Round jets impinging at a counter or a right angle are investigated by the three-dimensional vortex blob method. When the jets impinge at a counter angle, the circular shear layers roll-up into vortex rings that impinge successively in the following manner: As a vortex ring from each jet approach, each ring is stretched in the radial direction by the velocity induced by the counter part. Some distinct clumps are generated in the circumferential direction, growing into azimuthal waves by the symmetrical instability. This predicted mechanism is in good agreement with the experimental observation. On the other hand, when the jets impinge at a right angle, a new vortex ring is generated in the direction of the movement after the impingement. Thus, the vortex structure grows rapidly in this direction. The energy dissipation takes place actively in these vortex-reconnecting regions. It is also found that the velocity distribution normal to the impingement plane takes a Gaussian distribution.

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A two-color dual laser beam scanning PIV is applied to the wind tunnel experiments on a paraboloidal nose and cylindrical afterbody to measure flow fields around a body at high angles of attack. In order to record the image with the limited scattering efficiency of small tracer particles, two-color laser beam scanning method was employed with a 3-CCD color digital video camera. An obtained single frame/double exposure color PIV image was decomposed into double frame/single exposure image sequences according to the hue component of the pixel values. A double correlation PIV method was developed for the color double exposure PIV recordings to eliminate correlation anomalies. The developed technique is shown to provide sufficient velocity vectors in the plane normal to the symmetric axis of the body, with the exception in vortex cores. The agreement obtained between the PIV and flow visualization results was seen to be quite reasonable.

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