bluuebunny/crossref_metadata_2025 huggingface dataset:
Real Time Diagnostic Method of Gas Turbines Operating Under Transient Conditions in Hybrid Power Plants
Authors: Tsoutsanis Elias , Hamadache Moussa , Dixon Roger
Published: January 2021

Recent expansion of renewable power plants have transformed the role and operation of gas turbines to a great extent. From the base load operation era we are moving into a flexible and dynamic engine operation of gas turbines. In particular, aero derivative engines that have the capacity to start up, shut down in a short time frame are becoming quite popular for both hybrid power plant arrangements and distributed electricity generation. Advances in computational intelligence, such as digital twins, have amplified the importance of condition monitoring, diagnostics and prognostics capabilities in the face of gas turbine operation. Given the dynamic operating profile of the gas turbines, it is of paramount importance to develop, tune and deploy engine models that are accurate and robust to accommodate their nonlinear behavior. Performing diagnostics in transient conditions has recently gained attention, since the gas turbines are acting as partners of renewables and they have a supporting role. Among a family of diagnostics methods, one that has real time capabilities is based on zero-dimensional engine models. This paper present a novel diagnostic approach for determining the health of a gas turbine when it works in conjunction with a wind farm in hybrid power plant. In contrary to our earlier works, where we have mathematically modeled component maps to derive the health of an engine, in this paper we propose a model-based diagnostic method without reconstructing component maps according to their degradation. Once the engine model is initially adapted to its clean condition, it is subsequently tuned in real time to reflect the changes in both the operation and degradation with respect to a benchmark engine model. Time evolving multiple component degradation scenarios for a gas turbine operating in conjunction with a wind farm, are simulated to test the accuracy and efficiency of the proposed method. From a bank of simulated measurements, data trending is performed which facilitates the detection of degradation and provides useful conclusions about the health state of the engine. This diagnostic method is suitable for gas turbines that spend most of their life time in part-load and transient operation and it forms a simple and useful tool for operators in planning their assets maintenance in a computational efficient and accurate manner.
Effects of S-Shaped Intake on Aeromechanical Characteristics of a Transonic Fan
Authors: Zheng Yun , Xu Kang , Yang Hui , Gao Qingzhe , Jin Xiubo
Published: January 2021

S-shaped intakes are widely used in aero-engines of modern fighters because of the demand for reducing radar cross-section. Besides, boundary layer ingestion (BLI) configurations are proposed in civil engines recently due to the high propulsion efficiency and low fuel consumption. And S-shaped ducts are usually used as transition sections of diffusers in BLI intakes. Compared with normal straight intakes, it is inevitable to bring in the influence of inlet distortion and acoustic reflection for S-shaped intakes. Meanwhile, composite fan blades, shorter intakes and integrated blisks are common in engine designs. So, fan blades are prone to serious vibrations such as flutter and forced response, which may lead to high-cycle fatigue, and further cause structural failure.

The aeromechanical characteristics of a transonic fan (NASA rotor67) in presence of a s-shaped intake are predicted by an in-house integrated time-domain aeroelasticity code. The three dimensional, time-accurate, unsteady Reynolds-Averaged Navier-Stokes equations are solved in fluid domain, and the structural dynamic equations of blade vibration are solved with a modal superimposition method.

Mode shapes and natural frequencies of rotor blade are obtained with a commercial Finite Element code, and the Campbell diagram is presented. Full-annulus aeroelastic calculations are conducted to obtain the transient response and the aerodynamic damping of fan blades. Different techniques for interface between the intake and the rotor are used for comparison to demonstrate the influence of upstream interaction. A mixing-plane model is used at the interface to model the blade vibration without interactions with the distortion, while a sliding-plane model is used at the same condition to include the flow distortion and acoustic effects on the fan blade motion. S-shaped intakes with two different axial length are investigated for the forced response and flutter stability. This study indicates that the forced response level is attenuated due to the decrease of distortion level as the length increases, while the flutter stability is determined by the phase difference between the upstream and the reflective acoustic wave.
Numerical Simulation of a Particle in Air Flow Around a Turbine Blade
Authors: Oshima Ippei , Furuichi Mikito
Published: January 2021

The Steam turbine is widely used for generating electricity, in the thermal, nuclear and geothermal power generation systems. A wet loss is known as one of the degrading factors of the performance. To reduce the amount of liquid phase generated by condensation and atomization from nozzles, the prediction of the distribution of liquid mass flow rate inside the turbine is important. However, the quantitative understanding and the prediction method of the liquid flow inside the turbine remain unclear because physics inside a turbine is consisting of complex multiscale and multiphase events. In the present study, we proposed a theoretical model predicting the motion of droplet particles in gas flow based on Stokes number whose model does not require numerical simulation. We also conducted the numerical validation test using three-dimensional Eulerian-Lagrangian simulation for the problem with turbine blade T106. The numerical simulation shows that the particle motion is characterized by the Stokes number, that is consistent with the assumption of the theoretical model and previous studies. When Stokes number is smaller than one, the particle trajectory just follows the gas flow streamline and avoids the impacts on the surface of T106. With increasing Stokes number, the particles begin to deviate from the gas flow. As a result, many particles collide with the surface of T106 when the Stokes number is approximately one. When the Stokes number is extremely larger than one, particles move straight regardless of the background gas flow. The good agreements between the theoretical predictions and numerical experiment results justify the use of our proposed theoretical model for the prediction of the particle flow around the turbine blade.
Aerodynamics and Heat Transfer Inside a Gas Turbine Mid-Passage Gap
Authors: Shaikh Faisal , Rosic Budimir
Published: January 2021

Gas turbine blades and vanes are typically manufactured with small clearances between adjacent vane and blade platforms, termed the midpassage gap. The midpassage gap reduces turbine efficiency and causes additional heat load into the vane platform, as well as changing the distribution of endwall heat transfer and film cooling. This paper presents a low-order analytical analysis to quantify the effects of the midpassage gap on aerodynamics and heat transfer, verified against an experimental campaign and CFD.

Using this model, the effects of the gap can be quantified, for a generic turbine stage, based only on geometric features and the passage static pressure field. It is found that at present there are significant losses and a large proportion of heat load caused by the gap, but that with modified design this could be reduced to negligible levels.

Cooling flows into the gap to prevent ingression are investigated analytically and with CFD. Recommendations are given for targets that turbine designers should work toward in reducing the adverse effects of the midpassage gap. A method to estimate the effect of gap flow is presented, so that for any machine the significance of the gap may be assessed.
Numerical Study of Erosion due to Online Water Washing in Axial Flow Compressors
Authors: Di Gruttola Francesca , Agati Giuliano , Venturini Paolo , Borello Domenico , Rispoli Franco , Gabriele Serena , Simone Domenico
Published: January 2021

Recent year witnessed an increasing interest in online water washing technique since it allows to minimize compressor performance losses in the time interval between two off-line washing. However, the washing capability and the related erosion risk depend on several parameters such as the injection duration, the droplet size, the spray angle, the water mass flow rate and the injector positions. The influence of such parameters on the washing capability and erosion rate is analysed. Results are discussed with reference to number of impacts, wetted surface, capture efficiency, accumulated energy and erosion. The numerical simulation is performed with ANSYS Fluent in which a new water droplet erosion model, introduced in previous papers, is here included as a User Defined Function. The discussion provides useful information for prescribing the injector characteristics and the water washing procedure with the aim of minimizing the erosion risk.
Effects of Cooling Configurations on the Aerothermal Performance of a Turbine Endwall With Jet Impingement and Film Cooling
Authors: Bu Hongyan , Guo Zhendong , Song Liming , Li Jun
Published: January 2021

With the rapid increase of turbine inlet temperature and the application of premixed combustion, turbine components, particularly the turbine endwall, works in extremely harsh environment and must be effectively cooled to ensure the component durability. Recently, new cooling schemes that employ both external film cooling and internal jet impingement cooling have drawn much attention due to their extraordinary performance. In this study, a numerical model of turbine endwall with jet impingement and film cooling was established and validated against the experimental results. To investigate the effects of geometric parameters related with this cooling scheme, four parameters including impingement hole-to-hole pitch Pi, impingement hole diameter Di, impingement channel height H, film hole diamete Df, were selected to adjust within a reasonable range. The uniform design method was used to collect a database that represented the design space formed by the four parameters. Performance criterions including area-averaged overall cooling effectiveness, standard deviation of overall cooling effectiveness, total pressure drop coefficient of the cooling system were evaluated through CFD calculations. To explore and exploit the design space as much as possible, a Kriging surrogate model was built from the database. Analysis of variance (ANOVA) was conducted based upon the surrogate model to investigate the main effect of each parameter and the correlation between parameters. Finally, based upon the knowledge obtained from ANOVA, typical designs were selected from the database which yielded either best or poorest performances. Through detailed analysis of flow and heat transfer mechanisms of these typical designs, the influence of each parameter was illustrated clearly and suggestions for the design of similar cooling schemes were drawn.
Analysis of Failed Startup Sequence of a Single Spool Turbojet Engine
Authors: Sekar T. Chandra , Sundararaj Ramraj H. , Arora Rajat , Kushari Abhijit
Published: January 2021

During the static testing of a single spool turbojet engine (400 N Titan Engine) running on Jet A-1 as fuel, the starting sequence was unsuccessful, however, upon substituting the fuel with Diesel the engine started successfully. Till that point, the engine operation/performance was normal, and a series of tests were conducted for a total time of 5 hours. These 5 hours of testing spanned over five months during which ambient temperature varied from 5 °C to 37 °C, and relative humidity varied from 40% to 90%. The starting sequence was unsuccessful at the maximum ambient temperature (37 °C) and moderate relative humidity condition (50%). During the test, various parameters including pressure, temperature, rotor speed and mass flow rate were measured and recorded using a computer based data acquisition. For the failed start-up case, during the starting sequence, a sudden decrease in rotor speed was observed as the rotor reached ∼80% of the calibration value followed by flameout in combustion chamber. This sudden drop in rotor speed occurred due to mild-surge in compressor which continued up to flameout. The cause of mild-surge is attributed to the momentary blockage at the exit of the compressor caused by the combustion process. These pressure fluctuations propagated downstream leading to flame out. The combination of high ambient temperature (35 °C) and moderate humidity (∼50%) resulted in higher combustion chamber temperature which resulted in the momentary blockage at compressor exit during the transient operation. The substitution of Diesel as fuel resulted in lower combustion chamber temperature, and resolved the issue. It is important to note that, the mild-surge observed in this case is caused by downstream condition, and would occur only at some special situations (inlet conditions). Hence, it may be concluded, that the compressor surge in a jet engine may be caused by downstream components (under some special conditions), and design modifications to these downstream components may resolve the issue in those cases.
Experimental and Numerical Study of an Open Impeller Centrifugal Compressor Stage Utilising 3D Diffuser End Wall Contouring for Operating Range Extension
Authors: Hermann Daniel , Wirsum Manfred , Robinson Douglas , Jenny Philipp
Published: January 2021

Highly efficient and concurrent flexible operation are heavy demands on today’s centrifugal compressor units. Diffuser end wall contouring is a measure to delay the incipience of instability and therefore to extend the compressor’s operating range while maintaining efficient performance. In the presented paper, a hubside wall contouring, applied in the vaneless space upstream the diffuser’s leading edge and within the diffuser passage of a state-of-the-art centrifugal compressor with an open impeller is examined. CFD computations are performed for both a baseline diffuser design with parallel channel walls and the hub-side wall contoured diffuser design. Comparisons of characteristic and diffuser stability decisive flow variables are made in perpendicular sections along an extrapolated camber line of the diffuser vane for full span, near shroud and near hub wall. In operating points near the stability limit at two different stage Mach numbers, the stabilizing effect of the hub-side wall contouring on the diffuser flow is clearly shown. In a scale-model test rig, experimental data including pneumatic 5-hole probe data for a full diffuser blade-to-blade passage, static wall pressures at various planes as well as total temperature was measured. The experimental data is utilized for validation of the presented numerical calculations. The flow stabilizing effect of the hub-wall contouring is clearly visible in the measurements, which showed 8% range extension at highest stage Mach number Mu2 = 1.16 and a range extension of 2% at design stage Mach number Mu2 = 1.0.
Large-Eddy Simulation of Film Cooling Performance Enhancement Using Vortex Generator and Semi-Sphere
Authors: Wang Wen , Cui Jiahuan , Qu Shaoxing
Published: January 2021

Film cooling is an essential cooling method to prevent high-pressure turbine blade from melting down due to the high inlet temperature. In order to improve the film cooling efficiency, several flow control methods have been proposed. In this paper, large-eddy simulations are performed to study the effectiveness of a vortex generator (VG) and a semi-sphere installed downstream of the cooling jet. Before the detailed analyses, the numerical framework is validated against the available experimental data. Both the laminar and turbulent approaching boundary layers are considered. The turbulent boundary layer is generated by a numerical plasma actuator. After validation, the influence of VG and semi-sphere on the film cooling efficiency at various blowing ratios are analyzed. It is found that a counter-rotating vortex pair (CVP) is formed downstream and its strength increases with the blowing ratio in the configuration without VG/semi-sphere. When the VG is installed, it produces another vortex pair that rotates in the reverse direction of the CVP, which reduces the CVP strength and increases the lateral diffusion of the coolant. As a result, the film cooling efficiency is greatly improved, especially at a higher blowing ratio. For the case with a semi-sphere, the film cooling efficiency is also improved, especially at low–medium blowing ratios. However, it is not as effective as the VG in terms of enhancing cooling efficiency. In addition, the total pressure loss is calculated to examine the aerodynamic penalty associated with the VG and semi-sphere. It is found that the total pressure loss increased by only 1% due to the VG or semi-sphere, within the range of blowing ratio investigated in the current study. Considering the overall performance and the feasibility of being applied in practice, a semi-sphere installed downstream of the cooling hole is a promising method to improve the cooling efficiency.
Analysis of Design, Off-Design and Annual Performance of Supercritical CO2 Cycles for CSP Applications
Authors: Thanganadar Dhinesh , Fornarelli Francesco , Camporeale Sergio , Asfand Faisal , Patchigolla Kumar
Published: January 2021

Supercritical carbon dioxide (sCO2) cycles are studied as the next-generation power cycles in order to reduce the cost of Concentrating Solar Power (CSP) plants. The design performance of numerous cycles has been investigated, nevertheless, the off-design and annual performance of these cycles are seldom studied. This plays a critical role in selecting an optimal cycle for CSP application, as an efficient power cycle influences the solar field size, consequently affecting the Levelised cost of electricity (LCOE). In this study, the design, off-design and annual performance of three sCO2 cycles; simple recuperative, recompression and partial-cooling cycles are studied. Multi-objective optimisation was performed and the off-design Pareto fronts were compared for the changes in the power cycle boundary conditions. Annual performance simulation was carried out, and the performance of the three cycles was compared when the power cycle is operated in maximum efficiency mode, which facilitates selecting the optimal cycle. The LCOE of the simple recuperated cycle was higher by roughly 1.7¢/kWh than recompression cycle when maximising the power cycle efficiency and the partial cooling cycle is higher by 0.2¢/kWh. However, operating the power cycle in the maximum efficiency mode significantly lowers the plant capacity factor (around 10–20%).
Application of Uncertainty Quantification Methods to the Prediction of Effusion Cooled Combustor Liner Temperature
Authors: Gamannossi Andrea , Amerini Alberto , Poggiali Matteo , Elmi Carlo Alberto , Mazzei Lorenzo , Andreini Antonio
Published: January 2021

As far as the preliminary thermal design of gas turbine components is concerned, 1-D codes are still widely used in standard industrial practice. Among the different components, the combustor is one of the most critical ones and its thermal design still greatly affects the reliability and life of the entire engine. During the initial phases of the design process, parameters are often roughly known. For this preliminary phase, a low-order approach is preferred instead of a high-fidelity simulation: the exploration of the whole space is extremely important to better understand the behavior of the system and to focus on the design objectives. Uncertainty quantification (UQ) methods, mainly developed in recent years and applied in many fields, are useful tools for the preliminary design phase and provide support during the whole design process. The objective of this work is to estimate the main sources of uncertainties in the design phase of an aeroengine effusion cooled combustor. The test case is based on a full annular lean-burn combustor, tested during the LEMCOTEC (Low EMissions COre-engine TEChnologies) European project. Among the test points investigated in the experimental campaign, the Approach condition is here analyzed. The inner liner is taken into consideration to investigate the metal temperature. Therm-1D, a 1-D in-house simulation code, is used to model the combustor and the open-source tool DAKOTA is adopted for the uncertainty quantification analysis. The baseline case of the combustor is studied and several uncertainty analyses are investigated. They are divided into 3 main groups: geometrical, tuning modelling parameters and thermal loads. For each group, the most relevant parameters are considered as a source of input uncertainty. In particular, a classical Monte Carlo approach is compared with four innovative polynomial-chaos approaches for each group: Gauss quadrature, total order with LHS sampling, stochastic collocation, and Smolyak. The analyses proved how the last two methods give the best results with a sensible lower amount of simulation (depending on the number of input variables). Lastly, results are compared with experimental data to achieve a better understanding of the most relevant input parameters and the propagation of their uncertainty on the results.
A Friction-Enhanced Tuned Ring Damper for Bladed Disks
Authors: Lupini Andrea , Epureanu Bogdan I.
Published: January 2021

This paper introduces a new type of damper for turbomachinery blisks. The major pitfalls of the damper concepts currently employed are two: the low level of relative motion that is available at the damper attachment location, and the inability to control the preload at the frictional interface. To address these issues, the proposed damper is designed as a tuned vibration absorber, which allows energy transfer from the blades to the damper provided that the natural frequency of the damper is close to that of the host structure. Thanks to the enhanced energy transfer, the damper can experience increased relative motion. Frictional contacts are then included to dissipate the energy transferred to the damper. The control of the contact preload is also important, as the centrifugal loads acting on the damper are extremely large and could result in the damper being stuck in its groove and not dissipating energy. These two requirements result in competing priorities. The damper structure must be stiff enough to withstand centrifugal loading without affecting the preload too much. However, it also must be compliant to make sure that its natural frequencies can match the ones of the host structure. For this reason, the proposed damper involves a complex geometry that is stiff in the radial direction and softer in the circumferential direction, which is the direction of the relative motion. A model of the damper is created to damp the vibration of a realistic blisk based on the NASA Rotor 67. The effectiveness of the damper is investigated using high fidelity finite element models. Due to the nonlinear nature of the contact, the equations of motion are solved using harmonic balance, and the size of the (linear part of the) system is reduced using Craig-Bampton component mode synthesis. The frequency response of the system is obtained to analyze the effectiveness of the proposed design. Preliminary results show the potential of this technology for structures with such low damping.
Implementation of Hole-Pair in Ramp to Improve Film Cooling Effectiveness on a Plain Surface
Authors: Hussain Sadam , Yan Xin
Published: January 2021

Film cooling is one of the most critical technologies in modern gas turbine engine to protect the high temperature components from erosion. It allows gas turbines to operate above the thermal limits of blade materials by providing the protective cooling film layer on outer surfaces of blade against hot gases. To get a higher film cooling effect on plain surface, current study proposes a novel strategy with the implementation of hole-pair into ramp. To gain the film cooling effectiveness on the plain surface, RANS equations combined with k-ω turbulence model were solved with the commercial CFD solver ANSYS CFX11.0. In the numerical simulations, the density ratio (DR) is fixed at 1.6, and the film cooling effect on plain surface with different configurations (i.e. with only cooling hole, with only ramp, and with hole-pair in ramp) were numerically investigated at three blowing ratios M = 0.25, 0.5, and 0.75. The results show that the configuration with Hole-Pair in Ramp (HPR) upstream the cooling hole has a positive effect on film cooling enhancement on plain surface, especially along the spanwise direction. Compared with the baseline configuration, i.e. plain surface with cylindrical hole, the laterally-averaged film cooling effectiveness on plain surface with HPR is increased by 18%, while the laterally-averaged film cooling effectiveness on plain surface with only ramp is increased by 8% at M = 0.5. As the blowing ratio M increases from 0.25 to 0.75, the laterally-averaged film cooling effectiveness on plain surface with HPR is kept on increasing. At higher blowing ratio M = 0.75, film cooling effectiveness on plain surface with HPR is about 19% higher than the configuration with only ramp.
Unsteady Methods to Investigate Inlet Distortion in a Transonic Tail Cone Thruster Fan Stage With Boundary Layer Ingestion
Authors: Giri Ritangshu , Turner Mark G. , Celestina Mark L.
Published: January 2021

Boundary Layer Ingestion (BLI) engines have the potential to offer significantly reduced fuel burn, but the fan stage must be designed to run efficiently with a distorted inflow. It must also be able to withstand unsteady aerodynamic loads resulting from a non-uniform flowfield. In a multidisciplinary turbomachinery design cycle involving such a complicated flowfield, high fidelity numerical solutions are required. Two high fidelity unsteady Reynolds Averaged Navier-Stokes (URANS) methods for accurate analysis of a Tail Cone Thruster (TCT) transonic fan stage subjected to inlet distortion have been implemented. They are frequency domain based non-linear harmonic (NLH) and full-annulus complete time domain based time marching methods. This paper demonstrates that the relevant parameters required to accurately compute aerodynamic performance of a fan stage in distorted conditions can be accurately modelled with a few harmonics using the NLH method in a fraction of time compared to the full annulus time marching method. However, the complete aerodynamics of distortion transfer across different blade rows of a fan stage can only be analyzed using the time marching solution. Several physical mechanisms which govern the fan response to an inlet distortion and how different distortion profiles impact the aerodynamic performance of this fan stage are also explained.
Determining the Optimal Crystallographic Orientation in a Single Crystal Turbine Blade to Increase its Strength Reliability
Authors: Vasilyev Boris , Selivanov Alexander , Semenov Artem , Bortnikov Andrei , Limonova Valentina
Published: January 2021

The high-pressure turbine blades of most modern gas turbine engines are made of single-crystal alloys. Single-crystal materials have significant anisotropy characteristics; therefore, the orientation of the axes of the single crystal relative to the geometrical axes of the blade has a great effect on the stress-strain state, static strength, and dynamic characteristics of the blade.

Here, the necessary optimization of both the axial orientation (the optimal value of which may differ from <001>) and the azimuthal orientation is confirmed. The problem was solved by considering the anisotropic temperature–orientation characteristics of the alloy and the uneven temperature field of the blade. The values of the optimal crystallographic orientations were determined.

Notably, casting tolerances for the deviation of the crystallographic axes must be considered when searching for the optimal position of the axes of the single crystal.
Integration Options for Nuclear Steam Cycle Using Liquid Air Energy Storage
Authors: Heo Jin Young , Lee Won Woong , Park Jung Hwan , Lee Jeong Ik
Published: January 2021

To facilitate the energy transition, the conventional baseload nuclear power must be equipped with flexibility. By integrating grid-scale energy storage systems to the existing nuclear plants, they can curtail their load to avoid surplus generation. Liquid air energy storage (LAES) has been steadily investigated for their advantages, and this paper suggests an integrated layout using mechanical drive steam turbine and packed bed energy storage systems. Possible options for integration of LAES to the existing nuclear steam cycle are considered. The performance of packed bed storage systems is analyzed using transient modeling, and the results are fed into the overall cycle design using an in-house code. The results of the analysis suggests that the concept can reach up to 45.7–59.8% in round-trip efficiency, under much simplified cycle layout than the reference LAES layouts.
Comparative Study of Blades Reduced Order Models With Geometrical Nonlinearities and Contact Interfaces
Authors: Delhez Elise , Nyssen Florence , Golinval Jean-Claude , Batailly Alain
Published: January 2021

This paper investigates the use of different model reduction methods accounting for geometric nonlinearities. These methods are adapted to retain physical degrees-of-freedom in the reduced space in order to ease contact treatment. These reduction methods are applied to a 3D finite element model of an industrial compressor blade (NASA rotor 37). In order to compare the different reduction methods, a scalar indicator is defined. This performance indicator allows to quantify the accuracy of the predicted displacement both locally (at the blade tip) and globally. The robustness of each method with respect to variations of the external excitation is also assessed. The performances of the reduction methods are then compared in the case of frictional contact between the blade tip and the surrounding casing. This work brings evidence that reduced order models provide a computationally efficient alternative to full order finite element models for the accurate prediction of the time response of structures with both distributed and localized nonlinearities.
An Industrial Methodology for Erosion Analysis of FCC Expander Blades
Authors: Maceli Nicola , Maffulli Gianfranco
Published: January 2021

Fluid Catalytic Cracking (FCC) is a process for the conversion of heavy stocks recovered from different refinery operations into high-octane gasoline, light fuel oils and olefin rich light gases.

Zeolite particles are used as catalyst in the process to facilitate the cracking of long hydro-carbon molecules.

Because of the contact between catalyst and feedstock, coke deposits on the catalyst active surface reducing its activity, air is used to remove it from the catalyst, in the regenerator. The coke burning produces a hot flow of flue gas with a valuable energy content (700°C – 3bar) that can be recovered using a Hot Gas Expander HGE before releasing the exhausts in the atmosphere.

The flue gas is carrying a certain amount of catalyst so the expander hot parts (mainly blades but also the stator vanes) are constantly exposed to an abrasive medium that may compromise the reliability of the asset.

Understanding how the solid particle erosion works is one of the challenges that HGEs designer shall deal with.

To this purpose, a numerical approach was developed to account for some of the factors that are known to play a major role in erosion phenomena: particle velocity, angle of impact, composition and particle size, as well as the mechanical properties of the target surface at the operating temperature.

The methodology was then applied to a cascade blade for which erosion data collected in a stationary erosion test rig are available. The comparison between numerical and experimental data showed a good agreement therefore providing confidence on the proposed methodology.

Finally, the numerical procedure has been applied to a real case to show the effect of the different catalyst load on the life of the blades.
Characterising Hydrogen Micromix Flames: Combustion Model Calibration and Evaluation
Authors: López-Juárez Marcos , Sun Xiaoxiao , Sethi Bobby , Gauthier Pierre , Abbott David
Published: January 2021

Hydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. The ENABLEH2 project aims to demonstrate the feasibility of such a switch to hydrogen for civil aviation, within which the micromix combustion, as a key enabling technology, will be matured to TRL3. The micromix combustor comprises thousands of small diffusion flames for which air and fuel are mixed in a cross-flow pattern. This technology is based on the idea of minimizing the scale of mixing to maximize mixing intensity. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and low-temperature small diffusion flames in lean overall equivalence ratios.

For hydrogen-air mixtures there is a need to further characterise the physical importance and calibration process of the laminar Schmidt (Sc), Lewis (Le) and Prandtl (Pr) and turbulent Schmidt (Sc) numbers. In addition, there is limited numerical and experimental data about flame characteristics and emissions of hydrogen micromix combustor at high pressure and temperature conditions.

In this paper, the CFD software STAR-CCM+ was used with the FGM (Kinetic Rate) combustion model to simulate and calibrate hydrogen micromix flames. The research was divided into two parts. In the first part, the values of laminar Schmidt, Lewis and Prandtl numbers for H2 and air, non-reactive, flow mixtures were estimated as 0.22, 0.3 and 0.75 from correlations obtained in the literature. The typical Borghi diagram has been modified to represent this type of diffusion flame, since the assumption of Sc = Le = Pr = 1 can not be applied to hydrogen micromix flames and it is only for premixed flames. This diagram characterizes flame regime based on Damköhler (Da), Karlovitz (Ka) and turbulent Reynolds (Ret) numbers that were calculated from preliminary CFD simulations.

In the second part, the value of laminar Schmidt number was set as constant while laminar Lewis and Prandtl numbers were obtained from the flamelet tables. A Turbulent Schmidt number was then obtained by comparing RANS and LES simulations of a single injector. If Sct > 0.2, the predicted NOx production of RANS simulations approaches that of LES; while Sct < 0.2 provides similar overall flame structure between RANS and LES. It is concluded that, for the current simulations, Sct = 0.2 is a good compromise between flame structure and emissions prediction. Flame characteristics and NOx emissions given by Thickened Flame and FGM Kinetic Rate models in a single injector geometry were also compared.
Micro Gas Turbine Integrated With a Supercritical CO2 Brayton Cycle Turbine: Layout Comparison and Thermodynamic Analysis
Authors: Reale Fabrizio , Sannino Raniero , Tuccillo Raffaele
Published: January 2021

In an energetic scenario where both distributed energy systems and smart energy grids gain increasing relevance, the research focus is also on the detection of new solutions to increase overall performance of small-scale energy systems. Waste heat recovery (WHR) can represent a good solution to achieve this goal, due to the possibility of converting residual thermal power in thermal engine exhausts into electrical power. The authors, in a recent study, described the opportunities related to the integration of a micro gas turbine (MGT) with a supercritical CO2 Brayton Cycle (sCO2 GT) turbine. The adoption of Supercritical Carbon Dioxide (sCO2) as working fluid in closed Brayton cycles is an old idea, already studied in the 1960s. Only in recent years this topic returned to be of interest for electric power generation (i.e. solar, nuclear, geothermal energy or coupled with traditional thermoelectric power plants as WHR). In this technical paper the authors analyzed the performance variations of different systems layout based on the integration of a topping MGT with a sCO2 GT as bottoming cycle; the performance maps for both topping and bottoming turbomachinery have been included in the thermodynamic model with the aim of investigating the part load working conditions. The MGT considered is a Turbec T100P and its behavior at part load conditions is also described. The potential and critical aspects related to the integration of the sCO2 GT as bottoming cycle are studied also through a comparison between different layouts, in order to establish the optimal compromise between overall efficiencies and complexity of the energy system. The off-design analysis of the integrated system is addressed to evaluate its response to variable electrical and thermal demands.
Structural Dynamic and Inherent Damping Characterization of Additively Manufactured Airfoil Components
Authors: Goldin Andrew , Scott-Emuakpor Onome , George Tommy , Runyon Brian , Cobb Richard
Published: January 2021

The push for low cost and higher performance/efficient turbine engines has introduced a demand for novel technologies to improve robustness to vibrations resulting in High Cycle Fatigue (HCF). There have been many proposed solutions to this, some passive and some active. With the advent of Additive Manufacturing (AM), new damping techniques can now be incorporated directly into the design and manufacture process to suppress the vibrations that cause HCF. Recent work has been investigating new ways of using AM for turbine engine applications. A specifically innovative approach using Laser Powder Bed Fusion (LPBF) is of particular note. The use of internal pockets filled with the build powder but left unfused has proved to have damping quality with > 90% force response reduction. This study will investigate the as-manufactured parts, damping endurance, and structural dynamic changes when this technology is applied to a compressor-like blade. This will be done by using multiple testing methods to investigate the performance and dynamics of the blade. The study will use computed tomography (CT) scans to investigate the pockets, structured light scans to investigate the external geometry, Modal Assurance Criteria (MAC) to investigate the structural dynamics and a sinusoidal strain step test to investigate endurance. This study found similar endurance and damping capabilities as previously observed, in addition to finding that the inclusion of the unfused powder pockets did not affect mode shapes measured by the MAC.
Super Aggressive S-Ducts for Air Breathing Rocket Engines
Authors: Taylor J. V. , Flanagan F. , Dunlop A. , Grimshaw S. D. , Miller R. J.
Published: January 2021

Air breathing rocket engines require turbomachinery and ducting that is substantially lighter than that used in ground based or aerospace gas turbines. In order to reduce the weight of the axial compressor, the design of the inter-spool swan neck duct is targeted. In this paper a circumferential splitter blade is used to reduce loading and diffusion on the duct endwalls. The splitter and duct geometry are coupled and optimised together using 2D CFD. A design is selected that is 30% shorter than ducts that are currently used in aerospace gas turbines and the 3D flow features are investigated in further detail using an experimental rig and 3D CFD.

This paper shows that the “splittered” duct has 3 benefits over a conventional duct design: First, separation of the endwalls is prevented even at short duct lengths, this will reduce distortion into the downstream compressor. Second, losses generated by corner separations on structural struts can be reduced by 20%, enabling short ducts to achieve high performance. Third, splittered ducts are shown to be twice as robust to uncertain inlet flow conditions as conventional ducts. This allows a designer to target high performance short designs with reduced risk.
An Integrated Approach to Simulate Gas Turbine Secondary Air System
Authors: Izadi Ali , Madani Seyed Hossein , Hosseini Seyed Vahid , Chizari Mahmoud
Published: January 2021

One of the most critical parts of a modern gas turbine that its reliability and performance has a great influence on cycle efficiency is the secondary air system (SAS). Modern systems functions to supply not only cooling air flow for turbine blades and vanes but sealing flow for bearing chambers and turbine segments as well as turbine disks’ purge flow in order to eliminate hot gas ingestion. Due to the various interactions between SAS and main gas, consideration of the former is substantially crucial in design and analysis of the whole engine. Geometrical complexities and centrifugal effects of rotating blades and disks, however, make the flow field and heat transfer of the problem so complicated AND too computationally costly to be simulated utilizing full 3-D CFD methods. Therefore, developing 1-D and 0-D tools applying network methods are of great interests.

The present article describes a modular SAS analysis tool that is consisted of a network of elements and nodes. Each flow branch of a whole engine SAS network is substituted with an element and then, various branches (elements) intersect with each other just at their end nodes. These elements which might include some typical components such as labyrinth seals, orifices, stationary/rotating pipes, pre-swirls, and rim-seals, are generally articulated with characteristic curves that are extracted from high fidelity CFD modeling using commercial software such as Flowmaster or ANSYS-CFX. Having these curves, an algorithm is developed to calculate flow parameters at nodes with the aid of iterative methods.

The procedure is based on three main innovative ideas. The first one is related to the network construction by defining a connectivity matrix which could be applied to any arbitrary network such as hydraulic or lubrication networks. In the second one, off-design SAS calculation will be proposed by introducing some SAS elements that their characteristic non-dimensional curves are influenced by their inlet total pressure. The last novelty is the integration of the blades coolant calculation process that incorporates external heat transfer calculation, structural conduction and coolant side modeling with SAS network simulation. Finally, SAS simulation of an industrial gas turbine is presented to illustrate capabilities of the presented tool in design point and off-design conditions.
Optimization of Fan-Shaped Film Cooling Holes for Enhancing Cooling Effectiveness Under Variable Coolant Inlet Pressure Ratios
Authors: Liu Zhansheng , Yang Kefeng , Yang Xing , Liu Zhao , Feng Zhenping
Published: January 2021

In traditional film cooling design, holes had the same geometry in the same row of the blade and the same zone of the endwall. However, film cooling holes operate at different conditions when the positions are different, even in the same row. Additionally, geometry variables of the film cooling holes with the best cooling performance vary with the aerodynamic conditions. Optimization of film cooling hole geometry and arrangement has been paid much attention in recent years to improve the cooling performance. In this paper, a fan-shaped film cooling hole has been optimized on a plate model under variable coolant inlet pressure ratios to obtain the geometry parameters with better and more robust cooling performance. Two design variables, i.e., injection angle and expand angle were studied in the optimization. The coolant inlet pressure was different for each case during the optimization. The optimization objective was to increase the mean value and decrease the variance value of the area average cooling effectiveness downstream of the hole exit. The optimization system consisted of a self-programming parametric design and mesh generation tool, a CFD solver and a genetic algorithm (GA) coupled with surrogate model. At first, numerical simulation results were validated against the measured data, and agreed well with the experiment results. Range of the design variables were determined according to the sensitive analysis of the design variables. It was indicated that the film cooling hole obtained by the optimization showed remarkably higher cooling effectiveness than that of the original scheme. With the pressure ratio changing, the optimized cooling hole obtained could keep relatively high effectiveness. Additionally, the optimized film cooling hole was applied on a typical gas turbine vane endwall to examine the cooling performance in cascade passage. It could be observed that the optimal film holes performed better than that of the original design.
Performance and Operating Characteristics of Micro Gas Turbine Driven by Pulse, Pressure Gain Combustor
Authors: Sakurai Takashi , Nakamura Shunsuke
Published: January 2021

This paper presents the experimental results of a micro gas turbine driven by pulse, pressure gain combustor. The aim of this study is to demonstrate the improvement of the engine performance by applying the pressure gain combustion. The micro gas turbine is composed of a combustor having two combustion chambers and an automotive turbocharger which is used as a compressor and a turbine. The outlets of two combustion chambers are joined by a confluence part to connect with the turbine. By changing the combustion methods of each combustion chamber, the gas turbine was operated in three modes; normal combustion mode, pulse combustion augmented mode, and fully pulse combustion mode. In the normal combustion mode, two combustion chambers were operated under continuous, constant-pressure combustion. In the pulse combustion augmented mode, one combustion chamber was operated under continuous, constant-pressure combustion and the other was operated under pulse combustion. In the fully pulse combustion mode, two combustion chambers were operated under pulse combustion. The pulse combustion applied in this study was the forced-ignition type, active pulse combustion. Although the pressure increase was attained by the pulse combustion comparing with the normal combustion, the mass-averaged pressure in the combustor showed that the net pressure gain in the combustor was not attained. The engine performance such as thermal efficiency and work and operating characteristics of gas turbine were investigated for two operation modes. In the pulse combustion augmented mode, the gas turbine could successfully sustain its operation as well as normal operation mode. The increase in the combustor pressure affected the air mass flow rate and the compressor performance, resulted in the decrease of performance comparing with the normal combustion mode.