Theoretical Rotordynamic Coefficients of Labyrinth GasSeals: a Parametric Study on a Bulk Model

Abstract

To date, available mathematical bulk models for the determination of linearized rotordynamic coefficients of labyrinth gas seals yield results which are not always in good agreement with the experimental ones. The object of this work is to discuss the limits of these models and to point out possible improvements and aspects that need further investigation.After a study of the steady flow characteristics with an FEM code, a parametric computer program, based on a known two-volume model, has been developed. A perturbation approach has been applied to the governing equations of the bulk model to calculate the stiffness and damping coefficients. Predicted coefficients are compared to the results of an earlier onevolume model.The model has also been tested with different expressions of the axial velocities in the two volumes and different laws for leakage and shear stress. The theoretical results are compared to the published experimental ones, pointing out the small effect of the various parameters in improving the correlation and the need of more complex models.

The application of automatic differentiation techniques for the prediction of rotor-dynamic coefficients of labyrinth seals

“…The results obtained with current code labeled by "Fuerst, one volume" are compared to experimental results of Childs and Scharrer [10], "classical" one control volume code [1], and with the two control volumes code [11]. One can see that the results for cross coupled stiffness and direct damping corresponds very well to experimental data as well as to results obtained with other codes.…”

“…Unfortunately there is no or very little informations about precession speeds for the experimental data as well as for the results of Forte and Latini [11]. Nevertheless the description of the experimental apparatus states that the rotor makes linear side-to-side motion [10].…”

“…Nevertheless the description of the experimental apparatus states that the rotor makes linear side-to-side motion [10]. Similarly the "classical" perturbation based codes including those of [11] assume elliptical motion. In both cases the elliptical as well as the linear motion can be decomposed onto two circular orbits with opposite precession speeds.…”