Three-Dimensional In-Cylinder Flow-Field Structure before and after Distortion of Tumble

The influence of tumble intensity on the three-dimensional flow-field structure was analyzed numerically using the STAR-CD code. It was found that when the tumble intensity is extremely high, because the velocity component in the direction of the axis of tumbling air motion is small, the flow-field structure can be treated as two-dimensional. When the tumble intensity is moderate or weak, however, various flows in the direction of the tumble axis can be observed. Therefore, such a flow-field structure should be treated as three-dimensional. A new method to measure the three instantaneous 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 for preset durations and timings, velocity in the direction of the laser sheet depths can be derived. Employing this method, the flow-field structure at 15°BTDC was analyzed. It was confirmed that the distortion of tumble induces horizontal vortices in addition to the vertical vortex.