bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation of Gas Turbine Axial Diffuser Performance: Part I — Parametric Analysis of Influential Variables
Authors: Brown Kenneth , Guillot Stephen , Ng Wing , Iksang Lee , Dongil Kim , Hong Giwon
Published: January 2021

An experimental investigation of the effect of inlet flow conditions and improved geometries on the performance of modern axial exhaust diffusers of gas turbines has been completed. As the first of a two-part series, this article concentrates on characterizing diffuser sensitivity to parametric variations in internal geometry and inlet flow conditions. Full-factorial experiments were carried out on five parameters including the inlet Mach distribution, shape of the support struts, shape of the oil-drain strut, diffuser hade angle, and the hubcap configuration. To enable an efficient sweep of the design space, experiments were performed in this initial study at a down-scaled turbine exit Reynolds number (ReH roughly 3% of the value for an H-class diffuser) and at a full-scale turbine exit Mach number. The study was accomplished in a continuous, cold-flow wind tunnel circuit, and tailored distributions of Mach number, swirl velocity, and radial velocity derived from on-design conditions of an industry diffuser were generated. Measurements included 5-hole probe traverses at planes of interest. Diffuser performance was most sensitive to the inlet Mach distribution with losses of 0.081 points of pressure recovery due to a nonuniform Mach distribution with higher velocity near the hub versus a uniform one. Detailed comparisons of axial flow variation for a top-performing configuration versus related configurations shed physical insight regarding the evolution of kinetic energy distortion into viscous loss in the wake, as well as highlight the benefit of uniform inlet profiles in practice despite the lower theoretical recovery of such cases. The results presented here isolate the inlet flow distribution as a parameter of high interest for further study which is carried out for both on- and off-design conditions in the companion article [1].
Application of Model Based Systems Engineering for the Conceptual Design of a Hybrid-Electric ATR 42-500: From System Architecting to System Simulation
Authors: Cappuzzo Federico , Broca Olivier , Vouros Stavros , Roumeliotis Ioannis , Scullion Calum
Published: January 2021

The progress in aerospace technology over the recent years led to the development of more sophisticated and integrated systems. To cope with this complexity, the aerospace industry is seeing a progressive trend towards adopting Model-Based Systems Engineering (MBSE) in various stages of the product development cycle. The ability to capture emerging behavior, mitigation of risk and improved communication among different stakeholders are some key benefits that MBSE provides over traditional methods for complex systems and processes. This paper attempts to bridge the gap between system architecting and system simulation activities by proposing a methodology to facilitate seamless flow of information between the two development aspects. This methodology was applied to the development of a parallel hybrid-electric version of the ATR 42–500. The use case was designed for a regional mission of 400 nautical miles with the ability to meet regulation requirement of carrying enough reserves for landing at an alternate airport. An integrated systems model, consisting of gas turbine engine, electric powertrain, and flight dynamics, was developed with Simcenter Amesim to analyze the dynamics performance of the aircraft throughout the whole mission. The key metrics evaluated were fuel consumption, take-off weight and the Energy Specific Air Range (ESAR) of the aircraft. As environmental regulations are becoming more stringent, pollutant and noise emissions were considered in the study. The most promising hybrid configurations are recognized, the potential benefits are quantified highlighting the strong potential of System Architecting and System Simulation to provide valuable insights early in the development cycle, reducing the time and cost of product development.
Pulsed Impingement Turbine Cooling and its Effect on the Efficiency of Gas Turbines With Pressure Gain Combustion
Authors: Neumann Nicolai , Peitsch Dieter , Berthold Arne , Haucke Frank , Stathopoulos Panagiotis
Published: January 2021

Performance improvements of conventional gas turbines are becoming increasingly difficult and costly to achieve. Pressure Gain Combustion (PGC) has emerged as a promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine cycle. Previous cycle analyses considering turbine cooling methods have shown that the application of pressure gain combustion may require more turbine cooling air. This has a direct impact on the cycle efficiency and reduces the possible efficiency gain that can potentially be harvested from the new combustion technology. Novel cooling techniques could unlock an existing potential for a further increase in efficiency. Such a novel turbine cooling approach is the application of pulsed impingement jets inside the turbine blades.

In the first part of this paper, results of pulsed impingement cooling experiments on a curved plate are presented. The potential of this novel cooling approach to increase the convective heat transfer in the inner side of turbine blades is quantified. The second part of this paper presents a gas turbine cycle analysis where the improved cooling approach is incorporated in the cooling air calculation. The effect of pulsed impingement cooling on the overall cycle efficiency is shown for both Joule and PGC cycles. In contrast to the authors’ anticipation, the results suggest that for relevant thermodynamic cycles pulsed impingement cooling increases the thermal efficiency of Joule cycles more significantly than it does in the case of PGC cycles. Thermal efficiency improvements of 1.0 p.p. for pure convective cooling and 0.5 p.p. for combined convective and film with TBC are observed for Joule cycles. But just up to 0.5 p.p. for pure convective cooling and 0.3 p.p. for combined convective and film cooling with TBC are recorded for PGC cycles.
Integration of Computational Fluid-Particle Dynamics Techniques for the Instantaneous Estimation of Particle Erosion Damage on Axial Fan Blade Sections
Authors: Castorrini Alessio , Venturini Paolo , Corsini Alessandro
Published: January 2021

In the last decade, the authors focused their research in the development and implementation of accurate numerical tools and methods able to predict the erosion and deposit on turbomachinery blades operating with particle-laden flows. These models and methods give complete three-dimensional description of the phenomenon, but their application is limited to a single working condition of the blade. The present paper covers the first step in the definition of a general methodology to extend the applicability of these tools to a full range of the machines operating conditions. The method aims to obtain an instantaneous prediction of the expected damage pattern for a blade section, given its local working condition in terms of relative fluid-particle flow. The final result is based on a precomputed database associated to the blade section, where the single element is obtained by computing the erosion damage using the aforementioned numerical tools.

This paper will show the methodology to obtain the database associated to the midspan section of an induced draft fan subjected to erosion due to coal ash particle. The final database is then used to predict the damage state of the section associated to a given point in the characteristic curve of the fan.
Analysis of Time-Wise Compressor Fouling Phenomenon on a Multistage Test Compressor: Performance Losses and Particle Adhesion
Authors: Vulpio Alessandro , Suman Alessio , Casari Nicola , Pinelli Michele , Kurz Rainer , Brun Klaus
Published: January 2021

The analysis of the performance losses of a multistage compressor concerning the air contaminant is not widespread in literature and, the mutual interactions of particle materials, air humidity, and compressor load are not well studied. The airborne micrometric particles that enter the compressor can deposit on the internal surfaces, causing the loss of performance of the machine.

In this paper, several experimental tests have been carried out on a multistage compressor unit. A detailed analysis has been carried out considering soil and soot ingestion, as well as the air relative humidity (ranging from 50 %RH to 80 %RH) and compressor rotating velocity. Several combinations of particle diameter, material, and operating conditions have been considered. The amount of contaminant at the compressor outlet has been measured and the capture efficiency of the whole machine has been determined. Over the exposure time, the capture efficiency ranges from 0.2 to 0.6 according to the powder type and compressor inlet conditions. The capability of the compressor to collect particles changes over time as a function of the condition, even if, several tested cases appear characterized by an almost constant capture efficiency trend.

In addition, the performance degradation has been monitored over time and, with the reference of the particle concentration, the present experimental campaign covers about 500 operating hours of an actual installation. After a detailed evaluation of experimental uncertainty, the performance losses due to particle contamination has been assessed. The losses in the compressor performance have been estimated by means of the pressure ratio of the axial stages. The maximum degradation has been estimated equal to 0.53 % per hour for the compressor pressure ratio. Soot particles appear stickier, especially in the presence of higher humidity and represent the most detrimental operating conditions for the compressor unit.
Contribution of Tip Shroud Cavity to Loss Generation in the Main Flow of a Low Pressure Turbine Using Steady and Unsteady Numerical Approach
Authors: Perini Maxime , Binder Nicolas , Bousquet Yannick , Schwartz Eric
Published: January 2021

A lot of studies on turbomachinery main flow optimisation have been performed in order to reach current efficiencies. To go further in the study of aerodynamic losses sources, a better understanding of technological effects is required. Tip shroud cavities in low pressure turbine is an example. Indeed, the by-pass flow causes additional pressure losses. In addition, interactions between main flow and cavity flows, as well as the re-entering flow, cause mixing losses and modifications of flow angle. This paper investigates the contribution of tip shroud cavities in a low pressure turbine stage on the overall performance and flow structures. The ability of a steady simulation to predict this kind of flow by comparison with time-resolved results is poorly documented in the literature, and is an objective of this paper. Computations are compared with experimental data from low speed turbine test rig. Entropy production shows that a large amount of additional losses comes from the cavities themselves whichever the steady or unsteady treatment of the simulation. Additional losses generated in the rotor are more dependent on the presence of the shroud or not than the unsteady feature of the simulations.
Conceptual Design and Energy Storage Positioning Aspects for a Hybrid-Electric Light Aircraft
Authors: Gkoutzamanis Vasilis G. , Srinivas Arjun , Mavroudi Doukaini , Kalfas Anestis I. , Kavvalos Mavroudis D. , Kyprianidis Konstantinos G. , Korbetis George
Published: January 2021

This work focuses on the feasibility of a 19-passenger hybrid-electric aircraft, to serve the short-haul segment within the 200–600 nautical miles. Its ambition is to answer some dominating research questions, during the evaluation and design of aircraft based on electric propulsion architectures. The potential entry into service of such aircraft is foreseen in 2030. A literature review is performed, to identify similar concepts that are under research and development. After the requirements definition, the first level of conceptual design is employed. Based on a set of assumptions, a methodology for the sizing of the hybrid-electric aircraft is described to explore the basis of the design space. Additionally, a methodology for the energy storage positioning is provided, to highlight the multidisciplinary aspects between the sizing of an aircraft, the selected architecture (series/parallel partial hybrid) and the energy storage operational characteristics. The design choices are driven by the aim to reduce CO2 emissions and accommodate boundary layer ingestion engines, with aircraft electrification. The results show that it is not possible to fulfill the initial design requirements (600 nmi) with a fully-electric aircraft configuration, due to the far-fetched battery necessities. It is also highlighted that compliance with airworthiness certifications is favored by switching to hybrid-electric aircraft configurations and relaxing the design requirements (targeted range, payload, battery technology). Finally, the lower degree of hybridization (40%) is observed to have a higher energy efficiency (12% lower energy consumption and larger CO2 reduction), compared to the higher degree of hybridization (50%), with respect to the conventional configuration.
A Nitrogen Oxides Emission Prediction Model for Gas Turbines Based on Interpretable Multilayer Perceptron Neural Networks
Authors: Huang Dawen , Tang Shanhua , Zhou Dengji
Published: January 2021

Gas turbines, an important energy conversion equipment, produce Nitrogen Oxides (NOx) emissions, endangering human health and forming air pollution. With the increasingly stringent NOx emission standards, it is more significant to ascertain NOx emission characteristics to reduce pollutant emissions. Establishing an emission prediction model is an effective way for real-time and accurate monitoring of the NOx discharge amount. Based on the multi-layer perceptron neural networks, an interpretable emission prediction model with a monitorable middle layer is designed to monitor NOx emission by taking the ambient parameters and boundary parameters as the network inputs. The outlet temperature of the compressor is selected as the monitorable measuring parameters of the middle layer. The emission prediction model is trained by historical operation data under different working conditions. According to the errors between the predicted values and measured values of the middle layer and output layer, the weights of the emission prediction model are optimized by the back-propagation algorithm, and the optimal NOx emission prediction model is established for gas turbines under the various working conditions. Furthermore, the mechanism of predicting NOx emission value is explained based on known parameter influence laws between the input layer, middle layer and output layer, which helps to reveal the main measurement parameters affecting NOx emission value, adjust the model parameters and obtain more accurate prediction results. Compared with the traditional emission monitoring methods, the emission prediction model has higher accuracy and faster calculation efficiency and can obtain believable NOx emission prediction results for various operating conditions of gas turbines.
Multi-Channel Spectral Analysis of Non-Synchronous Vibrations of Bladed Disks Measured by Blade Tip Timing
Authors: Carassale Luigi , Coletti Francesca , Guida Roberto , Marrè-Brunenghi Michela , Rizzetto Elena
Published: January 2021

The paper proposes a method for the processing of BTT data deriving from non-synchronous vibrations measured at constant rotor speed by a set of non-uniformly distributed sensors. The sampled data are interpreted as members of a vector space whose characteristics are determined by the signal itself and by sampling pattern. If the signal contains a single harmonic component, its frequency can be estimated through a method that has been named harmonic matching. On the contrary, when more than one harmonic component is present, due to a multi-modal response, a component separation processing is necessary. To this purpose, it is proposed a technique based on the Independent Component Analysis (ICA). This approach is limited to constant speed regime, but has the benefit of using statistical estimators that enable a strong resistance to noise. The method is illustrated using academic examples and is employed to study a flutter-like non-synchronous vibration of a bladed disk.
Development of Experimental and Numerical Methods for the Analysis of Active Clearance Control Systems
Authors: Da Soghe Riccardo , Mazzei Lorenzo , Tarchi Lorenzo , Cocchi Lorenzo , Picchi Alessio , Facchini Bruno , Descamps Laurent , Girardeau Julian , Simon Matthieu
Published: January 2021

The ever increasing performance requirements of modern aero-engines necessitate the development of effective ways to improve efficiency and reduce losses. Casing temperature control is particularly critical from this point of view, since thermal expansion directly affects the blade tip clearance and thus the associated leakages. To limit the turbine tip flows, Active Clearance Control (ACC) systems have been implemented over the last decades. These systems are usually based upon impingement cooling, generated by a series of perforated manifolds enclosing the turbine casing.

When dealing with aeroengine low pressure turbines, the current trend in increasing the engine by-pass ratio, so as to enhance the system propulsive efficiency, pushes the limits of ACC traditional design performance. The reduction of the pressure head at the ACC system inlet requires lower nozzle-to-target distances as well as denser impingement arrays to compensate the reduction of the jets’ Reynolds number. Literature correlations for the impingement heat transfer coefficient estimation are then out of their confidence range and also RANS numerical approaches appear not suitable for future ACC designs.

In this work, methodologies for the development of accurate and reliable tools to determine the heat transfer characteristics of low pressure ACC systems are presented. More precisely, this paper describes a custom designed finite difference procedure capable of solving the inverse conduction problem on the target plate of a test sample. The methodology was successfully applied to an experimental setup for the measurement of the thermal loads on a target plate of a representative low pressure ACC impinging system. The experimental data is then used to validate a suitable numerical approach. Results show that RANS model is not able to mimic the experimental trends, while scale-resolving turbulence models provide a good reconstruction of the experimental evidences, thus allowing to obtain a correct interpretation of flow and thermal phenomena for ACC systems.
Part Load Strategy Definition and Annual Simulation for Small Size sCO2 Based Pulverized Coal Power Plant
Authors: Alfani Dario , Astolfi Marco , Binotti Marco , Silva Paolo
Published: January 2021

In the near future, due to the growing share of variable renewable energy (VRE) in the electricity mix and the lack of large-scale electricity storage, coal power plants will have to gradually shift their role from base-load operation to providing fluctuating back-up power to meet unpredictable and short-noticed load variations, in order to improve the stability of the electrical grid. However, current coal power plants have been designed to operate at base-load and are not optimized for flexible part-load operation, resulting in an intrinsic inadequacy for fast load variations. The founding idea of the H2020 sCO2-Flex project is to improve the flexibility of pulverized coal power plants by adopting supercritical carbon dioxide (sCO2) Brayton power cycles instead of common steam Rankine cycles. Despite the extensive available literature about the design of sCO2 power systems for different applications (concentrating solar power, waste heat recovery, 4th generation nuclear), there is still limited knowledge about part-load strategies that should be implemented in order to maximize system efficiency during real plant operation. This paper aims to provide a deeper insight about the potential of sCO2 power plants for small modular coal power plants (25–100 MWel) highlighting the difficulties that must be faced during part-load operation in order to ensure high system performances still guaranteeing a safe operation of the cycle components. The selected configuration is a recompressed cycle with high temperature recuperator bypass which is modelled in a MATLAB+REFPROP numerical tool specifically developed to optimize the plant nominal performance, to provide a preliminary sizing of each component and to evaluate and compare different off-design operating strategies. In particular, the off-design behavior and the operational constraints of each component will be implemented based on referenced numerical models, adopting reliable correlations and exploiting ad hoc codes for the performance evaluation.
Experimental and Computational Investigation of Shaped Film Cooling Holes Designed to Minimize Inlet Separation
Authors: Jones Fraser B. , Fox Dale W. , Bogard David G.
Published: January 2021

Film cooling is used to protect turbine components from the extreme temperatures by ejecting coolant through arrays of holes to create an air buffer from the hot combustion gases. Limitations in traditional machining meant film cooling holes universally have sharp inlets which create separation regions at the hole entrance. The present study uses experimental and computational data to show that these inlet separation are a major cause of performance variation in crossflow fed film cooling holes. Three hole designs were experimentally tested by independently varying the coolant velocity ratio (VR) and the coolant channel velocitty ratio (VRc) to isolate the effects of crossflow on hole performance. Leveraging additive manufacturing technologies, the addition of a 0.25D radius fillet to the inlet of a 7-7-7 shaped hole is shown to significantly improve diffuser usage and significantly reduce variation in performance with VRc. A second AM design used a very large radius of curvature inlet to reduce biasing caused by the inlet crossflow. Experiments showed that this “swept” hole design did minimize biasing of coolant flow to one side of the shaped hole and it significantly reduced variations due to varying VRc. RANS simulations at six VR and three VRc conditions were made for each geometry to better understand how the new geometries changed the velocity field within the hole. The sharp and rounded inlets were seen to have very similar tangential velocity fields and jet biasing. Both AM inlets created more uniform, slower velocity fields entering the diffuser. The results of this paper indicate large improvements in film cooling performance can be found by leveraging AM technology.
Effect of Struts Downstream of Low Pressure Turbine on Tone Noise Generation
Authors: Nigmatullin Ravil , Terenteva Larisa
Published: January 2021

In the present work a numerical study of tone noise generated by the last stage of the Low Pressure Turbine (LPT) of an aircraft engine designed for a medium-haul civilian aircraft has been conducted. The impact of struts on the tone noise characteristics is estimated. The method for turbine noise calculation is based on numerical integration of the three-dimensional unsteady Reynolds averaged Navier-Stokes equations using an in-house code for multi-stage simulations. To obtain the tonal characteristics of the generated noise, the pressure pulsation field is processed using the methods of radial mode analysis. The calculated pressure fluctuations contain all possible components of the frequency-modal spectrum, which allows us to determine profile of the generated tone noise and find propagating modes with maximum amplitude. The calculations showed that the presence of struts leads to a scattering effect, which manifests as an increase in the number of generated circumferential modes. These circumferential modes propagate both downstream and upstream and increase the total level of tone noise. The amplitudes of circumferential modes related to two different types of the interaction, rotor-stator and rotor-struts, are compared.
Active Flow Control Utilizing an Adaptive Blade Geometry and an Extremum Seeking Algorithm at Periodically Transient Boundary Conditions
Authors: Werder Tobias , Liebich Robert , Neuhäuser Karl , Behnsen Clara , King Rudibert
Published: January 2021

As a consequence of constant volume combustion in gas turbines pressure waves propagating upstream the main flow into the compressor system are generated leading to incidence variations. Numerical and experimental investigations of stator vanes have shown that Active Flow Control (AFC) by means of adaptive blade geometries is beneficial when such periodic incidence variations occur. A significant risk reduction in a compressor facing disturbances can thereby be achieved concerning stall or choke. Experimental investigations on such an AFC method with simultaneous application of a closed-loop control are missing in order to demonstrate its potential.

This work investigates a linear compressor cascade that is equipped with a 3D-manufactured piezo adaptive blade structure. The utilized actuators are piezoelectric Macro-Fiber-Composites. A throttling device is positioned downstream the trailing edge plane to emulate an unsteady combustion process. Periodic transient throttling events with a frequency of up to 20 Hz cause incidence changes to the blade’s leading edge. Consequently, pressure fluctuations on the blade’s surface occur, having a significant impact on the pressure recovery downstream of the stator cascade. Experimental results of harmonically actuating the piezo adaptive blade with the corresponding disturbance frequency show that the impact of disturbances can be reduced to approx. 50 %. However, this is only effective if the phase shift of the harmonic actuation is adjusted correctly. Using an inadequate phase shift reverses the positive effects, causing the aforementioned stall, choke, or significant losses. In order to find the optimum phase shift, even under varying, possibly unpredictable operating conditions, an Extremum Seeking Controller is presented. This gradient-based approach is minimizing the pressure variance over time by carefully adjusting the phase shift of the harmonic actuation of the AFC system.
Evaluation and Validation of Two-Phase Flow Numerical Simulations Applied to an Aeronautical Injector Using a Lagrangian Approach
Authors: Tillou Julien , Leparoux Julien , Dombard Jérome , Riber Eleonore , Cuenot Bénédicte
Published: January 2021

Non-reactive Lagrangian two-phase flow Large-Eddy Simulations (LES) of an industrial aeronautical injector are carried out with the compressible AVBP code and compared with an experimental database in an industrial context. While most of the papers are focused on simplex atomiser with only one fuel passage, we propose to account for specific industrial configurations based on duplex atomiser where both the primary and the secondary passages operate. For the second passage, the fuel spray angle is wider, leading to spray / wall interactions and airblast atomization.

The computation domain consists in the experimental mock-up without the fuel atomizer part. The liquid-injection boundary condition is applied through the phenomenological FIM-UR model, which prescribes droplet velocities and diameter distribution at the atomizer tip based on both the atomizer characteristics and the liquid mass flow rate. No specific models are used for spray / wall interaction, and droplets are assumed to slip on the walls. The numerical results are compared with the experimental database for Jet-A1 fuel, built through Phase Doppler Anemometry instrumentation, allowing access to local information regarding the droplets velocity components.

Three LES are performed for pressure loss ranging from 1 to 3%, covering an important part of the engine operating conditions, from high altitude relight to cruise operating point. Mean and fluctuating velocity profiles show a relatively good agreement with measurements, for all the operating points. It confirms that the spray/wall interactions, airblast and secondary breakup models may be neglected as a first approximation for configurations where only a relatively small amount of fuel impacts the wall.
Numerical Predictions of Turbine Cascade Secondary Flows and Heat Transfer With Inflow Turbulence
Authors: Kanani Yousef , Acharya Sumanta , Ames Forrest
Published: January 2021

Turbine passage secondary flows are studied for a large rounded leading edge airfoil geometry considered in the experimental investigation of Varty et al. (J. Turbomach. 140(2):021010) using high resolution Large Eddy Simulation (LES). The complex nature of secondary flow formation and evolution are affected by the approach boundary layer characteristics, components of pressure gradients tangent and normal to the passage flow, surface curvature, and inflow turbulence. This paper presents a detailed description of the secondary flows and heat transfer in a linear vane cascade at exit chord Reynolds number of 5 × 105 at low and high inflow turbulence. Initial flow turning at the leading edge of the inlet boundary layer leads to a pair of counter-rotating flow circulation in each half of the cross-plane that drive the evolution of the pressure-side and suction side of the near-wall vortices such as the horseshoe and leading edge corner vortex. The passage vortex for the current large leading-edge vane is formed by the amplification of the initially formed circulation closer to the pressure side (PPC) which strengthens and merges with other vortex systems while moving toward the suction side. The predicted suction surface heat transfer shows good agreement with the measurements and properly captures the augmented heat transfer due to the formation and lateral spreading of the secondary flows towards the vane midspan downstream of the vane passage. Effects of various components of the secondary flows on the endwall and vane heat transfer are discussed in detail.
Transient Aero-Thermo-Mechanical Multidimensional Analysis of a High Pressure Turbine Assembly Through a Square Cycle
Authors: Ganine Vlad , Chew John W. , Hills Nicholas J. , Mohamed Sulfi N. , Miller Matthew M.
Published: January 2021

Better understanding and more accurate prediction of heat transfer and cooling flows in aero engine components in steady and transient operating regimes are essential to modern engine designs aiming at reduced cooling air consumption and improved engine efficiencies. This paper presents a simplified coupled transient analysis methodology that allows assessment of the aerothermal and thermomechanical responses of engine components together with cooling air mass flow, pressure and temperature distributions in an automatic fully integrated way. This is achieved by assembling a fluid network with contribution of components of different geometrical dimensions coupled to each other through dimensionally heterogeneous interfaces. More accurate local flow conditions, heat transfer and structural displacement are resolved on a smaller area of interest with multidimensional surface coupled CFD/FE codes. Contributions of the whole engine air-system are predicted with a faster mono dimensional flow network code. Matching conditions at the common interfaces are enforced at each time step exactly by employing an efficient iterative scheme. The coupled simulation is performed on an industrial high pressure turbine disk component run through a square cycle. Predictions are compared against the available experimental data. The paper proves the reliability and performance of the multidimensional coupling technique in a realistic industrial setting. The results underline the importance of including more physical details into transient thermal modelling of turbine engine components.
Application of Digital Twin Concept for Supercritical CO2 Off-Design Performance and Operation Analyses
Authors: Moroz Leonid , Burlaka Maksym , Zhang Tishun , Altukhova Olga
Published: January 2021

To date variety of supercritical CO2 cycles were proposed by numerous authors. Multiple small-scale tests performed, and a lot of supercritical CO cycle aspects studied. Currently, 3-10 MW-scale test facilities are being built. However, there are still several pieces of SCO2 technology with the Technology Readiness Level (TRL) 3-5 and system modeling is one of them. The system modeling approach shall be sufficiently accurate and flexible, to be able to precisely predict the off-design and part-load operation of the cycle at both supercritical and condensing modes with diverse control strategies. System modeling itself implies the utilization of component models which are often idealized and may not provide a sufficient level of fidelity. Especially for prediction of off-design and part load supercritical CO2 cycle performance with near-critical compressor and transition to condensing modes with lower ambient temperatures, and other aspects of cycle operation under alternating grid demands and ambient conditions.

In this study, the concept of a digital twin to predict off-design supercritical CO2 cycle performance is utilized. In particular, with the intent to have sufficient cycle simulation accuracy and flexibility the cycle simulation system with physics-based methods/modules were created for the bottoming 15.5 MW Power Generation Unit (PGU). The heat source for PGU is GE LM6000-PH DLE gas turbine. The PGU is a composite (merged) supercritical CO2 cycle with a high heat recovery rate, its design and the overall scheme are described in detail. The calculation methods utilized at cycle level and components’ level, including loss models with an indication of prediction accuracy, are described. The flowchart of the process of off-design performance estimation and data transfer between the modules as well. The comparison of the results obtained utilizing PGU digital twin with other simplified approaches is performed. The results of the developed digital twin utilization to optimize cycle control strategies and parameters to improve off-design cycle performance are discussed in detail.
Effects of Endwall Film Coolant Flow Rate on Secondary Flows and Coolant Mixing in a First Stage Nozzle Guide Vane
Authors: Alqefl Mahmood H. , Nawathe Kedar P. , Chen Pingting , Zhu Rui , Kim Yong W. , Simon Terrence W.
Published: January 2021

Modern gas turbines are subjected to very high thermal loading. This leads to a need for aggressive cooling to protect components from damage. Endwalls are particularly challenging to cool due to a complex system of secondary flows near them that wash and disrupt the protective coolant films. This highly three-dimensional flow not only affects but is also affected by the momentum of film cooling flows, whether injected just upstream of the passage to intentionally cool the endwall, or as combustor cooling flows injected further upstream in the engine. This complex interaction between the different cooling flows and passage aerodynamics has been recently studied in a first stage nozzle guide vane. The present paper presents a detailed study on the sensitivity of aero-thermal interactions to endwall film cooling MFR (cooling mass flow to mainstream flow ratio). The test section represents a first stage nozzle guide vane with a contoured endwall and endwall film cooling injected just upstream of it. The test section also includes an engine-representative combustor-turbine interface geometry with combustor cooling flows injected at a constant rate. The approach flow conditions represent flow exiting a low-NOx combustor. Adiabatic surface thermal measurements and in-passage velocity and thermal field measurements are presented and discussed. The results show the dynamics of passage vortex suppression and the increase of impingement vortex strength as MFR changes. The effects of these changes of secondary flows on coolant distribution are presented.
Experimental Investigation on the Rubbing Process of Labyrinth Seals Against Honeycomb Liners
Authors: Munz Oliver , Hühn Lisa , Schwitzke Corina , Bauer Hans-Jörg , Fischer Tim , Ulan kyzy Sonun
Published: January 2021

Sealing systems contribute significantly to the efficiency of turbomachinery. Small gap widths, which are important for low leakage mass flows in labyrinth seals, combined with thermal and mechanical expansion of the rotor can lead to contact with the stator. During these so-called rubbing processes, it is necessary to make an accurate prediction with respect to the performance and service life of the seal. For this purpose, the influence of relative velocity in the contact (up to 165ms−1) and incursion rate (up to 0.5 mms−1) on the resulting thermal and mechanical loads as well as wear mechanisms are studied for the rubbing process between an inclined labyrinth seal fin and a honeycomb segment. Furthermore, different axial configurations of the seal fin with respect to the honeycomb structure are considered. The system reacts very sensitively to a change of the seal fin position relative to the honeycomb structure. The incursion per revolution reflects a change of the wear mechanism from abrasive to plastic for a certain value. The results of this study contribute to the optimization of labyrinth seals and the development of new types of liner materials as well as geometries.
Methods to Have Tighter Clearance in Gas Turbine: Turbine Section
Authors: Babu Santhana G. , Ramesh Kammalapalli , Tognarelli Leonardo
Published: January 2021

Typically, Gas turbine clearance between stator and rotor parts are governed by radial clearance which determines performance, cooling flow requirements, part performance etc. These clearances must be optimized to meet product requirements. Clearance which are kept too tight at assembly condition causes excessive rubbing during starting or shutdown of gas turbine which results in excessive heat generation and damage to rotating and statoric parts. In some cases, rubbing could cause tip liberations and damages to flow path which results in aero dynamic losses. Similarly, if rotor tip clearance is large at assembly condition results in aerodynamic losses. While designing component design at interface locations, tip clearance should be kept as minimum as possible to have proper balance between tip rubs at low speed and aero dynamic loss. In this paper describes the experience of Baker Hughes, wherein different design options which are considered to arrive at optimized clearance in low pressure turbine section of Gas turbine have been discussed. Typically, in low pressure turbine wherein the turbine airfoils were provided with tip rails and shrouds are brazed with honeycombs. These were allowed to rub during startup of Gas turbine engine and provide a tighter clearance at steady state operating condition. In this paper, to have tighter clearance in operating condition few methods of incorporating axial clearance in addition to radial tip clearance are discussed. By incorporating tighter axial clearance, it was found to be evident that performance estimated has improved compared to having only radial tip clearance. This paper also describes design considerations for honeycomb pertaining to axial clearance control and the methods for rubbing tip shroud with honeycomb. This paper highlights worm chart developed for a rotor blade and stator shroud configuration and highlight benefit of axial clearance control mechanism. This paper also covers different designs of heat dissipation methods in tip rails of a bucket while it is rubbing with honeycomb. In this paper, based analytical case study proves that, when axial clearance was made tighter, it reduces leakage flows and improves Low pressure turbine stage efficiency significantly.
Low-Order Modeling to Investigate Clusters of ITA Modes in Annular Combustors
Authors: Fournier Guillaume J. J. , Haeringer Matthias , Silva Camilo F. , Polifke Wolfgang
Published: January 2021

The intrinsic thermoacoustic (ITA) feedbackloop constitutes a coupling between flow, flame and acoustics that does not involve the natural acoustic modes of the system. One recent study showed that ITA modes in annular combustors come in significant number and with the peculiar behavior of clusters, i.e. several modes with close frequencies. In the present work an analytical model of a typical annular combustor is derived via Riemann invariants and Bloch theory. The resulting formulation describes the full annular system as a longitudinal combustor with an outlet reflection coefficient that depends on frequency and the azimuthal mode order. The model explains the underlying mechanism of the clustering phenomena and the structure of the clusters associated with ITA modes of different azimuthal orders. In addition, a phasor analysis is proposed, which enclose the conditions for which the 1D model remains valid when describing the thermoacoustic behavior of an annular combustor.
Aero-Thermal Coupled Design Optimization of a Turbine Vane and the Effect on Heat Load of Endwall
Authors: Liu Zhansheng , Yang Kefeng , Feng Zhenping
Published: January 2021

The 3D aerodynamic design optimization has been applied in the generation of modern turbine blade profile. However, the traditional design method paid little attention to the decrease of heat transfer coefficients on the blade external surface. In the present work, a typical high load turbine vane, VKI LS89 cascade, was optimized with the decrease of aerodynamic loss and heat load chosen as the optimization objective functions. Numerical simulation methods were validated by the experiment data, and simulations results agreed well with the measured values. Both 2D profiles and stagger curves of the vane were parameterized by no-uniform B-Spline. There were totally seven movable control points for the 2D profiles, and four movable control points for the corresponding stagger curves. And the locations of the B-Spline control points and stagger angles were taken as the design variables. Multi-objective genetic algorithm coupled with surrogate model was adopted to acquire the optimal cases with better aero-thermal performance. The profiles of the vane were firstly optimized in a linear cascade model, and then the stagger curves and sections stagger angle were modified for better overall performance. Mass flow rate of the mainstream and exit flow angle at outlet were constrained by the comprehensive objective functions during the 3D optimization process. The results showed that profiles with high aerodynamic efficiency and low heat load can be obtained by the 2D profiles optimization design. Additionally, the heat load could be decreased by the 3D optimization design. Furthermore, the effects of optimization on the heat load distributions of the endwall were studied, and it can be observed that the 3D optimization obviously modified the heat transfer patterns of the endwall.
Blades and Vanes Platform Laser Rebuilding
Authors: Gabrielli A. , Moretto M.
Published: January 2021

The evolution of industrial gas turbines towards increased efficiency and performance requires ever higher operating temperatures for the engines. In order to remain competitive in the market, OEM companies continuously need to develop maintenance programs and reconditioning technologies able to extend the life of these components as much as possible. During the operation, turbine blades and vanes are prone to deterioration due to the high temperature of the gas passing along the platform surface, causing hot corrosion and thermomechanical fatigue. In particular, this results in deterioration and crack formation at platform edges. If oxidized, cracked or otherwise deteriorated locations are found during service inspections, the component platform has to be rebuilt. The standard method for rebuilding the platform is to remove the deteriorated material volume and rebuild it by welding. In particular, the most common welding method for rotor blades and stator vanes restoration today is the tungsten inert gas welding (GTAW). However, tungsten inert gas welding has a large heat affected zone, which can later lead to major distortion, due the elevated thermal input, and loss of structural integrity of the reconditioned part. In particular, for single crystal material high thermal input can promote recrystallization issues and this phenomenon compromises the mechanical properties and considerably reduces the life of the component. The most recent reconditioning techniques developed by Ansaldo Energia involves the use of laser metal deposition technology to rebuild the damaged areas and restore the platform to the original shape. Prior to the automated process the area, on which the clad will be laid, requires precise preparation. This paper describes a customized, automatic process to restore the deteriorated blade or vane area by the laser metal deposition technique for equiaxial or single crystal material, minimizing the thermal input and resulting in high resistance rebuilding.
Development and Validation of a Continuous Random Walk Model for Particle Tracking in Accelerating Flows
Authors: Vadgama Nikul , Kapsis Marios , Forsyth Peter , McGilvray Matthew , Gillespie David R. H.
Published: January 2021

Stochastic particle tracking models coupled to RANS fluid simulations are frequently used to simulate particulate transport and hence predict component damage in gas turbines. In simple flows the Continuous Random Walk (CRW) model has been shown to model particulate motion in the diffusion-impaction regime significantly more accurately than Discrete Random Walk implementations. To date, the CRW model has used turbulent flow statistics determined from DNS in channels and experiments in pipes. Robust extension of the CRW model to accelerating flows modelled using RANS is important to enable its use in design studies of rotating engine-realistic geometries of complex curvature.

This paper builds on previous work by the authors to use turbulent statistics in the CRW model directly from Reynolds Stress Models (RSM) in RANS simulations. Further improvements are made to this technique to account for strong gradients in Reynolds Stresses in all directions; improve the robustness of the model to the chosen time-step; and to eliminate the need for DNS/experimentally derived statistical flow properties. The effect of these changes were studied using a commercial CFD solver for a simple pipe flow, for which integral deposition prediction accuracy equal to that using the original CRW was achieved. These changes enable the CRW to be applied to more complex flow cases.

To demonstrate why this development is important, in a more complex flow case with acceleration, deposition in a turbulent 90° bend was investigated. Critical differences in the predicted deposition are apparent when the results are compared to the alternative tracking models suitable for RANS solutions. The modified CRW model was the only model which captured the more complex deposition distribution, as predicted by published LES studies. Particle tracking models need to be accurate in the spatial distribution of deposition they predict in order to enable more sophisticated engineering design studies.