show the measurement results. As expected, the deformation increases quadratically with the flow velocity. At the second highest flow velocity of 45 m I s, resonance vibrations become apparent in the deformation values. Using video photogrammetry comprehensive and Figure 4: Windtunnel as a 3D Model precise 30 measurement data could be obtained Figure 5: lnterior of the wind tunnel within only a few hours and without substantial with optical markers. changes to the wind tunnel. We would like to thank the Institute for Fluid Mechanics of the TU Braunschweig for the good cooperation and the kind permission to use the images shown on the right.