Similarity criteria of target thermal radiation characteristics and their application to infrared radiation of jet engine exhaust system

In this study, the similarity criteria for thermal radiation characteristics of the target, such as gas flow, heat transfer, mass transfer and thermal radiation coupling effect, were considered. Only in the case where the criteria are based on the similarity of geometry, gas flow, heat transfer and component transportation, can the similarity of thermal radiation be possible. Similarity criteria of different physical mechanisms were obtained by adopting a dimensionless analysis of their governing equations. Every similarity criterion features the impact of each physical mechanism on thermal radiation of target. Thermal radiation similarity theory was applied to a single duct exhaust system and after theoretical analysis, the dominant similarity criteria were selected, while the others were neglected. It was pronounced that there are only three dominant similarity criteria for single duct exhaust system: a) the nozzle pressure ratio, b) the total temperature of the inlet and c) the optical depth. Three cases were simulated numerically using k-ε turbulent viscosity model and backward Monte-Carlo method for the verification of the above conclusion. The boundary conditions and characteristic lengths of the three cases were different but the dominant similarity criteria were respectively the same. Therefore, the results coincided adequately with each other, conclusion that corresponds to the predictions of the theory.