Gas Turbine Research Articles

Numerical and experimental investigation of film cooling effectiveness distribution predictions that considers the effects of the turbulent Schmidt number

Film cooling is a critical protective cooling technique that is used in gas turbine engines. However, predicting the film cooling effectiveness can be quite challenging due to the complex mixing processes involved. As a result, simulations commonly require experimental validation or modification of their numerical methods. In this study, predictions of film cooling effectiveness distributions were enhanced by an examination of the impact of the turbulent Schmidt number, Sct, on the coolant-covered areas. An existing turbulent viscosity modification method, the MIX model, was utilized to obtain more accurate flow field representations. The definition, physical implications, and role of the turbulent Schmidt number in numerical simulations, along with the principles of the pressure-sensitive paint measurement method, which was used to characterize the film cooling effectiveness, were explored. Both numerical simulations and experimental validation were employed. The study results revealed that small-scale turbulent eddies, which were averaged in the RANS method according to the Sct, critically influenced the mixing between the coolant and the mainstream, thereby impacting the cooling effectiveness. It was also revealed that as Sct decreased, the cooling effectiveness diminished in the streamwise direction but increased in the spanwise and vertical directions, regardless of the momentum ratio value. An Sct value of 0.3 was found to be more suitable than the commonly used value of 0.7, particularly for a low momentum ratio of 0.43. When Sct=0.3, the error in the area-averaged cooling effectiveness was 10 %, while it was 51 % when Sct=0.7. Additionally, an Sct value of 0.3 produced better overall cooling effectiveness distributions. Consequently, an Sct value of 0.3 is recommended for most low-speed and incompressible-flow simulation conditions.

Modeling of performance and thermodynamic study of a gas turbine power plant

The efficiencies and performance of gas turbine cycles are highly dependent on parameters such as the turbine inlet temperature (TIT), compressor inlet temperature (T1), and pressure ratio (Rc). This study analyzed the effects of these parameters on the energy efficiency, exergy efficiency, and specific fuel consumption (SFC) of a simple gas turbine cycle. The analysis found that increasing the TIT leads to higher efficiencies and lower SFC, while increasing the To or Rc results in lower efficiencies and higher SFC. For a TIT of 1400 ℃, T1 of 20 ℃, and Rc of 8, the energy and exergy efficiencies were 32.75% and 30.9%, respectively, with an SFC of 187.9 g/kWh. However, for a TIT of 900 ℃, T1 of 30 ℃, and Rc of 30, the energy and exergy efficiencies dropped to 13.18% and 12.44%, respectively, while the SFC increased to 570.3 g/kWh. The results show that there are optimal combinations of TIT, To, and Rc that maximize performance for a given application. Designers must consider trade-offs between efficiency, emissions, cost, and other factors to optimize gas turbine cycles. Overall, this study provides data and insights to improve the design and operation of simple gas turbine cycles.

Numerical implementation of electrostatic solver within OpenFOAM for GT intake filtration

Abstract Gas turbines require filtered air to preserve operability, availability, and efficiency. Fouling, corrosion, and erosion severely affect the performance of the axial compressor and it can be in part prevented by filtering the air intake. For this reason, it is possible to use multiple filter stages in series to obtain a high level of capture efficiency. Traditionally, separation is achieved using porous material cartridges, which guarantee a high level of filtration but with an increasing pressure drop over time. Another common type of filter is the inertial one, whose operating principle is based on the inertial force acting on the solid particles to separate them from the mainstream. The capturing efficiency of the inertial filter is not comparable with that of the porous one, so it is used upstream as a pre-filter. In recent years, another technique has been developed to filter air flows thanks to an electrostatic field induced inside the flow. In the present work, numerical investigations are carried out to simulate the effect of the electrostatic force on gas turbine filtering systems. The CFD tool used is OpenFOAM, whose official release does not contain a library able to simulate the electrostatic force acting on the discrete phase. A new library was developed to calculate: the electric field, the electric potential, and the charge density of the continuous phase. Simulation results show how the calculation of these quantities allows us to predict the electrostatic force acting on particle flows in the presence of electrostatic fields

Analysis of the effect of temperature on creep resistance in nickel-based alloys used in gas turbines

Analysis of the effect of temperature on creep resistance in nickel-based alloys used in gas turbines

Turbine system vs engine generator in the production of energy by methane in the pacific of Mexico: a technical, economic, and environmental analysis.

This paper aims to analyze the potential of energy production using methane from organic waste as a sustainable alternative to mitigate the environmental impact of energy generation from fossil fuels and the generation of Municipal Solid Waste (MSW). To carry out the analysis, two technologies were evaluated from technical, economic, and environmental perspectives. The LandGEM model was used to estimate the methane generation potential. The amount of energy produced, along with the respective financial indicators, was also calculated. The results showed that for an average feed of 671,892 tons per year of waste, 6160 ft3/min of CH4 would be generated at a maximum peak in the tenth year, with an annual average of 4735 ft3/min. Additionally, 0.831 million metric tons of CO2 equivalent would be avoided. In terms of power generation, a combined cycle micro-turbine system with an installed capacity of 11.35 MW would be feasible and would yield an Internal Rate of Return (IRR) of 35% and a Net Present Value (NPV) of $11,608,006 USD. For an engine-generator system, it was not possible to verify profitability due to a significant increase in capital and O&M costs. These results are intended to provide reference information to assist in the decision-making process related to the implementation of projects aligned with the Sustainable Development Goals within the framework of the 2030 Agenda.

Heat Transfer Rate and Fluid Flow Analysis with Design Parameters of Gas Turbine using Beta-clog2-LSTM

Heat Transfer Rate and Fluid Flow Analysis with Design Parameters of Gas Turbine using Beta-clog2-LSTM

Method for enhancing fault feature signals of rolling bearings in gas turbine engines

Aiming at the problem that the weak fault signal of rolling bearings in gas turbine engines (GTEs) is affected by environmental noise, which leads to the difficulty of effective information extraction and easy to ignore, the characterization method for cyclic extraction of main bearing fault feature components in GTEs is proposed. The proposed method begins by subjecting raw vibration signals to wavelet packet decomposition and correlating correlation coefficient and kurtosis values for each node component. These values are then normalized and amalgamated into a comprehensive parameter denoted as P. Subsequently, a confidence interval is established to categorize node components into three groups: high signal-to-noise ratio signals, low signal-to-noise ratio signals, and high-noise signals. Then, the high signal-to-noise ratio signals are continuously filtered according to the feature component cyclic extraction criterion until the termination condition is reached. Finally, all high signal-to-noise ratio signals are reconstructed, followed by envelope demodulation to extract subtle bearing fault characteristics. The findings underscore the efficacy of this approach in extracting fault features within the intricate transmission path of rolling bearings, offering a robust solution for the intricate signal processing and diagnosis of complex rolling bearing faults in GTEs.

The Concept of Technological Support of Operational Properties Based on Stabilization of Mechanical Properties of Gear Materials in a Gas Turbine Engine Drive System

Modern production of gears for gas turbine engines for aviation, marine and land use is inherently related to the calculation of the stress state of the working surfaces of the mating teeth. To create conditions for the operability of the gear train and the drive system as a whole, an engineering analysis of the contact endurance of the mating surfaces is a necessary criterion. The contact strength determines the life of the gear mechanism. The value of the contact strength, taking into account its distribution in the contact zone of the working mating surfaces of the gears, is determined by the processing technology and operation, but the mechanical properties and texture of the material have the greatest influence. This determines the requirements for the stability of the mechanical properties of the materials used for the manufacture of gears, making a topical question on their study. The technology of manufacturing the gears in the gas turbine engine drives forms the layer structure of the toothed crown because of the use of chemical-thermal treatment. The surface hardened layer of the gear tooth after chemical-thermal treatment is saturated with carbon and nitrogen, and as a result of thermal action acquires mechanical properties and structure different from the material in the supply. The paper presents the results of practical research of evolution of mechanical properties of structural steels 20H3MVF-Sh, 18H2N4MA, 16H3NVFM-Sh and 12H2N4A-Sh based on various types of chemical-thermal treatment, as well as microstructure of toughened layer and core of the part. The steel mechanical properties stabilization evaluation in the process of gear technology was performed. The presented results of experimental studies of mechanical properties of the material prove stabilization of mechanical and structural indicators, which are responsible for the contact strength of the mating surfaces of toothed gears.

Influence of Dilution and Effusion Flows in Generating Variable Inlet Profiles for a High-Pressure Turbine

Abstract The elevated flow temperatures and pressures exiting gas turbine combustors affect the efficiency and durability of the high-pressure turbine stage. Understanding the effects that result from the upstream dilution and effusion flow interaction in creating the combustor exit profiles is important to advancing gas turbines. Understanding how common combustor features, such as dilution jets and effusion cooling, interact based on computational predictions guided the design of a non-reacting profile simulator capable of producing a wide range of non-uniform temperature profiles representative of those entering high-pressure turbines. The mechanical design of a new simulator device, which will be experimentally tested in the future, is presented in this paper along with computational predictions of flow and thermal fields. The simulator was designed for modular installation into the Steady Thermal Aero Research Turbine (START), which is a continuous-duration, steady-state turbine facility that houses a single-stage test turbine. Features of the simulator included interchangeable liner panels with multiple rows of dilution jets and wall effusion cooling to study various hole diameters and patterns. The dilution jets generate elevated turbulence intensities and tailor the temperature profiles in the radial and circumferential directions. The air mass flow distribution and source flow temperatures are independently controlled. To aid in the simulator design, computational fluid dynamics (CFD) simulations using Reynolds-averaged Navier–Stokes modeling were conducted with a two-level Design of Experiments (DOE) approach to determine a number of engine-representative target profiles with temperature shapes that are mid-radius peaked, outer-diameter peaked, inner-diameter peaked, and uniform. A sensitivity analysis of the CFD DOE results determined which factors significantly affected the profile shape so that the target profiles could be produced. The analysis indicated that the main contributor to the temperature profile shape at near-wall vane radial span locations of 0–15% and 85–100% was the injection temperature of the effusion flow. The main contributor at radial span locations of 15–40% and 60–85% was the injection temperature of the third-row dilution jets, and at the mid-radius location of 40–60% vane radial span, the main contributor was the diameter of the first-row dilution holes.

Experimental study on thermal load characteristics of a U-bend pulse detonation combustor

The performance of pulse detonation turbine engines (PDTE) surpasses that of conventional turbine engines, primarily due to the pressure gain combustion process inherent in PDTE. A U-bend pulse detonation combustor (PDC) with a compact axial length was designed to meet the requirements of PDTE. However, the PDC introduces complex thermal management challenges. In this study, the wall temperature along the U-bend PDC was experimentally measured under various operating conditions, the thermal load characteristics were investigated. The results indicate that the external wall temperature increases monotonically with prolonged operation, whereas the internal wall temperature exhibits periodic fluctuations corresponding to the periodic filling and combustion process in the PDC. The temperature difference between the internal and external walls increases, then decreases over time, eventually fluctuates within a narrow temperature range. The wall temperature was observed to increase along the flow direction, peaking at 811 °C at 30 Hz at the location where the detonation wave is generated. Similarly, the heat flux of the PDC first increases, then decreases, and eventually reaches a constant value, indicating thermal equilibrium. The heat flux represents a significant energy loss, with the detonation section being the area of highest heat loss, reaching approximately 90.5 kW/m2 at 30 Hz.

An Experimental Study on the Effects of Nonuniform Vane Spacing on Forced Response Reduction in a Mistuned Rotor Blisk in a Multistage Axial Compressor

Abstract Stators with nonuniform vane spacing (NUVS) are known to effectively reduce the forced response of adjacent rotors by spreading the primary engine order (EO) excitation at a certain speed to a series of weaker excitations at nearby EOs over a wider speed range. To be used in a real gas turbine engine, it is essential to know the forced response vibratory reduction that can be achieved for a specific NUVS configuration at different operating conditions. The classical estimation method to predict the blade response reduction is to quantify the reduction of the forcing function at a potential resonance crossing by conducting a circumferential Fourier analysis of the asymmetric flow field. However, besides excitation reduction, the blade forced response also depends on other factors, such as damping and blade-to-blade interactions due to mistuning. To study the blade forced response reduction in a realistic environment, a comprehensive experimental study was conducted in the Purdue three-stage axial research compressor at three different loading conditions. The vibratory response of the first torsion (1 T) mode forced response of rotor 2 was measured by strain gages (SGs) for two different upstream stator 1 configurations: the symmetric 38-vaned stator 1 configuration and the NUVS stator 1 configuration with 18–20 vane halves. As expected, the strong 38EO-1T response from the symmetric stator reduced to a series of weaker responses from 35EO to 41EO in the NUVS configuration. The overlap of adjacent EO responses caused considerable beating phenomena in the blade SG time–history data. There was substantial blade-to-blade variation in blade response for both symmetric and asymmetric stator 1 configurations due to the inherent nonintentional mistuning in the rotor 2 blisk. This, in turn, causes a large blade-to-blade variation in the reduction factors. While higher responding blades tend to have larger reduction factors, some blades show almost no forced response reduction when switching to the NUVS stator. In addition, the reduction factors for each blade and the maximum reduction factor for the whole blisk also change significantly with loading conditions. The measured reduction factors and the peak response EO are not well predicted by the classical estimation method. This indicates that both damping and mistuning effects need to be considered in the NUVS reduction factor prediction.

Scaling Heat Transfer and Pressure Losses of Novel Additively Manufactured Rib Designs

Abstract Rib turbulators are a key cooling feature that enables increased heat transfer on the interior of gas turbine components. As metal additive manufacturing becomes available for developing turbine parts, it is becoming increasingly important to understand how the surface roughness intrinsic to this manufacturing method impacts the performance of rib turbulators. To explore what impact roughness has on rib turbulator performance, several relevant scale test coupons were manufactured on two different additive machines out of IN718. Additionally, several coupons were built at large scales to effectively reduce the relative roughness size impacts and determine scale effects. A range of different wavy broken rib designs, varying both rib wavelength and orientation within a channel were evaluated. Coupon geometry and surface roughness were characterized using both computed tomography scans and optical profilometry. Variations between the print methods were found to have limited impact on the surface roughness, but significant impact on the accuracy to meet the design intent with rib heights varying by 30%. Following characterization, coupons were flow tested and it was found that the ribs that more regularly disturbed the flow as a function of their geometry most significantly enhanced heat transfer and pressure drop. The performance index of the broken wavy ribs was similar to other advanced rib designs, such as broken or V shaped ribs, but augmentations to heat transfer and pressure drop were generally lower. The rib performance was compared as a function of relative roughness, and it was found that increases in relative roughness resulted in increased friction factor and heat transfer, especially at higher Reynolds numbers.

The Effect of Spray Distance on the Hot Corrosion Behavior of HVOF‐Sprayed NiCrAlY Coatings in a Simulated Gas Turbine Environment

ABSTRACTTo utilize the unique properties of coatings produced using the high‐velocity oxy‐fuel (HVOF) method, this study examined the effect of spray distance on the hot corrosion behavior of NiCrAlY coatings deposited on a steel substrate. The coating samples were obtained at spray distances of 20, 25, and 30 cm. The flow rates of oxygen and propane were maintained constant at 300 and 60 lit/min, respectively. Additionally, the powder feeding rate was 32 g/min. The samples were then subjected to the hot corrosion test in a salt mixture of Na2SO4−60% V2O5 at 900°C in an ambient atmosphere. The surface and the cross section of the samples were observed using a scanning electron microscope (SEM) and the chemical composition of different sections was determined by energy‐dispersive spectroscopy (EDS). The phases were also characterized using X‐ray diffraction analysis (XRD). The best corrosion resistance was found in the sample coating formed at a spraying distance of 20 cm, as the results showed that increasing the spraying distance led to a reduction in the thermal and kinetic energy of the flame, resulting in increased porosity in the coating. This behavior can be attributed to the low oxide content of the coating, the higher aluminum content, and the richer NiAl phase, which serves as a reservoir for aluminum.

A Reformulation of the Laminar Kinetic Energy Model to Enable Multi-mode Transition Predictions

AbstractThe paper describes the development of a novel transition/turbulence model based on the laminar kinetic energy concept. The model is intended as a base framework for data-driven improvements. Starting from a previously developed framework, mainly aimed at separated-flow transition predictions, suitable terms for model generalization are identified and reformulated for handling different transition modes, namely bypass and separated-flow modes. The ideology for the definition of new terms has its roots in mixing phenomenological and correlation-based arguments, ensuring generality and flexibility and allowing a variety of lines of action for improving model components via machine-learning approaches. The model calibration, carried out with reference to flat plate test cases subjected to different pressure gradients and freestream turbulence levels, is discussed in detail. Although the constructed model is calibrated on a group of classic flat plat cases, the validation campaign, mostly carried out on gas turbine cascades, demonstrates its ability to predict transitional flows with engineering accuracy. Finally, while the model is not specifically developed for natural transition predictions, satisfactory predictions are obtained in scenarios with low freestream turbulence for flat plate and airfoil flows.

RANS Capabilities for Transonic Axial Compressor: A Perspective From GPPS Computational Fluid Dynamics Workshop

Abstract Reynolds-averaged Navier–Stokes (RANS) simulations currently serve as the prevailing industrial method for simulating axial compressor flows, and this status is expected to persist in the foreseeable future. To evaluate the capabilities of contemporary RANS solvers for compressors, this article presents a statistical analysis of RANS simulation results submitted to the first and the second Global Power and Propulsion Society (GPPS) computational fluid dynamics (CFD) workshops, where blind tests on the TUDa-GLR-OpenStage transonic axial compressor were performed. The workshops were held online in December 2021 and in a hybrid format at Chania, Greece, in September 2022, which are the first primary turbomachinery CFD workshops following the 1994 International Gas Turbine Institute (IGTI) CFD blind test event on NASA Rotor 37. A total of 35 submissions were received from 12 distinct RANS solvers, contributed by 14 participants affiliated with 11 organizations across 5 countries. Participants include academic researchers, engineers from the turbomachinery industry, and developers of commercial CFD solvers. First, the grid convergence behavior exhibited by various solvers employing different turbulence models is examined. Afterward, the prediction accuracy of the ensemble of the simulation results is evaluated, and the representative simulation results are compared and analyzed in detail. The key factors that improve the prediction accuracy are identified. These results foster improved usage and further development of turbomachinery RANS solvers.

0-D Dynamic Performance Simulation of Hydrogen-Fueled Turboshaft Engine

In the last few decades, the problem of pollution resulting from human activities has pushed research toward zero or net-zero carbon solutions for transportation. The main objective of this paper is to perform a preliminary performance assessment of the use of hydrogen in conventional turbine engines for aeronautical applications. A 0-D dynamic model of the Allison 250 C-18 turboshaft engine was designed and validated using conventional aviation fuel (kerosene Jet A-1). A dedicated, experimental campaign covering the whole engine operating range was conducted to obtain the thermodynamic data for the main engine components: the compressor, lateral ducts, combustion chamber, high- and low-pressure turbines, and exhaust nozzle. A theoretical chemical combustion model based on the NASA-CEA database was used to account for the energy conversion process in the combustor and to obtain quantitative feedback from the model in terms of fuel consumption. Once the engine and the turbomachinery of the engine were characterized, the work focused on designing a 0-D dynamic engine model based on the engine’s characteristics and the experimental data using the MATLAB/Simulink environment, which is capable of replicating the real engine behavior. Then, the 0-D dynamic model was validated by the acquired data and used to predict the engine’s performance with a different throttle profile (close to realistic request profiles during flight). Finally, the 0-D dynamic engine model was used to predict the performance of the engine using hydrogen as the input of the theoretical combustion model. The outputs of simulations running conventional kerosene Jet A-1 and hydrogen using different throttle profiles were compared, showing up to a 64% reduction in fuel mass flow rate and a 3% increase in thermal efficiency using hydrogen in flight-like conditions. The results confirm the potential of hydrogen as a suitable alternative fuel for small turbine engines and aircraft.

Prediction model optimization of gas turbine remaining useful life based on transfer learning and simultaneous distillation pruning algorithm

For the application of deep learning (DL) models in the field of remaining useful life (RUL) prediction and predictive maintenance (PdM) of complex equipment, the insufficient training data and large model are the two major problems. To address these issues, a model training method based on transfer learning and a simultaneous distillation pruning algorithm were proposed. By introducing prior knowledge, three transfer learning modes are devised to reduce the demand of training data. Additionally, the simultaneous distillation pruning algorithm was devised to make the model lightweight, and an iterative pruning method was adopted to trim the large neural network model. By analyzing the performance of different transfer learning modes, the effectiveness of the proposed method can be demonstrated. The number of model parameters and the performance before and after pruning were compared. The results demonstrated that, without significant alterations to the prediction performance, the proposed model exhibited the capability to markedly reduce the number of model parameters. Based on the proposed methods, the challenges of insufficient data and efficiency encountered by DL models could be effectively addressed.

Performance and failure modes of thermal barrier coatings deposited by EB-PVD on blades under real service conditions in gas turbine

Thermal barrier coatings (TBCs) with a double columnar crystal structure of CoCrAlY/YSZ, prepared using electron beam physical vapor deposition (EB-PVD), were applied to turbine blades and tested in real gas turbine conditions. This study investigates their failure mechanisms under both actual operating conditions and simulated external loads, using three-point bending tests. The performance of full-sized, TBC-coated blades was analyzed through finite element modeling, while the thermomechanical and mechanical properties of the coatings after service were measured to support the simulation and provide insights into the failure processes. A new degradation mode, characterized by penetration cracking, was observed in the EB-PVD coatings. This behavior is linked to the columnar grain structure of YSZ and CoCrAlY, lower operational temperatures, and the reduced thickness of the YSZ layer. Surface cracks in the YSZ coating primarily occurred in regions with large curvature, where stress concentrations are higher. This study offers new insights into the failure modes of TBCs under real gas turbine operating conditions.

A numerical investigation of the polyethylene glycol‐based tetra hybrid nanofluid flow over a stretched porous rotatory disk

AbstractPolyethylene glycol (PEG) is a great heat and mass transmissive fluid that has promising applications in medical, pharmaceutical, and electronic industries. Tetra‐hybrid nanofluids (HNFs) are the most upgraded version of heat and mass transmissive nanofluids that are synthesized by dispersing four distinct nanoparticles in the carrier fluid. The study of the flow of nanofluids and their advanced classes across rotatory disks is receiving remarkable interest in research and innovation due to their considerable applications like gas turbine rotors, aeronautical, medical equipment, rotating machinery, thermal power developing systems, and so forth. Therefore, the present paper aims to inspect the magnetohydrodynamic, steady, three‐dimensional, and incompressible flow of a non‐Newtonian tetra‐HNF over a stretched porous rotating disk. The chosen tetra‐HNF consists of four distinct nanoparticles namely, molybdenum disulfide, copper oxide, magnesium oxide, and zirconium oxide with PEG as the carrier fluid. The flow model is modified with innovative impacts of variable thermal conductivity, thermal radiation, chemical reaction, variable mass diffusivity, and suction/injection to make this research more convenient. The mathematical computation is conducted via the bvp4c numerical method, and the outputs are determined via tables and graphs. Mounting values of the Deborah number amplify the axial velocity while augmentation is noticed in the fluid's radial and azimuthal velocities for rising values of the rotation parameter. Besides, the rotation parameter aids in enhancing both the heat and mass transportation rates while the chemical reaction parameter significantly aids the mass transportation rate. One of the significant results of this inspection is that tetra‐HNF exhibits better heat and mass transportation rates than the ternary‐HNF, and the HNF whereas it has lesser skin friction than the ternary‐HNF, and the HNF.

Effect of HIP on Creep Properties in the Single Crystal Superalloy

The Rene N5 is a second-generation single crystal superalloy containing 3wt% Re, commonly used in gas turbine blades for power generation at temperatures up to 1600°C due to its excellent creep life. Generally, single crystal (SX) and directionally solidified (DS) blades are not applied to hot isostatic pressing (HIP) because their porosities are lower than conventionally cast (CC) blades, and it causes recrystallization issue. However, in this study, HIP was chosen as a candidate to improve the mechanical properties of the second-generation single crystal superalloy Rene N5. HIP followed by ultra-rapid cooling rate of 660K/minute was applied in an attempt to address this issue. This approach was expected to enhance creep rupture properties through pore reduction and microstructural homogenization. Furthermore, by setting the HIP temperature and time identical to the solution treatment condition, the possibility of replacing solution treatment with HIP was discussed. As results of creep rupture tests, the rupture life was excellent in the order of specimens treated with HIP + solution + aging, solution + aging, and HIP + aging treatments. It is interesting that this is found to be primarily influenced by the size and shape of carbides and γ’ phases, with the effects of crystallographic orientation, shrinkage porosity, and eutectic phase being negligible.