Nonlinearities in ultrasonic flow measurement

The governing equations of flow acoustics including nonlinearities are solved and analyzed in terms of ultrasonic flow-measurement properties. The effect of nonlinearities for sound propagation is expected to be most significant for gas-flow measurement applications as gas-sound speeds are much smaller while fluid flows generally are much higher in the corresponding case of liquid-flow measurement applications. The equation framework is applied to the case of a sinusoidal ultrasound transducer speed excitation at one location and detected by a receiver at another location. Flowmeter errors due to nonlinearities are highlighted in this work based on the well-known transit-time reciprocal transducer system setup. It is found that accounting for nonlinear effects leads to, for a given flowmeter configuration and in a large flow range, an almost constant error which can be calibrated out in applications.