Fiber Optic Distributed Sensors for High-resolution Temperature Field Mapping

Abstract

The reliability of computational fluid dynamics (CFD) codes is checked by comparing simulations with experimental data. A typical data set consists chiefly of velocity and temperature readings, both ideally having high spatial and temporal resolution to facilitate rigorous code validation. While high resolution velocity data is readily obtained through optical measurement techniques such as particle image velocimetry, it has proven difficult to obtain temperature data with similar resolution. Traditional sensors such as thermocouples cannot fill this role, but the recent development of distributed sensing based on Rayleigh scattering and swept-wave interferometry offers resolution suitable for CFD code validation work. Thousands of temperature measurements can be generated along a single thin optical fiber at hundreds of Hertz. Sensors function over large temperature ranges and within opaque fluids where optical techniques are unsuitable. But this type of sensor is sensitive to strain and humidity as well as temperature and so accuracy is affected by handling, vibration, and shifts in relative humidity. Such behavior is quite unlike traditional sensors and so unconventional installation and operating procedures are necessary to ensure accurate measurements. This paper demonstrates implementation of a Rayleigh scattering-type distributed temperature sensor in a thermal mixing experiment involving two air jets at 25 and 45 °C. We present criteria to guide selection of optical fiber for the sensor and describe installation setup for a jet mixing experiment. We illustrate sensor baselining, which links readings to an absolute temperature standard, and discuss practical issues such as errors due to flow-induced vibration. This material can aid those interested in temperature measurements having high data density and bandwidth for fluid dynamics experiments and similar applications. We highlight pitfalls specific to these sensors for consideration in experiment design and operation.

Advanced Measurement and Visualization Techniques for High-Temperature Heat Pipe Experiments

“…As a relatively new technique, distributed temperature sensing using fiber-optic is based on Rayleigh scattering and swept-wavelength interferometry, thousands of temperature measurements can be acquired along a single optical fiber [30]. The scheme and principle of the distributed temperature sensing system is illustrated in Figure 12.…”

One-Step Ahead Prediction of Thermal Mixing Tee Sensors with Long Short Term Memory (LSTM) Neural Networks

“…Fiber readout consists of a 1550nm telecommunication wavelength laser continuously measures Rayleigh backscattering within the length of the fiber from sub-wavelength size intrinsic defects. The principle of distributed temperature measurements with the fiber optic sensors consists of thermal expansion of the fiber, which changes the pattern of Rayleigh scattering [7][8][9][10].…”

“…LSTM networks are trained on time series of each sensor, and then used to predict one-step ahead reading of each corresponding sensor. We have also conducted preliminary investigation of LSTM networks one-step ahead prediction of fiber optics-based distributed temperature sensing [7][8][9][10]. In predicting fiber-based temperature measurements, we treated each gauge pitch of the fiber as an independent sensor.…”

A method for volumetric visualization of temperature distribution: three-dimensional meshed infrared thermography

“…As they are compared with the infrared imaging methods, these methods have the advantage of higher time resolution and lower flow distortion due to the size of the target. There are also optical fiber method which has the same advantages of the thermistor (Lomperski et. al.…”