Evaluation of beam refraction effects in a 3D laser Doppler anemometry system for turbomachinery applications

The paper presents a general mathematical procedure for the calculation of the measuring location of three pairs of laser beams and of the shape of the created measuring volumes after refraction at curved surfaces. The relative displacement in space of the beams and the corresponding velocity component inclinations are also calculated. The beam equations are solved, without any small-angle approximations, for an arrangement corresponding to a 3D laser Doppler anemometer. The proposed method has been validated by comparison with experimental results. The correction procedure has been applied to a typical configuration of a turbomachinery passage and representative beam displacement calculations are presented. Possibilities offered by the method in designing experiments as well as correcting obtained results are discussed.