Abstract: A visualized test bed for the steady flow in engine air-passage is built based on tuft method to conduct visualized study on the flow field near cylinder wall, and meanwhile a numerical simulation on the same object is also performed using CFD technique, with both results verified each other. The results show that under steady flow conditions, the tuft motion can intuitively reflect the airflow movement near cylinder wall. Due to the effects of vortex generated by spiral air-passage, the moving direction of tuft is consistent with that of vortex. As for the flow field near cylinder wall at tangential air-passage side, its flow velocity reaches the maximum due to the co-action of the air-flow in tangential air-passage and the vortex motion, and accordingly the swing angle of tuft there also reaches its peak value. They are 110° and 90° for 8 and 12 mm valve lift respectively. In-cylinder transient flow field has both vortex and tumble motions, but they quickly merged into a single vortex motion

Key words: spiral air-passage; tangential air-passage; visualized steady flow test; in-cylinder flow field