bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Casing Coolant Injection on Aerodynamic Loss in a Linear Turbine Cascade With Tip Clearance
Authors: Hong Dunam , Choi Minsuk , Kim Myungho , Song Seung Jin
Published: October 2022

Deviation and loss have been measured and numerically analyzed in a linear turbine cascade with tip clearance and upstream casing coolant injection. Compared to the case without coolant injection, when a coolant flow of 0.5% of the mainstream mass flow rate with a non-dimensional swirl of 100% is injected into the mainstream, the following changes occur. The mass-averaged deviation decreases by 2.4 degrees. The decrease in deviation occurs mainly because the underturning and overturning due to the passage vortex (PV) and trailing shed vortex (TSV) increase; and the centers of both vortices move toward the midspan and pressure side. The mass-averaged loss increases by 15.9% primarily because the losses associated with the PV and TSV increase. Multiple vortices are formed at the exit of the coolant slot due to the Kelvin-Helmholtz instabilities. These slot exit vortices strengthen the PV and increase the associated loss, but they have little direct interaction with either tip clearance vortex (TCV) or TSV. The TSV is strengthened by both tip unloading and PV strengthening, and thus the associated loss increases. The loss due to the TCV decreases slightly due to the reduced incidence and decreased tip clearance flow rate. When the coolant is injected with less swirl — with non-dimensional swirl values of 85% and 70% — the loss increases are reduced to 9.3% and 6.7%, respectively, relative to the case without coolant. The change in loss with decreasing swirl is mainly due to the decreases in PV and TSV losses. The loss in the tip region is not sensitive to the coolant swirl.
Influence of Porosity on Double-Walled Effusion-Cooled Systems for Gas Turbine Blades
Authors: Courtis Matthew , Ireland Peter
Published: October 2022

Double wall effusion cooling (DWEC) systems for gas turbine blades utilise two skins connected by pedestals and take advantage of cooling benefits provided by impingement jets and film holes. The latter exhausts coolant externally onto the blade surface forming a protective layer against the high external heat loads, which can be enhanced via the beneficial influence of adjacent films. Consequently, increasingly porous outerskins are being considered in order to provide greater thermal protection and/or reduce the required coolant mass consumption. To realise such systems, further research must understand how the internal aerothermal field is affected by high porosity.

A semi-decoupled unit-cell computational fluid dynamics (CFD) method is applied to a range of DWEC systems to understand overall cooling effectiveness as well as internal characteristics. A comparison of internal convection highlights a shift in the breakdown of cooling performance, due to the large changes in wetted surface area of the outerskin. For low porosity, most of the internal cooling occurs through the jet impingement on the internal outerskin wall, while the addition of more film holes provides an increasingly greater proportion of convective heat transfer. On the external surface, porosity increased film effectiveness due to film superposition, provided a more uniform film coverage, and reduced the likelihood of jet-lift-off.

Coupling the benefits of internal cooling and film effectiveness resulted in a reduction of mean metal temperature, peak temperature and temperature gradient between the outer and inner walls. Criteria reflecting the main drivers for thermal fatigue. Despite these benefits, for the most porous DWEC configuration a variation in mass flow between film holes was observed, and in some cases the risk of hot gas ingestion was evident. DWEC components would benefit from further understanding of the susceptibility to blockage, the pressure margin limits and the extent of flow migration.
Numerical Investigation of Unsteady Flow Phenomena in a Centrifugal Compressor Operating Near Surge With a Geometrically Reduced Model
Authors: Paul Dominik , Eißler Werner
Published: October 2022

Deep surge is a time and system dependent phenomenon that might be triggered by a flow instability. This instability could be subsequently used as an indicator for the surge margin. Based on former numerical investigations concerning steady flow phenomena in a centrifugal compressor, published at “Turbo Expo 2021” by Hochschule RheinMain and TU Darmstadt the investigations have been continued. A speed line is divided into four sections based on its slope, which are examined for instabilities by means of transient simulations with a numerical reduced model. For this purpose, a detailed frequency analysis is carried out to detect unstable flow behaviour. It is shown that the characteristic of the speed line is in a good agreement with the analysed frequency spectrum and the associated unsteady flow phenomena. These are for instance a highly changing incidence triggered by vortex tubes at the impeller inlet. In addition, the computations show an instability in the vaneless space behind the trailing edge, the occurrence of which is in a relationship to the experimental stability limit. Regardless of the system volume, the phenomenon could be used as an indicator for the stability of the compressor wheel.

A second speed line is then used to validate this relationship.
Investigation of a High-Pressure Turbine Stage in a High-Speed Rotating Transient Test Facility for Rotor Tip Study and a Parametric Study for Improved Heat Transfer Calculation
Authors: Singh Deepanshu , Beard Paul F. , Cardwell David , Chana Kam S.
Published: October 2022

The first part of the paper presents commissioning of a single-stage high-pressure turbine employed in a series of extensive experiments to study the aerodynamics and heat transfer on the rotor surface and casing liner. The OTRF (Oxford Turbine Research Facility), a high-speed rotating transient test facility has the capability to take unsteady aerodynamic and heat transfer measurements at engine representative conditions with a variety of inlet temperature profiles including radial distortion and swirl. A temperature profile survey was conducted at the inlet of the high-pressure NGV (Nozzle Guide Vane). Static and total pressure and temperature measurements have been taken at various locations on the rig including NGV surface, inlet and exit, and rotor exit to establish rig operating conditions. Detailed description of mass flow rate measurements along with calculation of heat loss factor in the rig is presented. The second part of the paper presents a parametric study performed to improve heat transfer measurement calculations from high-frequency response thin-film gauges. The effect of parameters like material properties and thickness of substrate on heat flux has been studied. A detailed uncertainty analysis for heat flux is also presented. A thermal model calibrated with analytical solutions has been developed to optimise thin-film gauge configurations and to study side-conduction effects.
Hexavalent Chromium Observations on Serviced Components of Oil&Gas Gas Turbines: Formation Mechanism Study
Authors: Scrinzi Erica , Mochi Gianni , Melani Antonio , Del Puglia Eugenio , Pranzetti Alice
Published: October 2022

Hexavalent chromium Cr(VI) is one of the oxidation states (+6) of chromium. It is a recognized toxin and carcinogen, which if ingested or inhaled may affect the respiratory system, kidneys, and liver. It can also cause dermatitis and severe irritation to the eyes. It is widely present in electroplating, anodizing and dye production industries, but has recently been identified as contaminant on serviced components of gas turbines. To this regard, there is the potential for Cr(VI) compounds to be present on gas turbine components serviced at high temperature, if calcium-containing insulating, anti-seize or sealing products are used.

A systematic experimental campaign was carried out to investigate the mechanism and understand the influence of various factors on the formation of substances containing chromium in the hexavalent form. During the test campaign, anti-seize products, sealing products, insulating products but also environmental contaminants were tested on different bare materials in different service conditions.
Advanced Tip Repair of Single Crystal HPT Blades With LW3 and LW4280 Welding Materials
Authors: Chan Anthony , Gontcharov Alexandre , Lowden Paul , Mikolajewski Thomas , Sixsmith J. J. , Tollett Robert , Greer Clayton
Published: October 2022

High pressure turbine (HPT) blades manufactured from single crystal (SX) materials exhibit tip degradation during service resulting in loss of coatings and parent metal, primarily from abrasion, thermal-mechanical fatigue cracking (TMF), creep, and oxidation. Currently, Gas Tungsten Arc Welding (GTAW) and Laser Beam Welding (LBW) with Merl 72 and Rene 142 (R142) welding materials are used for repairing the tips of SX HPT blades. Tips repaired with Merl 72, despite the superior oxidation resistance of the cobalt welding material, are prone to cracking due to the low mechanical properties of the Merl 72 welds at temperatures exceeding 1800°F (982°C). Additionally, despite the high strength of R142 in its cast condition, R142 welds are prone to weld stress-strain cracking and thus require preheating of the blades above 1700°F (926°C) to repair the part with a predetermined level of micro cracking present. Preheating can adversely affect the inert atmospheric conditions of the argon protection. This inadequate shielding of the welding area may result in contamination of welds with non-metallic inclusions which reduce creep and TMF properties.

The current study focuses on substantiating the replacement of Merl 72 with alternative LW3 and LW4280 nickel based welding materials for minor dimensional restoration and full tip replacement on SX HPT blades with a solid tip cap. LW3 and LW4280 contain 28 vol.% and 49 vol.% gamma prime phase respectively, after post weld aging heat treatment. A time-transient thermal mechanical Finite Element Analysis (FEA) of the SX HPT blade was completed for takeoff, cruise, and landing conditions. The resultant temperature and stresses from the FEA study were used as the basis for qualification of the tip repair. Tensile and stress rupture properties of dissimilar SX-LW3 and SX-LW4280 welds produced at ambient temperature using manual GTAW and Laser Direct Energy Deposition (L-DED) on a LAWS1000 welding system utilizing a 3D additive manufacturing (AM) concept were studied. It was demonstrated that LW4280 welds had superior stress rupture, and fatigue properties when compared to M 72. Cyclic oxidation resistance of LW4280 at 2048°F (1120°C) was found to be sufficient to ensure required durability of repaired blades for 6,000 cycles in cases of damage to protective coatings. Some examples of repairs of HPT blades developed using these materials and technologies are provided.
A Coupled Computational Aero-Acoustics (CAA)/ Large-Eddy Simulation (LES) Approach for the Pressure Calculation in Internal Low-Mach Number Flows
Authors: Bénez Pierre , Lartigue Ghislain , Moureau Vincent , Ribert Guillaume , Robin Marine
Published: October 2022

The predictive unsteady simulation of pressure fluctuations in turbulent internal flows at low-Mach number is challenging because of the very different propagation speeds of the acoustic and entropy waves. In this paper, a hybrid Computational-Aero-Acoustics (CAA) / Large-Eddy-Simulation (LES) approach tailored for the numerical calculation of aero-acoustic noise and pressure in internal low-Mach number flow is developed to alleviate the acoustic time step restriction. The algorithm is based on the coupling of a fractional-step method used to solve the low-Mach number Navier-Stokes equations and a fully-implicit linear acoustics solver. The pressure field resulting from the Helmholtz equation computed by the acoustic solver is composed of both dynamic and acoustic contributions. The Newmark’s time integration method combined with implicit Non-Reflecting-Boundary-Conditions (NRBC) are implemented for solving implicitly the Helmholtz equation and then advancing the two solvers with the same convective time step. The properties of the linear acoustic solver are illustrated on simple test cases and the coupling method is then validated by performing the aero-acoustic simulation of the isothermal flow in a complex semi-industrial burner.
Modeling Power Constraints Using Maps and Field Data in Optimization Problems for Gas Transportation Systems
Authors: Allen Cody W.
Published: October 2022

Gas transmission networks have been and continue to be the most efficient method for transporting natural gas. As Hydrogen begins to emerge as one possible solution of renewable energy and starts mixing into gas networks, now more than ever, efficient operation is paramount. Part of the efficient pipeline operation puzzle is knowing how much power is available at a given compressor station, which constrains the head and flow that can be produced. This paper derives and implements driver constraints relating to gas pipeline optimization problems such as throughput maximization and compressor station power minimization at the pipeline level. In the literature the driver is often neglected in implementations of pipeline optimization problems. Often, only the compressor map is considered during the optimization procedure. In this work we develop the necessary physical relations and constraints between the gas compressor and driver. The addition of these constraints ensures that solutions are not only bounded by surge and stonewall curves as well as compressor speed, but also by available power from the driver given current ambient conditions. We also derive a method to fit constraints to observed data. The modified optimization problem results in more accurate solutions of pipeline optimization problems, giving operators more accurate data with which to make business decisions and operate pipelines.
Micromechanical Modeling of Time-Dependent Crack Opening Behavior in SiC/SiC Composites
Authors: Li Longbiao
Published: October 2022

Ceramic-matrix composites (CMCs) possess high specific strength and modulus at elevated temperature and have already been applied in hot-section components in commercial or military gas turbine engines. Due to low fracture strain in the brittle SiC ceramic, matrix microcracking occurs below the proportional limit stress (PLS). At elevated temperature, the opening of matrix microcracking affects the mechanical properties of CMCs when the oxygen or oxidative gas ingresses the composite through these cracks. To ensure the reliability, safety, and airworthiness level of CMCs components, it is necessary to understand the crack opening behavior of CMCs at elevated temperature. In this paper, a micromechanical approach is developed to predict the time-dependent crack opening behavior in SiC/SiC composite. Micro stress field in the different damage regions are obtained and the cracking opening displacement (COD) are calculated. Experimental CODs in SiC/SiC composite for different matrix crack lengths are predicted. Effects of composite material properties, stress level, and testing temperature on the time-dependent crack opening behavior in SiC/SiC composite are analyzed. Relationships between the cracking opening, composite’s constituent properties, stress level, and testing temperature are established. The analysis results can help the engineering designer better understanding the crack opening behavior in CMCs.
Automated Component Preliminary Design and Evaluation in the Overall Engine Using Fully Coupled Approaches
Authors: Schmeink Jens , Schnoes Markus
Published: October 2022

Engine development is a long and complex process. Errors or unfavorable decisions made in the preliminary design phase have a lasting negative impact on the entire development process. The later a bad design decision has to be corrected, the more costs, time and effort are required for the correction. It would therefore be better to make forward-looking decisions right from the start.

Thanks to today’s simulation methods, this is possible to the greatest possible extent. The use of suitable methods supports and significantly shortens the development time. With an additional process automation through the coupling of design programs from different disciplines, promising solutions can be separated from less good ones early on in the development process using a broad multi-disciplinary approach.

This paper presents a numerical approach to evaluate overall engine performance while designing the high-pressure compressor (HPC). A parametric component design process is used to generate a model for a 2-D through flow analysis. This is coupled with a performance program via the data model and process management of a gas turbine design framework. Design as well as the off-design information of thermodynamic engine and aerodynamic component simulation are shared with each other. This way, more information can be gained than it would be the case for both disciplines individually. Therefore, different approaches of this form of multi-disciplinary coupling, often referred to as zooming, are compared regarding their usability and their numerical effort for the design of an HPC in an overall engine. The approach that shows the best results in this comparison is used for an example optimization process of a military engine HPC.
Effect of Mixing on the Anchoring and Combustion Regimes of Pure Hydrogen Flames in Sequential Combustors
Authors: Solana-Pérez R. , Shcherbanev S. A. , Ciani A. , Noiray N.
Published: October 2022

In this work we perform an experimental study of the combustion of pure hydrogen in the sequential stage of a generic combustor. This academic test rig is a simplified model of an industrial sequential combustor. The sequential fuel is injected using different injector geometries. The composition and temperature of the hot stream at the inlet of the sequential burner are defined by the mass flows of the hot combustion products from the first stage (30 kW natural gas-air flame with equivalence ratio of 0.7) and of the dilution air. This temperature is varied between 1100 K and 850 K by modifying the dilution air mass flow in order to study the different combustion regimes of the sequential hydrogen flame. High-speed imaging of OH radicals chemiluminescence is performed with optical emission spectroscopy to measure vitiated gas temperatures. In particular, we investigate the transition from a flame anchored in the sequential combustion chamber, to the situation where it stabilizes upstream into the mixing section, when the inlet flow temperature is increased. Of particular interest is the increasing rate of formation of autoignition kernels in this transition process. The underlying combustion regime change is analyzed with 0D reactor simulations, and the limitations of such a simplified low-order model of the flame location are discussed. The effects and importance of the mixing process between fresh fuel and the hot vitiated co-flow is examined. Two different injectors are compared under the same operating conditions that create different flow structures along the mixing section. As a result of that, they provide different degrees of mixing between the hydrogen and the hot vitiated flow and allow to demonstrate the impact of mixing quality on the flame morphology.
Design and Operability Challenges for Supercritical CO2 Plants: The sCO2-Flex Centrifugal Compressor Test Experience
Authors: Manuele Bigi , Valentina Bisio , Silvia Evangelisti , Marco Giancotti , Alberto Milani , Tiziano Pellegrini
Published: October 2022

Interest in supercritical carbon dioxide (sCO2) cycles has grown significantly in recent years. The peculiar properties of the fluid open unique opportunities but also poses several challenges. Here we aim at narrowing the knowledge gap in operating such plants, leveraging the test experience of a full-scale 5 MW Centrifugal Compressor prototype designed for the sCO2-flex project (H2020 funded program, grant agreement #764690). The test rig replicated a complete recycle loop for the compressor. In addition to validating the compressor’s performances in its design condition, a larger envelope of operation and transients was explored. The paper describes engineering groundwork and design choices regarding: i) transient operation such as pressurized startups and emergency shutdowns; ii) safety relief valves and discharge lines, with possible CO2 solidification; and iii) vibrations due to extremely high density. For all these topics, specific challenges brought by the sCO2 are described. We show the most meaningful results, in excellent agreement with predictions, and discuss key learnings from the test experience. We highlight how important it was to anticipate risks during the design phase and we give recommendations for future installations. We conclude with hints on testing severe off-design conditions, with two-phase flow at compressor suction.
Accelerating the Development of a New Turbomachinery Concept in an Environment With Limited Resources and Experimental Data: Challenges
Authors: Rubini Dylan , Karefyllidis Nikolas , Xu Liping , Rosic Budimir , Johannesdahl Harri
Published: October 2022

This paper presents the requirements for a tailored design ecosystem to accelerate the development of a new turbo-reactor for hydrocarbon cracking. The objective of this novel turbo-reactor concept is to eliminate carbon emissions from the radiant section of the plant. However, the time constraint for this energy- and carbon-intensive cracking industry to fully decarbonize is severely restricted. Therefore, the development of this new concept must be accelerated to a market-ready product within a limited time frame. However, the novelty of the design requirements and the unique level of complexity of the flow physics result in inadequate experimental data, with insufficient time and resources to develop a new measurement database. This shifts the design system towards computer-aided engineering platforms; however for the turbo-reactor, the uncertainty level of these low-order numerical tools (e.g., RANS and throughflow solvers) is elevated for three reasons. First, blockage, deviation and loss correlations integrated within throughflow solvers are unsuitable to capture the flow physics in the turbo-reactor. Second, RANS turbulence closure models need to be re-calibrated for this machine. Finally, due to the chemical reactions, the working fluid properties vary significantly along the gas path and strongly influence the aerodynamics. A new tailored design ecosystem is proposed to address these challenges. The relatively low Reynolds number regime throughout the turbo-reactor enables upfront and routine eddy-resolving simulations to be performed. This allows the new design system to feature a feedback mechanism in which high-fidelity CFD data is used to calibrate lower-fidelity — but less CPU intensive — design tools and empirical correlations. Crucially, the new toolchain is customized in order to capture the influence of the reactions on the thermodynamic properties, as well as to provide the aerodynamic designer with immediate insight into how stage-design modifications influence the reaction product yield distribution. This paper demonstrates the capabilities of an efficient aerodynamic-chemistry coupling methodology that has been implemented within an in-house CFD solver.
Study on Titanium Aluminide Turbine Wheel Blade Machining for Turbochargers by Electrochemical Machining (ECM)
Authors: Aono Masahiro , Shimizu Tatsuya , Obi Nobuaki , Goto Akihiro
Published: October 2022

A turbocharger is the device of a car that is used to add extra air into the combustion chambers of an engine. Recently, researches have been conducted on the use of TiAl materials in turbine wheels to replace traditional Ni-based alloys. Since TiAl material has good heat resistance and is lightweight, it is effective in reducing the moment of inertia of the turbine wheel.

However, the TiAl material has a problem that it has high viscosity when it is melted and that it is not suitable for precision casting. Even when the thickness of the turbine wheel blades is increased to about 1 mm, the molten TiAl does not always flow to the tip of the mold, and the problem of chipped tip often occurs.

In this study, authors investigated the method of manufacturing blades with thickness of more than 1 mm by precision casting in a yield of almost 100%, and then machining them into thin shape of about half thickness by electrochemical machining (ECM).

In ECM, it is well known that the flow of the electrolyte affects the machined shape. It was difficult to finish the blade in the desired shape at first and unmachined area remained. Then authors examined the flow of electrolyte using computational fluid dynamics (CFD) analysis and tried to make it appropriate. As a result, a technology was established to machine turbine wheel blades that meet the requirements for shape accuracy and surface roughness in a short time of about 100 seconds.
The Design and Optimisation of a 100% Hydrogen Micro Gas Turbine Micromix Combustor: Preliminary Hydrogen Injection Depth Characterisation Using Cold Flow Steady RANS
Authors: Devriese Cedric , Snijders Simon , De Paepe Ward , Bastiaans Rob
Published: October 2022

In a modern electricity grid, with fluctuating renewable energy input and problems linked to construction of large power plants in densely populated areas, local, flexible, and zero-emission electricity and heat production becomes evermore important. Consequently, we research the design and optimisation of a hydrogen fuelled micro Gas Turbine (mGT). This paper focusses on our continued development and optimisation of the low-NOx hydrogen combustion chamber, based on the Micromix principle. Based on previous work, we observed that the hydrogen injection depth was critical in minimising thermal NOx formation. To characterise the hydrogen Jet in Cross Flow (JICF) mechanism more deeply, we first designed a simplified single nozzle variant of the micromix geometry. Using this test geometry, we analysed the relation between the hydrogen injection pressure and the hydrogen injection depth, perpendicularly into the air flow, using both an analytical model and cold flow steady RANS simulations. From these simulation results we obtained a preliminary optimal range for the injection pressure, so that the hydrogen does not protrude too far into the air stream (thereby increasing the residence time and increasing the possibility of higher thermal NOx formation), nor too little (thereby reducing the mixing of both fuel and air and increasing the chance of combustion too near to the wall). Based on these results, we can, using hot flow steady RANS simulations, validate the optimal hydrogen injection pressure range from the single-nozzle, cold flow results, for minimal thermal NOx formation, in a follow-up research.
Experimental Hydraulic Performance Study of a Primary Surface Recuperator With Cross-Wavy Microchannels for Portable Microturbines
Authors: Li Hui , Zou Zhengping , Chen Yiming , Li Huan , Fu Chao
Published: October 2022

Portable microturbines with high power and energy densities are attractive candidates for mobile power sources. Due to the limitations of compressor pressure ratio and turbine inlet temperature, a compact and lightweight recuperator is the mandatory component of this type of microturbines to achieve high thermal efficiency. Typically, microchannels with thin wall thickness are used for heat transfer enhancement. However, the reduction in channel size may significantly increase the pressure drop of both fluids. Owing to the lack of existing experimental data for ultra-compact microchannel recuperators of portable microturbines, the hydraulic performance of a newly-designed primary surface recuperator with cross-wavy microchannels (CW-PSR) was experimentally studied. The 50 μm-thick heat transfer plates were used for the CW-PSR core, in which the hydraulic diameters of gas and air channels are 848.8 μm and 598.6 μm, respectively. Hence, the surface compactness of the CW-PSR prototype is about 2428 m2/m3. We tested the hydraulic performance of the CW-PSR both under hot and cold conditions with Reynolds numbers ranging from 320 to 980. The experimental results show that the pressure drops on both sides increase with increasing mass flow rate, while the hot conditions with high inlet temperature result in larger pressure drops. Besides, it was confirmed that the friction pressure drop in the heat transfer region accounts for more than 60% of the total pressure drop. Finally, a new correlation of friction factors for cross-wavy microchannels was obtained based on experimental results.
Conjugate Heat Transfer of Cylindrical and Trenched Film Cooling Designs With Array Jet Impingement
Authors: Fischer Lukas , Sanchez Andrés , Schleich Fabian , Feller Fabian , Raffelt Richard , Pfitzner Michael
Published: October 2022

A numerical film cooling study involving different external cooling designs, thermal barrier coating (TBC) and internal cooling methods is performed. The steady Reynolds Averaged Navier Stokes (RANS) equations are solved including conjugate heat transfer (CHT). The heat transfer coefficient and material properties of the TBC and vane material lead to a proper scaling of the Biot number with respect to real engines. The cooling efficiency of the external surface and of the wall interface between TBC and vane are evaluated. Three film cooling designs, namely standard effusion hole film cooling as well as transverse and optimized trenches are investigated. Moreover, the effect of array jet impingement and convective channel cooling is investigated onto the external and interface cooling efficiency. The jet Reynolds number of the impingement and effusion cooling is varied between 3100–12300 at blowing ratios between 0.3 and 1.2. The main-stream Reynolds number varied between 4500 and 11000 depending on the tested density ratio. The external cooling efficiency of both trench designs showed to be superior to the standard effusion case. With respect to the interface cooling efficiency, there was an improvement in efficiency of 0.1 visible for the trenched designs compared to the standard effusion hole design. Moreover, flow ingestion into the trenches and the external heat flux and heat transfer coefficient are investigated.
LNG Regasification Plants Integrated With Low- and High-Temperature Organic Rankine Cycles
Authors: Tola Vittorio , Delogu Eliana , Finkenrath Matthias
Published: October 2022

The use of natural gas has continuously increased and reached 24.7% of the worldwide primary energy supply in 2020. The same trend applies to Liquefied Natural Gas (LNG), which contributed to 52% of overall natural gas trades in the same year. In this context, the recovery of the cold energy available at LNG receiving terminals during the process of regasification is of a critical importance.

This paper addresses the integration of the regasification process with an Organic Rankine Cycle (ORC) in order to exploit the available LNG cold energy, by condensing the organic fluid. In addition, a gas turbine exploits differences between regasification and distribution pressures. The analysis covers different organic fluids and two ORC heating source configurations: a) a low-temperature one, using seawater, and b) a high-temperature one, using exhaust gas. In addition, the integration of a natural gas-fired topping gas turbine, which uses the LNG cold energy by compressor inlet air cooling, was simulated. The performance of a medium size regasification terminal (50 kg/s) was evaluated as a function of both the regasification and the natural gas distribution pressures.

Dedicated models have been developed using Aspen Plus software to simulate the regasification process and the integrated topping cycles (Organic Rankine and Brayton), and their mutual energy integrations.

The analysis shows that ORC power outputs from 2 MW up to 4.5 MW in case a) and from 6 MW up to 9 MW in case b) can be reached. The topping gas turbine benefits from the inlet air cooling and can add a power output of 35 MW to 40 MW. R125 was the best working fluid for a low-temperature ORC, while R600a showed the best performance for a high-temperature application.
Machine Learning-Based Multi-Disciplinary Optimization of Transonic Axial Compressor Blade Considering Aeroelasticity
Authors: Kang Hyun-Su , Kim Youn-Jea
Published: October 2022

The optimal design of the turbomachinery field can produce the best results when considering multiple fields (e.g., structural vibration, aerodynamic, and aeroelasticity). Since multi-disciplinary phenomena are very complex and nonlinear, a higher level of optimization is needed. In this study, the transonic axial compressor blade was optimized using machine learning-based multi-disciplinary optimization techniques. The entire simulation includes important three factors to consider when designing the axial compressor blade: vibration, aerodynamic performance, and aeroelasticity. In the first step of the optimization, six variables that make up the blade design were used in a design of experiments to explore the design space.

Frequency, efficiency, pressure ratio, and aerodynamic damping ratio were used as the output parameter used in the optimal design. The first to third blade modes frequency from the modal analysis were used for parameters of vibration fields. The efficiency and pressure ratio are values that can be obtained from steady CFD calculations for evaluating aerodynamic performance. The aerodynamic damping coefficient was obtained from transient CFD, which is widely used to determine the presence or absence of fluid-induced vibration and flutter.

As a result of machine learning-based optimization, the optimized blade shape has a lower risk of blade resonance. Also, the aerodynamic performance of the axial compressor has been improved compared to the reference model. In addition, the aerodynamic damping coefficient, an important indicator in terms of aeroelasticity, rose by up to 15%, completing optimization considering the aeroelastic effect.
Inlet Flow Distortion Dependencies for Tail Mounted Ducted Fans on Hybrid-Electric Commuter Aircraft
Authors: Engelbrecht E. Geoffrey , Gkoutzamanis Vasilis G. , Nasoulis Christos P. , Kalfas Anestis I.
Published: October 2022

A numerical analysis based on Computational Fluid Dynamics (CFD) is carried out to investigate the influence of the fuselage transition and axial offset, on the inlet distortion and performance of a tail mounted fan, for a short-haul commuter aircraft. For the examined configurations, it is predicted that varying the angle of the fuselage transition does not have a significant impact on the radial distortion, for a typical fan mounted at the centreline of the fuselage. The wake behind the fuselage is predicted to increase in size as the slope of the fuselage is increased, however, the positive suction from the fan is sufficient for the flow to fully recover before the fan duct inlet. Nevertheless, it is predicted that offsetting the fan from the fuselage centreline produces a more significant increase in distortion in the circumferential direction. The propulsive power of the fan is predicted to increase slightly with increasing offset mainly due to the side of the fan which is less obstructed by the fuselage. However, the wake on the opposite side is predicted to increase significantly persisting almost to the inlet of the fan duct. A vortex formed upstream of the fan increases in strength with increasing offset. This vortex helps to offset the increase in circumferential distortion by re-energizing the flow in the wake of the fuselage. This causes the circumferential distortion to remain roughly constant between offsets of 25% and 50% of the fuselage radius. It is likely though that this vortex will deteriorate the performance of the fan.
Optimisation of an ORC Radial Turbine Using a Reduced-Order Model Coupled With CFD
Authors: Alvarez-Regueiro Eva , Yang Bijie , Barrera-Medrano Esperanza , Martinez-Botas Ricardo , Rajoo Srithar
Published: October 2022

This paper presents the geometry optimisation of a single stage radial turbine for an Organic Ranking Cycle system operating over a pressure ratio of 9. The specific fluid used in this investigation is R1233zd (E), but the methodology applies to other organic fluids as well. The ORC system is used to recover excess waste heat from the operation of an offshore oil and gas platform in the gulf of Thailand and its conditions will be replicated at pilot plant level.

The geometry is optimised for the highest total-to-static efficiency using non gradient based algorithms to allow for wide design space. Firstly, a 1D meanline geometry is optimised, which is followed by a Computational Fluid Dynamics (CFD) optimisation in 3D using a parameterised model. CFD validate and calibrate the meanline model as well as to understand the flow and the sensitivity of the design parameters not captured by the low-order model. Moreover, the flow field of the successful designs is analysed by CFD to identify the main flow structures that explain the difference in performance among the designs. The real gas thermophysical properties of R1233zd (E) are calculated using equations of state to account for the non-ideal gas behaviour.
Multi-Objective Development of Machine-Learnt Closures for Fully Integrated Transition and Wake Mixing Predictions in Low Pressure Turbines
Authors: Akolekar Harshal D. , Waschkowski Fabian , Pacciani Roberto , Zhao Yaomin , Sandberg Richard D.
Published: October 2022

In low pressure turbines (LPT), due to the low Reynolds number a large part of the blade boundary layer remains laminar and transition may occur due to flow separation. The boundary layer details at the blade trailing edge can change substantially depending on the transition region topology and can strongly influence the wake mixing occurring downstream. Accurately predicting these flow phenomena still poses a challenge for Reynolds averaged Navier-Stokes (RANS) and unsteady RANS methods. In this work a recently developed computational fluid dynamics (CFD) driven machine learning framework featuring multi-expression, multi-objective optimization is exploited for the first time to simultaneously develop transition models and turbulence closures in a fully coupled way, aimed at improving both transition and wake mixing predictions in LPTs. The T106A blade cascade with an isentropic Reynolds number of 100,000 is adopted as a training case. The baseline transition model is based on a laminar kinetic energy transport approach, and the machine learning approach is used to reformulate the source terms as functions of suitably defined non-dimensional ratios. Additionally, machine learning based explicit algebraic Reynolds stress models are used to improve wake mixing predictions, making use of a specifically and newly developed wake sensing function based strategy that allows an automated zonal application of the developed models. It is shown that both on-blade performance and wake mixing can be predicted accurately with data-driven transition and turbulence models that have benefited from CFD feedback in their development, ensuring that their mutual interactions are captured.
Heat Transfer Coefficient and Adiabatic Effectiveness on a Film-Cooled Pressure Side: Results and Assessment of the IR-Based Measurement Technique Reliability
Authors: Bacci T. , Picchi A. , Galeotti S. , Facchini B. , Cubeda S.
Published: October 2022

The precise knowledge of the external heat transfer coefficient and of the film cooling coverage characteristics is crucial to an efficient design of a turbine nozzle guide vane. From an experimental point of view, thermal methods allow to retrieve both the heat transfer coefficient and the adiabatic wall temperature, but their reliability is generally questionable, as they suffer from problems as thermal conduction. In the present work, a well-known literature nozzle guide vane (VKI LS89 profile) was provided with a simplified cooling system made by a single row of cylindrical holes on the pressure side. A transient thermal technique was employed to characterize both the adiabatic effectiveness and the heat transfer coefficient. The uncertainty and the reliability of thermal technique, which are generally a weak point, were evaluated. The former aspect was addressed by means of virtual experiments, considering both the effect of the measured temperature noise and of the inaccuracies introduced by the physical model adopted for the post-processing. For the latter aspect, adiabatic effectiveness findings were compared to the ones achieved on the same test article from Pressure Sensitive Paint measurements, which have a limited and known degree of uncertainty. The overall results showed that, once a proper approach is taken, the thermal technique is able to accurately retrieve reliable results with an acceptable resolution, even on a test case with dimensions close to real engines. Different fluid-dynamic conditions were investigated to assess the effect of blowing ratio and free-stream turbulence on film cooling performances. The results indicate that the introduction of film cooling on the vane surface significantly enhances the heat transfer coefficient with respect to the uncooled case. Net Heat Flux Reduction was also computed, showing that film effectiveness can not always compensate for the HTC augmentation, highlighting the necessity of properly considering the heat transfer coefficient enhancement.
Optimum Control Scheme for Deformable Blades Applied to Horizontal Wind Turbine
Authors: Jauregui-Correa Juan Carlos , Duran-Castillo Azael
Published: October 2022

Deformable blades are an option for load alleviation and power improvement for Horizontal Wind Turbines. The advantage of using a deformable blade is the load alleviation, the reduction of fatigue loads, and a small increment in power generation. The main drawback is the cost of the mechanical actuators and the need for special materials. Implementing shape morphing mechanisms requires new control schemes in the existing controllers. The proposed design is a cost-efficient and straightforward mechanism. These designs consist of a flexible glass fiber surface deformed with an elastic beam and a cam mechanism that modifies the aerodynamic profile. A single actuator moves a set of adjustable beams distributed along the blade. The operating conditions require the adjustment of two variables: the pitch angle and the modified profile. This paper presents an optimum scheme control that locates the best pitch angle and blade shape combination for incrementing the generated power and reducing the bending moment. The optimum control scheme results from the bending moment analysis and the estimation of the power coefficient for maximum power production. The mapping of these conditions was constructed using the Blade Element Momentum, and the results were verified with a Computational Fluid Dynamics analysis. The optimization process permits the definition of lookup tables that feed the control algorithm and set the controller’s parameters within the wind changes interval.
Low Reynolds Number Effects on the Endwall Flow Field in A High-Lift Turbine Passage
Authors: Donovan Molly H. , Rumpfkeil Markus P. , Marks Christopher R. , Robison Zachary , Gross Andreas
Published: October 2022

Understanding the endwall flow phenomena surrounding low-pressure turbine blades is key to improving performance, as these flow features contribute significantly to loss generation at low Reynolds number cruise. It is well documented that a horseshoe vortex system forms at the junction of the endwall and turbine blade. The vortices develop and gain significant strength in the passage and contribute to total pressure losses. During low Reynolds number conditions, the flow through a low-pressure turbine passage can be greatly impacted by a number of factors, including Reynolds number and incoming turbulence. The focus of this paper is on significant changes to the endwall flow field observed in experimental measurements and an accompanying implicit large-eddy simulation of the flow through a linear cascade of high-lift front loaded low-pressure turbine blades at low Reynolds number. Results show a significant effect on both the time-averaged endwall flow topology and the unsteady vortical flow characteristics when the Reynolds number based on inlet conditions was decreased to 30,000. Various techniques, such as spectral proper orthogonal decomposition, were used to analyze and compare both high-speed particle image velocimetry measurements and numerical results in order to extract the dominant structures and their unsteady behavior. The total pressure loss development through the passage was assessed in order to better understand how the observed changes in endwall flow structures contribute to the overall losses.
Numerical Modeling of Water Droplets in Compressible Two-Phase Flows Based on Eulerian-Eulerian Method
Authors: Furusawa Takashi , Sasao Yasuhiro , Takata Ryo , Miyazawa Hironori , Yamamoto Satoru
Published: October 2022

The slip velocity between water droplets and gas phase causes losses in steam turbines. The accurate prediction of the motion of coarse water droplets in wet-steam flows is crucial for the prediction of efficiency and erosion. In this study, the Eulerian-Eulerian method, which assumes water droplets as a continuous phase, was developed to simulate the motion of coarse water droplets in compressible two-phase flows. The conservation equations consisting of mass, momentum, energy, and number density for coarse water droplets, were coupled with compressible Navier-Stokes equations. Additionally, drag forces owing to the slip velocity between the water droplets and the gas phase were included in the model. Dry-air and moist-air flows through a subsonic turbine cascade were simulated. The inlet droplet sizes were set to 0.5, 5.0, and 10.0 μm in each computational case. Under dry conditions, the numerical results produced the increase in the loss in the wake region. Under wet condition, 0.5 μm droplets went through the cascade without colliding with the blade surface because of the high drag coefficient for fine droplets. 5.0 and 10.0 μm droplets partially collided with the blade surface owing to the slip velocity between the droplets and the gas phase. While the nondimensional losses in case of the 0.5 μm droplets were higher than experimental results at each pitch position, those of the 10.0 μm droplets had a maximum peak in the wake region. The present method enables to produced losses by the slip velocity in each droplet size. The nondimensional losses of the experiments were reproduced by considering the particle size distribution and volume rate of droplets.
LES Investigation of Low Rossby Number Buoyant Flow in Rotating Cavities
Authors: Sun Zixiang , Gao Feng , Chew John , Amirante Dario
Published: October 2022

Flow and heat transfer in axial compressor disc cavities involve strong interaction of axial throughflow at the disc bores with centrifugal buoyant flow in the cavities. This paper presents large eddy simulation (LES) of flow and heat transfer in rotating cavities with a heated shroud and a relatively weak axial cooling throughflow. The conditions considered for a single cavity configuration correspond to Rossby numbers Ro = 0.2 and 0.3, rotational Reynolds numbers ReΩ = 3.2 × 105 and 7.7 × 105, and buoyancy parameters βΔT = 0.24 and 0.26. Reasonable agreement of the results with shroud heat transfer measurements was confirmed for the Ro = 0.2 condition for which test data were available. A dual cavity configuration for Ro = 0.3 and ReΩ = 3.2 × 105 is also modelled.

The simulations show that, at low Ro conditions, flow reversals occur along the length of the bore flow path, upstream and downstream of the rotating cavities. With dual cavity this causes strong, unsteady interactions between the flows in the two cavities. These flow interactions result in less stable flow structures, higher air temperatures within the cavities and lower shroud and disc heat transfer compared to the single cavity case. FFT analysis reveals a complex phase-locking mechanism between flows in the two cavities.