The influence of the tumble intensity on the three-dimensional flow field structure was analyzed numerically using STARCD code. It was found that when the tumble intensity is extremely high, because the velocity component in the direction of theaxis of tumbling air motion is small, it can be treated as two-dimensional. When the tumble intensity is moderate or weak, however, various flows in the direction of tumble axis can be observed. Therefore, it should be treated as three-dimensional.A new method to measure the instantaneous three velocity components from a two-dimensional photograph was developed. By using three laser sheets composed of two continuous and one pulse laser light source with different colors radiated at scheduleddurations and timings, velocity in the direction of the laser sheet depths can be derived. Employing this method, flow field structure at TDC was analyzed. It was confirmed that the distortion of tumble induces horizontal vortices besides vertical vortex.
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