Fluid flow velocity and temperature measurement

Abstract

A method is provided for monitoring velocity of a fluid flow through a predetermined fluid flow space. A fiber optic conductor includes a flow measurement portion defining an elongated dimension extending across a portion of the fluid flow space. The fluid flow in the fluid flow space causes the measurement portion of the fiber optic conductor to flex in a direction transverse to the elongated dimension. Optical radiation is supplied to the fiber optic conductor, and optical radiation is received from the fiber optic conductor after the supplied optical radiation has passed through the measurement portion. The received optical radiation is analyzed to effect a determination of a flow velocity of the fluid flow.

What is claimed is: 
     
         1 . A system for monitoring velocity of a fluid flow through a predetermined fluid flow space formed by a wall defining and extending in a fluid flow direction, the system comprising:
 a base structure supported on the wall;   a fiber optic conductor including a base end supported on the base structure and an unrestrained free end located in the fluid flow and movable relative to the base end, the fiber optic conductor defining a flow measurement portion including a long period grating (LPG) structure extending from the wall across a portion of the fluid flow space and the fiber optic conductor including an elongated dimension extending transverse to the fluid flow direction for flexing in response to fluid flow against the flow measurement portion;   an optical radiation source supplying optical radiation to the fiber optic conductor;   a processing unit adapted to receive and analyze optical radiation from the fiber optic conductor after the supplied optical radiation has passed through the measurement portion to produce a determination of a flow velocity of the fluid flow with reference to cladding modes formed by the LPG structure.   
     
     
         2 . The system of  claim 1 , including a plurality of the fiber optic conductors supported on the base structure and each including a LPG structure, each of the fiber optic conductors extending outwardly from the wall into the fluid flow space, and including a supply fiber optic conductor extending from the optical radiation source and a splitter providing optical radiation from the supply fiber optic conductor to each of the fiber optic conductors. 
     
     
         3 . The system of  claim 2 , wherein the plurality of fiber optic conductors are arranged in a plurality of rows supported on the base structure, each row including a plurality of the fiber optic conductors. 
     
     
         4 . The system of  claim 1 , wherein the fiber optic conductor includes a reflective surface at an end distal from the base end for reflecting optical radiation including the cladding modes through the fiber optic conductor to the processing unit. 
     
     
         5 . The method of  claim 1 , wherein a plurality of fiber optic conductors are provided, each fiber optic conductor having a base end supported on a base structure and a free end located in the fluid flow, each fiber being free to bend in the fluid flow and having an LPG structure and each LPG structure having a set of cladding modes characteristic of the bending of a respective fiber optic conductor. 
     
     
         6 . The method of  claim 5 , wherein the received optical radiation comprises optical radiation reflected off ends of the fiber optic conductors distal from the base end. 
     
     
         7 . The method of  claim 5 , including comparing cladding modes of two or more of the fiber optic conductors to determine a direction of fluid flow.