Wind Tunnel Measurements of Flow-Induced Vibration of a NACA0015 Airfoil Model

The paper reports on interferometric measurements of flow over a NACA0015 airfoil model during flutter limit cycle oscillations. The airfoil model is fixed on an elastic support allowing motion with two degrees of freedom — pitch and plunge. The structural mass and stiffness matrices can be tuned to certain extent, so that the eigenfrequencies of the two modes approach as needed. The model is equipped with dynamic pressure probes and sensors measuring the airfoil vertical position. The flow field around the airfoil was measured by Mach-Zehnder interferometer and registered using a high-speed camera synchronously with the mechanical vibration and pressure measurements. The Mach number of the incident airflow was gradually increased and the response of the aeroelastic system to initial impulse measured, until the flutter instability onset occurred. Flutter boundaries were evaluated for various additional masses attached (i.e., for various plunging mode eigenfrequencies), and post-critical behavior of the system investigated. The interferograms recorded by the high-speed camera were postprocessed, yielding pressure distribution around the airfoil during its vibration and an estimate of the total aerodynamic force and energy transfer from the airflow to the structure.