Dependence of actively generated sound noise spectrum on flow-velocity

Flow-velocity measurement in the case in which the intensity of ultrasound is known to be generated by vortex and turbulent flow in the fluid is considerably influenced by external electrical and sonic noises because the desired sound intensity is very weak. Therefore, some serious measurement problems exist with regard to the proportionality and linearity between the flow velocity and ultrasound pressure level, and the reproducibility of spectrum distribution for the same flow velocity. In this study the intensity of flow-induced sound was increased by artificially introducing air bubbles and attaching an obstacle across the pipe, resulting in linearity and reproducibility. Spectrum analyses suggest that the spectra-dependent sound intensity may be used for the measurement of flow velocity with linearity and reproducibility if filtering and band choice are appropriately realized