Stereoscopic Measurements of Blade Deformation on a Shrouded Prop-Fan with Boundary Layer Ingestion by means of Image Pattern Correlation Technique

Abstract

The material presented herein describes the implementation of optical blade deformation measurements based on the image pattern correlation technique (IPCT) in a stereoscopic imaging configuration applied to the first rotor of a counter-rotating shrouded fan stage (CRISPMulti) which has a diameter of about 1m. The correlation-based stereoscopic image analysis is discussed, as well as the difficulties with regard to the correlation-based stereomatching of two camera views for the highly curved blade surface involving pattern displacements up to 12% of the image height. Cross-correlation of speckle images at reference positionwith images of the displaced positions recovered the full 3c displacement field in the optically assessable area of the suction side. The three-dimensional displacements could be evaluated with triangulation errors below 0.5mm at blade tip velocities exceeding 250m/s (4830rpm). Comparative measurements using a third camera imaging the blade tip match the stereo IPCT results within deviations of 0.5mm for the axial component whereby the circumference component matches closely.