Gas Turbine Applications Research Articles

Development and Assessment of a Miniaturized Test Rig for Evaluating Noise Reduction in Serrated Blades Under Turbulent Flow Conditions

The implementation of serrated stator blades in axial compressor and fan stages offers significant advantages, such as enhanced performance and reduced noise levels, making it a practical and cost-effective solution. This study explores the impact of serrated blade design on noise reduction under specific engine operating conditions. A small-scale experimental test setup with a turbulence-inducing grid was designed for testing multiple grid sizes in order to identify the most promising configuration which replicates rotor–stator interaction. Numerical simulations and early experimental tests in an anechoic chamber using a four-blade cascade configuration at an airflow speed of 50 m/s revealed a small but notable noise reduction in the 1–6 kHz range for a partially matched grid–blade geometry. Serrated blades demonstrated an overall sound pressure level reduction of 1.5 dB and up to 12 dB in tonal noise, highlighting the potential of cascade configurations to improve acoustic performance in gas turbine applications.

Design of a Thermal Performance Test Equipment for a High-Temperature and High-Pressure Heat Exchanger in an Aero-Engine

For next-generation power systems, particularly aero-gas turbine engines, ultra-light and highly efficient heat exchangers are considered key enabling technologies for realizing advanced cycles. Consequently, the development of efficient and accurate aero-engine heat exchanger test equipment is essential to support future gas turbine heat exchanger advancements. This paper presents the development of a high-pressure and high-temperature (HPHT) heat exchanger test facility designed for aero-engine heat exchangers. The maximum temperature and pressure of the test facility were configured to simulate the conditions of the last-stage compressor of a large civil engine, specifically 1000 K and 5.5 MPa. These conditions were achieved using multiple electric heater systems in conjunction with an air compression system consisting of three turbo compressor units and a reciprocating compressor unit. A commissioning test was conducted using a compact tubular heat exchanger, and the results indicate that the test facility operates stably and that the measured data closely align with the predicted performance of the heat exchanger. A commissioning test of the tubular heat exchanger showed a thermal imbalance of 1.02% between the high-pressure (HP) and low-pressure (LP) lines. This level of imbalance is consistent with the ISO standard uncertainty of ±2.3% for heat dissipation. In addition, CFD simulation results indicated an average deviation of approximately 1.4% in the low-pressure outlet temperature. The close alignment between experimental and CFD results confirms the theoretical reliability of the test bench. The HPHT thermal performance test facility will be expected to serve as a critical test bed for evaluating heat exchangers for current and future gas turbine applications.

Analysis of the Principle of Gas Turbine and State-of-art Applications

Abstract. As a matter of fact, gas turbines covers a large part in the maps of contemporary generators and propulsion systems. With this in mind, this study will offer a comprehensive evaluation as well as analysis of gas turbine working principles, key technologies, and cutting-edge applications. The study systematically elucidates the basic structure, thermodynamic cycle characteristics, and performance influencing factors of gas turbines. It focuses on the application of advanced gas turbines in fields such as power generation, aviation, and marine, demonstrating their advantages of high efficiency, cleanliness, and flexibility. This study analyzes the current challenges faced by gas turbine technology and points out that future research should focus on key technologies such as materials, cooling, and combustion to promote efficiency improvement, emission reduction, and fuel adaptability enhancement in gas turbines. This research deepens the understanding of gas turbine technology and can provide an important reference for engineering practice and innovative research.

Investigation of Ammonia/Hydrogen Mixtures and Pilot-Split Strategies in a Laboratory-Scale Radial Swirl Combustor

Abstract The transition to a decarbonized energy future relies on identifying the most suitable alternative fuels that can meet the needs of various energy sectors. While both ammonia and hydrogen are zero-carbon energy vectors, their physical properties and burning characteristics sit on either side of that of natural gas. Hence, mixtures of ammonia and hydrogen are being increasingly looked at as having the potential to fuel current energy systems without requiring significant combustor redesign. However, the combustion characteristics and operation limits for different ammonia/hydrogen mixtures still need to be evaluated. For gas turbine applications in particular, the effect of ammonia/hydrogen mixture composition and operating condition on flame behavior and stability is not well understood. The current work was carried out in a laboratory scale, radial swirl-stabilized turbulent combustor. A systematic study of two ammonia/hydrogen blend ratios (70:30 and 80:20 by volume) and a range of equivalence ratios were tested for different pilot-split ratios, to understand the effect on flame shape, stability and dynamics. Time-resolved pressure and integrated heat release fluctuations were measured to evaluate combustor dynamics, and NH2* chemiluminescence flame images were captured to understand spatial differences in flame structure. When comparing blend ratios, differences were observed in flame macrostructures and combustor dynamics, which could be largely attributed to the considerable difference in the laminar flame speeds of the blends. The addition of pilot generally improved the stability and lean operation for both blend ratios.

Investigation of Viscor and Methanol Spray Dynamics using Proper Orthogonal Decomposition in Siemens Energy Industrial Atomisers

Abstract The demand to reduce carbon emissions has prompted research into alternative fuels that can replace conventional fuels like diesel in industrial gas turbines. Among different potential biofuels and e-fuels, methanol emerges as a sustainable and high-performance alternative to diesel for gas turbine applications. It is well established that the fuel physical properties, spray dynamics and degree of atomisation are strongly correlated and affect the engine performance. In this study, Proper Orthogonal Decomposition (POD) was applied on spatio-temporally resolved images to characterise Viscor, here used as diesel surrogate, and methanol sprays of pressure-swirl atomisers employed in Siemens Energy industrial gas turbine (SGT-400) combustors. The methanol experimental results were then compared against Viscor results at analogous operating conditions, including density adjusted atomiser pressure drop and ambient pressures. Results confirmed that the methanol spray cone angle is slightly wider than Viscor at corresponding operating conditions. The POD analysis allowed to identify dominant spatial oscillation modes and characterise them in terms of oscillation amplitude, wavelength and onset distance from the atomiser edge for both fuels. Oscillation wavelengths and maximum amplitudes were found to correlate with Weber number, average SMD and axial jet velocities.

Tribological Performance of Soft Magnetic Composite Materials for Gas Turbine Applications

Abstract Soft magnetic composites (SMCs) have gained attention in the last years of their usage in more compact and powerful electromechanical systems. These materials are used to combine the application of metallic material to the capability of generating (without external supply) a magnetic field. Automotive and aerospace technologies push the applications of these original materials to even higher power and mechanical stress to reduce the number of components, the size, and, in turn, the weight of complex systems. Considering gas turbine application, SMCs were formerly developed for bearings, but in the last decades, the new era of gas turbine electrification (e.g., hybrid-electric fly) has determined the need for mechanical improvement of such materials. At the same time, the reliability of soft magnetic material has to be discovered to avoid failure and reduce the maintenance schedule. In the present work, tribological behaviors of SMCs were investigated by standard wear tests. Two different types of SMSc were prepared through the powder metallurgy technique. Tests were conducted by a tribometer using a ball-on-disk configuration in lubricated condition. The effect of oil temperature and applied load were investigated. In addition, an extensive post-mortem analysis was conducted on the worn surface to recognize the mechanisms responsible for the deterioration of the materials. The results showed the effects of the oil viscosity on the useful operating life of the SMCs. Removal mechanisms depend on the load conditions, and the proper selection of the oil characteristics and load was assessed.

Review of gliding arc plasma assisted ignition and combustion for gas turbine application

Abstract The potential of gliding arc plasma-assisted ignition and combustion technology to enhance ignition and combustion performance is attracting increasing attention from the scientific community. A multitude of experimental studies have been conducted by scientists and engineers on its application in gas turbine combustors. This paper presents a review of the research conducted on gliding arc plasma-assisted ignition and combustion over the past five years. Gliding arc plasma exerts a multitude of effects on combustion processes. These effects can be broadly categorized as follows: (1) reduction in ignition delay time; (2) expansion of ignition and lean blowout boundaries; (3) enhancement of ultra-lean burning combustion and low-temperature flame stability; (4) improvement in combustion efficiency; (5) reduction in pollutant emissions; (6) augmentation of stability of unstable fuels such as ammonia. Finally, a prospection on the application of gliding arc plasma assisted ignition and combustion technology in gas turbine combustor is presented.

Nonpremixed Approaches for Fuel Flexible, Low NOx Combustors in High-Efficiency Gas Turbines

Abstract Lean, premixed combustor designs have almost completely replaced non-premixed combustors for industrial gas turbine applications where NOx emissions are regulated. Nonetheless, these designs have also introduced turndown and fuel flexibility constraints and made combustion instabilities and flashback more problematic. Future gas turbine applications will require combustors to accommodate a range of alternative fuels, provide operational flexibility, and compete for services with a host of new technologies, including energy storage and fuel cells. The purpose of this paper is to propose nonpremixed, multi-stage designs for the next generation of high turndown, high fuel flexibility, low NOx combustion designs – referred to here as a Nonpremixed, Rich, Relaxation, Lean (NRRL) combustor. The key concept we explore is non-premixed combustion, followed by additional fuel mixing to locally fuel-rich conditions, a relaxation stage, and then a lean stage. This non-premixed approach can handle essentially any fuel composition, including pure hydrogen, liquid fuels, pure methane, pure ammonia, and any combination in between while breaking the NOx-CO tradeoff and reducing combustion instability risk. This paper provides chemical reactor network modeling calculations to identify key kinetic processes and time scales required for such a concept. This concept has completely inverted sensitivities from lean, premixed systems which prefer short residence times, low pressures, and low temperatures to minimize NO formation. This concept prefers long residence times, high pressures, and high temperatures, indicating a very different set of design trades for part load and off-design performance.

In-Situ and Ex-Situ Measurement of Stresses In Environmental Barrier Coatings

Abstract Ceramic Matrix Composites (CMCs) offer a step improvement in temperature capability over the current best high temperature super alloys for gas turbine applications. Silicon Carbide (SiC) based CMCs react with water vapor at temperature and therefore need an Environmental Barrier Coating (EBC) for protection against the water vapor attack. EBC is typically deposited on a CMC component through Air Plasma Spray (APS) process, which involves melting and fast quenching of molten ceramic powders (such as ytterbium disilicate and ytterbium monosilicate). The fast quenching and subsequent cool down to room temperature introduce residual stress in the EBC. In addition, EBC coated CMC components often go through a heat treatment process afterwards. For Ybsilicates, this both stabilizes/crystalizes the EBC and increases hermiticity by healing cracks and pores. This heat treatment at elevated temperature changes the coating residual stress state. It is important to be able to measure the coating stresses during deposition and heat treatment so that APS process improvement and EBC coating life assessment can be made. This paper describes novel methods to measure coating stresses continuously during APS and during heat treatment up to 1400°C, using an optical deformation and curvature-based approach.

Inlet injection as an alternative, simplified method of hydrogen application in a miniature gas turbine

Hydrogen-powered gas turbines have great potential, because, among other things, they allow the elimination of the use of fuels containing carbon in their composition, which involves the elimination of CO2 emissions, which are a product of the combustion of hydrocarbon fuels. The paper presents the results of experimental research conducted on a miniature gas turbine co-powered by hydrogen gas. The aim of the research was to demonstrate the impact of the addition of hydrogen on the operation of the unit and exhaust gas emissions during hydrogen application in a way that does not require engine modification. This was accomplished by applying hydrogen gas through the turbine inlet. Hydrogen gas accounted for up to 0.91% of the total volume of gas flowing through the compressor, which resulted in hydrogen contributing almost 10% of the energy supplied to the engine in the form of fuel. The research focused on measuring fuel consumption, thrust, and temperature, as well as the composition of exhaust gases. The emission of carbon monoxide, nitrogen oxides and the concentration of oxygen and carbon dioxide were measured. The addition of hydrogen resulted in a reduction of the total mass of fuel consumed by over 18%. It led to a significant decrease in the temperature behind the combustion chamber with an increase in the amount of hydrogen applied. The addition of hydrogen also resulted in a reduction in CO2 concentration in exhaust gases by more than 30%, but at the same time, an increase in NOx emissions was recorded. The obtained results were compared with the results of tests presented in the literature, in which hydrogen was supplied to units of analogous structure in a classical way, i.e. directly to the combustion chamber.

Marine Applications and Design of High-Efficiency Small-Scale Gas Turbines

Marine Applications and Design of High-Efficiency Small-Scale Gas Turbines

Flame characteristics and NO emission behaviors of methane/ammonia counterflow premixed flames with opposed N2 or air stream

Behaviors of methane/ammonia counterflow premixed flames and NO emission are numerically and experimentally investigated with opposed N2 or air stream by varying strain rate (ag) and equivalence ratio (ϕ). The premixed stream is 80% methane and 20% ammonia by volume mixed with air considering the utilization of ammonia by blending hydrocarbon fuels. The opposed stream is either N2 or air considering the potential application in gas turbines having single- or two-stage combustion. The simulations are conducted by increasing ag up to flame extinction for a specified ϕ and an experiment is conducted to evaluate various kinetic mechanisms. The extinction strain rate increases monotonically with ϕ with opposed air stream (AS), while increases and then decreases with opposed nitrogen stream (NS). The extinction mechanisms are explained by adopting the concepts of the local equilibrium temperature and heat loss ratio. For lean and rich mixtures with NS and lean mixtures with AS, the extinction occurs due to comparable effects of incomplete reaction and heat loss from the flame to the downstream burnt region. While for rich mixtures with AS, the extinction is attributed mainly to incomplete reaction. The contribution of thermal NO as compared with prompt NO in NO production is weak for all cases with NS and AS. The emission index (EINO) for lean and rich mixtures with NS and for lean mixtures with AS decreases monotonically with the increase of strain rate for all ϕ. Increasing equivalence ratio at a specified ag decreases NO production for lean and rich mixtures with NS and lean mixtures with AS. While for rich mixtures with AS, the EINO increases monotonically with ag. From the reaction pathway analysis, for lean mixtures, the effect of increasing ag on the reduction of NO production is attributed by weakening NH-related reaction paths, while NH2-related reaction paths change little. When ϕ increases for a specified ag with NS, NO production is reduced by weakening NH2-related reaction paths and strengthening NH-related reaction paths. For rich mixtures with AS, increasing ag increases NO production by strengthening NH2-related reaction paths.

Novel oxide based anti-corrosion composite coating for gas turbines

In the present study glass-ceramic−8YSZ based multilayered functionally graded corrosion resistant coating was developed for gas turbine applications. Corrosion resistance property of developed coating was evaluated by exposing coating to molten mixture of 80 wt% Na2SO4 + 20 wt% NaCl in air at 1000 °C up to 100 h. It was found that coating morphology was gradually changed with respect to time at 1000 °C. No thermally grown oxide (TGO) layer was observed within different layers of TBC. However, thin reaction film was developed at substrate-coating interface, which helped to increase adherence of coating with substrate. Tetragonal zirconia to monoclinic zirconia phase transformation was not occurred in top coat even after long corrosive salt attack that strengthened TBC system. Developed coating showed good potential to be used as corrosion resistant coating for actual superalloy based gas turbine engine components.

Experimental study on the performance of micro gas turbines under different intake environments

This article uses experimental methods to measure the operational performance and pollutant emissions of micro gas turbines in different intake environments, and analyzes the feasibility of replacing mine ventilation fans with micro gas turbines. The results show that when the compressor efficiency is increased from 70 % to 90 %, the total efficiency of the micro combustion engine is increased from 28% to 34 %, with an increase of up to 21.4 %. When the demand power is 25 kW, the fluctuation range of NOx emission concentration is within 5.4 %. When the intake opening is below 50 %, the effect is obvious. When the intake opening is reduced from 50 % to 25 %, the performance of the micro gas turbine decreases by 0.7 %; The influence of intake humidity on various operating parameters of micro gas turbines is generally within 3 %, which can meet the requirements of high humidity environment operation; The intake temperature has the greatest impact, with an increase in intake temperature leading to a decrease in power generation efficiency. After comprehensive analysis, we believe that the application of gas turbines in mines is feasible.

FGM vs ATF: A comparative LES analysis in predicting the flame characteristics of an industrial lean premixed burner for gas turbine applications

In the pursuit of decarbonization, the reduction of greenhouse gas emissions from power generation through gas turbine (GT) engines plays a crucial role in the whole industrial sector. As industries strive to transition towards cleaner energy sources, the design and optimization of novel GT burners require a deep comprehension of the complex interaction between fluid dynamics and combustion processes embedded within the system. Computational Fluid Dynamics (CFD) plays a pivotal role in these processes by providing valuable insights into the complex flow patterns, flame topology, and stability limits within the combustor. Concurrently, the burner design phase necessitates a considerable number of simulations to ascertain flame stability limits under various burner designs and operating conditions. Therefore, it is imperative to control computational costs while ensuring a high level of accuracy. The present work is focused on a comprehensive comparative analysis of two widely employed turbulent combustion closure models: the Flamelet Generated Manifold (FGM) and the Artificially Thickened Flame (ATF). Both models utilize extended versions with specific modifications aimed at effectively addressing their respective limitations. The investigation is performed through a Large Eddy Simulation (LES) based CFD analysis within the context of a lean premixed burner designed by Baker Hughes and operated with methane at atmospheric pressure. The primary benchmark for numerical validation will be provided by detailed chemiluminescence images from a test campaign conducted by the University of Florence, thereby yielding valuable insights into flame topology and positioning. Furthermore, potential disparities in the flow field and fuel concentration at the burner exit between the two models will be revealed.

Application and Optimization of Stationary Gas Turbine

Application and Optimization of Stationary Gas Turbine

Fine-Tuning Melt Pools and Microstructures: Taming Cracks in Powder Bed Fusion—Laser Beam of a non-weldable Ni-base Superalloy

Powder Bed Fusion – Laser Beam (PBF-LB) of high γ’ strengthened Ni-base superalloys, such as CM247LC, is of great interest for high temperature applications in gas turbines. However, PBF-LB of CM247LC is challenging due to the high cracking susceptibility during PBF-LB processing (solidification cracking) and heat treatment (strain age cracking, mostly caused by residual stresses). This study focuses on understanding the impact of process parameters on microstructure, residual stresses and solidification cracking. Laser power (P), speed (v) and hatch spacing (h) were varied while the layer thickness (t) was fixed. The melt pool size and shape were found to be key factors in minimizing solidification cracking. Narrower and shallower melt pools, achieved using a low line energy density (LED = P/v ≤ 0.1 J/mm), gave low crack densities (0.7 mm/mm2). A tight hatch spacing (h = 0.03 mm) resulted in reduced lack of fusion porosity. Electron backscatter diffraction investigations revealed that parameters giving finer microstructure with 〈100〉 crystallographic texture had low crack densities provided they were processed with a low LED. Atom probe tomography elucidated early stages of spinodal decomposition in the as-built condition, where Cr and Al cluster separately. The extent of spinodal decomposition was found to be affected by the LED and the hatch spacing. Samples with low LED and small hatch spacing showed higher degrees of spinodal decomposition. X-ray diffraction residual stress investigations revealed that the residual stress is proportional to the volumetric energy density (VED = P/(v. h. t)). Although low residual stresses can be achieved by using low VED, there is a high risk of lack of fusion. Hence, other parameters such as modified scan strategy, build plate pre-heating and pulsed laser mode, must be further explored to minimize the residual stresses to reduce the strain age cracking susceptibility.

Fuel effects on the electrostatic control of charged droplet trajectories

The use of electrostatic fields to control the trajectory of charged droplets is investigated as a new technology to enhance mixing in liquid-fuelled combustors. The canonical configuration of a spray in crossflow is numerically studied with a focus on the effects of the fuel type on the onset of charge-induced breakup and droplet trajectories for a range of bulk flow velocities and electrostatic field strengths at conditions relevant to gas turbine applications. The investigated fuels are ethanol, n-heptane, and n-decane. Operational maps for each fuel are provided to assist the selection of the external electrostatic field required to achieve a balance between the drag and electrostatic forces, and enable a system design that considers fuel flexibility. The results demonstrate that the fuel type has an important impact on the diameter at which the charge-induced breakup is achieved, which mainly depends on the droplet equilibrium temperature. It is also shown that, for cases where the droplet net charge is fixed to a given fraction of the maximum possible charge (based on the Rayleigh limit), the temperature of the droplet at injection could be used as a parameter to control the onset of secondary breakup. Analysis of the strength of the electrostatic field necessary to achieve droplet stabilisation in a bulk flow shows that a balance between the electrostatic and drag forces can only be achieved for relatively low values of the bulk flow velocity, if the strength of the electrostatic field is kept below the breakdown limit of the carrier phase. This balance mainly depends on the droplet net charge and flow conditions, whereas the effect of the type of fuel on the drag force is less important. When the charge is imposed as a fraction of the maximum possible value at injection, for low values of the bulk flow velocity, the strength of the electrostatic field that balances the drag tends to become independent of the droplet diameter for a wide range of droplet sizes. Further investigation of the trajectories of evaporating droplets demonstrates that, although affected by the type of fuel through the evaporation rate, with the same settings of the electrostatic field, it is possible to achieve evaporation in a confined region for all the fuels and ambient conditions studied in this work once the initial droplet charge and initial droplet diameter are fixed. The present findings offer new insights for the development of future technologies for fuel preparation with enhanced mixing and fuel flexibility.

Influence of IP-TIG welding parameters on weld bead geometry, tensile properties, and microstructure of Ti6Al4V alloy joints

Abstract The primary aim of this study is to analyze the influence of inter-pulse tungsten inert gas (IP-TIG) welding parameters (peak current, inter-pulse current, and inter-pulse frequency) on weld bead geometry, tensile properties, and microstructure of Ti6Al4V alloy joints for gas turbine applications. IP-TIG welding principally featured by magnetic arc constriction and pulsing was employed to overcome the high heat input problems in TIG welding of thin Ti6Al4V alloy sheets such as wider bead and HAZ, coarsening of beta grains, inferior ductility, distortion of joints, and atmospheric contamination which significantly deteriorates the mechanical performance of welded sheets. The tensile properties and microhardness of IP-TIG joints were evaluated and correlated to the microstructural features. The microstructural features were analyzed using optical microscopy. The fractured surfaces of tensile specimens were studied using scanning electron microscopy. Results showed that the Ti6Al4V alloy joints developed using peak current of 50 A, inter-pulse current of 30 A, and inter-pulse frequency of 20 kHz exhibited greater strength, hardness and elongation. It showed greater tensile strength of 1030 MPa, yield strength of 981 MPa, and elongation of 10 % and FZ microhardness of 391 HV0.2. It is mainly due to the development of refined grains in fusion zone (FZ).

Comparative Thermal Insulation Nature of Ca2FeMnO6−δ and Sr2FeMnO6−δ

In this study, we investigate the utility of Ca2FeMnO6-δ and Sr2FeMnO6-δ as materials with low thermal conductivity, finding potential applications in thermoelectrics, electronics, solar devices, and gas turbines for land and aerospace use. These compounds, characterized as oxygen-deficient perovskites, feature distinct vacancy arrangements. Ca2FeMnO6-δ adopts a brownmillerite-type orthorhombic structure with ordered vacancy arrangement, while Sr2FeMnO6-δ adopts a perovskite cubic structure with disordered vacancy distribution. Notably, both compounds exhibit remarkably low thermal conductivity, measuring below 0.50 Wm−1K−1. This places them among the materials with the lowest thermal conductivity reported for perovskites. The observed low thermal conductivity is attributed to oxygen vacancies and phonon scattering. Interestingly as SEM images show the smaller grain size, our findings suggest that creating vacancies and lowering the grain size or increasing the grain boundaries play a crucial role in achieving such low thermal conductivity values. This characteristic enhances the potential of these materials for applications where efficient heat dissipation, safety, and equipment longevity are paramount.