Gas Turbine Combustion Chamber Research Articles

Advances in effusive cooling techniques of gas turbines

Gas turbine combustion chambers and turbine blades require better cooling techniques to cope with the increase in operating temperatures with each new engine model. Current gas turbine inlet temperatures are approaching 2000 K. Transpiration-cooled components have proved an effective way to achieve high temperatures and erosion resistance for gas turbines operating in aggressive environments, though there is a shortage of durable and proven technical solutions. Effusion cooling, on the other hand, is a relatively simple and more reliable technique offering a continuous coverage of cooling air over the component’s hot surfaces. This paper presents a numerical model suitable to design the geometric features of effusive cooling systems of gas turbine hot components, and to evaluate their thermo-fluid-dynamic characteristics. The model has been developed specifically with the aim to show the potential advantages deriving from the adoption of the new Poroform ® technology. According to this technology the design of the distributions of the diameter and density of holes on the cooled surface allows complete freedom for the thermo-mechanical optimization of the cooled component, with a view to reducing the metal’s working temperature and achieving isothermal conditions for large blade areas. In this paper the diameter, density and spacing of the holes, the adiabatic film efficiency and the coolant air consumption of a first stage gas turbine effusion cooled blade are extensively discussed to highlight the system cooling capacity. The results of two cooling solutions for a first-stage gas turbine blade are presented, i.e. the thermo-fluid-dynamic optimized design and one possible manufacturing-oriented optimized design of the cooled component.

Comparison of LES, RANS and experiments in an aeronautical gas turbine combustion chamber

Although Large Eddy Simulations (LES) have demonstrated their potential in simple academic combustion chambers, their application to real gas turbine chambers requires specific developments and validations. In this study, three specific aspects of such chambers are discussed: multiple inlets, multi-perforated plates and film cooling. LES are used in an industry-like chamber and results are compared with predictions provided by Reynolds Averaged Navier–Stokes (RANS) simulations and experimental measurements. Multi-perforation is handled using a simplified effusive wall law while film cooling makes use of low resolution influx conditions (‘coarse LES’). Experimental results are well reproduced and qualitatively improved when compared to RANS predictions. LES results underline the potential of the approach for industrial use.

Large-Eddy Simulation of Realistic Gas Turbine Combustors

Large-eddy simulation is a promising technique for accurate prediction of reacting multiphase flows in practical gas-turbine combustion chambers involving complex physical phenomena of turbulent mixing and combustion dynamics. Development of advanced models for liquid fuel atomization, droplet evaporation, droplet deformation and drag, and turbulent combustion is discussed specifically for gas-turbine applications. The nondissipative, yet robust numerical scheme for arbitrary shaped unstructured grids developed by Mahesh et al. (Mahesh, K., Constantinescu, G., and Moin, P., New Time-Accurate Finite-Volume Fractional-Step Algorithm for Prediction of Turbulent Flows on Unstructured Hybrid Meshes, Journal of Computational Physics, Vol. 197, No. 1, 2004, pp. 215-240) is modified to account for density variations due to chemical reactions. A systematic validation and verification study of the individual spray models and the numerical scheme is performed in canonical and complex combustor geometries. Finally, a multiscale, multi physics, turbulent reacting flow simulation in a real gas-turbine combustor is performed to assess the predictive capability of the solver.

An expert system concept for diagnosis and monitoring of gas turbine combustion chambers

In this paper, the main principles of operation, the conceptual design and the development of an expert system for fault diagnosis and monitoring of gas turbine combustion chambers are presented. The concept of the gas turbine chamber expert system is based on the monitoring of the spatial and temporal distribution of the heat flux inside the combustion chamber and the simultaneous comparison of respective readings of diagnostic variables with values obtained through numerical model simulation of different situations which lead to the malfunction of combustion chamber and deterioration of its performance. The demonstration of the expert system will be performed at the VTI (All Union Energy Institute, Russia) gas turbine combustion chamber test facility.

Numerical Investigation of Gas Turbine Combustion Chamber Flows

Numerical Investigation of Gas Turbine Combustion Chamber Flows

STUDY OF FLAME STABILIZATION IN A SWIRLING COMBUSTOR USING A NEW FLAMELET FORMULATION

ABSTRACT The dynamics in a swirl-stabilized flame is studied using large eddy simulation (LES). We account for the effect of turbulence on the flame through a model based on a filtered flamelet technique. The model provides a consistent and robust reaction-diffusion expression for simulating the correct propagation of premixed flames. The filtered flamelet formulation has been implemented into a high-order-accurate LES code and used to study the flame stabilization and the combustion dynamics in a gas-turbine combustion chamber. The effects of inlet boundary conditions, in terms of velocity and equivalence ratio radial profiles, have been studied. The flow is found to be very sensitive to small changes in terms of flame shapes and anchoring position. The sensitivity of the results to the subgrid-scale flame thickness has also been investigated. The influence on the flame position is not significant. However, a too-large subgrid-scale flame thickness leads to different flame dynamics.

Prediction of temperature front in a gas turbine combustion chamber

Numerical computation has been applied to investigate the temperature field in a gas turbine combustion chamber. The simulation assumed that pressure imbalance conditions of air flow between primary and secondary inlets occur. The combustion chamber under study is part of a 70 MW gas turbine from an operating combined cycle power plant. The combustion was simulated with normal fuel–air flow rate assuming stoichiometric conditions. Under these conditions characteristic temperature and pressure fields were obtained provided equity of boundary conditions at air inlets applies. However, with pressure distribution imbalances of the order of 3 kPa between primary and secondary air inlets, excessive heating in regions other than the combustion chamber core were obtained. Over heating in these regions helped to explain what was observed to produce permanent damage to auxiliary equipment surrounding the combustion chamber core, like the cross flame pipes. It is observed that high temperatures which normally develop in the central region of the combustion chamber may reach other surrounding upstream regions by modifying slightly the air pressure. Microscope scanning of the damaged pipes confirmed that the material was exposed to high temperatures such as predicted through the numerical computation.

Flamelet Modeling of Pollutant Formation in a Gas Turbine Combustion Chamber Using Detailed Chemistry for a Kerosene Model Fuel

Combustion and pollutant formation in a gas turbine combustion chamber is investigated numerically using the Eulerian particle flamelet model. The code solving the unsteady flamelet equations is coupled to an unstructured computational fluid dynamics (CFD) code providing solutions for the flow and mixture field from which the flamelet parameters can be extracted. Flamelets are initialized in the fuel-rich region close to the fuel injectors of the combustor. They are represented by marker particles that are convected through the flow field. Each flamelet takes a different pathway through the combustor, leading to different histories for the flamelet parameters. Equations for the probability of finding a flamelet at a certain position and time are additionally solved in the CFD code. To model the chemical properties of kerosene, a detailed reaction mechanism for a mixture of n-decane and 1,2,4-trimethylbenzene is used. It includes a detailed NOx submechanism and the buildup of polycyclic aromatic hydrocarbons up to four aromatic rings. The kinetically based soot model describes the formation of soot particles by inception, further growth by coagulation, and condensation as well as surface growth and oxidation. Simulation results are compared to experimental data obtained on a high-pressure rig. The influence of the model on pollutant formation is shown, and the effect of the number of flamelets on the model is investigated.

04/02011 Technical, economic and environmental potential of cofiring of biomass in natural gas fired turbines and combined cycles: Zwart, R. ECN-R [Report], 2003, 1–8

In this paper, multivariant simulation calculations are performed for the following natural-gas fired combined heat-and-power plants with gas turbines: (1) a gas-steam combined heat-and-power plant with an extraction-condensing steam turbine, and (2) a gas-steam combined heat-and-power plant with a back-pressure steam-turbine. For these systems, mathematical models of the behaviours of their basic elements, such as: the block of the gas turbine (compressor, combustion chamber and gas turbine), heat-recovery steam generator and steam-turbine cycle were developed. On the basis of elaborate mathematical models, a computer program performed multivariant simulation calculations. For each variant, the following factors were calculated for particular types of combined heat-and-power plants: energy efficiency, efficiency of electric-energy generation, cogeneration index and cogeneration factor.

Exergy analysis of the recuperative auto thermal reforming (R-ATR) and recuperative reforming (R-REF) power cycles with CO 2 removal

Two relatively innovative gas turbine (GT) based power cycles with high CO 2 removal potential have been proposed and discussed in terms of exergy analysis. Fuel decarbonisation is applied by the means of auto thermal reforming (R-ATR) and simple reforming (R-REF), in order to convert the primary natural gas into a highly H 2 and CO 2 concentrated fuel. Thus, CO 2 is captured with amine chemical absorption into a specific unit and, finally, the decarbonised fuel is sent to the GT combustion chamber. No bottoming steam cycle is included, which should promote the size flexibility of the powerplant. The heat content of GT exhausts is employed partially to sustain the endothermic reforming reactions and partially for cycle recuperation. Moreover, the possibility of steam blade cooling has been investigated. The efficiency is optimised at low pressure ratios (7–10) in the steam cooled R-ATR, whereas higher values have been found in air cooled version (16–17). Generally, the R-ATR solution shows higher efficiency levels, mainly due to the reduced combustion chamber and CO 2 capture exergy destruction and higher cycle recuperation degree. The exergy analysis showed a relatively limited influence of combustion chamber losses on the primary fuel exergy input (20–23%). The relative loss of CO 2 removal unit is limited as well (5–7%) when compared with values of semi-closed GT configurations. The exergy destruction of R-ATR and R-REF CO 2 removal sections is greatly reduced if steam blade cooling is adopted. Generally, all the proposed cycles showed satisfactory values of efficiency (43–46% under optimised conditions) taking into account that they do not involve combined power plants.

On the Use of Helmholtz Resonators for Damping Acoustic Pulsations in Industrial Gas Turbines

In this work, the application of Helmholtz resonators for damping low-frequency pulsations in gas turbine combustion chambers is discussed. We present a nonlinear model for predicting the acoustic response of resonators including the effect of purging air. Atmospheric experiments are used to validate the model, which is employed to design a resonator arrangement for damping low-frequency pulsations in an ALSTOM GT11N2 gas turbine. The predicted damper impedances are used as the boundary condition in the three-dimensional analysis of the combustion chamber. The suggested arrangement leads to a significant extension of the low-pulsation operating regime of the engine.

Combined cycle power plant with integrated low temperature heat (LOTHECO)

The major driver to enhance the efficiency of the simple gas turbine cycle has been the increase in process conditions through advancements in materials and cooling methods. Thermodynamic cycle developments or cycle integration are among the possible ways to further enhance performance. The current paper presents the possibilities and advantages from the LOTHECO natural gas-fired combined cycle concept. In the LOTHECO cycle, low-temperature waste heat or solar heat is used for the evaporation of injected water droplets in the compressed air entering the gas turbine's combustion chamber. Following a description of this innovative cycle, its advantages are demonstrated by comparison between different gas turbine power generation systems for small and large-scale applications, including thermodynamic and economic analysis. A commercial gas turbine (ALSTOM GT10C) has been selected and computed with the heat mass balance program ENBIPRO. The results from the energy analysis are presented and the features of each concept are discussed. In addition, the exergy analysis provides information on the irreversibilities of each process and suggested improvements. Finally, the economic analysis reveals that the combined cycle plant with a heavy-duty gas turbine is the most efficient and economic way to produce electricity at base load. However, on a smaller scale, innovative designs, such as the LOTHECO concept, are required to reach the same level of performance at feasible costs.

Energy analysis of technological systems of natural gas fired combined heat-and-power plants

In this paper, multivariant simulation calculations are performed for the following natural-gas fired combined heat-and-power plants with gas turbines: (1) a gas-steam combined heat-and-power plant with an extraction-condensing steam turbine, and (2) a gas-steam combined heat-and-power plant with a back-pressure steam-turbine. For these systems, mathematical models of the behaviours of their basic elements, such as: the block of the gas turbine (compressor, combustion chamber and gas turbine), heat-recovery steam generator and steam-turbine cycle were developed. On the basis of elaborate mathematical models, a computer program performed multivariant simulation calculations. For each variant, the following factors were calculated for particular types of combined heat-and-power plants: energy efficiency, efficiency of electric-energy generation, cogeneration index and cogeneration factor.

LES of a Confined Configuration using Oscillating Inflow Conditions

AbstractIn actual turbulent flow problems, in particular in gas turbine combustion chambers, flows are three dimensional, recirculating and turbulent in confined and complex geometries. Instationarities due to turbulence, combustion instabilities and oscillating inflow conditions require a highly time and spatial resolving procedure. 3D Large Eddy Simulations (LES) are therefore used in this work to study two confined coaxial air jets with oscillating velocity inflow conditions. The influences of the inflow, in particular frequency (f = 0 ÷ 1600 [Hz]) and amplitude, on the velocity are analysed.

Analysis of the Effects of Water Injection on the Performance of a Gas Turbine

The effect of water injection in the combustion chamber of an industrial gas turbine is studied by means of analytic relations. Equations for the estimation of changes in the main performance parameters are provided. The relations are derived on the basis of an order of magnitude analysis and taking into account variation of gas properties due to water injection as well as changes in the interrelation of component performance parameters. It is shown that water/fuel ratio is the main parameter on which performance deviations depend. Data from the performance testing of an industrial gas turbine are used to check the validity of the proposed relations. The comparison of the predictions to the test data shows that the mechanisms of performance deviations are well modeled by the analysis presented.

Large Eddy Simulation of turbulent combustion processes

The application of Large Eddy Simulation to Turbulent Combusting flows is described and results are presented for a turbulent hydrogen-air jet flame and for a model can-type gas turbine Combustion chamber. In both cases the results are in good agreement with measurements. For the hydrogen flame and in contrast to the results of other approaches the profiles of all quantities and the rate of spread of the jet were all accurately reproduced by the computations without any modification to the model constants being necessary.

Fiber-coatings for fiber-reinforced mullite/mullite composites

Mullite-based fiber-reinforced composites are favorite candidates for the application in combustion chambers of gas turbines. The application requires damage tolerance, temperature and oxidation-resistance at high temperatures (>1200°C) over long terms. In order to realize crack deflection and fiber pull-out, an interphase coating of the mullite fibers (Nextel 720) is necessary to obtain a weak bonding between fibers and matrix. Two systems of interphases produced by CVD were described. The first system is a carbon/metal-oxide double layer (C/ZrO 2 , C/Al 2 O 3 ). Properties of the resulting composites after heat-treatment (1300°C, 1000 h) under cyclic and continuous heating conditions were described. The second system is the codeposition of La 2 O 3 and Al 2 O 3 on the fibers. After heat-treatment at 1300°C lanthanum hexaluminate (LaAl 11 O 18 ) with a magneto plumbite structure containing sliding planes should be formed.

Free radical imaging techniques applied to hydrocarbon flames diagnosis

This paper evaluates the utilization of free radical chemiluminescence imaging and tomographic reconstruction techniques to assess advanced information on reacting flows. Two different laboratory flow configurations were analyzed, including unconfined non-premixed jet flame measurements to evaluate flame fuel/air mixing patterns at the burner-port of a typical glass-furnace burner. The second case characterized the reaction zone of premixed flames within gas turbine combustion chambers, based on a laboratory scale model of a lean prevaporized premixed (LPP) combustion chamber. The analysis shows that advanced imaging diagnosis can provide new information on the characterization of flame mixing and reacting phenomena. The utilization of local C2 and CH chemiluminescence can assess useful information on the quality of the combustion process, which can be used to improve the design of practical combustors.

Correlation of high-temperature properties and interphase characteristics in oxide/oxide fibre-reinforced composites

Oxide/oxide fibre-reinforced composites are favorite candidates as liners for thermal protection of combustion chambers in gas turbines. This application requires damage tolerance over long terms at high temperatures. Damage tolerance in ceramic composites is achieved by energy dissipation e.g. due to fibre debonding and sliding. On the other hand, between the fibre and matrix, a good load transfer is requested to obtain high strength. Fibre/matrix interaction can be controlled by introducing interphases between the fibre and matrix. Mullite based fibre-reinforced composites having fibres with CVD-processed carbon (fugitive)-single layer and carbon (fugitive)/A12O3-double layer coatings were produced. Changes in microstructure and mechanical behavior due to constant and cyclic thermal loading were investigated. The oxide layer behind a carbon (fugitive) layer was found to increase the strength of the composite and maintain damage tolerance in contrast to only fugitive layer. Under cyclic heat treatment, composites showed significantly better damage tolerance than under constant thermal loading.

246PIVによる燃焼器内流れ場の解析

The flow field in a gas turbine combustion chamber was investigated experimentally by using a high-resolution PIV system. The shedding of vortices around the flamer holder in the combustion chamber was visualized quantitatively from the PIV measurement results. The PIV measurement results were also compared with LDV data and Large Eddy Simulation (LES) results to verify the present investigation.