bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oil-Air Flow Between the Cage and Inner Race of an Aeroengine Bearing
Authors: Adeniyi Akinola A. , Morvan Hervé , Simmons Kathy 
Published: September 2016

In aeroengines the shafts are supported on bearings that carry the radial and axial loads. A ball bearing is made up of an inner-race, an outer-race and a cage which contains the balls, these together comprise the bearing elements. The bearings require oil for lubrication and cooling. The design of the bearing studied in this work is such that the oil is fed to the bearing through holes/slots in the inner race. At each axial feed location the oil is fed through a number of equispaced feedholes/slots but there is a different number of holes at each location. Once the oil has passed through the bearing it sheds outwards from both sides into compartments known as the bearing chambers.
A number of studies have been carried out on the dynamics of bearings. Most of the analyses consider the contributions of fluid forces as small relative to the interaction of the bearing elements. One of the most sophisticated models for a cage-raceway analysis is based on the work of Ashmore et al. [1], where the cage-raceway is considered to be a short journal bearing divided into sectors by the oil feeds. It is further assumed that the oil exits from the holes and forms a continuous block of oil that exits outwards on both sides of the cage-raceway. In the model, the Reynolds equation is used to estimate the oil dynamics.
Of interest in this current work is the behaviour of the oil and air within the space bounded by the cage and inner race. The aim is to determine whether oil feed to the bearing can be modelled as coming from a continuous slot or if the discrete entry points must be modelled. A Volume of Fluid Computational Fluid Dynamics approach is applied. A sector of a ball bearing is modelled with a fine mesh and the detailed simulations show the flow behaviour for different oil splits to the three feed locations of the bearing thus providing information useful to understanding oil shedding into the bearing chambers.
The work shows that different flow behaviour is predicted by models where the oil inlets through a continuous slot compared to discrete entry holes. The form and speed of oil shedding from the bearing is found to depend strongly on shaft speed with the shedding speed being slightly higher than the cage linear speed. The break-up pattern of oil on the cage inner surface suggests smaller droplets will be shed at higher shaft speed.
Experimental Investigation of the Flow in a Control Valve of an Industrial Steam Turbine
Authors: Zeß Jan-Peter , Polklas Thomas , Joos Franz 
Published: September 2016

Unsteady flows in steam turbine control valves are becoming more and more a subject of interest for many reasons. In general, steam conditions have increased for both industrial and power plant turbines. Flexible operation conditions of industrial turbines are a field of research ever since, but became more and more interesting for power plants due to the significant rise of renewable energies and their natural inconstant supply.
In this paper the results of experiments in an original sized industrial steam turbine control valve are presented. The experiments with air as fluid focus on the flow in the diffuser and are recorded using PIV techniques. With the results typical flow patterns are derived and allocated to a number of operating points with variation in pressure and opening ratio and therefore also in mass flow.
LES-Based Assessment of Rotation-Sensitized Turbulence Models for Prediction of Heat Transfer in Internal Cooling Channels of Turbine Blades
Authors: Borello Domenico , Rispoli Franco , Properzi Ermanno , Salvagni Alessandro 
Published: September 2016

A comprehensive model for the prediction of flows in rotating internal cooling channel application is here presented and assessed. The flow field was modelled by using a rotation-sensitized version of the well known k-ε-ζ-f elliptic relaxation model.
Flow field features in selected planes are discussed to show the changes in velocity field due to the rotation. The discussion is focused on the increase of turbulence close to the ribbed (trailing) surface when rotation is present. In this case the increase of the wall normal pressure gradient leads to an early reattachment of the large recirculation bubble downstream from the rib and to an anticipated development of the boundary layer. Furthermore, Coriolis force enhances the secondary motion. Both phenomena increase mixing and are expected to also increase heat transfer efficiency of the heated surface.
This is confirmed by the results of the temperature field. Comparisons with the available experimental results confirm the quality of the prediction.
Experimental Analyses of a Static to Static Flex Seal and a Honeycomb Seal
Authors: Zierer Thomas , Bricaud Cyrille , Escudero-Olano Marcos , McNally Joshua , Mohammed Afzal Pasha 
Published: September 2016

Improvements in turbine performance are increasingly driven by the need to control leakage both in the main gas path as well as in the secondary air flow system. Seals for static to static interfaces have a wide usage in gas turbine for component interface locations and are becoming more important as engines reach higher temperature targets and compressor pressure ratios.
Both flex and honeycomb seals have been used for many years during other OEM seal service upgrades. These seals are designed to be capable of sustaining low leakage operation whilst achieving long lifetimes. To determine the sealing capability of honeycomb and flex seals an advanced hydraulically actuated rig was designed and constructed. A series of leakage performance tests were carried out that accurately simulate engine conditions, including pressure and relative axial and radial movements.
The results of these tests are compared against previously presented data on standard membrane seals. Compared to the membrane seal, the flex seal has approximately 60% lower equivalent clearance when tested with uneven (triangular) grooves. This reduction was due to the bending of the seal and subsequent closing of the seal gap under pressure. The flex and membrane seal performed similarly well under more nominal conditions. The honeycomb seal achieved a consistently low leakage under all pressure loadings. All three sealing types have their place in the required technology mix which is essential when aiming for maximized engine performance and lifetime.
Forced Vibration of Mistuned Bladed Discs in Last Stage LP Steam Turbine
Authors: Rzadkowski Romuald , Maurin Artur , Kubitz Leszek , Szczepanik Ryszard 
Published: September 2016

During the exploitation of a commercial LP steam turbine, self-excitation occurred in the last stage of slender blades, inducing high vibration amplitudes. These problems were solved by changing the geometry of certain blades (feathering) and arranging them in a specific order (alternating mistuning).
This paper presents free and forced vibrations of various mistuned steam turbine bladed discs. The natural frequencies and mode shapes of the steam turbine bladed discs were calculated using FEM models. Two different approaches to mistuning were applied: either the blade geometry or the Young’s Modulus were changed. Next, the results were compared. This showed that blade geometry mistuning gave the best results for long blades in the case of higher mistuning. The forced vibration analysis showed that the maximal blade stress location differed, depending on the kind of mistuning. The application feathering and alternating mistuning showed lower stress levels than the tip-timing measured standard mistuning pattern.
Numerical Investigation of the Flow Behavior Inside a Supercritical CO2 Centrifugal Compressor
Authors: Ameli Alireza , Turunen-Saaresti Teemu , Backman Jari 
Published: September 2016

Centrifugal compressors are one of the best choices among compressors in supercritical Brayton cycles. A supercritical CO2 centrifugal compressor increases the pressure of the fluid which state is initially very close to the critical point. When the supercritical fluid is compressed near the critical point, wide variations of fluid properties occur. The density of carbon dioxide at its critical point is close to the liquid density which leads to reduction in compressor work.
The investigated compressor is a centrifugal compressor tested in the Sandia supercritical CO2 compression loop. In order to get results with the high accuracy and take into account the non-linear variation of the properties near the critical point, the CFD flow solver is coupled with a lookup table of properties of fluid. Behavior of real gas close to its critical point and the effect of the accuracy of the real gas model on the compressor performance are studied in this paper and the results are compared with the experimental data from the Sandia compression facility.
Unsteady Forces in Last Stage LP Steam Turbine Rotor Blades With Exhaust Hood
Authors: Rzadkowski Romuald , Surwiło Jan , Kubitz Leszek , Lampart Piotr , Szymaniak Mariusz 
Published: September 2016

Several high vibration amplitude problems have been reported regarding the slender last stage blades of commercial LP steam turbines. This paper presents a numerical study of unsteady forces acting on rotor blades using ANSYS CFX. A 3D transonic viscous flow through the stator and rotor blades with an exhaust hood was modelled. The last stage was modelled as a full blade annulus, so that the axial, radial and circumferential distribution of flow patterns and blade forces could be examined. An unsteady flow analysis was conducted on a typically designed last stage and exhaust diffuser, with measured and calculated downstream static pressure distribution as the outlet boundary condition. The results showed that under off-design conditions, vortices occurred in the last stage and diffuser.
Unsteady aerodynamic forces were found at high frequencies (stator passing frequencies) and low frequencies (generated from asymmetric pressure distributions behind the rotor), with the relative dominance of these forces/frequencies shifting as a function of radial span. An FFT analysis was carried out. Three sections were investigated: the hub, midspan and peripheral (tip) section. The steady pressure behind the rotor blade was compared with experimental results in the LP last stage behind the rotor blades and in a specified cross-section of the exhaust hood. The lower frequency unsteady forces had a higher relative contribution towards the tip of the blade.
A Reliable Transition Duct With Separation Planes for the Annular Combustor of GT13E2 Gas Turbine
Authors: Tschuor Remigi , Trbojevic Bogdan , Markovic Alen 
Published: September 2016

Designing a state-of-the-art combustor requires an iterative process where mechanical design solutions in the early concept phase are continuously assessed using analytical cooling and lifetime assessments, which are later backed up with experimental investigations and validation measures.
This paper describes the integrated design process in terms of design, cooling, manufacturing, aerodynamic and mechanical integrity for the transition duct of the GT13E2 combustor, which houses the flame development region of the combustor.
The objective was to develop a retrofit design with reduced lifecycle costs, with no impact on the combustor-turbine interface and no impact on the overall engine performance. The major challenges were the on-site welding of the two half-shells as well as the increasing demand for cyclic operation of the engine.
During the development process, the focus was on selecting reliable and robust cooling schemes on the inner and outer shell to reduce mechanical deflections and thus to reduce the overall stress distribution.
Key features of the GT13E2 combustor zone 2 are the following:
• Drastically reduced lifecycle cost with no performance penalty (retrofit)
• Separation planes at 3 and 9 o’clock position with mechanical locking connections (bridges) and a recess weld with film cooling
• Bellmouth shaped inlet of cooling channel with improved impingement and convective cooling
• Unique membrane seals with great mechanical flexibility around the turbine inlet outer diameter including mitigation against hot gas ingress (bow wave effect)
• Improved cooling during transient conditions to reduce mechanical deflections
• Reduced reconditioning effort due to innovative manufacturing methods
The cooling schemes were successfully validated against laboratory experiments and integrated into a stable manufacturing process. Increased dimensional stability was achieved through higher rigidity and led to an improved on-site welding process for the separation planes. All the aforementioned features result in a marked improvement of the cyclic lifetime with no performance penalty. This is proven by the fact that the GT13E2 with annular combustor transition duct has now accumulated more than 30,000 operating hours with 1,200 starts.
Investigations of Flutter and Aero Damping of a Turbine Blade: Part 2 — Numerical Simulations
Authors: Ren Wei-Min , Seeley Charles E. , Zhang Xuefeng , Mitchell Brian E. , Ju Hongbin 
Published: September 2016

There is a demand for Modern Heavy Duty Gas Turbines (HDGT) to provide greater MW power output with higher efficiency. This trend leads to longer and slimmer turbine last stage blades with exposure to higher aerodynamic loadings. As a result, they are more prone to flutter risks. Turbine flutter risks must be addressed during the design phase and this requires the accurate prediction of the flutter boundary and the aero damping ratios with quantified uncertainties.
Numerical simulations, based on Computational Fluid Dynamics (CFD), of a two-passage linear turbine cascade were carried out. The results are presented in this paper aimed to study aspects of flutter. A time-linearized Navier–Stokes approach was applied to predict the aeroelastic response. Simulations were carried out for Mach numbers ranging from 0.4 to 1.2. The objective of this study is to quantify the aero damping prediction uncertainty.
CFD results showed successful prediction of the transonic flutter boundary. The predicted aero work was compared with the experimental data and good agreements were demonstrated for both the subsonic and supersonic flows. The steady and unsteady surface pressures on the test rig sidewalls, predicted by CFD, were then compared with the test data in great detail. Limitations of the linear approach are also discussed.
A Thermo-Mechanical Fatigue Crack Growth Accumulative Model for Gas Turbine Blades and Vanes
Authors: Riva Andrea , Costa Alessio , Dimaggio Dalila , Villari Paolo , Kraemer Karl Michael , Mueller Falk , Oechsner Matthias 
Published: September 2016

Heavy duty gas turbine blades and vanes are operated at high temperatures and high stresses, condition where several damage mechanisms can simultaneously be present. For example creep, fatigue and oxidation play an important role in the propagation of existing cracks. Crack growth models are employed for assessment criteria, interpretation of the field feedback and non-conformities management and they are required to be as accurate as possible when predicting crack propagation under the combined effect of all the three phenomena.
In this work, a Linear Elastic Fracture Mechanics (LEFM) model based on isothermal experimental tests and validated by Thermo-Mechanical-Fatigue Crack Growth tests (TMFCG), is employed to predict crack propagation of a cast Ni-base superalloy used in gas turbine blades and vanes. When calculating the individual propagation fractions of creep and fatigue crack growth, the model accounts for the instantaneous stress state and temperature in transient regime (i.e. a complete cycle of start-up, base-load and shut-down). The loss of γ’- precipitates at the crack tip due to surface oxidation is interpreted as environmental damage fraction.
A complete workflow for the systematic use of the approach, comprising an in-house software, has been defined and developed. Stress intensity factors used for LEFM calculations are determined either using tabulated weight functions or with the aid of Finite Element Analysis (FEA). This flexible approach is consistent with the industrial need of a given fracture mechanics calculation, which might require different levels of accuracy and resources/time consumption case by case. The software identifies the fraction of propagation caused by oxidation, creep crack growth or fatigue crack growth. This allows checking the physical realism of the results by comparing to metallographic analysis of fracture surfaces from broken TMFCG test specimen and/or real component damage information from field. Besides, this feature can be helpful to support the engineer in residual life evaluation under damage tolerant approach because it allows the identification of the type of operational regime that minimizes crack propagation. The software also allows the execution of sensitivity analyses via Monte-Carlo calculations, identifying for a given component and operational condition the more relevant calculation inputs. This feature also quantitatively supports the engineers in the identification of the most appropriate safety margins.
Forced Response Analysis of Supercritical CO2 Radial Inflow Turbine Designed for Concentrating Solar Power
Authors: Modir Shanechi Mohsen , Veidt Martin , Hooman Kamel 
Published: September 2016

The forced response of high-pressure sCO2 radial-inflow turbine blisk is studied with regards to internal mistuning and inherent characteristics of supercritical Brayton cycle. A novel preliminary meanline analysis led to the generation of turbine designs for the sCO2 Brayton cycle with respect to concentrating solar power (CSP) applications. Details of mentioned study are published in a separate paper. The sCO2 turbine with a pressure ratio of 2.2 and the mild inlet temperature of 560 C is studied for rotational speed ranging between 75000 and 125000 RPM.
Aiming to achieve an enhanced understanding of the fluid-structure-interaction in sCO2 radial-inflow turbine, a numerical method capable of predicting the forced responses of tuned and intentionally mistuned blisks due to aerodynamic excitation is presented. The numerical work involves the simulation of the transient flow field, and then the unsteady aerodynamic excitation forces on the blades are determined by modelling various resonance condition, including the influence of the operating condition and stator number. Performing the forced response of the structure, the transient and spatially resolved pressure distribution is used as a boundary condition in an FE model. As a result, the response amplifications of sCO2 turbines are eventually compared.
The similar geometrical turbine was designed and manufactured to be operated in subcritical state for the sake of validation. The results of the subcritical turbine are derived by means of experimental and numerical analyses. To update the effect of mistuning in the FE model, blade by blade measurements using the example of a subcritical turbine blisk is performed and results of well correlated FRFs are used as inputs to adjust the blade individual Young’s modulus. The tendency of results is approved by previous works done in subcritical state. The structural damping information to be considered in the update process is taken from results of an experimental modal analysis and the aerodynamic damping induced by blade vibration is computed using an energy balance technique.
It has been found that increase of the maximum forced response beyond that of the sCO2 turbine with higher rotational speed is not significant due to the existence of high pressure-density sCO2. This implies an occurrence of high aerodynamic damping which would cause a low vibrational amplitude in case of a mistuned blisk. Considering aeroelastic coupling, in supercritical turbine with small mistuning, no change of maximum response magnitudes is achieved for the fundamental bending mode; however, with large mistuning pattern, aerodynamic damping can cause significantly better response level. This result indicates considerable contrast with responses obtained from subcritical model which would be expressed by either characteristic or state of working fluid.
RNAs Containing Modified Nucleotides Fail To Trigger RIG-I Conformational Changes for Innate Immune Signaling
Authors: Durbin Ann Fiegen , Wang Chen , Marcotrigiano Joseph , Gehrke Lee 
Published: September 2016

ABSTRACT

Invading pathogen nucleic acids are recognized and bound by cytoplasmic (retinoic acid-inducible gene I [RIG-I]-like) and membrane-bound (Toll-like) pattern recognition receptors to activate innate immune signaling. Modified nucleotides, when present in RNA molecules, diminish the magnitude of these signaling responses. However, mechanisms explaining the blunted signaling have not been elucidated. In this study, we used several independent biological assays, including inhibition of virus replication, RIG-I:RNA binding assays, and limited trypsin digestion of RIG-I:RNA complexes, to begin to understand how RNAs containing modified nucleotides avoid or suppress innate immune signaling. The experiments were based on a model innate immune activating RNA molecule, the polyU/UC RNA domain of hepatitis C virus, which was transcribed
in vitro
with canonical nucleotides or with one of eight modified nucleotides. The approach revealed signature assay responses associated with individual modified nucleotides or classes of modified nucleotides. For example, while both
N-
6-methyladenosine (m6A) and pseudouridine nucleotides correlate with diminished signaling, RNA containing m6A modifications bound RIG-I poorly, while RNA containing pseudouridine bound RIG-I with high affinity but failed to trigger the canonical RIG-I conformational changes associated with robust signaling. These data advance understanding of RNA-mediated innate immune signaling, with additional relevance for applying nucleotide modifications to RNA therapeutics.

IMPORTANCE
The innate immune system provides the first response to virus infections and must distinguish between host and pathogen nucleic acids to mount a protective immune response without activating autoimmune responses. While the presence of nucleotide modifications in RNA is known to correlate with diminished innate immune signaling, the underlying mechanisms have not been explored. The data reported here are important for defining mechanistic details to explain signaling suppression by RNAs containing modified nucleotides. The results suggest that RNAs containing modified nucleotides interrupt signaling at early steps of the RIG-I-like innate immune activation pathway and also that nucleotide modifications with similar chemical structures can be organized into classes that suppress or evade innate immune signaling steps. These data contribute to defining the molecular basis for innate immune signaling suppression by RNAs containing modified nucleotides. The results have important implications for designing therapeutic RNAs that evade innate immune detection.