No abstract

Rotating parts of turbomachines are generally studied using different uncoupled approaches. For example, the dynamic behavior of shafts and wheels are considered independently and the influence of the surrounding fluid is often taken into account in an approximate way. These approaches, while often sufficiently accurate, are questionable when wheel-shaft coupling is observed or when fluid elements are strongly coupled with local structural deformations (leakage flow between wheel and casing, fluid bearings mounted on a thin-walled shaft, etc.). The approach proposed is a step toward a global model of shaft lines. The whole flexible wheel-shaft assembly and the influence of specific fluid film elements are considered in a fully three-dimensional model. In this paper, the proposed model is first presented and then applied to a simple disc-shaft assembly coupled with a fluid film clustered between the disc and a rigid casing. The finite element method is used together with a modal reduction for the structural analysis. As thin fluid films are considered, the Reynolds equation is solved using finite differences in order to obtain the pressure field. Data are transferred between structural and fluid meshes using a general method based on an interfacing grid concept. The equations governing the whole system are solved within a time marching procedure. The results obtained show significant influence of specific 3D features such as disc-shaft coupling and local disc deformations on global behavior.

While often sufficiently accurate, approaches using rotor dynamics and bladed disc dynamics are not adapted to the study of certain important cases, i.e., when observing wheel/shaft coupling or when fluid elements are strongly coupled with local structural deformations. The approach proposed here is a step toward a global model of shaft lines. The whole flexible wheel/shaft assembly and the influence of specific fluid film elements are considered in a full threedimensional model. A modal projection associated with a grid located at the interface of the fluid and structural domains provides an efficient and adaptable coupling. The equations governing the whole system are solved within a time marching procedure which alternatively considers the equations of fluid and structure. The technique chosen is applied to two different test cases. The first is composed of a disc and a thin-walled shaft mounted on a hydrodynamic bearing. The second is intended for studying a more realistic structure composed of a shaft and a wheel coupled with a fluid film between the wheel and a casing. These applications make it possible to identify trends related to fluid effects and couplings between the flexible structural parts.High performances, reliability, and safety require a highly accurate prediction of turbomachine behavior. In this context, the work proposed aims at developing a global model of wheel/shaft assemblies rotating in surrounding fluids.Two uncoupled approaches are generally used to predict the dynamic behavior of rotating parts of machines.

While often sufficiently accurate, approaches using rotor dynamics and bladed disc dynamics are not adapted to the study of certain important cases, i.e., when observing wheel/shaft coupling or when fluid elements are strongly coupled with local structural deformations. The approach proposed here is a step toward a global model of shaft lines. The whole flexible wheel/shaft assembly and the influence of specific fluid film elements are considered in a full threedimensional model. A modal projection associated with a grid located at the interface of the fluid and structural domains provides an efficient and adaptable coupling. The equations governing the whole system are solved within a time marching procedure which alternatively considers the equations of fluid and structure. The technique chosen is applied to two different test cases. The first is composed of a disc and a thin-walled shaft mounted on a hydrodynamic bearing. The second is intended for studying a more realistic structure composed of a shaft and a wheel coupled with a fluid film between the wheel and a casing. These applications make it possible to identify trends related to fluid effects and couplings between the flexible structural parts.

Rotating parts of turbomachines are generally studied using different uncoupled approaches. For example, the dynamic behavior of shafts and wheels are considered independently and the influence of the surrounding fluid is often taken into account in an approximate way. These approaches, while often sufficiently accurate, are questionable when wheel-shaft coupling is observed or when fluid elements are strongly coupled with local structural deformations (leakage flow between wheel and casing, fluid bearings mounted on a thin-walled shaft, etc.). The approach proposed is a step toward a global model of shaft lines. The whole flexible wheel-shaft assembly and the influence of specific fluid film elements are considered in a fully three-dimensional model. In this paper, the proposed model is first presented and then applied to a simple disk-shaft assembly coupled with a fluid film clustered between the disk and a rigid casing. The finite element method is used together with a modal reduction for the structural analysis. As thin fluid films are considered, the Reynolds equation is solved using finite differences in order to obtain the pressure field. Data are transferred between structural and fluid meshes using a general method based on an interfacing grid concept. The equations governing the whole system are solved within a time-marching procedure. The results obtained show significant influence of specific three-dimensional features such as disk-shaft coupling and local disk deformations on global behavior.