bluuebunny/crossref_metadata_2025 huggingface dataset:
Methodology for the Redesign of Compressor Blades Undergoing Nonlinear Structural Interactions: Application to Blade-Tip/Casing Contacts
Authors: Kojtych Solène , Nyssen Florence , Audet Charles , Batailly Alain
Published: October 2022

Over the past decade, the drive towards more efficient aircraft engines has pushed the boundaries of operating ranges far beyond a linear structural context. Nonlinear interfaces, such as blade-tip/casing contacts, are to be expected in nominal operating conditions. However, current blade design methodologies still rely on empirical structural considerations, often linear, which may lead to costly redesign operations. This work aims at proposing a methodology for the redesign of blades undergoing nonlinear structural interactions. A three-step redesign process is considered: (1) parameterization of an existing blade, (2) update of blade parameters with respect to a surrogate performance criterion and (3) performance check of the optimized blade. An original two-way parameterization method is proposed to parameterize existing blades and generate models from blade parameters. As a proof-of-concept, the redesign of the NASA compressor blade rotor 37 and fan blade rotor 67 with respect to blade-tip/casing contacts is considered. High-fidelity parameterized models of the initial blades are obtained and their dynamic response to contact interactions are analyzed. Geometries are updated with respect to their clearance consumption, as its minimization has shown beneficial effects on the considered contact interactions. The proposed methodology allows to better assess the relevance of this performance criterion in the context of blade-tip/casing contacts.
Analysis of the Condensation Phenomena Within the Radial Turbine of a Fuel Cell Turbocharger
Authors: Wittmann Tim , Lück Sebastian , Friedrichs Jens , Wiśniewski Piotr , Dykas Sławomir
Published: October 2022

Cathode systems of proton exchange membrane fuel cells are tasked with providing compressed air for the fuel cell stack. The exhaust gas from the fuel cell has a pressure potential which can be utilised in a turbine to partially power the compressor. Therefore, a radial compressor and a radial turbine are often combined with an electric motor to form an electric fuel cell turbocharger. The exhaust gas used to operate the turbine is humid and hence prone to condensation. Previous studies on such condensation only investigated a turbine segment and neglected the volute. This study overcomes this simplification and analyses the aerodynamics of the full-annulus flow of volute, stator and rotor. The focus is set on the effect of the circumferential asymmetry on the occurrence and strength of condensation in the turbine rotor. The effect of variations of the rotational speed is also investigated. The main finding is, that such asymmetries or speed changes can have a significant effect for operating points for which they are able to determine the occurrence of condensation. Operating points with no or with certain condensation are less affected.
Azimuthal Instabilities of an Annular Combustor With Different Swirling Injectors
Authors: Rajendram Soundararajan Preethi , Durox Daniel , Renaud Antoine , Candel Sébastien
Published: October 2022

Experiments are carried out on the laboratory-scale MICCA-Spray annular combustor to examine the effects of swirlers on combustion instabilities. This system comprises sixteen spray-swirl injectors and gives rise to instabilities coupled by azimuthal modes. Five types of swirlers producing clockwise rotation and varying in swirl numbers and pressure drops are considered. These swirlers can be broadly categorized into two groups, lower-swirl, and higher-swirl groups, based on their swirl numbers. An arrangement where clockwise and counterclockwise swirlers alternate is also studied. Experiments are performed systematically with liquid heptane at five levels of thermal power and six equivalence ratios. Results reveal that none of the swirlers in the lower-swirl category exhibit instability in the operating region considered, whereas the higher-swirl units feature strong azimuthal instabilities that trace an overall limit cycle envelope with a few short and random bursts. Among the higher-swirl group, a higher pressure drop swirler is associated with a broader instability map. This shows that the transition to instability mainly depends on the swirl number through its effect on the flame structure and that the pressure drop adds to further variations in amplitude and frequency of oscillation. The spin ratio time series indicate that the modes are of mixed type, and that its distribution depends on the operating condition. On specifically comparing the spin ratio distribution between a full set of clockwise rotating swirlers (CR) and a configuration where clockwise and counterclockwise rotating swirlers (CCR) are alternatively placed, it is found that there is no definite statistical preference for spin ratio linked to the effect of bulk swirl. In some cases, however, the CCR configuration promotes a broader distribution of spin ratios centered around the standing mode (s = 0) while the CR setup favors azimuthal modes spinning in the counterclockwise direction. An attempt is made to interpret the occurrence of instabilities by making use of flame describing functions (FDFs) measured in a single-injector combustor. It is found that the FDFs corresponding to the two swirler categories (lower swirl and higher swirl) are relatively distinct. The observed behavior is tentatively interpreted using an instability analysis in which the injector and upstream plenum are represented by an impedance which shifts the band of instability. The unstable behavior is then linked to the relative position of the FDF phase with respect to the instability band in the frequency range corresponding to the expected azimuthal mode frequency. The phase and gain of the FDF notably depend on the swirl number and it is possible to distinguish, for the present configuration, a category of low swirl number injectors inducing stable operation and another category of high swirl number units leading to oscillations.
Predicting Emissions Across Design Variations of an Aero-Engine Combustor Using FGM and PISO
Authors: Karalus Megan , Brandt Dustin , McManus Liam , Munktell Erik
Published: October 2022

A modeling approach for quickly predicting Carbon Monoxide (CO) and Unburned Hydrocarbon (UHC) emissions is assessed in Simcenter STAR-CCM+ version 2021.3. Both magnitude and trends are evaluated across design variations of an aero-engine test combustor operating at an idle condition. Large Eddy Simulation (LES) is used with the non-iterative Pressure Implicit by Splitting of Operators (PISO) scheme, and the Flamelet Generated Manifold (FGM) combustion model. There are four geometric design variations of the same test combustor where changes are made to the dome effusion cooling, main swirler, and downstream orifices. These four geometries are chosen for this study because they yield distinctly different CO and UHC emissions, thus reducing signal to noise in assessing the predictive capability of the modeling approach. Sensitivity of the results to a key parameter in the liquid fuel spray breakup model is provided. By varying the breakup rate, the prediction of the CO emissions is shown to compare very favorably both in magnitude and trend to the experimentally measured values. The UHC emissions are shown to compare well for three of the four designs. Results are also generated using the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) scheme; these show the same behavior as PISO. However, the results with PISO can be obtained between 2.5 and 3.5X faster than the more traditional approach. Combining the computational efficiency of FGM and PISO allows for fast and accurate predictions of regulated emissions, and therefore down-selection of designs earlier in the design process.
Heat Transfer and Pressure Loss of Additively Manufactured Internal Cooling Channels With Various Shapes
Authors: Wildgoose Alexander J. , Thole Karen A.
Published: October 2022

Additive manufacturing (AM) provides the ability to fabricate highly customized internal cooling passages that are relevant to gas turbine components. This experimental study examines the pressure loss and heat transfer performance of a range of fundamental channel shapes that were produced using direct metal laser sintering. Circular, hexagonal, pentagonal, elliptical, diamond, square, rectangular, trapezoidal, and triangular channel cross-sections were investigated. To maintain the same convective surface area between shapes, the wetted perimeters of the channel cross-sections were kept constant. Parallel computational fluid dynamic simulations were performed to understand the relationships in cooling performance between several channel shapes. Several characteristic length scales were evaluated to scale the pressure loss and heat transfer measurements. Among the channel shapes investigated, the diamond channel showed the lowest Nusselt number and friction factor. The pentagon exhibited a similar Nusselt number as the circular channel despite having a lower friction factor. There was no difference in scaling the friction factor or Nusselt number results of the different channels shapes between using the square root of cross-sectional area compared to hydraulic diameter as the characteristic length scale.
The Ignition of C1–C7 Natural Gas Blends and the Effect of Hydrogen Addition in the Low and High Temperature Regimes
Authors: Mohamed A. Abd El-Sabor , Bikram Sahu Amrit , Panigrahy Snehasish , Bourque Gilles , Curran Henry
Published: October 2022

New ignition delay time (IDT) measurements for two natural gas (NG) blends composed of C1 – C7 n-alkanes, NG6 (C1:60.625%, C2:20%, C3:10%, C4:5%, nC5:2.5%, nC6:1.25%, nC7:0.625%) and NG7 (C1:72.635%, C2:10%, C3:6.667%, C4:4.444%, nC5:2.965%, nC6:1.976%, nC7:1.317%) by volume with methane as the major component are presented. The measurements were recorded using a high-pressure shock tube (HPST) for stoichiometric fuel in air mixtures at reflected shock pressures (p5) of 20–30 bar and at temperatures (T5) of 987–1420 K. The current results together with rapid compression machine (RCM) measurements in the literature show that higher concentrations of the higher n-alkanes (C4 – C7) ∼1.327% in the NG7 blend compared to the NG6 blend result in the ignition for NG7 being almost a factor of two faster than NG6 at compressed temperatures of (TC) ≤ 1000 K. This is due to the low temperature chain branching reactions that occur for higher alkane oxidation kinetics in this temperature range. On the contrary, at TC > 1000 K, NG6 exhibits ∼20% faster ignition than NG7 primarily because about 12% of the methane in the NG7 blend is primarily replaced by ethane (∼10%) in NG6, which is significantly more reactive than methane at these higher temperatures. The performance of NUIGMech1.2 in simulating these data is assessed and it can reproduce the experiments within 20% for all the conditions considered in the study. We also investigate the effect of hydrogen addition to the auto-ignition of these NG blends using NUIGMech1.2 which has been validated against the existing literature for natural gas/hydrogen blends. The results demonstrate that hydrogen addition has both an inhibiting and promoting effect in the low- and high-temperatures regime, respectively. Sensitivity analyses of the hydrogen/NG mixtures are performed to understand the underlying kinetics controlling these opposite ignition effects. At low temperatures, H-atom abstraction by ȮH radicals from C3 and larger fuels are the key chain-branching reactions consuming the fuel and providing the necessary fuel radicals which undergo low temperature chemistry (LTC) leading to ignition. However, with the addition of hydrogen to the fuel mixture, the competition for ȮH radicals by H2 via the reaction H2+ȮH↔Ḣ+H2O reduces the progress of the LTC of the higher hydrocarbon fuels thereby inhibiting ignition. At higher temperatures, since Ḣ+O2↔Ö+ȮH is the most sensitive reaction promoting reactivity, the higher concentrations of H2 in the fuel mixture leads to higher Ḣ atom concentrations leading to faster ignition due to an enhanced rate of the Ḣ+O2↔Ö+ȮH reaction.
Impact of Ceramic Matrix Composite Topology on Overall Effectiveness
Authors: Edelson Ryan D. , Thole Karen A.
Published: October 2022

Ceramic matrix composites (CMCs) are a material of interest for components in the hot section of gas turbine engines due to their high strength-to-weight ratio and high temperature capabilities. CMCs are a class of material made of macro scale woven ceramic fibers infiltrated with a ceramic matrix making them significantly different than their nickel superalloy counterparts. As CMCs are implemented into gas turbine engines, the effects of the inherent topology of the CMC weave on convective heat transfer must be understood. In this study, film cooling holes were integrated into a representative CMC weave for three test coupons that were printed using additive manufacturing. The three coupons included: one having a weave topology along the surface of the internal channel supplying coolant to the film cooling holes; one having a weave topology along the external film cooled surface; and one having a weave topology on both the coolant supply channel as well as the external film cooled surface. Overall effectiveness levels for the two cases with a weave surface on the external film cooled wall were measured to be lower than levels for the case with the smooth external surface. The external weave significantly increased the mixing of the coolant jet with the hot mainstream resulting in poor cooling.
Experimental Investigation on Heat Transfer Characteristics in an Impingement/Effusion Cooling System of a Ribbed Turbine Casing
Authors: Li Guodong , Guo Tao , Qiu Changbo , Liu Cunliang , Zhu Huiren , Li Jichen
Published: October 2022

The present paper reports an impingement/effusion cooling structure applied to the turbine casing. The structure consists of three rows of jet holes and two rows of effusion holes, both of which are in a staggered arrangement. A high rib exists inside the impinging chamber for structural support, which is connected to the effusion plate and divides the impinging chamber into two interconnected small chambers, one of which is arranged with effusion holes and the other is not. Transient liquid crystal (TLC) experiments were conducted to investigate the influence of the Reynolds number based on the jet hole diameter (ReD), distance between impingement plate and effusion plate (H), hole pith in Y direction (A) and X direction (C), with a parameter range of 1100 ≤ ReD ≤ 5100, 2.5 ≤ H/D ≤ 7.5, 4.0 ≤ A/D ≤ 14.0 and 8.0 ≤ C/D ≤ 14.0, on the heat transfer characteristics of the effusion plate. The results show that the region averaged Nu increases with an increase in ReD for all studied cases and there is a linear relationship between the ReD and the region averaged Nu in the logarithmic coordinate. The change of H/D has an obvious effect on the heat transfer in the 2D-3D region from the stagnation point. As the H/D increases, the entrainment effect that makes the surrounding fluid continuously enter the jet, resulting in the velocity of the jet decreasing, and the enhanced heat transfer at the effusion plate becomes weaker. When 38 < Y/D < 42 and 0 < Y/D < 1, the Nu increases with the increase of H/D due to the weakening of the flow separation of the wall jet. The variation of A/D has little effect on the enhanced heat transfer in Region1 (surface without effusion hole), but for Regions2-4 (surface with effusion holes), decreasing or increasing A/D is unfavorable to the uniformity of the Nu distribution. The heat transfer enhancement is mainly influenced by C/D. As C/D decreases, the proportion occupied by the stagnation region gradually increases, thus the surface Nu increases significantly.
Aerodynamic Design of Cooling Guide for Electrical Machine in Electric Ducted Fan
Authors: Hu Xuanyang , Qian Yuping , Yang Bijie , Dong Chaofan , Zhang Yangjun , Zhuge Weilin
Published: October 2022

Electric ducted fan has newly emerged as the most compact type of propulsion fan for flying cars, because of its flexible configuration arrangement, low noise level and high safety level operation. Typically, an electric ducted fan is composed of a hub-driven fan and a hub-mounted inner rotor electrical machine. The thermal management of the hub-mounted electrical machine is essential because it determines the machine’s continuous output power and reliability, as well as the fan thrust force. The heat transmitted from the stator winding to the cooling fin is dissipated by introducing the air flow at hub region to the cooling fin. Therefore, in order to better improve the thermal performance of the cooling fin, an aerodynamic design of cooling fin is proposed in this paper for better thermal management of stator end-windings. Firstly, for a certain desired power output of electrical machine under temperature constraints of stator winding, lumped thermal network is established to derive the requirement of heat transfer coefficients of the cooling fin. Then, from engineering feasibility, three different cooling fin designs including straight type, arc-shape type and airfoil shape type are tested by computational fluid dynamics. The evaluation of the cooling fin designs includes the flow characteristics, power requirements and thermal characteristics for stator winding cooling purposes. In comparison with the conventionally straight type cooling fin, improvements are gained from the designed arc-shape type and airfoil shape type cooling fin configurations, whereas the fan thrust force remains the same simultaneously. It is verified that the arc-shape type and airfoil shape type cooling fins are promising in enhancing the thermal management performance of the electrical machine stator winding with little power requirement.
Large Eddy Simulation on the Turbulent Heat Transfer of Supercritical Fluid
Authors: Zhang Junqiang , Zou Zhengping
Published: October 2022

In the present study, the discretizing and synthesizing random flow generation (DSRFG) technique was used to generate three-dimensional instantaneous inflow turbulence with predefined characteristics according to the real turbulence energy spectrum. A large eddy simulation (LES) was utilized to study the turbulent heat transfer of supercritical methane in a horizontal pipe under forced convection. The results show that the thermo-physical properties of the working fluid change rapidly under high heat flux conditions, which leads to a non-uniform distribution of wall temperature in the circumferential direction. The temperature of the upper wall is higher than that of the lower wall, and the temperature difference increases gradually along the axial. The proper orthogonal decomposition (POD) analysis is conducted here by the snapshot method for the turbulent fields. It is found that there are obvious large-scale flow structures on the lower wall. These large-scale structures are arranged in the spanwise direction alternately as well organized clockwise and counterclockwise streamwise swirling motions, enhancing the heat transfer process in the lower wall region. However, there is no coherent structure of the same order near the upper wall. The buoyancy has different effects in the radial direction. It strengthens the turbulent behavior at the lower wall and inhibits the turbulent behavior at the upper wall to a certain extent, which may be an important reason for the increase of heat transfer at the lower wall and the decrease of heat transfer at the upper wall.
Loss Analysis of Cavity Leakage Flow in a Compressor Cascade
Authors: Deng Hefang , Xia Kailong , Teng Jinfang , Lu Shaopeng , Zhu Mingmin , Qiang Xiaoqing
Published: October 2022

The cavity flow of shrouded stators is quite complex and not yet completely understood, especially for its loss characteristics. In this paper, a matrix of numerical simulations was designed and conducted to investigate the loss characteristics of the cavity flow in a compressor cascade, with a wide range of incidence, two flow coefficients, and three seal clearances. The effect of the skewed boundary layer was introduced to simulate the practical compressor environment as far as possible. The results show that the total pressure loss coefficient is unable of evaluating the cavity leakage loss correctly since it ignores the temperature rise. With the reduction of the flow coefficient, the entropy loss coefficient and thermal entropy generation rate trend to increase, while the change of the viscous entropy generation rate is dependent on the incidence since the high tangential velocity deteriorates the flow of the pressure side at large negative incidence but significantly improves the flow of the suction side as the incidence increases. In addition, there is a significant difference in loss sensitivity to the seal clearance at various incidences. One of the major reasons is the change of pressure difference between the downstream and upstream. And the other major reason is the distribution difference of the high-loss fluid caused by the variation in the passage vortex. These key findings are able to provide insights leading to reducing the compressor loss due to the cavity leakage flow.
Comparative Study of Two Data-Driven Gas Path Fault Quantification Methods for a Single-Shaft Gas Turbine
Authors: Xia Shuocheng , Chi Zhongran , Zang Shusheng
Published: October 2022

According to the types of input parameters, data-driven gas path fault quantification methods for gas turbine engines can be divided into two categories: those based on measured parameters and those based on measurement deviations relative to the healthy state. In this paper, the differences between these two kinds of methods are analyzed based on simulation and experimental data.

Based on the thermodynamic model of a single-shaft gas turbine engine, the above two gas path fault quantification methods are established. Through the test data generated by the model, the accuracy of component fault quantification of the two methods is compared. In addition, two sets of experiments are carried out. One is a steady-state test of new and degraded gas turbines, and the other is a gas path component reassembly test. According to the experimental data, the performance and differences of the two methods are compared from three aspects: (a) fault quantification accuracy, (b) ability to capture performance differences between new and degraded components, and (c) consistency of fault quantification results before and after reassembly.

The results show that the performance of the two methods is similar. However, the method based on measured parameters has advantages in computational cost and complexity because it does not need to use the thermodynamic model to convert the measured parameters to measurement deviations during the diagnosis process. In addition, this kind of method requires less training data to achieve the same accuracy.
Flow Design Using CFD for a Constant-Section Recursive Sequential Combustor
Authors: Hofer Andrea , Paulitsch Nina , Giuliani Fabrice
Published: October 2022

The project MOeBIUS stands for MOmentum-Enhanced Blend of the reactants with recIrculated bUrnt gaseS. It is a new combustion concept based on the principle of recursive sequential combustion (RSC), as described in paper GT2021-59592. The aim is to assert the feasibility of a recursive sequential combustor using CFD simulations and to evaluate the most promising flow design for a 3D printed prototype. This paper focuses on the latest developments of the variant called constant section, with a short overview of the geometry’s design iterations. Based on previous simulation results the combustion chamber is torus-shaped with a double-spiral-like cross section. The simulated domain covers a sector of the torus, with interpolated results to augment the data points. Two air inlets and one fuel inlet (currently modelled with Methane) feed the combustion chamber to create a stable, lean, and continuous flame. Flue gas is partly fed back into the combustion process, this recirculation increases lean combustion robustness and decreases the amount of generated nitrogen oxides. The circular combustion chamber and guiding vanes in the in- an outlet pipes generate a flow dynamic that combines a swirling motion necessary to stabilise the flame to a flow circulation along the torus. This flow pattern is driven by the elevated momentum flux at the injection. The air outlet is designed to enforce interaction between outgoing burnt gasses and fresh inlets while facilitating the split of a fraction of the flue gas that follows the torus’ curvature. The simulations confirm the presence of a large swirl in the chambers section, as well as the maintenance of a circulation in the toroidal direction, which is essential to the concept. This is in good agreement with the desired flow design, and the constant section concept is therefore feasible and valid. Ongoing simulations implying fine-tuning of the parameters are carried out in 3D to ensure stable combustion behaviour and meet expectations in terms of functionality.
On the Effect of Side Clearance in the Vaned Diffuser of a Centrifugal Compressor
Authors: Gibson Lee , Spence Stephen , Stuart Charles , Starke Andre , In Kim Sung
Published: October 2022

Environmental and regulatory pressures have prompted original equipment manufacturers (OEMs) to explore highly boosted internal combustion (IC) engines as a means to minimize toxic air pollutants and meet strict legislative targets. The exhaust gas turbocharger is a key technology used to achieve the boost pressures necessary for advanced engines of the future. Centrifugal compressors with vaneless diffusers have been widely implemented in turbochargers for IC engines, particularly passenger vehicles, mainly due to their compact size and ability to deliver high pressure ratios over a wide range of flow rates. Methods to improve compressor efficiency near surge without reducing the surge margin have received considerable interest in the past. In many situations, changes to the impeller blade design and/or diffuser are limited by the need to meet the strict engine rated power target. Such competing demands have encouraged designers to develop variable geometry compressors with the aim of improving near surge performance without sacrificing rated power performance.

The on/off type vaned diffuser is a variable geometry compressor capable of delivering a pressure ratio benefit near surge by utilizing a vaned diffuser rather than a vaneless diffuser. The vanes are retracted prior to the diffuser choking at higher engine speeds to form a vaneless diffuser in order to reach the rated power condition. Diffuser vane shaped clearances in the hub or the shroud end wall, termed side clearances, enable axial sliding variability of the vanes into and out of the diffuser passage. Unfortunately, the clearances manifest themselves as a discontinuity in the flow field which gives rise to an efficiency penalty. It is not yet clear how the side clearance geometry and position affect the compressor performance i.e., efficiency and stability. Hence, a numerical and experimental investigation was carried out to determine the impact of side clearance geometry and end wall position on compressor performance. It was found that a side clearance positioned at the shroud end wall reduced the surge margin of the investigated compressor for both types of clearance geometry considered. In contrast to this, a clearance positioned at the hub end wall improved the compressor surge margin but had the lowest efficiency benefit near surge. An experimentally validated Computational Fluid Dynamics (CFD) model was used to inspect the flow field and to elucidate the reasons behind the changes in compressor performance.
A Numerical Investigation on the Influence of Reynolds Number on the Performance of Volute Stages of Centrifugal Compressors
Authors: Wolbert D. , Schmitt M. , Koenig S. , Wannek M. , Hartmann J.
Published: October 2022

This paper presents the results of a numerical investigation on the influence of Reynolds number on the performance of a single stage centrifugal compressor with an outward wound volute with circular cross section. The main objectives of the presented work were to gain further knowledge on the flow behavior inside the volute with regard to Reynolds number and operating point (surge, best efficiency point and choke) and to compare the numerical results with an existing Reynolds number correction method. The investigation was carried out with steady state simulations and the industry standard SST turbulence model with enabled Reattachment Modification, in which the Reynolds number was systematically varied, and its influence evaluated by a thorough performance and flow analysis. Despite identical stage inlet conditions, a moderate variation of volute inflow conditions was observed with the variation of Reynolds number, which led to a significant impact on the volute efficiency. Therefore, the numerical approach was extended to ensure identical volute inlet conditions which enabled a scientific evaluation of the Reynolds number’s influence on the volute performance. As a result, the expected influence of the Reynolds number on the volute performance was clearly observable, with a decrease of the skin friction losses with increasing Reynolds number. Furthermore, a good agreement with the tested Reynolds number correction method was observed.
Design Methodology and Mission Assessment of Parallel Hybrid Electric Propulsion Systems
Authors: Ghelani Raj , Roumeliotis Ioannis , Saias Chana Anna , Mourouzidis Christos , Pachidis Vassilios , Norman Justin , Bacic Marko
Published: October 2022

An integrated engine cycle design methodology and mission assessment for parallel hybrid electric propulsion architectures are presented in this paper. The aircraft case study considered is inspired by Fokker 100, boosted by an electric motor on the low-pressure shaft of the gas turbine. The fuel burn benefits arising from boosting the low-pressure shaft are discussed for two different baseline engine technologies.

A three-point engine cycle design method is developed to redesign the engine cycle according to the degree of hybridization. The integrated cycle design and power management optimization method is employed to identify potential fuel burn benefits from hybridization for multiple mission ranges. Genetic algorithm-based optimizer has been used to identify optimal power management strategies. The sensitivity of these mission results has also been analyzed for different assumptions on the electric powertrain.

With 1 MW motor power and a battery pack of 2307 kg, a maximum of 3% fuel burn benefit can be obtained by retrofitting the gas turbine for 400 nm mission range. Optimizing the power management strategy can improve this fuel burn benefit by 0.2–0.3%. Redesigning the gas turbine and optimizing the power management strategy, finally provides a maximum fuel benefit of 4.2% on 400 nm.

The results suggest that a high hybridization by power, low hybridization by energy, and ranges below 700 nm are the only cases where the redesigned hybrid electric aircraft has benefits in fuel burn and energy consumption relative to the baseline aircraft.

Finally, it is found that the percentage of fuel burn benefits from the hybrid electric configuration increases with the improvement in engine technology.
Computation of Intrinsic Instability and Sound Generation From Autoignition Fronts
Authors: Gopalakrishnan Harish Subramanian , Gruber Andrea , Moeck Jonas
Published: October 2022

Burning carbon-free fuels such as hydrogen in gas turbines promises power generation with minimal emissions of greenhouse gases. A two-stage sequential combustor architecture with a propagation-stabilized flame in the first stage and an autoignition-stabilized flame in the second stage allows for efficient combustion of hydrogen fuels. However, interactions between the autoignition-stabilized flame and the acoustic modes of the combustor may result in self-sustained thermoacoustic oscillations, which severely affect the stable operation of the combustor. In this paper, we study an ‘intrinsic’ thermoacoustic feedback mechanism in which acoustic waves generated by unsteady heat release rate oscillations of the autoignition front propagate upstream and induce flow perturbations in the incoming reactant mixture, which, in turn, act as a disturbance source for the ignition front. We first perform detailed reactive Navier-Stokes (DNS) and Euler computations of an autoignition front in a one-dimensional setting to demonstrate the occurrence of intrinsic instability. Self-excited ignition front oscillations are observed at a characteristic frequency and tend to become more unstable as the acoustic reflection from the boundaries is increased. The Euler computations yield identical unsteady ignition front behaviour as the DNS computations, suggesting that inviscid mechanisms control the instability. In the second part of this work we present a simplified framework based on the linearized Euler equations (LEE) to compute the sound field generated by an unsteady autoignition front. Unsteady autoignition fronts create sources of sound due to local fluctuations in gas properties, in addition to heat release oscillations, which must be accounted for. The LEE predictions of the fluctuating pressure field in the combustor agree well with the DNS data. The findings of the present work are essential for understanding and modeling thermoacoustic instabilities in reheat combustors with autoignition-stabilized flames.
Design of a Compact Dry Cooler With an Aluminum Heat Exchanger Core for a Supercritical CO2 Power Cycle Is Evaluated for a Concentrating Solar Power Application
Authors: Katcher Kelsi M. , Amogne Dereje , Patil Abhay
Published: October 2022

As the supercritical CO2 power cycle develops and the component technologies mature, there is still a need to reduce the associated capital and operating costs to maintain a competitive levelized cost of electricity (LCOE) in order to enter the market. When considering concentrating solar power (CSP) coupled with an sCO2 power block and sensible thermal storage, the technology presents a clean source for utility-scale power generation to support baseload or peak-load electrical demand. However, the LCOE of the technology is still considered higher than the competing technologies and should be reduced to better compete in the market; 2030 targets for dispatchable solar plants are 5¢/kWh for baseload CPS and 10¢/kWh for peaker plants, as set by the United States Department of Energy. In response to this need, this study is targeting improvements in the power cycle pre-cooler to reduce power block contribution to LCOE.

This study considers a dry cooler, as CSP plants are sensitive to water consumption because many installations are slated for remote or arid locations where solar irradiance is very high, but water is scarce. Furthermore, the power block footprint for an sCO2 system is quite compact, especially as compared to a steam cycle. Therefore, there is interest in installing a more compact dry cooler that is proportional to the reduced footprint sCO2 power block, while conventional dry coolers are an order of magnitude larger. The competing goals of size, performance, and cost were considered in this study to develop a compact dry cooler that can easily be packaged with the power block, significantly reducing the installation and transport cost compared to the current state of the art, while maintaining or improving upon the heat transfer performance and impact on plant LCOE. This paper details the high-level findings of a large dry cooler sensitivity study for design point selection, design of the compact dry cooler, expected year-round performance for the dry cooler and the power cycle, and the predicted LCOE for a 30-year plant life. It was found that an aluminum heat exchanger core can be suitably designed to meet the pressure and temperature requirements for a pre-cooler in an sCO2 recompression Brayton cycle. The dry cooler assembly was found to have improved heat transfer performance, allowing for increased cycle efficiencies and a reduced plant LCOE. When coupled with a centrifugal blower and compact transition duct, the dry cooler assembly was able to reduce the installation footprint by over 50%.
Unsteady Investigation of the Effect of Purge Air on the Flow Field Inside a Turbine Vane Frame Using Particle Image Velocimetry
Authors: Schien Malte , Hafizovic Asim , Planck Florian , Merli Filippo , Woisetschläger Jakob , Göttlich Emil
Published: October 2022

The urgent need to reduce the emission of greenhouse gases, in combination with high fuel expenses, motivates manufacturers to design more efficient civil aircraft engines. In the case of directly driven jet engines, this is possible through the increased by-pass ratios for high propulsive efficiencies. This tendency implies a change in the operating condition of the low-pressure turbine (LPT) towards lower rotational speeds at larger diameters. Turbine vane frames (TVFs) constitute a new generation of inter-turbine ducts that guide the airflow from the high-pressure turbine (HPT) to the LPT in radial and circumferential direction. The TVF setup integrates turning vanes, and thus removes the need for a separate vane blade-row in the first LPT stage. Consequently, the TVF yields a benefit for overall engine weight and length, resulting in overall efficiency gains. This paper offers new insight into airflow through a TVF duct. Experimental measurements have been conducted at the two-spool test rig at the Graz University of Technology, consisting of a single-stage HPT, the TVF, and the first LPT rotor. Engine-relevant flow conditions are achieved at the TVF inlet, including HPT tip clearance and purge air effects. Particle Image Velocimetry (PIV) was used to capture the flow field in between two struts of the TVF. Inside each strutted segment, splitter vanes are located along the second half of the TVF axial length. This paper presents new results for a TVF based on measurements from a PIV test section located upstream of the splitter vanes in the first half of the TVF duct. Flow data in the area of strong transient interactions between the HPT and the TVF is recorded and discussed in terms of aerodynamic performance. To reveal the unsteady behavior of the fluid, the flow field has been recorded at six serial stator-rotor positions. In addition, two data sets of varying HPT purge flows were obtained and discussed in order to characterize the effect of purge air inside the measurement domain.
Characterization Methods to Evaluate Recrystallization and Weld-Repair in Single Crystal Nickel-Base Superalloys
Authors: Bridges Alex , Shingledecker John , Griscom Eeva , van Esch Hans , Pietersen Stijn , Zuber Robert , Greaves Wayne
Published: October 2022

Single crystal (SX) nickel-base superalloys have been extensively used for the highest temperature gas turbines blades. In power generation turbines, these alloys are often exposed to high temperatures and stresses for extended periods of time and microstructural evolution occurs. Rejuvenation heat treatments and numerous repair methods can be successfully utilized to extend the life of components manufactured from SX alloys. These repair methods may include surface modifications such as shot-peening and welding along with subsequent heat-treatments. These repair processes may lead to recrystallization in the SX materials, and the presence and extent of grain boundaries can have deleterious effects on local high-temperature mechanical properties.

The research in this paper focuses on characterization methods for evaluating recrystallization in SX nickel-base superalloys during the repair process. Micro hardness mapping, micro x-ray fluorescence (μXRF) and several different scanning electron microscopy (SEM) tools were used to evaluate recrystallization and microstructural features in both weld repairs and shot peened samples subjected to various heat-treatments. Simulated weld repairs consisted of both SX castings in Rene N4 and Rene N5 that were welded with Haynes 230 and Rene 80 filler metals using a gas tungsten arch welding process. The effect of recrystallization from shot peening was also evaluated on both alloys. Additionally, various samples were given either a full solution, partial solution or stress relief heat treatment to evaluate microstructural changes which may be used to the repair/rejuvenation process.

The findings in this research show that several different characterization tools can be effectively used to evaluate recrystallization in SX nickel-base superalloys. Micro hardness and μXRF mapping showed local changes in hardness and chemical composition across the weld metal, heat affected zone and base metal as a function of weld metal selection. Electron backscattered diffraction SEM based techniques was particularly effective in identifying changes in recrystallization due to various processing methods. The research shows that filler metal selection, shot-peening control, and heat-treatment conditions all need to be carefully considered in the development of repair processes to minimize recrystallization effects.
Vane-Probe Interactions in Transonic Flows
Authors: Torre A. F. M. , Patinios M. , Lopes G. , Simonassi L. , Lavagnoli S.
Published: October 2022

In this paper, a numerical investigation of the effect of a miniaturized five-hole probe downstream of a transonic low-pressure turbine vane row is presented.

Firstly, a numerical calibration of the probe was performed in uniform flow conditions, as is the case for any traditional calibration, for a wide range of Mach number, yaw and pitch angle conditions.

The effect of the probe on the general flow-field throughout the turbine vane segments was then evaluated by performing a comparison between a set-up with vanes-only (no probe) and with vanes and probe. It was found that, as the probe traverse downstream the vane, the probe impact on the vane isentropic Mach number depends on the probe circumferential position. The highest impact was observed when the probe is located at the upper mid passage (θ = 0.5), consisting on a relatively small reduction of the isentropic Mach number on the vane suction side of just 0.02.

To assess the accuracy of the quantities ‘measured’ by the probe, the probe-determined flow-field was compared to the flow-field of the vanes-only set-up.

A non-negligible modification of the probe-determined local distributions of Mach number, yaw and pitch angle is revealed with respect to the undisturbed flow. Further investigation involving stagnation point tracking showed that the artificial high circumferential variation of the yaw angle is not caused by a modification of the vane outlet flow angle, but is induced by non-uniform flow conditions downstream of the vanes.

With knowledge of the above, a two-step correction is used to account for the effects of the non-uniformity of the flow and its impact is evaluated on 2D and 3D flow regions.

A significative effect of the correction was found on the probe-determined yaw angle, in which the difference from the vanes-only data was reduced to below 1 degree, except near the endwalls where larger discrepancies remain due to probe-endwall interactions. A shortfall of the correction was instead observed on the probe-determined Mach numbers.

Finally, the pitch-wise averaged quantities were evaluated. It was observed that the highest differences between probe-determined and undisturbed data occur where radial gradients of total pressure are stronger and that the two-step correction had almost negligible impact on the pitch-wise averaged quantities.
A Comparison of Static and Rotordynamic Characteristics for Three Types of Impeller Front Seals in a Liquid Oxygen Turbopump
Authors: Jin Zhihong , Li Zhigang , Li Jun
Published: October 2022

Annular seals are widely used to minimize the leakage, improve efficiency and rotordynamic stability in turbomachinery. In a liquid oxygen turbopump, the operating conditions of annular seals are harsher with the high-pressure cryogenic propellant. Researches show that the primary leakage of a liquid oxygen turbopump is from the front and rear shoulder seals of the impeller. Moreover, the impeller shoulder seal sustains the largest pressure drop and highest swirl velocity in machine. Therefore, the shoulder seal plays an important role in rotor stability and successful full load operation of the turbopump, due to the significant seal fluid response forces.

Previous literature shows that the hole-pattern seal has excellent performance in rotordynamic characteristics, and its leakage rate shows a very weak sensitive to the rotating speed. For helical-groove seal, however, the leakage shows a significant decrease with the increasing rotating speed and the roughness on stator surface can enhance the “pump effect” of helical-groove. The static and rotordynamic characteristics of annular seals with cryogenic liquid oxygen are limited in the previous literature.

To make use of the advantages of both types of seals and address the sealing challenge in liquid oxygen turbopump, three types of liquid annular seals were designed for the front shoulder seal of a liquid oxygen turbopump, which include a hole-pattern seal (HPS), a double helical-groove seal (DHG), and a hybrid damper seal (HDS, with hole-pattern on stator and helical-groove on rotor). To assess and compare the leakage and rotordynamic characteristics of the present three types of annular seals under the liquid oxygen medium, a steady three-dimensional (3D) CFD method was developed to predict the seal leakage, based on the Frozen Rotor interface model. A transient 3D CFD-based perturbation method was also proposed to predict the seal rotordynamic characteristics, based on the subdomain method, mesh deformation technique and multiple-frequency elliptical-orbit whirling model. The accuracy and reliability of the present numerical methods were demonstrated based on the experimental data of leakage rates and rotordynamic coefficients for an experimental hole-pattern seal and an experimental helical-groove seal using water as working fluid. The leakage rate and rotordynamic coefficients of these three types of annular seals were calculated and compared under six variable load operating conditions of a liquid oxygen turbopump, focusing on the seal leakage rate, effective stiffness and damping. The numerical results show that compared with the traditional hole-pattern seal and helical-groove seal, the novel hybrid damper seal possesses the much less leakage flow rate and much better rotordynamic characteristics, so is a desired seal scheme for the impeller shoulder seal.