Gas Turbine Operating Conditions Research Articles

Computational Analysis of Surface Curvature Effect on Mist Film-Cooling Performance

Air-film cooling has been widely employed to cool gas turbine hot components, such as combustor liners, combustor transition pieces, turbine vanes, and blades. Studies with flat surfaces show that significant enhancement of air-film cooling can be achieved by injecting water droplets with diameters of 5–10 μm into the coolant airflow. The mist/air-film cooling on curved surfaces needs to be studied further. Numerical simulation is adopted to investigate the curvature effect on mist/air-film cooling, specifically the film cooling near the leading edge and on the curved surfaces. Water droplets are injected as dispersed phase into the coolant air and thus exchange mass, momentum, and energy with the airflow. Simulations are conducted for both 2D and 3D settings at low laboratory and high operating conditions. With a nominal blowing ratio of 1.33, air-only adiabatic film-cooling effectiveness on the curved surface is lower than on a flat surface. The concave (pressure) surface has a better cooling effectiveness than the convex (suction) surface, and the leading-edge film cooling has the lowest performance due to the main flow impinging against the coolant injection. By adding 2% (weight) mist, film-cooling effectiveness can be enhanced approximately 40% at the leading edge, 60% on the concave surface, and 30% on the convex surface. The leading edge film cooling can be significantly affected by changing of the incident angle due to startup or part-load operation. The film cooling coverage could switch from the suction side to the pressure side and leave the surface of the other part unprotected by the cooling film. Under real gas turbine operating conditions at high temperature, pressure, and velocity, mist-cooling enhancement could reach up to 20% and provide a wall cooling of approximately 180 K.

Mist film cooling simulation at gas turbine operating conditions

Air film cooling has been successfully used to cool gas turbine hot sections for the last half century. A promising technology is proposed to enhance air film cooling with water mist injection. Numerical simulations have shown that injecting a small amount of water droplets into the cooling air improves film-cooling performance significantly. However, previous studies were conducted at conditions of low Reynolds number, temperature, and pressure to allow comparisons with experimental data. As a continuous effort to develop a realistic mist film cooling scheme, this paper focuses on simulating mist film cooling under typical gas turbine operating conditions of high temperature and pressure. The mainstream flow is at 15 atm with a temperature of 1561 K. Both 2D and 3D cases are considered with different hole geometries on a flat surface, including a 2D slot, a simple round hole, a compound-angle hole, and fan-shaped holes. The results show that 10–20% mist (based on the coolant mass flow rate) achieves 5–10% cooling enhancement and provides an additional 30–68 K adiabatic wall temperature reduction. Uniform droplets of 5–20 μm are used. The droplet trajectories indicate the droplets tend to move away from the wall, which results in a lower cooling enhancement than under low pressure and temperature conditions. The commercial software Fluent is adopted in this study, and the standard k– ε model with enhanced wall treatment is adopted as the turbulence model.

Gas Turbine Combustion Technology Reducing Both Fuel-NOx and Thermal-NOx Emissions for Oxygen-Blown IGCC With Hot/Dry Synthetic Gas Cleanup

Abstract In order to improve the thermal efficiency of the oxygen-blown integrated gasification combined cycle (IGCC) and to meet stricter environmental restrictions among cost-effective options, a hot/dry synthetic gas cleanup is one of the most hopeful choices. The flame temperature of medium-Btu gasified fuel used in this system is high so that NOx formation by nitrogen fixation results to increase significantly. Additionally, the gasified fuel contains nitrogenous compound, as ammonia, and it produces nitrogen oxides, the fuel NOx, in the case of employing the hot/dry gas cleanup. Low NOx combustion technology to reduce both fuel-NOx and thermal-NOx emissions has been required to protect the environment and ensure low cost operations for all kinds of oxygen-blown IGCC. In this paper, we have demonstrated the effectiveness of two-stage combustion and nitrogen injection techniques, and also showed engineering guidelines for the low-NOx combustor design of oxygen-blown gasified, medium-Btu fuels. The main results obtained are as follows: (1) Based on the basic combustion tests using a small diffusion burner, we clarified that the equivalence ratio at the primary combustion zone has to be adjusted according to the fuel conditions, such as methane concentration, CO∕H2 molar ratio, and calorific values of gasified fuels in the case of the two-stage combustion method for reducing fuel-NOx emissions. (2) From the combustion tests of the medium-Btu fueled combustor, two-stage combustion with nitrogen direct injection into the combustor results in reductions of NOx emissions to 34ppm (corrected at 16% O2) or less under the gas turbine operational conditions of 25% load or higher for IGCC in the case where the gasified fuel contains 0.1% methane and 500ppm of ammonia. Through nitrogen direct injection, the thermal efficiency of the plant improved by approximately 0.3% (absolute), compared with the case where nitrogen was premixed with gasified fuel. The CO emission concentration decreased drastically, as low as 20ppm, or combustion efficiency was kept higher than 99.9%. The above results have shown that a two-stage combustion method with nitrogen direct injection is very effective for reducing both fuel-NOx and thermal-NOx emissions at once in IGCC, and it shows the bright prospects for low NOx and stable combustion technology of medium-Btu fuel.

The effects of water addition on pollutant formation from LPP gas turbine combustors

Lean premixed prevapourised (LPP) combustion of liquid fuels with steam dilution and under high pressure conditions is numerically assessed. A detailed chemical kinetic mechanism for n-heptane and iso-octane combustion is assembled on the basis of existing detailed mechanisms and validated against experimental data from laminar premixed flames. A computational singular perturbation (CSP) method is then used to analyse and reduce the mechanism to one global step. This reduced mechanism forms the basis for the reaction progress variable (RPV) approach from the CFI combustion model. The obtained one-step combustion mechanism is validated by comparing the CFI model results, stored in a thermochemical database as a function of the RPV, with detailed laminar flame solutions in reaction progress variable space. The single step global mechanism is then used to assess, under LPP gas turbine operating conditions, the influence of dilution and fuel equivalence ratio on iso-octane and n-heptane combustion. The above formulation is shown to accurately capture NO and CO emission trends.

Experimental and Kinetic Modeling of Kerosene-Type Fuels at Gas Turbine Operating Conditions

Experimental and kinetic modeling of kerosene-type fuels is reported in the present work with special emphasis on the low-temperature oxidation phenomenon relevant to gas turbine premixing conditions. Experiments were performed in an atmospheric pressure, tubular flow reactor to measure ignition delay time of kerosene (fuel–oil No. 1) in order to study the premature autoignition of liquid fuels at gas turbine premixing conditions. The experimental results indicate that the ignition delay time decreases exponentially with the equivalence ratio at fuel-lean conditions. However, for very high equivalence ratios (>2), the ignition delay time approaches an asymptotic value. Equivalence ratio fluctuations in the premixer can create conditions conducive for autoignition of fuel in the premixer, as the gas turbines generally operate under lean conditions during premixed prevaporized combustion. Ignition delay time measurements of stoichiometric fuel–oil No. 1∕air mixture at 1 atm were comparable with that of kerosene type Jet-A fuel available in the literature. A detailed kerosene mechanism with approximately 1400 reactions of 550 species is developed using a surrogate mixture of n-decane, n-propylcyclohexane, n-propylbenzene, and decene to represent the major chemical constituents of kerosene, namely n-alkanes, cyclo-alkanes, aromatics, and olefins, respectively. As the major portion of kerosene-type fuels consists of alkanes, which are relatively more reactive at low temperatures, a detailed kinetic mechanism is developed for n-decane oxidation including low temperature reaction kinetics. With the objective of achieving a more comprehensive kinetic model for n-decane, the mechanism is validated against target data for a wide range of experimental conditions available in the literature. The data include shock tube ignition delay time measurements, jet-stirred reactor reactivity profiles, and plug-flow reactor species time–history profiles. The kerosene model predictions agree fairly well with the ignition delay time measurements obtained in the present work as well as the data available in the literature for Jet A. The kerosene model was able to reproduce the low-temperature preignition reactivity profile of JP-8 obtained in a flow reactor at 12 atm. Also, the kerosene mechanism predicts the species reactivity profiles of Jet A-1 obtained in a jet-stirred reactor fairly well.

Interaction between struts and swirl flow in gas turbine exhaust diffusers

The increasing use of gas turbines in combined cycle power plants together with the high amount of kinetic energy in modern gas turbine exhaust flows focuses attention on the design of gas turbine diffusers as the connecting part between the Brayton/Joule and the Rankine parts of the combined cycle. A scale model of a typical gas turbine exhaust diffuser is investigated experimentally. The test rig consists of a radial type, variable swirl generator which provides the exhaust flow corresponding to different gas turbine operating conditions. Static pressure measurements are carried out along the outer diffuser walls and along the hub of the annular part and along the centerline of the conical diffuser. Velocity distributions at several axial positions in the annular and conical diffuser have been measured using a Laser Doppler Velocimeter (LDV). Pressure recovery coefficients and velocity profiles are depicted as a function of diffuser length for several combinations of swirl strength, tip flow and strut geometries. The diffuser without struts achieved a higher pressure recovery than the diffuser with struts at all swirl angle settings. The diffuser with cylindrical struts achieved a higher pressure recovery than the diffuser with profiled struts at all swirl angle settings. Inlet flows with swirl angles over 18° affected the pressure recovery negatively for all strut configurations.

Catalytic methane combustion on Pd-Pt-La catalysts and their surface models

Catalytic combustion of methane has been studied over a library of Pd, Pt, and La in mono-, bi-, and tri-element system supported on γ-Al2O3 washcoated ceramic monolith using an eight-tubular flow reactor. Simulated operating conditions of a small-size gas turbine were employed to investigate the combustion activity. Lead formulations from an initial high throughput screening were classified into two categories: Pd-Pt bi-element catalysts, and Pd-Pt-La tri-element catalysts with relatively constant 20% Pd (equivalent to 1% Pd of 5% total elemental loading). The substitution of Pd by Pt, while maintaining 5% total loading, was observed to improve the combustion activity as expected due to the co-existence of PdO and Pd–Pt alloy on the catalytic surface. However, its combustion activity was only slightly decreased when Pt was further substituted by La with relatively fixed 20% Pd loading due to the metal dilution by La. Nevertheless, the catalyst with Pd and Pt in equivalent amount with three times of La dilution (Pd:Pt:La=1:1:3) was suggested to be the best formula not only due to its high combustion activity at even low temperatures, but also the reduction of noble metal usage.

Heat transfer in rotating channel with open cell porous aluminium foam

The convective heat transfer of pressurized airflow in a radially rotating serpentine channel inside porous aluminum material is examined experimentally. The most important governing parameters are the Prandtl number, the Reynolds number for forced convection, the rotation number for the Coriolis force-induced cross stream secondary flow and the Grashof number for natural convection. This work maintains the parameters of the test rig at approximately the values of those in a real engine, to simulate the operating conditions of a real gas turbine. The local heat transfer rates for radially rotating serpentine channels with porous aluminum foams were measured and compared with those of staggered half-V ribbed and smooth walls in previous literature. This paper investigates the heat transfer capability of porous aluminum foams in rotating channels

Medium-Btu Fueled Gas Turbine Combustor for Use in LGCC (1st Report, Low NOx Combustion Method Using Nitrogen Injection

The flame temperature of oxygen-blown medium-Btu gasified coal fuel is higher and so NOx production from nitrogen fixation is expected to increase significantly. We have started to develop low NOx and stable combustion technology using medium-Btu gasified coal fuel. In this paper, based on the fundamental combustion tests using the small diffusion burner, we have through out the new combustion technique which injects nitrogen directly into the high temperature region in the combustor for low NOx and stable combustion. A gas turbine combustor with a swirling nitrogen injection function designed with new combustion technique was constructed and the performance of this combustor was evaluated under atmospheric pressure conditions and operational conditions. From the test results, it is confirmed that : (1) This new combustion technique with nitrogen direct injection results in a significant reduction in NOx production from nitrogen fixation, 8 ppm or less (corrected at 16% O2) in the gas turbine operational conditions for IGCC ; and (2) CO emission concentration decreased to a significant level, as low as 10 ppm, under operational conditions, or combustion efficiency was almost always 100%. From the above results, this combustor has an excellent performance under the operational conditions in IGCC, and bright prospects of low NOx and stable combustion technology of the medium calorific fuel are obtained.

A Method to Estimate Service Boundary Conditions for Hot-Gas-Path Components of a Gas Turbine by Using a Design of Experiments. 1st Report. Residual Life Assessment Using an Inverse Analysis.

Gas turbine operating conditions are severe, especially for hot-gas-path components. The components are subjected to the conditions of thermal load, dynamic pressure oscillation, and environmental attack due to hot gas. However, the service conditions are complex and difficult to determine. To improve the accuracy of the life assessment of such components, an analytical method for estimating the service boundary conditions for these components has been developed. This method consists of FEA (finite element analysis), design of experiments, and metallurgical inspection of actual machine components. The FEAs varied with boundary conditions are analyzed using an orthogonal array. In each analysis, difference between results of an FEA and results of the metallurgical inspection are estimated. The model is modified to reduce the difference by using analyses of variance. The modified model is applied to damage analyses and life assessment. The method was applied to a gas turbine blade and the good agreement between the analysis results and the inspection data confirmed the validity of the method.

Numerical study of spray dispersion in a premixing chamber for Low-NOx engines

The present work describes a numerical study of a confined two-phase flow under high-pressure conditions, typical of gas turbine combustors. An Eulerian frame was used for the gas phase together with a Lagrangian approach to describe the dispersed phase. The computational method was extended to high-pressure environments, which are more representative of the practical gas turbine operating conditions. The results are compared with experimental data, and revealed the ability of the model to increase the knowledge of the turbulent dispersion phenomena for this type of practical conditions (high pressure and confined flow).

Heat Transfer of Compressed Air Flow in a Spanwise Rotating Four-Pass Serpentine Channel

Convective heat transfer of compressed air flow in a radially rotating four-pass serpentine channel is investigated experimentally in the present study. The coolant air was compressed at 5 atmospheric pressure to achieve a high rotation number and Reynolds number simultaneously. The main governing parameters are the Prandtl number, the Reynolds number for forced convection, and the rotation number for the Coriolis-force-induced cross-stream secondary flow and the Grashof number for centrifugal buoyancy. To simulate the operating conditions of a real gas turbine, the present study kept the parameters in the test rig approximately the same as those in a real engine. The air in the present serpentine channel was pressurized to increase the air density for making up the low rotational speed in the experiment. The air flow was also cooled to increase the density ratio before entering the rotating ducts. Consequently, the order of magnitude of Grashof number in the present study was the same as that in real operating conditions. The local heat transfer rate on the walls of the four-pass serpentine channel are correlated and compared with that in the existing literature.

Numerical simulation of the two-dimensional flow in high pressure catalytic combustor for gas turbine

The objective of this paper is modeling the mechanism of high pressure and high temperature catalytic oxidation of natural gas, or methane. The model is two-dimensional steady-state, and includes axial and radial convection and diffusion of mass, momentum and energy, as well as homogeneous (gas phase) and heterogeneous (gas surface) single step irreversible chemical reactions within a catalyst channel. Experimental investigations were also made of natural gas, or methane combustion in the presence of Mn-substituted hexaaluminate catalysts. Axial profiles of catalyst wall temperature, and gas temperature and gas composition for a range of gas turbine combustor operating conditions have been obtained for comparison with and development of a computer model of catalytic combustion. Numerical calculation results for atmospheric pressure agree well with experimental data. The calculations have been extended for high pressure (10 atm) operating conditions of gas turbine.

Study on catalytically ignited premixed combustion

This paper describes some of the major issues related to catalytically ignited premixed combustion and the effect of pressure and velocity on the mass transfer of the catalytic reaction. The first issue is concerned with partial burning of the fuel air mixture on the catalyst surface prompting gas phase combustion to take place downstream of the catalyst layer. The latter part of this paper deals with the potential for reduced combustion efficiency from a mass transfer perspective, when going from atmospheric testing conditions to actual high pressure gas turbine operating conditions.

Development of a Liquid-Fueled, Lean-Premixed Gas Turbine Combustor

Development of a lean-premixed, liquid-fueled combustor is in progress to achieve ultra-low NOx emissions at typical gas turbine operating conditions. A filming fuel injector design was tested on a bench scale can combustor to evaluate critical design and operating parameters for low-emissions performance. Testing was completed using No. 2 diesel. Key design variables tested include premixing length, swirler angle, injector centerbody diameter, and reduced liner cooling. NOx emissions below 12 ppmv at 9 bar pressure were measured. Corresponding CO levels were 50 ppmv. An optimized injector design was fabricated for testing in a three injector sector of an annular combustor. Operating parameters and test results are discussed in the paper.

Analytical Investigation on the Cooling Performance of a Return-Flow Gaseous-Gooled Gas Turbine Rotor Blade.

The cooling characteristics are theoretically investigated in the case of a return-flow type of gaseous-cooled gas turbine rotor blade. The blade model is intended for the application of a closed-circuit gaseous coolant system. An analytical method based on one-dimensional fluid flow and heat transfer is proposed for calculating temperatures of the blade metal, incoming coolant, and outgoing coolant at various spanwise positions, and also pressure losses of the coolant at each cooling passage. The numerical analysis is carried out for a steam-cooled rotating blade under reasonably selected gas turbine operating conditions. In comparing both cooling characteristics of the blade with and without rotation, it is shown that the pumping effect on the cooling performance and pressure loss is relativery small in this study.

Large chord turbine cascade testing at engine Mach and Reynolds numbers

A technique is presented for producing a flow through a linear cascade of turbine blades of large chord which gives the pressure distribution around a blade the same as that obtained in an infinite cascade for Mach and Reynolds numbers typical of gas turbine operating conditions. Results of experiments with a cascade of three blades of large chord are compared with results from a cascade of nine blades of smaller chord to confirm the validity of the technique. Experiments are performed on the large-chord cascade to examine surface phenomena with high spatial resolution. Boundary layer scales are also increased and profiles on both suction and pressure surfaces of the blade are obtained.

Creep-fatigue phenomena and creep-fatigue damage in CrMoV steel forgings: Kadoya, Y., Goto, T., Kawamoto, K. and Sugai, K.J. Soc. Mater. Sci., Japan May 1990 39, (440), 516–521 (in Japanese)

Gas turbine blades are exposed to high-temperature degradation environments due to flames and mechanical loads as a results of high-speed rotation during operation. In addition, blades are exposed to thermo-mechanical fatigue due to frequent start and shutdown. Therefore, it is necessary to evaluate the lifetime of blade materials.In this study, the TMF life of a Ni-base superalloy applied to gas turbine blade was predicted based on LCF and TMF test results. The LCF tests were conducted under various strain ranges based on gas turbine operating conditions. In addition, IP (in-phase) and OP (out of-phase) TMF tests were conducted under various strain ranges.Finally, a fatigue life prediction model was drawn from the LCF and TMF test results. The correlation between the LCF and TMF test results was also evaluated with respect to fatigue life.

Hot Salt Stress Corrosion Cracking of a Titanium Alloy: The Phenomenon in View of Aero Gas Turbine Operating Conditions

Hot Salt Stress Corrosion Cracking of a Titanium Alloy: The Phenomenon in View of Aero Gas Turbine Operating Conditions

Casing Vibration and Gas Turbine Operating Conditions

The results from an experimental investigation of the compressor casing vibration of an industrial gas turbine are presented. It is demonstrated that statistical properties of acceleration signals can be linked with engine operating conditions. The power content of such signals is dominated by contributions originating from the stages of the compressor, while the contribution of the shaft excitation is secondary. Using nonparametric identification methods, accelerometer outputs are correlated to unsteady pressure measurements taken by fast response transducers at the inner surface of the compressor casing. The transfer functions allow reconstruction of unsteady pressure signal features from the accelerometer readings. A possibility is thus provided for “seeing” the unsteady pressure field of the rotor blades without actually penetrating through the casing, but by simply observing its external surface vibrations.