Development of two camera filtered thermography system for hypersonic ablation experiment

• Main Author: Yu, Chengxin
• Other Authors: New Tze How, Daniel
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Aeronautical engineering::Aerodynamics; Science::Physics::Heat and thermodynamics
• Online Access: https://hdl.handle.net/10356/169480
• Institution: Nanyang Technological University

This final year project aims develop a novel filtered thermography technique for hypersonic re-entry pre-heated ablation experiments in the X2 Expansion Tube located at the University of Queensland, Australia. Thermography is typically employed as in-situ thermocouples are unable to measure the extreme temperatures that the models reach and are invasive techniques. At these high temperatures, emissivity changes of the model material can no longer be assumed constant. However, ratio of spectral radiance at 2 different wavelengths can eliminate emissivity by Planck’s Law. The rotating wheel filtered camera system is modified to a dual camera with a 50-50 beam splitter system secured in a rigid cage. Each camera is equipped with a filter holder that allows for hot swapping of filters. The dual camera beam splitter system was calibrated against a blackbody furnace and integrating spheres of known temperature values up to 3300K. Only 500, 600, 700, 800nm filters are utilised. An empirical factor using least-fit method is applied to the theoretical transmission-inclusive Planck’s Law spectral ratio curve of each filter pair to better match the experimental data. A mini spectrometer is also calibrated using the same sources with a calibration function as well to provide live temperature feed during heating as the camera data must be post-processed. Testing of these equipments against the known sources show an underprediction of 302.2K ± 15.3K and of 777.6K ± 9.9K for the camera and mini spectrometer system respectively. For the camera system, this may be due to the Planck’s Law factored fit not passing though perfectly through all datapoints, especially at high temperatures, or the deviation of transmission properties of the optics provide by manufacturers. For the mini spectrometer system, the assumption that the calibration factor is constant may not hold and would require further investigation. Bench test results show that the new graphite test model of size 10mm wide and 3mm thick can only reach temperatures of up to 2900K, compared to simulations that suggest it can exceed 3300K, when around 580A is passed through the strip. This underprediction may stem from the errors present in the camera system or poor contact between the clamps and the strip. Heating profile was unable to be determined due to rectifier data acquisition system malfunction, and other strip geometries were not tested due to time limitations.