
FLEXTURBINE
Allocation
Abstract
The project is a part of a larger European collaboration, called FLEXTURBINE, which seeks to bridge the gap between the current and the next generation energy demands by improving the design of the power plant turbines. The task assigned to LTU is to support the development of a new Tilting Pad Journal Bearing; this is done in collaboration with Siemens in Germany.
To make theoretical predictions on the performance of the bearing, the commercial software Comsol Multiphysics is used as a tool for the modeling and for the numerical simulations. Comsol uses finite elements to solve coupled physics problem and for this project the main challenge is to solve for the, partially turbulent, lubricant flow in 3D. The fluid flow is also coupled to elastic deformations, which are due to pressure and heat generation in the lubricant, and to the heat transfer to and from the surrounding surfaces. Other effects to include are the phenomena of film rupture, i.e. cavitation, and the viscosity temperature dependence. Lastly, a moment and force equilibrium equation has to be solved to obtain the correct tilting angles of the pads and the translational position of the rotating shaft center; there is also a need to solve an equation governing the mesh displacement since the fluid domain is changing its shape in each iteration.
Now, since the shaft is rotating at a surface velocity of around 80 m/s, the boundary condition for the heat equation at the fluid/shaft interface is not trivial and the current methods, in static calculations, involves limiting simplifications. To study in detail how the temperature field in the shaft evolves, one would ideally do a transient study where the rotation of the shaft is resolved in time. Using this type of transient study, it would also allow one to very accurately simulate the dynamic properties of the bearing.
