Abstract: Combining equal strength cantilever with Fiber Bragg Grating (FBG), a target-type FBG flow velocity sensor is developed to monitor the pipeline and the fracture flow velocity on-line. The force produced by flow works on the special shape target, then the level and cantilever structure transform the force into the wavelength shift of the FBG and the dual FBG structure is adopted to eliminate temperature effect. In order to determine the target force characteristics in the fracture and the equivalent pipeline diameter under equal force, finite element simulation is carried out using FLUENT6.3. Simulation results show that the velocity sensitivity of the sensor is 8.71?10^-4 s²/m² in the fracture at the flow section of 5 mm?2000 mm. The pipeline calibration experiments indicate that, in the measuring range of 0 m/s~1.20 m/s, the maximum error of the sensor is 0.02 m/s. The sensor is used in the drainage experiment of simple fracture water model. The results indicate the velocity increases when the inlet valve is enlarged. After the valve is turned on, the velocity in the rear drainage pipeline decreases. The trend of velocity change at the same section is in agreement with each other.

Key words: optoelectronics and laser technology, fiber Bragg grating, flow velocity sensor, model test, fracture water