A Generalized Prediction Method for Rotordynamic Coefficients of Annular Gas Seals

The improvement in rotordynamic performance of the annular gas seal requires efficient and accurate prediction methods of rotordynamic coefficients. Although the existed transient computational fluid dynamics (CFD) methods in published literature have excellent numerical accuracy, most of them face the challenge due to rotordynamic coefficients at every excitation frequency to be solved by a separate transient CFD prediction thus much time-consuming. In this paper, a generalized prediction method is proposed to address this difficulty. Based on the Laplace transform method, the solution procedures for the reaction force/motion equation of the annular gas seal are deduced. With the specified excitations (rotor motion), the rotordynamic coefficients at all excitation frequencies can be solved by only one or two transient CFD solutions. To verify the present generalized method, the rotordynamic coefficients of two typical hole-pattern seals are computed and compared to the available experimental data. The results show that the predicted rotordynamic coefficients are in good agreement with the experimental tests. Compared to the previous transient CFD methods, the computational time of the present generalized method is reduced significantly while the accuracy is still maintained.