bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of the Fuel Distribution in a Shockless Explosion Combustor
Authors: Yücel Fatma Cansu , Habicht Fabian , Jaeschke Alexander , Lückoff Finn , Oberleithner Kilian , Paschereit Christian Oliver 
Published: January 2021

Abstract
Shockless explosion combustion is a promising concept for implementing pressure gain combustion into a conventional gas turbine cycle. This concept aims for a quasi-homogeneous autoignition that induces a moderate rise in pressure. By this, considerable losses due to entropy generation by inherent shock waves of detonation-based concepts can be avoided. Since the ignition is not triggered by an external source but driven by chemical kinetics only, the homogeneity of the autoignition is very sensitive to local perturbations in equivalence ratio, temperature, and pressure that produce undesired local premature ignition. Therefore, the precise injection of a well-defined fuel profile into an convecting air flow is crucial to ensure a quasi-homogeneous ignition of the entire flammable mixture. The objective of this work is to demonstrate that the injected fuel profile is preserved throughout the entire measurement section. For this, two different control trajectories are investigated. Optical measurement techniques are used to illustrate the effect of turbulent transport and dispersion caused by boundary layer effects on the fuel concentration profile inside the combustor. Results from line-of-sight measurements by tunable diode laser absorption spectroscopy indicate that the transport of the fuel-air mixture is dominated by turbulent diffusion. However, comparisons to numerical calculations reveal the effect of dispersion towards the bounds of the fuel concentration profile. The spatially resolved distributions of the fuel concentration inside the combustor gained from acetone planar laser induced fluorescence replicates a typical velocity distribution of turbulent pipe flow in radial direction visualizing boundary layer effects. Comparing both methods provide deep insights into the transport processes that have an impact on the operation of the shockless explosion combustor.
On the Effect of Supplied Flow Rate to the Performance of a Tilting-Pad Journal Bearing: Static Load and Dynamic Force Measurements
Authors: San Andrés Luis , Jani Hardik , Kaizar Hussain , Thorat Manish 
Published: January 2021

Abstract
Rotating machinery relies on engineered tilting-pad journal bearings (TPJB) to provide static load support with minimal drag power losses, safe pad temperatures, and ensuring a rotordynamic stable rotor operation. End users focus on reducing the supplied oil flow rate into a bearing to both lower operational costs and to increase drive power efficiency. This paper presents measurements of the steady-state and dynamic forced performance of a TPJB whilst focusing on the influence of supplied oil flow rate, below and above a nominal condition (50% and 150%). The test bearing has five pads, slenderness ratio L/D = 0.4, spherical pivots with pad offset = 50% and a preload ∼ 0.40, with a clearance to radius ratio (Cr/R) ≈ 0.001 at room temperature. The bearing is installed under a load-between-pads (LBP) orientation and has a flooded housing with end seals. The test conditions include operation at various shaft surface speeds (32 m/s-85 m/s) and specific static loads from 0.17 MPa to 2.1 MPa. A turbine oil lubricates the bearing with a speed-dependent flow rate delivered at a constant supply temperature. Measurements obtained at a steady thermal equilibrium include the journal static eccentricity and attitude angle, the oil exit temperature rise, and the pads’ subsurface temperatures at various locations, circumferential and axial. The rig includes measurement of the drive torque and shaft speed to produce the bearing drag power loss. Dynamic force coefficients include stiffness, damping, and virtual-mass coefficients. As expected, the drag power and the lubricant temperature rise depend mainly on shaft speed rather than on applied load. A reduction in oil flow rate to 50% of its nominal magnitude causes a modest increase in journal eccentricity, a 15% reduction in drag power loss, a moderate raise (6°C) in pads’ subsurface temperatures, a slight increase (up to 6%) in the direct stiffnesses, and a decrease (up to 7%) in direct damping coefficients. Conversely, a 1.5 times increase in oil flow rate causes a slight increase (up to 9 %) in drag power loss, a moderate reduction of pads’ temperatures (up to 3°C), a maximum 5% reduction in direct stiffnesses, and a maximum 10% increase in direct damping. The paper also presents comparisons of the test results against predictions from a thermo-elasto-hydrodynamic lubrication model. In conclusion, a 50% reduced oil flow rate only causes a slight degradation in the test bearing static and dynamic force performance and does not make the bearing operation unsafe for tests with surface speed up to 74 m/s. As an important corollary, the measured bearing drag power differs from the conventional estimate derived from the product of the supplied flow rate, the lubricant specific heat and the oil exit temperature rise.
New Insights From Conceptual Design of an Additive Manufactured 300 W Micro Gas Turbine Towards UAV Applications
Authors: Badum L. , Leizeronok B. , Cukurel B. 
Published: January 2021

Abstract
Owing to the high energy density of hydrocarbon fuels, ultra-micro gas turbines with power outputs below 1 kW have clear potential as battery replacement in drones. However, previous works on gas turbines of this scale revealed severe challenges due to air bearing failures, heat transfer from turbine to compressor, rotordynamic instability and manufacturing limitations. To overcome these obstacles, a novel gas turbine architecture is proposed based on conventional roller bearing technology that operates at up to 500,000 RPM and an additively manufactured monolithic rotor in cantilevered configuration, equipped with internal cooling blades. The optimum turbomachinery design is elaborated using diabatic cycle calculation, coupled with turbomachinery meanline design code. This approach provides new insights on the interdependencies of heat transfer, component efficiency and system electric efficiency. Thereby, a reduced design pressure ratio of 2.5 with 1200 K turbine inlet temperature is identified as most suitable for 300 W electric power output. In following, a review of available additive manufacturing technologies yields material properties, surface roughness and design constraints for the monolithic rotor. Rotordynamic simulations are then conducted for four available materials using a simplified rotor model to identify valid permanent magnet dimensions that would avoid operation close to bending modes. To complete the baseline engine architecture, a novel radial inflow combustor concept is proposed based on porous inert media combustion. CFD simulations are conducted to quantify compressor efficiency and conjugate heat transfer analysis of the monolithic rotor is performed to assess the benefit of the internal cooling cavity and vanes for different rotor materials. It is demonstrated that the cavity flow absorbs large amount of heat flux from turbine to compressor, thus cooling the rotor structure and improving the diabatic cycle efficiency. Finally, the results of this conceptual study show that ultra-micro gas turbine with electric efficiency of up to 5% is feasible, while energy density is increased by factor of 3.6, compared to lithium-ion batteries.
Boundary Layer Flashback Limits of Hydrogen-Methane-Air Flames in a Generic Swirl Burner at Gas Turbine Relevant Conditions
Authors: Ebi Dominik , Jansohn Peter 
Published: January 2021

Abstract
Operating stationary gas turbines on hydrogen-rich fuels offers a pathway to significantly reduce greenhouse gas emissions in the power generation sector. A key challenge in the design of lean-premixed burners, which are flexible in terms of the amount of hydrogen in the fuel across a wide range and still adhere to the required emissions levels, is to prevent flame flashback. However, systematic investigations on flashback at gas turbine relevant conditions to support combustor development are sparse. The current work addresses the need for an improved understanding with an experimental study on boundary layer flashback in a generic swirl burner up to 7.5 bar and 300° C preheat temperature. Methane-hydrogen-air flames with 50 to 85% hydrogen by volume were investigated. High-speed imaging was applied to reveal the flame propagation pathway during flashback events. Flashback limits are reported in terms of the equivalence ratio for a given pressure, preheat temperature, bulk flow velocity and hydrogen content. The wall temperature of the center body along which the flame propagated during flashback events has been controlled by an oil heating/cooling system. This way, the effect any of the control parameters, e.g. pressure, had on the flashback limit was de-coupled from the otherwise inherently associated change in heat load on the wall and thus change in wall temperature. The results show that the preheat temperature has a weaker effect on the flashback propensity than expected. Increasing the pressure from atmospheric conditions to 2.5 bar strongly increases the flashback risk, but hardly affects the flashback limit beyond 2.5 bar.
Possibilities and Limitations of Early Fault Detection in Gas Turbines
Authors: Persigehl Bernhard , Gellermann Thomas , Thumm Stefan , Stoiber Johannes 
Published: January 2021

Abstract
Since the 1960’s the maintenance concepts of gas turbines have remarkably changed. Nowadays, condition monitoring systems supervise modern gas turbines. These systems are capable of avoiding failures that are developing slowly. The actual enhancement of early fault detection is predictive maintenance where big data from different sources is used to predict the behavior of gas turbines.
In this paper eight different actual gas turbine failures are presented, beginning with the damage event and the root cause and followed by a discussion, whether the failure could have been avoided by predictive maintenance. In some cases, e.g. during commissioning, a successful early fault detection with predictive maintenance cannot be achieved, since the failure often occurs suddenly and is unforeseen. In others cases, especially during operation, the failure could have been prevented by predictive maintenance. However, it has to be stated, in all these cases significantly more measuring devices would have been necessary.
The potential exists that more failures can be avoided by predictive maintenance in the future. However, there are also damage scenarios that cannot be prevented by any early fault detection system. Thus, the Possible Maximum Loss, an important figure for technical insurances, remains unchanged independent of the application of predictive maintenance.
Modeling of Cyclic Life for Compressor Rotor of Gas Turbine Engine Taking Into Account Production Deviations
Authors: Arkhipov Alexandr N. , Ravikovich Yury A. , Matushkin Anton A. , Kholobtsev Dmitry P. 
Published: January 2021

Abstract
The regional aircraft with a turbofan gas turbine engine, created in Russia, is successfully operated in the world market. Further increase of the life and reduction of the cost of the life cycle are necessary to ensure the competitive advantages of the engine.
One of the units limiting the engine life is the compressor rotor. The cyclic life of the rotor depends on many factors: the stress-strain state in critical zones, the life of the material under low-cycle loading, the regime of engine operation, production deviations (within tolerances), etc.
In order to verify the influence of geometry deviations, the calculations of the model with nominal dimensions and the model with the most unfavorable geometric dimensions (worst cases) have been carried out.
The obtained influence coefficients for geometric and weight tolerances are then used for probabilistic modeling of stresses in the critical zone. Rotor speed and gas loads on the blades for different flight missions and engine wear are determined from the corresponding aerodynamic calculations taking into account the actual flight cycles (takeoff, reduction, reverse) and are also used for stress recalculations.
The subsequent calculation of the rotor cyclic life and the resource assessment is carried out taking into account the spread of the material low-cycle fatigue by probabilistic modeling of the rotor geometry and weight loads.
A preliminary assessment of the coefficients of tolerances influence on stress in the critical zone can be used to select the optimal (in terms of life) tolerances at the design stage.
Taking into account the actual geometric and weight parameters can allow estimating the stress and expected life of each manufactured rotor.
A Damage-Based Fatigue Model of Braided Ceramic Matrix Composites at Elevated Temperature
Authors: Liu Changqi , Shi Duoqi , Yang Xiaoguang , Teng Xuefeng 
Published: January 2021

Abstract
Ceramic matrix composites (CMCs) play an increasingly significant role in the modern aerospace industry due to their excellent high-temperature mechanical properties. Fatigue property at elevated temperatures is an essential issue for their application, especially for the turbine blades of aircraft engines subjected to cyclic loading under extreme conditions. A progressive fatigue damage approach was established to predict the damage initiation and evolution of braided SiC/SiC CMCs under tension-tension cyclic loading. The main framework was achieved via a user-material subroutine UMAT in ABAQUS with FORTRAN code. Different damage initiation criteria are introduced for fiber bundles, matrix and interface. Related experimental results reveal that the main reasons for the failure of composites under cyclic loading are the loss of bearing capacity of the matrix, the decrease of fiber strength in high-temperature oxidation environment and the interface wear. Hence, the stiffness and strength degradation of matrix and fiber bundles as well as the interfacial shear stress reduction are used to describe the fatigue damage in this method. And a specific proportion of failure elements on the loading surface is regarded as the symbol of the eventual failure of the composites. Damage evolution of different constituents during the fatigue process can be simulated with this method. Subsequently, the simulation results of static and fatigue analysis were compared with relevant experimental results at 1300°C. It indicates that the predicted static tensile strain-stress curve, and curves of maximum strains vs cycles in the fatigue analysis are in good agreement with that measured during the experiments. Besides, the predicted fatigue life also exhibits an acceptable consistency.
An Experimental and Computational Investigation of a Pulsed Air-Jet Excitation System on a Rotating Bladed Disk
Authors: Kurstak Eric , D’Souza Kiran 
Published: January 2021

Abstract
Non-synchronous vibrations are a difficult problem to address for turbomachines due to the complex nature of the forcing. Such vibrations can be caused by vortex shedding, flow instabilities, stall cells, or flutter. Testing a design with such excitations can be difficult in practice due to the required forcing. This work demonstrates an experimental excitation method using pulsed air jet excitation to create non-synchronous vibrations in engine hardware rotating at nominal design speeds. Experimental runs were conducted to excite a number of engine orders. Blade tip timing was used to measure the blade response without interfering with the blade dynamics. The bladed disk was held at a constant rotational speed while the air jets were pulsed at a sweeping frequency to simulate rotating forcing. Computational models of the physical system were constructed using parametric reduced order models that incorporate the effects of rotational speed and small mistuning. The computational model was used in simulations that mimic the experiment; the forcing was swept across the blades while being pulsed. This results in a system response that cannot be captured using traditional harmonic analyses. The computational and experimental datasets were compared through mistuning values, amplitudes, and the nodal diameter content in the system response.
Numerical Modeling of the Effects of Leading-Edge Erosion and Trailing-Edge Damage on Wind Turbine Loads and Performance
Authors: Papi Francesco , Cappugi Lorenzo , Bianchini Alessandro , Perez-Becker Sebastian 
Published: January 2021

Abstract
Wind turbines often operate in challenging environmental conditions. In hot and dusty climates, wind turbine blades are constantly exposed to abrasive particles that, according to many field reports, cause significant damages to the blade’s leading edge. On the other hand, in cold climates similar effects can be caused by prolonged exposure to hail and rain. Quantifying the effects of airfoil deterioration on modern multi-MW wind turbines is crucial to correctly schedule maintenance and to forecast the potential impact on productivity. Analyzing the impact of airfoil damage on fatigue and extreme loading is also important to improve the reliability and longevity of wind turbines. However, this is a topic that has not yet been extensively investigated. In this work, a blade erosion model is developed and calibrated using Computational Fluid Dynamics (CFD). The DTU 10MW Reference Wind Turbine (RWT) is selected as the case study for the analysis, as it is representative of the typical size of the future generation wind turbines. Lift and Drag polars are generated using the developed model and a CFD numerical set-up. Power and torque coefficients are compared in idealized conditions at two wind speeds, i.e. the rated speed and one below it. Full aero-servo-elastic simulations of the turbine are conducted with the eroded polars using NREL’s BEM-based code OpenFAST. Sixty-six ten-minute simulations are performed for each stage of airfoil damage, reproducing operating conditions specified by the IEC 61400-1 power production DLC-group, including wind shear, yaw misalignment and turbulence. Performance data, fatigue and extreme loads are compared for the aeroelastic simulations, showing maximum decreases in CP of about 12% as well as reductions in fatigue and extreme loading.
The Endwall Effects of Stators With and Without Simplified Penny Gaps in a High-Loaded Multistage Compressor
Authors: Wang Xiaochen , Ren Xiaodong , Li Xuesong , Wu Hong , Gu Chunwei 
Published: January 2021

Abstract
A simplified configuration of variable stator vanes, which has a uniform hub clearance and a stationary hub surface, is applied to a high-loaded multistage compressor. Comparisons of endwall flow structures are made between the ideal and the simplified configurations. After validating numerical results of the ideal stator configuration with experiment data, the third stator and all stators are modified with the simplified configuration in two separate cases. Flow structures and loss characteristics in the endwall region are investigated numerically in detail at design point. Limited corner separation near the suction side and comparatively strong secondary flow near the pressure side make similar contributions to endwall loss at design point for the baseline configuration, while the shear flow of the blade tip and the endwall boundary layer are regarded as important sources of loss for the modified configuration.
Experimental Investigation and Numerical Modelling of a Large Heavily-Loaded Tilting Pad Journal Bearing With Polymer Lined Pads
Authors: Cangioli Filippo , Livermore-Hardy Richard , Pethybridge Guy , Mermertas Uemit , Stottrop Michael , Bender Beate 
Published: January 2021

Abstract
A large tilting-pad journal bearing (TPJB) with “PEEK” polymer-lined pads was tested over a range of operating conditions representative of those experienced on turbogenerators used in fossil fuel power plants. The 500 mm diameter test-bearing has four offset-pivot pads, ball and socket pivots, load-between-pivot configuration, directed lubrication and hydrostatic jacking features. The operating conditions explored during the test campaign characterize the static and dynamic behaviour of the bearing over a range of shaft surface speeds between 40 m/s and 95 m/s and maximum specific load of 4.75 MPa. Similar test conditions were previously investigated on the same bearing with whitemetal lined pads, allowing for a direct comparison.
A thermo-elasto-hydrodynamic (TEHD) model for TPJBs with polymer-lined pads is introduced in this paper and validated against experimental test data.
Experimental data along with numerical results reveal and confirm the superior performance that can be attained using TPJBs with polymer lined pads at high specific loads.
A Method for the Simulation of Time-Dependent In-Service Performance Change
Authors: Evans Rich , Dawes Bill , Meah Nabil , Kudryavtsev Andrey , Hunt Matthew 
Published: January 2021

Abstract
Most numerical engineering simulation is performed on pristine, as-designed representations of the components and systems in question. Although the rate of through-life performance degradation is hugely important when considering the total cost/benefit of a system, engineers have had profound difficulties in modelling the physical changes that components undergo in service due to the quasi-random and organic nature of the mechanisms such as wear, corrosion, icing and fouling. Typically, the creation of ‘worn’ models is based on a posteriori inspection or scanning of a failing or failed component.
This paper presents a novel method for modifying geometry in response to scalar field variables directly accessed from the embedded physical models within physics-based simulation. It uses a distance field, managed as a Level-set, to drive time-dependent changes to the geometry surface, borrowing heavily from technology which has seen widespread use in the computer graphics industry to create and modify items in a natural organic way. A computational mesh can then be constructed around and within the modified geometry so that the simulation can be performed on the now ‘in-service’ version of the components. This greatly improves the predictive power of such simulations and provide a priori predictions of component performance in response to, for example, corrosive environments.
The method is robust, can manage and create meshes for arbitrarily complex geometry, is insensitive to large scale topology changes such as hole blockage or passage burn-through, is highly suitable for automated simulation workflows and can represent both additive (fouling, icing) and reductive (erosion, corrosion, burn though) shape change.