Ultrasonic gas-flow measurement using correlation methods

Abstract

Cross-correlation functions are in widespread use especially for the measurement of wave-propagation time and all kinds of velocity. The coincidence of turbulent structures in a gaseous flow with ultrasonic waves raises many questions concerning physics and signal processing, in particular on account of dissipating structures between the two ultrasound barriers. It appeared that the flow velocity measured by the cross-correlation function of the complex modulated signals is determined by the most frequent velocity components in the fluid. Besides, the ultrasonic beam measures along a line, whereas the average flow velocity is defined by an area integral. This velocity-dependent nonlinear effect necessitates a calibration of the measurement device. Uncertainties better than one percent are obtainable. Even disturbed flow by single and double elbows or pulsation can be measured in a qualified sense concerning uncertainty and scattering. Multipath arrangements can improve scattering. Furthermore, using special algorithms the profile of disturbed or undisturbed flow can be represented by tomography. © Springer-Verlag Berlin Heidelberg 2005.