The normal spectral emittance of the real surface from worked aero-engine nozzle

Highlights: • The radiative properties of real worked surfaces are investigated. • The effects of oxidation, roughness and contaminants on emittance are discussed. • The impacts of various factors on the emittance have a certain degree of additivity. -- Abstract: The radiative properties of the surfaces of aero-engine components have significant impact on inner heat transfer. It is necessary to research the radiative properties of surfaces which have experienced real working conditions. In this paper, samples were cut from an aero-engine exhaust nozzle which was in operation in the engine and have complex surface properties. Some samples were further processed by grinding or scrubbing to produce a substrate alloy sample and a sample without contaminants. The normal spectral emittances of each sample have been measured for wavelengths ranging in 2.5–20 μm at different temperatures (400–1200 K) using Fourier Transform Infrared (FT-IR) spectrometer. The emittance of the substrate alloy increases as temperature increases and wavelength decreases. By comparing different measurement results of samples, it can be inferred that there are three main factors affecting the radiative properties, including oxidation, surface roughness and contaminants. Oxidation can elevate the normal spectral emittance of sample surfaces and give more weight to short-wavelength range. Roughness would mainly affect radiative properties in long-wavelength range. It seems that contaminants change the radiative properties in the whole wavelength range. In reality, these factors usually exist simultaneously and are related to each other. Though the radiative properties of realistic alloy surfaces are relatively complex, it can be analyzed by different factors.