Deformation measurement of flexible birdlike airfoil with optical flow

The application of the Lucas-Kanade (LK) optical flow technique has seen a huge success in a wide variety of fields. The goal of this paper is to apply the Lucas-Kanade technique in measuring the deformation of flexible birdlike airfoil due to steady aerodynamic loads at transitional low Reynolds-numbers with a single pixel resolution. A pyramidal scheme is used to implement a coarse-to-fine warping strategy to allow large displacements. A nonlinear structure tensor is employed to diffuse local data anisotropically to preserve discontinuities in the optical flow field. Median filtering is introduced after each iteration to remove outliers. The upper surface of the airfoil is sprayed with stochastic ink dot pattern for easy capture by two cameras observed from two different angles above the airfoil to create a pattern on the airfoil for the deformation measurement. Finally, a general result of wind tunnel experiments is selected, two optical flow fields are calculated on two images generated from each camera respectively, and the optical flow results are compared with the image correlation results.