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A bstract : A new 3D-PTV technique has been developed using GA (Genetic Algorithm). The measurement system consists of three CCD cameras, Ar-ion laser, an image grabber and a host computer. One-to-one correspondences are made by taking advantage of the combinatorial optimization of the genetic algorithm for the whole particles of the two images during the time interval of image frames. Two fitness function s are introduced in order to enhance the correspondences of the particles. One is based on the concept of continuum theory and the other one is based on the minimum error of threedimensional distance. Performance of the developed algorithm is tested using a set of virtual images construct ed by the use of LES data set on an impingin g jet. The developed 3D-PTV system is successfully applied to the measurement of flow characteristics of the wake of a circular cylinder.

A large eddy simulation method based on a fully unstructured finite volume method was developed, and the unsteady aerodynamic response of a road vehicle subjected to transient crosswinds was investigated. First, the method was validated for a 1/20-scale wind-tunnel model in a static aerodynamic condition; this showed that the surface pressure distributions as well as the aerodynamic forces and moments were in good agreement with wind-tunnel data. Second, the method was applied to two transient crosswind situations: a sinusoidal perturbation representing the typical length scale of atmospheric turbulence and a stepwise crosswind velocity corresponding to wind gusts. Typical transient responses of the aerodynamic forces and moments such as phase shifting and undershooting or overshooting were observed, and their dependence on the frequency and amplitude of the input perturbation is discussed. Thus, the utility and validity of the large eddy simulation was demonstrated in the context that such transient aerodynamic forces are difficult to measure using a conventional wind tunnel.

3D-PTV measurements were conducted on the wake of a sphere. The Reynolds number is 1130 with diameter d = 30 mm. The measurement system consisted of three CCD cameras, an image grabber, an Ar-ion laser and a host computer. Structural analysis was adopted for the analysis on the wake using the obtained velocity profiles. Statistical turbulent properties were quantitatively clarified using the time-consecutive instantaneous three-dimensional vectors obtained by the 3D-PTV system. The spatial velocity profiles of the sphere wake seemed to have a strong relationship with the spiral motion of the vortices that were shed from the surface of the sphere.

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