Investigation on Sensor Layout of Optical Fiber Distributed Acoustic Sensing Technology for Flow Velocity Measurement in Pipes

Pipes may have leakage, breakage, and local blockage during the long-term service period, which may lead to insufficient flow velocity and low water supply pressure. Therefore, measuring flow velocity in pipes is crucial for diagnosing damage, ensuring safe operation, and managing maintenance. Current flow velocity measurement techniques exhibit poor stability over long-term measurements in complex environments, and the measurement quality is affected by the physical and chemical properties of the transported medium. To address these issues, this study employs distributed optical fiber sensors (DOFSs) for measuring flow velocity in water-filled pipes, and the effectiveness is validated by the fiber Bragg grating (FBG) sensors. Based on the phase change of optical fiber demodulated by a distributed acoustic sensing (DAS) device, the flow velocity is accurately measured. Test results demonstrate a quadratic relationship between flow velocity and phase change of optical fiber based on the DAS system, with all fitting effects exceeding 0.95, consistent with theoretical analysis. The influence of different sensor layouts of the distributed optical fibers on the monitoring data is also carefully checked, and the testing results show that bonding the optical fiber on the pipes can achieve better measurement quality, compared to the free optical fiber without constraint around the pipe. This study contributes to improving the measurement accuracy and stability of optical fiber sensors by using the DAS system.