Research Of High-accuracy Infrared Radiation Thermometry

Aero engines are highly complex and precise thermal machines.The temperature of the turbine blades is significant for engine testing and development.However,the harsh environment makes it extremely difficult to measure the temperature of the turbine blades.Radiation thermometry is suitable for turbine blade temperature measurement due to its good characteristics like non-contacting targets,fast response speed,and being suitable for moving targets.However,it also with difficulties caused by obtaining radiation signals,emissivity varying,and background radiation interference.These difficulties hinder the development of radiation thermometry for turbine blades.Thus,this dissertation studied the above problems and designed a radiation thermometry system suitable for aero engine blades.First,the impact of emissivity changes on radiation thermometry was analyzed,and the emissivity-changing mechanism of alloys used in engines during the oxidation was studied.The emissivity changing 0.1 would cause more than 2% relative error for brightness radiation thermometry and would make the colorimetric thermometry to be unavailable.The emissivity of the GH3044 and TC4 were measured during the hightemperature oxidation,and the emissivity oscillation caused by the interference effect of the oxide film was observed.The oscillation of the emissivity at short wavelengths disappeared faster than at longer wavelengths.A method for calculating the emissivity of unknown rough surfaces based on constructing random rough surfaces was proposed.Using this method,the effect of roughness on the emissivity of gray and non-gray body solids was calculated.It was found that surface roughness has an enhancing effect on the emissivity,but the enhancement decreases with the increase of roughness and original emissivity.Based on this method,the spectral emissivity of GH3044 and K465 superalloys with different roughness was calculated,and the maximum relative error between the calculated and experimental results was less than 3%.Then,the effect of background radiation on thermometry was studied,and the error caused by the background radiation on brightness thermometry and colorimetric thermometry was calculated.It was found that the influence of background radiation increases as the target temperature increases for brightness rightness thermometry,and50% background radiation would cause near 8% relative error.For colorimetric thermometry,the influence of background radiation decreases as the target temperature increases,and 50% increase of background radiation caused near 3% relative error.At the same time,the heat sources distribution around the turbine blades was analyzed.A quantitative calculation model for background radiation was established,and the background radiation source distribution on the target blades under different operating conditions was calculated.Finally,a generalized inverse matrix-particle swarm optimization(GIM-PSO)multispectral radiation thermometry data processing algorithm that considered the influence of background radiation was proposed.When there was 5%random noise in the measurement spectral channel,the relative error of the algorithm was still less than 1%.Finally,a radiation thermometry system suitable for high-speed rotating targets working in harsh working containing high-temperature and high-pressure was designed.Based on ANSYS,the temperature and structural strength of the probe were calculated to evaluate the reliability in aero-engine.The results showed that when the hot gas was with temperature of 1773 K,pressure of 1.5 MPa,and flow rate of 1 Mach(340 m/s),the probe could still work well.The radiation thermometry system was tested under laboratory conditions and simulated working conditions.Under the steady-state environment in the laboratory,the relative error was less than 1%,and the emissivity error of each wavelength was less than 0.05.Under simulated conditions,the radiation temperature measurement system stably measured the temperature of samples,and no safety accidents or probe failures occurred during the measurement.In the optimal scanning range of the probe,the maximum relative error of the system was less than 2%.The experimental results showed that this system could finish the measurement under high-temperature and high-pressure conditions.The accuracy of the system under simulated working conditions was lower than that in the laboratory environment,so this system needs to be further optimized.This research would help to develop turbine blade radiation temperature measurement technology and provide important support for the research of development and testing of aero-engines.