Abstract: In order to achieve a high-precision experimental measurement of the vortex flow field in a hydrodynamic coupling,main error sources of the internal flow experimental measurement by particle image velocimetry (PIV) technology are investigated,and the influence of the tracer particle selection,the image acquisition strategy and the flow velocity extraction algorithm on the measurement precision of the internal flow field is analyzed.Then,some methods are proposed to reduce and eliminate the errors.The results show that (1) when 1. 0 g PSP tracer particles of an equivalent diameter of 1. 5 μm are put into a 2710 mL water-medium hydrodynamic coupling,the collected flow images are better and the particle concentration can meet the requirements of the PIV speed measure- ment; (2) designing the outer surface of the hydrodynamic coupling as a large plane collection area can effectively avoid the reflective phenomenon and reduce the off-axis angle error and the optical refractive error; and (3) by a- dopting the recursive cross-correlation algorithm and the adaptive interrogation window analysis method to carry out three iterations,the characteristics of both the large-scale vortex flow in a mainstream region and the small-scale vortex structure on local corners can be extracted more effectively.The conclusions will provide a vital reference for the accurate measurement of the vortex flow field in the hydrodynamic coupling．

Key words: hydrodynamic coupling, vortex, tracer particle, light refraction, recursive cross correlation algorithm