Numerical Investigations on Rotordynamic Characteristic of Hole-Pattern Seals With Two Different Hole-Diameters

Abstract

The rotordynamic characteristic of the hole-pattern seals with two different hole-diameters was investigated using the unsteady Reynolds-averaged Navier–Stokes (URANS) equations solutions and bulk flow methods. The mesh deformation method combined with elliptical orbit model was adopted to numerically solve the transient flow fields. By integrating the transient reaction forces on the rotor surface, the rotordynamic coefficients of the hole-pattern seals at a set of excitation frequencies were obtained with the reaction-force/motion model. The effects of mesh density, constant temperature assumption, and turbulence model on the numerical accuracy were analyzed for both large hole-diameter hole-pattern (LDHP) and small hole-diameter hole-pattern (SDHP) seals. The comparisons between the two bulk flow methods (i.e., the isothermal bulk flow method (ISOTSEAL) and the ideal gas bulk flow method with energy equation (ideal gas bulk flow model)) and transient computational fluid dynamics (CFD) method were performed. It shows that, compared to the experimental data, the isothermal URANS (constant temperature assumption) and total energy URANS (consider the temperature varying) solutions almost have the same accuracy with respect to the rotordynamic coefficients predictions. However, for the direct damping coefficient predictions, the total energy URANS method has a slight advantage over the isothermal URANS for both SDHP and LDHP cases. For the LDHP seal, the predicted rotordynamic coefficients are not sensitive to the selected turbulence models, but as the hole-diameter becomes smaller, the effect of turbulence model on the numerical accuracy becomes pronounced. Among the studied numerical methods, the isothermal URANS solutions with standard k–ε turbulence model have a good performance taking both numerical accuracy and computational time into consideration. For the SDHP seal, the present ideal gas bulk flow method and ISOTSEAL can provide the reasonable predictions of the rotordynamic coefficients. However, for the LDHP seal, both of them show a low accuracy in predicting the rotordynamic coefficients.