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Simulation of Leakage Characteristics of Combined Seal Structure under Rotational Conditions

In order to reduce fluid leakage and improve the working efficiency of rotational machinery, a three-dimensional (3D) model of combined seal structure (CSS) was established to study the influence of pressure ratio (π, the ratio of the leakage port pressure to the outlet pressure) and rotational speed (n) on the leakage characteristics of CSS with a traditional labyrinth seal structure (LSS) and pocket damping seal structure (PDS) under rotational conditions. Two turbulence models, the standard k-ε model and the SST k-ω model, were used for turbulence closure and the results of the standard k-ε model were found to be more accurate based on comparison with experimental results. The results revealed that under rotational condition, the leakage rates of LSS, CSS and PDS all decreased with the increase in π and n. Under the same axial length of seal structure and π of 0.5 and n of 6000 r/min, the leakage rate of CSS is approximately 8.56% less than LSS, and approximately 0.51% more than PDS. There is a critical value for the influence of n on the leakage rate. The critical n of CSS is close to that of LSS, about 1000 r/min, which is greater than the critical n of 500 r/min for PDS. Finally, the sealing mechanism of CSS was studied using a two-dimensional (2D) model, and was found that the jet structure has a greater influence on the sealing characteristics. Among them, when the ΔP (internal resistance of the device) is the same, the shape of the jet structure, the position of the guide tube and the nozzle radius have a greater impact on the leakage rate, and the shape and length of the extended section have a small effect on the leakage rate.