Dynamic deformation measurements of an aeroelastic semispan model

The techniques used to acquire, reduce, and analyze dynamic deformation measurements of an aeroelastic semispan wind tunnel model are presented. Single-camera, single-view video photogrammetry (also referred to as videogrammetric model deformation, or VMD) was used to determine dynamic aeroelastic deformation of the semispan “Models for Aeroelastic Validation Research Involving Computation” (MAVRIC) model in the Transonic Dynamics Tunnel at the NASA Langley Research Center. Dynamic deformation was determined from optical retroreflective tape targets at 5 semispan locations located on the wing from the root to the tip. Digitized video images from a charge coupled device (CCD) camera were recorded and processed to automatically determine target image plane locations that were then corrected for sensor, lens, and frame grabber spatial errors. Videogrammetric dynamic data were acquired at a 60-Hz rate for time records of up to 6 seconds during portions of this flutter/Limit Cycle Oscillation (LCO) test at Mach numbers from 0.3 to 0.96. Spectral analysis of the deformation data is used to identify dominant frequencies in the wing motion. The dynamic data will be used to separate aerodynamic and structural effects and to provide time history deflection data for Computational Aeroelasticity code evaluation and validation. INTRODUCTION Video photogrammetry was used to measure dynamic deformation on the Models for Aeroelastic Validation Research Involving Computation semispan model (MAVRIC-I), a business jet wing-fuselage flutter model, in NASA Langley’s Transonic Dynamics Tunnel (TDT). The overall objective of this test is to provide benchmark validation data on a representative configuration that exhibits nonlinear, transonic aeroelastic response, specifically limit cycle oscillations and buffet onset. Instrumentation included unsteady pressure transducers, accelerometers, and strain gages. Computational aeroelastic analysis will be conducted as part of this research to assess and refine state-of-the-art design tools. The primary objective of this series of MAVRIC tests was to provide detailed experimental wind-tunnel data suitable for Computational Aeroelasticity (CAE) code evaluation and validation at transonic separation onset conditions. Unsteady pressures and wing responses were obtained for three wingtip configurations: clean, * Research Engineer, Member AIAA. † Research Engineer, Senior Member AIAA. ‡ Senior Research Engineer, Fellow AIAA. § Senior Research Engineer, Associate Fellow AIAA. Copyright 2001 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner. tipstore, and winglet. Traditional flutter boundaries were measured over the range of M = 0.6 to 0.9 and maps of Limit Cycle Oscillation (LCO) behavior were made in the range of M = 0.85 to 0.95. The dynamic pressure transducers provide time histories of the pressure distribution on the wing as it encounters the flutter or LCO phenomena. However, these pressures are directly dependent on the motion of the wing. Accurate measurement of the wing motion is a critical item when comparing the unsteady surface pressures with computed results. Modern computational aeroelasticity programs are capable of simultaneously computing both the vehicle motion and dynamic loads on the vehicle. However, accurate simultaneous computation of these components is difficult for highly nonlinear problems such as LCO and it is very beneficial to be able to isolate the various components of the problem. This is where the videogrammetry data is of greatest use. Specifying the model motion using data obtained through the videogrammetric system, the issue of computing the model motion can be eliminated from the computational problem, and a direct comparison of computed and wind tunnel pressures can be performed. Researchers previously depended on strain gage and accelerometer data to estimate the wing motion. Videogrammetry provides a significantly more accurate and direct method for obtaining these data. The intent of this paper is to relate experiences using the videogrammetry technique in a large production wind tunnel for dynamic deformation measurements in order to aid potential users of the technique at the TDT and other facilities. Rather than presenting extensive deformation data, only representative data will be included. The data acquisition procedure and interaction with the facility data acquisition system will be described. This work is part of an overall effort to develop a dynamic model deformation measurement capability up to 1000 Hz.