bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady Pre-Stall Behavior in a Centrifugal Compressor With Vaned Diffuser
Authors: Suzuki Yutaro , Fujisawa Nobumichi , Ohta Yutaka
Published: September 2023

Unsteady pre-stall behavior in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analysis. The pre-stall disturbances occurred at a slightly higher flow coefficient at the stall point in the diffuser region. Five disturbances occurred in the circumferential direction, and each rotated at approximately 1.7%N at this flow coefficient. Numerical analysis showed that five stall cells rotated at approximately 2.0%N within the diffuser passage. To understand this pre-stall phenomenon, we focused on the rotation mechanism and initiation process of the five-cell rotating stalls. Each of the five-cell stalls was found to rotate by the following mechanism. When the preceding low-velocity region moved to an adjacent passage, the high-velocity region was circumferentially pushed by the low-velocity area and reached the following passage. The incoming flow collided with the back flow around the throat area, and the flow bent at the diffuser inlet of the passage. Consequently, the incidence angle toward the adjacent passage increased, and a separation was induced at the leading edge of the succeeding diffuser vane. Subsequently, the mass flow rate of the succeeding passage started to decrease. These phenomena occurred sequentially, causing the five-cell stalls to rotate. Five stationary low-velocity regions that did not rotate were observed before the initiation of the five-cell rotating stalls. When the outlet mass flow rate decreased, a one-cell rotating stall appeared within the diffuser passage. It provided a low-energy fluid to the diffuser passages where the low-velocity regions existed. Subsequently, five lowvelocity regions were clearly formed, which started rotating according to the rotating mechanism explained above.
Combined Joule-Humphrey-Recuperator Cycle: Performance and Parametric Analysis Evaluation Towards More Efficient Air Transportation
Authors: Saavedra Jorge , Cadarso Luis
Published: September 2023

A three-stream combined Joule-Humphrey cycle that employs a heat recovery stream to function as a recuperator is presented. Based on an in-house developed thermodynamic performance tool, the operation of a modified dual-shaft turbofan engine is proposed. The engine core is modified by adding an intercooler and a re-heating chamber to approach isothermal compression and expansion processes. A fraction of the primary flow is introduced into a re-heat chamber that uses Rotating Detonation Combustion (RDC) technology. The outflow of the RDC is then merged with the rest of the nucleus current before being discharged to the next turbine stage.

The overall system behavior is captured by means of a nonlinear mathematical model featuring eight decision variables, including mass flow rates and compression ratios. A parametric analysis identifies the operational and performance envelope of the proposed engine concept. Ultimately, the model is endowed with an objective function, which includes global efficiency and thrust looking for an operation regime that boosts the thermodynamic performance. A Generalized Reduced Gradient based algorithm is used to solve the nonlinear model, where each iteration solves a linearly constrained subproblem to generate a search direction. The performance and operational envelope presented here could be used as guidance for others considering the implementation of any of the discussed Joule cycle modifications or assessing the cost-effective balance of their use.
Insights Into Frictional Brush Seal Hysteresis
Authors: Phan Hien M. , Pekris Michael J. , Chew John W.
Published: September 2023

Brush seals offer a superior sealing effectiveness compared to labyrinth seals. However, widespread use of brush seals is constrained by deleterious behaviors such as pressure-stiffening and hysteresis. For the latter, the bristles bend during the shaft incursion process and do not fully recover during the shaft retraction process. An opening gap is created, which increases seal leakage unless the pressure load drops to a certain level. In the present work, analytical and numerical models based on a single bristle are proposed to capture the seal’s response to shaft displacement with and without pressure loading. The models are validated using static stiffness tests at an unpressurized condition from literature. The main results show that modeling of the backing ring friction is essential to capture the bristle hang-up behavior. Shaft friction dominates at unpressurized conditions, while backing ring friction dominates at high pressure loading. An expression for shaft hang-up displacement has been derived. A sensitivity study shows that seals with shallow lay angle, short bristle length, and large bristle diameter are less prone to hang-up problems. The models developed in the present framework have been shown to qualitatively capture the pressure stiffening, hysteresis, bristle hang-up, and shaft rotation effects.
Intermittency of Flame Structure and Thermo-Acoustic Behavior in a Staged Multipoint Injector Using Liquid Fuel
Authors: Truffot Marie , Renaud Antoine , Zimmer Laurent , Richecoeur Franck , Cayre Alain , Méry Yoann
Published: September 2023

This study investigates the impact of the staging factor, the ratio between the fuel injected through the pilot stage and the multipoint injection, on the flame dynamic. The BIMER combustor is an atmospheric pressure rig equipped with two co-rotating swirling air injections (a fixed amount of around 87% of the air goes inside the multipoint stage) and two fuel injection paths for staged combustion. Liquid dodecane is injected with air preheated at 437K with a global equivalence ratio of 0.6 and a thermal power around 72 kW. The change of the staging factor from 100% (pilot-only injection) toward 0% (multipoint-only injection) generates changes in the flame-shape which bifurcates from an anchored V-flame into a lifted flame. This flame shape bifurcation appears at a staging factor around 25%.

Around this staging factor, one can witness multistable flames where the flame structure transits randomly between five different states. Processing microphone signals recorded in the chamber provides an understanding of the flame dynamics. The attached flame presents limited pressure fluctuations level at 270 Hz, while the lifted flame features high-pressure fluctuations at 323 Hz. The intermittency between the five states (including the two stable states) is investigated.
Influence of Steam and Elevated Ambient Conditions on N2O in a Premixed Swirling NH3/H2 Flame
Authors: Pugh Daniel , Bowen Philip , Goktepe Burak , Giles Anthony , Mashruk Syed , Valera Medina Agustin , Morris Steven
Published: September 2023

Renewably generated NH3 has the potential to support future energy demand, however combustor designs and strategies require considerable development to ensure reduced NOx emissions. Expanding on previous work, a turbulent swirl burner was used to appraise potential NOx reduction pathways, both experimentally and numerically, with a premixed NH3/H2/air flame. With a 100-year global warming potential ∼265 times that of CO2, particular emphasis was given to N2O. Maintaining a constant thermal power, reactants were supplied at elevated temperature, with parametric changes made to pressure and humidity. Favourable agreement was demonstrated between exhaust emission measurements and simulations performed using a chemical reactor network model. NO and N2O emissions were shown to be sensitive to operational equivalence ratio, increasing by several orders of magnitude across the experimental range. An increase in combustor pressure was experimentally shown to reduce exhaust N2O concentrations with this globally lean fuel mixture, alongside NO. Steam injection was also explored in detail for the first time and shown to provide contrasting trends, with a reduction in NO, and a rise in N2O, as water loading was increased. Both pressure increase and steam injection were combined to give optimal NOx performance for the evaluated dataset. Changes in chemical kinetic pathways were investigated in detail, and compared to high-speed OH*, NH2*, and NH* chemiluminescence.
A Critical Analysis on the Impact of External Losses on the Performance of a Centrifugal Compressor Stage – Experimental and Multi-Fidelity Numerical Assessment
Authors: Baroni Alberto , Catalani Iacopo , Romani Luca , Bicchi Marco , Balduzzi Francesco , Marconcini Michele , Bianchini Alessandro , Arnone Andrea , Ferrara Giovanni , Toni Lorenzo , Biliotti Davide
Published: September 2023

The study presents a combined experimental and numerical analysis of the impact of external losses in defining the real performance of a model stage. This is of particular importance in the early-validation phase, where novel solutions going beyond the state of the art need to be verified for the first time. Due to the number of simulations to be carried out during preliminary design, in fact CFD calculations often focus on main flow path analyses and neglect these losses. If optimization is carried out within a known design space, this does not create any problem and the different solutions can be analyzed in a comparative way. On the other hand, when a new design solution comes into play, possible changes in the impact of losses can lead to unfair comparison between numerical predictions and test-rig experimental data.

In particular, the results of detailed experimental tests carried out in the test rig developed by the University of Florence in support of its industrial partner Baker Hughes are presented here. In the test, different seals at the impeller’s eye are compared. Results are then compared to numerical simulations of the stage that include cavities and resolve leakage flow, and of those of a newly-developed integrated and computationally-efficient tool that combines CFD simulations of only the main flow path with engineering corrections for loss sources. Results show that indeed a comprehensive CFD model that resolves cavity leakage is able to correctly replicate experimental results, although this is obtained with a notable calculation cost, which is often not affordable at industrial level. On the other hand, almost the same accuracy is reached with the combination of a main flow path-only CFD model and correction method, thus proving the interest for this type of approach in the industrial context.
Compressor Water Extraction
Authors: Farman Judith R. , Day Ivor J. , Dickens Tony M. J. , Taylor James V. , Hussain Zahid
Published: September 2023

The effect of putting a bleed slot behind the rotor or stator of a modern representative IP compressor stage has been investigated using a purpose built test rig. The first part of the paper, goes over the construction and operation of a rig, which for the first time allows for accurate measurement of water extraction and rapid testing of a variety of bleed slot geometries. Using this test rig it was found that the use of a bleed slot behind the rotor increases water extraction by up to 40% compared to placing it behind the stator. The overall extraction efficiency for the rotor exit was above 70% for all bleed rates considered from 0% to 30% and is relatively constant. Whilst rotor exit bleed might be advantageous for water extraction, further improvements in extraction efficiency are required for future engines with low fan speed and low blade solidity. The final part of the paper, looks at the effect of a bleed lip protrusion to improve water extraction, as this can be retrofitted in engines. An extra 5% can be achieved by doing this without a penalty operability. This has been explained using 3D CFD by examining the flow separation topology.
Loss Analysis in Radial Inflow Turbines for Supercritical CO2 Mixtures
Authors: Aqel Omar , White Martin , Sayma Abdulnaser
Published: September 2023

Recent studies have indicated the potential of CO2-mixtures to lower the cost of concentrated solar power plants. Based on aerodynamic and cost considerations, radial inflow turbines (RIT) can be a suitable choice for small to medium sized sCO2 power plants (about 100 kW to 10 MW). The aim of this paper is to quantify the effect of doping CO2 on the design of RITs. This is achieved by comparing the 1D mean-line designs and aerodynamic losses of pure sCO2 RITs with those of three sCO2 mixtures containing tetrachloride (TiCl4), sulphur dioxide (SO2), and hexaflourobenzene (C6F6).

Results show that the optimal turbine designs for all working fluids will have similar rotor shapes and velocity diagrams. However, factors such as the clearance-to-blade-height ratio, turbine pressure ratio, and the difference in the viscosity of the fluids cause variations in the achievable turbine efficiency. Once the effects of these factors are eliminated, differences in the total-to-static efficiency amongst the fluids may become less than 0.1%. Moreover, if rotational speed limits are imposed, then greater differences in the designs and efficiencies of the turbines emerge amongst the fluids. It was found that limiting the rotational speed reduces the total-to-static efficiency in all fluids; the maximum reduction is about 15% in 0.1 MW CO2 compared to the 3% reduction in CO2/TiCl4 turbines of the same power.

Among the mixtures studied, CO2/TiCl4 achieved the highest performance, followed by CO2/C6F6, and then CO2/SO2. For example, 100 kW turbines for CO2/TiCl4, CO2/C6F6, CO2/SO2, and CO2 achieve total-to-static efficiencies of 80.0%, 77.4%, 78.1%, and 75.5% respectively. Whereas, the efficiencies for 10 MW turbines are 87.8%, 87.3%, 87.5%, and 87.2%, in the same order.
Supercritical CO2 Compressor and Expander Design for Industrial Waste-Heat Valorization
Authors: Toni Lorenzo , Bisio Valentina , Milani Alberto , Biliotti Davide , Bellobuono Ernani Fulvio , Valente Roberto , Dozzini Matteo , Bigi Manuele , Generini Giulio
Published: September 2023

Within the energy transition framework, it is believed that supercritical carbon dioxide (sCO2) power cycles can significantly contribute to climate change goals. Compared to other energy conversion technologies, higher efficiency can be achieved thanks to the minimized compression work, driven by the peculiar properties of sCO2. Footprint reduction coupled with good operational flexibility and reduced water consumption are additional advantages.

The present work discusses design challenges and solutions studied for an sCO2 power system object of the CO2OLHEAT project, “Supercritical CO2 power cycles demonstration in Operational environment Locally valorizing industrial Waste Heat”, European Union Horizon 2020 funded program (grant agreement # 101022831). The project aims at demonstrating the first MW-scale waste heat recovery system employing sCO2 in the EU; the demo cycle will be installed in an existing industrial plant. Object of the authors’ work includes the design and testing of a turboexpander driving the cycle compression phase.

In this paper, the main challenges faced in the conceptual design phase of turbomachinery will be assessed. The centrifugal compressor, whose inlet conditions are in proximity to CO2 critical point to get the highest cycle efficiency, has been designed using specific equilibrium models and equation of state to both properly consider phase-change regions and strong gradients of thermodynamic properties. Regarding the expander, the paper will describe how the inlet conditions (pressure and temperature) represented specific challenges in particular for mechanical configuration and safe operation of crucial components such as the Dry Gas Seals (DGS), for which dedicated thermal analyses were conducted. The paper concludes with considerations on design choices for turbomachinery made to improve the operability of the complete cycle even in off-design conditions such as possible variations in minimum and maximum CO2 temperatures due to external factors.
Machine Learning Based Optimizer for Tilting Pad Journal Bearing Inlet Flowrate
Authors: Gheller Edoardo , Chatterton Steven , Panara Daniele , Turini Gabriele , Pennacchi Paolo
Published: September 2023

In view of the green economy and energy transition, the reduction of the environmental impact of the power generation sector plays a key role. Fluid film bearings are the most common bearing for industrial turbomachinery and new design requirements have a direct impact on bearings operation. In fact, to achieve higher levels of efficiency, bearings must support higher specific loads and higher peripheral speeds. Furthermore, there is great interest in reducing the oil flowrate required for the bearing operation as much as possible. In this work, an optimization strategy for reducing the flowrate fed to tilting pad journal bearings (TPJBs) is proposed. An artificial neural network (ANN) is trained to estimate the static and dynamic performance of the bearings. The training dataset is built with a Reynolds-based thermo-hydrodynamic model. The trained ANN is then used in a constrained optimization that has the goal of minimizing the oil flowrate while ensuring safe bearing operation. Predictions are compared with experimental data from Compressor Mechanical Running Tests. The proposed model is an effective tool that can help industry achieve the goals required by the energy transition and can help in the development of optimized fluid film bearings.
Neutron Characterization of 3D Printed Gas Turbine Alloy With Internal Cooling Structure
Authors: Raju Nandhini , Fouliard Quentin , Bunn Jeffrey R. , Subramanian Ramesh , Kapat Jayanta , Raghavan Seetha
Published: September 2023

The objective of this research work is to investigate the residual strains induced by the presence of a exit hole and internal hollow geometry present in a 3D printed IN718 similar to that seen in a gas turbine blade. The specimens were manufactured with an internal hollow structure that ended with an exit hole, and fabricated by direct metal laser sintering additive manufacturing technique. Using this technique, metal powder was melted by a laser source and rapidly cooled to form the part layer by layer. Rapid heating and cooling generate large thermal gradients and residual stresses in the 3D printed material. To be aligned with industry standards, specimens were heat-treated to relieve most of the residual stresses as well as to investigate whether IN718 still preserved a nonhomogeneous stress state after the thermal treatment. Roughness and microstructure analysis was performed to understand the heat-treated sample properties. To investigate the volumetric residual strain, the neutron diffraction technique was used with a definite neutron wavelength. Bragg’s law was used to determine lattice spacing. Interplanar lattice spacing and stress-free state lattice spacings were measured to calculate the strains. Residual strains were measured in the x and y direction to understand the impact of the presence of a exit hole and internal hollow geometry. The results of volumetric residual strain in the x and y directions showed no significant variations in the distribution of the strain due to the presence of a hollow structure as well as the exit hole. Overall, no significant stress concentration was observed in the heat treated sample. Sample geometry, instrumentation for neutron diffraction, and material properties are discussed in detail in this paper.
Adjoint-Based Aeroacoustic Optimization of NASA Rotor37
Authors: Katsapoxaki Pelagia , Hottois Romain , Tran Thanh-Son , Schram Christophe , Coussement Grégory , Verstraete Tom
Published: September 2023

Within the past decades, numerous optimization methods have been developed to maximize the aerodynamic characteristics of various turbomachinery components. Lately, more attention is being paid to methods able to enhance their aero-acoustic performance due to the increasing demand for quiet propulsion systems for the aircraft industry. In the framework of the present work, a multi-disciplinary, multi-objective, gradient-based shape optimization is performed to minimize the shock-associated tonal noise of NASA Rotor37, while maximizing its isentropic efficiency. The rotor’s flow field is obtained through three-dimensional Reynolds averaged Navier Stokes simulations with the Spalart-Allmaras turbulence model, while the corresponding sound power level is obtained using a simple noise calculation tool based on the flow perturbations at the rotor’s inlet. An adjoint approach is used for computing the gradients of the objective functions with respect to the 41 design variables, which parametrize the geometry of the blade. A Sequential Quadratic Programming optimization algorithm is used to identify several trade-off points of the noise-efficiency Pareto front. Constraints are added to the optimization problem to keep the mass flow within a given range. Results show a substantial improvement in the overall performance of the rotor, with 2.75dB of sound power level reduction and a 1.4% increase in isentropic efficiency. Compared to a similar study that was conducted with a gradient-free algorithm, these results are obtained at a limited computational effort thanks to the adjoint-based methodology. The flow fields of the baseline and optimized designs are analyzed to understand the mechanisms behind the performance improvements.
Modelling of Combustor Non-Uniformities Evolution Through a High-Pressure Turbine Stage
Authors: Notaristefano Andrea , Gaetani Paolo
Published: September 2023

In modern gas turbines, the reduction of pollutant emissions can be achieved by employing lean-burn combustors. At the combustion chamber outlet, the flow is non-uniform and characterized by a residual swirl superimposed to steady (hot streak) and unsteady (entropy waves) temperature disturbances. During the transport from the combustor outlet to the turbine inlet, these disturbances are weakly dissipated and persist at the turbine inlet. Therefore, the interaction between the combustor non-uniformities and the turbine has to be deeply studied.

To study combustor-turbine interaction experimentally, a common practice is to install combustor simulators on non-reactive turbine test facilities. For this purpose, a combustor simulator was designed and installed at Politecnico di Milano turbine test facility. This device can generate a combined steady/unsteady temperature disturbance and swirl profile at the turbine inlet. Using this layout, several experimental campaigns have been carried out changing the type of injected disturbance, the injection position and the turbine operating condition. In this paper, the data collected from these experiments have been used to develop simplified models to predict the transport and dissipation of combustor perturbations through a turbine first stage. In the open literature, few attempts are discussed regarding the modelling of combustor-turbine interaction that — in authors’ opinion — represents an important tool for preliminary turbine design.
Experimental Characterisation of the Dynamics of Partially Premixed Hydrogen Flames in a Lean Direct Injection (LDI) Combustor
Authors: Ezenwajiaku Chinonso , Balachandran Ramanarayanan , Ducci Andrea , Picciani Mark , Talibi Midhat
Published: September 2023

Hydrogen continues to show significant promise as a zero-carbon energy carrier in the pursuit of global decarbonisation targets. Hydrogen has wide flammability limits which means it can operate at considerably leaner conditions for reduced NOx emissions. However, fuel-lean operation makes these systems more susceptible to thermoacoustic instabilities and flame blow-off. Combustor configurations such as jet-in-crossflow are gaining popularity in industry for 100% hydrogen as they can help mitigate risk of flashback, but detailed characterisation of flame dynamics is still necessary.

In this study, the combustion dynamics of partially premixed hydrogen flames in a lean direct injection (LDI) multi-cluster combustor were investigated at atmospheric conditions. The combustor inlet consisted of nine circular air channels, with hydrogen injected inwards through two diametrically opposite holes into each air channel. Dynamic pressure and OH* chemiluminescence measurements were employed to study the effect of varying key parameters, such as Reynolds number and global equivalence ratio, on combustor dynamics. High-speed OH-PLIF imaging was conducted to understand flame dynamics.

The results showed that self-excited oscillations were observed at all tested conditions and the dynamical behaviour of the combustor was complex with strong dependency on global equivalence ratio and bulk velocity conditions. The magnitude of self-excited thermoacoustic oscillations initially increased with a decrease in global equivalence ratio, but subsequently decreased at leaner conditions (below global equivalence ratio 0.3). Similar observations were noted for all bulk velocities. High speed OH-PLIF imaging indicated that the heat release oscillations were influenced by vortex-flame roll up and possible global lean extinction events. The results from this work have the potential to inform design efforts towards development of new architectures for stable, low-emission 100% hydrogen combustors.
Performance Investigation of a Bladeless Air Compressor Using Numerical Simulation
Authors: Tiwari Ravi Nath , Traverso Alberto , Pascenti Matteo , Ferrari Mario Luigi
Published: September 2023

In recent years, the demand for lightweight, compact, cost-effective, and low-noise-emission machines has increased significantly. Tesla or bladeless machines can meet the current market’s demands, especially at a small scale. This article examines Tesla compressor performance numerically, which is influenced by a number of factors related to rotor and stator design. This study examines multiple aspects of Tesla’s compressor in order to improve its overall performance, including the rotor, stator impact, and statorless or volute casing. An innovative bladeless rotor has been independently studied and optimized based on the Ekman number and diameter ratio. The disk gap and radius ratio are crucial to the performance of bladeless rotors. The rotor-only analysis determined an isentropic efficiency of 95%, which is in line with expectations.

An optimized rotor is initially simulated with a stator (vane diffuser) and subsequently with a volute casing. In the diffuser case, it has been numerically demonstrated that bladeless compressors can achieve an overall efficiency up to 53%. It should be noted, however, that compressor performance depends on the number of diffuser vanes and the stator-rotor interaction. With an increase in diffuser vanes, overall performance may be affected by a significant increase in frictional losses and stator-rotor interaction. In order to improve performance, the volute casing is examined, which reveals that efficiency is improved by 3%–5% as compared to the best-vaned diffuser case. Even if the final choice of the designer will depend on the performance requirements and level of complexity acceptable for the specific application, this study demonstrates that Tesla compressor with volute, i.e. statorless, overperform any vaned diffuser configuration both in terms of efficiency and pressure ratio.
Lean Flame Stabilization With Nanosecond Plasma Discharges in a Gas Turbine Model Combustor
Authors: Blanchard Victorien P. , Roqué Frédéric , Scouflaire Philippe , Laux Christophe O. , Ducruix Sébastien
Published: September 2023

This paper presents an experimental study of lean flames stabilization with nanosecond repetitively pulsed discharges. The two-stage, swirled-stabilized, multipoint injector BIMER operates at atmospheric pressure with methane-air mixtures in the present study. It is representative in its design of a realistic lean premixed prevaporized injector of gas turbine engines operated at a lab-scale level. The lean blow-off extension with plasma is characterized. The combustion efficiency and the pollutant emissions are quantified near blow-off with and without plasma for 50-kW flames. We show that it is possible to stabilize lean flames down to an equivalence ratio of 0.3, with less than 5 ppm of NOx emitted, thanks to NRP discharges with an electric power that represents less than 0.25% of the flame thermal power. This study also clearly shows that it is necessary to account for the plasma system integration at the early stage of the combustor design to fully benefit from the plasma stabilizing effects on the flame.
LES Modeling of High-Lift High-Work LP Turbine Profiles: Part I: Approach
Authors: Ni Michael , Ni Ron-Ho , Clark John P.
Published: September 2023

The Low Pressure Turbine (LPT), commonly used in both commercial and military engines, generally experiences low Reynolds numbers at high altitude cruise conditions. Understanding the complex flow physics in an LPT stage is critical in providing adequate work output while maintaining target efficiency at low Reynolds number situations.

With the complex laminar to turbulent transition flow physics in mind, the high lift LPT design requires an understanding of the turbulent transition response to design and operating conditions which is not currently met with existing design methodologies. The RANS based turbulence models like k-ω and SST, are not able to provide meaningful transition analysis.

This paper presents Large Eddy Simulations (LES) of 4 LPT cascades airfoils over a range of Reynolds’ numbers from 60,000 to 20,000 compared against 1D experimental data. The objective of the work is to define a controlled numerical procedure that minimizes the number variables affecting the LES. The controlled numerical procedure will then be used to understand the LES time-step size requirements needed for consistent Reynolds Lapse rate characterization. Simulations are run with identical mesh count, mesh topology as well as with identical inlet and exit flow conditions. The Reynolds number was varied through the modification of the Kinematic viscosity, enabling effective evaluations of time-step size sensitivity of LES simulations upon the time-averaged total pressure losses.

Findings include that time step size needs to be small enough to promote the creation of 3D eddies and that the time step size used for the Dual-Time Stepping method needs to be smaller than the convection time step size (ΔTc) to provide consistent Pt loss estimation. This methodology is then applied to new cascades and the results presented in Part II.
Predicting Premature Failures in Small Wind Turbines With Recurrence Plots
Authors: Jauregui Juan C. , Torres-Contreras Ignacio
Published: September 2023

This paper presents the application of the Recurrence Plot as an alternative for pre-processing the raw data. The Recurrence Plots can extract the non-linear and transient response and are sensitive to slight variations in the signal frequency, amplitude, and waveform. Thus, it is an alternative technique for improving the sensitivity; consequently, the prognostic algorithms can predict with better resolution. The data were obtained from an experimental 12 m wind turbine. The transmission was instrumented with three accelerometers and three gyroscopes; the generator’s current and voltage were monitored. The difficulty in producing the phase plane using acceleration data is its integration to obtain the kinetic and potential signal energies. This limitation is overcome by integrating the data using the Empirical Mode Decomposition and the shift principle. The results show good sensitivity for predicting variations in the operating conditions and are the basis for other prognostic analyses.
Numerical Assessment of the Effect of Hydrogen Enrichment of a Technically Premixed Swirl-Stabilized Natural Gas Flame
Authors: Pachano Leonardo , Surapaneni Anurag , Both Ambrus , Ax Holger , Petry Niklas , Boxx Isaac , Mira Daniel
Published: September 2023

High-fidelity large eddy simulations (LES) are conducted for lean natural gas flames with different levels of hydrogen enrichment in a technically premixed swirl-stabilized combustor (PRECCINSTA) operated at atmospheric pressure. The modelling approach relies on tabulation of premixed flamelets and presumed-shape probability density functions (PDF) to account for subgrid turbulence-chemistry interactions. Results are presented for non-reacting and reacting conditions with 0, 40 and 50% hydrogen content in the natural gas. The influence of hydrogen-enrichment is investigated here by combining LES with Raman measurements. The assessment of LES shows good predictions of the flame stabilization mechanism, flow field and flame dynamics as compared to experiments. The natural gas flame develops a self-excited flow oscillation characterized as a precessing vortex core, which is well reproduced by the LES. The lean operation of the burner with natural gas shows a stable M-shape flame that transitions to a V-shape fully attached flame as the main fuel is blended with hydrogen. Raman measurements are compared with LES data to examine the flame structure and burning characteristics. It is concluded that hydrogen addition makes the flame more compact, induces higher reactivity of the fuel-air mixture and leads to a stable V-shape flame fully attached to the burner’s nozzle-cone.
Options for Improving Performance of Additively Manufactured Nickel-Base Superalloys for Gas Turbine Applications
Authors: Bridges Alex , Shingledecker John , Clark John , Crudden David , Kirka Michael , Fernandez-Zelaia Patxi
Published: September 2023

Additive manufacturing (AM) has been increasingly used for gas turbine components over the last decade. Many different components can successfully be designed, printed and used in the gas turbine. However, there still exist questions on the use of AM components in hot-section areas. These components are typically fabricated from nickel-base superalloys that are known to have superior mechanical properties at elevated temperatures (e.g. creep and fatigue). Research over the last decade has been primarily focused on the printability of nickel-base superalloys and there still exists a gap in understanding the high temperature processing-structure-properties-performance relationships of these alloy systems.

This study evaluates the effect of processing methods, such as laser-based powder bed fusion (LBPBF) and electron beam powder bed fusion (EBPBF), on resulting microstructure and time dependent mechanical properties of a nickel-base superalloy (ABD®900). Material after each build was subsequently heat treated using both near-solvus (at or slightly below the gamma prime solvus temperature) and super-solvus (above gamma prime solvus temperature) conditions. Multi-step aging was then carried out to produce a bi-modal distribution of gamma prime precipitates as is typical in similar alloys. Microstructure was evaluated in both the as-built and fully heat-treated conditions for each processing technique. Mechanical testing was conducted to evaluate the effects of AM build methods, microstructure, and heat treatment on high temperature mechanical properties.

The results show there are several methods which can be used to improve the performance of components built using AM. The creep testing results for ABD900-AM clearly show an improvement in properties (rupture life and ductility) at all test conditions compared to testing in the prior AM alloy of the same class. A super-solvus heat treatment improved creep rupture strength by ∼3X in the LBPBF material compared to the near-solvus heat treatment. These findings provide directions for future studies to advance the overall state of gas turbine technology by enabling ABD®900-AM material and other AM alloys to be used in more innovative hot-section components.
Numerical Study on the Aeroacoustics of a Propeller-Wing Integration at Various Advance Ratios
Authors: Huang Guangyuan , Sharma Sidharath , Ambrose Stephen , Jefferson-Loveday Richard
Published: September 2023

Driven by increasing demands for a sustainable and ecofriendly future in aviation, Distributed Electric Propulsion (DEP) systems have received much attention for their high aerodynamic efficiency. DEP systems with lower noise emissions are desired by customers and policymakers and therefore it is important to understand the noise generation mechanism, propeller-propeller and propeller-wing interactions of DEP aeroacoustics. In this paper, the effect of flow conditions on the aeroacoustics of a propeller-wing integration is investigated numerically with various advance ratios. The integration consists of a Mejzlik 2-blade propeller installed on the leading edge of a NACA0018 airfoil. The propeller is designed using Clark-Y airfoil sections and a constant pitch with a pitch-to-diameter ratio of P/D = 0.5. Different rotating and forward-flight velocities are studied, corresponding to the advance ratio J ranging from 0.485 to 1.575. A hybrid computational aeroacoustics (CaAA) method is performed, where the near-field aeroacoustics is solved by compressible coarse-grid large-eddy simulations (LES), and the corresponding far-field acoustics is calculated by the Ffowcs Williams and Hawkings (FW-H) equation. The results have shown significant effects of the flow conditions on the propeller-wing integration in terms of the aerodynamic and acoustic features. The aerodynamic performance and near-field flow structures are investigated first. Then the sound generation from the propeller and wing is revealed respectively.
Operational Strategies of 2-Spool Micro Gas Turbine With Alternative Fuels: A Performance Assessment
Authors: Gaitanis Aggelos , Tiwari Ravi Nath , De Paepe Ward , Ferrari Mario Luigi , Contino Francesco , Breuhaus Peter
Published: September 2023

The demand for efficient, cost-effective, and low-emission decentralized electricity and heat production is rapidly increasing. Micro Gas Turbines (mGT) have not yet succeeded in conquering the small-scale combined heat and power (CHP) market. The main reason is that their electrical efficiency is not high enough to maintain a cost-effective operation at low heat demand. A two-shaft intercooled mGT has the potential to meet the current market demand for decentralized power generation. This technology maintains a high level of electrical efficiency even at part load and coupled with its fuel-flexible combustion chamber, makes it an ideal candidate for CHP concepts in a renewable future.

The energy transition however also requires mGTs to be able to run on alternative fuels, such as hydrogen and syngas, which shifts its operating conditions and requires significant modification in the cycle’s part-load control to ensure the stable operation of the components such as the compressor. Therefore, in this paper, performance analysis on a 2-spool mGT is carried out using a mixture of natural gas, syngas, and hydrogen as a fuel. Specific attention is given to the low-pressure and high-pressure compressors and the variation of surge margin by adding hydrogen and syngas into the fuel. Two control strategies of the 2-spool mGT are adopted. In the first scenario, the two shafts have the same rotational speed while in the second one, the shaft speeds are controlled independently. In both part-load strategies, the specific performance of the two compressors keeps high isentropic efficiency which leads to high electrical efficiency at nominal power when natural gas-syngas mixture is used as fuel. When the engine is operated with equal shaft speeds, the maximum performance with 100 vol.% of syngas is observed at 85% of the nominal load while 100 vol.% of hydrogen shows maximum efficiency at an electric load of 63.7%. Also, at electric power lower than 60% of the nominal and for high amounts of syngas in natural gas, the low-pressure compressor (LPC) operates closely to surge line. In the second part-load strategy, the efficiency increases as the load decreases and the LPC runs in an efficient and safe operating region. Moreover, the performance of the 2-spool mGT is significantly influenced by the amount of nitrogen in syngas. At 200 kW, 45 vol.% of nitrogen decreases the airflow rate of the cycle by 7.4% compared to 0 vol.%. The results indicate that the amount of nitrogen in syngas and also the part-load strategies significantly influence the safe operation of the LPC component.
Numerical Study of Radiative Heat Transfer Through Next-Gen Thermal Barrier Coating Topcoats
Authors: Mulla Jaasim , Satpathy Radhakanta , Kaka Fiyanshu
Published: September 2023

With the world coming to terms with the consequences of climate change, the aviation sector has continued pushing towards increased efficiency to lower emissions. Other than the use of eco-friendly fuels, it is a fact that to achieve higher efficiency and thrust, it is essential to raise the turbine entry temperature in the engine. Increased temperatures in the turbine section intensifies the thermo-mechanical stresses on the hot-end components reducing their life exponentially. Higher temperatures also lead to an increased fraction of heat transfer via the mode of radiation, which has been largely neglected in turbine design until recently. Hence, the heat transfer to the substrate needs to be minimized by reflecting or radiating the heat. The goal of this study has been to model the propagation of thermal radiation through a novel thermal barrier coating topcoat focused on reducing radiative heat transport to the super-alloy substrate. The radiation has been modeled with a finite-difference-time-domain approach to gather a broadband response across the target wavelength range. A range of topcoat morphologies were studied numerically, amounting to ≈ 8500 core hours, in search of an ideal structure that minimizes the radiation throughput to the substrate. The study found a strong angle dependency of reflectance with varying pore morphologies. The analysis done in this first of its kind study on the morphology dependence of reflectance in plasma-sprayed alumina coatings is expected to lay the foundation for future research, leading to a more accurate understanding of the mixed modes of heat transfer phenomenon in the turbine environment and higher turbine inlet temperatures.
Numerical and Experimental Investigations on the Leakage Flow Characteristics and Temperature Distributions of Brush Seals
Authors: Song Pengfei , Ma Dengqian , Li Zhigang , Li Jun
Published: September 2023

Investigation on leakage flow and heat transfer characteristics in the bristle pack attaches significant importance to performance enhancement of brush seals. The experimental leakage flow rates were obtained for brush seals with two alternative backing plate configurations at pressure ratio (Rp) up to 2.8 and rotating speed (n) up to 3000 r/min. The leakage characteristics of tested seals were simulated using the RANS equation coupled with porous medium model solutions. The frictional heat effect and heat transfer characteristics of the two brush seals are investigated by means of the porous medium model coupled with the FEA. The calculated leakage flow rates are consistent with the experimental results. The leakage of the two brush seals increases linearly with the increase of Rp and decreases slightly with the increase of n. There will be the blow-down effect in brush seals with the increase of Rp, resulting in bristles extending to the rotating shaft, which slows down the trend of leakage increases with the Rp. The existence of the pressure relief groove can effectively alleviate the hysteresis effect but increase the leakage of brush seals in high pressure drop. The increase in rotating speed can also weaken the hysteresis of brush seals. The aerodynamic force, frictional force and frictional heat flux of two brush seals were calculated according to the experimental conditions. The temperature distribution of two kinds of brush seals were analyzed and discussed. It occurs the stiffening effect in bristles with the existence of pressure drop, which causes a significant increase in the friction between the bristles and the shaft. The friction heat flux increases approximately linearly with the increase of Rp and n, which makes the temperature of the bristles tip increase significantly, but the leakage air can take away part of the friction heat.
Wind Tunnel Experimental Study of the Effects of Blade Number on the Performance and Starting Behavior of a Low Tip-Speed Ratio and Micro-Scale Wind Turbine at Fixed Blade Geometry
Authors: Bourhis Martin , Zhang Shuo , Pereira Michael , Ravelet Florent
Published: September 2023

The effects of the number of blades on the efficiency and starting behavior of low tip-speed ratio micro-scale wind turbines are controversial. In contrast to modern 3-bladed fast large-scale horizontal axis wind turbines, these runners are multi-bladed to increase torque and to perform efficiently in low wind speed conditions. While an optimal number of blades for large-scale wind turbines has been established, it is still under consideration for small wind energy harvesters. The aim of this research is to examine the influence of the number of blades, while maintaining a constant blade chord length, on the power and torque coefficients of micro-scale wind turbines that are specifically designed to work at low tip-speed ratio. Seven 200 mm high-solidity wind turbines with a number of blades varying from 4 to 16 were designed, manufactured, and tested in a wind tunnel to collect the full power and torque coefficients vs. tip-speed ratio characteristics. We found that turbines with a large number of blades are more efficient in low wind speed conditions and have a lower cut-in wind speed than turbines with fewer blades. The experimental results emphasize the existence of an optimal range of blade numbers for our specific blade geometry, between 12 and 14 blades, that decreases the cut-in wind speed while maximizing the power coefficient. Furthermore, we observed that the performance curves of the wind turbines change as the number of blades increases, emphasizing the existence of blade interactions that alter blade aerodynamic properties. In addition, this experimental study provides some guidelines for the development of efficient micro wind energy harvesters.
The Impact of the Off-Design Conditions on the Entropy Wave Interaction With a High-Pressure Turbine Stage
Authors: Pinelli Lorenzo , Giannini Giovanni , Marconcini Michele , Pacciani Roberto , Notaristefano Andrea , Gaetani Paolo
Published: September 2023

The study of component interactions in aeronautical engines is a key aspect to improve the aerodynamic, aeromechanical and thermal performance and to reduce greenhouse gas and noise emissions. In this context, combustor systems (working with lean and premixed flames) generate pressure, velocity and temperature fluctuations that interact with the turbine module producing combustor instability, performance degradation and noise generation. A correct understanding of this interaction is thus required by the designers, especially with a view to introducing sustainable aviation fuel to achieve zero-emission aviation. The paper tackles this topic from a numerical and experimental point of view, focusing on off-design turbine conditions possibly encountered during an aeroengine mission. In detail, the effect of different stage loadings (obtained by keeping the stage pressure ratio and modifying the rotational speed) on engine-representative entropy waves evolving through the turbine stage is investigated. The combination of numerical and experimental results, that show a good agreement in terms of disturbance evolution within the stage, allows a deeper understanding of the flow field features that impact the stage aerodynamics and modify the secondary flow structures and the entropy wave transport, diffusion and decay through the rotor. Moreover, the most loaded operating condition reveals the appearance of a rotating instability at the rotor tip that also interacts with the injected disturbance. Finally, the numerical results (coming from full annulus URANS computation with incoming disturbances) are further post-processed to extract indirect noise emissions at the different load conditions and to assess the additional loading on the rotor blade caused by the presence of the disturbance.