NON-AXISYMMETRIC FLOWS AND ROTORDYNAMIC FORCES IN AN ECCENTRIC SHROUDED CENTRIFUGAL COMPRESSOR: PART 2 — ANALYSIS

摘要

An integrated analytical model to predict non-axisymmetric flow fields and rotordynamic forces in a shrouded centrifugal compressor has been newly developed and validated. The model is composed of coupled, conservation law-based, bulk-flow sub-models, and the model takes into account the flow coupling among the blades, labyrinth seals, and shroud cavity. Thus, the model predicts the entire flow field in the shrouded compressor when given compressor geometry, operating conditions, and eccentricity. When compared against the experimental data from Part 1, the new model accurately predicts the evolution of the pressure perturbations along the shroud and labyrinth seal cavities as well as the corresponding rotordynamic stiffness coefficients. For the test compressor, the cross stiffness rotordynamic excitation is positive - the contribution of the shroud is the highest; the contribution of the seals is less than but on the same order of magnitude as that of the shroud; and contribution of impeller blades is insignificant. For accurate flow and rotordynamic force predictions, it is critical to model the coupling among the components (e.g., impeller, shroud, labyrinth seal, etc.) which determines the non-axisymmetric boundary conditions for the components. The new model also enables insight into the physical mechanism for pressure perturbation development. The labyrinth seal pressure distribution becomes non-axisymmetric to satisfy mass conservation in the seal cavity, and this non-axisymmetry, in turn, serves as the influential boundary condition for the pressure distribution in the shroud cavity.