Transit time measurement for ultrasonic tomographic velocimeters

The transit time measurement for ultrasonic tomographic velocimeters is bothered by poor signal noise ratio (SNR) and multipath interferences. Hence, a neighborhood assessment correlation method was proposed in this paper. First, an improved Hilbert transform correlation algorithm was employed for preliminary transit time measurement, and the reliabilities of the measurement results were evaluated by the normalized correlation coefficients. Then, the unreliable measurement results were further revised by a neighborhood assessment process. As demonstrated by the experiments, this method could eliminate all cycle-slipping errors in the flow velocity range of 0 m/s-3.83 m/s, and the transit time measurement precision was up to 52.2 ns. The flow velocity fields reconstructed from the transit time fit well with the simulation results.