Imaging system considerations in Doppler global velocimetry

Abstract

Doppler Global Velocimetry (DGV) is a full-field optical technique for the measurement of fluid flow velocities. The flow is illuminated using a light sheet, and the Doppler shift imposed on light scattered from moving particles within the sheet is imaged through a cell containing iodine vapor onto a solid-state array camera, thereby converting the Doppler frequency shifts into intensity variations in the image. In this paper, a DGV system is presented based around an argon-ion laser source and a fast digital image-processing system, which allows the DGV velocity map to be updated at camera frame rate. Interpretation of DGV images is complicated by errors which arise at positions some way out in the field of view due to the modified illumination and viewing vectors corresponding to these positions. Typical magnitudes of such errors are calculated. Significant errors can arise for points more than about 5 degree(s) out from the center of the field of view, and for divergence angles of the illumination beam exceeding about 10 degree(s) at a distance of 5 cm from the beam axis. Other considerations affecting system accuracy are also discussed.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.