Experimental study on the film cooling effectiveness of turbine blade with light-field multispectral radiation thermometry

Aero-engine performance critically depends on the film cooling effectiveness of turbine blades, traditionally optimized through point-wise thermocouple and infrared thermography measurements of coolant flow rate and temperature ratio. However, conventional methods face inherent limitations in capturing comprehensive heat transfer characteristics due to spatial resolution constraints and thermal interference from high-temperature mainstream gases. This study introduces a novel measurement framework employing near-infrared light-field multispectral radiation thermometry (NIR-MSLF), which integrates light-field imaging with spectral filtering technology to capture four discrete wavelength bands within a single exposure. This advancement enables high-fidelity two-dimensional temperature mapping with spectral-spatial demultiplexing capabilities. Experiments were conducted on a mid-temperature (823 K) turbine blade test rig, featuring thermocouples embedded at the mid-span section of the test blade for reference measurements. Comparative analysis confirmed NIR-MSLF's measurement accuracy with maximum deviations of 20 K relative to thermocouple data. The investigation systematically analyzed blade cooling performance under varying operational conditions, revealing distinct thermal characteristics: elevated temperatures at the leading edge and pressure surface regions adjacent to endwalls, contrasted with cooler suction surface zones. Among investigated parameters, coolant flow rate (FR) emerged as the dominant influence on average cooling effectiveness, demonstrating a near-linear correlation between FR increments (0.02-0.08) and average 2 cooling effectiveness enhancements from 0.28 to 0.71. Conversely, temperature ratio (TR) variations (1.56-2.36) exerted minimal impact on average cooling effectiveness values, which remained stable within 0.69-0.71 across tested conditions.