Evaluation of fluid trajectory in time-resolved PIV

A new time-resolved PIV (TR-PIV) method is introduced by integrating both two concepts, the fluid parcel tracking [1] and the ensemble averaged correlation [2, 3]. The dynamic range is extended by applying the polynomial trajectory as the fluid motion [1]. The tracking procedure is not performed by using individual locations of the fluid parcel along the time, but the ensemble averaged cross-correlation value of the trajectory. The random errors caused by the crosscorrelation maps could be then reduced. Each polynomial coefficient is considered individually for economizing the computational cost by introducing the V-cycle search [4]. To taking into account the curved fluid motion, a new iterative corrector based on the shear rate of deformed image according to the trajectory is proposed for stabilizing the process. Not only the present method, but also the state-of-the-art TR-PIV methods, such as the trajectory correlation method [1] and the multi-frame pyramid correlation method [3] are carried out for the comparison. The quantitative evaluations are performed by analyzing synthetic image sequences of translation and rotation motions. An experimental image sequence of the flow around an airfoil is obtained by the High Rate-PIV measurement system, and used to evaluate the performances of the methods. The material acceleration from each methods is also calculated from the trajectory profile or the spatial velocity derivatives with respect to the measurement grid.