In order to obtain high performance, to increase the lifespan of a Gas Turbine and the reliability of its operation, designers of the Secondary Air System need to ensure:

·         minimal bleeding of cooling flow from various compressor stages

·         safe cooling of high temperature vane and turbine blades and the turbine and stator discs

·         that the temperature within the blades and discs is not in excess of a thermal limit and that the temperature distribution prevents excessive thermal stress

·         prevention of ingestion of hot gas into the wheel cavities

·         proper sealing of bearing chambers and minimisation of thrust on the bearings

To achieve this, it is necessary to model both the secondary air flow and the temperature distribution in solid components. System CFD is used to solve flow, pressure and temperature distributions and a thermal solver is used to perform a thermal analysis of the blade and disc solids that interacts with the flow system.  The thermal interaction of the secondary flow system together with the solid components is a key part of the model and is known as conjugate heat transfer analysis.

In the past such analysis often resorts to either real-time ^\[1,2\]^ or off-line ^\[3\]^ co-simulation deploying 1D CFD fluid system analysis tool like Simcenter Flomaster and 3D thermal analysis tools like Nastran and Ansys, among many other tools.  This approach, albeit useful, has a number of disadvantages such as accuracy limited to the lower fidelity solution offered by 1D system model but consuming large time and effort associated with the 3D thermal analysis.  It also requires detailed geometry of design for 1D thermal analysis and incurs the costs of needing two or more tools.

This paper presents the work of model based system modelling of both thermal fluids system and the thermal solid system with conjugate heat transfer within a single 1D system analysis tool Simcenter Flomaster.  This offers the advantage of faster modelling and consistent model accuracy of both thermal fluids and thermal solid system models, especially in the early concept design stage of the V-cycle of the engineering design, where either the detailed geometry of the solid thermal system is yet to be decided or the design is subject to rapid change.  It also eliminates the need of co-simulation and the related extra costs of needing multiple simulation tools.  The 1D system model of conjugate heat transfer between the thermal fluids and solid thermal system has been validated with an idealised analytical solution.  It is shown that the model can be applied to the analysis of a gas turbine secondary air system including both the flows inside the cavities and the thermal analysis of the gas turbine rotor and stator discs forming the boundaries of these cavities using Simcenter Flomaster alone, providing the gas turbine engineer the required design data of the mass flowrates, pressure, temperature, swirl distribution in the secondary air flow system and the temperature distribution in the rotor and stator discs. 

Reference:

1.       Vlad Ganine, Nick Hills, Matt Miller, Chris Barnes, Steve Curzons, Lynne Turner and Peter Smout; IMPLICIT HETEROGENEOUS 1D/2D COUPLING FOR AERO-THERMO-MECHANICAL SIMULATION OF SECONDARY AIR SYSTEMS; Proceedings of ASME Turbo Expo 2015: Turbine Technical Conference and Exposition; June 15 – 19, 2015, Montréal, Canada; GT2015-43406.

2.       WU Hong, LI Peng and LI Yulong, Simulation of Unsteady State Performance of a Secondary Air System by the 1D-3D-Structure Coupled Method; Journal of Thermal Science Vol.25, No.1 (2016) pp68-77.

3.       Guilherme Tondello, Wolodymir Boruszewski, Fernando Mengele, Marcelo Assato, Silvio Shimizu and Shayne Ziegler;      COUPLED SIMULATION OF THE SECONDARY AIR FLOW, HEAT TRANSFER, AND STRUCTURAL DEFLECTION OF A GAS TURBINE ENGINE; Proceedings of ASME Turbo Expo 2012, June 11-15, 2012, Copenhagen, Denmark; GT2012-69924.


Modelling Conjugate Heat Transfer Within a Gas Turbine Secondary Air System Using Thermo-Fluid System Simulation

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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