Transition to Turbulence near a Flexible Interface

Abstract

Transition to turbulence was observed in water flowing in a narrow rectangular channel provided with a flexible interface by making use of measurements of instantaneous velocity, as indicated by a deposited-film constant-temperature anemometer. The characteristics of the transition from laminar flow near the entrance of the channel to the fully turbulent condition downstream may be described as consisting of a series of random bursts of flow fluctuations separated by steady-flow conditions. The number of turbulence bursts in unit time interval increases monotonically on a sigmoid curve in the transition region. A measure of the degree of turbulence based on a counting technique was developed for this study. Transition to turbulence sets in earlier for some types of flexible surfaces than it does for rigid walls. However, the rate of increase was greatest for the rigid walls. [This work was sponsored by the David Taylor Model Basin.]