A fiber-optic Bragg grating sensor for simultaneous static and dynamic temperature measurement on a heated cylinder in cross-flow

A fiber-optic Bragg grating (FBG) sensor is proposed to measure the local static temperature ̄θsand the fluctuating temperature θson the surface of a heated circular cylinder subjected to a cross-flow. In order to validate the new technique, a type-K thermocouple and a single hot wire are used to measure ̄θsand the near-wake streamwise fluctuating velocity u, respectively. The FBG sensor measurement of ̄θsagrees well with that simultaneously obtained by the thermocouple. The θs-spectrum exhibits a prominent peak at the vortex shedding frequency, fs*= fsd/U∞≈ 0.2 (U∞is the free-stream velocity and d is the cylinder diameter), consistent with the u-spectrum. In fact, the θsand u signals are almost perfectly correlated at fs*. Furthermore, the measured ̄θsand root mean square value of θsare agreeable with previously reported Nusselt number data. These results demonstrate that the FBG sensor can be used to measure reliably both static and fluctuating temperatures. It is expected that the FBG sensor, because of its uniqueness in many aspects and being at an affordable cost, has an excellent prospect in temperature measurements.