bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas Labyrinth Seals: Improved Prediction of Leakage in Gas Labyrinth Seals Using an Updated Kinetic Energy Carry-Over Coefficient
Authors: Wu Tingcheng , San Andrés Luis 
Published: January 2021

Abstract
Though simple and fast, bulk-flow models (BFMs) for gas labyrinth seals (LSs) often predict the mass flow inaccurately. The BFM models rely on classical Neumann’s equation model to characterize the flow through a labyrinth tooth. Presently, a CFD analysis quantifies the effects of tip clearance (Cr) and operating conditions on the prediction of LS mass flow, and then derives an updated kinetic energy carry-over coefficient (μ1i) to improve the accuracy of Neumann’s leakage equation. μ1i is a function of the seal tip clearance (Cr), the tooth pitch, and the total teeth number; but it does not depend on the seal supply or discharge pressures. The analysis selects a fourteen teeth on stator LS (Length/Diameter = L/D = 0.29) with clearance Cr = (1/733)D and operating at nominal supply (Pin) and discharge (Pout) pressures equal to 73 bar and 51 bar, respectively, and at a rotor speed of 12 krpm (surface speed = 138 m/s.). The CFD produces flow fields for LSs with a clearance varying from 80% to 200% of the nominal Cr, a gas supply pressure from 60 bar to 100 bar, and with various discharge pressures giving a pressure ratio (PR = Pout/Pin) ranging from 0.40 to 0.85. The numerous predictions deliver the mass flow as well as the bulk-flow velocities and cavity pressures within the seals. The kinetic energy carry-over coefficient (μ1i) increases with respect to the seal radial clearance (Cr). μ1i shows a parabolic correlation with PR; at first μ1i increases with a rise in PR from a low value; and then a further increase in PR leads to a decrease in μ1i. The coefficient μ1i is only sensitive to the pressure ratio and not to the magnitude of either the supply or discharge pressures. Lastly, for use with Neumann’s leakage model, the CFD predictions produce an updated μ1i, a function of the seal geometry and the PR condition. Integration of the new μ1i correlation into a BFM code improves its accuracy to predict LS mass flow rate, a 19% difference against test data reduces to within 6%. A TOS LS tested by Ertas et al. (2012) serves to further validate the accuracy of the modified leakage model.
Flow Distortion Into the Core Engine for an Installed Variable Pitch Fan in Reverse Thrust Mode
Authors: Rajendran David John , Pachidis Vassilios 
Published: January 2021

Abstract
The flow distortion at core engine entry for a Variable Pitch Fan (VPF) in reverse thrust mode is described from a realistic flow field obtained using an integrated airframe-engine model. The model includes the VPF, core entry splitter, complete bypass nozzle flow path wrapped in a nacelle and installed to an airframe in landing configuration through a pylon. A moving ground plane to mimic the rolling runway is included. 3D RANS solutions are generated at two combinations of VPF stagger angle and rotational speed settings for the entire aircraft landing run from 140 to 20 knots. The internal reverse thrust flow field is characterized by bypass nozzle lip separation, pylon wake and recirculation of flow turned back from the VPF. A portion of the reverse stream flow turns 180° with separation at the splitter leading edge to feed the core engine. The core engine feed flow exhibits circumferential and radial non-uniformities that depend on the reverse flow development at different landing speeds. The temporal dependence of the distorted flow features is also explored by an URANS analysis.
Total pressure and swirl angle distortion descriptors, as defined by the Society of Automotive Engineers (SAE) S-16 committee, and, total pressure loss into the core engine are described for the core feed flow at different operating conditions and landing speeds. It is observed that the radial intensity of total pressure distortion is critical to core engine operation, while the circumferential intensity is within acceptable limits. Therefore, the baseline sharp splitter edge is replaced by two larger rounded splitter edges of radii, ∼0.1x and ∼0.2x times the core duct height. This was found to reduce the radial intensity of total pressure distortion to acceptable levels. The description of the installed core feed flow distortion, as described in this study, is necessary to ascertain stable core engine operation, which powers the VPF in reverse thrust mode.
Factors of Influence on the Leakage of Brush Seals
Authors: Fuchs Alexander , Göttler Johann , Haidn Oskar J. 
Published: January 2021

Abstract
Based on previous research from the authors a modeling approach for brush seals is developed further. Each individual bristle is reproduced in both the fluid dynamics and the structural mechanics model. An investigation regarding the influence of the free bristle height and the sealing gap on the leakage mass flow rate is carried out. Results are compared to experimental and literature data. Furthermore, preliminary results of the segregated fluid-structure interaction model are presented briefly, and matched to literature data.
Influence of Pressure Surface Winglets on the Tip Leakage Flow in a Compressor Cascade With High Subsonic Mach Numbers
Authors: Wu Wanyang , Zhong Jingjun , Kan Xiaoxu , Huang Zhenyu 
Published: January 2021

Abstract
The improvement of compressor performance is facing a new technological challenge, as the compressor is considered as one of the core components in a gas turbine. Tip leakage flow affects the aerodynamic performance of the compressor rotor directly, then the compressor performance can be improved by reasonably controlling it. In recent years, the blade tip winglet has been certainly concerned as an effective flow control method for reducing the leakage loss. The mechanism of using tip winglets to control tip leakage flow in compressor cascade has been investigated in the condition of low Mach number, whereas the research in high subsonic incoming conditions also needs to be considered.
To investigate the effect of the pressure surface winglet on the aerodynamic performance of a compressor cascade at high subsonic inlet Mach numbers, an experiment compared cascades with no winglet and different width pressure surface tip winglets at different inlet Mach numbers (Ma = 0.5, 0.6 and 0.7). Results show that the pressure surface winglet weakened the pressure gradient on both sides of the blade and reduced flow loss in the condition of high subsonic Mach numbers, which in turn tip clearance flow. When pressure surface tip winglet width increased, the improving degree is increased. At the same time, a change in Mach number had a proportional the effect on tip leakage flow control. The most effective pressure surface winglet was PW2.0 at the inlet Mach number of 0.7, which produced the most significant cascade loss reduction of 6.53% when compared to the original cascade at the same inlet Mach number.
To investigate the characteristics of the compressor cascade at different incidences, the Mach number was set at 0.7 and the characteristics of cascade flow at −6°, −3°, 0°, +3° and +6°were studied. Pressure surface winglets with different widths reduced both the influence range of the leakage flow and the strength of the leakage vortex. As the tip winglet width increased, the influence of the tip winglet on the cascade flow increased. When incidences moved from negative to positive, the improvement effect of the cascade flow field with the pressure surface winglet was enhanced. When the incidence was+6°, for example the improvement effects the PW2.0 on cascade loss was 12.4%.
The flow characteristics in the compressor cascade with the pressure surface winglets behave better at different Mach numbers and incidences. Through the research in this paper, the improvement effect and mechanism of the aerodynamic performance of the pressure surface winglet in high subsonic Mach number are clearer, and the application range of the winglet is widened, which provides a rich reference for the optimization design of compressor with high subsonic Mach number.
Reduced Order Method Based on an Adaptive Formulation and its Application to Fan Blade System With Dovetail Joints
Authors: Yuan Jie , Schwingshackl Christoph , Salles Loic , Wong Chian , Patsias Sophoclis 
Published: January 2021

Abstract
Localized nonlinearities due to the contact friction interfaces are widely present in the aero-engine structures. They can significantly reduce the vibration amplitudes and shift the resonance frequencies away from critical operating speeds, by exploiting the frictional energy dissipation at the contact interface. However, the modelling capability to predict the dynamics of such large-scale systems with these nonlinearities is often impeded by the high computational expense. Component mode synthesis (CMS) based reduced order modelling (ROM) are commonly used to overcome this problem in jointed structures. However, the computational efficiency of these classical ROMs are sometimes limited as their size is proportional to the DOFs of joint interfaces resulting in a full dense matrix. A new ROM based on an adaptive formulation is proposed in this paper to improve the CMS methods for reliable predictions of the dynamics in jointed structures. This new ROM approach is able to adaptively switch the sticking contact nodes off during the online computation leading to a significant size reduction comparing to the CMS based models. The large-scale high fidelity fan blade assembly is used as the case study. The forced response obtained from the novel ROM is compared to the state-of-the-art CMS based Craig-Bampton method. A parametric study is then carried out to assess the influence of the contact parameters on the dynamics of the fan assembly. The feasibility of using this proposed method for nonlinear modal analysis is also characterised.
Noise Attenuation Potential Using Helmholtz Absorbers Integrated in Low Pressure Turbine Exit Guide Vanes and Turbine Exit Casing End Walls
Authors: Zenz Manuel , Simonassi Loris , Bruckner Philipp , Pramstrahler Simon , Heitmeir Franz , Marn Andreas 
Published: January 2021

Abstract
To further reduce the noise emitted from modern aircrafts, every possibility has to be taken into account. Acoustic liners are successfully used in the inlet or the bypass duct of aircraft engines to mitigate the noise emitted by the fan. Due to the rough environment (high temperature, flow velocity, higher order duct modes), the exhaust duct is of limited use concerning the application of acoustic liners. It is well known that the last stage low pressure turbine (LPT) has a dominant influence onto the emitted noise of an aircraft engine especially at low load conditions such as approach. A noise reduction in this area could lead to a beneficial result of decreasing the noise content which is directly emitted in the environment.
This paper is about noise attenuation using Helmholtz absorbers in various parts of a turbine exit casing (TEC). These single degree of freedom absorbers have been integrated in turbine exit guide vanes (TEGVs), with the openings on the vanes suction side, as well as in the inner and outer duct end walls. Different absorber neck diameters were investigated and combined with different vane designs. The vane designs studied included a state of the art set-up as well as vanes with a lean. Test runs were performed with altered combinations of vanes and end walls under engine relevant operating conditions in a subsonic test turbine facility for aerodynamic, aeroacoustic and aeroelastic investigations (STTF-AAAI) located at the Institute of Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. Comparisons between all these setups and the respective hard wall reference cases were done. The resulting sound pressure levels as well as sound power levels of all investigated combinations are listed and compared concerning each configurations noise attenuation potential. Additionally, the flow field downstream of every setup is analysed if the aerodynamic behaviour is changing.
The investigated operating point is the noise certification point Approach (APP) which is of high importance because of the high acoustical impact onto the environment around airports during the landing procedure of an aircraft.
The acoustical data has been obtained by using flush mounted condenser microphones located downstream of the TEC. The whole test section was rotated over 360 deg around the flow channel. To detect if the aerodynamical behaviour changes by including openings into the flow channel end walls as well as into the vanes, aerodynamic measurements have been performed downstream of the TEC. The aerodynamical data was obtained by using an aerodynamic five-hole-probe (5HP) as well as a trailing edge probe.
Finite Element Velocity Perturbation Application in Investigating Compressor Dovetail Fretting in Time Domain
Authors: Duong Loc Q. , Lamicq Olivier J. 
Published: January 2021

Abstract
In the design of a gas turbine airfoil, avoiding resonance at all conditions is impossible. The airfoil may vibrate fiercely during resonant passages, which then may induce small oscillation motion at the disk attachment. Due to microslip at the contact regions, fretting would occur in conjunction with the reduction of material fatigue properties. This paper presents a finite element analysis using the Velocity Perturbation Method (VPM) in predicting airfoil attachment nonlinear fretting-behavior in the time domain at a resonant frequency of interest. Numerical simulation, showing design fretting fatigue characteristics based on fundamental Ruiz and Smith-Watson-Topper (SWT) criteria, is demonstrated on two models, simplified and representative. The simplified model was used for detail analysis set-up and basic post-processing while the representative model illustrated the difference in nonlinear contact response of an industrial compressor under bending and torsional modes in the time domain.
This Finite Element velocity perturbation approach can be used to study the main factors affecting fretting of any two bodies in contact: load, coefficient of friction, contact geometry and impact of different frequencies or modal shapes in the time domain.
Effect of the In-Hole Vortical Structures on the Cylindrical-Hole Film-Cooling Effectiveness
Authors: Agarwal Shubham , Gicquel Laurent , Duchaine Florent , Odier Nicolas , Dombard Jérôme 
Published: January 2021

Abstract
Understanding the flow from a cooling hole is very important to be able to properly control film cooling of turbine blades. For this purpose, large eddy simulation (LES) investigation of the flow inside a cylindrical film cooling hole is presented in this paper. Two different geometries, with different hole metering lengths, are investigated at a blowing ratio of 0.5. The main flow structure in the hole are the hairpin vortices that originate from a shear layer formed due to flow separation near the hole entry. The comparison of these hairpin vortices in the two cases with different hole metering length is presented in detail. The results show that in case of the hole with longer length the hairpin vortices dissociate within the hole itself. In such a case a uniform flow is seen at the hole exit. However, when the hole length is significantly decreased, it is shown that these vortices exit the hole and effect the vortex structures outside the hole, thereby accounting for the reduction in film cooling effectiveness. Overall, these results bring forth one other major reason for the reduction in film cooling effectiveness with reduction in hole length, i.e. the exit of in-hole hairpin vortices into the crossflow.
Non-Uniform Two-Phase Flow of Supercritical Carbon Dioxide Centrifugal Compressor
Authors: Bao Wenrui , Yang Ce , Fu Li , Yang Changmao , Ji Lucheng 
Published: January 2021

Abstract
An asymmetric structure of volute in a supercritical carbon dioxide centrifugal compressor induces a non-uniform circumferential distribution of the upstream flow field, which inevitably affects the formation of a two-phase region of carbon dioxide in an impeller. In this work, unsteady simulations for centrifugal compressors were conducted. First, the influence of low static strip induced by low static pressure near volute tongue on the impeller flow field was presented. Then, the non-uniform flow field distribution in the impeller passages and flow characteristics of the passages at the impeller inlet were obtained. Finally, the two-phase regions in the impeller were presented. The results demonstrate that for a centrifugal compressor with volute, the two-phase region appears not only on the suction surface of the leading edge of the blade, but also in some impeller passages, on the pressure surface of the blade near the leading edge, and in the leading edge and mid-chord of tip clearance, under the design conditions. The low static pressure strip induced by the volute leads to a high-speed region in the impeller passages where the temperature and pressure of supercritical carbon dioxide fall below the critical point and carbon dioxide enters the two-phase region. Meanwhile, the static pressure on the blade surface is distorted under the influence of a high-speed region in the passages, resulting in the formation of a two-phase region at the tip clearance. The flow distortion of passages at the impeller inlet results in the appearance of two-phase regions on the both sides of leading edge of the blade. The dryness on the suction side of the blade leading edge and the leading edge of the tip clearance is lower, which indicated that the proportion of liquid-phase carbon dioxide is higher in these two-phase regions.
Potential of Decentralized Container-Scale PtL Plants for Aviation: From Crude to Post-Processed FT-SPK
Authors: Jürgens Sophie , Selinsek Manuel , Bauder Uwe , Rauch Bastian , Köhler Markus 
Published: January 2021

Abstract
In today’s pressing quest of emission and pollution reduction in all energy sectors, research on renewable and sustainable fuels is a key component. The Institute of Combustion Technology at the German Aerospace Center strives to assess new, renewable fuel in a gear wheel approach of interdependent linked experiments, database comparison and model-based assessment, allowing for a fast iterative feedback to the fuel producer and giving a detailed valuation of fuels as well as a distinguished preselection when presented with numerous fuel samples.
Synthetic fuels as a substitute for fossil fuels are becoming increasingly important within the framework global climate protection goals. Power-to-X technologies such as Fischer-Tropsch synthesis can be used to produce carbon-neutral fuels using carbon dioxide from air (direct air capture) and hydrogen obtained by water electrolysis using green electricity. This fuel assessment has been iteratively performed for the post-processing of a Fischer-Tropsch fuel, produced in the module-based, compact and highly innovative PtL plant erected by INERATEC GmbH.
The aim of the present work was to evaluate the postprocessing steps hydration and distillation of the crude Fischer-Tropsch products with hindsight to “fit-for-purpose” properties of the resulting products for aviation. The chemical composition was determined using comprehensive two-dimensional GCxGC chromatography. Numerical blending analysis was performed utilizing the DLR SimFuel platform to evaluate the range of blending ratios of the Fischer-Tropsch fuels with conventional jet fuels. It could be demonstrated that the post-processed Fischer-Tropsch fuels display a beneficially high blending potential with conventional jet fuels considering the chemical composition and combustion behavior.
Conditioning of Leakage Flows in Gas Turbine Rotor-Stator Cavities
Authors: Darby P. W. , Mesny A. W. , De Cosmo G. , Carnevale M. , Lock G. D. , Scobie J. A. , Sangan C. M. 
Published: January 2021

Abstract
Ingress is the penetration of hot mainstream fluid into the cavity formed between the turbine disc (rotor) and its adjacent casing (stator). Gas turbine engine designers use rim seals fitted at the periphery of the discs and a superposed sealant flow — typically fed through the bore of the stator — is used to reduce, or in the limit prevent, ingress. Parasitic leakage enters the cavity through pathways created between mating interfaces of engine components. Owing to the aggressive thermal and centrifugal loading experienced during the turbine operating cycle, the degree of leakage and its effect on ingress are difficult to predict.
This paper considers the potential for leakage flows to be conditioned in order to minimise their parasitic effect on disc cooling, and ultimately engine, performance. Measurements of static and total pressure, swirl and species concentration were used to assess the performance of a simple axial clearance rim-seal over a range of non-dimensional leakage flow-rates. A computational model was used to provide flow visualisation to support the interpretation of flow structures derived from the experiments.
Data is presented to investigate the effects of swirling the leakage flow in accordance with, and counter to, the disc rotation. The injected momentum from the leakage created a toroidal vortex in the outer part of the cavity. Co-swirl was found to improve the sealing effectiveness by up to 15% compared to the axially-introduced baseline and counter-swirled configurations. Varying the momentum of the leakage flow was considered by passing consistent mass-flows through a range of leakage outlet areas. Increasing the momentum was seen to increase the influence of the toroidal vortex on the flow structure in the cavity, which in turn influenced the sealing effectiveness.
Rotordynamic Performance of the Interlocking Labyrinth Seal With a Tilting Rotor
Authors: Zhang Wanfu , Wang Yingfei , Gu Qianlei , Yin Lu , Yang Jian-gang 
Published: January 2021

Abstract
Numerical analysis model of an interlocking labyrinth seal (ILS), including 6 seal cavities and 7 seal teeth (3 teeth on the rotor, 4 teeth on the stator), is established for studying the effect of tilting rotor on its rotordynamic characteristics. The dynamic characteristic identification method based on infinitesimal theory is applied to solve the dynamic force coefficient of the annular seal with arbitrary elliptical orbits and eccentric positions under field conditions. The paper investigated the dynamic characteristics of the interlocking labyrinth seal with various misalignment angles (θ = 0, 0.1°, 0.2°, 0.3°, 0.4°, 0.5°, 0.6°), different pressure ratios (Pin = 6.9 bar, PR = 0.5, 0.8), locations of misalignment center (Loc = 0, L/2, L). Results show that the tilting rotor could minimize the leakage flow rate of the ILS. When the misalignment angle θ = 0.6°, the mass flow rate can be reduced about 2.5%. The tilting rotor will cause the geometric deformation of the ILS cavity and the changes in the radial clearance of the teeth, which results in an increasing pressure drop in the seal cavity. The effect of each cavity in the ILS on the stability of the system is different. The cavity with the inlet close to the rotor and the outlet away from the rotor helps to improve the system stability due to its locally anti-rotational flow. The effective damping of the entire ILS increases as the misalignment angle increases. The system shows the best stability when the misalignment center is close to the seal inlet. The stability of the seal cavity C1 can be improved for any misalignment centers. The stability of the seal cavity C2 decreases when the misalignment center moves toward the seal outlet. For the seal cavities C3∼C6, their stability can be improved for Loc = 0, L/2, and decreases for Loc = L. The tilting rotor has a positive effect on the stability of the ILS only except for high whirling frequency (&gt; 100 Hz) under Loc = L.