ACCELERATED AND DECELERATED FLOWS IN A CIRCULAR PIPE (2ND REPORT, TRANSITION OF AN ACCELERATED FLOW).

In a preceding paper, it was made clear that there exists two types of flow transition from laminar to turbulent in an accelerated flow depending on the degree of acceleration. In order to determine the mechanism of these types of transition the Present measurements were performed and the change of the velocity profile at each time step was compared at two different stations. The results show that in the case of relatively large acceleration (ro/UstT greater than 10** minus **1), flow transition takes place simultaneously over the whole area in a pipe due to the flow instability. On the contrary, in the case of relatively small acceleration (ro/UstT greater than 10** minus **3), flow transition takes place near the pipe inlet and forms a discontinuous surface (transition surface) propagating to the downstream with a velocity larger than the mean flow velocity. In this case the velocity profile changes smoothly from laminar to turbulent in the upstream but becomes peculiar in the downstream due to the development of the transition region.