bluuebunny/crossref_metadata_2025 huggingface dataset:
Test Bench for Characterization and Design Against Steam Turbine Fouling
Authors: Girezzi Gabriele , Checcacci Damaso , Cosi Lorenzo , Maggi Andrea , Sani Alessandro , Achilli Andrea
Published: September 2021

The fouling phenomenon addressed in this paper is related to the deposition within steam turbines of steam impurities and to the presence of solid debris, coming from upstream plant sections, that can create solid build-ups in stationary and moving parts inside the turbine. As a consequence, fouling causes unit efficiency decline but, in severe cases, it may also lead to sticking of moving components, such as valves, that may be critical in machine control and/or safety.

Despite well-studied and well-considered in design and operation of large power utility plants, where steam quality is of primary importance for boilers, super-heaters, turbines and condensers, this subject is often overlooked in small power generation or industrial applications, where efficiency may be less critical but turbine availability is of paramount importance for plant operation (e.g. LNG plants).

The steam fouling is a subject that, despite widely studied in the past, has been quite neglected in more recent years.

This paper, with the aim of underlining the importance of fouling in the operation of turbines for industrial applications, starts with examples of field evidences of severe fouling. Then the design of a test bench for the experimental characterization of fouling rates and validation of turbine components, exposed to fouling conditions, is presented along with the description of the deposition models that were developed on the basis of the physical phenomena involved in the fouling process.

This study addresses the main deposition physical principles and their implications in the thermodynamic design of the test bench, on the basis of the specific physical properties of the impurities of interest. To better match plant real cases, the contaminants tested included those which have been usually identified within the units during maintenance activities and for which specific limits are prescribed by OEMs.

In the following section, details relevant to the main deposition mechanisms due to different geometries and flow-fields are discussed.

The results obtained are qualitatively in line with literature and internal practices, yet, through the test activities, it has been possible to establish a quantitative relationship between the concentrations of each contaminant at inlet section and the different thermodynamic conditions along the test bench, so capturing the impact of solubility changes along with the steam expansion.
High-Resolution Thermal Profiling of a Combustor in a Non-Dedicated Test Using Thermal History Coatings
Authors: Peral David , Zaid Ahmed , Benninghoven Christoph , Araguas-Rodríguez Silvia , Kluß David , Karagiannopoulos Solon , Krewinkel Robert , Feist Jörg
Published: September 2021

The requirement for reduced emissions and the growing demand on gas turbine efficiency are in part met through increasing firing temperatures. However, development budgets leave only limited time for dedicated thermal testing. Consequently, manufacturers are seeking novel temperature measurement technologies to validate new engine designs. This paper will demonstrate how a new temperature mapping technology can be utilized for non-dedicated (multi-cycling) testing while still delivering high-resolution temperature data in a non-dedicated test on a combustor of an industrial gas turbine.

Typically, thermocouples are used to monitor the temperature during tests, but they only provide one data point. Colour changing thermal paints are used to deliver measurements over complete surfaces, but they require dedicated testing with short-duration exposure, necessitating dismantling and re-assembling the engine for further testing.

Thermal History Coatings (THC) present an alternative solution to providing high-density temperature information. This coating permanently changes consistent with the maximum temperature of exposure during test. A laser-based instrumentation technique is then used to obtain temperatures. The maximum temperature profile of the surface can be determined through a customized calibration. Given the complex cooling system of a combustor, the high temperatures and the long-time exposure, this case offers a unique possibility for the testing of the coating under real engine conditions. The coated region covered the external surface of the can. Highly significant is the number of measurement points in excess of 7,000 (2 × 2 mm resolution, which enables advanced analysis. This provides insight into the impact of local features, e.g. the region adjacent to a cooling hole.

The temperature profile is compared to a CFD-CHT model and thermocouple measurements for the calibration of cooling pre-design methods.
Evaluation of Thermoacoustic Applications Using Waste Heat to Reduce Carbon Footprint
Authors: Spoor Philip , Prabhudharwadkar Deoras , Somu Srinath , Saxena Saumitra , Lacoste Deanna , Roberts William
Published: September 2021

Thermoacoustics (TA) engines and refrigerators typically run on the Stirling cycle with acoustic networks and resonators replacing the physical pistons. Without moving parts, these TA machines achieve a reasonable fraction of Carnot’s efficiency. They are also scalable, from fractions of a Watt up to kW of cooling. Despite their apparent promise, TA devices are not in widespread use, because outside of a few niche applications, their advantages are not quite compelling enough to dislodge established technology.

In the present study, the authors have evaluated a selected group of applications that appear suitable for utilization of industrial waste heat using TA devices and have arrived at a ranked order. The principal thought is to appraise whether thermoacoustics can be a viable path, from both an economic and energy standpoint, for carbon mitigation in those applications. The applications considered include cryogenic carbon capture for power plant exhaust gases, waste-heat powered air conditioning/water chilling for factories and office buildings, hydrogen liquefaction, and zero-boiloff liquid hydrogen (LH2) storage. Although the criteria used for evaluating the applications are somewhat subjective, the overall approach has been consistent, with the same set of criteria applied to each of them. Thermoeconomic analysis is performed to evaluate the system viability, together with overall consideration of a thermoacoustic device’s general nature, advantages, and limitations.

Our study convincingly demonstrates that the most promising application is zero-boiloff liquid hydrogen storage, which is physically well-suited to thermoacoustic refrigeration and requires cooling at a temperature and magnitude not ideal for standard refrigeration methods. Waste-heat powered air conditioning ranks next in its potential to be a viable commercial application. The rest of the applications have been found to have relatively lower potentials to enter the existing commercial space.
Combination of Turbocharger and Industrial Technologies for the Development of an Improved Mixed-Flow Turbine Design
Authors: Franz Holger , Niewöhner Jens , Mühlenbrock Stefan
Published: September 2021

A new mixed-flow radial turbine design for industrial applications was developed and experimentally investigated. The presented mixed-flow turbine recovers energy in industrial processes, which have unused pressurized, hot off-gas available. The design parameter values are very similar to the ones of mixed-flow turbines for turbocharger applications. Consequently, a turbocharger design was used as starting basis. The mechanical requirements of the industrial application are less challenging for the turbine design. It was possible to extend the design space of the blades far beyond the typical radial fiber constraint, which is usually used to fulfill the mechanical restrictions. This gives more freedom for the parameters used in the blade geometry generation. The final design has an increased efficiency and operating range.

In addition to a maximized design point efficiency, a wide operating range is one of the major requirements concerning the turbine performance. During the development process of the radial turbine’s wheel, an automated optimization was used. Due to the competitive design targets, multiple objectives and constrains were formulated. To satisfy the off-design efficiency requirements, each geometry was analyzed by means of six operating points. The mechanical integrity was checked by directly coupled FE simulations. The final design is further investigated and the reasons for the gained improvements are discussed. An experimental investigation of a prototype confirmed the numerically predicted improvements. A comparison of the measurements and the numerical results are shown.

The objective of the paper is to show the possible potentials in efficiency and operating range of radial turbines with low mechanical restrictions. In many energy recovery applications, the operating conditions are well known and within clearly defined boundaries. For these applications, it is possible to engineer mixed-flow turbines primarily from the aerodynamical point of view ans secondly from the mechanical one. In the following described work, it was possible, starting from a good turbocharger design, to increase the turbine’s performance. An automatic multi-point and multi-physics optimization was set up to reach the performance improvements.
Prediction of Pressure Rise in a Gas Turbine Exhaust Duct Under Flameout Scenarios While Operating on Hydrogen and Natural Gas Blends
Authors: Ugarte Orlando , Menon Suresh , Rattigan Wayne , Winstanley Paul , Saxena Priyank , Akiki Michel , Tarver Terry
Published: September 2021

In recent years, there is a growing interest in blending hydrogen with natural gas fuels to produce low carbon electricity. It is important to evaluate the safety of gas turbine packages under these conditions, such as late-light off and flameout scenarios. However, the assessment of the safety risks by performing experiments in full-scale exhaust ducts is a very expensive and, potentially, risky endeavor. Computational simulations using a high fidelity CFD model provide a cost-effective way of assessing the safety risk. In this study, a computational model is implemented to perform three dimensional, compressible and unsteady simulations of reacting flows in a gas turbine exhaust duct. Computational results were validated against data obtained at the simulated conditions in a representative geometry. Due to the enormous size of the geometry, special attention was given to the discretization of the computational domain and the combustion model. Results show that CFD model predicts main features of the pressure rise driven by the combustion process. The peak pressures obtained computationally and experimentally differed in 20%. This difference increased up to 45% by reducing the preheated inflow conditions. The effects of rig geometry and flow conditions on the accuracy of the CFD model are discussed.
Temperature-Dependent Fracture Mechanics-Informed Damage Model for Ceramic Matrix Composites
Authors: Skinner Travis , Chattopadhyay Aditi
Published: September 2021

This work presents a temperature-dependent reformulation of a multiscale fracture mechanics-informed matrix damage model previously developed by the authors. In this paper, internal state variable theory, fracture mechanics, and temperature-dependent material properties and model parameters are implemented to account for length scale-specific ceramic matrix composite (CMC) brittle matrix damage initiation and propagation behavior for temperatures ranging from room temperature (RT) to 1200°C. A unified damage internal state variable (ISV) is introduced to capture effects of matrix porosity, which occurs as a result of material diffusion around grain boundaries, as well as matrix property degradation due to matrix crack initiation and propagation. The porosity contribution to the unified damage ISV is related to the volumetric strain, and matrix cracking effects are captured using fracture mechanics and crack growth kinetics. A combination of temperature-dependent material properties and damage model parameters are included in the model to simulate effects of temperature on the deformation and damage behavior of 2D woven C/SiC CMC material systems. Model calibration is performed using experimental data from literature for plain weave C/SiC CMC at RT, 700°C, and 1200°C to determine how damage model parameters change in this temperature range. The nonlinear, temperature-dependent predictive capabilities of the reformulated model are demonstrated for 1000°C using interpolation to obtain expected damage model parameters at this temperature and the predictions are in good agreement with experimental results at 1000°C.
Part-Load Operation of Gas Turbines Induced by Co-Gasification of Coal and Biomass in an Integrated Gasification Combined Cycle Power Plant
Authors: Ravelli Silvia
Published: September 2021

This study takes inspiration from a previous work focused on the simulations of the Willem-Alexander Centrale (WAC) power plant located in Buggenum (the Netherlands), based on integrated gasification combined cycle (IGCC) technology, under both design and off-design conditions. These latter included co-gasification of coal and biomass, in proportions of 30:70, in three different fuel mixtures. Any drop in the energy content of the coal/biomass blend, with respect to 100% coal, translated into a reduction in gas turbine (GT) firing temperature and load, according to the guidelines of WAC testing. Since the model was found to be accurate in comparison with operational data, here attention is drawn to the GT behavior. Hence part load strategies, such as fuel-only turbine inlet temperature (TIT) control and inlet guide vane (IGV) control, were investigated with the aim of maximizing the net electric efficiency (ηel) of the whole plant. This was done for different GT models from leading manufactures on a comparable size, in the range between 190–200 MW. The influence of fuel quality on overall ηel was discussed for three binary blends, over a wide range of lower heating value (LHV), while ensuring a concentration of H2 in the syngas below the limit of 30 vol%. IGV control was found to deliver the highest IGCC ηel combined with the lowest CO2 emission intensity, when compared not only to TIT control but also to turbine exhaust temperature control, which matches the spec for the selected GT engine. Thermoflex® was used to compute mass and energy balances in a steady environment thus neglecting dynamic aspects.
Numerical Investigation of Potential Cause of Instabilities in a Hydrogen Micromix Injector Array
Authors: Sun Xiaoxiao , Abbott David , Vir Singh Abhay , Gauthier Pierre , Sethi Bobby
Published: September 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. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and small diffusion flames at lean overall equivalence ratios.

There is limited published information on the instabilities of such hydrogen micromix combustors. Diffusion flames are less prone to flashback and autoignition problems than premixed flames as well as combustion dynamics issues. However, with the high laminar flame speed of hydrogen, lean fuel air ratio (FAR) and very compact flames, the risk of combustion dynamics for micromix flames should not be neglected. In addition, the multi-segment array arrangement of the injectors could result in both potential causes and possible solutions to the instabilities within the combustor.

This paper employs numerical simulations to investigate potential sources of instabilities in micromix flames by modelling an extended array of injectors, represented by either single or multiple injectors with appropriate boundary conditions at elevated pressure and temperature. Both RANS and LES simulations were performed and used to derive the Flame Transfer Function (FTF) of the micromix flames to inform lower order thermoacoustic modelling of micromix combustion. LES simulations indicate that the gain of the FTF is lower than predicted from the RANS simulations indicating a lower risk of high frequency thermoacoustic issues than suggested by RANS.

When LES simulations are conducted for certain representative configurations it is observed that there are persistent high-frequency instabilities due to the interaction of the flames. This phenomenon is not observed when only a single injector is modelled. LES simulations for two injectors are conducted with various geometries and radial boundary conditions to identify the cause of the instabilities. It is concluded that the observed high-frequency instabilities are related to aerodynamic jet instabilities enhanced by both aerodynamic and acoustic feedback and key geometric features affecting the occurrence of the instabilities are identified. Only transient simulations such as LES are able to capture such effects and RANS simulations typically used in early stage design will not identify this issue.
A Hybrid Adjoint Network Model for Thermoacoustic Optimization
Authors: Schäfer Fellcitas , Magri Luca , Polifke Wolfgang
Published: September 2021

A method is proposed that allows the computation of the continuous adjoint of a thermoacoustic network model based on the discretized direct equations. This hybrid approach exploits the self-adjoint character of the duct element, which allows all jump conditions to be derived from the direct scattering matrix. In this way, the need to derive the adjoint equations for every element of the network model is eliminated. This methodology combines the advantages of the discrete and continuous adjoint, as the accuracy of the continuous adjoint is achieved whilst maintaining the flexibility of the discrete adjoint. It is demonstrated how the obtained adjoint system may be utilized to optimize a thermoacoustic configuration by determining the optimal damper setting for an annular combustor.
Fretting Fatigue – An Integral Simulation Approach to Strengthening by Shot Peening
Authors: Gerken Patrick , Richter Christoph H.
Published: September 2021

Fretting fatigue is a limiting factor in blade attachment design for turbomachinery. Shot peening is known to be a strength increasing measure against fatigue. It is applied not only to free surfaces of components under fatigue but also to contacting surfaces subject to fretting fatigue.

The present work examines the effect of shot peening on fretting fatigue resistance in fixtures of rotor blades. The chosen integral approach allows the consideration of shot peening and subsequent fretting loading in one simulation. Thus, the residual stresses and material strengthening as well as the surface waviness due to the shot peening process are included in the fretting fatigue simulation. To achieve reasonable computation times a 2D model, calibrated to a 3D unit cell model, is employed. A comparative study on fatigue endurance limits is presented for the cases with and without shot peening. With view to the different failure mechanisms met in these two cases, an initiation evaluation is carried out with the Sines criterion for the un-peened condition; a fracture mechanics approach is shown to be necessary for the evaluation of the shot peened condition.
Data Driven Approach to Analyzing The Impact of Power Plant Cycling on Air Preheater Degradation and Remaining Useful Life
Authors: Sharma Himanshu , Adetola Veronica , Marinovici Laurentiu , Schaef Herbert T.
Published: September 2021

Due to the increased penetration of renewable energy generation sources, and fluctuations of the oil and gas prices, modern coal burning power plants deal with increased variability in the demand for power generation. These varying demands result in their intermittent under-capacity operation (cycling). Periodical ramping down and back up to follow the daily power demands causes damages to the plant components reducing its operational life. In this paper we analyze the impact of cycling on a rotary Ljungstrom air preheater (APH) unit installed at a coal fire power plant in the US. An inefficient air preheater can significantly impact boiler performance. Due to the repeated boiler’s hot-cold start, the APH experiences fluctuating operating conditions that result in accelerated degradation mechanisms, such as dew-point corrosion, fouling/deposition plugging, and air heater leakage. The analysis in this paper utilizes field data related to APH basket replacement, and the number of cycles experienced by the boiler to model the life expectancy of the baskets. The data-driven model enables preventive maintenance strategies for the APH by predicting how long the APH baskets will last in a probabilistic sense. The analysis showed that an increase in cycling for a fixed operation time can reduce the APH basket remaining useful life by about 30%.
Design, Optimization and Experimental Verification of a Metal Rubber Isolator for Momentum Wheels
Authors: Ma Yanhong , Tang Xiangxin , Hong Jie
Published: September 2021

The inertial actuator, such as momentum wheels, is the key mechanical component of spacecraft for attitude stability and accuracy maintenance. However, the inertial actuators are under excessive vibration during the rocket launch phase. In order to prevent the inertial actuators from structural damage and equipment failure, isolating vibration from the base must be considered.

Metal rubber (MR) is a kind of porous functional damping material, manufactured through the process of entangling, stretching, weaving and molding of metallic wires. With its excellent mechanical properties of high damping, designable stiffness and environmental adaptability, MR is widely used in the area of aerospace and aviation for vibration isolation.

To this end, a method to design and optimize a MR isolator for momentum wheels is developed. The MR isolator consists of a transverse groove spring and MR in parallel. A FEM model coupling the transverse groove spring and the simplified momentum wheel is established to assist in the optimization of the configuration of the spring, and the goal is to minimize the frequency bandwidth of the first six modes. The influence of the parameters on the frequency of the first six modes is also discussed. The MR is then designed to provide damping and additional stiffness. Finally, the performance of the MR isolator is analyzed by simulation and verified through experiments.
Accounting for Circumferential Flow Nonuniformity in a Multi-Stage Axial Compressor
Authors: Lou Fangyuan , Matthews Douglas R. , Kormanik Nicholas J. , Key Nicole L.
Published: September 2021

The flow field in a compressor is circumferentially non-uniform due to geometric imperfections, inlet flow nonuniformities, and blade row interactions. Therefore, the flow field, as represented by measurements from discrete stationary instrumentation, can be skewed and contribute to uncertainties in both calculated one-dimensional performance parameters and aerodynamic forcing functions needed for aeromechanics analyses. Considering this challenge, this paper documents a continued effort to account for compressor circumferential flow nonuniformities based on discrete, under-sampled measurements. First, the total pressure field downstream of the first two stators in a three-stage axial compressor was measured across half of the annulus. The circumferential nonuniformities in the stator exit flow, including vane wake variability, were characterized. In addition, the influence of wake variation on stage performance calculations and aerodynamic forcing functions were investigated. In the present study for the compressor with an approximate pressure ratio of 1.3 at design point, the circumferential nonuniformity in total pressure yields an approximate 2.4-point variation in isentropic efficiency and 54% variation in spectral magnitudes of the fundamental forcing frequency for the embedded stage. Furthermore, the stator exit circumferential flow nonuniformity is accounted for by reconstructing the full-annulus flow using a novel multi-wavelet approximation method. Strong agreement was achieved between experiment and the reconstructed total pressure field from a small segment of measurements representing 20% coverage of the annulus. Analysis shows the wake-wake interactions from the upstream vane rows dominate the circumferentially nonuniform distributions in the total pressure field downstream of stators. The features associated with wake-wake interactions accounting for passage-to-passage variations are resolved in the reconstructed total pressure profile, yielding representative mean flow properties and aerodynamic forcing functions.
Transient Analysis of Aircraft Oil Supply System With Fuel-Oil Heat Exchangers During Abrupt Change in Engine Operating Modes
Authors: Yevlakhov Viktor , Moroz Leonid , Khandrymailov Andrii , Hyrka Yuriy
Published: September 2021

During different airplane flight modes, various effects may appear that need to be analyzed for both the oil and the fuel system at steady-state and transient operating modes. The effects, which relate to the cold temperature, associated with fuel freeze or wax point, cause a malfunction in the fuel pumps, nozzles, and other areas of the fuel system. On the other hand, high fuel temperature also leads to negative effects — the most common failure of high-flow fuel systems is cavitation, or “vapor-lock.” The combination of too much heat or too much inlet restriction can create this operating condition, where the liquid fuel literally boils inside the fuel pump. These effects are eliminated by the fuel/oil heat exchange system. In case of low fuel temperature, the fuel is used as a refrigerant to cool down hot oil coming from bearings. And in case of high fuel temperature, the oil serves as a coolant.

This paper considers the method of evaluating normal and critical aircraft engine operation modes of the oil supply system with a fuel-oil heat exchanger utilizing an unsteady-state thermal-fluid network approach. The analyses are done based on the aircraft engine example to evaluate fuel and oil systems parameters variation in time under different flight conditions — the amount of fuel in the tank, inertial thermal effects, and the response time of the system to the regulation of the heat exchanger. The article is focused on sudden switching from a high to low gas engine operating mode. Fuel consumption to the engine is reduced abruptly, but the heat transfer from the bearings to the oil is still high due to thermal inertia. In this situation, a large amount of heated fuel must be returned to the fuel tank. At a certain point in time, the temperature of the fuel can reach a critical value. At the same time bearing cooling becomes ineffective, which leads to overheating. The calculation of thermal management system was performed at nominal conditions to obtain the initial data for low power settings analysis. As results of analysis at the low power settings mode the oil temperature before fuel cooled oil cooler is reached above 138 °C, which is high value. The failure of flow return valve is considered. The variations of oil temperature after the tank and increasing of fuel temperature at the tank in case of emergency situation are obtained. The influence of cooled fuel amount on the system thermal management is analyzed.
Physics-Based Thermal Management System Components Design for All-Electric Propulsion Systems
Authors: Jafari Soheil , Nikolaidis Theoklis , Sureddi Roopesh Chowdary
Published: September 2021

Although electrification allows a significant reduction in fuel burn, noise, and emissions, one of the main challenges in this technology is to deal with the thermal loads generated by the electrified propulsion system components. This is to guarantee the safe and optimal operation of the propulsion system as well as the aircraft. This challenge needs to be addressed to enable this important technology to be adopted by aircraft manufacturers. This paper presents a methodological approach to calculate the heat load values generated by electric components in All-Electric Propulsion (AEP) architectures. Initially, the architecture of an AEP system will be presented and explained. Then, for each component, physics-based models based on associated heat loss mechanisms will be developed and presented. For this purpose, thermal models for battery packs, electric motors, inverters, and rectifiers are generated and a MATLAB/Simulink library is developed to calculate the thermal loads generated by each component at different working conditions. The developed models’ results are validated against publicly available data to confirm the effectiveness of the proposed approach. The simulation results confirm that the developed library is able to predict the thermal loads generated by lithium-ion battery packs, permanent magnet synchronous electric motors, multi-stage inverters, and rectifiers with less than 1%, 9.9%, 9.2%, and 0.5% errors respectively. Finally, an AEP architecture is simulated as the case study and the total heat loads generated by different components have been calculated at the design point to confirm the capability of the developed framework in system-level analyses.
Frequency Dependancy of Dynamic Force Coefficients for Hermetic Squeeze Film Dampers Utilizing Fluid-Bounding Flexible Structures
Authors: Ertas Bugra , Gary Keith
Published: September 2021

The following paper focuses on the dynamic behavior of hermetic squeeze film dampers (HSFD) that utilize fluid-bounding flexible members as a part of the support structure. More specifically, the current paper advances an engineering design modification to the existing HSFD concept, which is aimed at rendering the dynamic force coefficients frequency independent. The paper builds on past HSFD testing and modeling approaches to develop higher fidelity analytical models, which are used to investigate different damper configurations while taking keen interest in the frequency dependency of force coefficients. The analytical study leverages commercially available finite element analysis (FEA) and computational fluid dynamics (CFD) software to conduct several fluid-structure-interaction (FSI) simulations of various damper architectures. In addition to the FSI analysis a more computationally efficient reduced order model (ROM) was developed, coupling structural flexibility with the fluid dynamics in the damper. Ultimately, these design tools were used to identify critical design features and configurations needed for constant linear frequency independent force coefficients. The results show a damper configuration with minimal frequency dependency of the stiffness and damping coefficients when incorporating pass through channels in combination with accumulator volumes. The paper also uses the improved design approach of the HSFD to put forth a notional integrated bearing design incorporating the new HSFD concept.
The Use of Enhanced Nozzle Maps for Gas-Turbine Performance Modelling
Authors: Al-Akam Aws A. , Nikolaidis Theoklis , MacManus David G. , Pellegrini Alvise
Published: September 2021

The use of a simulation tool to predict the aero-engine performance before committing to a final engine design has become one of the most cost-saving approaches in this field. However, most of these tools are based on low fidelity thermodynamic models, which are incapable of fully capturing the impact of three-dimensional flow characteristics.

An aero-engine exhaust-system is one of the essential components that affect the engine performance. Currently, engine performance models tend to utilize simplified nozzle performance maps. These maps typically provide information over a very limited range of nozzle geometries, which may not apply to the wide range of architectures and designs of aeroengines.

The current paper presents a methodology for the development of nozzle performance maps, which takes into account the aerodynamic and the geometric parameters of the nozzle design. The methodology is based on the reduced-order models. These models are integrated into a zero-dimensional engine performance code to improve the accuracy of its thrust calculation.

The impact of the new thrust model on the overall engine performance and the operating point is analysed and discussed. The results showed that the implementation of the modified maps, which take into account the flow characteristics and the geometry of the nozzle, affects the thrust calculation. In a typical case of a turbofan operating at cruise conditions, the net thrust estimation with the modified nozzle maps showed a difference of 0.2%, compared with the simple nozzle maps. The new thrust calculation method has the advantage in capturing the multidimensional impact of the flow of the nozzle as compared with the conventional one. Furthermore, the implementation of the new method reduces the uncertainties introduced by a simplified nozzle model and, consequently, it can support the decision-making process in the design of the engine.
Experimental Investigation of Rossiter Modes for an Open Box Cavity With Adjustable Depth
Authors: Hammer Steffen , Fridh Jens , Billson Mattias
Published: September 2021

Resonance in aerospace is a phenomenon that engineers have been trying to predict and avoid for a long time. Acoustic resonance is only a part in this field. When it was previously studied, it was mostly in connection with long slender gaps at the fuselage of aircrafts. Lately it has become a focus in the development of highly efficient aero engines. Bleed systems in the compressor part of engines are needed but not easy to place aerodynamically. Additionally, these bleed systems have complex geometries. These geometries coupled with the operational range of modern aircraft from low to high subsonic Mach numbers can create unwanted acoustic resonances.

This paper is part of project study of these resonances. Here the bleed geometry is simplified to an open box cavity that is studied experimentally in order to measure its acoustic behavior in low to high subsonic flow. The experimental data is compared to theoretical prediction models to create a baseline for future studies. The results show a good agreement between Rossiter prediction and experiments for a shallow cavity of L/D = 4. Deeper cavities with a length to depth ratio of one and 0.5 represent more organ pipe resonance phenomena. This is especially governed by the geometry of the cavity itself and the height of the test section. All cavities experience a shift in modes depending on the operating point. This mode shift pattern is similar for deeper cavities. However, the operating range can be divided into four sections in which a mode shift occurs for all cavities.
An Experimental Study of Turbine Vane Film Cooling Using Endoscope-Based PSP Technique in a Single-Passage Wind Tunnel
Authors: Wang Kechen , Shao Hongyi , Zhang Xu , Peng Di , Liu Yingzheng , Zhou Wenwu
Published: September 2021

Limited optical access has been a challenge in gas-turbine related researches since the small blade pitch makes it difficult to arrange the camera at a proper viewing angle. In this paper, the application of an endoscopic system in a single-passage wind tunnel is presented. The film cooling effectiveness over the turbine vane’s pressure side with two types of holes was measured using the pressure-sensitive paint (PSP) technique. With the 7-7-7 shaped hole serving as the baseline, the sister shaped hole was compared side-by-side to examine its cooling performance at exit Ma = 0.84. Carbon dioxide (i.e., DR = 1.53) as coolant was discharged into the flow passage through two rows of holes (i.e., 4D spacing between holes and 1.5D spacing between rows) with blowing ratio (M) varied from 0.6 to 2.0. Through the implementation of the homography algorithm, the distorted coolant traces were recovered from the cambered surface. It was found that the film cooling effectiveness of both holes was greatly influenced by the blowing ratio. The sister shaped hole exhibited a relatively high effectiveness distribution at low M but its effectiveness decreased at high M due to the coolant jet detachment. In contrast, the 7-7-7 shaped hole demonstrated significantly higher effectiveness at high M, which can be attributed to the lower momentum flux ratio results of its larger exit area. The endoscope-based PSP technique and the obtained adiabatic effectiveness results may lay the foundation for other investigations and support other CFD studies in the gas turbine community.
Mechanical Testing of Additively Manufactured Superalloy Lugs
Authors: Roychowdhury Sushovan , Karlsson Henrik , Henriksson Björn , Carlson Pher-Ola
Published: September 2021

Additively manufactured parts, in spite of their many advantages, face substantial challenges on the path towards certification. This challenge is more pronounced in the quality-demanding aviation industry, where the safety considerations are paramount. A major reason for this challenge is the lack of history associated with additively built parts compared to the traditional cast and wrought components. In assessing the structural integrity of cast and wrought components, material properties obtained from laboratory coupon tests are routinely applied for design calculations of large components. However, for AM parts, questions remain over transferability of properties over multiple length scales due to possible variations in material chemistry, microstructure, and defect. In this work, this issue is investigated by conducting mechanical tests on small simplified lugs of nickel-based superalloy Haynes 282. The lugs are produced by the laser powder bed fusion process. After appropriate heat treatment and machining operations, the lugs are subjected to strength, low cycle fatigue, and crack propagation tests. Multiple tests are carried out in order to assess repeatability. Design calculations are performed to assess whether the test results can be predicted with standard methods. The results in the current work generate confidence in predictable, repeatable behavior of the AM built lugs. Continuation of this approach over larger length scales has the potential to build enough confidence so that additively manufactured parts can be used in load-bearing structural elements of the aircraft engine.
Details of Shrouded Stator Hub Cavity Flow in a Multi-Stage Axial Compressor Part 2: Leakage Flow Characteristics in Stator Wells
Authors: Kamdar Nitya , Lou Fangyuan , Key Nicole L.
Published: September 2021

The flow in shrouded stator cavities can be quite complex with axial, radial, and circumferential variations. As the leakage flow recirculates and is re-injected into the main flow path upstream of the stator, it deteriorates the near-hub flow field and, thus, degrades the overall aerodynamic performance of the compressor. In addition, the windage heating in the cavity can raise thermal-mechanical concerns. Fully understanding the details of the shrouded-hub cavity flow in a multi-stage environment can enable better hub cavity designs. In the first part of the paper, the influence of the hub leakage flow on compressor performance and its interactions with the primary flow were investigated. While the impact of hub leakage flow on the primary passage is readily available in the open literature, details inside the cavity geometry are scarce due to the difficulties in instrumenting that region for an experiment or modeling the full cavity geometry. To shed light on this topic, the flow physics in the stator cavity inlet and outlet wells are investigated in the present paper using a coupled CFD model with inclusion of the stator cavity wells for the Purdue 3-Stage (P3S) Axial Compressor, which is representative of the rear stages of a high-pressure-compressor in core engines. At the inlet cavity, the presence of at least one pair of vortices influences the trajectory of the cavity leakage flow. The amount of leakage flow also determines the size of the vortical structures, with larger clearances creating a smaller vortex and vice versa. After passing through the labyrinth seals, the leakage flow travels along the stator landing first and then transitions to the rotor drum. In general, a flow path closer to the rotor drum achieves higher circumferential velocity but also exhibits significant temperature rise. A rise in circumferential velocity directly corresponds to a rise in temperature. In addition, the windage heating increases with increasing seal clearance. Furthermore, the inlet well contributes the most to overall windage, nearly 50% of the total windage heating, while the labyrinth seals and outlet well account for very little.
Anomaly Detection for Large Fleets of Industrial Equipment: Utilizing Machine Learning With Applications to Power Plant Monitoring
Authors: Allen Cody W. , Holcomb Chad , de Oliveira Maurício
Published: September 2021

This paper covers three contemporary topics in the development and deployment of machine learning based diagnostics for large fleets of industrial machines. First, we address the philosophy of monitoring as to whether anomaly detection versus specific failure classification should be pursued, utilizing published statistics of reliability of industrial machines. Second we address the question of unsupervised versus supervised methods using a simulated example of a typical industrial machine fault, where we apply a number of popular unsupervised and supervised algorithms and directly compare their alerting ability. Lastly, model development and deployment at global scale is discussed, with application to a global fleet of gas turbines. The application includes a framework of neural network models that have been trained to find anomalous behavior for a system of the gas turbine package. The remainder of the paper includes a discussion of the results from the fleet application. Specifically, we discuss the fleet training procedure and hardships incurred in moving from proof of concept designs to full deployment on global production asset monitoring. Selected training models that failed to be of production quality are examined and the source of training error is identified. Throughout, the paper provides lessons learned, broad insights gained, and productionization issues that still need improvement as it relates to development and deployment of machine learning models at the scale of global industrial machine monitoring.
Investigation on Flow Mechanism Driving Heat Transfer Enhancement in a Wide Channel With Staggered Square Pin Fins
Authors: Duan Jingtian , Zhang Ke , Xu Jin , Lei Jiang , Wu Junmei
Published: September 2021

Particle Image Velocimetry (PIV) was used to measure the flow field of staggered square pin-fin array in a wide rectangle channel (AR = 4). The experiment was conducted at two Reynolds number, 10000 and 20000, based on the hydraulic diameter and bulk velocity of the channel. The distribution of flow field properties was compared with that of Nu to analysis the key flow physics driving heat transfer enhancement in channel with square pin fin. The Nusselt number was achieved through temperature measurement using thermochromic liquid crystal in the same geometry setup. Results were compared with those for circular pin fin to study the effect of geometry on flow physics driving heat transfer enhancement. It was found that the wake length of square pin fin is longer than that of circular pin fin, which indicated flow around square pin fin requires longer distance to develop. Compared to circular pin fin, small scale disturbances in the shear layer of square pin fin show its contribution to local end wall heat transfer enhancement. Large motions benefit end wall heat transfer more effectively at lower Re. Small scale unsteadiness contributes more to heat transfer augment as flow develops or Reynolds number increases while large scale motions get weaker.
Application of Large Eddy Simulation for HA_Class Combustion System Design to Mitigate Combustion Instabilities (Frequency, and Amplitude)
Authors: Hajiloo Azardokht , Narra Venkat , Krumenacker Erin , Karim Hasan , Shunn Lee , Bose Sanjeeb , Ham Frank
Published: September 2021

Enabled by national commercialization of massive shale resources, Gas Turbines continue to be the backbone of power generation in the US. With the ever-increasing demand on efficiency, GT combustion sections have evolved to include shorter combustion lengths and multiple axial staging of the fuel, while at the same time operating at ever increasing temperatures.

This paper presents the results of very detailed Large Eddy Simulations of one (or two) combustor can(s) for a 7HA GE Gas Turbine Engine over a range of operating parameters. The model of the simulated combustor can(s) includes (include) all the details of the combustor from compressor diffuser to the end of the stationary part of the first stage of the turbine. It includes the geometries of multiple pre-mixers within the combustion can(s) and the complete design features for axial fuel staging.

All simulations in this work are performed using the CharLES flow solver developed by Cascade Technologies. CharLES is a suite of massively parallel CFD tools designed specifically for multiphysics LES in high-fidelity engineering applications.

Thermo acoustic results from LES were validated first in the physical GE lab and then in full-engine testing. Both the trend as well as the predicted amplitudes for the excited axial dominant combustion mode matched the data produced in the lab and in the engine. The simulations also revealed insight into the ingestion of hot gases by different hardware pieces that may occur when machine operates under medium to high combustion dynamics amplitudes. This insight then informed the subsequent design changes which were made to the existing hardware to mitigate the problems encountered.
An Efficient Prediction Method for the Azimuthal Migration of Combustion Inhomogeneity in Multi-Stage Cooled Turbines
Authors: He Qingfu , Chi Zhongran , Zang Shusheng
Published: September 2021

The outlet temperature of combustor is commonly monitored by thermocouples at the turbine exhaust. In order to establish the corresponding relationship between the temperature measured by each thermocouple and the working state of each burner, the azimuthal migration of the combustion hot/cold streaks in the multi-stage turbines needs to be quantified. Experiments to measure this migration have high cost and considerable error. It is also difficult to quantify the migration under multiple working conditions. Three-dimensional full-annulus unsteady simulation can obtain this migration. But the unsteady simulation of a single working condition could take several weeks, which is too expensive for engineering usage.

A method named Steady-state Computation of Azimuthal Migration (SCAM) is proposed in this paper. By establishing and solving the transport equation of the migration angle, the azimuthal migration of hot/cold streaks can be predicted by steady-state numerical simulation using the mixing plane at rotor-stator interface. The migration computed by this method is compared with the full-annulus unsteady simulation results in multiple working conditions. The results of SCAM method show good agreement with full-annulus simulations, while costing only 0.01% of the CPU hours. It is also found that the error of SCAM is mainly caused by the fixed boundary value at coolant source terms. The optimal spanwise location of the thermocouples at turbine exhaust is discussed based on the results. The method proposed could be applied to the fault diagnosis and precise repair of the combustors of gas turbines.