Finite Element Analysis of Eroding Type Surface Thermocouple with Application to Engine Heat Flux Measurement

A two-dimensional finite element model has been used to analyze the unsteady heat conduction behavior of an eroding type of surface thermocouple. The impulse response of the thermocouple was analyzed by using both a one-dimensional solution and a two-dimensional model. The experimental impulse response of the thermocouple was investigated by a laser impulse excitation experiment to validate the modeling results. The modeling results showed that there was a significant difference between the two-dimensional modeling and the one-dimensional analytical solution, especially before 1 ms. The two-dimensional modeling result is closer to the laser impulse experiment result, which implies the existence of a multi-dimensional effect on the transient heat conduction within the eroding thermocouple. Engine heat flux measurements were obtained using the impulse response analysis, and a comparison of the computed heat flux has been made using the experimental impulse response and the different models. The use of a laser impulse calibration is recommended. If a model is to be used then it should be a 2-D model, but if only a 1-D model is available, then the 1-D model should be based on the properties of the alumel.