bluuebunny/crossref_metadata_2025 huggingface dataset:
The Onset of Low Reynolds Number Separation in High-Lift High-Work LPT Passages
Authors: Marks Christopher R. , Fletcher Nathan , Donovan Molly , Clark John P.
Published: August 2024

Low Reynolds number conditions occur over portions of the operating envelope in the low-pressure turbine section of aircraft engines, leading to a reduction in efficiency due to laminar boundary layer separation. The resulting “Reynolds-lapse” can greatly influence the performance of high-lift high-work low-pressure turbine blades. While the mid-span Reynolds-lapse phenomena has attracted much attention in the literature, the focus of the current paper is on the evolution of separation across the blade span. Extensive experimental measurements were obtained in a low-speed linear cascade arrangement of low-pressure turbine research profiles. Two different high-lift (Zw = 1.78 and Zw = 1.88) high-work profiles were considered. Multiple planes of high-speed particle image velocimetry were acquired to study the development of separation across the span as flow conditions were varied through the Reynolds-lapse curve. In the case of the Zw = 1.78 airfoil, the suction surface boundary layer separation bubble size increases steadily and monotonically as Re is decreased to the lowest Reynolds number measured, Re = 15k. However, the Zw = 1.88 profile experiences a rapid onset of un-reattaching separation at the knee in the curve. A unique four camera composite velocimetry measurement of the suction surface flow was used to capture the progression in separation across the span. A difference in the onset of separation between the two blade profiles was observed. In one case, the separated flow region progressed from the endwall toward the mid-span; and in the other blade set, it progressed from the mid-span toward the endwall. The findings provide a new and deeper understanding of the separation development across the passage of high-lift high-work turbine blades at low Reynolds number.
Assessing the Environmental Impact of Aircraft / Engine Integration With Respect to Contrails
Authors: Ramsay Joseph , Tristanto Indi , Shahpar Shahrokh , John Alistair
Published: August 2024

In recent years, the radiative forcing of aircraft contrails and aircraft-induced contrail cirrus have been highlighted as a serious short-term climate impact of the aviation industry. Greater understanding of factors influencing contrail properties are required if routes to mitigation are to be explored. In the current work, a parametric turbofan powered aircraft model has been created to study the impact that aircraft design, in particular the interaction between the jet and wingtip vortex, can have on ice crystal formation, growth, and dynamics within a contrail. To investigate this, a contrail microphysics module has been developed and integrated within Rolls-Royce in-house Hydra CFD code. Three-dimensional Reynolds-Averaged Navier-Stokes simulations are conducted over the jet and early vortex regime, covering an area which is often simplified in most contrail modelling approaches. It is found that the position of the engine along the wing of an aircraft can impact the formation of the wingtip vortex, altering the contrail properties and distribution downstream of the aircraft. The effect of multi-engine architecture is also assessed and shown to influence the magnitude of exhaust entrainment into the vortex.
The Investigation of Inlet Condition Effect on the Surge Recovery Process of a S-CO2 Radial Compressor
Authors: Kim Gihyeon , Lee Jeong Ik
Published: August 2024

The supercritical carbon dioxide (S-CO2) Brayton cycle is a power conversion cycle that utilizes supercritical carbon dioxide as the working fluid. One of the main characteristics is that the compressor operates with inlet conditions close to the critical point. However, approximating the S-CO2 compressor as an ideal gas turbomachinery model is limited by the rapid change in fluid properties near the critical point. Additionally, unlike most air Brayton cycles, the S-CO2 Brayton cycle is designed as a closed loop. To study the surge recovery process of the S-CO2 compressor, this study utilized an integral test loop with a turbo-alternator-compressor equipped with active magnetic bearings. Surge recovery performance tests were conducted at various speeds to investigate the effects near the critical point. Surge recovery performance was observed by reducing the compressor mass flow rate to induce a surge and then restoring the flow rate. The compressor instability was classified into surge and stall on the basis of speed, and the change of compressor inlet conditions affected the surge recovery performance of the S-CO2 compressor. The experimental results propose modifying the Greitzer B parameter as a means of estimating surge and stall in S-CO2 compressors.
Aero-Engine Remaining Useful Life Prediction via Physics-Informed Self-Attention Encoder
Authors: Zhang Xuanwu , Lou Jiayue , Zhang Jifa , Zheng Yao , Xia Yifan
Published: August 2024

Prediction of aero-engine remaining useful life (RUL) is crucial for the aeronautic industrial. In recent years, the deep learning enhanced methods for the aero-engine RUL prediction has attracted more and more attention by the community. However, how to correctly process information, extract features and carry out feature fusion from cluttered sensors is still a challenging problem. In this paper, a hybrid framework containing a method of data reduction and feature extraction based on physics-informed self-attention encoder (PISAE) is proposed to predict the RUL of aero-engines. The self-attention mechanism is used to process the data. In the part of feature extraction, the encoder-decoder architecture is applied to reduce the data dimensions and extract the features. In the encoder section, data features are embedded in vectors of low dimensions. Then, a neural network based on the self-attention mechanism is constructed to make predictions of the RUL. Physical information is embedded into the training process. The proposed framework is experimentally evaluated on the Commercial Modular Aeronautical Propulsion System Simulation (C-MAPSS) dataset. Results show that the framework can effectively improve the prediction accuracy of the remaining service life by information processing and feature extraction. In addition, the proposed framework improves the interpretability in the process of data processing and feature extraction, and has high applicability in predictive maintenance.
A Data-Driven Method for Predicting the Overall Performance of a Three-Rotor Dual-Variable Cycle Engine
Authors: Yuan Qiyu , Qiu Tian , Qu Guixian , Liu Peng , Liu Chuankai , Ding Shuiting
Published: August 2024

In order to meet the high maneuverability and long-range design requirements of the new generation of aeroengines, variable cycle engines (VCEs) with variable geometry characteristics and multiple mode adjustments have become a mainstream research direction. A three-rotor dual-variable cycle engine (TDCE) configuration with both turbofan and turbojet modes is proposed for the 0–30 km, 0–5 Ma flight envelope. Based on an integrated aeroengine simulation platform (IASP), a comprehensive performance model of the variable cycle engine is established, and the engine characteristics under four modes, low-subsonic mode (M-Lsub), middle-supersonic mode (M-Msup), high-supersonic mode (M-Hsup), and top-supersonic mode (M-Tsup) are analyzed with various adjustment features. For this configuration, a surrogate model for predicting overall performance deviations is established using a radial basis function neural network to quantify the impact of design performance deviations of rotating components on the overall engine performance parameters. neural network. The overall engine prediction model based on the Radial Basis Function (RBF) neural network approach shows high accuracy with an R-squared value exceeding 0.85, according to the experimental results. This indicates that the model fits the test set well and allows for a rapid evaluation of the effect of component design on overall performance. The outcomes of the investigation can provide technical assistance in the design of the TDCE configuration and enhance the effectiveness of the collaborative design procedure for advanced aeroengines.
A Reduced Order Model Based on Aerodynamic Influence Coefficients for Aeroelastic Computations in Transonic Compressors
Authors: Casoni Marco , Klausmann Fabian , Benini Ernesto
Published: August 2024

Reliable and computationally affordable aeroelastic simulations of compressor blades are of capital relevance today, as modern turbomachinery for aircraft propulsion are expected to meet stricter goals on weight saving and fuel efficiency through slender and highly-loaded geometries with a reduced number of blades, that may ultimately lead to a higher flutter susceptibility. In this paper, an aeroelastic reduced order model (ROM) based on the aerodynamic influence coefficient (AIC) technique for flutter simulation in transonic compressor blades is adopted to compute the aerodynamic damping for two resonance conditions. The ROM is capable of performing flutter simulations in both an uncoupled and a coupled way. In the former, the motion of blades is imposed as a travelling wave vibration pattern, with constant amplitude, frequency and phase, and the exchanged work between the fluid and the blade is used to assess stability; in the latter, a structural and an aerodynamic subsystem are built for each blade, exchanging displacements and forces respectively at the blade surface in a time-marching model. The key point in model order reduction is the accurate representation of unsteady aerodynamic forces. To this purpose a training simulation is setup, which relates the displacement of a blade to the induced aerodynamic loads on the neighbouring ones, called aerodynamic influence coefficients. In the uncoupled model the unsteady pressure field on the blade surface is adopted as AIC, while in the coupled version the AIC are the modal aerodynamic forces, related to the motion of blades with system identification techniques. The ROM is applied to the TU-Darmstadt Open Test Rotor geometry, a representative case of modern transonic compressor designs. Two resonance conditions are selected, where the crossing between a natural frequency and the rotational speed allows the experimental measurement of aerodynamic damping of the selected mode at several mass flows through a blade tip-timing system. Validation of the CFD model is performed by computing the compressor map in steady conditions and comparing the data against experimental measurements. After that, the uncoupled ROM accuracy is assessed, by comparing the aerodynamic damping for the two resonances at different mass flows and IBPA to full order flutter simulations adopting Fourier transformation and harmonic balance methods. The coupled ROM is then setup and compared to experimental data on damping ratio at the same conditions. The results prove the accuracy of the developed ROM, as well as a consistent reduction in computational cost compared to full order calculations.
Novel Microturbine Engine Test Stand for Rapid Assessment of New Materials and Manufacturing Procedures
Authors: Krizak Troy , Scott-Emuakpor Onome , Johnson Philip , D’Souza Kiran
Published: August 2024

New materials and advanced manufacturing techniques are essential for creating more effective, efficient, and innovative turbomachinery systems. The current process for developing these new components has many lengthy and costly steps, which slows the adoption of new designs and materials. This work outlines a new, easy to assemble and operate microturbine engine test stand that will allow for rapid testing of new turbomachinery component prototypes, materials, and manufacturing techniques. The goal for this test stand is to allow for quick proof of concept testing that can then be used to determine if full system demonstrations of the new technologies are desirable. The engine test stand will be implemented to demonstrate the performance of the newly designed, manufactured, and/or novel material hardware and their effects on engine performance at design speeds. In addition, the test stand will be supplemented by computational analysis tools that reduce the risk of catastrophic events. Moreover, these tools will be able to accurately predict failure to assure safe demonstrations while still gathering essential performance information. Analyses include, but are not limited to, understanding stage efficiency, total engine efficiency, structural dynamic responses, and rotordynamic assessments. This work discusses the key characteristics of the equipment and some initial results demonstrating the effectiveness of the new testing facility.
NASA HECC Geometry and Performance Review Part 1: Validation of a Computational Model for the Vaneless Diffuser Configuration With As-Manufactured Impeller Geometry
Authors: Robles Vega Gregorio , Bosshart Alec J. , Ni Michael , Ni Ron-Ho , Harrison Herbert M. , Nguyen-Huynh Tammy
Published: August 2024

An investigation of the NASA High Efficiency Centrifugal Compressor (HECC) vaneless diffuser configuration was performed. This multipart investigation presents an extensive validation of the computational model against experimental data. The validated model was then used to explore the effects of geometric differences between the as-manufactured and design-intent impellers. Lastly, the validated model was used for comparison against an experimental tip clearance study.

Part I of the investigation focused on describing the HECC vaneless computational model and its validation against the experimental data published in GT2023-103128. To generate the model, a verification of the manufactured impeller was performed and was confirmed to match the impeller CAD. Section data from the impeller CAD, referred to as the As-Manufactured geometry, were used for development of the computational model. Steady RANS simulations utilizing the Wilcox K-Omega 98 turbulence model and a multiblock structured mesh were used to conduct a mesh convergence study. The resultant mesh was then used for simulations at both designspeed and off-design speed conditions. Due to the challenges and uncertainties regarding the HECC performance and geometry, the model was extensively validated for use in Parts 2 and 3 of the paper The simulations compared well to data in both 1D and 2D terms for the major performance metrics of efficiency, total pressure rise, and total temperature rise. Based on the observed results the model was deemed validated and was used in the latter two parts of the multipart investigation.
Impact of Turbine-Strut Clocking and Turbine Outlet Swirl on the Heat Transfer and Film Cooling in an Aggressive Turbine Center Frame
Authors: Jagerhofer Patrick R. , Glasenapp Tobias , Patzer Bastian , Göttlich Emil
Published: August 2024

This study focuses on the thermal impact of the clocking position of the high-pressure turbine (HPT) vanes with respect to the turbine center frame (TCF) struts and the thermal impact of the HPT outlet swirl. The TCF is a stationary duct equipped with non-turning airfoils (struts), and it connects the HPT to the low-pressure turbine (LPT). The heat transfer coefficient and the purge film cooling effectiveness are measured in an aggressive TCF for two turbine-strut clocking positions and two HPT outlet swirl levels. The measurements are carried out in a product-representative 1.5-stage HPT-TCF-LPT vane configuration under Mach-similarity. The unshrouded HPT is fully purged with four individually adjustable purge flows, and the film cooling effectiveness of these purge flows in the downstream TCF is investigated.

The biggest influence of turbine-strut clocking was found for the heat transfer coefficient on the struts. By clocking the HPT vanes by half a vane pitch from the thermally least to the most favourable position, a significant heat transfer reduction was achieved for both, the nominal and the increased HPT outlet swirl. Increasing the HPT outlet swirl increased the flow incidence of the TCF struts and affected the heat transfer along the struts significantly. On the TCF hub, the averaged heat transfer coefficient and the averaged purge film cooling effectiveness responded relatively robustly to all imposed operating point deviations with differences of less than 2%. However, the effects on the local heat transfer and film cooling distributions on the hub were more significant.
Design of a Multi-Purpose High-Speed Rotating Rig, for the Rapid Testing of Compressor, Turbine and Fan Single Stages
Authors: Harman Leon , Mahon Kristian , Lock Richard , Bradwell Thomas , Atkins Nick , Yasa Tolga , Taylor James
Published: August 2024

This paper summaries the design and analysis activities completed in the development of the new high-speed rotating rig for the National Centre for Propulsion and Power (NCPP) located at the Whittle Laboratory, University of Cambridge, UK. The test rig is intended to provide flexibility to work in multiple modes to test axial compressors, turbines, or fans. To facilitate this functionality, the rotating rig must be able to drive the test article via an electric motor or be driven by the oncoming airflow, with the motor acting as a generator. The primary objective of the test rig is to enable rapid testing of single stages over a range of test conditions, from a blade relative Mach number 0.5 up to 1.3 and from a Reynolds number based on chord from 80,000 up to 2,000,000.

This paper details five of the main design considerations which were pivotal in enabling the ability to test any configuration rapidly and at full engine conditions. First, the choice of the overall architecture to facilitate rapid access and strip down. Second, the design methodology for ensuring uniformity of flow distribution at the inlet to the test articles. Third, design of the rotatives and driveline so that it can withstand axial loading in both directions whilst remaining adequately sealed. Fourth, the detailed rotordynamic design which ensures the test articles can be operated over a wide range of speeds and sizes. Finally, a rapidly removeable containment solution to mitigate against blade-off or disc-burst failure modes.
A Surrogate Model Approach to Predict O&M Cost for Combined Cycle Power Plant
Authors: Choi Woosung , Webb Bobby M. , Noble David R.
Published: August 2024

For carbon-neutral 2050, the proportion of renewable energy is increasing, and the problem of power grid instability is emerging due to the load variability of renewable energy. For grid stabilization, the need for flexible operation of gas turbine combined cycle (GTCC) power plants that can handle peak loads are increasing. In GTCC power generation, O&M (Operation and Maintenance) cost is the next most important after fuel and initial investment cost, and it is necessary to predict O&M cost according to changes in the operating environment for efficient and stable operation of GTCC power plant. However, various uncertainties exist when estimating O&M costs because actual design information is limitedly disclosed due to maintenance contracts between operators and manufacturers, and it is difficult to obtain accurate variables according to the operating condition.

In this paper, the correlation was analyzed considering the uncertainty of the factors affecting the O&M cost of the GTCC power plant through sensitivity analysis, and the main factors were defined. In addition, a surrogate model was used that can quickly calculate fixed and variable costs according to changing operating scenarios such as shortening start-up time, enhancing ramp rate, or lower minimum load. Through the case study, short-term and long-term O&M costs can be estimated due to changes in the operating environment of the GTCC power plant currently being operated. In addition, long-term O&M costs for new power generation facilities such as hybrid GTCC (GT+ESS) can be estimated relatively easily and quickly, which can help establish long-term investment plans.
Development of a Modular Engine Performance Calculation Tool for Prediction of Conventional and Hybrid-Electric Aircraft Engines
Authors: Wiegand Marcus , Schuchard Lukas , Krüger Tony , Mailach Ronald
Published: August 2024

Reducing climate-damaging emissions is a key objective of today’s aviation industry. Suitable approaches include emission-optimized flight profiles and the use of hybrid-electric propulsion technologies. In order to quickly identify and quantify their potential, powerful 0D engine models are needed to calculate the performance of conventional thermal and hybrid-electric propulsion systems at the design point and in off-design conditions.

This paper presents the model Maple (“Modular Aircraft Engine Performance for Sustainable Aviation”) for such performance calculation, emission and mass estimation. Special emphasis is laid on a flexible, modular design, so that the framework can be extended by new configurations and additional components, e.g. electric subsystems or heat exchangers. Established turbojet, turbofan, and turboprop configurations as well as various (hybrid-)electric configurations are implemented. Validation against an established commercial reference shows deviations well below one percent. For the analysis along entire flight missions, off-design operating points are computed quasi-steadily depending on atmospheric boundary conditions and thrust requirements. The latter are determined using the open source tool OpenAP. Thereby, the influence of additional mass due to more sophisticated engine configurations is taken into account.

To illustrate the capabilities of the performance tool, it is used to compare and discuss the performance of a conventional turbofan engine and a parallel hybrid-electric engine by calculating two exemplary flight missions with two battery technology assumptions. The benefits and challenges of using hybrid-electric engines are highlighted. These include the need for careful matching of conventional and electric components, gas turbine retrofit, and advanced thermal management.

Overall, the strengths of the developed tool are demonstrated. The modular structure and easy adaptability are ideal for the efficient design and calculation of state-of-the-art and future aircraft engines. The tool allows estimating their impact on flight mission fuel consumption and emissions, and thus on the climate.
Design Strategy of Thrust Gas Bearings for Refrigerant Compressors Considering Effects of Centrifugal Force and Convective Inertia
Authors: Prabhakar Arvind , Kim Daejong
Published: August 2024

This paper studies and compares 3D thermo-hydrodynamic (THD) performance of rigid thrust gas bearings lubricated with R1234ze gas using Reynolds Equation and commercial computational fluid dynamics (CFD) software. The gas bearing consists of six pads operated in both hydrodynamic and hybrid modes at high ambient pressures typical to the bearing compartment of refrigerant compressors. The CFD simulations adopted an advanced turbulence model and Peng-Robinson real gas equation of state while the Reynolds Equation-based THD model adopted NIST Refprop for real gas model. Results from the two models are compared, and detailed observations on gas bearing performance are presented including load capacity, pressure profiles, streamlines, effect of convective inertia and Mach number, etc. Further, the effects of inlet dead volume (IDV) region in such modeling are included to capture complete detailed flow behaviors for the presented high-density refrigerant gas flows within such bearings.

The CFD results demonstrate that convective inertia increases load capacity significantly for refrigerant gases. Both models capture temperature drops around the orifice curtain area from isentropic expansion, but CFD predicts more accurate isentropic expansion not only in temperature drop but also in pressure drop. Furthermore, convective inertia effects are not substantial for air bearings at lower ambient boundary pressures but are still significant for refrigerants at low ambient boundary pressures. Another important feature captured from CFD is the possibility of sub-ambient pressure at certain inner and outer boundaries of the bearing due to high Mach numbers of the leakage flows, and resultant sub-ambient static pressures and lower load capacity when ambient pressure is too low. However, such sub-ambient pressure is not prominent in typical operating conditions of refrigerant gases.
Research on Film Cooling Characteristics and Mechanism of Longitudinal Corrugated Heat Shield in Afterburner
Authors: Fu Song , Liu Hai-yong , Wang Zi-wen , Bai Xiao-hui , Liu Cun-liang
Published: August 2024

Taking into consideration both the cooling performance of the afterburner and its effect on suppressing combustion oscillations, the longitudinally corrugated heat shield has found widespread application in the afterburner. This paper employs computational fluid dynamics (CFD) and experimental methods to elucidate the influence mechanisms of key parameters such as momentum ratio, open area, and non-dimensional amplitude on the film cooling effectiveness characteristics of the corrugated plate thermal insulation structure. The results indicate that with an increase in the momentum ratio, the effectiveness of gas film cooling rises, and downstream stabilization occurs with the accumulation of the gas film. However, when the momentum ratio exceeds a certain threshold and continues to increase, excessive local momentum downstream results in a decline in gas film cooling efficiency. Additionally, as the non-dimensional amplitude increases, there is a decrease in gas film cooling efficiency, exacerbated by the increasing oscillations of corrugation. Furthermore, at a constant unit area cold air flow rate, the efficiency of gas film cooling increases with an increase in porosity.
A Wind Turbine Power Forecasting Method Based on MTGP Transfer Learning
Authors: Hui Huaiyu , Jiang Xiaomo , Chen Huize , Zhang Kexin
Published: August 2024

Wind turbine power forecasting plays an increasingly important role in the safety, reliability, and stability of both the power grid and the electricity market. Owing to the fluctuating and intermittent nature of the wind resource, it is very challenging to accurately forecast the wind power for either a newly constructed or existing farm. Most existing related research has not considered the data uncertainty and insufficiency in wind power forecasting so that the yielded model cannot produce the desirable result in practice. This paper presents a BDWPT-MTGP hybrid approach to accurately forecast the wind power in the scenario of data insufficiency. The Bayesian Discrete Wavelet Packet Transform (BDWPT) denoising approach is employed to improve wind power forecasting accuracy with data imperfection. A multi-task Gaussian process (MTGP) transfer learning model is developed for power forecasting of wind turbines based on limited operating data, thus addressing the data insufficiency issue. A MTGP model is constructed by leveraging available wind farm data alongside limited power data. The proposed BDWPT-MTGP hybrid method is validated by using the operating data acquired from real-world wind turbines. Numerical results demonstrate that the proposed methodology provides a promising tool for accurately forecasting wind power with data uncertainty and insufficiency.
Extension of the MULTALL Open Source Throughflow Code for the Improved Off – Design Calculations
Authors: Bilgiç Mustafa , Baran Özgür Uğraş , Aksel Mehmet Halûk
Published: August 2024

Throughflow calculations play an important role in the design stages of a turbomachinery. After the one-dimensional mean line calculations have been completed, the throughflow solver used in the design mode to perform the blade hub to shroud analysis can also be activated in the analysis mode to perform the off-design analysis. The original MULTALL code applies a uniform friction coefficient (Cf) to all wet surfaces in the turbomachinery passage and uses this Cf to calculate wall friction and hence loss. Although this approach is more physical than the source term approach, it does not capture certain physical phenomena in the turbomachinery passage. In the previous step of this study, the MULTALL code is modified to give a more realistic end wall loss distribution [18]. In this study, the code is further modified to perform off-design analysis and is given the capability to perform off-design analysis. Just as the constant Cf imposed in the design condition gives an unphysical loss distribution along the blade, it also gives inaccurate results for off-design. Since different angles of incidence and mass flows in off-design conditions will result in different loss distributions, the constant Cf must be adjusted according to the changing conditions. Considering a classical compressor or turbine performance curve, the angles of incidence change as the mass flow changes, and the losses increase according to the design condition. In addition, the shock losses also increase at high mass flow rates (“choked region” on the performance map). Therefore, to calculate an accurate loss prediction in off-design conditions, the Cf distribution used in the design condition should be modified due to diffusion effect, incidence and shock losses. In this paper we present parts of the MULTALL solver modified for off-design analysis and validate the results obtained with two compressor test cases. The results show the absolute improvement, especially towards the stall point.
Mass and Heat Exchange in Rotating Compressor Cavities With Variable Cob Separation
Authors: Nicholas Tom E. W. , Pernak Mikolaj J. , Lock Gary D. , Scobie James A. , Tang Hui
Published: August 2024

Next generation aeroengines will operate at ever-increasing pressure ratios with smaller cores, where the control of blade-tip clearances across the flight cycle is an emerging design challenge. Such clearances are affected by the thermal expansion of the compressor discs that hold the blades, where acute thermal stresses govern operating life. The cavities formed by co-rotating discs feature a heated shroud at high radius and cooler cobs at low radius. A three-dimensional, unsteady and unstable flow structure is induced by destabilising buoyancy forces. The radial distribution of disc temperature is driven by a conjugate heat transfer at Grashof numbers of order 1013. Such flows are further influenced by the heat and mass exchange with an axial through-flow of cooling air at low radius, where the interaction depends on the Rossby number and separation of the disc cobs.

This paper is the first to study the effect of cob separation ratio on mass and heat exchange for compressor cavities. A model is developed to predict the cavity-throughflow interaction, and disc and fluid-core temperatures. The judicious use of a physics-based methodology provides reliable, reduced-order solutions to the complex conjugate problem, thereby making it appropriate for practical engine thermo-mechanical design. The model is validated by detailed experimental measurements using the Bath Compressor Cavity Rig, where variable disc cob spacings were investigated over a range of engine-representative conditions. The unsteady pressure measurements collected in the frame of reference of the rotating discs reveal new insight into the fundamentally aperiodic nature of the flow structure. This new understanding of heat transfer informs an expedient reduced-order model and enables more efficient design of future high pressure-ratio aeroengines.
Enhancing Total Temperature Measurement Accuracy: Calibration Procedures and Novel Two-Wire Probes
Authors: Sánchez de la Rosa Diego , Paniagua Guillermo
Published: August 2024

Total Temperature measurement with thermocouple probes suffers from errors due to heat transfer effects. Two dominant sources of errors are convection and conduction between the thermocouple, the support, and the flow. These effects can be treated in two different categories: the velocity error, created by convection from the internal flow velocity in the probe shield, and the conduction error, involving heat transfer through the wire to the shield and the probe stem due to temperature differences between each component. This paper presents a robust approach to experimentally assess and reduce both errors.

An open jet test stand at the Purdue Experimental Turbine Aerothermal Laboratory is used to evaluate the effects of the velocity error at various Mach numbers. Infrared thermography measurements have been conducted to assess temperature gradients on the probe support during this calibration. With this information, it is possible to correct for conduction errors during the calibration and obtain a recovery factor that is solely dependent on upstream velocity. Recovery factor of 0.94 +/−0.05 for Mach 0.2 and 0.98 +/−0.005 for Mach 0.9 are obtained.

Progress has been made on a two-wire thermocouple approach to address conduction errors in the testing scenario, where IR thermography is not possible. The readings from two wires with different length-to-diameter ratios are used with a novel linear correction method to correct for the flow total temperature. Advances in the design and manufacturing of the probe are presented, facilitating faster design iterations and implementation, and providing full control over the calibration procedures. This method can correct conduction errors within 0.2 K for Mach 0.6.
Analysis of NH3 Powered Turbofan Engine With sCO2 Waste Heat Recovery System
Authors: Andress William , Paniagua Guillermo , Vesely Ladislav , Otto Marcel , Kapat Jayanta
Published: August 2024

In the search for alternative aviation fuels, ammonia shows much promise. The higher density and boiling point of ammonia compared to hydrogen could mean ammonia could be used without a dramatic rethinking of aircraft architecture. Instead, the possibility exists that current aircraft and engines could be retrofitted to use ammonia instead of traditional jet fuel. This paper aims to address the engine aspect of such a retrofit. The open-source Toolbox for Modeling and Analysis of Thermodynamic Systems (T-MATS) is modified to allow for the modeling of ammonia fueled engines and the addition of heat exchangers and other technologies. A thermodynamic cycle model of a baseline ammonia engine is created retaining the turbomachinery maps, duct sizes, nozzle areas, and bleed flow rates from a kerosene engine. This engine is then modified by adding heat exchangers and a supercritical CO2 waste heat recovery (WHR) cycle to produce power for the engine and aid in the preheating of the ammonia. Preliminary analysis is performed to determine the ideal location of heat exchangers to benefit cycle efficiency. This analysis suggests that using the ammonia as a heat sink to intercool and recuperate the engine allows for significant improvements over baseline performance. From there, optimization of the geometry of the added heat exchangers is performed to limit heat exchanger size and minimize engine fuel consumption at cruise. The addition of these heat exchangers allows for a reduction in fuel burn of 3%–9% over the baseline engine. Additionally, the WHR cycle can produce the required 250 horsepower (186 kW) of electrical power for the aircraft and the ammonia temperature is increased from 420°R to over 1400°R (233K to 778K). Investigating the results of the optimization shows that making more substantial changes to engines could allow for further improvements to engine performance past that of a retrofit.
Off-Design Heat Exchanger Modelling for Transcritical CO2 Heat Pump Cycles
Authors: Wolscht Leonhard , Podeur Maxime , Adams Martin , Jacquemoud Emmanuel
Published: August 2024

In previous publications, MAN Energy Solutions discussed the steady-state [1], dynamic modelling and validation of large-scale transcritical CO2 heat pump cycles [2]. The current study focuses on the off-design modelling of heat exchangers and presents new models with the aim of capturing the performance of a sea water heat pump subject to large variation in operating and boundary conditions following seasonal variations.

This study shows the impact of novel heat exchanger models on overall heat pump performance throughout its operating envelope as well as on the boundary of the latter restricted by components limitation such as the motor envelope or compressor surge. This allows the identification of the most impactful heat exchanger performance parameters on the overall cycle performance, namely the evaporator and gas cooler HTC. Both steady and unsteady model predictions are validated against manufacturer data and show a relative difference below 1% and 3% for respectively the duty and pressure drop prediction, illustrating the capabilities of off-design models. Moreover, the dynamic modelling of a shell- and tube evaporator is presented and depicts the impact of heat source temperature variation on the evolution of the refrigerant level and its performance. All the above findings contribute to providing reliable and efficient heating and/or cooling services in a wide range of process conditions.
Verification of an Adjoint Code for FGM Combustion
Authors: Duranti Stefano , Jones Dominic , Zhang Yongzhe , Goldin Graham
Published: August 2024

The adjoint method efficiently computes the sensitivity of a global output objective function, such as a combustor outlet temperature uniformity or NOx emission, with respect to a large number of input design variables, such as the centroids of the wall boundary faces. This sensitivity gradient can be used in an optimization algorithm, in particular for shape or topology design to extremize the objective function. In this work, the adjoint model in Simcenter STAR-CCM+ is extended to the Flamelet Generated Manifold (FGM) combustion model. The discrete adjoint is solved by differentiating the linearized flow solver using Automatic Differentiation, transposing these operations, and executing the code in the reverse order. Since the code is complex with a large number of interacting models, a careful verification is required to ensure that the important parts of the code are differentiated properly, and the order of code execution is correct. A global sensitivity for a simple mixing layer flame is compared for forward derivatives (tangent mode), reverse derivatives (adjoint mode) and finite differences. Despite vastly different code path execution for adjoint, tangent and finite-difference, the close agreement of various objective function calculations verifies the correct implementation of the adjoint and tangent code.
Mapping Temperatures on Turbocharger Bearing Cartridge Assemblies Using Thermal History Paints
Authors: Hickey Jim , Kaspschik Nestor , Albrecht Eva , Fischer Christian , Wendel Oliver , Rode Martin , Araguas Rodriguez Silvia , Karagiannopoulos Solon , Feist Jörg
Published: August 2024

In this study, temperatures were mapped on four off turbocharger bearing cartridges, each subject to four different gas-stand tests using Thermal History Paints (THPs). The temperature maps were used to inform initial axial end play settings (and resulting mounted end play) for proper turbocharger performance. THPs are ceramic-derived sensor coatings doped with a lanthanide ion, giving the THP luminescent properties. Exposure to temperatures permanently alters the THP’s luminescent properties. Therefore, by optically probing the THP across the painted bearing cartridge surfaces to trigger its luminescence, historic maximum exposure temperatures maps were evaluated.

Each gas stand test was devised to test each cartridge to the most severe temperature conditions the turbocharger was expected to be exposed to, including one with a heat-soak without water cooling. The tests lasted at least 15 minutes to ensure the cartridge assemblies were fully heat-soaked. THP measurements were taken across pre-determined surfaces of the inner rings and outer ring of all cartridge assemblies. The THP measurement point pitch was 1 mm, providing a unique insight into the historic thermal maps across the cartridge surfaces.

The THP temperature mapping had excellent coverage across each cartridge assembly surface. Some THP detachment occurred, especially on the edges of the inner and outer rings and close to the bearing racers. The THP was especially manufactured for this project to measure lower temperatures (< 200 °C), but this was at the expense of THP durability and adherence.

As expected from the thermal profile of a turbocharger, the turbine-side inner ring was the hottest for all cartridge assemblies. The compressor side inner ring, and outer ring were the coolest. Notably, the outer ring temperature gradient was low, providing confidence in the overall cooling conditions of the cartridge assemblies. The end play of the turbocharger is driven more by the thermal expansion of the outer ring rather than the inner ring. As such, knowledge that it remains cool throughout the test helps inform setting the most appropriate axial end-play clearance.
Partitioned Coupled Heat Transfer Fluid-Structure Interaction for Transient and Steady State Analysis of Aero Engines Applications
Authors: Israel Ute , Cottier Francois , Gier Jochen
Published: August 2024

Designing future gas turbines needs sufficiently accurate methods for determining the temperature distribution parts under high mechanical and thermal loads. Furthermore, to calibrate analytical thermal models with engine test data, which is an important step in the development process, strong engineering judgement and experience is required, and generally an extensive iterative process is needed to reach the predefined matching quality. Coupled simulations can significantly improve quality of conjugate heat transfer calculations and reduce the thermal matching effort. A method for strong aero-thermal coupling for specific demands of aero engine heat transfer is presented. It is based on a partitioned approach designed to integrate standard processes, methods and tools (like mapping methods and solvers) for industrial applications. An efficient approach to take the interaction of the material with the convecting fluid into account is to embed stationary CFD analysis in a flight mission calculation. This enables much fewer steps than necessary for a monolithic coupling like CHT and therefore saves computational effort.

The presented multi-fidelity approach includes strong system coupling of 1D, 2D and 3D models.

A high pressure compressor of a real aero engine has been thermally investigated using the reported coupling method. CFD was used in the rotor drum cavity and standard thermal modeling with FEM for the solid parts combined with flow network/correlations for the low fidelity flow areas. Steady state calculations for high and low loading cases and a transient acceleration were performed. The results are compared with measurements via a calibrated standard thermal model.
Gaseous and Particulate Emissions of an Allison 250-C20B Turboshaft Engine Running on HEFA-SPK and its Jet A-1 Blends
Authors: Rabl Alexander , Rohkamp Marius , Saraji-Bozorgzad Mohammad Reza , Helcig Christian , Sallinen Reetu , Vilja Jesse , Bendl Jan , Adam Thomas , Hupfer Andreas , Gümmer Volker
Published: August 2024

Aviation is widely recognized as a significant source of air pollutant emissions, encompassing gaseous products such as CO2, CO, NOx, and particulate matter (PM), especially in the form of soot. This study conducted comprehensive emission measurements on an Allison 250 C20B turboshaft engine to investigate sustainable aviation fuel (SAF) impact on emissions. Two conventional Jet A-1 fuel blends with 30% and 50% HEFA-SPK synthesized paraffinic kerosene derived from hydro-processed esters and fatty acids (HEFA-SPK) content together with 100% HEFA-SPK were tested regarding their emissions and compared against neat Jet A-1. The study’s primary focus was quantifying ultrafine particulate matter in terms of number and size. The selection of distinct engine power settings was based on the thrust ratios specified in the International Civil Aviation Organization’s (ICAO) Landing and Take-off-cycle (LTO-cycle). PM emissions were characterized using multiple measurement techniques. These included the application of two distinct electrical mobility analyzers. An additional concentration particle counter (CPC) was utilized to underscore the reliability of the findings. A standard FTIR/O2/FID system was used to assess gaseous emissions, a well-established method for measuring fundamental combustion products such as CO2, CO, unburned hydrocarbons (UHC’s) and NOx. The particle measurement systems revealed a decrease in both the number and size of particles with increasing HEFA-SPK content. This decrease in particle number appeared linear for the 30% and 50% HEFA-SPK blends and was more pronounced for the 100% HEFA-SPK. Furthermore, a more substantial reduction in PM emissions, reaching up to 82%, was observed at lower load settings, such as Ground Idle (GI), compared to higher load settings like Take-Off (TO), where the reduction was up to 40%. Results of the gaseous emissions are also presented in the study.
Modeling Combustor Turbine Interaction Using Efficient Joint Simulation Strategy
Authors: Verma Ishan , Zori Laith , Basani Jaydeep , Kamrath Benjamin , Brandt Dustin
Published: August 2024

Computational modeling of hot streak migration in gas turbines is challenging due to multi-scale physics and dynamic interaction between the combustor and the high-pressure turbine (HPT) first stage. The standard practice for modeling such interactions has been performing a 1-way transfer of boundary conditions from the combustor exit to the turbine inlet. This approach is simple but not ideal for capturing the intricate flow perturbations that travel across the components and, hence, not suitable for accurately predicting hot streak migration. An improvement on the standard practice is to conduct separate component simulations and use a 2-way boundary-condition exchange process, which we call co-simulation. In co-simulations, the information between the combustor and the HPT is exchanged in an iterative loop until convergence is achieved. The co-simulations are performed on the hot section of a Honeywell turbofan engine using Stress Blended Eddy Simulation (SBES) in the reversed flow annular combustor and Reynolds Averaged Navier Strokes (RANS) in the HPT.

However, the most accurate combustor-turbine interactions are modeled using joint simulation in which the combustor and the HPT stage are in the same computational domain. Therefore, the joint simulation process excludes the need for any boundary condition exchange. The SBES turbulence model, Flamelet combustion model, and discrete phase-based spray model are applied to the entire domain. Inherent to joint simulations, the transient HPT calculations require the time scale to be that of HPT, which is generally one order of magnitude lower than the combustor time-scale. As a result, joint simulations are computationally very costly (in most situations, prohibitive) compared to co-simulations. In this paper, the computational viability of joint simulations, as a better alternative to co-simulations, is explored using a mixing-plane interface in the HPT. Such an approach ameliorates the disparity in time-scale between the combustor and rotor, which is observed in calculations of joint simulations. As the calculations in joint simulations are performed at combustor time-scale, the overall process hence becomes computationally faster than co-simulations.

The hot streak migration in the HPT is modeled by using a separate simulation of the HPT with sliding mesh (advanced at rotor time-scale). The aero-thermal flow solution and hot-streak migration in the HPT stage are compared between the 1-way transfer, co-simulation, and joint simulation. The distribution of near-wall blade temperatures (instantaneous, period-averaged, maximum, and minimum) is analyzed.