Abstract: Using heavy gas as the wind tunnel medium effectively alleviates the long-standing model overweight issue in transonic flutter testing. However, heavy gas is a typical non-ideal gas, and differences in its thermodynamic properties lead to significant variations in flutter characteristics between heavy gas and air, with no established flutter similarity theory for these two media to date. Adopting the frequency-domain flutter equation as the governing equation, the similarity conditions and similarity laws for transonic flutter in heavy gases are derived via the similarity transformation method, and a design methodology for heavy-gas wind tunnel test models is established. Taking the AGARD 445.6 wing in heavy gas as the research object, the accuracy of the CFD/CSD coupled analysis method for calculating flutter characteristics of wing laws for heavy gases are applied to design the heavy-gas test model, and the flutter characteristics of both the prototype and the heavy-gas test model are obtained through the CFD/CSD coupled analysis method. The results show that the flutter boundary of the wing prototype without guidance from similarity theory is higher in heavy gas than that in air, while the flutter characteristics of the air prototype can be accurately predicted via the heavy-gas test model. The similarity degree of the dimensionless flutter velocity between the heavy-gas test model and the prototype reaches 94.45%, and that of the dimensionless flutter frequency reaches 94.12%. After converting the flutter dynamic pressure of the heavy-gas test model to the air environment via the similarity laws, the similarity degree between the converted flutter dynamic pressure and that of the prototype is 89.04%. The transonic flutter similarity theory for wings established in this paper accurately realizes the transformation of flutter characteristics between heavy gas and air, provides a theoretical foundation for future engineering practices in heavy-gas wind tunnels, and strongly supports the development of transonic flutter testing technology in heavy-gas wind tunnels.

Key words: Wing tunnel testing, heavy gas medium, flutter, Similarity theory