Method for simultaneous measurement of velocity and direction of fluid flow using fiber Bragg gratings

This work is devoted to the development and research of a new optical method for measuring the velocity of a fluid flow and determining the orthogonal directions of such a flow. Comparing with gas flow, measuring the fluid flow rate requires higher heating power and insulation, which is taken into account in this work. The standard hot-wire anemometry method is taken as a basis, but instead of a metal thread, optical fiber is used for measurements. The article presents the design of a sensitive element consisting of two optical fibers. The first fiber contains an array of fiber Bragg gratings and is used as a measurement element. The second fiber has a region with a tapered structure and is used to create a heated area. Velocity measurements are given for the range of 0.02–0.05 m/s, but are limited only by the capabilities of the measuring stand. A unique method for identifying the orthogonal flow direction, which has not been described in the literature before, is presented. Differences in the shapes of the curves for the dependences of flow rates moving in the direction and orthogonally to the axis of the sensitive element are presented. The stability of the device is also confirmed by continuous experiments for 70 min.