Vorticity and turbulence production in pattern recognized turbulent flow structures

Abstract

A pattern recognition technique has been applied to data obtained in a turbulent channel flow. The u signal patterns are recognized using several simple criteria, but simultaneously, other signals are processed. A newly designed probe provides, in addition to simultaneous u, v, and w signals, vorticity signals, ωz and ωy, and a signal which can be interpreted as the instantaneous turbulence production, uv (∂U/∂y). The ensemble averaged results provide insight into the vorticity dynamics and turbulence production characteristics of organized structures. The instantaneous turbulent production results show that ejection-type motions are the principal turbulent energy producers and that the interesting dynamics occur during the acceleration phase of the recognized pattern. A partial model of the flow which explains the results is offered.