Particle Image Velocimetry(PIV)techniques were developed to measure the convec- tive N_2-air flow under gradient magnetic fields.The velocity fields were calculated by the Minimum Quadratic Difference(MQD)algorithm and spurious vectors were eliminated by Delaunay Tessellation. The N_2-air flow was measured as the magnetic flux density varying from 0～1.5 T.A strengthened vortex flow of air was observed under the condition that the magnetic field was applied,and the ve- locity of N_2 jet rose with the increase of the magnetic density.The experimental results show that the magnetic force will induce a vortex flow and cause a convection flow of the air mixture when both gradients of the O_2 concentration and the magnetic field intensity exist.
A new algorithm using polar coordinate system similarity （PCSS） for tracking particle in particle tracking velocimetry （PTV） is proposed. The essence of the algorithm is to consider simultaneously the changes of the distance and angle of surrounding particles relative to the object particle. Monte Carlo simulations of a solid body rotational flow and a parallel shearing flow are used to investigate flows measurable by PCSS and the influences of experimental parameters on the implementation of the new algorithm. The results indicate that the PCSS algorithm can be applied to flows subjected to strong rotation and is not sensitive to experimental parameters in comparison with the conventional binary image cross-correlation （BICC） algorithm. Finally, PCSS is applied to images of a real experiment.
