This paper presents the transient aerothermal analysis of a gas turbine internal air system through an engine flight cycle featuring multiple fluid cavities that surround a HP turbine disk and the adjacent structures. Strongly coupled fluid-structure thermal interaction problems require significant computational effort to resolve nonlinearities on the interface for each time step. Simulation times may grow impractical if multiple fluid domains are included in the analysis. A new strategy is employed to decrease the cost of coupled aerothermal analysis. Significantly lower fluid domain solver invocation counts are demonstrated as opposed to the traditional coupling approach formulated on the estimates of heat transfer coefficient. Numerical results are presented using 2D finite element conduction model combined with 2D flow calculation in five separate cavities interconnected through the inlet and outlet boundaries. The coupled solutions are discussed and validated against a nominal stand-alone model. Relative performance of both coupling techniques is evaluated.

Coupled Fluid-Structure Transient Thermal Analysis of a Gas Turbine Internal Air System With Multiple Cavities

Use of computational fluid dynamics (CFD) to model the complex, 3D disk cavity flow and heat transfer in conjunction with an industrial finite element analysis (FEA) of turbine disk thermomechanical response during a full transient cycle is demonstrated. The FEA and CFD solutions were coupled using a previously proposed efficient coupling procedure. This iterates between FEA and CFD calculations at each time step of the transient solution to ensure consistency of temperature and heat flux on the appropriate component surfaces. The FEA model is a 2D representation of high pressure and intermediate pressure (IP) turbine disks with surrounding structures. The front IP disk cavity flow is calculated using 45 deg sector CFD models with up to 2.8 million mesh cells. Three CFD models were initially defined for idle, maximum take-off, and cruise conditions, and these are updated by the automatic coupling procedure through the 13,000 s full transient cycle from stand-still to idle, maximum take-off, and cruise conditions. The obtained disk temperatures and displacements are compared with an earlier standalone FEA model that used established methods for convective heat transfer modeling. It was demonstrated that the coupling could be completed using a computer cluster with 60 cores within about 2 weeks. This turn around time is considered fast enough to meet design phase requirements, and in validation, it also compares favorably to that required to hand-match a FEA model to engine test data, which is typically several months. [DOI: 10.1115/1.4003242]

Coupled Aerothermomechanical Simulation for a Turbine Disk Through a Full Transient Cycle

The optimization of heat transfer between fluid and metal plays a crucial role in gas turbine design. An accurate prediction of temperature for each metal component can help to minimize the coolant flow requirement, with a direct reduction of the corresponding loss in the thermodynamic cycle. Traditionally, in industry fluid and solid simulations are conducted separately. The prediction of metal stresses and temperatures, generally based on finite element analysis, requires the definition of a thermal model whose reliability is largely dependent on the validity of the boundary conditions prescribed on the solid surface. These boundary conditions are obtained from empirical correlations expressing local conditions as a function of working parameters of the entire system, with validation being supplied by engine testing. However, recent studies have demonstrated the benefits of employing coupling techniques, whereby computational fluid dynamics (CFD) is used to predict the heat flux from the air to the metal, and this is coupled to the thermal analysis predicting metal temperatures. This paper describes an extension of this coupling process, accounting for the thermo-mechanical distortion of the metal through the engine cycle. Two distinct codes, a finite element analysis (FEA) solver for thermo-mechanical analysis and a finite volume solver for CFD, are iteratively coupled to produce temperatures and deformations of the solid part through an engine cycle. At each time step, the CFD mesh is automatically adapted to the FEA prediction of the metal position using efficient spring analogy methods, ensuring the continuity of the coupled process. As an example of this methodology, the cavity flow in a turbine stator well is investigated. In this test case, there is a strong link between the thermo-mechanical distortion, governing the labyrinth seal clearance, and the amount of flow through the stator well, which determines the resulting heat transfer in the stator well. This feedback loop can only be resolved by including the thermo-mechanical distortion within the coupling process

Thermo-Mechanical Finite Element Analysis/Computational Fluid Dynamics Coupling of an Interstage Seal Cavity Using Torsional Spring Analogy

Use of large-scale computational fluid dynamics (CFD) models in aeroengine design has grown rapidly in recent years as parallel computing hardware has become available. This has reached the point where research aimed at the development of CFD-based ‘virtual engine test cells’ is underway, with considerable debate of the subject within the industrial and research communities. The present article considers and illustrates the state-of-the art and prospects for advances in this field. Limitations to CFD model accuracy, the need for aero-thermo-mechanical analysis through an engine flight cycle, coupling of numerical solutions for solid and fluid domains, and timescales for capability development are considered. While the fidelity of large-scale CFD models will remain limited by turbulence modelling and other issues for the foreseeable future, it is clear that use of multi-scale, multi-physics modelling in engine design will expand considerably. Development of user-friendly, versatile, efficient progr...

Computational fluid dynamics and virtual aeroengine modelling

The prediction of the preswirl cooling air delivery and disk metal temperature are important for the cooling system performance and the rotor disk thermal stresses and life assessment. In this paper, standalone 3D steady and unsteady computation fluid dynamics (CFD), and coupled FE-CFD calculations are presented for prediction of these temperatures. CFD results are compared with previous measurements from a direct transfer preswirl test rig. The predicted cooling air temperatures agree well with the measurement, but the nozzle discharge coefficients are under predicted. Results from the coupled FE-CFD analyses are compared directly with thermocouple temperature measurements and with heat transfer coefficients on the rotor disk previously obtained from a rotor disk heat conduction solution. Considering the modeling limitations, the coupled approach predicted the solid metal temperatures well. Heat transfer coefficients on the rotor disk from CFD show some effect of the temperature variations on the heat transfer coefficients. Reasonable agreement is obtained with values deduced from the previous heat conduction solution.

Evaluation of Computational Fluid Dynamics and Coupled Fluid-Solid Modeling for a Direct Transfer Preswirl System

Accurate temperature predictions are essential to the optimization of gas turbine component design. This paper provides an update on the application of recent developments in heat transfer boundary condition derivation and finite element model validation. Computational fluid dynamics (CFD) is increasingly being used to determine cooling flow distributions and convective heat fluxes on a range of components. Validation of the CFD methodology for internal cavity heat transfer is also a key focus of major research programmes. In this paper, further results are presented for selected engine and rig cavities. A fully coupled CFD/finite element thermal model solution is also demonstrated. Increasingly, the application of optimization techniques to the thermal model calibration process is showing that significant savings in analysis time can be achieved for a given accuracy of ‘match’. The optimization process is described and sample results are presented from the calibration of a typical thermal model. ...

Recent developments in gas turbine component temperature prediction methods, using computational fluid dynamics and optimization tools, in conjunction with more conventional finite element analysis techniques

J. A. Dixon

Papers

Recent developments in gas turbine component temperature prediction methods, using computational fluid dynamics and optimization tools, in conjunction with more conventional finite element analysis techniques