Fiber-Optic Hot-Wire Anemometer With Directional Response Based on Symmetry-Breaking Induced Heat Transfer Mechanism

Optical fiber hot-wire anemometer is an emerging technique for wind speed measurement. In many practical applications, both the magnitude and the direction of the flow need to be obtained. However, most of previously reported fiber optic anemometers show omnidirectional response, rendering difficulty in recognizing the flow direction. Here, we propose a simple and effective fiber-optic flow sensor with directional response based on an asymmetric coating of single-wall carbon nanotubes (SWCNTs) on the surface of tilted fiber Bragg grating (TFBG), paving the way for the vector analysis of wind flow field. FLUENT software was employed to analyze the wind speed field, temperature distribution field, and vortex street. The temperature field shows asymmetrical distribution directly related to the wind directions, causing directional response of the sensor to the wind flow. In the experiments, with optimized 12˚ TFBG with 1.3 μm thick asymmetric SWCNTs coating, three wind directions at different angle (0˚, 180˚, 270˚) were clearly distinguished. Moreover, high sensitivity and efficiency were also achieved by investigating and optimizing the system parameters like pumping power, coating thickness. In addition to directional response, the proposed sensor exhibits many advantages such as simple structure, low power consumption, small size, and high sensitivity, which has good potential application for infield static wind field and slowly varying wind (SVW) measurement.