bluuebunny/crossref_metadata_2025 huggingface dataset:
sCO2 Bottoming Cycle for Off-Shore Applications – An Optimization Study
Authors: Persico Giacomo , Sanchez David T. , Alfani Dario , Silva Paolo , Vijgen Rene , Ruggiero Marco , Glos Stefan , Le Pierres Renaud , Schmitz Ulrich , Rubycz Rasmus , Cagnac Albannie , Macadam Scott , Orhon Dominique H.
Published: September 2023

Closed Joule-Brayton thermodynamic cycles working with CO2 in supercritical conditions (sCO2) are presently receiving great attention, for their multiple attractive aspects: high energy conversion efficiency, compact size, flexibility of operation, integration with energy storage systems. These features make the sCO2 technology interesting for several energy and industrial sectors, including renewable sources and waste heat recovery.

A further promising area of application of sCO2 systems is bottoming gas turbines in combined cycles, replacing steam. The use of steam implies large-scale components and demands for large space availability for the plant installation. In some relevant applications, such as in off-shore platforms, the lack of space complicates the implementation of steam combined cycles, unless accepting a significant efficiency penalty, along with operation issues related to the necessary use of saltwater as cooling medium as well as the need of continuous supervision by dedicated personnel. In such a context, the combination of gas turbines with sCO2 cycles could open the way for developing new efficient, compact, and flexible combined cycles, potentially suitable for off-shore systems but also attractive for several other sectors which might take advantage from the footprint savings, the enhanced flexibility, and the fast dynamics of sCO2 systems.

In this work we investigate the thermodynamic potential of combining sCO2 cycles with an existing gas turbine for off-shore applications. In particular, we consider a mid-size (25 MW) gas turbine available on the market, and perform a series of thermodynamic optimizations of the sCO2 bottoming cycle in order to maximize the exploitation of the heat discharged by the gas turbine. Systematic optimization strategies are applied to the sCO2 cycle, considering four alternative configurations and including realistic technical constraints, evaluated by leveraging on the most recent technical outcomes from ongoing sCO2 research projects. A comparison is also proposed with a state-of-the-art steam Rankine cycle, in terms of system efficiency and footprint of the main components. The study clarifies the advantages and challenges of applying sCO2 in combination with gas turbines. The comparison with steam technology clearly indicates the relevance of sCO2 systems for off-shore applications and calls for further technical studies in the field.
Entropy Loss Breakdown Comparison for LES and RANS of a Transonic Compressor Stage Midspan Section
Authors: Borcherding Till , Bode Christoph , Rosenzweig Marco , Przytarski Pawel J. , Leggett John , Sandberg Richard D.
Published: September 2023

Further improvements in aero-engine efficiencies require accurate prediction of flow physics, such as shock-boundary layer interaction and incurred loss. The current best-practice of using (U)RANS for such predictions in design iterations can lead to inconsistent loss predictions. To assess where RANS-based approaches produce errors, in this paper we perform a detailed entropy loss breakdown of a modern transonic compressor stage under varying inflow conditions, using the high-fidelity flow field data of the midspan section presented at ASME Turbo Expo 2022 (GT2022-81673, GT2022-82474). From the datasets produced by highly resolved large-eddy simulations the results of this paper will show where loss is generated. Following the loss analysis approach introduced by Zhao and Sandberg (TURBO-20-1017), the entropy transport equation is used to decompose the entropy generation process into different physical mechanisms leading to entropy generation as a representation of loss generation. The introduction of inflow disturbances leads to an increase in stage loss by 23%, mainly caused by the shock and SBLI in the rotor domain. A comparison of LES results with URANS predictions shows that URANS adequately predicts the general flow behavior. However, significant deficits are identifiable in predicting the shock and boundary layer flow near the shock location on the rotor suction side.
Experimental Characterization of a Two Stage Brush Seals: Leakage and Torque Measurements
Authors: Jolly Pascal , Arghir Mihai , Bonneau Olivier , Coirier Rémi , Fiore Giuseppe
Published: September 2023

Two-stage brush seals were experimentally investigated in the present work. The test rig was originally developed to operate with pressurized hot water but was recently adapted also for pressurized air. The brush seals were designed to seal high pressure differences. The bristles are made of Haynes 25 and the rotor is coated with a layer of chromium carbide. Brush seals had identical back and front plates inner diameters, a small fence height and a bristle pack/rotor interference (negative clearance). They were tested for both water and air. The inlet mass flowrates were measured for centered operating conditions while the supply pressure was modified for constant discharge pressure. Water tests were performed for various rotation speeds. The resistive torque, the water temperatures and pressures along the housing were measured. Results are discussed in order to highlight the impact of rotor speed, supply pressure and wear on brush seals performance. In the second part of this work, the results obtained for air are compared to data from the literature, using the equivalent effective clearance. Then, another approach is used for estimating the leakage rate of brush seals by considering the brush as a porous medium. The identified values of the permeability in the Darcy law for air and water are very close. The calibration of the porous medium is then independent of the incompressible or compressible character of the fluid because the velocities through the bristle pack are very small. Moreover, the identified permeability is in agreement with theoretical values. Thus, an accurate estimation of the leakage flow rate of brush seals of similar design can be easily made.
Leveraging Additive Manufacturing to Fabricate High Temperature Alloys With Co-Designed Mechanical Properties and Environmental Resistance
Authors: Pillai Rishi , Ren Q. Q. , Su Yi-Feng , Kurfess Rebecca , Feldhausen Thomas , Nag Soumya
Published: September 2023

A paradigm shift in the traditional sequential design approaches is critically essential to create application-specific hierarchical and multifunctional materials with superior long-term performance for next-generation energy technologies involving extreme environments. In the current work, we aim to leverage the flexibility and geometric/compositional complexity offered by additive manufacturing to demonstrate this new approach by co-designing a compositionally graded Ni-based alloy for molten salts\sCO2 heat exchangers to enable mitigation of environmental degradation of surfaces exposed to molten halide salts, while simultaneously suppressing the consequent deterioration in mechanical stability. Thermokinetic modeling describing the underlying physics of thermally- and environmentally induced spatiotemporal compositional and microstructural evolution will be employed to predict the parameter space of material deposition processes and precisely identify the required composition gradient. Preliminary corrosion and mechanical testing of the dual material demonstrated the potential of the material to replace existing solid solution strengthened materials for this application.
Numerical and Experimental Investigation of Riblet-Coating Impact on Centrifugal Compressor Stage Performance
Authors: Jörg Sophia , Wirsum Manfred , García De Albéniz Mikel Lucas , Leitl Peter , Flanschger Andreas , Kowalik Yvonne , Jenny Philipp
Published: September 2023

Rising energy costs and increasing efforts to reduce greenhouse gas emissions strengthen the demand for highly efficient operation of centrifugal compressors. This applies both to new machines as well as to compressor units with long operation times. One possible measure to reduce drag in flow channels and thus increase compressor efficiency are microstructured riblet-surfaces. Riblets imitate the structure of shark skin and are streamwise aligned grooved surfaces which diminish the viscous drag in turbulent boundary layers.

This paper presents the results of a numerical and experimental investigation regarding the application of riblet structures in centrifugal compressor stages focusing on the aerodynamic performance. Steady-state computational fluid dynamics (CFD) calculations were used for the riblet design in dependence on the design operating conditions. Two different riblet sizes were identified for the application in diffuser and volute. The expected impact resulting from these riblet structures was calculated for compressor design and off-design operation.

Subsequently, the riblet structure was applied on the compressor volute by a dual-cure coating-system consisting of a clear coat, which combines UV-curable resins with aliphatic polyurethanes. To allow for a sufficient accessibility for the manual coating process, the volute was manufactured featuring a vertically split geometrical design.

A closed-loop centrifugal compressor test rig was utilized to investigate the stage performance characteristics at three different tip speed Mach numbers while accounting for tip speed Reynolds similarity. In the scale-model compressor stage, consisting of a shrouded impeller, vaned diffuser and a circular volute, static and total pressures as well as temperatures were measured to quantify the riblet impact. As a main result, the experimental data show an increase in polytropic efficiency of up to 0.5–1.4 %-points for selected operating points based on the riblet coating of the outlet volute. A drag reduction in the volute is indicated leading to lower total pressure losses.
Numerical and Experimental Approaches for Inertial Particle Separator Design
Authors: Saat Ahmet , Işık Halime Esra , Arslan Ahmet , Erdem Erinç , Kaptan Yalın
Published: September 2023

Gas turbine engines, especially turboshaft engines, can be exposed to the unfavourable environmental conditions including ingested sand, dust, rain and salt spray etc. that can cause significant deterioration in engine life and affect its performance. Engine Air Particle Separators (EAPS) fitted to intakes are used for protection of engine parts from the ingestion of foreign particles. Since integrated inertial particle separators (IPS), one of the EAPS’s, have more advantageous characteristics compared with other solutions they are widely preferred. The main aim of this article is to provide insight into the aerodynamic design and performance characteristics of the IPS system using both numerical and experimental approaches. Aerodynamic assessment and particle trajectories have been evaluated through two-way coupled CFD analysis. In addition, the effects of different design such as split area factor, ramp angle, and flow rate on IPS system performance have been investigated. Current study also includes experimental investigation of IPS system test facility based on a sectoral geometry with initial measurement results to validate numerical methodology. During the test campaign, detailed aerodynamic measurements have been conducted and global IPS separation efficiencies have been deduced with different sand types. Results have shown that a very good agreement is observed between the numerical approaches and the test results. Proposed methodology can be considered as an initial part of a well-rounded study to achieve robust IPS system design.
Fluid Dynamic Behaviour of Conventional and Pressure Relieving Brush Seals
Authors: Bowen Joshua P. , Bird Joshua J. , Cross Harry , Jenkins Matthew R. , Bowsher Aaron A. , Crudgington Peter F. , Sangan Carl M. , Scobie James A.
Published: September 2023

Brush seals consist of a static ring of densely packed, flexible, fine wire bristles that provide resistance to the flow. Pressure relieving brush seals can be employed to overcome issues such as hysteresis that affect seal durability by reducing friction between the bristle pack and back plate surface. The impact of such designs on the fluid dynamic behaviour of brush seals was studied following a concomitant methodology that exploited the benefits of both engine representative and large-scale testing facilities. Leakage data were fitted using a porous medium model found in the literature to quantify viscous and inertial resistance coefficients.

Shaft rotation was shown to cause a reduction in seal leakage and an increase in static pressure on the back plate surface. The pressure relieving back plates also resulted in increased static pressures at this location, causing a reduction in flow resistance that increased leakage through the porous bristle pack. Interrogation of the large-scale inter-bristle pressure field for the two back plate designs revealed the distributions of axial pressure diverged towards the rear of the bristle pack. The detail gathered using the large-scale study has been shown to be representative, hence the insight is generically applicable to brush seals.
Techno-Economic Performance of the Allam-Fetvedt Cycle With Oxygen Storage
Authors: Pryor Owen , Moore J. Jeffrey , Cormier Ian , Fetvedt Jeremy , Burlaka Maksym , Goldenberg Vlad
Published: September 2023

A model was developed to predict the operation and performance for liquid oxygen storage coupled with the Allam-Fetvedt Cycle (AFC), a direct-fired supercritical carbon dioxide cycle. The cycle uses liquid oxygen to time-shift the major parasitic of the cycle, the air separation unit (ASU), to minimize the economic costs of air separation. This paper presents significant improvements to the model and the techno-economic analysis in the forms of improvements to the assumptions, an exploration of different ASU architectures, potential improvements to the AFC for coupling with liquid oxygen and a sensitivity study on the impact of variables on performance. Several assumptions were updated or added to improve the accuracy of the system. These include adding utilities such as water requirements or fuel usage during ASU operation. In addition, an aerodynamic analysis on three different architectures for the main air compressor (MAC) were compared focusing on the performance at both full load and part load. It was determined that the best architecture for the MAC depended on the underlying economic market. An integrally-geared compressor performed the best in markets with high renewable penetration and frequent short-term cycling due to the improved part load performance. For markets with more seasonal trends, the more efficient axial-radial architectures performed better. In addition to improvements to the charge system, several different modifications were explored to improve the AFC. The first was to use the CO2 stream to vaporize the liquid oxygen, reducing the inlet temperature of the CO2 entering the compressor. Another was to pump the oxygen and CO2 separately to full pressure before mixing the oxidant streams. The potential technology improvements resulted in additional power output of the system that improved the net present value overall. All of the results were compared to each other in a sensitivity analysis that compared how 8 different parameters affected the results for different markets.
Advanced Turbine Efficiency Package (ATEP) Upgrade for The SGT5-4000F Service Fleet
Authors: Vogel Tobias , Kunte Robert , Tertilt Marc , Timmermann Julian , Mihalyovics Jan , Beiler Jan-Dirk
Published: September 2023

Affordability, reliability, and sustainability are the core properties for power generation towards a new energy system. Therefore, our Siemens Energy gas turbine technologies and our large operating service fleet are the backbone of our business. Siemens Energy, as Original Equipment Manufacturer (OEM), has developed the Advanced Turbine Efficiency Package (ATEP) to support the competitiveness of our SGT5-4000F gas turbines. The improvement of the combined cycle power output and efficiency helps to optimize fuel costs at constant power output to decarbonize existing assets and offers additional peak power in case of high electricity demand in fluctuating grids.

The ATEP turbine blades and vanes were developed based on a multi-point and multi-discipline optimization of the turbine section using the latest HL-class design tools and features from the Siemens Energy design chain. Since the ATEP upgrade is focusing on the existing fleet, the entire design process chain considered the constraints and limitations of the related SGT5-4000F customer assets. Thus, the ability to retrofit into service customer assets was ensured, while enabling remarkable performance benefits.

This paper describes the technical details of the ATEP upgrade, the underlying design approach, and summarizes the First Time Application (FTA) that was conducted in 2022 at the Enecogen 10 power plant in the Netherlands. Along with the related product verification and applied testing methods. In the results section, the testing results from the FTA are compared with the predicted Computational Fluid Dynamics (CFD) and Conjugated Heat Transfer (CHT) design values. Furthermore, the key performance parameters, power output and efficiency, are presented and classified via a comparison to appropriate baselines. Hereby, the ATEP upgrade’s capability for increasing gas turbine power output and efficiency was demonstrated within the FTA. Resulting in combined cycle application benefits of up to 40 MW additional power output and 1.5 %-pts efficiency increase. Through efficiency improvement ATEP upgrade is supporting asset decarbonization, while providing notable supplementary commercial benefits.
Axial Compressor Transonic Rotor Shock Interaction With Upstream Stator Row
Authors: Koyyalamudi V. V. N. K. Satish , Burberi Corrado , Lorusso Salvatore , Michelassi Vittorio , Scotti Del Greco Alberto
Published: September 2023

Modern high-performance multistage axial compressors are designed for high aerodynamic loading and efficiency, wide range and operate front stages with rotor inlet relative Mach number above one over a large portion of span. Understanding unsteady flow phenomena and rotor-stator interactions is paramount in the design of front stages. With increased aerodynamic loading, rotor shock waves may propagate upstream and interact with stator vanes. Such interaction may affect both performance and aeromechanics as shock propagation and reflection may destabilize boundary layers leading to higher aerodynamic losses and unsteady pressure pulsations. Unsteady numerical simulations prove to be necessary to predict and minimize the impact of rotor to upstream stator shock interactions. This paper discusses rotor-stator shock interactions using unsteady numerical simulations. The computations are performed on three stage designs, under the constraint of same capacity and total pressure ratio but differ in axial gap and load distribution in stator and rotor. Speedlines from steady and unsteady computations compare the different designs, and the detailed flow fields are analyzed at design and close to stall conditions. The analysis reveals the importance of relative orientation of shocks generated in the rotor row with the upstream stator camber line, while steady simulations predict a different stator-rotor loss split. This orientation affects the intensity of the shock boundary layer interactions and the shock reflections as well as compressor performance. The comparison of the designs suggests possible ways to mitigate the growth of shock-driven losses.
Influence of Casing Roughness on the Tip-Leakage Loss in a Linear Turbine Cascade
Authors: Huser Lukas , aus der Wiesche Stefan , Schatz Markus
Published: September 2023

The present experimental study was intended to investigate the impact of casing roughness on the tip leakage flow and the loss in a linear turbine cascade. Detailed flow measurements utilizing a five-hole probe, namely the so-called Oxford probe, and a miniaturized Pitot probe were made upstream and downstream of a row of steam turbine blades with variable tip gaps and different levels of casing roughness. It was found that casing roughness affects the position of the tip-leakage vortex in the linear cascade, but it does not reduce its loss contribution. An increase in the total loss was observed, which could be attributed to a rise in the secondary loss due to roughness. This result indicates that potential loss-reduction mechanism might be caused by the relative motion of the blade tip surface and the rough casing wall or by vortex interactions.
Preliminary Investigation of a Combined Heat and Power Reversible-Brayton System Integrated With a Renewable Power Source
Authors: Ancona Maria Alessandra , Bianchi Michele , Branchini Lisa , De Pascale Andrea , Melino Francesco , Ottaviano Saverio , Peretto Antonio , Poletto Chiara
Published: September 2023

Pumped Thermal Electricity Storage (PTES) technology is drawing increasing attention as a promising solution to limit the mismatch between the electric demand and the renewable production.

In this context, a preliminary model of a reversible Brayton PTES is developed on a commercial software to finalize a comprehensive performance investigation. In the proposed arrangement, the system allows to store the surplus of electric renewable production, by converting it into heat, through an inverse cycle, and then to convert it back into electric energy when needed, through a direct cycle. A systematic analysis comparing two configurations (base and recuperated) of the reversible Brayton system is carried out to assess the performance of the system.

Since thermal and electric energy flows are involved, PTES is particularly interesting when adopted to satisfy both thermal and electric demands, in a combined heat and power (CHP) system. To this aim, the system has been simulated when delivering both thermal and electric energy, in different partitioning. Results show that if 25 % of the stored heat is addressed to a thermal user the integrated system can be convenient in terms of saved primary energy, compared to conventional separate production. In case 70 % of the stored heat is delivered to a thermal user and 30 % reconverted into electricity, the maximum investment cost to have a return of the investment in 10 years is assessed to be between 2000 and 5000 €/kW, depending on the configuration.
A Novel Optimisation of a Transonic Centrifugal Impeller Based on 3D Inverse Design Approach
Authors: Wang Peng , Zhang Mingding , Zangeneh Mehrdad
Published: September 2023

A key step in optimising a centrifugal impeller is the parametrisation of the blade profile, which could easily call for many control parameters to define the profile with high-enough resolution and smoothness. As the number of parameters increases, the complexity of optimisation is amplified drastically, resulting in skyrocketing demand for computational resources and time. For the industry, rather than the design methods and guidelines, which are available in a number of good textbooks, it is the accurate yet fast and affordable optimisation for product development aiming to achieve multiple operating points that still remain an onerous task. In this paper, a novel design and optimisation strategy coupling the 3D inverse approach and DoE (design of experiment) study is developed, and it has been used for the redesign and optimisation of a well-known transonic centrifugal compressor. CFD analysis confirmed that the redesigned compressor wheel has increased the efficiency over the entire performance map significantly, and the detailed internal flow visualisation shows that the reduction of leaking loss is the main contributor to this improvement. The cost of CFD times is only within several days on a 32-core computer rather than weeks. The approach used in this work can be extended to different machine types.
A New RANS Based Reynolds Stress and Turbulent Heat Flux Treatment and Challenges in Predictions of Mixed Convection Type of Flows
Authors: Murat Oguzhan , Rosic Budimir
Published: September 2023

RANS based turbulence models are still gold standard in industry despite their limitations. Traditionally, the development of turbulence models for heat transfer problems is driven by applications with either natural or forced convection dominated flows. Surprisingly, far too little attention has been paid to mixed convection problems with various buoyancy domination in the literature despite its importance for variety of engineering problems. Mixed type of flows exhibit complex flow interactions between buoyancy induced flows and inertial forces. The commonly used linear eddy viscosity and diffusivity models fail to reconstruct the Reynolds stress and turbulent flux profiles, which are mainly responsible for inaccurate heat transfer predictions, and suffer from severe convergence difficulties. Turbine casing cavity flows during different shut-down regimes, which are characterised by a wide range of mixed convection flows, are used as a platform for the development of a novel physics-based universal model to be used within RANS concept for mixed type of flows, which is presented in this paper. The model incorporates and blends a constitutive relation for Reynolds stress and a new generalised gradient diffusion hypothesis for turbulent heat fluxes. The new model, New Nonlinear RANS (NNR), has been developed to overcome the convergence difficulties with conventional RANS and to improve heat transfer predictions without having to solve any additional transport equation.
Roughness Related to Cooling Performance of Channels Made Through Additive Manufacturing
Authors: Wildgoose Alexander J. , Thole Karen A. , Tuneskog Erika , Wang Lieke
Published: September 2023

The complex surface morphology and multiscale surface features inherent with additively manufactured (AM) components contributes to the overall flow characteristics and heat transfer of cooling passages. As the AM process and cooling data in literature continues to evolve, so does the need for more accurate heat transfer and pressure loss correlations for AM cooling schemes. This study improves the predictability of pressure loss and heat transfer for AM cooling passages by fabricating a range of coupons and investigating samples in literature. Twenty-seven test coupons were manufactured using direct metal laser sintering in an assortment of build directions and build locations that produced a variety of surface morphologies. Nondestructive evaluation, computed tomography scanning, was used to quantify the surface morphology as well as capture the as-built geometric dimensions of the cooling schemes. Friction factor and bulk Nusselt number of the coupons were measured using an experimental rig. Pressure loss and heat transfer correlations in literature were compared with the experimental results from the current coupons and datasets from literature. Arithmetic mean roughness correlations in literature struggled to predict the cooling performance of AM channels since the bulk roughness statistic did not capture the overall form of the surface morphology. A combination of root mean square roughness and skewness of the roughness was able to best predict pressure loss and heat transfer for the present samples and those in literature while being independent of build location, build direction, material, machine, and laser parameters. The maximum absolute error was 25% and average absolute error was 12% for the friction factor correlation. The maximum absolute error was 39% and average absolute error was 8% for the Nusselt Number correlation.
Measurement of Temperature and Load vs. Bearing Displacement in a Thrust Foil Bearing: Differences Between Light Load and High Load Operation
Authors: San Andrés Luis , Duran-Castillo Azael , de Santiago Oscar , Jauregui Juan , Lubell Daniel
Published: September 2023

This paper presents a revamped test rig for the evaluation of gas thrust foil bearings (GTFB) and details measurements of load capacity conducted with a commercial GTFB having inner and outer diameters equal to 35.6 mm and 71 mm, respectively. The test GTFB comprises a single 360°, 0.127 mm thick top foil divided into six continuous arc segments with a formed taper of 0.102 mm. The top foil rests on a stack of shims that contact on the outer ring, and position the top foil above the underspring an optimized amount. Six anvils in one of the shims engage the top foil axially. Underneath the shims there are six underspring structures, each comprising three strips of bump foils. The number of bumps differs along the radial direction. Made of an application-appropriate stainless steel, the spring is 0.102 mm thick. All the foil components making the GTFB have a combined thickness of 0.737 mm. The top foil is coated with a Teflon® layer. Measurements include the applied static load and ensuing break-away torque, rotor speed, GTFB axial displacements at three locations 120° apart, the flow of a cooling stream of supplied air, and bearing temperatures in and out of the bearing. Static load tests produce the underspring structure deformation and a dry-sliding friction coefficient f∼0.12. The underspring is rather flexible though quickly hardening for specific load (P*) > 25 kN/m2 to reach an ultimate structure deformation of ∼ 0.320 mm. Measurements at 30 krpm (OD surface speed = 111 m/s) obtained for increasing static loads produce GTFB displacements that parallel the displacements recorded without shaft rotation. Most importantly, the difference between displacements approaches ∼0.060 mm for P* > 45 kN/m2. The test GTFB operated safely to a unit load (P*) = 90 kN/m2 and failed at P* = 120 kN/m2. When heavily loaded, the GTFB is significantly stiffer than when lightly loaded. Designed for easiness of installation and operation, the test GTFB demonstrated a stable and repeatable performance with likely a uniform gap or film thickness even for the largest loads applied.
Development of Multiphase Computational Fluid Dynamics Simulation for Predicting Last Stage Low Pressure Steam Turbine Blade Water Droplet Erosion
Authors: Landrum Evan , Wu Zhilei , Kulkarni Anand , Musch Christian
Published: September 2023

Water droplet erosion has emerged as a reliability concern in steam turbines, resulting from exhaust flow recirculation in combination with the presence of down-stream moisture. Last-stage blades in Low-Pressure (LP) steam turbines interact with water spray systems in the condenser housing, which leads to blade trailing edge erosion. Such erosion can result in unplanned service outages, costly repairs or even blade liberation. It is for this reason that a computational fluid dynamics (CFD) model was developed to predict water droplet erosion for the last stage low pressure turbine blade in certain axial flow turbine configurations. In this study, Lagrangian multiphase physics were employed in a control volume representing an LP turbine configuration with an axial exhaust diffuser and short-coupled water-cooled condensers. Four critical, part load operating points were investigated which enable the conditions required for turbine water droplet erosion including active water spray systems and diffuser recirculation. First, a gaseous steam flow field is established, and then discrete particles representing water droplets are injected into the continuum. Particles are tracked as they redistribute throughout the domain, collide and breakup with boundary walls. An erosion wear model was implemented on blade surfaces of interest which included the influences of wall material, impact speed and incidence angle.

Blade surface erosion rate distribution and surface integrated erosion rates were calculated for each case. Qualitative comparisons have been made between blade impact erosion observed in the field and CFD simulations. Mitigation solutions to reduce blade erosion were also studied for relative change.
Performance Improvement of Savonius-Type Hydrokinetic Turbine With Bucket Airfoil Profile
Authors: Osama Shehab , Emam Mohamed , Ookawara Shinichi , Ahmed Mahmoud
Published: September 2023

A new design to enhance the output power of a Savonius hydrokinetic turbine by using buckets with airfoil profile instead of a conventional semi-circular design is developed. Effects of different camber angles of buckets’ airfoil at 105°, 120°, 130°, and 140° are investigated and compared with the conventional profile. In addition, the influence of varying the buckets’ camber position of the airfoil is considered to determine the camber angle at the maximum output power. Accordingly, a two-dimensional, unsteady incompressible turbulent flow model is developed and numerically simulated. The predicted results from the simulations are validated using available measurements. Results show that a significant enhancement of maximum output power is obtained using the airfoil profile at all studied camber angles compared to the traditional Savonius turbine with a semicircular profile. Furthermore, using a camber angle of 140° attains the highest output power compared to other designs. At a water current speed of 0.4 m/s, and the overlap ratio of 0.15, the maximum power coefficient is 0.193. However, for the conventional design with a semi-circular profile, the maximum attainable power coefficient is 0.1 at the same operating conditions. The current findings provide an alternate direction in utilizing Savonius turbines with bucket airfoil profiles.
Ultra High Efficient Power Generation With SOFC-Gas Turbine Systems: Different Options for 80%+ Efficiency Power Cycles
Authors: Alpegiani Francesco , Zelaschi Andrea , Cammarata Alberto , Chiesa Paolo , Campanari Stefano , Martelli Emanuele
Published: September 2023

This work aims to design and simulate an ultra-high-efficient triple combined cycle for large-scale power generation, integrating an intermediate temperature Solid Oxide Fuel Cell (SOFC) with a gas turbine and a bottoming steam cycle. The power plant implements a large cathodic recirculation to preheat the air flow, while the inlet anodic stream is preheated by using steam produced in the heat recovery steam generator and anodic recirculation. System simulations are performed by using GS, a software developed and validated by Politecnico di Milano. State-of-the-art parameters are used for the SOFC, the H-class gas turbine and the steam cycle. Moreover, in order to identify the operating conditions that maximize the efficiency, a sensitivity analysis is performed on the compression ratio, the secondary fuel mass flow rate, the single-pass utilization factor and the cell voltage. The results show that the triple combined cycle may achieve an outstanding net electric efficiency of 84.4% (LHV basis). The sensitivity analysis indicates that adding secondary fuel to a supplementary burner ahead the gas turbine tends to decrease the system efficiency, while also adopting relatively low SOFC voltages (0.775V) or single-pass utilization factors (70%) it is possible to maintain the efficiency above 80%.
Modeling Flame Transfer Functions of an Industrial Premixed Burner
Authors: John Tony , Magina Nicholas , Han Fei , Kaufmann Jan , Vogel Manuel , Sattelmayer Thomas
Published: September 2023

This paper presents an analysis of the unsteady heat release rate response of industrially relevant axisymmetric premixed flames to harmonic velocity perturbations. The heat release rate response, quantified using the Flame Transfer Function (FTF) definition, is measured from an acoustically forced swirl burner under perfectly premixed conditions. To understand the features of the measured FTF, a physics based analytical model is developed in this study. To describe the heat release rate dynamics, a model for the flame spatiotemporal response is derived in the linear limit using the G-equation formulation. Inputs to the flame response model are selected to be consistent with values observed in the corresponding industrial burner, based on experimental and numerical studies. The relative contributions of acoustic and convecting vortical disturbances on specific features of the FTF are explored in this study. The results highlight the importance of capturing the appropriate disturbance velocity field as an input to the flame response model for accurate FTF predictions.
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

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

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

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

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

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.