研究目的
To demonstrate the applicability of a method using laser heating for thermography measurements to detect flow topologies of fast-rotating quadcopter rotors and to reveal the limitations of this technique.
研究成果
IR thermography measurements using a high-power infrared laser can detect steady-state flow topologies at high rotational frequencies reliably and with high image quality. Differential infrared thermography (DIT) results indicate that some unsteady changes in flow topology can be detected, but further work is needed to improve detectability of unsteady phenomena over the whole extent of the blade.
研究不足
The minimal pulse duration was limited by the laser’s power supply. With rather long laser pulses, thermal load on the rotor hub was high and limited the achievable heat flux density. The achievable temperature differences with the given heat input were not sufficient for detection by the infrared camera over the whole extent of the blade in forward flight conditions.
1：Experimental Design and Method Selection:
The study employed active infrared thermography with a high-power infrared laser to heat the blade surface of quadcopter rotor blades. The method was designed to increase the distance between the heat source and the measuring object compared to conventional heat sources.
2：Sample Selection and Data Sources:
Four differently sized and shaped quadcopter rotors made from carbon fiber reinforced polymer (CFRP) were studied. A black matt coating was applied to the rotor surfaces for increased emissivity.
3：List of Experimental Equipment and Materials:
An industrial infrared diode laser (Jenoptik JOLD-1250-CABN-25A) was used to heat the suction side surface of the rotor blade. A high-speed infrared camera (IRCAM EQUUS 327k L) was operated in triggered mode. A model aircraft motor (D-POWER AL 50-04) was used to drive the rotors.
4：Experimental Procedures and Operational Workflow:
The rotor blades were studied at three rotational frequencies. A phase-averaging method was applied to reduce noise and increase image quality. Oil-film interferometry measurements were performed to validate the results from thermographic measurements.
5：Data Analysis Methods:
The subtraction of a reference image from an image of the pulse-heated blade was used to remove the factor of adiabatic surface temperatures increase from the images. A temperature correction was applied to account for non-uniform heating of the blade.
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