Application of infrared imaging technology in bounder layer transition measurement for metal model

Due to fast heat conduction of metals, the thermal equilibrium state can be reached within a short period of time, which causes a significant difficulty in measuring the transition of metal models when using infrared thermal imager. To solve the problem, an alternative method was presented in this paper by CARDC (China Aerodynamics Research and Development Center) to spray the thermal-insulating coating on the surface of a metal rotor airfoil model in the 3.2 m low speed wind tunnel. Then the infrared thermal imager can be used to measure the temperature distribution, and the transition position of model can be determined through the temperature jump. Since the infrared thermal imager was usually fixed to the test section, therefore, when adjusting the angle of attack, the position of model varied in the obtained infrared images, making it inconvenient to compare the transition positions. Thus, the infrared thermal imager was fixed to the rotating platform during the experiment, to synchronize with the rotation of the model, which eliminated the position difference of model images under different angles of attack. In this way, a highly accurate transition position and a more precise mapping between the infrared thermal images and model coordinates were obtained.