Objective With the development of gas turbines toward higher parameters and greater efficiency, the demands for thermal protection and condition monitoring of high-temperature components have become increasingly urgent. Infrared thermometry, as a non-contact and highly responsive temperature measurement technique, often suffers from significant errors in practical applications due to the inaccuracy of surface emissivity data. At present, most studies on the emissivity of rough metal surfaces rely on geometric optics approximations or empirical models, which are insufficient to accurately describe the influence of microstructural features on infrared radiation behavior. In view of this, this study proposes a surface emissivity calculation method for high-temperature components of gas turbines based on wave optics principles, aiming to establish a high-accuracy, scenario-adaptive emissivity model to provide theoretical support for improving the precision of infrared thermometry.

Methods A calculation method for the surface emissivity of high-temperature gas turbines turbine components based on wave optics principles was proposed in this study. The metal surface is modeled as a three-dimensional rough surface that follows a Gaussian random distribution. A computational domain incorporating metallic micro-elements is established in COMSOL 6.2 (Fig.1), where the propagation of electromagnetic waves is governed by the Helmholtz equation. Furthermore, an infrared radiation characteristics calculation method is developed by coupling the emissivity model, which integrates the Z-buffer algorithm with the radiative transfer equation. Based on this approach, the infrared radiation characteristics of a simulated turbine blade model are numerically evaluated under various camera viewing angles (Fig.9-Fig.10).

Results and Discussions The calculated emissivity demonstrates distinct variation trends within the infrared wavelength range of 1.7-12 μm and emission angles from 0° to 85°. Three surfaces with different roughness levels—polished, sandblasted, and oxidized—were analyzed in detail. It was observed that emissivity decreases gradually at emission angles between 0° and 75°, while a more rapid decline occurs beyond 75° (Fig.2). At a wavelength of 1.7 μm and a viewing angle of 60°, the emissivity of the three surfaces was only 88%, 86%, and 75% of their respective normal-direction values (Fig.3). Moreover, the emissivity increment is approximately proportional to the increase in surface roughness, as greater roughness leads to more pronounced surface undulations and an increase in the effective radiating area per unit nominal area (Fig.4). Overall, the surface emissivity of turbine blades increases with surface roughness, but decreases with increasing emission angle and wavelength (Fig.5). These results are of great significance for understanding the radiative mechanisms of complex rough surfaces.

Conclusions An emissivity calculation method based on wave optics principles was developed. By computing the emissivity of three nickel alloy rough surfaces within the wavelength range of 1.7-12 μm and emission angles from 0° to 85°, the variation characteristics of emissivity in the near-infrared region were summarized. When compared with existing experimental data, the calculated emissivity exhibited consistent trends, with deviations within 1%, demonstrating the high accuracy of the proposed method. Furthermore, by accounting for the angular dependence of emissivity, the temperature measurement error at the blade edge under high camera viewing angles was reduced by 1.43%, indicating a significant improvement in infrared thermometry accuracy. This method exhibits strong theoretical consistency and provides a feasible numerical tool for the development of high-precision radiation thermometry techniques for high-temperature components.