bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of High-Frequency Dynamics of a Reacting Jet in Crossflow Based on Large Eddy Simulation
Authors: Bonnaire Philip , Polifke Wolfgang
Published: September 2023

Distributed combustion systems have shown the potential to reduce emissions as well as increase load and fuel flexibility. A characteristic feature of such systems is a reacting jet in cross-flow, which exhibits complex vortical structures. In this paper, a generic combustion chamber with elliptic reacting jets in cross-flow is examined, operating under lean-premixed conditions at elevated pressure and exhibiting high-frequency transverse mode shapes. It can be seen that depending on the orientation of the elliptical shape of the jet to the crossflow, thermoacoustic modes can be suppressed. A multidimensional Fast Fourier Transform shows that low aspect ratios (major axis of the jet aligned with the crossflow) result in the mixed 1L1T mode of first longitudinal and first transverse structure, while this mode disappears at high aspect ratios. To get a more detailed insight into the different vortex systems of the various aspect ratios, Dynamic Mode Decomposition is applied. This modal decomposition technique reveals for low aspect ratios a shear layer mode that oscillates at a frequency close to the acoustic mixed mode. For this configuration, a mode representing a flapping motion is also identified. For high aspect ratios, the shear layer vortex increases its frequency and a higher-frequent mode appears in the acoustic spectrum.
Study of the Variation in Component Level Characteristics of a Centrifugal Compressor Across the Compressor Map Using CFD and Experiments With Detailed Instrumentation on a Gas Stand
Authors: Thiyagarajan Janakiraman , Fredriksson Carl , Anton Nicholas , Fridh Jens , Genrup Magnus
Published: September 2023

A compressor map with variations in component level characteristics is introduced. This novel approach to plot component level characteristics identify and give context to the critical design parameters such as flow angles, pressure coefficients, and loss coefficients across the entire compressor map along with the conventional performance parameters. Compressor design involves a significant amount of CFD at a stage level, but the decisive importance of component performance, design and analysis are many times overshadowed by 3D CFD, both steady RANS and unsteady RANS/LES/DES. Although the authors support the development of high-fidelity computational tools, validating these computational results with experimental measurements is essential. A detailed analysis of the Scania’s in-house designed compressor stage tested in the Scania Gas stand shows that in order to create an optimal design, component level performance assessment is necessary for the impeller, diffuser and volute. The variation of performance parameters along a speed line and across varied tip speeds are shown along with indications for the onset of instabilities at a component level. This is a crucial input for the design of a compressor stage. In addition to detailed analysis of experimental results, this work includes predictions from two different CFD solvers and discussion of deviations between them. Both the CFD solvers can be used to predict performance parameters at a stage level for most parts of the map. For operating conditions close to surge and higher tip speeds (565 m/s), there are major deviations in the CFD solvers’ predictions. The impeller pressure rise and efficiency could be predicted well with the CFD solvers for most of the tip speeds. However, deviations between measurements and predictions increase with increasing tip speeds. The diffuser performance is predicted well by one of the solvers. The other solver underpredicts the diffuser and overpredicts the volute performance. These are also important inputs for 1D design and also for positioning of the best characteristics on the compressor map for the optimal operation of the machine. The goal of this work is to quantify performance predictions on a component level accurately, so that stage level optimization is worth executing. Further, such validated models could aid reliable design predictions and an optimization of the entire compressor stage.
Laminar Burning Speed Measurements of Hydrogen/Natural Gas Mixtures
Authors: Yovino Louis , Kim Gihun , Rahman Ramees Khaleel , Vasu Subith S.
Published: September 2023

To address the shortage of fossil fuels and the environmental impact of exhaust emissions, research efforts in combustion seek to identify candidates for sustainable fuels. Hydrogen is an example, from which water is produced as the main combustion product. However, when used as neat hydrogen, it is very difficult to control hydrogen combustion due to its high flame speed, pre-ignition propensity, and flashback characteristics. One method to control hydrogen combustion is to blend it with a well-established fuel. Natural gas is a common fuel for use in engines or gas turbines. Natural gas is characterized by slow flame speeds and poor lean-burn ability; thus, engine power is decreased in the lean-burn region. Consequently, natural gas engines are typically operated at stoichiometric conditions to maximize output. Blending hydrogen to natural gas has several advantages: (i) Control of hydrogen’s ignition characteristics, (ii) extension of Natural gas’s lower flammability limit — making it easier to ignite, and (iii) reduced greenhouse gas emissions. In this study, the laminar burning speed (LBS) for neat natural gas and natural gas/hydrogen mixtures at 5 atm and 296 K were measured. Schlieren optical imaging was utilized to validate laminar flame conditions and further investigate the structure of natural gas/hydrogen flames. Results indicate that replacing 50% of natural gas with hydrogen increases the peak laminar burning velocity by a factor of ∼1.6 times. LBS simulations were conducted with NUI 1.1 and UCF NG/H2 mechanisms; Predictions by both mechanisms were found to be satisfactory for neat NG mixtures. However, for 50% NG/ 50% H2 mixture, the true LBS for fuel-lean conditions was under-predicted by both models, while predictions for fuel-rich conditions were satisfactory. Additionally, a literature review and similar experimental analysis will be performed for methane, ammonia, and hydrogen fuel blends to better understand the combustion phenomena of natural gas fuels.
Characterization of Spray Field for Water-Emulsified Diesel Using a Pressure Swirl Atomizer Under a Non-Reacting Environment
Authors: Suleiman Baha , Selim Hatem , Dawood Alaaeldin , Song Jinkwan , Lee Jong Guen , Khalidi Abdurrahman , Al-Ahmadi Kamal , Al-Ghamdi Ibrahim , Badr Eid , Al-Gahatani Mohammed
Published: September 2023

Employing a mixture or an emulsion of water and diesel fuel is considered a way to reduce gas emissions such as NOx and soot in a gas turbine. This study presents detailed experimental results on the spray characteristics of a water-diesel emulsion injected by a pressure swirl atomizer with a 90-degree spray angle and a flow number of 0.58 under a non-reacting environment at high pressure and temperature conditions. Acquiring this data is a key step when configuring a combustor that will employ emulsified fuels. In addition, this study seeks to confirm that the emulsion stays intact when it gets sprayed into the combustor. Furthermore, this study attempts to understand if a water-diesel emulsion prepared by a sonicator improves fuel atomization as compared to a water-diesel mixture prepared by a static mixer, i.e., not a proper emulsion.

Tests are conducted in a high pressure and temperature testing facility at two ambient pressure and three ambient temperature conditions and the mass-based water to diesel ratio (W/D) is varied from 11% to 100%. Phase Doppler Particle Anemometry (PDPA) is employed to measure the spray characteristics. Through a backlit high-speed photography, overall spray patterns over different test conditions are visualized. Mie-scattering and planar laser-induced fluorescence imaging are utilized to visualize the mixture field.

In general, the results indicate that emulsion stays intact as it gets sprayed into the combustor; and emulsion is a better solution to reduce emissions than a statically mixed mixture.
Observations in the High-Temperature Creep Performance of Diffusion Bonds for sCO2 Heat Exchangers
Authors: Shingledecker John , Kumar Vikash , Bridges Alex
Published: September 2023

In support of understanding the long-term performance of high-temperature diffusion bonded heat exchangers for sCO2 power cycle application, a commercially produced alloy 316 diffusion bonded block was characterized and subjected to uniaxial creep testing in air at temperatures of 600 to 750°C with varying sample sizes with some tests durations exceeding 7,000 hours. The results show a range of different behaviors when comparing between samples sizes and in comparison to wrought alloy 316. At lower testing temperatures, some sample sizes did not meet average rupture life predictions while others did. At intermediate and higher temperatures, sample size effects were not as prevalent. While measured ductility was large for the standard and larger samples, unique observations from post-test metallurgical analysis identified non-uniform strain distributions leading to sample ovality. Additionally, failures occurred on the bond lines with oxidation potentially impacting longer-term and higher-temperature tests. Overall, these results demonstrate that careful selection of sample size and test conditions is required for engineering studies on diffusion bond performance to ensure a relevant assessment of component performance. Furthermore, the results show microstructural texture effects in the starting sheet may persist after diffusion bonding and therefore should be explored in more detail as part of future research. Finally, pre and post-test characterization suggest that procedures to quantify grain growth and bond-line features (voids and oxides) which are not measured using the standard acceptance tests may be needed for further advancement of the technology.
Numerical Analysis to Optimize and Study the Impact of Area Profiling on the Performance of a Rotating Detonation Engine
Authors: Raj Piyush , Meadows Joseph
Published: September 2023

Current gas turbine technology utilizes deflagration combustion, but an rotating detonation engine (RDE), if integrated successfully, has the potential to significantly increase thermal efficiency. The shock-laden RDE exit flow is highly unsteady and spatially non-uniform (hydrodynamically and thermally), with a high degree of periodicity. In contrast, gas turbines are designed to operate with relatively small velocity and temperature fluctuations at the inlet. The objective of the current work is to optimize and study the impact of area profiling in an annular RDE configuration. A computational approach is used to condition the flow within the RDE channel by strategically constricting the flow area to convert the unsteady supersonic/subsonic flow exiting the combustor into a relatively uniform steady flow with minimum pressure loss. In the current work, a 3D non-reacting optimization methodology is developed for the wall profiling of the combustor. The emphasis is to reduce the computational cost needed for design optimization. A Design of Experiment (DoE) study is conducted, and the geometry is parametrized for the constriction on the inner wall. It consists of a constant area section up to the detonation wave height, followed by a parabolic area profile (rapid reduction in area), and finally linear profile (gradual reduction in area) till the RDE exit. Three geometric parameters are varied, which include the length of the parabolic section, the area ratio at the end of the parabolic section (with respect to the constant area section), and the throat area ratio (with respect to the constant area section) at the exit. The output parameters include three primary indicators: equivalent available pressure (EAP), axial velocity unsteadiness, and circumferential velocity unsteadiness. The initial points in the DoE are coarsely populated, and an initial response surface is generated using the Kriging method. Next, the response surface is refined based on the adaptive sampling technique. Finally, design optimization is performed to determine the optimal design configuration that maximizes the pressure gain and minimizes the unsteadiness. A CFD simulation with constant area cross-section for pure CH4 with enriched-oxygen air is validated with experimental data followed by the validation of the rapid to gradual area reduction (RTG) profile simulation with experiments. The benefits of the RTG profile are compared with a constant cross-section area to delineate the impact of area reduction on flow uniformity at the exit of the RDE.
Application of Machine Learning for Prediction of Turbofan’s Airflow
Authors: Rejeb Sara , Duveau Catherine , Rebafka Tabea
Published: September 2023

For an improved control of the production process of aircraft engines, a new databasis has been built containing a huge number of geometrical characteristics of the engine’s parts as well as performance measurements obtained during the final acceptance test of the engine. The goal is to use these data to build a new prediction model of the performance that has high accuracy and detects drifts at an early stage of the production process. More precisely, we are interested in the prediction of the engine’s total airflow and data are mainly about characteristics of the fan blades and conditions of the test bench.

In this work we present the database and illustrate its specific characteristics like strong correlations among some of the features, missing values and general temporal drifts. In addition, we explore classical machine learning models to determine the relationship between fan blade production and the engine’s total airflow. In a second step we apply different time series models to better model the dependencies, such as ARIMA and LSTM, for the prediction of the airflow. It turns out that it is particularly difficult to disentangle the impact of the geometric measurements and the production drifts on the performance. This calls for methods that go beyond conventional machine learning models and that are specifically designed for our data.
Numerical Prediction of the Heat Loads on a Non-Reactive Test Rig for Combustor-Turbine Interaction by Using Hybrid RANS-LES Approach
Authors: Tomasello S. G. , Andreini A. , Bacci T. , Facchini B. , Cubeda S. , Andrei L.
Published: September 2023

In order to further improve gas turbine efficiency and performance and reduce NOx emissions, the ever-increasing employment of lean-premix combustors results in very severe, complex and unsteady conditions at the inlet of the first stage nozzle, introducing a possible alteration of the aerothermal behavior of the component. This is considered a recurring problem especially during the gas turbine engine design process and, for this reason, in the recent years, it has become an important and discussed topic in the framework of gas turbines design.

In the present study, an annular sector rig, made by a non-reactive, trisector combustor simulator and nozzle cascade, where both adiabatic effectiveness and HTC measurements had been carried out, is investigated by performing a systematic computational study by using a hybrid RANS-LES approach. Firstly, in accordance with the standard industrial design practice, a periodic configuration of the stand-alone NGV was created in order to evaluate HTC on the vane surface by performing RANS simulations and by using 1D profiles from the experiments as inlet boundary conditions. Then, in order to improve the accuracy and reliability of the prediction of the HTC on the NGV and of the flow field outgoing from the combustor, a fully integrated combustor-stator periodic domain has been investigated by performing a SBES simulation. Moreover, in order to carry out further analyses on the nozzle, in correspondence of the position of the interface plane between the combustor and the stator, a set of unsteady data have been extracted and stored from the fully integrated SBES calculation in order to generate realistic unsteady inlet boundary conditions for the non-cooled NGV configuration. In particular, the NGV has been then studied by carrying out RANS and SBES simulations as well by employing the k-ω SST and Transition SST to model the turbulence effects. Eventually, numerical results have been compared to the experiments in order to evaluate the discrepancies between different CFD approaches.

The comparison between numerical predictions and the available experimental results was exploited to assess the capability of advanced scale-resolving methods in the characterization of the mutual combustor-turbine interaction, along with the heat transfer coefficient behavior. This evaluation aims thus to assess if such more advanced and more time-consuming methods, including also turbulence models able to capture the transition, can be more reliably used for a proper prediction of the vane thermal loads.
Experimental Investigation of Synchronous Flow Induced Blade Vibrations on a Radial Turbine - Part 1: Nominal Inlet Guide Vane
Authors: Schafferus Markus , Sasakaros Marios , Wirsum Manfred , Zobel Arthur , Vogt Damian , Nakos Alex , Beirow Bernd
Published: September 2023

The service life of today’s turbochargers is limited among other things by the mechanical load caused by blade vibrations. In this context, the precise determination of the resonance operating points and the estimation of the vibration magnitudes are essential for an accurate assessment of the service life of the turbocharger components. Forced blade vibrations in radial turbines are primarily flow induced. Flow induced blade vibrations are caused by the nonuniform flow field in the circumferential direction which acts on the blades as a cyclic pressure fluctuation. Previous studies identified the inlet guide vane (IGV) as well as the spiral turbine housing as the primary sources of the non-uniform flow field.

In the present study a thorough experimental investigation of the synchronous blade vibrations of a radial turbine is performed. A detailed description of the experimental setup is given. In this setup the vibrations are captured with two redundant measurement systems during real turbocharger operation. Strain gauges, applied on certain blades, as well as optical tip-timing sensors distributed on the circumference of the turbine shroud are used. The advantages of the combined usage of these two measuring systems are shown in the paper.

Initially, the blade vibration modes are determined experimentally in stand still tests and numerically calculated through FEM models. This served for the creation of a Campbell diagram, which determined the speed ranges that are examined. The mistuning, which is not taken into account in the numerics, is therefore determined via the experiment. In addition, the experimental results are compared with those of numerics and the frequencies from standstill test. The first part of this two-part paper is focused on the vibrations caused by the “nominal” IGV. This “nominal” IGV has twice the number of blades compared to the rotor. Part 2 will analyze the changes of the blade vibrations due to the application of two different IGVs.
Development of Additive Manufacturing Gas Turbine Hot Gas Path Vanes at Baker Hughes
Authors: Cecconi Massimiliano , Giovannetti Iacopo
Published: September 2023

This paper describes the efforts, the lessons learned and the success that led, over a period of 5 years, to the development, validation and finally industrialization of high-pressure turbine vanes manufactured with additive Direct Metal Laser Melting (DMLM) technology.

The introduction of the study collects the requirements for gas turbine vanes in the range of F class and identify the material’s grade and chemical composition of the alloys. As well it is summarized the conflict among the processability and desirable mechanical properties of Nickel base alloys.

The paper explains the procedure used to simultaneously optimize the alloy and the DMLM process parameters for a Nickel based superalloy with high gamma prime content to manufacture complex geometries as high-pressure vanes in the turbine hot section. Metallurgical defects formation in additively manufacturing superalloys are strongly linked to process parameters, such as laser power, scan speed, layer thickness, scan strategy, etc. but are also directly linked to the specific geometry of the component to be processed.

Contouring parameters as downskin/upskin that have higher influence in the residual stresses of the parts and lead to a mechanical properties debit to fatigue resistance.

A “fast-work” approach was used starting with a limited validation of the components in a back-to-back comparison with the traditional technology in lab environment. Over the standard mechanical testing samples, it is introduced subsize component mechanical testing and full-scale component thermal cycle above 1’000°C.

A second step to mature the technology has been to produce and install a first set of vanes and shrouds to be tested in a real validation engine to verify resistance to the main failure modes, in particular cyclic type of damage as low cycle fatigue and crack propagation.

In the paper the final validation step is also presented. In this phase the components are installed in a production engine and monitored by periodic inspections. This allows to complete the durability assessment in real service environment.

The work is completed with an overview on the industrialization challenges of the technology. It has been provided guidelines in components design and printing strategy to mitigate macro cracks formation on high gamma prime content material, including post-print processes as EDM cut removal, thermal and surface treatments.

It is finally compared the CO2 footprint of additive technology versus investment casting, demonstrating a significative reduction in the CO2 emission in gas turbine vanes manufacturing process using additive technology.
Performance Enhancement Kit for Existing Heavy-Duty MS5001 Machines
Authors: Soman Abhimanyu , Santhana Gopalakrishnan Babu , Raghavan Srinivasan , Venna Sudha
Published: September 2023

A Performance Enhancement Kit is introduced to upgrade Fr5001 fleet, there by existing customers benefit from the opportunity for increased output or extended inspection intervals, improved reliability, and operability. The KIT includes advanced-technology combustion system with the new-technology turbine’s stage 1 nozzle and bucket. The components in the KIT are designed for 1) increased power output of 6% or 2) increased maintenance interval from 24 khrs to 35 khrs of mean time between maintenance. Increased power output has been achieved by increasing the firing temperature and improved maintenance has been achieved by new reduced constraint reactions using spring loaded liner and transition piece stops which reduce dynamic forces / displacements and usage of improved wear-resistant materials at sliding interfaces. As a result of improved dynamics and use of wear resistant materials, the overall reliability of the combustor is enhanced. In hot gas path component, stage 1 nozzle life has been improved by redesign of the nozzle’s cooling method and by changing the nozzle architecture, i.e., the cantilever support design of the nozzle to a simply support design. The interface components of the first stage nozzle are also redesigned to accommodate nozzle’s required design modifications. For the stage 1 bucket, the creep life has been improved to satisfy higher temperature or longer repair/replace intervals by the introduction of a high-grade nickel-based alloy, with better creep property. The above design modifications resulted in improved reliability as well as availability of the machine.
Reduced Order Models for Bladed Disks With Contact Mistuning at Blade Root Joints
Authors: Pinto Valeria , Battiato Giuseppe , Firrone Christian Maria
Published: September 2023

Mistuning occurring in bladed disks is a well-recognized problem in the turbomachinery industry, since it may significantly affect the dynamic behavior of the system by inducing localized amplification of the blade vibration when compared to the cyclically symmetric (tuned) configuration. Identifying the highest blade vibration amplitude requires the performance of a large number of simulations, which are usually run by introducing the mistuning in a Reduced Order Model (ROM), obtained from an initial very large Finite Element (FE) model. The traditional introduction of mistuning as blade frequency variation is being progressively replaced by methods that can correlate mis-tuning to a specific source (e.g.: geometric variations, changes in material properties, etc.). In this context, a novel reduction technique has been developed by the authors to take into account mistuning due to the contact uncertainties at the blade root joint, which can be caused by design tolerances, manufacturing processes, assembly procedures, and wear. The technique relies on the Craig-Bampton Component Mode Synthesis (CB-CMS) applied to the uncoupled blade and disk sector, which is usually included in most FE software. Afterward, the full set of master degrees of freedom is reduced using a suitable modal basis, according to the Gram-Schmidt Interface (GSI) method. The proposed reduction technique is firstly numerically validated in terms of modal parameters estimation and forced response computation. Afterward, the method is subjected to an experimental validation on a dummy bladed disk, which requires the previous estimation of the contact stiffness at the blade root-disk interface. Even if the contact stiffness parameter shows a limited influence on the system’s linear behavior, the choice of a suitable value of this parameter is deemed to become relevant when the nonlinear behavior of contact interfaces is studied through penalty contact methods. The ultimate goal of the introduced technique is to obtain a good estimation of the maximum forced response of the bladed disk with a limited computational cost and with sufficient accuracy, provided by appropriate modeling of the mistuning at the blade-disk contact interface.
sCO2 Based Pumped Heat Thermal Energy Storage Systems Valorizing Industrial Waste Heat Recovery: A Techno-Economic Analysis of the Role of High Temperature TES
Authors: Shamsi Syed Safeer Mehdi , Maccarini Simone , Trevisan Silvia , Barberis Stefano , Guedez Mata Rafael Eduardo
Published: September 2023

In the current renewable energy dominated power system, as power production is becoming more and more unpredictable, it would be important to act at two levels: integrating relevant power/energy capacity of energy storage and making demand more controllable. At this purpose, acting on industrial energy demand via integration of energy storage and electrification of local processes, could provide a significant contribution. At the same time, waste heat recovery (WHR) is quite a consolidated industrial practise. Nevertheless, WH valorisation is usually performed via bottoming cycles, such as steam, ORC or supercritical CO2 (sCO2) power cycles. The development of thermo-mechanical storages to be installed at industrial level, can contribute in this direction through the use of traditional technologies (rotating machinery) employed in power plants as well as in Waste-heat-to-power (WH2P) plants.

This paper presents a thermo-economic analysis of Pumped Thermal Energy Storages (PTES) for sCO2 cycles, comparing market available thermal energy storage materials for different temperature range of operation. The proposed system is purposefully designed to exploit the waste heat sources for the temperature ranges of 150–400°C, difficult to exploit for WH2P solutions and rarely addressed in literature so far. The use of sCO2 enhances the techno-economic features of these systems, the independent charging and discharging system proposed in this study can also provide a keen sense of flexibility especially for the upscaling of a PTES plant to reach an equal grid flexibility power for charging and discharging. At the same time, the valorisation of low temperature waste heat enables industries to enhance their energy efficiency, limit their operational costs and environmental impact, whilst becoming an active part in the regulation of the grid. At this purpose optimal system configurations and dispatch strategies are identified based on typical load curves of specific EU markets.

Starting from an identified reference case (a cement production plant with WH temperature to be valorized around 330°C), different PTES cycle layouts and TES technological solutions are compared on a techno-economic basis. The waste heat integration to the PTES system has been found to add satisfactory value in terms of RTE. On the other hand, it proves to be an optimal use case of waste heat valorisation than traditional waste heat to power cycles when compared in terms of exergy, capital cost and dispatchability in ever increasing RES penetration scenarios. The identification of the most optimal TES however is driven by economic factors too as presented in CAPEX and dispatchability analysis.
NASA Small Engine Components Compressor Test Facility: High Efficiency Centrifugal Compressor Vaneless Diffuser and Transition Duct Configurations
Authors: Harrison Herbert M. , McNichols Ezra O. , Blaha Matthew R.
Published: September 2023

The original vaned configuration of the High Efficiency Centrifugal Compressor (HECC) was developed with aggressive design targets to facilitate advancement of state-of-the-art technology in gas turbine compressors. This work documents modifications to the Small Engine Components Compressor Test Facility to support testing of the HECC vaneless diffuser and transition duct configurations, both of which are open geometries. These configurations were developed as follow-up studies to improve understanding of the differences between the predicted and actual performance of the original HECC vaned diffuser stage. Specifically, the vaneless diffuser was designed to provide the impeller with ideal exit conditions such that the impeller performance could be isolated from downstream stationary components, and the additively manufactured transition duct inlet configuration enables investigation into the effects of the inlet flow path on the stage performance. Features of note in the facility are active clearance control, bleed flow regulation, modular inlet configurations, and steady-state and fast-response instrumentation throughout the flow path. Details of the facility and instrumentation are presented as well as the baseline performance of the compressor stage. The geometry, performance, and detailed aerodynamic data have been made available to the public at https://storage.googleapis.com/hecc-data/NASA-HECC-Data-Archive.zip.
Experimental and Numerical Investigation of Forced Ventilation Loss in Gas Turbine Package
Authors: Asti Antonio , Crugnola Federico , De Leo Elena , Lucherini Gabriele , Minotti Stefano , Singh Rajnish Kumar
Published: September 2023

Whenever a gas turbine is installed inside an acoustic enclosure, a ventilation system is required to cool down the package and dilute any accidental gas leakage. Due to the possible presence of gas, all items installed inside the enclosure shall be suitable and hence certified as per hazardous area requirements to prevent them from being source of ignition. For this reason, the correct operation of the ventilation system is essential to meet the certification limits and consequently to safely run the gas turbine train. A malfunction of this system can result in a reduction or a complete loss of ventilation flow in the worst case. In this event, an emergency shut down of the gas turbine train is triggered by the control system after a short transient operating condition. A robust design of a gas turbine package shall also consider such transient condition of ventilation loss to encompass all possible operating scenarios and to verify that each item stays within the certification limits during this time frame. Furthermore, each item, including the engine itself, must not fail and remain ready for the next restart.

Since ventilation fans are usually driven by AC power motors, AC power loss is the most common cause of ventilation loss. For this reason, Baker Hughes performed an experimental test on a full scale package of a Nova LT family turbine. The real scenario occurring in situ in case of AC loss was exactly replicated and several measurements were acquired with dedicated instrumentation installed inside the package. The purpose of this test was to check the thermal field inside the gas turbine enclosure and the amount of natural convection flow which is generated by the “chimney/stack effect”, in order to verify that the certification limits were not exceeded during the transient event of ventilation loss.

Additionally, the natural convection flow inside the GT internal path (intake, engine and exhaust) was also measured to better understand the contribution given by this flow in terms of heat removal from the engine casing. Measurements confirmed that the combined effect of both flows was sufficient to guarantee an adequate ventilation cooling of the package without impacting the package design. Moreover, the naturally established flow was sufficient also to avoid any possible rotor lock in, so that the engine stays ready for restart as soon as normal conditions are restored.

From the numerical point of view, a CFD model was built and run replicating the same transient scenario. The model was then fine-tuned and validated using the experimental data. In this way, having a reliable predictive method, it was also possible to simulate the natural convective flow and its related thermal field when modifications are introduced in the ventilation ducts design, as well as for gas turbine models that are different from the tested one.
Dynamic Performance of Liquid Smooth Annular Seal Operating in the Transition Regime
Authors: Hyun Seung-Hyeop , Delgado Adolfo
Published: September 2023

This paper presents the experimental leakage and rotordynamic performance for a liquid smooth annular operating in the transition regime. The test conditions include pressure differentials up to 64 bars with 1∼2 bar increments for 6 rotor speeds (2.5, 3.8, 5, 7.5, 8.8, and 10 krpm) as well as non-rotating rotor case under zero pre-swirl condition. The rotordynamic coefficients for all the test conditions are obtained by pseudo-random excitation of the seal at multiple subsynchronous frequencies. By considering the transition Reynolds number (1000 < Re < 3000) and Taylor Number (Ta) vs Axial Reynolds Number (Rez), the variations in the direct stiffness coefficients (K) can be found to be an indirect indicator of the flow regime transition boundaries. The direct stiffness K resulting from the Lomakin and hydrodynamic effects significantly drops until Rez reaches approximately 1500. For higher Rez, K increases mainly due to hydrodynamic effects. When K drops, the cross-coupled stiffness k, the direct damping C and the cross-coupled virtual mass m increase while the cross-coupled damping c and virtual mass M decrease. None of predictions based on either laminar or turbulent flow show the variations in rotordynamic coefficients obtained from experimental results. The leakage is not highly influenced by rotor speeds for low speed cases crossing laminar boundary as ΔP increases, however, results for higher speeds in the superlaminar region show reduced leakage rates.
Aeroacoustic Scaling of Axial Low-Pressure Fans With Leading Edge Serrations
Authors: Balde Nina Maimuna , Biedermann Till M. , Kameier Frank , Pohlmann Tobias
Published: September 2023

Previous as well as ongoing studies have shown that bioinspired modifications of the leading edge of axial fans, so-called leading edge serrations, have beneficial effects on sound radiation in rotating systems such as a broadband noise reduction. The objective of this study is to elaborate on the comparability of two geometrically similar low-pressure axial fans that differ in fan diameters. For this purpose, a fan design based on the geometric characteristics of an existing fan, which had been tested in previous studies, was developed with and without leading edge serrations at a scale of 1:3. Extensive experiments were carried out to gather detailed data on the aerodynamic and aeroacoustic performance of the specimen. Similarity laws and non-dimensional parameters are used to investigate whether a transferability comparison of the aerodynamic and aeroacoustic experimental results of these geometrically similar axial fans is possible. The latter also includes an analysis of the spectral range. The results prove that it is possible to derive a comparability of the aerodynamic parameter of the flow coefficient and thus of the flow rate of the fans. Furthermore, a correlation between the noise reduction potential of the two models can be established through spectral Strouhal number normalization. The proposed aerodynamic and aeroacoustic coherences ensure transferability from the model fan to an upscaled fan and thus allow generalized statements to accurately transfer the aeroacoustic potential of leading edge serrations for different geometrically similar fan applications.
Hot Section Thermal Imaging Technology Development: Lessons and Implications for Engine Focused Transient Measurement Techniques
Authors: Anthony Richard J. , Haldeman Charles W.
Published: September 2023

This paper describes non-proprietary rotating high-pressure turbine (HPT) blade thermal imaging results taken in a transient, full-scale, short-duration turbine blowdown facility as part of a larger instrumentation development program for operational aeroengine applications. While thermal imaging of stationary parts is routine, and several institutions use thermal imaging in turbine rig operations, the leap to capture HPT rotor blade transients inside operational aeroengines entail unique challenges. This paper describes an approach that inverts the traditional development path with early exposure to the real engine environment first, followed by turbine rig testing in the AFRL Turbine Research Facility (TRF) for cost-effective system improvement and enhancement between engine tests. Due to the TRF’s transient, short duration, and relatively low temperature operation, results show it is ideal for testing extreme limits of temporal, thermal, and spatial resolution needed for capturing fast engine transients. This demonstrated a new role for the TRF later in the development cycle; specifically, improving instrumentation hardware and software for engine use, while continuing its role as a design validation rig for turbomachinery research and development. Since the first thermal imaging of full speed rotating HPT blades in an operational aeroengine in 2008, the “inverted” instrumentation development path described in this paper provides lessons for future gas turbine sensing developments supporting integrated prognostic health monitoring, digital twin/digital thread, and fleet sustainment.
Experimental Investigation of Combustion Instabilities in a Laboratory-Scale, Multi-Can Gas Turbine Combustor
Authors: Beita Jadeed , Talibi Midhat , Rocha Nuno , Ezenwajiaku Chinonso , Sadasivuni Suresh , Balachandran Ramanarayanan
Published: September 2023

Can and can-annular (can-type) combustors are widely employed in stationary gas turbines. While majority of combustion instability research so far has focused on single can combustors, studying combustion dynamics in multi-can configurations holds more practical relevance. In can-type combustors, the annular gap between the transition ducts and first stage nozzles, known as the ‘cross-talk’ region, promotes strong can-to-can acoustic interactions. In this study, coupled interactions between neighbouring cans are experimentally investigated in a laboratory-scale, atmospheric, two-can combustor rig. Results demonstrate that an out-of-phase longitudinal mode, characterised by pressure anti-nodes in the cans and a pressure node in the cross-talk area, is preferentially excited in the multi-can combustor. Investigation into the effects of combustor flow rate and cross-talk geometry on the can-to-can dynamics revealed an increase in the amplitude of the limit cycle oscillations with mass flow rate, cross-talk volume and cross-talk exit area reduction. However, these factors exerted a weak influence on the frequency of the oscillations and did not impact the mode shape of the resonant can-to-can mode. These findings would help better understand the complex dynamical interactions that occur in multi-can systems towards model validation and tool development, while highlighting the significance of factoring in thermoacoustic aspects in the design of the combustor-turbine interface.
Co-Firing of Hydrogen and Natural Gas in a Practical DLN Combustor Model
Authors: Zhao Rang , Igie Uyioghosa , Abbott David , Wiranegara Raditya Yudha
Published: September 2023

To reduce carbon dioxide emissions, the combustion of natural gas-hydrogen blends in a lean premix gas turbine combustor has been investigated. Previous studies have mostly investigated the fuel blends at relatively low pressure (up to 5 bar) with relatively low hydrogen concentrations (up to 50vol%) on lab-scale or generic burner configurations. However, the influence of higher pressure and higher hydrogen content (over 50vol%) has not been widely studied, particularly on a practical industry-scale lean premixed burner as presented in this study. Such an operation is more challenging as it increases the turbulent flame speed gradient, which is an important factor in determining the likelihood of boundary layer flashback. A preliminary RANS-based Computational Fluid Dynamics (CFD) study has been conducted using ANSYS Fluent 2021R1, employing the Realizable K-Epsilon turbulence model and the Flamelet-Generated Manifold (FGM) combustion model. The combustor consists of a diffusion pilot and premixed main fuel nozzles. Methane-hydrogen blends of up to 90vol% hydrogen were investigated at a fixed fuel energy input. 100vol% methane at 15 bar pressure was taken as the baseline reference case. To investigate the flame characteristics, contour plots of OH mass fraction, equivalence ratios and temperatures (at different planes) are presented.

This study shows that the expected reduction in the flame length with increasing hydrogen concentration occurs up to 40vol%. Significantly different flame shapes (as indicated by OH contours) were seen at higher hydrogen content. For this model, the flashback occurred at 90vol% H2 as indicated by a premature development of the flame within the nozzle of the main fuel burner. NOx emissions are shown to progressively rise with increasing hydrogen content up to 60vol% but reduce as the hydrogen content increases to 70vol%. The decrease appears to be related to an improvement in the quality of fuel-air mixing. It is important to note that the apparent rate of increase in NOx with increasing hydrogen is dependent on the reporting approach used. When reporting conventionally (parts per million by volume corrected to 15% O2 on a dry basis) the increase is significantly greater than when reporting on a mass per fuel energy input basis (gram per Joule). Reporting in the conventional manner disadvantages hydrogen because of the impact of oxygen consumption and water production on the corrections.
Novel Architectures for Transcritical CO2 Refrigeration Cycle Using Rotary Pressure Exchanger
Authors: Sarawate Neelesh , Thatte Azam , Samudrala Omprakash
Published: September 2023

This paper highlights utilization of a rotary gas pressure exchanger (PX G) to increase efficiency of CO2 refrigeration systems using CO2, which is a natural, low global warming (GWP) refrigerant. PX G uses the high-pressure discharge of the condenser/gas cooler as a motive fluid to compress the low-pressure flash gas with minimal external energy input, thus reducing the power consumption of the main compressor. PX G simultaneously expands the high-pressure supercritical/liquid CO2 into a two-phase CO2 ready for heat absorption, thus also emulating the functionality of a typical high-pressure expansion valve.

Several new architectures using PX G are presented to increase the coefficient of performance (COP, i.e. efficiency) of such refrigeration cycles. Because of inherent small pressure losses in PX G, as well as in the gas cooler circuit and piping, two additional low differential pressure auxiliary lift devices are added to help achieve optimal volumetric flow rate through PX G. To avoid the need for auxiliary high-pressure lift devices, additional architectures explore utilizing a secondary gas cooler operating at a reduced pressure compared to the primary gas cooler. Another architecture repurposes the existing low temperature compressor to supply the low-pressure inlet of PX G, thus further eliminating auxiliary low-pressure lift devices.

This paper also describes the modeling method to solve the system of simultaneous energy balance and mass balance equations governing the cycle integrated with PX G. Mass flow constraints based on PX G’s internal physics and density ratio between low-pressure and high-pressure streams entering PX G are also put in place. Various performance metrics such as overall system COP, work done by MT and LT compressors, liquid content after expansion through PX G, flash gas production, and superheat control are analyzed for a wide range of ambient temperatures, evaporator duty, and load split between MT to LT evaporators. This paper further investigates the optimization of key system parameters such as gas cooler pressure and receiver pressure.
Turning Region Heat Transfer in Five, Stationary and Rotating, Multi-Pass Channels With Various Aspect Ratios
Authors: Chen I-Lun , Wright Lesley M. , Han Je-Chin
Published: September 2023

This work summarizes studies that experimentally investigated the effect of rotation on heat transfer in the 180-deg tip and hub turns of cooling channels with various aspect ratios (ARs). The studied AR ranges from 1:4 to 4:1, which is the typical range within turbine blades. In addition to the smooth surface case (baseline case), the cases with 45-deg angled ribs and turning vanes are also included in this work. For several designs, the effect of channel orientation with respect to the angle of rotation is also investigated. This work covers a wide range of Reynolds and buoyancy numbers. The rib turbulators are found to have higher heat transfer enhancement and larger disturbance on the flow impingement on the tip and hub walls in channels with a wider aspect ratio. The rotational effect is reduced by the presence of ribs and turning vanes, and it is also reduced in the blade-shaped channels with the angled rotation feature. The tip wall heat transfer is increased by rotation due to the pumping effect from the centrifugal force; however, the hub wall heat transfer is reduced. The effect of rotation is most prominent in the first pass of the channels and is gradually mitigated in the following pass after the turns. This work provides stationary and rotational heat transfer coefficients in the tip and hub turning regions in blades, and heat transfer correlations for a variety of cooling channel designs are generated, which is of benefit to the gas turbine community.