Approach for Acoustic Transit Time flow measurement in sections of varying shape: Theoretical fundamentals and implementation in practice

• The issues specific for the Acoustic Transit Time flow measurement in irregular sections are described.
• The theoretical derivation of the generalized governing equation is conducted.
• The proposed realization of the generalized theory involves numerical methods.

This paper focuses on the generalization of the Acoustic Transit Time (ATT) flow measurement method currently embodied in ultrasonic flow meters. First, the existing theoretical fundamentals that cover flow measurement in regular conduits are presented and relevant design features of typical ultrasonic flow meters are described. A detailed derivation of a measurement method for the generalized theoretical fundamentals of multipath ATT flow is then presented. This generalization consists of extending the existing theoretical background in the case of an irregular section, which is defined as a section that has a non-standard shape and/or a varying shape and size, e.g. one that has transition from a rectangular to a circular section. On the basis of the derived generalized theory, the approach for flow measurement in such irregular sections is developed. This approach is then tested numerically using an example of a converging measurement section that represents the water intake of the Kaplan unit. During the test of the new approach, the flow rate and flow profile at the inlet were varied to investigate the effect of such variations on the accuracy of flow rate determination. Results for a significant flow profile and flow rate variations show that the overall error dispersion of the flow rate evaluation is of the order of 0.5%.