Flow
rate measurement system includes two measurement regions 14,16 located an average
axial distance ΔX apart along the
pipe 12, the first measurement region 14 having two unsteady pressure sensors 18,20, located a distance X1 apart, and the second measurement region 16, having two other unsteady pressure sensors 22,24, located a distance X2 apart, each capable of measuring the unsteady pressure in the
pipe 12. Signals from each pair of pressure sensors 18,20 and 22,24 are differenced by summers 44,54, respectively, to form spatial
wavelength filters 33,35, respectively. Each
spatial filter 33,35 filters out acoustic pressure disturbances Pacoustic and other
long wavelength pressure disturbances in the
pipe 12 and passes short-
wavelength low-frequency vortical pressure disturbances Pvortical associated with the vortical flow field 15. The spatial filters 33,35 provide signals Pas1,Pas2 to band pass filters 46,56 that filter out
high frequency signals. The Pvortical -dominated filtered signals Pasf1,Pasf2 from the two regions 14,16 are cross-correlated by Cross-Correlation Logic 50 to determine a time
delay τ between the two sensing locations 14,16 which is divided into the distance ΔX to obtain a
convection velocity Uc(t) that is related to an average flow rate of the fluid (i.e., one or more liquids and / or gases) flowing in the pipe 12. The invention may also be configured to detect the velocity of any desired inhomogeneous pressure field in the flow. The invention may also be combined with an instrument, an opto-electronic converter and a controller in an industrial
process control system.