Safe Operation Of Gas Turbine Research Articles

Study on characteristics and mechanism of re‐entrainment in intake filtration components of the gas turbine

AbstractAiming at the problem that the droplet re‐entrainment in the intake filtration components affects the gas intake quality and the safe operation of gas turbines, the characteristics and mechanism of the re‐entrainment in a marine double‐hook inertial stage filter are studied, and the distribution of liquid film and re‐entrainment under different inlet air velocities and droplet size distributions are compared. The results show that, due to the influence of inertia and turbulent dispersion, droplets tend to deposit on draining hooks and the lower surface of the leeward side of the blade to form a liquid film. Film stripping is the main form of re‐entrainment under ship‐driving conditions. Due to the high airflow velocity and the large film thickness, hook peaks are the most prone to film stripping, and the critical airflow for film stripping velocity is 14.8 m/s. With the increase of the inlet air velocity, the film thickness at the draining hooks increased first and then decreased, and the film stripping positions were extended from the hook peaks to the rear. Different droplet size distributions mainly affect the liquid film thickness at the draining hook and leeward side of the blade, which in turn affects the film stripping mass.

High-Temperature Materials for Complex Components in Ammonia/Hydrogen Gas Turbines: A Critical Review

This article reviews the critical role of material selection and design in ensuring efficient performance and safe operation of gas turbine engines fuelled by ammonia–hydrogen. As these energy fuels present unique combustion characteristics in turbine combustors, the identification of suitable materials becomes imperative. Detailed material characterisation is indispensable for discerning defects and degradation routes in turbine components, thereby illuminating avenues for improvement. With elevated turbine inlet temperatures, there is an augmented susceptibility to thermal degradation and mechanical shortcomings, especially in the high-pressure turbine blade—a critical life-determining component. This review highlights challenges in turbine design for ammonia–hydrogen fuels, addressing concerns like ammonia corrosion, hydrogen embrittlement, and stress corrosion cracking. To ensure engine safety and efficacy, this article advocates for leveraging advanced analytical techniques in both material development and risk evaluation, emphasising the interplay among technological progress, equipment specifications, operational criteria, and analysis methods.

Unveiling particle deposition characteristics on flat plate with a shaped film cooling hole

Particle deposition on turbine blades poses a significant challenge to the safe operation of gas turbines. The blockage of film-cooling holes and alteration in the aerodynamic shape of blades affect the turbine's efficiency, highlighting the importance of reducing particle deposition on turbine blades. To investigate the characteristics and potential mechanisms of deposition, experimental and numerical studies were conducted on two typical film-cooling holes: cylindrical and 777-shaped. A multi-perspective scanning method was used to measure the three-dimensional deposition topography on flat plates under a particle-laden environment. The wax deposition experiments showed that the deposition thickness of both holes increased with the blowing ratio. However, the 777-shaped hole exhibited a 10–40% reduction in deposition compared with the cylindrical hole. The computational predictions of deposition patterns agreed well with the experimental results. The numerical simulations revealed that the presence of film cooling reduced deposition in some areas but increased deposition in the vicinity of the film coverage region owing to the entrainment of vortices. Overall, this study further elucidates particle deposition characteristics and the influencing factors, which can guide the design of blade cooling systems with reduced deposition.

3D positioning of defects for gas turbine blades based on digital radiographic projective imaging

During the manufacturing and service process of gas turbine blades, various types of defects may be formed and bring huge threat to the safe operation of gas turbine. To confirm whether the gas turbine blades with defects could be in safe service for some period of time, the residual strength and fatigue life of gas turbine blade should be analyzed and predicted based on the 3D spatial position of defect, which significantly determines the degree of effect on the strength of gas turbine blade. Considering the characteristics of shape (free-from surface) and material (high density superalloy), the digital radiographic imaging techniques could be used in the non-destructive testing of gas turbine blades. However, the projective nature of digital radiography (DR) technique results in the unavailability of position in the transmitting direction of X-ray beam and brings difficulty to the 3D characterization of defect. Aiming at this critical issue, based on the exploration of the changing rule for the projection of a point feature relative to the irradiating angle, a new method is presented to obtain the 3D spatial position of defect. Finally, the accuracy of the proposed method is validated using a metrological computed tomography (CT) system. It can be learned that the proposed DR based method could obtain the 3D spatial position of defect with a relative error less than 2%. The 3D spatial position of defect could be used in the following residual strength analysis and fatigue life prediction of gas turbine blade.

Fault signal reconstruction for multi-sensors in gas turbine control systems based on prior knowledge from time series representation

Improving efficiency through intelligence is the current development trend of industrial gas turbines. Among the fault statistics of gas turbines, the number of sensor fault is the highest during use. The fault signal diagnosis and reconstruction are of great significance to the efficient and safe operation of gas turbines. In order to eliminate the sensor fault signal and transmit the normal signal to the control system, a multivariate fault signal reconstruction method based on the prior knowledge of the time-series representation was proposed in this work. The proposed multivariate signal reconstruction method can reconstruct almost all fault cases with high accuracy by training only one model. Firstly, the prior knowledge is applied to improve the conventional time series data representation. Secondly, three steps are employed to utilize spatial or temporal information and obtain three intermediate data. The masks combine the third intermediate data and the original time series to obtain the final reconstruction results. Then, reconstruction data sets are built based on exhaust gas temperatures (EGTs) from real-world power plant to verify the effectiveness of the proposed method. Different evaluation metrics and visualization reveal the high accuracy results. Compared results with different reconstruction algorithms reflect both the robustness and high speed of this reconstruction method. Finally, three typical fault signal reconstruction cases reveal the generalizability of this model.

Evaluating the adequacy of dynamic pressure remote sensing method in a model gas turbine combustor

Direct measurement of dynamic pressure in a combustor using a flush sensor mounting generally shortens the lifetime and lowers the measurement accuracy of the sensor due to its direct exposure to hot-burnt gases. Thus, indirect remote sensing methods are typically employed in combustion systems; however, the measurements may contain errors. Therefore, in this study, the feasibility of a remote sensing method for measuring dynamic pressure is verified by conducting an acoustic forcing experiment in a model gas turbine combustor. Sensing performance of the sensor adapters are evaluated based on their measurement locations for a driving frequency of 50–5000 Hz. In an experiment with different measurement locations, mode shapes corresponding to a resonant frequency of 160 Hz are clearly observed. Furthermore, in a sensor-adapter performance experiment, the effects of hole-size and length of a dynamic pressure propagation tube on the sensing characteristics are investigated and the optimum design shape is obtained. The results indicate an increase in the accuracy of dynamic pressure measurements and a subsequent decrease in the risk of combustion instability accidents. Therefore, the findings of this study and optimal design methodology for remote sensing equipment could positively contribute to the safe operation of gas turbines.

Blade Crack Detection using Blade Tip Timing

The harsh working environment of compressor threats the integrality of bladed disk. Crack is one of the most fatal faults of rotating blades. Detecting the crack of blades at early stage could ensure the safe operation of gas turbine and save economic costs. Blade tip timing (BTT) is a noncontact blade vibration measurement technique, which is widely used in recent years. In this article, a procedure of crack detection using BTT data is proposed. First, some typical parameters are taken into consideration, including resonance frequency, amplitude change of natural frequency, amplitude of blade tip, phase, and interblade spacing. It has been found that the frequency of the blade will decrease with the increment of crack length and reduction of crack height. In addition, the resonance frequency of the bladed disk will split when the blade cracks. The amplitude of different orders of resonance frequency varies with cracks. The amplitude of the first order changes very slightly, whereas the second and third orders are relatively obvious. The blade tip vibration amplitude and phase change with cracks without obvious regularity. The interblade distance will change due to the appearance of cracks. According to the above rules, the frequency and the interblade distance are adopted as crack diagnosis indicators. First, we use the Lomb-Scargle periodogram to quickly determine whether the crack appears and then use the blade frequency and interblade distance to locate the number of the blade having crack. In the experimental test, BTT data measured on a titanium bladed disk is used to verify the effectiveness of our method.

Detection of Three-Dimensional Parameter of Defects for Gas Turbine Blades Based on Two-Dimensional Digital Radiographic Projective Imaging

During the manufacturing and service process of turbine blades, various types of defects may be formed and bring huge threat to the safe operation of gas turbine. However, if qualifying the turbine blade only by the existence of defects, it will lead to the unavoidable large waste. Preferably, it should determine whether the turbine blades with defects could be in safe service for some period of time. Therefore, the residual strength and fatigue life should be analyzed and predicted based on the three-dimensional feature of defect, such as size, location. Considering the characteristics of shape (free-from surface) and material (high density superalloy), the radiographic imaging based techniques could be used in the non-destructive testing of turbine blades. For one thing, although the industrial computed tomography can obtain the three-dimensional feature of defects, the low efficiency and high cost may limit its practical application. For another, the projective nature of digital radiographic imaging technique results in the unavailability of geometric parameter in the transmitting direction and brings difficulty to the three-dimensional characterization of defect. Aiming at this critical issue, a new method based on the determination of mapping relationship between the thickness of material and the gray value of image is presented in this paper. By acquiring the thickness of two defects in a gas turbine blade, the three-dimensional geometric parameter (volume) can be calculated. Finally, the accuracy of the proposed method is verified using a test specimen. In comparison with the industrial CT, the proposed method could have relative high efficiency and low cost in the application of the three-dimensional quantitative characterization of defects for gas turbine blades.

Laser Cladding of Embedded Sensors for Thermal Barrier Coating Applications

The accurate real-time monitoring of surface or internal temperatures of thermal barrier coatings (TBCs) in hostile environments presents significant benefits to the efficient and safe operation of gas turbines. A new method for fabricating high-temperature K-type thermocouple sensors on gas turbine engines using coaxial laser cladding technology has been developed. The deposition of the thermocouple sensors was optimized to provide minimal intrusive features to the TBC, which is beneficial for the operational reliability of the protective coatings. Notably, this avoids a melt pool on the TBC surface. Sensors were deposited onto standard yttria-stabilized zirconia (7–8 wt % YSZ) coated substrates; subsequently, they were embedded with second YSZ layers by the Atmospheric Plasma Spray (APS) process. Morphology of cladded thermocouples before and after embedding was optimized in terms of topography and internal homogeneity, respectively. The dimensions of the cladded thermocouple were in the order of 200 microns in thickness and width. The thermal and electrical response of the cladded thermocouple was tested before and after embedding in temperatures ranging from ambient to approximately 450 °C in a furnace. Seebeck coefficients of bared and embedded thermocouples were also calculated correspondingly, and the results were compared to that of a commercial standard K-type thermocouple, which demonstrates that laser cladding is a prospective technology for manufacturing microsensors on the surface of or even embedded into functional coatings.

Design and analysis of internal cooling passage of gas turbine using computational fluid dynamics

ABSTRACTIn advanced gas turbines, the turbine blade-operated temperature is above the melting point of blade material. A sophisticated cooling scheme must be developed for continuous safe operation of gas turbines with high performance. This report describes the development and application of a validated computational fluid dynamics (CFD) modelling approach for internal cooling passages in rotating turbomachinery which analyse change in pressure, velocity, temperature, and pressure of fluid in the passage. Velocity changes in the passage help to determine turbulence created in the passage. The CFD analysis is conducted with smooth passage, straight turbulator passage, skewed turbulator passage with different inlet conditions and best model is finalised with high turbulence output. The analysis is carried out using commercial CFD software on k-ϵ model. On evaluating results of different velocity and temperatures, it is found that straight turbulator has more turbulence when compared to smooth and skewed turbulators.Abbreviations: CFD: computational fluid dynamics; CAD: computer-aided design; k-ε: Eddy-viscosity model

CFD ANALYSIS ON RADIALCOOLING OF GAS TURBINE BLADE

Gas turbines are extensively used for air craft propulsion, land based power generation and industrial applications. Thermal efficiency of gas turbine improved by increasing turbine rotor inlet temperature. The current rotor inlet temperature in advanced gas turbine is for above the melting point of blade material. A sophisticated cooling scheme must be developed for continuous safe operation of gas turbines with high performance. Gas turbines are cooled externally and internally. Several methods have been suggested for the cooling of blades and vanes. The techniques that involve to cool the blades and vanes by using cooling methods is to have radial holes to pass high velocity cooling air along the blade span. In this thesis, a turbine blade is designed and modelled in CATIA v5and ICEM CFDsoftware. The turbine blades are designed using cooling holes. The turbine blade is designed with 12 holes. CFD analysis is done to determine the pressure distribution, velocity, temperature distribution and heat transfer rate by applying the inlet velocities. Thermaland Structural analysis is done to determine the heat transfer rates and strength of the blade. The present used material for blade is chromium steel. In this thesis, itis replaced with Titanium aluminium alloy. The better material for blade is analyzed

Influence of the upstream slot geometry on the endwall cooling and phantom cooling of vane suction side surface

Modern gas turbines always operate at a high level of inlet temperature. The current inlet temperature in the aircraft and heavy duty gas turbines is higher than the melting point of the guide vane material. Consequently, advanced cooling schemes must be developed to ensure the safe operation of gas turbines. In the current study, numerical simulations were conducted to investigate the influence of the upstream slot geometry on the endwall cooling and phantom cooling of the vane suction side surface. Three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) equations combined with the shear stress transport (SST) k-ω turbulence model were solved to conduct the simulations based on the validated turbulence model. The results indicate that the adiabatic cooling effectiveness in the upstream region of the stagnation is significantly increased by introducing the contoured upstream slot. However, the normal upstream slot obtains a relatively high adiabatic cooling effectiveness level in the downstream region of the stagnation. In the present research, the case with normalized amplitude A‾=0.75, initial phase angle φ=45° achieves the largest overall adiabatic cooling effectiveness near the vane leading edge. In contrast, the case with A‾=0.75, φ=30° attains the smallest overall adiabatic cooling effectiveness on the endwall surface. Moreover, the phantom cooling effectiveness on the vane suction side surface is relatively small relative to the adiabatic cooling effectiveness on the endwall. The case with the normal upstream slot achieves the largest phantom cooling effectiveness on the vane suction side surface compared with the contoured upstream slot. Overall, the contoured upstream slot significantly enhances the endwall cooling effectiveness by rearranging the distribution of the coolant mass flowrate at the slot outlet.

RETRACTED: Design and thermal analysis of cooling of Gas turbine blade through radial holes

Abstract Gas turbines are extensively used for air craft propulsion, land based power generation and industrial applications. Thermal efficiency of a gas turbine can be improved by increasing turbine the rotor inlet temperature. The current rotor inlet temperature in advanced gas turbine is far above the melting point of blade material. So a sophisticated cooling system must be developed for continuous safe operation of gas turbines with high performance. Several methods have been suggested for the coolingof blades and one such technique is to have radial holes to pass high velocity cooling air along theblade span. The present work is carried out by performing the heat transfer analysis of gas turbine with four differentmodels consisting of blade with, without holes and blades with varying number of holes (5, 9&13). The analysis is carried out using commercial CFD software FLUENT. On evaluating the graphs drawnfor total heat transfer rate and temperature distribution, the blade with 13 holes is considered to be moreoptimum. The Steady state thermal and structural analysis is done using ANSYS software withdifferent blade materials such as Chromium steel and N155. While comparing the results, N155 has proved to have better thermal properties and also induced stresses are less than the Chromium steel.

Experimental Study on the Wet Electrostatic Precipitator for Purifying Biomass Fuel Gas

Recently, biomass fuel gas from the gasification furnace is widely used for power generation. However, there are many kindes of impurities in the biomass fuel gas. If they aren’t removed, they will have great disadvantages on the safe operation of gas turbine. So it must be purified before combustion in order to protect the gas turbine. Wet electrostatic precipitator can be used for purifying the biomass fuel gas for its high collection efficiency. The characteristics of biomass dust and collection efficiency of wet electrostatic precipitator are presented in the paper. A compared study on collection efficiency between dry electrostatic precipitator and wet one are carried out at the same condition. The results show that the dust in biomass fuel gas contains many elements, such as Si, O, Mg, Al, K, Ca and Fe. Its median diameter d50 is 26.05 μm. Collection efficiency gradually increases with the water pressure at beginning of test. It doesn’t increase until the water pressure is 0.4 MPa. The higher the wind speed in electric field, the lower the collection efficiency is. Collection efficiency can be improved by adding alkali to the spraying water. When the polar matching is RS tubular barbed wire with 480C plate, water pressure is 0.4 MPa and gas velocity is 1.0 m/s, collection efficiency of the wet electrostatic precipitator is 5% more than the dry one.

Prediction of Auto-Ignition Temperatures and Delays for Gas Turbine Applications

Gas turbines burn a large variety of gaseous fuels under elevated pressure and temperature conditions. During transient operations, variable gas/air mixtures are involved in the gas piping system. In order to predict the risk of auto-ignition events and ensure a safe operation of gas turbines, it is of the essence to know the lowest temperature at which spontaneous ignition of fuels may happen. Experimental auto-ignition data of hydrocarbon–air mixtures at elevated pressures are scarce and often not applicable in specific industrial conditions. Auto-ignition temperature (AIT) data correspond to temperature ranges in which fuels display an incipient reactivity, with timescales amounting in seconds or even in minutes instead of milliseconds in flames. In these conditions, the critical reactions are most often different from the ones governing the reactivity in a flame or in high temperature ignition. Some of the critical paths for AIT are similar to those encountered in slow oxidation. Therefore, the main available kinetic models that have been developed for fast combustion are unfortunately unable to represent properly these low temperature processes. A numerical approach addressing the influence of process conditions on the minimum AIT of different fuel/air mixtures has been developed. Several chemical models available in the literature have been tested, in order to identify the most robust ones. Based on previous works of our group, a model has been developed, which offers a fair reconciliation between experimental and calculated AIT data through a wide range of fuel compositions. This model has been validated against experimental auto-ignition delay times corresponding to high temperature in order to ensure its relevance not only for AIT aspects but also for the reactivity of gaseous fuels over the wide range of gas turbine operation conditions. In addition, the AITs of methane, of pure light alkanes, and of various blends representative of several natural gas and process-derived fuels were extensively covered. In particular, among alternative gas turbine fuels, hydrogen-rich gases are called to play an increasing part in the future so that their ignition characteristics have been addressed with particular care. Natural gas enriched with hydrogen, and different syngas fuels have been studied. AIT values have been evaluated in function of the equivalence ratio and pressure. All the results obtained have been fitted by means of a practical mathematical expression. The overall study leads to a simple correlation of AIT versus equivalence ratio/pressure.

Ignition time of hydrogen–air diffusion flames

The ignition time of hydrogen–air diffusion flames is a quantity of utmost interest in a large number of applications, with implications regarding the viability of supersonic combustion and the safe operation of gas turbines. The underlying chemistry and the associated ignition history are very different depending on the initial temperature and pressure. This article addresses conditions that place the system above the so-called second explosion limit, as is typically the case in SCRAMJET operation, so that a branched-chain explosion characterizes the ignition process. The roles of local radical accumulation, molecular transport, and chemical reaction in nonpremixed ignition are clarified by considering the temporal evolution of an unstrained mixing layer formed between two semi-infinite spaces of hydrogen and air. The problem is formulated in terms of a radical-pool mass fraction, whose evolution in time is studied with a WKB expansion that exploits the disparity of chemical time scales present in the problem, leading to an explicit expression for the ignition time. The applicability of the analytical results for obtaining predictions of ignition distances in supersonic-combustion applications is also considered.

Operation of Gas Turbine Engines in an Environment Contaminated With Volcanic Ash

Airborne volcanic ash poses a significant threat to the safe operation of gas turbine powered aircraft. Recent volcanic activity in Iceland and other parts of the world have resulted in interruption of air traffic and in the case of the April 2010 eruption of the Eyjafjallajökull volcano in Iceland, the interruption resulted in a significant loss of revenue. Over the past 30 years there have been several events involving commercial aircraft that have suffered significant damage to the propulsion system as a result of ingesting volcanic ash during a flight event, but a relevant engine focused database to provide guidance for dealing with the problem has not been generally available until recently. In Sept. 2010 after the Iceland volcano activity, a body of data that had not been in the public domain was released and those measurements that are described in some detail herein can be helpful to the airlines, the aircraft manufacturers, the engine manufacturers, those responsible for flight operations, and hopefully to the flight crews. The intent of this paper is to describe some of the more notable aircraft/ash cloud events, the available data associated with those encounters and how those data can be used to effectively deal with this problem while maintaining safe flight operations. The paper specifically (a) illustrates the engine damage mechanisms, (b) estimates the potential operational life of a particular class of engines if the ash concentration is at a very low level, and (c) illustrates how this database is helpful in dealing with future interruptions of flight routes caused by volcanic eruptions. A section at the end of this paper provides the comments and concerns of the industry and government stakeholders regarding this general problem area.

Effect of Ambient Temperature on Three-Shaft Gas Turbine Performance under Different Control Strategy

Gas turbine is sensitive to ambient temperature. Different ambient temperature could change the state of the inlet air of compressor and make the gas turbine work in off design conditions. Research the effect of ambient temperature on gas turbine performance is valuable to the long-term safe operation of gas turbine. In this paper, a thermodynamic model of a simple cycle gas turbine which has three shafts was established, and steady-state performance simulation under different ambient temperature was carried out. In the two conditions of 1.0 and 0.35 work states, the effect of ambient temperature on thermodynamic parameters, specific power and thermal efficiency of gas turbine were analyzed. The result shows that: effect of ambient temperature on three-shaft gas turbine is different under different work state, and relevant factors must be considered to select the appropriate control strategy

Conjugated heat transfer analysis of gas turbine vanes using MacCormack's technique

It is well known that turbine engine efficiency can be improved by increasing the turbine inlet gas temperature. This causes an increase of heat load to the turbine components. Current inlet temperature level in advanced gas turbine is far above the melting point of the vane material. Therefore, along with high temperature material development, sophisticated cooling scheme must be developed for continuous safe operation of gas turbine with high performance. Gas turbine blades are cooled internally and externally. Internal cooling is achieved by passing the coolant through passages inside the blade and extracting the heat from outside of the blade. This paper focuses on turbine vanes internal cooling. The effect of arrangement of rib and parabolic fin turbulator in the internal cooling channel and numerical investigation of temperature distribution along the vane material has been presented. The formulations for the internal cooling for the turbine vane have been done and these formulated equations are solved by MacCormack's technique.

Recent Development in Turbine Blade Film Cooling

Gas turbines are extensively used for aircraft propulsion, land-based power generation, and industrial applications. Thermal efficiency and power output of gas turbines increase with increasing turbine rotor inlet temperature (RIT). The current RIT level in advanced gas turbines is far above the .melting point of the blade material. Therefore, along with high temperature material development, a sophisticated cooling scheme must be developed for continuous safe operation of gas turbines with high performance. Gas turbine blades are cooled internally and externally. This paper focuses on external blade cooling or so-called film cooling. In film cooling, relatively cool air is injected from the inside of the blade to the outside surface which forms a protective layer between the blade surface and hot gas streams. Performance of film cooling primarily depends on the coolant to mainstream pressure ratio, temperature ratio, and film hole location and geometry under representative engine flow conditions. In the past number of years there has been considerable progress in turbine film cooling research and this paper is limited to review a few selected publications to reflect recent development in turbine blade film cooling.