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

Abstract

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.

Turbulence intensity measurement in the wind tunnel used for airfoil flutter investigation

“…The model design builds on previous experience obtained in the Institute of Thermomechanics in the years 2006-2012, when self-oscillating models of the NACA0015 and DCA18% airfoils with two degrees of freedom were designed and the methodology of the measurements developed [6,7,3]. The airfoil, supported by a linear and torsional springs, is fixed in a suctiontype wind tunnel with optical access through the side walls for Schlieren visualizations and interferometric measurements of the flow field.…”

“…During last years, the fundamental properties of a self-oscillating NACA0015 airfoil with two degrees of freedom have been studied in a high-speed suction-type wind tunnel of the Institute of Thermomechanics in Nový Knín [3]. For low inlet air speeds, damped oscillations were observed.…”

“…The experimental setup allows dynamic measurement of the flow-induced oscillations and time-resolved measurements of the static pressure at four pressure ports on the surface of the airfoil. Synchronously, the flow fields around the airfoil can be monitored either using time-resolved interferometric measurements [3,4] or Schlieren visualizations [5].…”

CFD simulation of flow-induced vibration of an elastically supported airfoil

“…The physical setup in Figure 1 is a redesigned and improved version of a model reported in [2]. The airfoil, supported by a linear and torsional springs, is fixed in a suction-type wind tunnel with optical access through the side walls for …”

“…Such system can model a real aircraft wing, with pitching corresponding to torsional vibration of the elastic aircraft wing structure, and plunge corresponding to vibrations in the bending mode. The CFD model was designed according to parameters of the physical model used for wind tunnel measurements [2][3][4][5], so that the results of the CFD simulations can be compared with the experimental results.…”