Visualization and measurement of spatial structures in turbulent flow

Abstract

The chapter explains vortical spatial structures quantitatively visualized in turbulent pipe flow by means of particle image velocimetry and subsequent decomposition of velocity data. The experiments are performed at Reynolds numbers of the order of 105. The experimental results serve for explaining quantitatively the process of signal formation for a particular correlation-based ultrasound flow meter. The signals are formed by an interaction of the ultrasound waves with the coherent structures in the flow. Evidencing the structures can be reduced to a difference of two coordinate systems moving with respect to each other: the system of physical flow and the system in which images are recorded. Different structures appear if the relative velocity between the two systems is changed. The higher Reynolds numbers in experiments are chosen because it is anticipated that coherent structures in the turbulent flow dominate the signal formation in a particular set-up for ultrasonic flow metering, and the interest in this method lies particularly at flow conditions with high Reynolds numbers. These results now allow optimizing the configuration of the meter and the algorithms for signal processing.