Optical model for 3D reconstruction of aerodynamic surfaces on blades by using pattern projection

In this work we describe a stereo vision model to design Ronchi-Hartmann type patterns for testing, either qualitatively or quantitatively the geometric shape of the aerodynamic profiles or surface in a blade section of a low-power wind turbine. We calculate both non-regular fringes and non-uniform drop shape spots patterns to project and illuminate an array uniformly distributed on the aerodynamic surface, considering that a camera is placed at an angle to the center of the surface. We can evaluate the expected deformed patterns at the CMOS sensor to reconstruct the 3D surface. The design of these projected patterns is based on the knowledge of the ray trace along two different pinhole systems, taking account three positions, a projection plane, a reference plane or surface of interest and the detection plane. The experimental setup for a qualitative test consists of a commercial projector, a flat surface for calibration, and a CMOS camera. We evaluate qualitatively two blade sections formed by the NACA 0012 airfoil, one where the profile does not change throughout the section and second has a variable torsion from 0-10 degrees.