bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-Averaged Aerodynamics of a High-Speed Low-Pressure Turbine Cascade With Cavity Purge Flow and Unsteady Wakes
Authors: Lopes Gustavo , Simonassi Loris , Lavagnoli Sergio
Published: September 2023

The time-averaged aerodynamics of a high-speed low-pressure turbine (LPT) cascade were investigated under the impact of unsteady wakes and purge flows. The tests were performed at an outlet Mach (M) and Reynolds numbers (Re) of 0.90 and 70k, respectively. Unsteady wakes were simulated by means of a spoked-wheel type wake generator (WG) and a reduced frequency of 0.95 was achieved. The development of a purge flow system to operate at low pressure levels is presented alongside guidelines for the operation of the circuit. The new purge system was commissioned in terms of its long-term stability and flow uniformity at the cascade inlet. The impact of varying purge flows from a cavity versus a flat endwall was assessed by means of static pressure measurements on the blade pressure side (PS) and suction side (SS) and traverses performed downstream with a miniaturized multi-hole probe. Differences in the secondary flow structures resultant from injecting purge flow into the flowfield are observed, namely the intensification of the trailing shed vortex (TSV) and passage vortex (PV) that is also displaced away from the endwall. An increase of the endwall losses occurs as the flat endwall was replaced with a cavity geometry and the cavity purge flow rate increases.
Multi-Objective Experimental Combustor Development Using Surrogate Model-Based Optimization
Authors: Reumschüssel Johann Moritz , von Saldern Jakob G. R. , Ćosić Bernhard , Paschereit Christian Oliver
Published: September 2023

The majority of premixed industrial gas turbine combustion systems features two or more separately controlled fuel lines. Every additional fuel line improves the operational flexibility but increases the complexity of the system. When designing such a system, the goals are low emission of various pollutants and avoiding lean blow out or extinction. Typically, these limitations become critical under different load conditions of the machines. Therefore, it is particularly challenging to develop combustors for stable and clean combustion over a wide operating range. In this study, we adopt the machine learning method Gaussian process regression for application to burner development, aiming to improve the process, which is often driven by a trial-and-error approach. To do so, a special pilot unit is installed into a full-scale industrial swirl combustor. The pilot features 61 positions of fuel injection, each of which is equipped with an individual valve, allowing to modify the fuel-air mixture close to the flame root in various degrees. In fully automatized atmospheric tests, we use the pilot system to train two surrogate models for different design objectives of the combustor, relevant for full load and part load operation, respectively. Once trained, the models allow for prediction for any possible injection scheme. In combination they can be used to identify pilot injector configurations with an improved operation range in terms of low NOx emissions and part load stability. The adopted multi-model approach enables combustor design specifically for high operational flexibility of gas turbines, but can also be extended to other similar industrial development processes.
Integrated Hybrid Air Foil-Magnetic Thrust Bearing (i-HFMTB) Part I: Preliminary Experimental Test for Rotordynamic Parameter Identification and Behavior With PD Control
Authors: Ha Yunseok , Kim Jungwan , Lee Yongbok
Published: September 2023

The selection of a thrust bearing for the operational reliability of turbomachinery is very important because it supports axial loads and influences the lateral vibration caused by the thrust collar tilt. A type of integrated hybrid air foil-magnetic thrust bearing (i-HFMTB) is hereby proposed to overcome the limitations of the air foil thrust bearing (AFTB) and the active magnetic thrust bearing (AMTB). The AFTB is composed of four top foils and three bump strips. It is spot-welded on a non-magnetic Inconel X-750 (relative permeability ≈ 1) pad so that it does not affect the magnetic flux when combined with AMTB. A slot is made so that the pad can be coupled to the outer pole of the AMTB, and the nominal air gap does not increase in the axial direction because of the inserted pad. i-HFMTB is used to design a different area to compensate for the slotted area and the nominal air gap. Moreover, it is unaffected by the flux imbalance owing to flux density differences because of the design. In the experiments involving the i-HFMTB, the test apparatus is supported by an active magnetic journal bearing (AMJB) to evaluate its performance. A PD (proportional and differential) feedback control system was applied to the i-HFMTB, and a Bode plot was obtained using an external excitation signal to determine the efficacy of the design. An experimental percentage overshoot method was used to validate the theoretical dynamic coefficient of the i-HFMTB. In addition, the effect of reducing the lateral vibration through the i-HFMTB at the critical speed of the rotor was experimentally determined. The proposed i-HFMTB can effectively control the rotor system.
PSP and LES Investigation on the Impact of Trench Depth on Flat Plate Film Cooling Through Shaped Holes
Authors: Abdeh Hamed , Barigozzi Giovanna , Zamiri Ali , Taek Chung Jin
Published: September 2023

To increase film cooling effectiveness levels downstream of film cooling holes, trenches manufactured in the thermal barrier coating can be adopted. The performance of this solution depends on the trench geometrical characteristics, namely its depth and width. A LES based numerical study has been performed at Korea University to investigate the effects of trench configuration on the thermal protection, resulting in a 22% increase in cooling performance compared to the reference case without a trench. The present paper reports the results of an experimental investigation carried out at Bergamo University on a Plexiglass flat plate model with a set of three fan-shaped holes incorporated into an existing wind tunnel, replicating the numerical setup. PSP technique was used to measure the adiabatic film cooling effectiveness. Besides the standard shaped hole case, the best and worst trench configurations coming from a DoE approach have been examined at various coolant to mainstream blowing ratios M in the range between 0.5 and 3. Cases at M = 1.5 were used to cross check the prediction capability of the LES numerical simulation for the selected trenched cases. PSP and LES result to be in good agreement, also with literature data. The high depth/low width trench was shown to give improved performance for M larger than 1.
Experimental Test on Centrifugal Pump Handling Mining Slurries
Authors: Zanini Nicola , Suman Alessio , Pinelli Michele
Published: September 2023

Non-Newtonian fluids are involved in many industrial processes, for example in food and Oil and Gas applications. Drilling operations require massive employment of drilling fluids, such as mixtures of water and bentonite, to maintain a cooling and lubricating environment. Centrifugal pumps are usually employed instead of positive displacement pumps in these applications due to the greater flow rates that can be provided. The viscosity of a non-Newtonian fluid varies with the imposed stress and rheology, and consequently, pumping this type of fluid can lead to a considerable variation in the pump performance. Both the pump head and particularly efficiency are adversely affected, and the performance of small pumps is impaired to the greatest extent. Previous experimental works with bentonite slurries reported that detrimental effects arise at low flow rates. Since most of the manufacturers test their pumps only with water, the selection of the appropriate slurry pump may result very challenging. As a consequence, oversized pumps are commonly installed. In this work, a small centrifugal pump handling mixtures of water and bentonite was tested on an on-purpose test loop. Different solid concentrations were considered during tests. A critical analysis was conducted to relate the pump performance drops with the slurry’s rheological properties.
Progress on the Complete and Low-NOx Combustion of Eco-Fuels Using a Thermo-Acoustically-Driven, Hydrogen-Powered Pilot Stage
Authors: Paulitsch Nina , Giuliani Fabrice , Hofer Andrea , Hofer Johannes , Andracher Lukas
Published: September 2023

Thermo-acoustic forcing of premixed lean combustion of conventional, carbon-based fuels can increase — if well chosen — the mixing rate, energy density in the flame due to its deformation, and the combustion efficiency leading to reductions in CO and NOx emissions [GT2017-64429]. It was shown for instance that the flame appears more robust versus lean blowout when thermo-acoustically excited, while simultaneous improvements in the combustion performance take place.

The combustion of hydrogen is a key element of the energy transition. However, premixed hydrogen combustion is not trivial. In premixed burners, high hydrogen content tends to flashback, forms high amounts of thermal NOx and triggers combustion instabilities. To address these challenges the thermo-acoustic forcing was already applied on lean premixed hydrogen combustion in a previous study [GT2022-80886]. It could be shown that thermo-acoustic excitation can be a significant driver in terms of flame position and stabilization.

This follow-up paper reports on the progress on atmospheric combustion experiments performed with lean premixed hydrogen in the kW range using a pulsation device of type siren for thermo-acoustic forcing. A test case is presented, including robust hydrogen flame stabilization against flashback when thermo-acoustically excited via a siren. More exactly, the flame is forced to stabilize further away from the injection, and the drive effect is well-controlled and reproducible. Two experiments performed with hydrogen and with a blend of hydrogen and ammonia, respectively, show a significant decrease in NO emissions when thermo-acoustically excited at a certain frequency. The specifics of the two atmospheric test rigs used and a developed hydrogen fast premixer, as well as the sensing methods, are described. All experimental results are presented and discussed in detail. Furthermore, the early findings of staged combustion experiments with ammonia using the hydrogen-powered pilot stage are shown. This contribution ends with the projection of this principle for greater scales in the MW range.
LES of Hydrogen-Enriched Methane Flames in a Lean-Burn Combustor With Axial Air Injection
Authors: Ferrante Gioele , Doodeman Lennard , Rao Arvind Gangoli , Langella Ivan
Published: September 2023

Large eddy simulation (LES) paradigms are employed to analyse the internal flow field of a lean premixed swirl-stabilized combustor with axial air injection at both non-reacting and reacting conditions, for a methane and a methane-hydrogen fuel mixture. The thickened flame combustion model (TFM) with detailed chemical kinetic mechanism is employed to simulate the flow. An adaptive mesh strategy is used to maximise the mesh resolution in the flame and boundary layer regions. The numerical results for the methane flame are firstly validated against experimental velocity measurements obtained via particle image velocimetry (PIV). Subsequently the LES is employed to simulate hydrogen-enriched methane flames by keeping the same output power in the combustor, in order to obtain insights on the flow behaviour when hydrogen is added, in terms of flame stability and emissions. A POD analysis reveals the presence of a precessing vortex core (PVC) in both reacting and non-reacting conditions, and how this PVC is affected by the reactants mixture is discussed in the paper. Moreover, the flame is observed to propagate upstream in the jet core despite the use of axial air injection, although flashback is not observed. In terms of emissions, significant reduction in CO and NOx is observed when adding the hydrogen to the reactants mixture despite the higher flame speed, the reason for are discussed in the paper.
Empirical Loss Model Optimization for the Prediction of Centrifugal Compressor Off-Design Performance
Authors: Howard Jonathon , Knudsen Peter , Engeda Abraham
Published: September 2023

Certain critical process applications, such as sub-atmospheric re-compression of cryogenic helium gas supporting particle physics and other scientific research, require operating multi-stage centrifugal compressors over a wide operating range. Customarily, turbomachines are designed for a specified design condition, but in these applications it is essential that these machines behave stably at off-steady-state-design conditions due to actual processes conditions and requirements that are inherently transient. Predictive algorithms have been developed which adopt various empirical correlations that estimate individual losses, thus allowing the compressor performance to be estimated. Some of these algorithms require complete knowledge of the impeller geometry to enable performance estimation at varying process conditions. However, often such complete knowledge may not available for differing reasons, although basic dimensions and geometry information is obtainable. The objective of the present study is to examine the numerous loss correlations available in open literature and evaluate the effects of each proposed correlation on performance prediction accuracy, thereby permitting an accurate and robust method to predict compressor performance over a wide range of operation. This paper recommends a methodology and set of loss correlations to accurately predict the pressure ratio and isentropic efficiency of centrifugal compressors operating over a wide range of off-design conditions.
A Novel Multiaxial Strain-Life Approach for Nickel-Base Superalloys
Authors: Irmak Firat , O’Nora Nathan , Gordon Ali P.
Published: September 2023

Nickel-base superalloys (NBSAs) are a group of materials that are extensively used in high-temperature applications such as aero and industrial gas turbine applications. These alloys can endure high temperatures and stresses for extended periods, they also exhibit excellent fatigue life and corrosion-resistant properties. Multiaxial states of stress and strain are very common in engineered parts. Components such as blades, crankshafts, pressure vessels, welded joints, heavy construction equipment, and the like experience external loads in multiple axes. Multiaxial approaches have been introduced to give improved predictions of fatigue life under complex states compared to what can be attained with uniaxial methods alone. A novel multiaxial strain-based life approach is developed in this study. Coffin-Manson and Basquin equation is modified to include multiaxial strain range values. In this approach, all the modeling parameters are obtained from uniaxial low-cycle fatigue (LCF) experiments. Generic modeling parameters are provided to ease the material characterization process of newly developed NBSAs. These parameters are optimized by a MATLAB function to achieve accurate fit. The goal is to reduce number of complex and costly multiaxial fatigue experiments for the material characterization process of NBSAs. A yield criterion, developed by the authors, is utilized to obtain effective strain values and to capture multiaxial state of strain. This criterion is a modified version of Hill’s yield approach. Certain parameters are added to include anisotropy of NBSA to the well-known Hill’s approach. The multiaxial strain life approach is exercised and compared with experimental data from various single crystal (SX) NBSAs. A comprehensive database is created to include all the available multiaxial fatigue data on NBSAs in literature.
Loss Reduction in an Ultra-High-Loaded Low Pressure Turbine Cascade by a Combined Flow Control Strategy
Authors: Xue Yapeng , Li Ziliang , Wu Yanhui
Published: September 2023

Modern low pressure turbines (LPT) always suffer from unexpected endwall flow losses due to the enhanced aerodynamic load. Thus, there is a demand for much more efficient methods to improve the endwall performance of modern LPT. In this paper, a novel flow control method (denoted by FILLET&NEC) which combines leading edge fillet configuration (denoted by FILLET) and non-axisymmetric endwall contouring (denoted by NEC) was applied to an ultra-high-loaded LPT cascade (denoted by REF, Zweifel = 1.59) to explore its flow control potential and underlying mechanisms for endwall secondary flow control. Numerical investigation verified by experiments was used to make comparisons of flow control effects in FILLET, NEC, and FILLET&NEC. Based on the coupled design of FILLET&NEC’s 5 design parameters, Latin hypercube sampling was used for parametric research to get the preferred model. The results show that the total pressure loss coefficient and non-dimensional secondary kinetic energy are reduced by 15.07% and 40.09%, respectively, with the application of FILLET&NEC. This coupled design significantly suppresses the development of passage vortex and wall vortex, while the overturning and underturning of outlet flow angle is reduced. The introduction of NEC effectively reduces the cross-passage pressure gradient near endwall, making up for FILLET’s shortcomings. Simultaneously, FILLET helps NEC decrease the size and strength of horseshoe vortex, improving the flow conditions in cascade passage. Coupled design FILLET&NEC fully highlights the advantages of FILLET and NEC, while avoids their own shortcomings when independently applied. This paper confirmed that the combined design of FILLET and NEC is effective in reducing the endwall secondary losses, providing a valuable reference for the coupled design applications and future advanced ultra-high-loaded LPT designs.
A Semi-Empirical Model for Conceptual Turbine Vane Cooling Design and Optimization
Authors: Schöffler Robin , Grunwitz Clemens , Brakmann Robin G.
Published: September 2023

Efficient turbine vane cooling designs are increasingly important to improve the thermal efficiency of gas turbines. Evaluating the performance of a cooling design requires the knowledge of the temperature distribution on the vane surface and the cooling air mass flow rate. The estimation of the vane temperature distribution is considered as a conjugate heat transfer problem, which usually requires a computationally intensive 3D CFD-FEM simulation. However, this approach is not suited for an early design phase, when the cooling design frequently changes. A simplified, yet physical approach is necessary to develop an initial cooling design, which can be used as a baseline for more detailed investigations. This paper presents a predictive model for turbine vane cooling and it’s integration into an optimization tool chain. The model uses a vane geometry model, the aerodynamic flow field and the coolant conditions from an in-house turbine design tool chain. The cooling geometry is divided into multiple interior sections with their own parameterizations, characterizing the cooling method and it’s geometric representation. Internal cooling, such as impingement or convective cooling, as well as external cooling, namely film cooling, is considered. Taking the material properties of the vane into account, the model calculates the temperature distribution on the vane surface and the coolant mass flow rate to identify critical hot spots and to evaluate a cooling concept. The capabilities of the model are demonstrated in an optimization process to improve the cooling design of a modern high pressure nozzle guide vane. Compared to a manually created cooling concept, the coolant mass flow rate was reduced by more than 20 % while simultaneously a more uniform metal temperature was achieved.
Analysis of Failure Forms of Bevel Gear, Shaft and Bearing Structure System Considering Multi-Mode Damage Accumulation
Authors: Han Xudong , Hong Jie , Chen Cheng , Chen Xueqi
Published: September 2023

During the working process, the structural system, including bevel gear, shaft and bearing, located in the front journal of the high pressure compressor of the aeroengine rotor is affected by various loads such as assembly load, centrifugal load, temperature load and meshing excitation, and it leads to different modes of interface damage, for example, wear, slip and fatigue. With the increase number of working cycles, different interface damage modes affect each other and damage gradually accumulates, which leads to the degradation of the mechanical properties of each component. Finally, the function of the weakest component is lost, resulting in the failure of the structural system. Consequently, the comprehensive influence of multiple failure forms caused by interface damage at different positions results in the failure of the structural system, where the damage position and the failure position are different, and the final failure form is uncertain. In this paper, a damage accumulation mechanical model considering multi-mode damage interaction is established for bevel gear, shaft and bearing structure system. And the damage-failure mechanical process of the structural system and its key influencing factors under complex environment loads are studied. The results showed that the failure forms of the structural system were closely related to the assembly and load characteristic parameters of the components. Therefore, considering the randomness of the initial assembly state and environment loads, the damage accumulation mechanical process and the final failure forms of the structural system have significant uncertainty.
Acoustic and Aerodynamic Performance of Serrated Leading Edges on the Bypass Outlet Guide Vanes
Authors: Cuciumita Cleopatra , Qin Ning , Shahpar Shahrokh , Namgoong Howoong
Published: September 2023

The reduction of noise for commercial aircraft has become an important challenge for engineers, with engine noise being one of the major contributors to the overall sound levels near airport. For modern turbofan engines, characterized by high bypass ratios, one of the main noise sources is the interaction between the turbulent rotor wake and the leading edge of the downstream outlet guide vanes. A passive noise control method that has been gaining interest in the research community is the use of serrated leading edges for the vanes. Studies done on flat plates and airfoils with serrated leading edges showed a reduction in airfoil turbulent flow interaction noise, with an increased benefit when increasing the serrations amplitude and the existence of an optimal wavelength. From an aerodynamic standpoint, some studies show that serrations delay stall, but with a cost in aerodynamic performance at design point. Very little data exists for assessing the acoustic benefits of serrations on the leading edge of outlet guide vanes, where the noise predictions require addressing both the broadband and tonal noise. Preliminary results indicate some noise reduction, but without quantifying the benefits against the serrations parameters. It is also unclear how the total pressure losses in the outlet guide vanes row are affected by the presence of serrations. In this paper, we report a parametric study based on leading edge serrations to investigate the effect of the amplitude and wavelength on noise levels, as well as on aerodynamic performance. The NASA source diagnostic test (SDT) fan with swept outlet guide vanes was used as the test case, being representative of a modern turbofan. The unsteady flow and radiated noise were computed using a hybrid Lattice-Boltzmann/very-Large-Eddy-Simulation model implemented in the PowerFlow computational fluid dynamics solver. The flow characteristics and the noise levels were validated for the datum geometry against existing experimental data. Correlations for the far-field overall sound pressure level and the total pressure loss coefficient were built in relation to the serration parameters and a discussion on the best combination of serrations amplitude and wavelength has been given. These correlations can be further used in a multidisciplinary optimisation process.
Dynamic Characterization of an Adaptive Film-Riding Seal
Authors: Bird Joshua , Keogh Patrick , Sangan Carl , Bowsher Aaron , Crudgington Peter , Scobie James
Published: September 2023

Shaft seals control the leakage of fluid between areas of high pressure and low pressure around rotating components inside turbomachinery. Static seals are often subject to damaging rubs with the shaft, caused by assembly misalignments and rotordynamic vibrations during operation. Adaptive seals aim to reduce leakage flows whilst minimizing wear. The Film Riding Pressure Actuated Leaf Seal (FRPALS) is one such design which utilizes a large installation clearance and is blown down towards the shaft under pressure.

This paper presents a numerical model which can be used in the design and development of adaptive shaft seals, validated by experimental data from the literature. The model uses a modified version of the Reynolds equation to predict the dynamic, frequency-dependent stiffness and damping coefficients of the fluid film. The dynamic coefficients have been solved for different operational clearances and pressure differences to generate coefficient maps. These maps have been incorporated into a blow down model with compliant mechanical leaves to predict the transient translational and angular displacement paths of the FRPALS when subject to an increasing pressure drop.

The blow down model has been compared against experimental measurements collected from a specially designed test facility for the characterization of shaft seal performance. Eddy current probes were used to measure the displacement paths of the FRPALS with the experimental values showing that the model can accurately predict the dynamic movement of the seal when subject to a pressure difference.
Effect of the Structure of Flow Deflector on Ignition and Flame Shape of The Centrally Staged Combustor
Authors: Ma Jinglong , Hui Xin , Han Xiao , Han Meng
Published: September 2023

Centrally staged premixed is a practical method to reduce NOx emission in aero-engines. Previous research has demonstrated that the flow inside the combustor has a significant effect on the ignition performance and flame shape. In this paper, the local flow field in a model combustor is changed by mounting a flow deflector at the main stage channel outlet. The effect of the length and central angle of the flow deflector on the ignition performance is investigated experimentally. The time scale of each phase of a successful ignition event is extracted using Otsu’s threshold segmentation method. It is found that the flow deflector significantly improves the ignition performance of the centrally-staged combustor and extends the ignition boundary. Based on this, the shape of the flame at different flow deflector lengths and central angles is also captured by a high-speed camera. The spatial patterns of the flame dynamic are identified using the proper orthogonal decomposition (POD) method. Additionally, the first few order modes, whose energy proportions are relatively larger, dominate the flame dynamics. The results indicate that as the length of the flow deflector increases, the flame primarily presents the vortex shedding mode, while as the central angle of the flow deflector decreases, the circumferential rotation mode dominates. There is a greater fluctuation in the zone where the chemiluminescence of the flame is stronger.
Manufacturing and Hydro Testing of a 10 MWe sCO2 Axial Turbine
Authors: Klaerner John D. , Moore J. Jeffrey , Robinson Kyle , Wade Jonathan L. , McClung Aaron
Published: September 2023

Supercritical CO2 [sCO2] power cycles designed for thermodynamic efficiencies above 50% push component designs into pressure and temperature combinations that approach the limits of American Society of Mechanical Engineers [ASME] Boiler and Pressure Vessel Code and ASME Piping Design Codes with Turbine inlet conditions near 250 bar and 715°C. These design conditions which limit available materials to high nickel alloys are compounded by the high fluid densities of sCO2 at these conditions which result in very compact machinery at the 10 MWe class which are currently being developed for the DOE Supercritical Transformational Electric Power [STEP] program1.

Design of the STEP Turbine is complete with integrated lessons learned from a previous 1 MWth sub-scale demonstration of a high temperature 10 MWe Turbine designed under the DOE SunShot Program2. Fabrication of the STEP Turbine is nearing completion with all housings and pressure containing components in hand. This paper provides a detailed look at design intentions and limitations for the pressurized sections of the main pressure casing and the fabrication of key turbine components. Additional discussion is provided regarding post-fabrication inspection and acceptance of the casing for use after issues with casing welds were identified late in the fabrication process.
The Effects of Channel Supplies on Overall Film-Cooling Effectiveness
Authors: Veley Emma M. , Thole Karen A. , Bogard David G.
Published: September 2023

Cooling components in the hot section of a gas turbine is essential to component durability. Common methods of cooling include rib turbulators in internal passages and film cooling on external surfaces. The holes that produce the film cooling are fed from the internal channels often containing ribs. Consequently, there is an interdependence of internal heat transfer and external film cooling. The purpose of this study was to obtain a better understanding of the interaction of ribs and film cooling. To quantify the cooling performance the surface temperatures were measured from which overall effectiveness was calculated. For the experiments, additively manufactured test coupons were made of Inconel 718 to match engine Biot numbers. These test coupons had internal feed channels with and without ribs and had both cylindrical holes and meter diffuser shaped holes with 15° lateral expansion angles and a 1° forward expansion angle. A single rectangular channel was one type of feed channel. The other type of feed channels was individual circular channels with each circular channel supplying an individual film-cooling hole.

The experimental results showed that the circular individual channels have 80% higher baseline overall effectiveness than the single rectangular channel without any film cooling. Ribbed turbulators without film cooling also increased the overall effectiveness by 21% for single rectangular channel and by 29% for the circular individual channels compared to the respective non-ribbed channels. While the film cooling increased the overall effectiveness of all geometries, the single rectangular channels had increased overall effectiveness levels by up to twice that of the no film-cooling case. On average the single rectangular channels had an 80% improvement from film cooling, whereas the individual channel feeds on average had only a 50% improvement given their high baseline effectiveness levels.
Impact of sCO2 Waste Heat Recovery System Air Cooler Integration on Aircraft Engine Thrust Performance
Authors: Bury Claire-Phonie , Vesely Ladislav , Stoia Michael , Fernandez Erik , Kapat Jayanta
Published: September 2023

The aviation industry has established a goal to reduce net carbon emissions by 50 % relative to 2005 levels by 2050. Carbon emissions can be reduced through direct or indirect methods. Direct approaches include alternative fuels, while indirect approaches can include waste heat recovery (WHR) from engine exhaust using a supercritical CO2 (sCO2) Brayton power cycle. Power cycle component design, particularly the heat sink heat exchanger (i.e., Cooler), are strongly influenced by changes in engine operating conditions. The present work focuses on integration of a sCO2 power system into an aircraft propulsion system and evaluation of its performance. The first part addresses the operation of the WHR unit under different operating conditions for an aircraft engine with a nominal thrust of 30 kN. The second part addresses the impacts of operating the sCO2 cycle near the critical point, Cooler heat addition and pressure drop in the engine bypass flow path, and Cooler design under different engine operating conditions. Analysis results show that the sCO2 WHR system can generate approximately 492 kW of electrical power with a cycle efficiency between 24 % and 28 % across different aircraft operating regimes.
Bayesian Information Fusion for Gas Turbines Diagnostics and Prognostics
Authors: Zaccaria Valentina , Fentaye Amare D. , Kyprianidis Konstantinos
Published: September 2023

Prognosis, or the forecasting of remaining operational life of a component, is a fundamental step for predictive maintenance of turbomachines. While diagnostics gives important information on the current conditions of the engine, it is through prognostics that a suitable maintenance interval can be determined, which is critical to minimize costs. However, mature prognostic models are still lacking in industry, which still heavily relies on human experience or generic statistical quantifications. Predicting future conditions is very challenging due to many factors that introduce significant uncertainty, including unknown future machine operations, interaction between multiple faults, and inherent errors in diagnostic and prognostic models. Given the importance to quantify this uncertainty and its impact on operational decisions, this work presents an information fusion approach for gas turbine prognostics. Condition monitoring performed by a Bayesian network is fused with a particle filter for prognosis of gas turbine degradation, and the effect of diagnostic models uncertainty on the prognosis are estimated through probabilistic analysis. Gradual and rapid degradation are simulated on a gas turbine performance model and the impact of sensor noise and initial conditions for the particle filter estimation are assessed. This work demonstrates that the combination of Bayesian networks and particle filters can give good results for short-term prognosis.
Simultaneous Damping and Mistuning Identification Using Nonlinear Optimization of Blade Tip Timing Data
Authors: Kurstak Eric , D’Souza Kiran
Published: September 2023

Empirically characterizing the dynamical properties of systems plays a crucial role in helping develop more accurate computational models of turbomachinery. Since computational models are only approximations of the physical system, there is an active need to constantly tune models to better mimic the real system. Extracting valuable information from test data can be challenging, especially for under-sampled data sets generated from blade tip timing systems. The use of tip timing systems is becoming more common due to the ease of use and the fact that systems maintain the original dynamics. Two commonly computed quantities from tip timing data are the system damping values and blade mistuning information. In this work, a method is proposed that simultaneously calculates the blade damping and mistuning values of a bladed disk using blade tip timing data from a synchronous vibration resonance crossing. The proposed method modifies an existing mistuning identification approach from the literature by increasing the applicability of the method for directly calculating mis-tuning values. A key benefit of the proposed approach is that blade-to-blade coupling effects are included in the parameter estimations. The blade responses between the experimental runs and computational simulations were compared to show agreement and that the computational model can accurately predict the motion of the blades when subjected to specific forcing conditions.
A Novel Axial Energy-Imparting Turbomachine for High-Enthalpy Gas Heating: Robustness of the Aerodynamic Design
Authors: Karefyllidis Nikolas , Rubini Dylan , Rosic Budimir , Xu Liping , Purola Veli-Matti
Published: September 2023

Hard-to-abate industrial processes, such as petrochemicals and cement production, have long been considered technically challenging to decarbonize. In response to the urgent demand to eliminate industrial CO2 emissions, a new class of energy-imparting turbomachines has been developed. These devices aim to convert mechanical into internal energy instead of pressurizing the gas, which enables high-temperature gas heating (up to 1700 °C) for a variety of applications. This paper is organized into three parts. First, the paper aims to demonstrate the capabilities of the novel, high-capacity, customizable, repeating-stage axial turbo-heater architecture for a hydrocarbon cracking example application. The study presents the new design requirements and working principles of this energy-imparting concept. The radically different objectives compared to a compressor enable ultra-high loading stage designs by avoiding the stability and efficiency constraints imposed on compressors. Within this new design space, the turbo-heater is able to achieve a loading coefficient ψ ≥ 4.0. Second, detailed numerical simulations of a multistage axial turbo-reactor with various vaneless space lengths are conducted. This work conclusively demonstrates the robustness and flexibility of the aerodynamic design despite employing a uniform blade design. It is emphasized that the concept is tolerant to unsteady interstage turbulent disturbances, enabling nominal work-input conditions to be achieved even for the most compact arrangements. Finally, having confirmed that the aerothermal restrictions on the vaneless space length can be removed, the designer is free to tailor the design to optimize the chemical reaction by (1) tailoring the residence time distribution to improve the yield and coking rate (2) homogenizing reaction progress by mixing-out concentration gradients and (3) adjusting the rotational speed to account for variations in the reaction dynamics for different feedstocks.
An Experimental Investigation of Heat Transfer for Supercritical Carbon Dioxide Cooling in a Staggered Pin Fin Array
Authors: Wardell Ryan J. , Richardson John , Otto Marcel , Smith Matthew , Fernandez Erik , Kapat Jayanta
Published: September 2023

Pin fin geometry in the trailing edge as turbulators in turbine blades has been a subject thoroughly researched for the past several decades. To improve the efficiency of turbomachinery, higher turbine inlet temperatures are necessary, introducing the need for internal cooling channel features, such as pin fin arrays. These solutions are necessary to avoid material failure at higher operating conditions by enhancing the heat transfer of the blade. Over the past decade, a shift toward applying supercritical carbon dioxide or sCO2 cycles has shown increased potential compared to the industry standard air cycles. Promising higher cycle efficiency, smaller footprints, and zero greenhouse gas emissions, sCO2 has become an attractive alternative to well-established air cycles. This alternative cycle introduces the need to re-visit the heat transfer capabilities of internal cooling geometries within this novel operating fluid environment. The first objective of this paper is to experimentally demonstrate the heat transfer characteristics of sCO2 as the secondary internal cooling fluid environment through testing a pin fin array in a closed loop at 200 bar and 400 Celsius inlet conditions, which stands well within the supercritical region of sCO2. Secondly, the experimental process aims to validate numerical simulation methodology for studying sCO2 environments for internal cooling of turbine blades in a matching pin fin geometry.
Damping and Fatigue Performance of Additive Manufactured Particle Damper Infused Instrumentation Rake
Authors: Celli Dino A. , Janczewski Timothy , Sheridan Luke , Scott-Emuakpor Onome , Warner Justin , Smith Lucas , Hollkamp John , Napper Lorean , George Tommy
Published: September 2023

Recently, laser powder bed fusion (LPBF) has been implemented as an enabling technology to create intentional large cavities during the print process to leave behind sections with embedded metal powder to act as particle dampers within the component. This novel application of particle damping has been applied to beam specimens with the additive manufactured (AM) particle damper technology and shown to attenuate resonant excitation and therefore stress in the component by up to 90% when compared to fully fused parts subjected to the same base excitation. More recently however, the AM damping technology has been applied to turbine engine relevant blade and hardware geometries. In this work, the damping and fatigue performance of a representative aerodynamic instrumentation rake are investigated. Four successful builds of the rakes were performed with and without internal pockets as well as with 0- and 45-degree printing orientations. Four internal configurations of the rakes are printed to include a 0.254mm, 0.381mm, 0.508mm, “fully fused” or 0mm pocket thicknesses. Each specimen is first scanned and three dimensionally reconstructed and analyzed to compare the nominal CAD drawing to as-printed and received geometry using blue light and CT scanning. Vibrational tests for the rake specimens are performed on a 20,000lb Unholtz-Dickie shaker and a OFV-505 single-point laser vibrometer and strain gages are utilized to measure the velocity and strain response respectively of the rake specimens. Sine wave down-chirp sweeps are conducted to excite the specimen in a 2nd bend mode to collect amplification and Q factor, or quality factors, to evaluate the damping performance amongst the rakes. Finally, vibration fatigue tests are performed, in the 2nd bend mode, to validate the improved fatigue performance of inherently damped rake components compared to the fully fused control group and demonstrate the novel additive damping technology to a commonly used experimental instrumentation fixture.
The Influence of Surface Roughness on Flow Transition by Well-Resolved Large Eddy Simulations
Authors: Jain Ishita , Wajih Issam , Sarkar Subrata
Published: September 2023

The transition of a spatially developing boundary layer is studied through highly resolved Large Eddy Simulations (LES) when subjected to external disturbances in the presence of surface roughness. Three rough wall conditions are considered in the present analysis, where roughness elements are homogeneous in the spanwise direction with cross-sectional shapes taken as triangle, square and semi-circle. The aspect ratio (s/k) considered here is 3, where k is the roughness height, and s is the spacing between the consecutive rows of roughness elements in the streamwise direction. The inlet flow Reynolds number based on the momentum thickness and freestream velocity (Reθ) is 360, while the freestream turbulence (fst) is 2.5%. The transition mechanisms are observed to change significantly with roughness shapes. Attributing to the sharp tip of the triangular shape, the shear layer trips to transition from laminar to turbulent flow via Kelvin-Helmholtz (K-H) instability. Whereas Λ-vortices and longitudinal streaks are the geneses for the boundary layer transition in square and semi-circular elements, respectively. Further, the influence of roughness on transition onset is explored by analyzing the turbulence statistics such as rms quantities, shear stress and spectral response.
Assessment of Airborne Contaminant Encountered During a Flight Mission
Authors: Suman Alessio , Zanini Nicola , Pinelli Michele
Published: September 2023

Flight missions are usually scheduled and managed on safety, cost, and commercial requirements. Depending on the aircraft or helicopter duties, the mission path, in terms of spatial coordinates and altitude, is guided by conditions that consider the scheduled mission’s scope and aim. For example, commercial aircraft transport passengers from two specific airports in a predetermined timetable. Conversely, helicopters for rescue or firefighting operations are employed in harsh conditions without a predetermined timeframe and schedule. In both cases, aircraft interact with the environment, usually contaminated by airborne particles, commonly known as soil and soot. These contaminants are due to the flight route, cruise altitude, take-off, and landing; therefore, they are specific for each aircraft mission. In the present work, the assessment of the airborne contaminant encountered by an aircraft has been proposed. A representative scheduled flight and a life-saving helicopter mission have been taken to propose a methodology for estimating the contamination that occurred to the engine based on the encountered contaminants. The contamination data was inferred by the Cloud-aerosol lidar and infrared pathfinder satellite observations while the flight data from the onboard aircraft transponder. Based on an open database, the methodology shows how contamination occurs over subsequent missions depending on the mutual interaction between route and environment conditions. The assessment of the engine contamination has been proposed in terms of equivalent dose, which is recognized as a helpful parameter to estimate the margin between safe-flight and dangerous-flight regimes.
On the Modelling of the Overspeed Performance of a Single Stage Turbine
Authors: Eryilmaz Ibrahim
Published: September 2023

This manuscript is on the aerodynamic characterization of a turbine particularly when the turbine loses its load permanently such as after a shaft or transmission failure. These conditions cause excessive acceleration of the turbine stage or stages. If not mitigated, a disk burst may lead to hazardous conditions threatening the passenger and the flight safety. Modelling brings the possibility of controlling the event and provides design flexibility for a lightweight and fail-safe system design.

Additional to the control system action through fuel shut-off, there are variety of conditions which affect the acceleration. Friction and blade damage in unlocated failures are examples of these. The aerodynamic performance is another important aspect as the turbine operates at far off-design conditions.

NASA E3 single stage high pressure turbine has fewer airfoils than the base two stage version and operate at a higher loading. Single stage turbine RANS CFD model has been prepared and the turbine is characterized at overspeed conditions up to 200% speed. Later, the tip clearance of the stage was increased up to 15% of the blade height to assess the performance deterioration. Finally, two more damage scenarios were introduced through truncating the blade tips from leading edge only and trailing edge only. Study shows that significant efficiency decrease occurs, which can be considered as a parameter in safety calculations and flight certification.
Windage Torque Reduction in Low-Pressure Turbine Cavities - Part 1: Concept Design and Numerical Investigations
Authors: Li Zhihui , Christodoulou Loizos , Jefferson-Loveday Richard , Ambrose Stephen , Jackson Richard , Lock Gary D. , Sangan Carl M. , Scobie James A.
Published: September 2023

The windage torque on rotational walls has negative effect on the performance of the low pressure turbine. In this paper, three novel flow control concepts (FCCs) were proposed to reduce the windage torque within a turbine stator well, with upstream and downstream cavities connected by an interstage labyrinth seal. The swirl and flow pattern inside a reference turbine cavity was first investigated and the potential locations for the FCCs were identified using numerical simulations. FCC1 was a circumferential row of leaned deflectors downstream of the labyrinth seal. FCC2 was a set of deflector vanes and platform to optimize the ingress swirl at high radius in the upstream cavity. FCC3 combined the two flow concepts and the superposition resulted in a stator well windage torque reduction of 70% when compared to the baseline design. The FCCs also showed performance benefits at off-design conditions and over a range of secondary flow rates to the cavity. In Part 2 [1], the numerical analysis and performance of the FCCs are validated in an experimental rig, using additively-manufactured components.