Analysis of Heavy Duty Gas Turbine Stator-Rotor Cavity Through 3D CFD-1D Fluid Network — Field Measurements Combined Approach

An effective design and development of the Secondary Air System of a heavy-duty gas turbine is crucial for many purposes, such as cooling and sealing air supply, pre-swirling features, leakages control, casings and rotor thermal state assessment and rotor axial thrust management. All of these features directly impact on the performances and integrity of the whole machine and accordingly require advanced design approaches. The first stage stator-rotor turbine cavity of Ansaldo E-Class heavy-duty gas turbine AE94.2 underwent design modifications to adjust its internal pressure and consequently lower the global rotor axial load acting on the thrust bearing. This goal had to be reached while maintaining safety against hot gas ingestion from the turbine section main flow into the cavity, thus preserving the GT integrity. A multi-purpose analysis was then carried out on the cavity Secondary Air System. This involved steady 3D CFD calculations with a computational domain comprising the first turbine stage and the corresponding stator-rotor wheelspace. A combined use of CFD and SASAC, the in-house Ansaldo 1D fluid network code, finally led to an upgraded design of the cavity. Two field measurement campaigns were subsequently carried out on an AE94.2 GT to validate both the baseline configuration and the upgraded one, by means of 6 pressure and temperature sensors in the cavity and 12 load cells/thermocouples on the thrust bearing. The CFD model and results are presented, the fluid network tuning is discussed and the experimental setup and main outcomes of the two field campaigns are reported. Constant references to the definitive literature are made, with an effort to correlate at best research and industrial practice. These integrated activities allowed to perform a reliable verification against hot gas ingestion into the stator-rotor cavity and to successfully develop an effective solution, which reduced the GT rotor residual axial thrust by up to 25% less.

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1D Tool for Stator-Rotor Cavities Integrated Into a Fluid Network Solver of Heavy-Duty Gas Turbine Secondary Air System

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2010-22203 ◽

2010 ◽

Author(s):

F. Bonzani ◽

L. Bozzi ◽

M. Mantero ◽

A. Vinci ◽

L. Innocenti ◽

...

Keyword(s):

Gas Turbine ◽

Gas Turbines ◽

Operating Conditions ◽

Heavy Duty ◽

Ambient Conditions ◽

Hot Gas ◽

Fluid Network ◽

Air System ◽

Air Flows ◽

Secondary Air

In order to improve performance of heavy-duty gas turbines, in terms of efficiency and reliability, accurate calculation tools are required to simulate the SAS (Secondary Air System) and estimate the minimum amount of cooling and sealing air to ensure the integrity of hot gas path components. A critical component of this system is the cavity formed between coaxial rotating and stationary discs, that needs a sealing flow to prevent the hot gas ingestion. This paper gives a general overview of a 1D tool for the analysis of stator-rotor cavities and its integration into an “in-house” developed fluid network solver to analyse the behaviour of the secondary air system over different operating conditions. The 1D cavity solver calculates swirl, pressure and temperature profiles along the cavity radius. Thanks to its integration into the SAS code, the cavity solver allows estimation of sealing air flows, taking into account directly of the interaction between inner and outer extraction lines of blades and vanes. This procedure has been applied to the AE94.3A secondary air system and the results are presented in terms of sealing flows variation for the cavities of second and third vane on gas turbine load and ambient conditions. In some different load conditions, calculated secondary air flows are compared to experimental data coming from the AE94.3A Ansaldo fleet.

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Design and Analysis of a Real-Time Hot Gas Temperature Estimator for Heavy-Duty Gas Turbines

Volume 6: Ceramics; Controls, Diagnostics and Instrumentation; Education; Manufacturing Materials and Metallurgy; Honors and Awards ◽

10.1115/gt2015-42192 ◽

2015 ◽

Author(s):

Eric A. Müller ◽

Adrian Ticǎ

Keyword(s):

Real Time ◽

Gas Turbine ◽

Gas Turbines ◽

Gas Temperature ◽

Heavy Duty ◽

Component Level ◽

Load Range ◽

Hot Gas ◽

Dynamic Tracking ◽

Heavy Duty Gas Turbine

The knowledge about a relevant process and lifetime indicative quantity, such as the hot gas temperature, is crucial for the control of a gas turbine. Since this indicative process quantity usually cannot be directly measured, it has to be estimated. The paper describes a model-based method to accurately estimate in real-time the hot gas temperature of a heavy-duty gas turbine. The method follows a well-balanced trade-off between resulting prediction accuracy and involved computational complexity. It takes advantage of the capability of a component-level dynamic model to predict the system behaviour and of the capacity of a dynamic tracking filter to adapt to the current gas turbine conditions. In a simulation study, it is shown that the proposed design can provide an accurate hot gas temperature estimation over the entire gas turbine load range, along the gas turbine lifecycle, and during fast transient manoeuvres.

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Numerical and Experimental Investigation of Secondary Flows and Influence of Air System Design on Heavy-Duty Gas Turbine Performance

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2012-68392 ◽

2012 ◽

Author(s):

Luca Bozzi ◽

Enrico D’angelo

Keyword(s):

Gas Turbine ◽

Gas Turbines ◽

Engine Performance ◽

Combined Cycle ◽

Secondary Flows ◽

Operating Conditions ◽

Heavy Duty ◽

Turbine Performance ◽

Air System ◽

Secondary Air

High turn-down operating of heavy-duty gas turbines in modern Combined Cycle Plants requires a highly efficient secondary air system to ensure the proper supply of cooling and sealing air. Thus, accurate performance prediction of secondary flows in the complete range of operating conditions is crucial. The paper gives an overview of the secondary air system of Ansaldo F-class AEx4.3A gas turbines. Focus of the work is a procedure to calculate the cooling flows, which allows investigating both the interaction between cooled rows and additional secondary flows (sealing and leakage air) and the influence on gas turbine performance. The procedure is based on a fluid-network solver modelling the engine secondary air system. Parametric curves implemented into the network model give the consumption of cooling air of blades and vanes. Performances of blade cooling systems based on different cooling technology are presented. Variations of secondary air flows in function of load and/or ambient conditions are discussed and justified. The effect of secondary air reduction is investigated in details showing the relationship between the position, along the gas path, of the upgrade and the increasing of engine performance. In particular, a section of the paper describes the application of a consistent and straightforward technique, based on an exergy analysis, to estimate the effect of major modifications to the air system on overall engine performance. A set of models for the different factors of cooling loss is presented and sample calculations are used to illustrate the splitting and magnitude of losses. Field data, referred to AE64.3A gas turbine, are used to calibrate the correlation method and to enhance the structure of the lumped-parameters network models.

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An Efficient Procedure for the Analysis of Heavy Duty Gas Turbine Secondary Flows in Different Operating Conditions

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2010-22935 ◽

2010 ◽

Author(s):

Matteo Cerutti ◽

Luca Bozzi ◽

Federico Bonzani ◽

Carlo Carcasci

Keyword(s):

Gas Turbine ◽

Gas Turbines ◽

Cooling System ◽

Secondary Flows ◽

Operating Conditions ◽

Heavy Duty ◽

Efficient Procedure ◽

Air System ◽

Secondary Air ◽

Flow Functions

Combined cycle and partial load operating of modern heavy-duty gas turbines require highly efficient secondary air systems to supply both cooling and sealing air. Accurate performance predictions are then a fundamental demand over a wide range of operability. The paper describes the development of an efficient procedure for the investigation of gas turbine secondary flows, based on an in-house made fluid network solver, written in Matlab® environment. Fast network generation and debugging are achieved thanks to Simulink® graphical interface and modular structure, allowing predictions of the whole secondary air system. A crucial aspect of such an analysis is the calculation of blade and vane cooling flows, taking into account the interaction between inner and outer extraction lines. The problem is closed thanks to ad-hoc calculated transfer functions: cooling system performances and flow functions are solved in a pre-processing phase and results correlated to influencing parameters using Response Surface Methodology (RSM) and Design of Experiments (DOE) techniques. The procedure has been proved on the secondary air system of the AE94.3A2 Ansaldo Energia gas turbine. Flow functions for the cooling system of the first stage blade, calculated by RSM and DOE techniques, are presented. Flow functions based calculation of film cooling, tip cooling and trailing edge cooling air flows is described in details.

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Development of Numerical Tools for Stator-Rotor Cavities Calculation in Heavy-Duty Gas Turbines

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2008-51268 ◽

2008 ◽

Cited By ~ 3

Author(s):

C. Bianchini ◽

R. Da Soghe ◽

B. Facchini ◽

L. Innocenti ◽

M. Micio ◽

...

Keyword(s):

Heat Transfer ◽

Gas Turbine ◽

Gas Turbines ◽

Inlet Temperature ◽

Heavy Duty ◽

One Dimensional ◽

Air System ◽

Numerical Tools ◽

Secondary Air ◽

The One

In high performance heavy-duty engines, turbine inlet temperature is considerably higher than the melting point of the metals used for turbine components e.g. nozzle guide vanes, turbine rotor blades, platforms and discs, etc. Cooling of those components is therefore essential and is achieved by diverting a few percent of the compressed air from extraction points in the compressor and passing it to the turbine through stationary ducts and over rotating shafts and discs. All those elements form the so-called secondary air system of the gas turbine, whose correct design is hence fundamental for safety, reliability and performance of the engine. Secondary air system analysis is generally performed using one dimensional calculation procedures, based correlations both for pressure losses and heat transfer coefficient evaluations. Such calculation approach, usually used in industry, takes advantages in terms of reduced computational resources. Besides, for those elements of air systems where multidimensional flow effects are not negligible and the flow field structure is highly complex, the one-dimensional–correlative modeling needs to be supported by CFD investigations. Among these elements, rotating cavities need a careful modeling in order to correctly estimate discs temperature and the minimum amount of purge air to prevent hot gas ingestion. Ansaldo Energia is facing the investigation of secondary air system of Vx4.3A gas turbine models also by using numerical tools developed by Dipartimento di Energetica “Sergio Stecco” of University of Florence. They include both a one-dimensional cavity solver and a 3D unstructured finite volume code of compressible Navier-Stokes Equation based on open source C++ Open-Foam libraries for continuum mechanics. The first numerical tool has been widely employed in simplified analysis of stator-rotor cavities and is undergoing to be integrated into a in-house lumped-parameters fluid network solver simulating the entire secondary air system. This paper is aimed at discussing some interesting results from numerical tests performed with the above discussed programs on stator-rotor cavities of a V94.3A2 gas turbine. Such numerical analysis was addressed both for better understanding the flow phenomena in the wheel space regions and for testing and verifying the experimental correlations and the calculation procedure implemented in the one-dimensional program. A detailed comparative analysis between the two different codes will be shown, both in adiabatic and heat transfer conditions.

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A System Integration Approach for Heavy-Duty Gas Turbine Upgrades Using Improved Rotor Thrust Predictions and Application of Advanced Thrust Bearing Designs

Volume 5B: Heat Transfer ◽

10.1115/gt2017-63647 ◽

2017 ◽

Author(s):

Francesco Bavassano ◽

Marco Mantero ◽

Riccardo Traverso ◽

Richard Livermore-Hardy ◽

Barry Blair

Keyword(s):

Gas Turbine ◽

Gas Turbines ◽

Thrust Bearing ◽

Load Sharing ◽

Operating Conditions ◽

Heavy Duty ◽

Original Design ◽

Axial Thrust ◽

Worst Case ◽

Lining Material

The progressive upgrading of heavy-duty gas turbines, aimed at increased performance, can ultimately introduce more onerous operating conditions, to the point that original design limits can be approached. An increased gas turbine pressure ratio together with compression and expansion line adjustments can directly affect the rotor axial thrust. Other than the individual forces acting on the rotor, a key component to be taken into account is the fluid film thrust bearing, which should assure safe and reliable operation during the worst case operating conditions. Typically, such bearings are designed with large safety margins, yet it is possible that the new and more challenging conditions require a bearing capability upgrade, especially when field retrofit needs pose additional constraints. A succession of performance upgrades have been carried out on Ansaldo Energia’s AE94.2 E-Class GT. An accurate understanding of the thrust-related phenomena proved necessary and drove improvements in the thrust bearing design along with hardware adjustments to lower the rotor thrust. This paper addresses calculations and experimental arrangements for the rotor axial thrust evaluation on the aforementioned GT and considers both the matters related to the secondary air system for the thrust generation and the mechanical/functional matters for the bearing upgrade. It is shown that issues such as uneven load sharing across the thrust bearing, or the variability of rotor thrust from engine to engine within the fleet, strongly affect the maximum thrust assessment and thus the requirements used in the process of selecting a suitable bearing. A predictive calculation method is described considering the main thrust contributions. Field experimental setups and main observations are reported. Measurements have been carried out using thermocouples and load cells placed on many of the thrust bearing pads. Moreover, the engine cavities carrying the highest and/or the most uncertain thrust share have been instrumented and characterized by pressure sensors. The development of an upgraded thrust bearing is finally depicted through the main issues addressed, such as improved thrust pad lining material, increased load sharing efficiency and enlarged thrust bearing active surface area. Waukesha Bearings test results on the upgraded lining material, a high-tin aluminium alloy are reported as well. A multidisciplinary approach is presented as necessary to manage the crucial challenge of improving the thrust balancing system, especially in the case of a formerly designed engine which receives a powerful upgrade.

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