Re-evaluation of Change of Mean Velocity Profiles in Turbulent Open-Channel Flows due to Introducing Sediment Particles

摘要

Since Vanoni suggested reduction of the Karman constant in 1946, it is well known that sediment particles introduced in open-channel turbulent flows change the mean velocity profile of flow. Many researches supported his opinion. Some researchers, on the other hand, have insisted that the Karman constant remained constant regardless of introduction of the sediment particles. Though Vanoni's suggestion was put in some sediment-related textbooks as an established theory, it has been debated, up to now, how the sediment particles would take such a role and what parameters would be changed. The purpose of the present study is to re-evaluate carefully the previous studies on this issue. The present study revealed some questionable approaches or methods in the previous researches and elucidated the reason why this issue has been debated for a long time. The results indicate that the Karman constant is reduced by adding sediment particles, but the amount of reduction is much smaller than the amount proposed by previous researches. Finally, a mechanism for the calculation of the Karman constant reduction due to sediment introduction was proposed.