bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental and Numerical Characterization of the Self-Excited Dynamics Behavior of a Technically Premixed Burner
Authors: Meloni R. , Gori S. , Riccio G. , Chiarizia N. , Pampaloni D. , Andreini A.
Published: October 2022

In this paper, the numerical findings of a high fidelity CFD model will be compared with the experimental data of a test campaign devoted at characterizing the performance of a technically premixed industrial burner regarding the thermoacoustic instabilities.

The data are retrieved at relevant gas turbine conditions in a test bench where the flame tube can change its length during the test execution allowing its fundamental acoustic frequencies to be modified and, in case, triggered. Mimicking the test configuration, several Large-Eddy Simulations are performed with different lengths of the flame tube in order to verify the ability of the numerical model to reproduce the excited dominant frequency and the corresponding limit cycle amplitude measurements. The numerical model demonstrates the ability to correctly reproduce the frequency triggered during the test and to reach different limit cycle amplitudes along different flame tube lengths in agreement with the tests, as well. However, it is found that the amplitude of the acoustic pressure fluctuation during the limit cycle is generally under-predicted. Despite this, the proposed approach demonstrates to be a robust tool for the characterization of a given design, allowing to dramatically reduce the computational cost of the analysis, at least in the early design phase.

Since the numerical model can correctly reproduce the behavior of the investigated design, a deep post-processing of the solutions is performed to shed light on the physical mechanisms sustaining the thermo-acoustic instability. Among the numerical techniques employed at this purpose, the Phase-Locked Average and the Extended-POD are applied trying to correlate the fluctuations of the different quantities inside the premixed channel of the burner and the primary zone as well.
The Role of Turbine Operating Conditions on Combustor-Turbine Interaction – Part 2: Loading Effects
Authors: Notaristefano Andrea , Gaetani Paolo
Published: October 2022

Aeroengine combustors burn a lean and premixed blend releasing vorticity and temperature perturbations. Interacting with the first turbine stage, these disturbances impact the cascade aerodynamics, add criticality to the blade cooling and are sources of noise. The first of these issues is addressed in this paper, focusing on off-design turbine conditions, as experienced by aero-engines in their duty. This paper, part II of a two-fold contribution, analyses the effect of the stage loading obtained by changing the RPM (three different values) at the same expansion ratio of 1.4, representative of subsonic flow conditions.

Engine-representative disturbances are generated by a combustor simulator able to produce a swirling entropy wave. Two injection positions and four injection patterns are considered. Experimental measurements are carried out through the stage, measuring the injected disturbance and the aerothermal flow field downstream of the stator and the rotor.

Results show that the swirl profile mostly impacts the stage aerodynamics. The different work extraction and the interaction with secondary flow structures change the entropy wave transport, diffusion and decay through the rotor. Furthermore, the increased angle of the incidence caused by the injected disturbance can make the blade stall under the most loaded operating condition.
Metamodelling of Ignition Delay Time for Natural Gas Blends Under Gas Turbine Operating Conditions
Authors: Yousefian Sajjad , Bourque Gilles , Monaghan Rory F. D.
Published: October 2022

Characterisation of autoignition risk is crucial for designing and optimising low-emission combustion systems as there is an increased demand for highly reactive and novel fuel mixtures. Achieving a residence time to prevent autoignition and obtaining an adequate mixing quality is a challenging trade-off for these fuels in lean-premixed combustion systems. The level of complexity increases further due to low-temperature chemical pathways and pressure-dependent reactions that strongly influence ignition delay at engine operating conditions. Detailed chemical kinetic mechanisms with hundreds of species and thousands of reactions are developed and employed to address this complexity and predict ignition delay accurately, especially for heavier hydrocarbons. However, direct implementation of these kinetic mechanisms is computationally prohibitive in high-fidelity CFD approaches such as large eddy simulation (LES) and stochastic simulation tools that require a large number of evaluations. Advanced stochastic methods are essential tools to quantify uncertainties due to the inherent variabilities in ambient, operating conditions and fuel composition on ignition delay time calculation for practical applications. This study introduces and implements a computationally efficient method based on metamodellig to predict ignition delay time over a wide range of operating conditions and fuel compositions for gas turbine combustion systems. A metamodel or surrogate model is an accurate and quick approximation of the original computational model based on a detailed chemical kinetic mechanism. Polynomial chaos expansion (PCE) as an advanced method is employed to build metamodels using a limited set of runs of the original ignition delay time model based on NUIGMech1.0 chemical kinetic mechanism as the most detailed and state-of-the-art chemical kinetic mechanism for natural gas. Developed metamodels for ignition delay time are valid over operating conditions of P = 20–40 bar and T = 700–900 K for natural gas containing C1 to C7 hydrocarbons at stoichiometric condition. These metamodels provide a fast, robust, and considerably accurate framework instead of a detailed chemical kinetic model that facilitates (a) characterising ignition delay time at different operating conditions and fuel compositions, (b) designing and optimising premixers and burners and (c) conducting uncertainty quantification and stochastic modelling studies.
Development of Oil Free Centrifugal Blower As Enabling Technology for Solid Oxide Fuel Cell Anode Gas Recycling
Authors: Wooding Rochelle S. , Lea Hannah G. , Córdova José Luis
Published: October 2022

Broad commercialization of solid oxide fuel cells (SOFCs), requires anode offgas recycle blowers (AORB) that are specifically designed for handling the challenging operating conditions presented by the SOFC process gases. Otherwise, they can be susceptible to frequent maintenance, low reliability, and short life. This work presents details of the development and testing of an oil-free, low cost centrifugal AORB based on compliant foil bearing (CFB) technology for support of a 100 kW solid oxide fuel cell power plant. The advantages of this novel technology are discussed, particularly its long life and maintenance-free operation, which are derived from the use of CFBs. Also included are preliminary techno-economic analysis considerations for cost-effective deployment of the technology.
Design of an Additively Manufactured Recuperator With 800 °C Inlet Temperature for sCO2 Power Cycle Application
Authors: Marshall Michael , Akbari Meysam , Zhao Ji-Cheng , Hoopes Kevin
Published: October 2022

Recuperators with design temperatures at and above 800 °C can further increase the thermal efficiency of supercritical CO2 power cycles by enabling higher turbine exhaust temperatures. Mar-M247 is a well-suited nickel-based superalloy for high temperature service due to its high creep strength that prevents excessive material thickness being required for pressure containment. While not compatible with the diffusion bonding process due to its low ductility, additive manufacturing using a high-speed laser directed energy deposition (DED) process presents a promising solution with the ability to produce non-conventional flow channels for enhanced heat transfer. A design process is presented that includes aerothermal and mechanical evaluation to maximize performance within the constraints of the manufacturing process. The conceptual design stage evaluates the feasibility of numerous heat transfer concepts from a unit cell perspective. A 2-D heat transfer network and pressure drop code allows prediction of flow distribution in each passage and its effect on overall thermal performance. Established literature correlations, along with CFD simulation, inform the prediction of heat transfer coefficients and friction factors for the flowpaths and enhancement features in the heat exchanger core. Sizing codes for the heat exchanger distribute wall thicknesses for pressure containment according to creep life data for Mar-M247. Mechanical evaluation using FEA modeling with the intent of the ASME BPVC Section VIII, Div 2 assesses the operational safety of the design. The capabilities of the laser DED process and the build strategy for minimizing total build time is discussed, along with the results of build trials that evaluate the settings of the powder nozzle and laser and their effect on deposition rate and susceptibility to build defects. Major considerations affecting the core geometry include the overhang angle of passage structures and the alignment of enhancement features for time efficient builds. The presented detailed design features annular finned passages that take advantage of helical flow paths to distribute the flow from separated headers to shared heat transfer surfaces. Performance predictions for the recuperator at a 50 kW scale provide insights on the feasibility of the AM process to produce recuperators on a commercial scale that extend existing operating envelopes.
Novel UAS Propeller Design Part 2: Design Hub and Tip Angle of Attack Sensitivity of UAS Propellers Designed for Minimum Induced Drag
Authors: Van Treuren Kenneth , Wisniewski Charles
Published: October 2022

Increased interest in eVTOL (electronic vertical take-off and landing) vehicles is growing. These vehicles will become urban air taxis and delivery vehicles, reducing the time involved for moving people and goods in the cities. There is also growth in the small Unmanned Aircraft System (sUAS). The propulsion system for both vehicles use an electric motor with propellers. These vehicles need propellers which are more efficient and have reduced noise generation if they are to coexist in either an urban environment or be used on ISR missions.

Previous studies show that a propeller designed for minimum induced drag using a 50% “hub” break with a “tip” break of 90% leading to zero tip thrust loading results in a propeller that is both quieter and more aerodynamically efficient. This design incorporates a constant angle of attack (AOA) from the hub to an r/R of 50% where the section propeller thrust loading then dropped to an AOA with zero lift at an r/R of 90%. AOA sensitivity of both the hub and the tip are studied. Using a hub AOA lower than the value for Cl/Cd max can result in an mechanical power reduction of 6.4% compared to a commercial propeller. A slightly less negative tip AOA than zero lift will also lead to the lowest mechanical power required. However, if a lower sound pressure level is desired, then, for the lower hub angles of attack, a tip angle of attack slightly more negative than zero lift should be used, resulting in up to a 7.8% reduction in SPL. As seen in the data, there exists a tradeoff with between lower aerodynamic power and lower SPL using various combinations of hub and tip angles of attack.
Numerical Investigation at Nominal and Off-Design Operations Of a Supersonic Turbine for Liquid Rocket Engines With Full and Partial Admission Nozzles
Authors: Yamamoto Keita , Ukai Satoshi , Fukasawa Osamu , Fukuda Taro , Negishi Hideyo
Published: October 2022

In recent years, various types of liquid rocket engines have been developed to achieve different types of mission, and modern rocket engines are required to operate at different conditions depending on flight situations such as launch and landing. Thus, rocket engines are required to be more reliable and robust. One of the key components for a rocket engine to enable flexible operating conditions is a turbine since it determines a power of feed-line systems and an efficiency of rocket system itself. To fulfill the requested output of the entire systems, an appropriate design of the turbine, including the selection of full/partial admission configurations, is of crucial importance. On the other hand, the development of supersonic turbines in turbo-pumps remains a challenge due to their complex internal flow structures and systems with high rotational speed. Furthermore, it is necessary to achieve high performance and stable operations under extensive operating range in respect of innovative transport technologies including the development of reusable launch vehicles. However, detailed flow characteristics at off-design conditions of supersonic turbines are yet to be fully understood. Therefore, this paper aims to study internal flow characteristics and performance of a supersonic turbine at different operating points.

The present study first demonstrates the comparisons of 3D RANS simulation results of the selected supersonic turbine (JAXA subscale M-1 turbine) consisting of two stages with full admission nozzles and partial admission nozzles, where the experimental results with the partial admission configuration are available to validate the simulation results. The simulations are conducted with full stages and the entire circumferential configuration at 5 different operating conditions defined by the velocity ratio (the ratio between the turbine rotational velocity and isentropic velocity at the turbine outlet) including the nominal condition. The internal flow structures under off-design operations for both full and partial admission nozzle configurations are investigated to address profound features of the flow field at off-design operations in a supersonic turbine. The analysis is furthermore extended to reveal the mechanisms of the energy loss by comparing the results of the full admission and two different configurations of the partial admission nozzles at different operating conditions. As a result, an empirical method to determine nozzle and ventilation loss curves based on velocity ratio is proposed, and also it is demonstrated that these curves can be applied to predict energy loss of various partial admission configurations at different operating conditions.
Numerical Research on Near Stall Characteristics of a Transonic Axial Compressor Based on Wavelet Analysis
Authors: Xia Kailong , Feng Junda , Zhu Mingmin , Deng Hefang , Qiang Xiaoqing , Teng Jinfang
Published: October 2022

An axial single-stage high-speed test rig was numerically studied in this paper with half-annulus URANS simulations to describe the flow characteristics at the near stall condition. Numerical probes were arranged circumferentially near the casing in each rotor passage from the leading edge to the trailing edge evenly. Wavelet analysis was applied to demonstrate the time-frequency characteristics of the wall pressure signals captured by the probes located at different axial positions. The detailed tip flow fields and wavelet transform results were combined to depict the generation and propagation of the spike type stall inception.

According to the wavelet spectrum, characteristic frequencies correspond to the temporal and spatial features of the rotating stall, such as the fluctuation of the shock wave, self-oscillation and propagation of tip leakage vortex et al. Consequently, the detection of typical spike stall inception can be significantly brought forward through identifying the crucial rotating disturbance and its development for the onset of stall inception. Then, the specific flow fields verified by previous researchers are also discussed to reveal the flow mechanism of stall inception evolution, including the leading edge spillage and the trailing edge backflow. Further investigation showed that the stall inception with smooth casing corresponds to the radial separation vortex caused by the tip leading edge spillage, which continues to develop and propagate in the circumferential direction and finally induces the stall.
High-Fidelity Simulation Study of the Unsteady Flow Effects on High-Pressure Turbine Blade Performance
Authors: Leggett John , Zhao Yaomin , Sandberg Richard D.
Published: October 2022

Unsteadiness, in the form of both broadband background disturbances and discrete coherent wakes, can have a strong effect on the performance of turbomachinery blades. The influence of the state of the incoming flow has received much interest in turbomachinery research as it inevitably affects the state of blade boundary layers and develops as it passes through the machine. In the work presented here we build on this knowledge and further investigate the effect of unsteady flow on high-pressure turbines (HPT), using high fidelity data sets of an HPT stage produced using wall resolved large-eddy simulation (LES) (Zhao and Sandberg, GT2021-58995). The effects of incident wakes from an upstream stator, compounded by the presence of free-stream turbulence, on the performance of a downstream rotor are investigated. Based on analyzing cases for which the incoming turbulence is prescribed with different turbulence intensities and length scales, we show that changing the free-stream turbulence characteristics has a direct effect on the unsteady behavior of the stator wakes. As a result, the aerothermal performance of the rotor is also significantly affected. By detailing the influence of the wake-turbulence interaction on the performance of the rotor, we aim to distinguish driving forces on rotor performance, be it changes in the incident wakes or direct influence from the free-stream turbulence. Furthermore, the different aerothermal behaviours on the pressure-side and suction-side of the rotor blades have been extensively investigated, showing that the blade boundary layers on the suction and pressure sides respond differently to external disturbances. The insights gained can provide designers with guidelines in understanding the unsteady flow effects of a given flow state, and how the turbulence present, either broadband or deterministic, will affect the performance of downstream blades.
Transient Engine Condition Monitoring of Micro Gas Turbines in a Highly Dynamic Setting
Authors: Varchev Tihomir , Weiss Matthias , Staudacher Stephan , Koch Christian
Published: October 2022

Measurements recorded continuously throughout a flight at high sampling rates facilitate transient engine condition monitoring. This promises the generation of a large number of residual values resulting in improved detection and identification of engine component faults. The wavelet transformation is directly applied to residual values in a moving window followed by image classification using a Deep Convolutional Neural Network to detect and identify engine faults. This approach is demonstrated using simulated in-flight residual values considering Gaussian noise and measurement bias as well as engine deterioration. Three types of component faults were investigated. They are a change in efficiency, flow capacity and a combination of those two. The capability of the approach to detect and identify engine component faults was examined in three numerical experiments of increasing complexity. If a fault was detected, the approach was capable of correctly identifying the faulty engine component in all three numeric experiments. However, the ability of the approach to detect the presence of an engine component fault as well as its ability to correctly identify the particular fault type were shown to be affected by measurement uncertainty and engine deterioration.
Thermal Bowing of Steam Turbine Shafts: Prediction Methods and Field Data Matching
Authors: Vegesna Rama Raju , Checcacci Damaso , Girezzi Gabriele
Published: October 2022

The availability of steam turbines for prompt start-up, especially from hot or warm conditions, relies on the correct conditions for turbine cooldown, involving both the external casing and the shaft.

While several works are available about the prediction and optimization of cooling for steam turbines, with focus on casing temperature matching and shell thermal humping prediction, very little is available with reference to rotor bowing. Yet, in case the shaft is not maintained in slow turning during cooling, its bowing can very quickly lead to large unbalance and, eventually, to the impossibility of further turning, because of internal rubbing. These conditions may lead either to very high vibrations at restart or to the unavailability of the turbine, requiring its complete cooldown to fully recover the thermal bowing and allow a safe restart. In this work the modelling of thermal bowing of steam turbine shafts is presented. The bases of the adopted physical model are discussed, along with the necessary assumptions about transient fluid conditions around the hot shaft during its cooling at stand-still. The main model parameters affecting the shaft bowing are analysed and the transient displacements resulting from the thermal model are then quantitatively compared, for matching, with real field data. The best selection of model parameters and adopted assumptions are finally discussed.
Development, Atmospheric Testing and Field Operation of a Fuel Flexible Gas Turbine Combustion System for Crude Oil Volatile Organic Compounds
Authors: Bouten Thijs , Gralike Nick , Axelsson Lars-Uno
Published: October 2022

Volatile Organic Compounds (VOCs) evaporate from crude oil due to their volatile characteristics. These VOCs are conventionally vented, thereby contributing significantly to the harmful emission in the crude oil loading, storage and transport on offshore platforms, ships, storage tanks, terminals and shuttle tankers. The VOCs can be captured by a VOC recovery system, thereby reducing the harmful emissions significantly. The heavier fractions (mainly C3+) out of VOCs can be stored as liquid VOC (LVOC). The non-condensable fraction is a surplus gas (SVOC) mainly consisting out of lighter hydrocarbons and inert gases. The composition of LVOC and SVOC significantly varies depending on the type of crude oil. The application of both LVOC is challenging due to the high volatility, high dew point and varying compositions, while the SVOC is challenging because of the high variation in inert gas concentration, which depends on the crude oil level in the cargo tank. This paper will present the development and testing of a new tubular combustion system that can operate on the LVOC and SVOC from a VOC recovery unit as well as on LNG in case the VOC recovery plant is not operational. The challenges of the high variety in fuels are mainly translated in a dedicated fuel nozzle for the low calorific fuel combustor. This novel nozzle allows for stable operation on a wide variety of fuels with limited supply pressure requirements.

The combustor has been tested in OPRA’s state-of-the-art atmospheric combustor test rig. Hereby various fuels have been supplied. The results presented in this paper focus on the validation of flame stability, operational window, turn down and emissions operating on different mixtures of low calorific gas (SVOC) and high calorific gas (LVOC, propane and natural gas).

After successful completion of the atmospheric testing, a full-scale engine test has been performed with the OP16 gas turbine in OPRA’s engine test cell. Multiple gensets are installed on shuttle tankers and have been successfully commissioned with the various fuels. Operational experience from these sea trials are discussed. It has been proven that the OPRA OP16 gas turbine can utilize 100% of the VOC emissions recovered from the shuttle tanker, whereby power is supplied to the vessel. This results in a significant reduction of the ship’s emissions.
Experimental Investigations of Hydrogen Fuelled Pulsed Detonation Combustor
Authors: Cojocea Andrei V. , Cuciuc Tudor , Porumbel Ionuţ , Gall Mihnea , Gherman Bogdan , Crunţeanu Daniel E.
Published: October 2022

Detonation combustion unveils avenues towards increased performances and efficiencies of classic deflagration architectures and enables opportunities for supersonic flight platforms. Furthermore, their primarily fuel candidate, Hydrogen, which is prone to detonation, has enormous potential in both industrial and mobility decarbonization. Nonetheless supersonic flame propagation is associated with disadvantages in terms of aerodynamic and thermal losses, which raises difficulties in achieving practical applications. Moreover, to achieve a safe and reliable energy conversion, Hydrogen combustion needs special attention. This paper addresses the analysis of a Hydrogen fuelled pulsed detonation combustor, to contribute to the understanding of the high-speed mixing performance and to improve the specific know-how regarding pressure gain combustors. By means of Z-type Schlieren visualization technique, the structure of the engine’s exhaust plume is determined to capture the intrinsic unsteady phenomena of the detonation process. Qualitative instantaneous static pressure results are presented and correlated to the Schlieren images to evaluate the cycle stages and its operating frequency.
A Linearization Method Based on 3D Contact Model for the Steady-State Analysis Towards Complex Engineering Structures Containing Friction
Authors: Xiao Fucai , Li Lin , Wu Yaguang , Fan Yu , Zhang Hui
Published: October 2022

In this paper, a linearization method based on 3D contact model for the steady-state response analysis of dry friction systems is proposed from the perspective of engineering application. The core is to equivalently express the nonlinear force described by the 3D contact model into distributed local linear damping and stiffness by means of linearization, and apply it to the finite element model of linear substructures with MATRIX 27 elements. In this way, the steady-state response can be calculated in ANSYS. The 3D contact model ensures the accuracy of the algorithm, and the linearization improves the efficiency. Besides, the stress can be directly displayed in ANSYS post-processing. The effectiveness and efficiency are verified both on the contact interface level and the structure level. Finally, the proposed method is applied to a real multi-stage stator casing with a friction ring damper. Results show that for this finite element model with 1944 nonlinear degrees of freedom, the average calculation time for one frequency is less than 5 s. The larger the scale of the model, the greater the benefit of efficiency.
Analysis of Cavity Leakage Effects on Coupled Non-Axisymmetric Endwall-Airfoil Optimization in a Low-Speed Compressor Tandem Stator
Authors: Straccia Mattia , Giannini Samuele , Gümmer Volker
Published: October 2022

This paper aims at describing the effects of the hub leakage flow on non-axisymmetric endwall contouring and airfoil optimization in a highly-loaded tandem vane, in order to give a better understanding of the potential of the approach, independently of the seal leakage. Since its first applications on highly-loaded compressor stages, it has been highlighted how the non-axisymmetric contouring can be effective in manipulating the secondary flow behavior close to the endwalls. Many cases have proven its positive influence on the flow field behavior for single and tandem vanes, drawing general guidelines for the preliminary design phase, thanks to the usage of optimization tools. An interesting question still to be addressed in a general sense is at which specific conditions designers should rely on endwall contouring and when they should not, considering the obvious additional manufacturing expenses associated. First studies on this subject, assumed the interchangeability of non-axisymmetric endwall contouring with radial stacking laws. Nowadays, fully 3D optimized airfoil geometries being state of the art, it appears evident that new general guidelines are needed. In this context, the influence of the hub leakage flow on the definition and effectiveness of the endwall contouring is investigated, isolating its beneficial influences, which will be described independently of the topology of the low momentum fluid present close to the endwalls. Therefore, the reference geometry is varied in mass leakage flow by varying the geometry of the cavity of the shrouded tandem stator arrangement. Then, the new configuration is optimized via non-axisymmetric endwall contouring and hub airfoil profile optimization, carried out by means of a meta-heuristic approach. The investigation based on total pressure losses and static polytropic efficiency will show the break-even point of the beneficial influence of the non-axisymmetric contour with respect to the reducing leakage mass flow. Moreover, the change of design strategies adopted by the optimizer among the different flow field configurations shall serve as a reference guide for every future design choice incorporating non-axisymmetric endwall contouring.
Estimation of Resultant Airframe Forces for a Variable Pitch Fan Operating in Reverse Thrust Mode
Authors: Rajendran David John , Tunstall Richard , Pachidis Vassilios
Published: October 2022

The resultant forces with a reverse thrust Variable Pitch Fan (VPF) during the aircraft landing run are computed from the installed reverse thrust flow field obtained from an airframe-engine-VPF research model. The research model features a reverse flow capable VPF design in a future, geared, high-bypass ratio 40000 lbf engine as installed onto a twin-engine airframe in landing configuration, complete with a rolling ground plane to mimic the runway. The reverse thrust flow field during the aircraft landing run is obtained from 3D RANS/URANS solutions of the model. The evolution of the installed dynamic reverse thrust flow field is characterized by the interaction of the VPF induced reverse flow with the free stream. Several flow features like reverse flow wash-down by the freestream, external swirling helical flow development, pylon flow obstruction, 180° flow turn into the engine, subsequent separated flows, wake interactions and multi-pass recirculating flows are observed.

The resultant airframe forces due to the reverse thrust flow field is estimated by adaptations of momentum based far-field and near-field methods. In the active thrust reverser engagement regime of 140 to 40 knots, the VPF generates a sufficient axial airframe decelerating force in the range of 45% to 8% of maximum take-off thrust. A drag decomposition study and a notional ‘blocked-fan’ analysis are described to understand the stack-up of the axial decelerating force. Additionally, the resultant force has a landing speed dependent lateral force component because of the pylon obstruction induced flow non-uniformity. A beneficial downforce component due to upward deflection of streamlines is also observed. The quantification of the resultant forces from the baseline installed airframe-engine-VPF reverse thrust flow field is a necessary step to explore the feasibility of the VPF reverse thrust system for future efficient turbofan architectures, understand force generation mechanisms and to identify areas for subsequent design improvement.
Assessment of Low Engine Order Excitation of a Contaminated Turbocharger Radial Turbine Stage Using a Nozzle Ring Only Computational Model
Authors: Beierl Michaela R. , Vogt Damian M. , Fischer Magnus , Müller Tobias R. , So Kwok Kai
Published: October 2022

The use of critical fuels such as Heavy Fuel Oil (HFO) usually leads to deposits of combustion residues in the turbocharger turbine stage, foremost in the nozzle ring where flow channels can get partially or completely clogged. The resulting change in geometry is heavily asymmetrical and therefore induces Low Engine Order (LEO) excitation, which may lead to resonant excitation of rotor blades and potentially to High Cycle Fatigue (HCF) failure. The accurate prediction of LEO excitation is computationally intensive especially in the context of a probabilistic analysis.

The current study investigates the suitability of using a simplified model that only contains the nozzle ring in the assessment of LEO excitation with the goal to reduce computational costs. The aerodynamic excitation is assessed from the circumferential variation of the nozzle ring outflow. The results obtained with this simplified model are compared to results of validated forced response analyses. Two deteriorated nozzle rings are used for validation purposes, a generic one having one passage blocked by 90 percent and a digital replica of a real contaminated nozzle ring. It is shown that the simplified model is suitable for the qualitative prediction of the aerodynamic excitation if the contamination patterns feature sufficiently large differences and that the computational costs can be greatly reduced.
Improving the Aerodynamic Performance of a High-Loading Turbine Blade by End-Wall Surface Structures
Authors: Xi Yueyun , Lu Shaopeng , Jiang Hongmei , Zhang Qiang
Published: October 2022

In turbomachinery, the end-wall secondary flow introduces significant aerodynamic penalty, especially for high-loading turbine blade designs. The advances in manufacturing technology offer increased design flexibility, especially on surface structure design and fabrication, opening a new option for secondary flow control. The present combined experimental and numerical study explores the potential aerodynamic performance benefit of end-wall surface structures. Aerodynamic loss measurements were performed by using a five-hole probe in a low-speed wind tunnel. The secondary flow structures of blades with normal and high loading were studied. End-wall surface structures were added to the high-loading blade design to mitigate the secondary flow developments. RANS CFD was conducted with the same inlet and exit boundary conditions measured in the experiments. Both the numerical and experimental results demonstrate that the end-wall surface structures can effectively reduce the secondary flow loss and alleviate the lift-off motion of passage vortex. The working principle of the end-wall structures is revealed through detailed analysis of the end-wall region flow structure. The end-wall structures have to be carefully designed according to the local development of secondary flow, and there is a large space for design optimization.
Mitigation of BLI Circumferential Distortion Using Non-Axisymmetric Fan Exit Guide Vanes
Authors: Hall David , Greitzer Edward , Tan Choon
Published: October 2022

This paper presents an assessment of the effect of non-axisymmetric fan exit guide vanes (FEGVs) to mitigate, or even reduce to zero, the impact of circumferential flow distortion — such as created by boundary layer ingestion (BLI) — on fan rotor efficiency and vibratory structural forcing. The fan response to circumferential non-uniformities is characterized, for two-dimensional flow, in terms of the variations in incidence angle and unsteady rotor forces. FEGV designs with non-axisymmetric exit flow angle perturbations can eliminate either of these. More importantly, non-axisymmetric stator row designs can reduce both non-uniformities relative to the influence of an axisymmetric stator row. This suggests that design for distortion need not involve a trade-off between performance and aeromechanics; a non-axisymmetric aerodynamic design approach can improve both simultaneously. Analysis of the impact of stage design parameters has been carried out to determine FEGV exit flow angle variations that shield the rotor from the adverse effects of circumferential distortions representative of BLI. The results indicate inlet distortion effects can be mitigated with realizable non-axisymmetric FEGVs. The magnitude of the geometry variations required decreases with decreased axial rotor-stator spacing and increased flow coefficient.
On the Scatter of Creep Data: Methods to Increase Modelling Accuracy Accounting for Batch-to-Batch Dispersion
Authors: Riva Andrea
Published: October 2022

Gas turbine components and many industrial high temperature components suffer from creep, a viscous effect of the material that induce irreversible deformation, microstructural damage, and eventually failure. Creep strain (where the creep strain εcr is a function of time, stress, temperature) and creep rupture models (where the rupture time texp is a function of stress and temperature) are fitted to the results of expensive and time-consuming experimental tests, which can last for several years (e.g. test duration up to 100kh – 200kh). At longer times, in the range of components expected life target, when it is more likely to observe creep damage, the accuracy of creep models is required to be as high as possible. It is therefore crucial to optimize the model fitting process in order to minimize the error and reduce the number of tests required. To achieve such results the experimental result dispersion needs to be properly addressed. In particular, the differences between the different heats of the same material are known to be a dominant source of uncertainty in the experimental results. The differences are mainly linked to small variations in the fabrication process or chemical composition (even within the allowed variations of the purchase specification or standard recommendations), which can generate different microstructures and mechanical behavior. This is known as batch-to-batch dispersion and this phenomenon is responsible for significant creep strength differences between heats.

It is essential for the model reliability to gain the best possible insight of how the model itself can be influenced by the peculiarities and homogeneity of the available data. In order to achieve such goal, many analyses can be performed: quantitative identification strong/weak batches, analysis of the dataset inhomogeneity (i.e. a predominance of weak batches at a certain temperature or times), identification of correlations (e.g. tensile strength and chemistry, etc.), identification of creep mechanisms transitions that affect the applicability range of the model.

A statistical analysis of the test results is conducted in order to enable a non-deterministic modelling of creep rupture and strength, separately accounting for in-batch and batch-to-batch sources of dispersion. The soundness of the proposed probabilistic framework is validated via Monte Carlo simulation.

The paper is intended to provide an overview of the most recent proposals and progresses of the existing methods to deal with the problem and propose additional original methods to improve the analysis and the fitting procedure.
A Hybrid, Runtime Coupled Incompressible CFD/CAA Method for Analysis of Thermoacoustic Instabilities
Authors: Reinhardt Hanna , Alanyalıoğlu Çetin , Fischer André , Lahiri Claus , Hasse Christian
Published: October 2022

Thermoacoustic instabilities in gas turbine engines are of increasing interest for design of future low-emission technology combustors. Numerical methods used to predict thermo-acoustic instabilities often employ either fully compressible resource-intense Computational Fluid Dynamics (CFD) simulations, or two-step approaches where source terms extracted from CFD simulations are supplied to subsequent Computational Aero Acoustics (CAA) simulations. The present work demonstrates an analysis of self-excited thermoacoustic instabilities using a hybrid method based on runtime coupling of incompressible CFD and CAA simulations. A prior implementation for the computation of combustion noise through one-way coupling of CFD and CAA solvers has been extended to a two-way coupling that allows acoustics to influence the flow field. The resulting hybrid method couples acoustic and convective physical phenomena by using mean flow field quantities and the thermoacoustic energy source term obtained from the solution of the Navier-Stokes equations in the low Mach number limit as an input for the Acoustic Perturbation Equations (APE). The fluctuating acoustic quantities pressure and velocity obtained from the solution of the APE are in turn included in the solution of the low Mach number Navier-Stokes equations, influencing the convective dynamics of the flow field. The suitability of the present implementation to capture thermoacoustic feedback is demonstrated through analysis of the well-known self-excited instability observed in a Rijke Tube. The results are presented and discussed in comparison with a fully compressible reference solution.
Thermal Management for Electrification in Aircraft Engines: Optimization of Coolant System
Authors: Raske N. , Ausin Gonzalez O. , Furino S. , Pietropaoli M. , Shahpar S. , Montomoli F.
Published: October 2022

This work shows the application of fluid Topology Optimization for the thermal management of electric parts in aircraft engines. There is a growing trend in electrification of current engines, but this requires higher power to be dissipated. Standard coolant systems based on serpentines are not effective enough to remove the heat produced by these systems. In this work a new solution is shown which has a higher heat dissipation, lower pressure loss and a reduction in the mass of the heat exchanger. The optimization is carried out with the commercial solver TOffee. Manufacturing constraints allow the part to be manufacturable using two different methods: additive manufacturing and milling with diffusion bonding.

Overall, the optimized geometry, a nearly 2D coldplate with extruded channels, shows higher heat dissipation and a reduction of weight of 38.5% if compared with the baseline heat exchanger. The overall pressure drop has been also reduced by 65%.
Study on Unsteady Flow Characteristic in a Transonic Axial Compressor Rotor at Near Stall Condition
Authors: Zhang Ziyun , Wu Yanhui , Li Ziliang
Published: October 2022

In this paper, the three dimensional single-channel numerical simulation has been undertaken to analyze unsteady flow characteristic and fluctuation mechanism at near stall condition in a transonic compressor rotor. It has been found that at near stall condition, strong unsteady fluctuations appeared at the region near the downstream of shock wave and leading edge to 80% axial chord of blade pressure side in rotor tip. Then, detailed analysis of the tip flow field showed that the interaction between tip leakage vortex (TLV) and shock waves causes the spiral type breakdown of TLV, and caused reverse flow periodic shedding in the recirculation region, both of the effects given rise to the large fluctuation of the rotor tip field. Periodic shedding of the reverse flow affected the pressure distribution of blade pressure side so that the blade tip was unloaded and the tip leakage vortex breakdown was thus suppressed, thereby forming a self-sustaining unsteadiness. The TLV breakdown was the decisive factor leading to the flow unsteadiness.
Solution-Based Mesh Adaption Criteria Development for Accelerating Flame Tracking Simulations
Authors: Shrivastava Sourabh , Verma Ishan , Yadav Rakesh , Nakod Pravin
Published: October 2022

Accurate flame tracking plays a vital role in predicting the combustion characteristics of a system. This is even more critical for systems that evolve over time. Predicting relight performance of an aero combustor, predicting flame propagation due to gas leakage from a storage tank or during the thermal runaway of batteries, are some examples of such dynamic systems. Predicting accurate flame position also plays an important role in deriving the correct pollutant formation rate from a combustion system.

The challenge with flame tracking through a 3D computational fluid dynamics (CFD) simulation comes from the requirement to have a good resolution of gradients along the flame front. This requirement can push the overall mesh count of any industrial cases to a very large value (several million-mesh count). Further, the global drive towards using hydrogen or hydrogen blended fuels for different combustion applications pushes the limits on having even finer cells since hydrogen is a fast-burning fuel and has a much thinner flame front compared to hydrocarbons.

Solution-based mesh adaption approaches have been widely studied and tested by different research groups to generate the required finer meshes in the critical regions on the fly while keeping the overall mesh count to a manageable level. However, these approaches are typically applicable for a set of problems, and therefore, there is a need for a generic approach suitable for a broader range of problems. This work explores various parameters and specific weightage factors to predict correct flame-tracking outcomes for different types of flames. The selections of flow quantities (flow-variables, their gradients, curvatures) are performed using simple flames and flow configurations. The functions based on selected flow-quantities derived from these studies are then tested to predict the results for the more complex set of published flames like the Engine Combustion Network (ECN) spray flame and Knowledge for Ignition, Acoustics and Instabilities (KIAI) five-burner configuration (liquid and gas fuel). Derived adaption criteria are found to predict the correct flame tracking behavior in terms of transient evolution of flame front, flame propagation, and ignition timing of burners. The parameters used for the study are identified keeping genericity as the key point, and thus making sure that the derived adaption functions can be applied across different types of fuel blends, combustion systems (gaseous or liquid fuel-based systems) and combustion models, for example species transport or mixture fraction-based models.
Condition Monitoring of Wind Turbines Based on Anomaly Detection Using Deep Support Vector Data Description
Authors: Peng Dandan , Liu Chenyu , Desmet Wim , Gryllias Konstantinos
Published: October 2022

Wind turbine condition monitoring is considered as a key task in wind power industry. A plethora of methodologies based on machine learning have been proposed but the absence of faulty data, at the amount and the variety needed, still set limitations. Therefore Anomaly Detection methodologies are proposed as alternatives for fault detection. Deep learning tools have been introduced in the research field of wind turbines’ monitoring for the purpose of higher detection accuracy. In this work, a deep learning-based anomaly detection method, the Deep Support Vector Data Description (Deep SVDD), is proposed for the monitoring of wind turbines. Compared to the classic SVDD anomaly detection approach, this method combines a deep network, more specifically a Convolutional Neural Network (CNN), with the SVDD detector in order to automatically extract effective features. To test and validate the effectiveness of the proposed method, the Deep SVDD method is applied on SCADA data from a real wind turbine use case, targeting to the ice detection on wind turbine blades. The experimental results show that the method can effectively detect the generation of ice on wind turbines’ blades with a successful detection rate of 91.45%.