Fluctuating temperature measurements on a heated cylinder placed in a cylinder near-wake

The local time-averaged temperature ̄qs and its fluctuating component θs on the surface of a heated circular cylinder immersed in a cylinder near-wake were measured using a fiber-optic Bragg grating (FBG) sensor. Three cylinder center-to-center spacing, i.e., L/d = 5.20, 2.50, and 1.18, were investigated. In order to validate the FBG sensor measurement, a thermocouple and a single hot-wire were employed to measure ̄qs on the heated cylinder and streamwise fluctuating velocity u in the near-wake of the downstream cylinder, respectively. The FBG sensor measurement of ̄qs is in good agreement with that simultaneously obtained by the thermocouple. The measured θs is closely correlated to the hot-wire measurement: the θs-spectrum exhibits a pronounced peak at the vortex shedding frequency as identified in Eu, for each L/d. The results suggest that the FBG sensor can be used to measure reliably both time-averaged and fluctuating temperatures. The heat transfer characteristics of the heated cylinder are examined for different L/d and further compared with the case of an isolated cylinder.