A new particle tracking algorithm using the concept of match probability between two consequent image frames has been developed to obtain an instantaneous 2-dimensional velocity field. Our proposed algorithm for correctly tracking particle paths from only two image frames is based on iterative estimation of match probability and no-match probability as a measure of the matching degree. A computer simulation has been carried out to study the performance of the developed algorithm by comparing with the conventional 4-frame Particle Tracking Velocimetry (PTV) method. The effect of various thresholds used in the developed algorithm on the recovery ratio and the error ratio were also investigated. Although the new algorithm relies on the iterative updating process of match probability which is time consuming, computation time is relatively short compared to that of the 4-frame PTV method. Additionally, the new 2-frame PTV algorithm recovers more velocity vectors and has a higher dynamic range and a lower error ratio.

List of symbols

A, B

constants (A < 1,B > 1)

A_{0}

image area

I

grey level distribution of flow image

d_{0}

average particle spacing

d_{ij}

displacement vector between x_{i} and y_{j}

F^{k}

digital image frame captured at (k-1) Δt

N

number of points y_{j} satisfying |d_{ij}| <T_{m}.

N_{0}

total number of particles in an image frame

P_{i}^{*}

match probability that x_{i} would coincide to y

P_{i}^{*}

no-match probability that x_{j} has no corresponding y_{j} onF^{2}