Abstract
In order to study the effect of unsteadiness on the transition to turbulence in boundary layers, measurement of velocities in the purely oscillatory flow and also that in the steady uni-directional flow have been made, the former having been performed in a large oscillating tunnel. the flow visualization technique of thin-layered milk method developed by the senior writers has been used for clarifying the difference between the transition phenomenon observed in the case of oscillating boundary layer and that in the case of steady uni-directional flow, employing the same water tunnel.
The comparison made between the two cases shows that the processes of transition to turbulence are basically similar in the both cases, but that the initial disturbances formed during the deceleration period of the oscillatory flow have relatively strong characteristic of two-dimensionality and do not have the appearance of forming such turbulent spots as in the steady uni-directional flow, the character of disturbances formed in which is of more three-dimensionality.
