bluuebunny/crossref_metadata_2025 huggingface dataset:
Boundary Layer Analysis of a Transonic High-Pressure Turbine Vane Using Ultra-Fast-Response Temperature-Sensitive Paint
Authors: Petersen Anna , Hilfer Michael
Published: September 2023

The focus of this paper is the impact of surface roughness on the boundary layer caused by a 7YSZ thermal barrier coating (TBC). Experimental investigations are conducted on a NGV installed inside the Wind Tunnel for Straight Cascades Göttingen (EGG). The shape of the vane has been altered in a way that eliminates the influence of the TBC’s thickness. Therefore it is expected that only the surface roughness is influencing the location of the separation and boundary layer transition. The transition next to the roughness can also be affected by positive and negative pressure gradients, separation, and interacting shocks.

The impact of TBC on the turbulent wedges’ appearance, separation bubble’s position and length, and transition location is examined in this study. This research, combined with prior investigations, provides comprehensive understanding of a turbine vane’s aerothermodynamics. To investigate unsteady flow phenomena on a TBC coated NGV, ultra-fast-response temperature-sensitive paint (iTSP) is utilized. This dataset will serve as a reference point for developing new turbine vane designs that include TBC and extensive cooling. Furthermore, the findings will be employed as a benchmark for improving numerical models.
A CFD-Assisted Throughflow Approach for the Map Calculation of Centrifugal Compressors
Authors: Labat Casajust Sandra , Möller Daniel , Jeschke Peter
Published: September 2023

In this paper we describe the development of a CFD-assisted throughflow approach for the map calculation of centrifugal compressors with an unshrouded impeller. We focus on the modeling of slip factor, impeller outlet aerodynamic blockage, and entropy loss coefficient as a means of controlling our performance prediction of pressure ratio and efficiency, and study two compressors of similar nominal characteristics. Firstly, we build a baseline calculation with a unified combination of literature models. To address the discrepancies between the baseline solution and CFD results, we define a calibration approach which is based on parameters that can be extracted from a throughflow method and that are representative of secondary flows and flow separation. This approach leads to an improved efficiency prediction for both of our test cases, especially for the lowest and highest rotational speeds. As regards the pressure ratio, an accuracy improvement of 12.9% is achieved for the 100% speed line of one of our compressors. To summarize, we present here a methodology that is able to successfully correct the performance prediction of throughflow calculations for centrifugal compressors. Although the number of machines under consideration in this paper is relatively low to establish general correlations, the approach can be potentially generalized to cover other similar compressors, thus allowing continuous improvement of the models with new data.
On the Effect of Purge Air on the Aerodynamic Performance of a State-of-the-Art Turbine-Rear-Frame Guide Vane
Authors: Schien Malte , Wakelam Christian , Graiff Mattia , Göttlich Emil , Marn Andreas
Published: September 2023

It is well known that the total pressure ratio and the turbine inlet temperature need to be increased to raise the thermal efficiency of a turbine stage. Therefore, a high exit gas temperature of the combustion chamber is essential to increase the thermal efficiency of aero engines. Consequently, the fluid temperature at the inlet of the Turbine Rear Frame (TRF) rises, too. Without any countermeasures, too hot fluid can enter the cavities between stationary and rotating parts through axial gaps causing damage to structural parts. To prevent such ingression of hot fluid, cold purge air is blown out of the cavities and hence interacts with the main flow of the low-pressure turbine.

The present paper investigates the effect of purge air on the aerodynamic performance of a state-of-the-art Turbine Exit Guide-Vane (TEGV) design. For this purpose, five-hole-probe data for three different purge-air flow rates are compared at the inlet and the exit plane of a scaled full annular TEGV cascade. It was found that purge air migrates along the hub end wall toward one TEGV suction side, corresponding to the cross-flow pressure gradient, where it accumulates. The accumulated purge air curls into one vortex. The influence of three TEGV incidence angles, high-negative and high-positive values, is discussed for the nominal purge condition. The investigation was conducted at the Institute of Thermal Turbomachinery and Machine Dynamics of the Graz University of Technology.
Self-Organization of Unsteady Full-Annulus Flows in a Gas Turbine Compressor Under Operating Conditions
Authors: Hagita Yasuharu , Hayakawa Riku , Miyazawa Hironori , Furusawa Takashi , Yamamoto Satoru
Published: September 2023

In Japan, gas turbine combined cycle (GTCC) power plants are currently operated under rapid start-up, shutdown, and partial-load conditions to maintain a stable power supply, suppressing the fluctuation of electric power due to renewable energy sources such as solar and wind power. The off-design condition may cause unsteady and unstable flows in the compressor stage, increasing mechanical stresses on the blades. To reveal the critical flow behavior and avoid blade failure, an innovative method that can clarify the flow physics in these systems is urgently required.

This study proposes a classification method for time-series big data obtained from full-annulus flow computations under various flow conditions assisted by the self-organizing map (SOM) method, which is a popular machine-learning technique. First, full-annulus unsteady flow computations under various flow conditions were conducted for an actual compressor in an industrial gas turbine at a GTCC power plant. The inlet guide vane (IGV) angle was set to various values that corresponded to the full-load operation and transitional flow rate conditions during partial-load operation. The time-series data of the load on the blades in the various cases were obtained from the computations. All time-series data were converted into frequency data using fast Fourier transform (FFT) and classified by the SOM. As a result, the proposed classification method could appropriately classify the critical flow conditions in which large and unstable pressure fluctuations are observed. This method may be used to avoid critical operating conditions that lead to blade failure.
Realtime CFD Based Shape Optimization Using Geometric Deep Learning for Families of Turbomachinery Applications
Authors: Gouttiere Alexandre , Alessi Giacomo , Wunsch Dirk , Zampieri Luca , Hirsch Charles
Published: September 2023

A Machine Learning approach is applied to the open domain test case Rotor 37 to predict the performance of a family of turbomachinery. A deep learning approach implemented in the form of a geometric convolutional neural network is used. A first low geometrical variability parametric representation of the Rotor 37 is created to build training dataset from which the machine learning model is trained. After the training, the model predicts machine performance parameters in a few seconds. Then, this AI model is used in an optimization process to improve Rotor 37 performance and an increase in isentropic efficiency of 2.86% is obtained. A CFD validation is performed to confirm the improvement with an increase of 1.81% in isentropic efficiency. However, the achievable performance increase is limited by the parametric representation generated, given its low degree of freedom. Therefore, a new parametric representation is generated allowing more complex variations of the Rotor 37 design. It is demonstrated that a continuous learning approach, which is used to extend the model can successfully be applied to extend the trained AI model to the larger geometrical variability at significantly reduced model training costs. Then the optimization procedure is repeated and an increase of isentropic efficiency of 3.25% is obtained. A CFD simulation confirms an improvement of the performance of 2.35% in isentropic efficiency.
Rotor Clearance Flow Measurements Employing a Novel Miniature Sensor
Authors: Eck Mario , Peitsch Dieter
Published: September 2023

A miniature flow sensor has been used to investigate the unsteady over-tip flow field in an axial compressor rotor. Flush mounted on the casing wall, the sensor yields the two-dimensional flow field over the rotor blade tip, both in the absolute and relative frames of reference or the wall shear stress distribution on the casing wall. The velocity vector fields phase-averaged to the rotor have been used to compute streakline patterns providing insights into secondary flows including the clearance vortex dynamics, as if the oil flow visualization had been applied in the rotor frame of reference. Using the velocity vector field, the blockage factor has been determined for each individual rotor passage, indicating noticeable variance over the circumference. The variance also increased non-linearly while throttling of the compressor. The vector patterns additionally served to characterize the shear layer between the clearance and the main flow. For this purpose, 2D contours of the divergence and the shear strain rate have been processed first. In a second step, both quantities were reduced to scalar values for each rotor passage by integrating them along the shear layer. This allowed identifying a clear correlation between blockage, divergence and shear strain rate as a function of mass flow. The results contribute significantly to a better understanding of the clearance flow in axial compressors operating at near stall conditions.
Turn-Down Capability of Ansaldo Energia’s AE94.3A
Authors: Piola Stefano , Bavassano Francesco , Benvenuto Marcello , Canepa Roberto , Garbarino Tiziano , Pestelli Elena
Published: September 2023

At an ever-faster pace, market’s requirements for operational flexibility and turn-down capabilities are becoming the fundamental driver for heavy-duty gas turbine design and upgrade. This enables better compensation of the natural intermittence of renewable energy sources such as wind and solar by effectively compensating for both surpluses and shortages compared to the electric grid power request. Gas turbine-based energy plants require a lowest Minimum Environmental Load (MEL) for times when the power request is mainly covered by renewable sources and, however, need to promptly respond to green energy shortages. Ansaldo Energia has been addressing such requirements overall its gas turbine portfolio for several years, recently including further extension of MEL for GT26, as discussed in GT2021-59457.

The present paper addresses the development project carried out to reduce the MEL for AE94.3A via a modular upgrade package especially intended for the wide existing Service fleet, made of more than 110 units. In order to accomplish the AE94.3A MEL reduction, several features were designed and tested including VIGV extra-closure, air bypass through compressor blow-off lines and extended use of anti-ice air recirculation. None of these require major hardware changes but only upgrades within a normal service outage, together with minor control system adaptations. The wide-ranging technical challenges attached to the MEL reduction features are discussed. Validation on field via special instrumentation focused on compressor, secondary air system and turbine for several engines is also presented. The achieved Minimum Environmental Load reduction is shown and its potential discussed together with some features already in place, such as the use of CO catalyzer or the regulation of control valves put on external cooling lines. The readiness and performance level of this MEL upgrade package, already in operation on several power plants, is here demonstrated. This makes the AE94.3A gas turbine more flexible towards current and future market requirements.
Tail-Integrated Boundary Layer Ingesting Propulsion Systems for Turbo-Electric Aircraft
Authors: Chen Zhibo , Galbraith Marshall C. , Spakovszky Zoltán S. , Greitzer Edward M. , Sabnis Jayant S.
Published: September 2023

This paper presents conceptual design guidelines and results for a tail-integrated propulsion system for a turbo-electric civil transport aircraft with boundary layer ingestion (BLI). The aerodynamic performance goal is separation-free and shock-free operation at cruise with fuel burn reduction, compared with a baseline conventional aircraft for the same mission. The assessment of BLI benefits is based on calculations using CFD and TASOPT software, both to characterize the design challenges and to establish the physical mechanisms for resolving these challenges. The guidelines include a “horseshoe” inlet to accept the non-uniform flow without incurring separation, a nacelle profile similar to supercritical airfoils to reduce shock strength, and an annular nozzle to eliminate flow separation between tail-BLI propulsors. The conceptual design has nine BLI propulsors with electric fans on an axisymmetric tail of a single-aisle aircraft. The fans are powered by twin underwing turbofans. The estimated benefit of the tail-BLI, twin underwing turbofan aircraft is 10.4% in Payload-Range Fuel Consumption (PRFC) at a cruise Mach number of 0.8, compared to a baseline twin underwing turbofan configuration. Sensitivity studies further show that a 1% increase in installed (i.e. with BLI) fan isentropic efficiency translates to 0.8% rise in PRFC benefit.
Validation of Filtered Rayleigh Scattering Optical Rake Measurement Techniques in Turbomachinery Applications and Boundary Layers
Authors: Powers Sean W. , Byun Gwibo , Lowe K. Todd
Published: September 2023

Filtered Rayleigh scattering (FRS) is a non-intrusive, laser-based optical technique for measuring 3-component velocity, static temperature, and static density with high spatial resolution and low uncertainty. FRS can be used to derive total values as well as turbomachinery efficiencies. The Virginia Tech team has been developing this seedless technique for simultaneous planar (or line) measurements to overcome the limitations associated with seed-based laser measurement techniques such as laser Doppler velocimetry (LDV), particle image velocimetry (PIV), and Doppler global velocimetry (DGV) as well as limitations with physical probe rakes such as blockage and wake production. This technique is especially attractive in flow cases or environments where the aforementioned seed-based laser measurement techniques are limited or not possible. A combination of specially designed boundary layer total pressure probe rake measurements, FRS optical rake measurements, and computational fluid dynamics (CFD) results in the inlet of a Honeywell TFE731-2 turbofan are presented. Results show that all three techniques (FRS, probe, and CFD) match within approximately 2% root-mean-square error (RMSE). Inlet efficiency was derived and found to be within 2.3% difference for all three techniques.
Performance Assessments of a Novel Oxy-Fuel CO2 Cycle
Authors: Sammak Majed , Thanganadar Dhinesh , Dawood Alaaeldin , Suleiman Baha , Kulkarni Parag
Published: September 2023

This paper presents a novel way of improving CO2 intensity simple cycle gas turbines. We present a novel combined cycle that consists of an integrated semi-closed oxy-fuel gas turbine topping cycle and a sCO2 bottoming cycle. This sCO2 bottoming cycle offers compactness, operation without water or steam, and improves overall cycle performance. The semi-closed oxy fuel gas turbine working fluids are mainly CO2 and water making it feasible to separate CO2 by condensing water vapor. Also, since O2 is used as an oxidizer instead of air in the combustion, NOx emissions are almost zero.

Here we analyze a generic mid-sized oxy-fuel gas turbine cycle. The air separation unit and the CO2 compression were also modeled, and their parasitic loads included in the overall performance.

We further studied three sCO2 bottoming cycle configurations for optimizing the oxy-fuel gas turbine heat recovery. The analyzed sCO2 cycle configurations were simple sCO2, cascade sCO2 and advanced sCO2 cycle.

This paper also studies the oxy-fuel gas turbine integration with sCO2 at different gas turbine pressure ratios varying from 13 to 55 with a turbine inlet temperature of 1500°C.

The advanced sCO2 output was almost 16% higher than simple sCO2 configuration. The overall cycle efficiency for advanced sCO2 was around 10% higher than simple sCO2 configuration in all studied pressure ratios. The study also shows that the overall cycle output and efficiency were almost flat at pressure ratio above 35. The overall cycle output for advanced sCO2 was 110 MW and the overall efficiency was 45.7% at pressure ratio 35.

Furthermore, the study includes a sensitivity study on the advanced sCO2 at pressure ratio 35 and different cooling ambient temperatures. Here we show that the advanced sCO2 cycle output dropped by 19% when the ambient temperature increased from 20°C to 45°C.

The advanced CO2 cycle configuration has shown to be an interesting decarbonization solution for simple cycle gas turbines, more specifically when operating in remote locations with limited access to water or steam.

The paper is based on granted GE patent WO/2023/009161.
Numerical Simulation of Turbulent Premixed Flames Using Thickened Flame Model
Authors: Xia Yu , Newale Ashish , Yadav Rakesh , Verma Ishan , Bessette Didier
Published: September 2023

This work numerically investigates the application of a Thickened Flame Model (TFM) for a premixed methane/air Bunsen flame (Chen F3 flame), using Large Eddy Simulation (LES) for turbulence and Finite-Rate Chemistry (FRC) for combustion. Due to a premixed flame front usually being very thin, a very fine mesh is required to resolve the flame structure if using LES/FRC. The TFM model has therefore been utilized to artificially increase the flame thickness without changing the flame speed, allowing the flame simulation on much coarser meshes. However, the thickening of a flame also reduces the capability of turbulent eddies to wrinkle the flame surface, leading to an underpredicted heat release rate. Efficiency functions have therefore been proposed for TFM to compensate for the reduced flame surface area and the lowered heat release rate. The state-of-the-art efficiency functions require an accurate estimation of the velocity fluctuations at the test filter scale that corresponds to the thickened flame thickness. This work compares different TFM efficiency functions and velocity fluctuation models for the Chen F3 flame, and validates the predicted flow variables against experimental data. The mesh resolution and numerical schemes have been carefully selected, offering a workflow for TFM simulations. The impacts of reaction mechanisms and chemistry acceleration tools, e.g., Dynamic Mechanism Reduction (DMR), on the solution accuracy and computational costs of the present LES/FRC simulations have also been evaluated.
Field Performance of an Innovative AMB-Supported Turboexpander-Generator for Natural Gas Pressure Letdown
Authors: Liu Jeremy , Najeeb Ovais , Hawkins Larry , Khatri Rasish
Published: September 2023

This paper is a follow up to GT2022-82293, which discusses the design validation of an innovative turboexpander-generator (TEG) used for natural gas pressure letdown (PLD). This paper presents the field performance data of the 280kW machine and compares it to predictions. The TEG has a flanged housing that is directly mounted on a pipeline. The high-speed motor is supported by active magnetic bearings (AMB) in the hydrocarbon environment without lubrication. The paper discusses power performance of the impeller and compares it to the power prediction from a mean line aerodynamic analysis presented previously. Additionally, this paper compares magnetic bearing dynamic controls and transfer functions measured in air to those with gas flow in the pipeline; the effect of gas flow on the closed-loop dynamics is discussed. The authors review the thrust balancing design and the axial control current as a function of gas flow. The magnetic current is linearly related to load, and thus gives a good approximation of aerodynamic load vs flow. This paper also presents the results of a non-linear auxiliary back-up bearing high-speed rotor drop simulation and compares it to measured rotor drop data. The drop testing was conducted as part of the design verification of the prototype unit, and the results are discussed in depth in GT2022-82293.
Axial Compressor Map Generation Leveraging Autonomous Self-Training Artificial Intelligence. Phase 2
Authors: Burlaka Maksym , Podlech Sascha , Moroz Leonid
Published: September 2023

This paper discusses a study performed by SoftInWay as part of a Phase II SBIR project funded by NASA.

In contrast with the Phase I project (published in paper GTP-22-1328 [1]) where three discrete compressors were considered, the Phase II study was focused on addressing the problem of axial compressor long development time and cost with the use of AI models capable of predicting the geometry and performance of various multi-stage axial compressors with multiple variable vanes. The applicability of the AI models to various compressors enables the opportunity to avoid iterations between engine cycle analysis and compressor design.

In this paper, automated compressor design and performance generation workflows are described. The approach for autonomous selection of the architectures and hyperparameters of Machine Learning (ML) models is explained. The uncertainty quantification techniques are considered. The developed ML-powered methods for compressor geometry prediction are discussed. The ML models’ accuracy values and representations of typical geometry and performance predictions are given. The utilization of the ML models in engine cycle analysis is discussed.
Guidelines for the Aerodynamic Design of sCO2 Centrifugal Compressor Stages
Authors: Romei Alessandro , Gaetani Paolo , Persico Giacomo
Published: September 2023

This paper explores the viability of established criteria to design centrifugal compressor stages that operate CO2 close to the critical point. The work is split into two complementary studies. At first, several stage configurations are generated by varying characteristic design parameters, such as the inlet and outlet flow coefficient, work coefficient, and stage Mach number. Then, three selected configurations are optimized with a surrogate-assisted evolutionary strategy to refine specific geometrical parameters, which control the meridional shape and splitter location. The stage aerodynamics and performance are assessed with a validated RANS solver based on the homogeneous equilibrium assumption for the two-phase mixture.

One of the key findings of the parametric studies is that designing a stage with a flow coefficient smaller than that suggested by design practices prevents the occurrence of two-phase flows. The onset of a secondary phase at the impeller intake alters the fluid compressibility, producing density gradients across saturated condition that can cause flow separation. Such separation occurs for liquid-like CO2 but not for vapor-like CO2, implying that consolidated design rules can apply to the latter case notwithstanding the presence of condensing flows.

Shape optimizations reveal that modest efficiency improvements can be gained by changing the meridional channel and splitter location. Moreover, the optimization problem is highly multi-modal, as more than 30 different geometries can yield equivalent design efficiency. As a side effect of the optimization, the rangeability is significantly modified. Specifically, increasing the inlet slope angle of the shroud contour extends the operating range at high flow rates but reduces it at low flow rates. Therefore, this geometrical parameter can be controlled to adjust the stage rangeability without compromising design efficiency.
Direct Numerical Simulation of an HPT Stage: Unsteady Boundary Layer Transition and the Resulting Flow Structures
Authors: Wang Taiyang , Zhao Yaomin , Leggett John , Sandberg Richard D.
Published: September 2023

In the present study, we investigate the unsteady boundary layer transition based on the direct numerical simulation (DNS) database of a high-pressure turbine (HPT) stage (Zhao and Sandberg, GT2021-58995), focusing on the transition mechanisms on the rotor blade, which are affected by the incoming periodic wakes and also by the background free-stream turbulence (FST) introduced at the inlet. Based on the fully-resolved DNS flow fields, we are able to provide detailed analysis of the flow structures responsible for the transition, and two distinctive paths to laminar-turbulent transition have been identified. The first path is the typical bypass transition via the instability of Klebanoff streaks, which happens when the transition region is not directly affected by the wake. It is noted that the suction-side boundary layer is disturbed at the leading edge, resulting in the formation of streamwise streaks. These streaky structures endure varicose instability in the region with adverse pressure-gradient (APG), then quickly break down into turbulent spots, which then evolves into fully turbulence. The other transition path is a consequence of the direct interaction between the wake structures and the blade boundary layer, when the wake apex starts to affect the transitional region. To be specific, the wake structures seem to directly interact with the separation bubble in the APG region, causing sudden break down into turbulence. The turbulent boundary layer induced by the periodic wake are usually followed by a calmed region as the wake travels away from the passage. It is also observed that the recovery to a calmed region can be impacted by the FST, as the calmed region in case with no FST is much longer compared to cases with stronger FST.
A Superposition Technique for Predicting Overall Effectiveness With Multiple Sources of Individually Characterized Internal and External Coolant Flows
Authors: Fuqua Matthew N. , Rutledge James L.
Published: September 2023

High performance gas turbine engines rely on intricate cooling schemes to protect turbine components from the high temperature freestream gas. Determining the optimal placement of film cooling holes in optimal locations while remaining mindful of the consumption of precious coolant air is therefore an interesting design challenge. For several decades a method of superposition has been in use that provides a reasonable prediction of the adiabatic effectiveness in a region influenced by multiple rows of film cooling holes acting together if the adiabatic effectiveness distributions resulting from individual rows are already known. This classical superposition technique has been used with success to at least provide a first cut at determining where coolant holes might be placed on turbine components. One of the shortcomings of the method is that it strictly applies only to prediction of adiabatic effectiveness which is indicative of the adiabatic wall temperature, not the actual surface temperature of the turbine component. Indeed, the overall effectiveness, which is indicative of the actual surface temperature is somewhat more complicated as it is influenced not only by the external cooling, but also internal cooling. In the present work, a method of superposition of overall effectiveness data is proposed, thereby allowing prediction of the actual surface temperature distribution on a component. Experimental results show that it is possible to use knowledge of the overall effectiveness distributions resulting from individual internal cooling and associated film cooling holes acting alone to determine how they are likely going to act when combined. This technique shows promise for a turbine designer to use superposition for actual surface temperature prediction, not just adiabatic wall temperature prediction and therefore higher quality initial cooling designs.
Integrated Aerodynamic and Mechanical Design of a Large-Scale Axial Turbine Operating With Supercritical Carbon Dioxide Mixtures
Authors: Abdeldayem Abdelrahman , Paggini Andrea , Diurno Tommaso , Orazi Claudio , White Martin , Ruggiero Marco , Sayma Abdulnaser
Published: September 2023

In this paper, the design of a large-scale axial turbine operating with supercritical carbon dioxide (sCO2) blended with sulfur dioxide (SO2) is presented considering aerodynamic and mechanical design aspects as well as the integration of the whole turbine assembly. The turbine is 130 MW, designed for a 100 MWe concentrated-solar power plant with turbine inlet conditions of 239.1 bar and 700 °C, total-to-static pressure ratio of 2.94 and mass-flow rate of 822 kg/s. The aerodynamic flow path, obtained in a previous study, is first summarised before the aerodynamic performance is evaluated using both steady-state and unsteady 3D numerical models to simulate the aerodynamic performance of the turbine. Whole-annulus unsteady simulations are performed for the last turbine stage and the exhaust section to assess the unsteady loads on the rotor due to downstream pressure field distortion and to assess aerodynamic losses of the diffuser and exhaust section. The potential low engine order excitation on the last rotor stage natural frequency modes due to downstream pressure distortion is assessed. The design of the turbine assembly is constrained by current manufacturing capabilities and the proposed working fluid properties. High-level flow-path design parameters, such as pitch diameter and number of stages, are established considering a trade-off between weight and footprint, turbine efficiency and rotordynamics. Rotordynamic stability is assessed considering the high fluid density related to cross coupling effects. Finally, shaft end sizing, cooling system design and the integration of dry gas seals are discussed.
Thrust Rebalance to Extend Engine Time On-Wing With Consideration of Engine Degradation and Creep Life Consumption
Authors: da Mota Chiavegatto Rafael , Li Yi-Guang
Published: September 2023

Over the years, airlines have consistently attempted to lower their operational costs and improve aircraft availability by applying various technologies. Engine maintenance expenses are one of the most substantial costs for aircraft operations, accounting for around 30% of overall aircraft operational costs. So, maximizing aircraft time between overhaul is crucial to lowering the costs. The engine time on-wing is often limited by the expiration of Life Limiting Parts, performance deterioration, maintenance schedule, etc.

This paper presents a novel method of rebalancing the thrust of engines of an aircraft to maximize the time between overhauls of the aircraft considering the performance degradation and creep life consumption of the engines. The method is applied to a model aircraft fitted with two model engines similar to GT90 115B to test the feasibility of the method with one engine degraded and the other engine undegraded. The obtained results demonstrate that for the aircraft flying between London and Toronto with 5,000 nominal flight cycles given to the engines, the time on-wing of the degraded engine could drop from 5,000 to 2,460 flight days due to its HP turbine degradation (1% efficiency degradation 3% flow capacity degradation), causing the same level of drop of time between overhauls of the aircraft. The time on-wing of the degraded engine could increase from 2,460 flight days without thrust rebalance to 3,410 flight days with thrust rebalance, i. e. around 38.6% potential improvement for the time between overhauls of the aircraft at the expenses of increased creep life consumption rate of the clean engine. The proposed method could be applied to other aircraft and engines.
Experimental Investigation of Synchronous Flow Induced Blade Vibrations on a Radial Turbine - Part 2: Influence of Different Inlet Guide Vane Configurations
Authors: Sasakaros Marios , Schafferus Markus , Wirsum Manfred , Zobel Arthur , Vogt Damian , Nakos Alex , Beirow Bernd
Published: September 2023

The occurrence of blade vibrations in radial turbines leads to limit cycle oscillations, which in time increase the risk of component failure due to high cycle fatigue. In this context, the precise determination of the resonance operating points and the estimation of the vibration magnitudes are essential for an accurate assessment of the service life of the turbocharger components. In radial turbines forced blade vibrations are primarily flow induced. These vibrations are produced by the non-uniform flow field in the circumferential direction which acts on the blades as a cyclic pressure fluctuation. Previous studies have identified the inlet guide vane (IGV) and the spiral turbine housing as the primary sources of the non-uniform flow field.

In the present study a thorough experimental investigation of the synchronous blade vibrations of a radial turbine is performed. First, the blade vibration modes were measured experimentally and calculated numerically for the determination of the speed ranges that need to be examined. Subsequently, the vibrations were captured with two redundant measurement systems during real turbocharger operation. Strain gauges were applied on certain blades while eight optical sensors were distributed on the circumference of the turbine shroud for the measurement of the blades tips deflection through a commercial tip-timing system.

In the first part, the blade vibrations caused by the “nominal” IGV are presented. Part 2 analyses the changes of the blade vibrations due to the application of two different IGVs. The first IGV has the same number of vanes as the “nominal” IGV. Nevertheless, it generates additional low engine order excitations by intentionally varying the distance between the vanes. Next, an IGV with a higher number of vanes is employed for the excitation at higher frequencies and thus of higher blade modes. Contrary to expectations, certain synchronous vibrations can be measured in the experiments of all IGVs. These cannot be attributed to the spiral turbine casing.
Modeling a Water-Cooled Printed Circuit Heat Exchanger Condensing CO2 for Use in sCO2 Cycle System Optimization Studies
Authors: Liese Eric , Pidaparti Sandeep
Published: September 2023

This work describes a one-dimensional model of a water-cooled printed circuit heat exchanger (PCHE) condensing CO2. The model is developed for use in cycle optimization studies (e.g., minimizing levelized cost of electricity) as either the main heat rejection cooler and/or a compressor intercooler for recompression closed Brayton supercritical CO2 power cycles. Sensitivity and case studies are used to illustrate the impact of important model parameters, and this includes allowing for independent variation of zig-zag channel wave angles on the CO2 and water side. Results show that for a given CO2 design pressure (and thus saturation temperature), the PCHE design inlet water temperature has a significant impact on the PCHE size. Results also demonstrate that if wave angles are the same on the CO2 and water side, the water side pressure drop will have more influence on determining the optimum PCHE mass than the CO2 side pressure drop. Reducing the water side wave angle to near straight channel flow offers a more compact design for a similar water side pressure drop (and pump power requirement). Cases are also shown for further increasing the compactness and how the PCHE mass is affected along with water pump power.
Nonlinear Response of the Rotor Supported by Gas Journal Bearings Considering Stationary and Rotating Herringbone Grooves
Authors: Kochurov Roman , Moroz Leonid , Martynenko Volodymyr
Published: September 2023

This paper presents an approach to determine the stability of the rotor in herringbone groove gas journal bearings (HGGJB) based on nonlinear transient analysis. The approach considers rotating (on a rotor) or stationary (on a bearing shell) grooves. The bearing gas film model is described by the Reynolds equations. The finite element (FE) method has been applied to obtain an accurate solution for the HGGJB design. The rotor model is discretized with Timoshenko beam finite elements.

A study on the stability of a rotary machine supported by HGGJBs is performed to investigate threshold rotating speeds for the cases of stationary and rotating grooves applying a nonlinear transient analysis procedure. As a result, the influence of rotating grooves on system stability improvement has been investigated. Additionally, the correspondence of the calculated results to the experimental data available in publications and the nonlinear effects presented on Waterfall plots are also discussed in the article.

The presented method is an extension of previously developed techniques that engineers can use for design and calculation purposes. The nonlinear approach allows accurate simulation of coupled rotor-HGGJB systems and has no limitation for designs with a small number of grooves, as the FE method is used for bearings discretization. The method allows the physical effects of rotating/stationary grooves to be accounted for.
Development of a Conduction-Free Total Temperature Probe Based on the Two-Wire Thermocouple Concept
Authors: Nares Alcala Roberto Felix , Bhatnagar Lakshya , Paniagua Guillermo
Published: September 2023

Thermocouple measurements suffer from errors due to several heat transfer effects. A dominant error source is conduction error due to a difference in the junction and support temperature. Correction for conduction is critical in both steady and transient temperature measurements. The effect of conduction is reduced by using a high length-to-diameter ratio of the wire, but this becomes unfeasible in high-speed flows due to structural limitations. This paper presents a new procedure to perform thermocouple measurement with unprecedented accuracy using a two-wire thermocouple probe.

Our novel numerical correction method necessitates two temperature readings from two different thermocouple diameters. The temperature values are different because the conduction error is a function of their length-diameter ratio and material properties. The two thermocouple readings combined with Conjugate Heat Transfer Simulations (CHT) are used to correct the temperature readings and deliver the actual temperature of the flow free of conduction error. The Conjugate Heat Transfer simulations are run at different temperature boundary conditions and flow Reynolds numbers. This method is generalizable and can correct conduction errors within 0.1K. The paper includes a comprehensive uncertainty quantification approach based on Monte Carlo simulations. This correction was demonstrated experimentally to measure the inlet temperature of a turbine test rig compared against a standard one-wire thermocouple probe, and the uncertainty of the method was quantified.
Validation and Assessment of a Hybrid VOF-Lagrangian Numerical Methodology for Turbulent Liquid Fuel Jets in High-Speed Crossflow
Authors: Zghal Malika , Gauthier Pierre , Sun Xiaoxiao , Wijesinghe Charith , Sethi Vishal
Published: September 2023

For gas turbine combustors using liquid fuel injectors, introducing the spray into crossflowing air to achieve superior fuel-air mixing characteristics can improve performance and reduce emissions. Robust numerical design tools are needed to accelerate the development of low-emissions technologies. CFD models are used to assess the design, performance, and emissions of novel combustion systems. Atomization modelling is often facilitated by using the Lagrangian approach with breakup models rather than the more complex and computationally expensive higher-fidelity Volume-of-Fluid (VOF) approach. However, breakup models used in state-of-the-art CFD rely on empirical constants that have not yet been fully calibrated for jets in crossflow or for representative gas turbine conditions.

Coupling the Lagrangian and VOF approaches could deliver a better compromise between accuracy and computational cost. Among the few studies conducted on the VOF-Lagrangian approach for jets in crossflow, validation was often limited to the near-field spray trajectory under low Weber numbers using either non-turbulent jets or water at ambient pressure. The predictive capabilities in the far-field region were only validated using deterministic breakup models and for non-turbulent jets under low pressure conditions.

This study proposes and validates a novel numerical methodology for coupling the Lagrangian and VOF approaches using a Stochastic Secondary Droplet (SSD) breakup model with Adaptive Mesh Refinements (AMR) for turbulent liquid fuel jets in high-speed crossflow at more representative conditions. The predictions within both near and far-field breakup regions were validated using experimental datasets at high pressures (1–8 bar), Weber numbers (720–1172) and momentum flux ratios (6–33). The predictive capabilities and computational cost were also compared to the Lagrangian approach used with LES and used with an unsteady RANS numerical methodology previously developed and validated by the authors. The effects of different VOF-Lagrangian transition criteria on the computational cost were also assessed and recommendations have been provided for further improvements. The overall predictive capabilities of LES were significantly improved by the novel hybrid methodology proposed by the authors. Although it tends to underpredict the spray trajectory and Sauter Mean Diameter (SMD), it better captures the SMD in the wake region of the jet and the overall droplet velocities compared to the URANS methodology.
Investigation of High-Pressure Ignition Phenomena of CO2-Diluted Syngas in Shock Tubes
Authors: Mohr Darryl J. , Cooper Sean P. , Hay Matthew K. , Kulatilaka Waruna D. , Petersen Eric L.
Published: September 2023

With the rise in popularity of syngas comes the need to better understand the chemistry and combustion phenomena that occur during its use in applications such as the Allam-Fetvedt cycle that utilizes supercritical-CO2 (sCO2) as a working fluid. Several recent studies have shown significant model discrepancies in ignition delay time (IDT) data of syngas diluted in CO2 from shock-tube facilities. However, undesirable inhomogeneous ignition may occur at high pressures behind reflected shock waves in a shock tube. Understanding these undesirable events and when they arise during CO2-diluted syngas combustion is crucial to produce data for chemical mechanism refinement. To allow for imaging studies of these ignition and combustion events, a new addition has been made to the High-Pressure Shock Tube facility at the TEES Turbomachinery Laboratory at Texas A&M University. This paper presents the findings from that facility during the ignition and combustion of CO2-diluted syngas from reflected-shock ignition experiments. Pressures from 12 to 43 atm were studied in a 0.05 H2 + 0.05 O2 + 0.05 CO + 0.85 CO2 blend. Results from high-speed OH* imaging through the endwall showed evidence of homogeneous ignition and combustion within a central core region, but with a clear delineation between the central core and a concentric band adjacent to the sidewall, likely due to reflected-shock bifurcation. Follow-on imaging experiments are suggested before a complete understanding of syngas-CO2 ignition at high pressures in shock tubes is obtained.
Combustion Analysis of a Can Combustor With CH4/NH3 Blended Fuels for a Micro Gas Turbine
Authors: Shih Hsin-Yi , Ho Sz-Pei , Cheng Cheng
Published: September 2023

Ammonia has been proposed as a hydrogen carrier and a potential alternative fuel to achieve low-carbon emissions. Due to its high ignition energy, limited flammable range, and low heating value compared to hydrogen and typical hydrocarbon fuels, it is challenging to sustain stable ammonia combustion. Blending ammonia with natural gas can increase the possibility of combustion applications. This work is to investigate the combustion performance of a micro gas turbine combustor with CH4/NH3 fuel blends. Results indicated the flame temperature declined with increasing NH3 mole fractions at constant fuel flow rates due to lower heating value of ammonia. To maintain the same power output with increasing NH3 contents, the mass flow rates of the fuel blends were raised, which pushed the flame downstream and resulted in severe temperature fluctuation at combustor exit. At higher NH3 fractions, the high-temperature regions shrank again because of lower residence time for any significant reactions. NOx emission was increased due to fuel-NOx production with NH3 addition. However, the non-monotonic trend of NO emission indicated a competition between thermal-NO and fuel-NO productions. Further considerations of flame stabilization and dilution strategy are essential for the implementation of the fuel blends in this micro gas turbine.
CFD Model and Design for Gas Turbine Inlet Plenum With EGR
Authors: Devi Ravindra , Lorusso Salvatore , Michelassi Vittorio , Scotti Del Greco Alberto
Published: September 2023

‘Exhaust Gas Recirculation’ (EGR) with a ‘Carbon Capture Unit’ (CCU) for an industrial gas turbine is one of the widely explored options towards minimizing the detrimental effect of greenhouse gases on the environment. System level studies of gas turbine combustion system conclude an acceptable EGR volume as high as 80%. Considering the large install base units versus new units, industry focus is on a retrofit solution. Introducing such a large percentage of exhaust gas in the intake system of a heavy-duty gas turbine without affecting the flow distortions at the compressor inlet is a challenge. In the current work, an existing intake system is modified to intake up to 50% exhaust gas. Various designs are evaluated using ANSYS CFX 2021R2, a commercial CFD code; CFD domain extends from air-intake region up to compressor ‘Inlet Guide Vane’ (IGV) leading edge, while including details such as filters and silencer. Filters are modeled as porous media. Mixing of exhaust gas and air is modeled using component mixture model; modeling considerations are elaborated. A retrofit arrangement is designed considering the effect of design features such as position, orientation, and cross section of the exhaust gas duct on the flow physics. CFD analysis results show that the flow distortions levels for total pressure, total temperature, and swirl are as good as the intake system without EGR duct. Compared to designs seen in the literature, the retrofit design is simpler to manufacture and maintain. Design is optimized using splitters to reduce footprint and metal weight. Robustness of the design is assessed for extreme air & gas temperatures, duct approach direction, inlet flow non-uniformity due to upstream duct bends and various EGR percentages.
Secondary Flow Patterns Through a Turbine Vane Frame
Authors: Graiff Mattia , Staggl Marian , Wakelam Christian , Laufer Anna-Lisa , Göttlich Emil
Published: September 2023

The Turbine Vane Frame (TVF) is an integrated component interposed between the High-Pressure Turbine (HPT) and the Low-Pressure Turbine (LPT). It carries structural loads, provides shrouded paths for oil and service lines, guides the flow in the transition from small HPT radius to large LPT radius, and imparts to the flow the level of swirl required by the first LPT stage. Integrating these requirements in a single component offers significant size and weight benefits; it poses however a significant challenge to the aerodynamic design. The TVF takes the form of an S-shaped annular duct with low aspect ratio turning vanes. The strong development of secondary flow within the TVF is therefore a matter of particular interest; the scope of this paper is to expand the understanding of secondary flow patterns with respect to the widely accepted models based on linear blade cascades. Numerical and experimental results are leveraged to obtain insights into the flow structures; a method to evaluate vortical structures from experimental data based on a modified version of the Q Criterion is introduced. Experiments are performed in the Sector Cascade rig at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz Unversity of Technology. Two TVF geometries with differing strut counts are furthermore compared.