Abstract
In order to control the thermo-mechanical stresses that large heavy-duty power generation turbines have to face nowadays in their frequent operational transients, the analysis of the heat transfer between main flow, secondary air systems and structural components has to consider multi-physics coupled interactions, and has to be carried out with a whole engine modelling approach, simulating the entire machine in the real operating conditions. This is fundamental to guarantee a reliable assessment of life timing consumption and optimize clearances and temperature picks, through an efficient secondary air system design. It is here proposed a comprehensive description of modelling features and assumptions needed for the transient thermo-mechanical characterization of the whole engine through the application of a FEM-fluid network coupling methodology developed in collaboration with Ansaldo Energia and based on the open source code CalculiX®. In the present work the transient thermal modelling capability of the procedure will be verified through its application to a real whole engine geometry under a realistic transient cycle, comparing results with those of a reference FEM code.
Highlights
Controlling gaps and clearances affects engine efficiency and component failures
The procedure is based on a FEM-fluid network coupling approach through a customized version of the open source code CalculiX®
Mass flow rates and pressures obtained from a prior secondary air system (SAS) aerodynamic solution are applied in the thermal network available in the FEM model, providing an intrinsic coupling of the fluid-solid interactions in the thermo-mechanical solution, with the evaluation of the fluid-metal temperatures and displacements by means of a single model
Summary
Controlling gaps and clearances affects engine efficiency and component failures. Achieving effective secondary air system (SAS) design means to fulfil all the functionalities required to the secondary air system (cooling, sealing, purging, etc) with the minimum air consumption, in order to limit the penalty on the cycle performances. Air consumption is directly affected by mass flow splits and pressure losses, and by sealing gaps and cross section areas of flow passages The weight of these topics, always relevant for aeronautical engines, increases today in the heavy-duty gas turbines field. Transient operation should be very fast, in order to achieve rapidly the required load, circumstance that causes strong changes in temperature that components must face, which are responsible for significant deformations of geometries and thermo-mechanical stresses. Managing such complex systems and multi-physic phenomena can be possible only developing a procedure that involves all the components of the engine and allows its comprehensive simulation. A Whole Engine Modelling (WEM) approach for the prediction of the engine operation in transient conditions is necessary to monitor the overall thermo-mechanical behaviour of the engine and achieve a functional design able to control the expansion rates of parts and ensure good seals, guaranteeing integrity and efficiency of the whole system
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