bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Numerical Simulation of Transitional and Turbulent Flows Over Multi-Scale Surface Roughness - Part I: Methodology and Challenges
Authors: Nardini Massimiliano , Kozul Melissa , Jelly Tomas O. , Sandberg Richard D. 
Published: September 2023

Abstract
High-fidelity simulation of transitional and turbulent flows over multi-scale surface roughness presents several challenges. For instance, the complex and irregular geometrical nature of surface roughness makes it impractical to employ conforming structured grids, commonly adopted in large-scale numerical simulations due to their high computational efficiency. One possible solution to overcome this problem is offered by immersed boundary methods, which allow wall boundary conditions to be enforced on grids that do not conform to the geometry of the solid boundary. To this end, a three-dimensional, second-order accurate Boundary Data Immersion Method (BDIM) is adopted. A novel mapping algorithm that can be applied to general three-dimensional surfaces is presented, together with a newly developed data-capturing methodology to extract and analyze on-surface flow quantities of interest. A rigorous procedure to compute gradient quantities such as the wall shear stress and the heat flux on complex non-conforming geometries is also introduced. The new framework is validated by performing a Direct Numerical Simulation (DNS) of fully-developed turbulent channel flow over sinusoidal egg-carton roughness in a minimal-span domain. For this canonical case, the averaged stream-wise velocity profiles are compared against results from the literature obtained with a body-fitted grid. General guidelines on the BDIM resolution requirements for multi-scale roughness simulation are given. Momentum and energy balance methods are used to validate the calculation of the overall skin friction and heat transfer at the wall. The BDIM is then employed to investigate the effect of irregular homogeneous surface roughness on the performance of an LS89 high-pressure turbine blade at engine-relevant conditions using DNS. This is the first application of the BDIM to realize multi-scale roughness for transitional flow in transonic conditions in the context of high-pressure turbines. The methodology adopted to generate the desired roughness distribution and to apply it to the reference blade geometry is introduced. The results are compared to the case of an equivalent smooth blade.
Comparison of Hydrogen and Ammonia Co-Firing With Natural Gas Using a Practical Gas Turbine Combustor (501F) Under Atmospheric Conditions: Changes in Metal Temperature, Pattern Factor, and NOx Emission
Authors: Park Seik , Shin Jugon , Park Jungkeuk , Lee Sanghyup , Choi Nakjeong 
Published: September 2023

Abstract
The world is undergoing energy transformation in various If global carbon neutrality is to be achieved by 2050, energy generation must improve. Here, we explore whether hydrogen and ammonia co-firing with natural gas (NG) in an industrial gas turbine improved the environmental performance of existing combined cycle power plants. Combustion tests were performed at atmospheric pressure under various conditions to define the safe operating range of a combustion test rig equipped with a real-world gas turbine combustor (501F).
The combustion characteristics were evaluated under co-firing with hydrogen at 15–30% by volume, and NG, from partial to full load conditions based on heat rate. As the co-firing hydrogen ratio increased, the metal temperature of a specific part of the combustor liner (the basket) tended to rise. The NOx emissions remained at about 20 ppm from partial to full load. Still, the NO2/NOx ratio was higher under partial load than full load due to NO oxidation by HO2 radicals at the low-temperature flame region at part load. This ratio also increased as the proportion of hydrogen rose, which was attributable to the higher HC radicals produced by adding H2 fuel.
Experiments with ammonia were conducted only during partial loading. Unlike hydrogen, the flame position (reaction zone) in the combustor moved slightly downstream, given the low reactivity of ammonia. In terms of emissions, if even a tiny amount (5% vol) of ammonia was supplied, the NOx emission level exceeded 600 ppm because of fuel NOx. The Thermal NOx Mechanism, which analyzes the generation of trace amounts of NOx in the flame field, which was applied during hydrogen co-firing, is unsuitable for ammonia fuels. Therefore, we tried to quantitatively analyze the effect of fuel-borne nitrogen according to the increase in the co-firing ammonia ratio. Based on this, a nitrogen oxide reduction strategy was proposed when the ammonia was applied in an actual gas turbine.
Due to additional fuel reactivity, the pattern factors associated with the lives of high-temperature parts (turbine blades and vanes) slightly changed. Hydrogen, which is highly reactive, reduced the flame and formed local hot spots, while ammonia showed the opposite tendency with a low heat release rate. Thus, we explored parameters that limited operation. This represents the first step toward creating guidelines for safe operation when various carbon-free fuels are used under multiple loading conditions.
Comprehensive Simulation of Moisture Loss in LP Steam Turbine Based on 3D Unsteady Eulerian-Lagrangian Solver
Authors: Sasao Yasuhiro , Kudo Takeshi , Segawa Kiyoshi , Tabata Soichiro , Senoo Shigeki , Takata Ryo 
Published: September 2023

Abstract
Moisture loss that occurs inside a steam turbine is the sum of complex multi-physics phenomena such as the thermodynamic behavior of steam accompanying a phase change, the exchange of momentum between two phases of gas and liquid, and the mechanical transfer of liquid. In this study, on the basis of the output characteristics predictions of the 0.33 scaled model turbine with the inlet stagnation temperature as a variable by the three-dimensional unsteady Eulerian-Lagrangian solver, the quantitative understanding of moisture loss and the mechanism of its occurrence are comprehensively discussed. Our numerical method makes it possible to grasp the spatial distribution of condensation loss, supercooling loss, acceleration loss, capturing loss, pumping loss and breaking loss, and the predicted turbine output characteristics were in good agreement with the measured results. In the small scaled turbine, the expansion rate is higher, and the supercooling temperature is higher than in a real turbine. For this reason, the supercooling loss was the most dominant factor in moisture loss. In addition, the spatial distribution of momentum exchange between the two phases of gas and liquid that causes acceleration loss and the dynamic behavior of coarse water droplets and water films are discussed.
Part-Load Behavior and Start Up Procedure of a Reverse Rankine High Temperature Heat Pump With Water As its Working Medium
Authors: Kriese Maximilian , Klöppel Steffen , Setzepfand Nico , Schaffrath Robert , Nicke Eberhard 
Published: September 2023

Abstract
In recent years, the issue of sustainability, especially in terms of resource utilization, has become increasingly prominent. In contrast, even today a large part of the process heat required in industry is obtained by burning fossil fuels. In order to meet this demand sustainably, the development of high-temperature heat pumps has steadily increased in recent years. Nowadays, heat pump systems are mostly commercially available up to a temperature level of 90 °C. Even taking into account the few demonstration pilot plants up to temperature levels of 160 °C, there is a certain gap up to 200°C which would by needed for a variety of industrial applications. To overcome this gap and their experimental evidence the DLR has designed the pilot plant ZiRa. In this paper, the construction of the plant and the steady state simulation results are presented. Based on the reversed Rankine cycle the pilot plant is able to lift the temperature from 120 °C at source to 200 °C at the sink with a COP of 3.4. This is achieved by a three-stage compression. The compressors are described by their respective performance maps, which are used to investigate the operating range of the plant by varying the source temperature between 100 °C and 130 °C. In addition, the performance of the system was investigated in relation to the compressor part-load range. It has been shown that even with small changes in the respective compressor speed, the performance varies in terms of discharge pressure and sink temperature. Finally, the start-up procedure of the pilot plant is described.
Redesign of Gas Turbine Nozzles for Introduction of Additive Manufacturing Technology for Services Market
Authors: Soman Abhimanyu , Ragni Giacomo , Del Turco Paolo , Colantoni Simone , Ceccanti Filippo , Kemble Simon , Delfino Matteo 
Published: September 2023

Abstract
Baker Hughes is providing gas turbine solutions and services across the world since 1950s. There are many legacy engines still working at customer sites requiring services every year. The different models/upgrades of Frame 3 and Frame 5 introduced to the market from 1950’s to 1990’s led to the existence of many parts resulting in complex supply chain management to maintain an active and high-quality production. This is true especially for the components which require an investment casting process, such as nozzle and blades. The investment casting tooling requires a minimum number of produced sets per year to ensure a high-quality production and so it needs to be re-qualified in case of low production. On the other side increasing the volume more than the requirements may lead to higher inventory management. In addition, conventional manufacturing processes need higher lead time to deliver the spare parts, that may cause the risk to not fulfill the customer expectations/needs. To avoid such challenges, additive manufacturing is introduced to move the manufacturing of service parts from external suppliers to inhouse, developing a full internal vertical capability through printing, post-processing, and final machining operations. This helps in improving the lead time as well as the part management and allowing the internal Product Leadership office to develop and speed-up the internal strategy for service parts. This paper explains the design considerations made during the introduction of additive manufacturing technology to produce nozzle spare parts for Frame 3 and Frame 5 machines. Material is selected for the printing, in such a way that the material property derived from a printed specimen is aligned or better than the material property of the original part. The design of the nozzles has been improved with changes at life critical locations, injecting the latest design technologies developed for new products inside the old nozzle layout and boundaries, taking advantage of huge fleet experience acquired in these years. The mechanical robustness of the innovative design has been verified according to the current analytical internal process and it has been proven through a field validation being several nozzles sets installed, operated, and inspected in Service fleet.
Adaptation of VKI’s Isentropic Compression Tube Facility for High-Speed Low-Pressure Turbines Testing
Authors: Torre Antonino Federico Maria , Merli Filippo , Da Valle Lorenzo , Patinios Marios , Lavagnoli Sergio , Pintat Ludovic 
Published: September 2023

Abstract
This paper presents the commissioning of a newly designed High-Speed Low-Pressure Turbine (LPT) stage, operating at transonic exit Mach numbers and low Reynolds numbers, typical of modern geared turbofan (GTF) applications. The work falls within the scope of the Clean Sky 2 project SPLEEN (Secondary and Leakage Flow Effects in High-speed Low-pressure Turbines), which consists of an extensive experimental characterization of LPTs for GTFs. Geometries and measurements will constitute a valuable open-access database for the validation of simulation methods and data analysis tools.
At first, the characteristics of the research turbine are illustrated. The LPT stage is designed with an equal number of stationary vanes and shrouded rotor blades. The upstream and downstream hub cavities are purged and feature engine-realistic rim seals. The nominal operating condition of the stage is reported, along with a set of off-design conditions, obtained by varying rotor speed and purge mass flows.
The second part of the paper describes the substantial revamping of the CT3 large-scale compression tube at Von Karman Institute for Fluid Dynamics, traditionally employed for high-pressure turbine testing, now adapted to host a high-speed LPT stage.
The third section is an overview of the time-averaged and fast-response instrumentation. The test article is heavily instrumented, to maximize the amount of acquired data, while minimizing the number of blow-down tests. The dataset for each operating conditions includes aerothermal measurements in the annulus flow, in the hub cavities and in the shroud labyrinth seal. In addition, in this section is presented the design of an in-house traversing system for continuous probe traversing during the test.
Finally, the outcome of the commissioning phase is discussed, with particular emphasis on the operating conditions stability, as well as on the inlet and cavity injection uniformity. The commissioning of a traversing system for continuous probe traversing during the short-duration test is also discussed.
Research on Robustness Analysis and Evaluation Method of Inter-Shaft Bearing-Rear Journal of Low Press Turbine System
Authors: Liu Fangming , Hong Jie , Ma Yanhong , Chen Xueqi 
Published: September 2023

Abstract
The bearing outer ring with a flange is often used in advanced aero-engines, for the purpose of reducing weight of the engine and improve impact resistance. Cons and pros, in the working process, the rotor is subjected to complex loads such as centrifugal forces, periodic impact excitation and lateral inertia forces caused by overload on rotor. When the bearing is operating under heavy loads, a relatively large deflection occurs in the outer ring, causing deformation incoordination between the outer ring and rear journal. As a result, damage accumulation and structural failure such as wear, sliding and fatigue may occur on the contact interface.
This survey gives an insight to the deformation distribution and other contact characteristics of the interfaces in the Inter-shaft bearing outer ring — the low pressure turbine rotor system (ISBLPT) in detail, in order that stable contact in the connection structure is ensured with a reasonable structural design scheme. For typical ISBLPT, a dynamic model considering the interfacial contact characteristics of flange bolt was promoted. Then, based on possible failure modes, a contact damage assessment method and structural system robustness evaluation method is proposed.
The results show that different loads in inter-shaft bearing-rear journal system will lead to different damage failure modes, leading to uncertain damage failure modes in engine operation. And the change of interface contact characteristics will also have a significant impact on the stiffness characteristic.
Numerical Investigation of Flashing Flow in a Convergent-Divergent Nozzle
Authors: Kumar Amit , Tammone Carlotta , Haglind Fredrik 
Published: September 2023

Abstract
In order to reduce CO2 emissions, it is important to utilize renewable energy sources to their fullest. The output of renewable energy sources fluctuates which can be addressed through reliable storage. Liquid air energy storage can be used as an alternative energy storage method. Replacing the Joule-Thompson valve in the liquefaction process with a turbo-expander can increase the round-trip efficiency of the liquid air energy storage system. When the expansion occurs in two-phase conditions, the flow undergoes a flashing expansion with simultaneous acceleration and nucleation of vapor. To perform an efficient design of the turbo-expander, it is imperative to understand the flashing phenomenon and to model it accurately. The main objective of this paper is to identify the correct modeling approach available in commercial computational fluid dynamics software to predict the flashing phenomenon of water. Super Moby Dick and Abuaf nozzles were investigated using 2D Reynolds-averaged Navier-Stokes equations coupled with a two-phase mixture model. The Zwart-Gerber-Belamri model, Schnerr and Sauer model, and Lee model were used to model the interphase mass transfer. The results of the numerical simulations were compared with experimental data in order to evaluate which approach is the most suitable to model the flashing phenomenon. The results indicate that all models are strongly sensitive to the values of the model constants, as they govern both the onset of vapor nucleation and the vaporization rate. Therefore, in order to accurately predict the flashing phenomenon, a tuning of these parameters is needed. Overall, the error in the pressure profile increases as the inlet temperature increases, due to an increasing influence of non-equilibrium effects. Despite the fact that flashing and cavitation appear to have similar macroscopical characteristics, their underlying phase-change mechanisms are different. Additionally, owing to the absence of a wall nucleation model, it is not possible to accurately capture localized flow phenomena.
Design and Analysis of a Low Inlet Temperature Turbine Using a Supersonic Rotor
Authors: Martínez-Alvarado Luis Enrique 
Published: September 2023

Abstract
In this paper the study of an axial turbine with a supersonic rotor has been performed for a full stage turbine. The state-of-the art supersonic stages include supersonic stators that create shock waves that enter the rotor stage disturbing the flow. The current study proposes a semi-shockless approach which consists of using a supersonic rotor (altogether with a subsonic stator) and force the generation of the shockwave outside of the rotor passage. A method to design supersonic rotors is presented by using blade deflection angle and Mach number profiles along the blade length. Several 2D simulations using the SU2 solver were performed to evaluate the transition behavior at supersonic flow with different outlet pressures. The proposed rotor geometry allows to control by design the position and intensity of the generated shockwave. Thus, it was chosen to position the shock wave at the end of the rotor blade and to minimize its intensity. As an additional feature, the stator blades were replaced by a volute in order to reduce the quantity of components used in a full stage turbine for turbine designs having a volute just before the stator. A full stage 3D CFD analysis was performed using Ansys CFX solver. This approach has helped for the design of supersonic turbine stages with lower shock wave interactions between components.
Numerical Investigations of Reactive Reversible Blade Turbine for Slow Moving Currents
Authors: Patil Abhay , Nielson Jordan , Allison Tim , Cummings Scot 
Published: September 2023

Abstract
A reactive Reversible Blade Turbine (RRBT) is a drag-type hydrokinetic turbine consisting of movable blades designed to pivot around their axes to reduce drag and optimize the power coefficient. RRBT allows for reverse rotation of the opposing blades, with reduced drag during the rotation of the turbine. The blade “reverse slices” through the water to a neutral position and then rests against a stop which causes the turbine to rotate with reduced opposing drag on the opposite side of the turbine shaft. While the construction is simple, there is obscurity surrounding the quantitative gain in performance due to the proposed modification. The current study focuses on the development of a numerical model to quantify RRBT performance gain due to the reactive blade operation. The numerical model employs a sliding mesh model to simulate the single-blade motion in loaded positions to quantify the flow physics and performance estimation. The preliminary outcomes reveal power coefficient values comparable to the existing state of the art, however, peaking at a much lower tip speed ratio. The power coefficient (Cp) estimation of 0.219 using CFD agrees well with the test prediction of 0.2 at 0.32 Tip Speed Ratio. The study concludes with the evaluation and discussion of the performance gain using two different stop locations, and steady-state analysis to provide initial estimation of blade relative motion in reactive modes.
Simulating Part-Span Snubber in Low Pressure Steam Turbine Rotor With Simplified Methods for Aerodynamic and Aeromechanical Assessment
Authors: Mariotti Filippo , Lilli Leonardo , Pinelli Lorenzo , Arcangeli Lorenzo , Maceli Nicola , Brazzini Filippo , Marconcini Michele , Arnone Andrea 
Published: September 2023

Abstract
The present paper aims at investigating the impact of part-span snubber applied on a last rotating blade of an industrial low pressure steam turbine. The large increase in steam specific volume during the expansion forces low pressure turbine designers to develop high aspect ratio blades for the last stage. Considering also the relatively low thickness of the airfoil required to keep a high efficiency, the rotor becomes prone to aerome-chanical instabilities. Therefore, the design process must search for a tradeoff between aerodynamical and mechanical requirements that are usually conflicting. Part-span snubbers can be employed to grant additional mechanical stability to the blade thus avoiding the onset of vibrations which could lead to high cycle fatigue blade failure. In this work, a part-span snubber was introduced in the numerical model of an industrial rotor to assess its impact on the aerodynamic performance. The impact on the flow solution and on the computational cost was evaluated by using two different simplified approaches: firstly, the presence of the damping wire was introduced by means of a body forces model without any change in the aerodynamic geometry (that is blade without snubber). Then, the airfoil shape was modified to include the connections between the blade and the damping wire without a physical description of the damping wire itself which was once again modelled by the body forces. The CFD simulations were performed on hexaedrical structured grids, and a sensitivity with respect to the grid clustering near the damper devices was carried out to select a suitable tradeoff between computational cost and discretization accuracy. The aerodynamic analyses were performed with RANS computations and the flow distortions induced by the snubber are described in detail. In addition, uncoupled time domain flutter simulations were also performed to test the capability of the mesh deformation strategy to deal with snubber elements ensuring a smooth grid deformation without any cell interlacing. The simplified body forces model showed a good balance between results accuracy and computational cost, while the more complex model turned out to be more time consuming because of both the higher grid density required to correctly capture all the geometrical features of the connections, and for the higher efforts in generating a good quality mesh.