bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved Methodologies for Time Resolved Heat Transfer Measurements, Demonstrated on an Unshrouded Transonic Turbine Casing
Authors: Collins Matthew , Chana Kam , Povey Thomas 
Published: August 2015

The HP rotor tip and over-tip casing are often life-limiting features in the turbine stages of current gas turbine engines. This is due to the high thermal load, and high temperature cycling both at low and high frequency. In the last few years there have been numerous studies of turbine tip heat transfer. Comparatively fewer studies have considered the over-tip casing heat transfer. This is in part, no doubt, due to the more onerous test facility requirements to validate computational simulations. Because the casing potential field is dominated by the passing rotor, to perform representative over-tip measurements a rotating experiment is an essential requirement.
In this paper we describe improved methodologies for time resolved heat transfer measurements. Specifically we show that:
1. Changes in driving temperature (within limits) can be accounted for in both time-resolved and steady heat transfer measurement processing. This allows useful data to be extracted even under varying inlet temperature.
2. Superposition of several runs with different starting wall temperatures can be used to improve the accuracy of time resolved regressions by extending the wall temperature range over which the unsteady regressions are conducted.
3. A new time-resolved data processing technique that can be applied to data sets involving changes in wall temperature has been developed and is applied to experimental measurements to compute time resolved TAW and Nu.
These improvements are demonstrated using unsteady heat transfer measurements conducted on the stationary casing above an unshrouded transonic turbine. The measurements were taken in the Oxford Turbine Research Facility (OTRF), an engine-scale rotating turbine facility which replicates engine-representative conditions of Mach number, Reynolds number, and gas-to-wall temperature ratio. High density arrays of miniature thin-film heat-flux gauges were used with a spatial resolution of 0.8 mm and temporal resolution of ∼120 kHz. The small size of the gauges, the high frequency response, and the improved processing methods allowed very detailed measurements of the heat transfer in this region. Time-resolved measurements of TAW and Nu are presented for the casing region (−30 % to +125% CAX) and compared to other results in the literature. The results provide an almost unique data set for calibrating CFD tools for heat transfer prediction in this highly unsteady environment dominated by the rotor over-tip flow.
Effects of Inlet Air Distortion on Gas Turbine Combustion Chamber Exit Temperature Profiles
Authors: Maqsood O. , LaViolette M. , Woodason R. 
Published: August 2015

Localized damage to turbine inlet nozzles is typically caused by non-uniform temperature distributions at the combustion chamber exit. This damage results in decreased turbine performance and can lead to expensive repair or replacement. A test rig was designed and constructed for the Rolls-Royce Allison 250-C20B dual-entry combustion chamber to investigate the effects of inlet air distortion on the combustion chamber’s exit temperature fields. The rig includes a purposely built water cooled thermocouple rake to sweep the exit plane of the combustion chamber. Test rig operating conditions simulated normal engine cruise conditions by matching the quasi-non-dimensional Mach number, equivalence ratio and Sauter mean diameter. The combustion chamber was tested with an even distribution of inlet air and a 4% difference in airflow at either combustion chamber inlet.
An even distribution of inlet air to the combustion chamber did not produce a uniform temperature profile and varying the inlet distribution of air exacerbated the profile’s non-uniformity. The design of the combustion chamber promoted the formation of an oval-shaped toroidal vortex inside the combustion liner, causing localized hot and cool sections separated by 90° that were apparent in the exhaust. Uneven inlet air distributions skewed the oval vortex, increasing the temperature of the hot section nearest the side with the most airflow and decreasing the temperature of the hot section on the opposite side.
Aerodynamic Quenching and Burning Velocity of Turbulent Premixed Methane-Air Flames
Authors: Nivarti Girish V. , Cant R. Stewart 
Published: August 2015

Industry-relevant turbulent premixed combustion models continue to rely on empirical expressions for turbulent flame speed in closure modelling for the mean turbulent reaction rate. To date, an accurate sub-model for turbulent flame speed has not been proposed for flows with high turbulence intensities. Experimental studies in the pertinent combustion regime, known as the Thin Reaction Zones (TRZ) regime, are limited by the existing techniques of turbulence generation whereas, until recently, the high computational expense involved in solving such problems has restricted theoretical studies.
We investigate the behaviour of premixed flames in the TRZ regime by conducting a parametric 3D Direct Numerical Simulation (DNS) study of stoichiometric methane-air mixtures using single-step chemistry in an inflow-outflow configuration. Inflow turbulence intensity is varied while keeping the integral length scale constant across six separate simulations which span altogether a significant portion of the TRZ regime. The resulting variation of turbulent flame speed with turbulence intensity demonstrates the well-known bending phenomenon and conforms with recent experimental observations of freely-propagating premixed flames in this regime.
As turbulence intensity is increased, the calculated flame surface exhibits an increasing degree of wrinkling and pocket-formation. In addition, the internal thermo-chemical structure of the flame is greatly affected when the turbulence intensity is more than an order of magnitude higher than the laminar flame speed. These qualitative observations establish the present DNS framework as a powerful tool for capturing turbulence-chemistry interactions that influence the bending phenomenon. Hence, this work forms the basis for further analysis using a detailed chemical description to investigate these interactions and, thereby, improve combustion models of industrial relevance.
Validation of a Novel LES Approach Using Tabulated Chemistry for Thermoacoustic Instability Prediction in Gas Turbines
Authors: Dederichs Stefan , Zarzalis Nikolaos , Beck Christian 
Published: August 2015

For the prediction of thermoacoustic instabilities in gas turbines, a compressible, unsteady LES approach was validated for 1D, lab-scale and technical-scale test cases. The simulations were performed with a novel combustion model, which relies on a combination of tabulated chemistry and flame thickening.
A 1D case was used for fundamental verification and to quantify the mesh resolution dependent error. The verification demonstrated sufficiently accurate predictions. In a second step an elevated pressure lab-scale flame was considered to calibrate the model parameter of the turbulence chemistry interaction at relevant conditions. For this case CO2 field data measured with the Raman scattering method is available. Finally, a test rig configuration of a can type combustor was investigated. The comparison between experiment and simulation was performed in terms of thermoacoustic pressure amplitudes at stable and unstable operating conditions.
The LES combustion model relies on an artificial thickened flame approach to ensure that the flame propagation speed is reproduced with tolerable error. Tabulated chemistry provides the source term for CO2 (governing species) as a function of the mixture fraction and the CO2 concentration based on premixed, laminar flamelets. The model distinguishes between inherent thickening due to sub grid scale turbulence and explicit laminar thickening. This novel thickening approach is presented for the first time. The presented approach was able to predict the thermoacoustic stability behavior of a gas turbine combustion system correctly.
Influence of Geometrical Parameters on the Performance of Brush Seals for Aero-Engines Bearing Chambers
Authors: Outirba Bilal , Hendrick Patrick 
Published: August 2015

Recent developments in the aeronautic domain focus on the optimization of the lubrication oil system for civil aircraft gas turbine engines, in order to reduce air and oil consumptions. Specifically, over the last few decades, as brush seals have shown tremendous leakage performance in sealing secondary flows compared to classic labyrinth seal, an increasingly popular idea is to extend their utilization to bearing chambers applications.
In the frame of the European FP7 E-Break project, the Aero-Thermo-Mechanics department of ULB collaborates with French aircraft engine manufacturer SNECMA in order to investigate experimentally the brush seal behaviour in an environment simulating the bearing chamber working conditions. The aim is first to deepen the brush seal behaviour knowledge by identifying the most influential geometric parameters acting on the leakage performance on both sides of the seal (oil and air), and on its wear, and by evaluating the friction torque and the dissipated heat.
The paper will first highlight the effect of the brush seals geometric parameters on the air consumption and the torque friction. Results highlight a trade-off to be made between these two performance levels. Also, relations have been developed to predict the performance of a carbon brush seal with non-canted bristles. The bristle free length and the axial density must carefully be chosen first to dictate the brush seal porosity. The distance between the backing plate and the front plate acts as a secondary parameter to adjust the bristle pack stiffness, and it is proposed to mount such a carbon brush seal with a reduced interference to limit the effect of the brush seal wear on the air consumption. Finally, the carbon brush seals performance was compared with the latest ones, with promising results being shown to expect carbon brush seals to be employed at a higher scale in bearing chambers in the future.
Generation, Characterization and Ignition of Lube Oil Mists
Authors: Dufaud Olivier , Charvet Augustin , Mougel Grégoire , Luthun Stéphane , Molière Michel , Brunello David , Perrin Laurent , Delimoges Sylvain , Couchot Myriam 
Published: August 2015

In this work, the generation conditions of lube oil mists by spray, their droplet size distributions and their flammability characteristics were studied.
At first, tests were carried out on brand new lube oil having a viscosity of 32 mm2.s−1 at 40°C (ISO VG32) and a flashpoint higher than 200°C. Experiments were performed in a vertical semi-open tube with a 0.07 m-square cross section connected to ignition systems supplying energies ranging from 1 mJ to 5 kJ. The average droplet diameter, determined using a laser diffraction sensor, ranged from 4 to 60 μm depending on operating parameters.
In the case of brand new mineral oil mists, the probability of ignition by a spark discharge can be considered as low, the minimum ignition energy (MIE) being 2 kJ for 5 μm droplets. The minimum explosive concentration is fairly high, in the order of 250 g.m−3. For mists with droplet diameters around 60 μm, MIE slightly increases to reach 2.5 kJ.
The flammability of oil mists generated in case of maloperation (accidental fuel/lube mixing) was also studied. The ignition properties of used lube oil were not notably modified with regard to the brand new oil. However, the addition of organic volatiles compounds leads to a modification of mists flammability, nevertheless it is only perceptible for fuel contents greater than 20%v.
Comparison and Synthesis of Performance and Aerodynamic Modeling of a Pass-Off Turbofan Engine Test Cell
Authors: Marx Martin , Kotulla Michael , Kando André , Staudacher Stephan 
Published: August 2015

To ensure the quality standards in engine testing, a growing research effort is put into the modeling of full engine test cell systems. A detailed understanding of the performance of the combined system, engine and test cell, is necessary e.g. to assess test cell modifications or to identify the influence of test cell installation effects on engine performance.
This study aims to give solutions on how such a combined engine and test cell system can be effectively modeled and validated in the light of maximized test cell observability with minimum instrumentation and computational requirements.
An aero-thermodynamic performance model and a CFD model are created for the Fan-Engine Pass-Off Test Facility at MTU Maintenance Berlin-Brandenburg GmbH, representing a W-shape configuration, indoor Fan-Engine test cell. Both models are adjusted and validated against each other and against test cell instrumentation. A fast-computing performance model is delivering global parameters, whereas a highly-detailed aerodynamic simulation is established for modeling component characteristics. A multi-disciplinary synthesis of both approaches can be used to optimize each of the specific models by calibration, optimized boundary conditions etc. This will result in optimized models, which, in combination, can be used to assess the respective design and operational requirements.
Unsteady Thrust Force Loading of a Turbocharger Rotor During Engine Operation
Authors: Lüddecke Bernhardt , Nitschke Philipp , Dietrich Michael , Filsinger Dietmar , Bargende Michael 
Published: August 2015

The bearing system of a turbocharger has to keep the rotor in the specified position and thus has to withstand the rotor forces that result from turbocharger operation. Hence, its components need to be designed in consideration of the bearing loads that have to be expected.
The applied bearing system design also has significant influence on the overall efficiency of the turbocharger and impacts the performance of the combustion engine. It has to ideally fulfil the trade-off between bearing friction and load capacity. For example, the achievable engine’s low end-torque is reduced, if the bearing system produces more friction losses than inherently unavoidable for safe and durable operation because a higher portion of available turbine power needs to be employed to compensate bearing losses instead of providing boost pressure. Moreover, also transient turbocharger rotor speed up can be compromised and hence the response of the turbocharged combustion engine to a load step becomes less performant than it could be.
Besides the radial bearings, the thrust bearing is a component that needs certain attention. It can already contribute to approx. 30 percent of the overall bearing friction, even if no load is applied and this portion further increases under thrust load. It has to withstand the net thrust load of the rotor under all operating conditions resulting from the superimposed aerodynamic forces that the compressor and the turbine wheel produce.
A challenge for the determination of the thrust forces appearing on engine is the non-steady loading under pulsating conditions. The thrust force will alternate with the pulse frequency over an engine cycle what is caused by both the engine exhaust gas pressure pulses on the turbine stage and — to a smaller amount — the non-steady compressor operation due to the reciprocating operation of the cylinders.
The conducted experimental investigations on the axial rotor motion as well as the thrust force alternations under on-engine conditions employ a specially prepared compressor lock nut in combination with an eddy current sensor. The second derivative of this signal can be used to estimate the occurring thrust force changes. Moreover, a modified thrust bearing — equipped with strain gauges — was used to cross check the results from position measurement and thrust force modeling. All experimental results are compared with an analytical thrust force model that relies on the simultaneously measured, crank angle resolved pressure signals before and after the compressor and turbine stage.
The results give insight into the axial turbocharger rotor oscillations occurring during an engine cycle for several engine operating points. Furthermore, they allow a judgment of the accuracy of thrust force modeling approaches that are based on measured pressures.
Turbine Noise Reduction: Axial Spacing and Embedded Design
Authors: Faustmann C. , Zerobin S. , Bauinger S. , Marn A. , Heitmeir F. , Göttlich E. 
Published: August 2015

This paper deals with the investigation on the acoustics of different turning mid turbine frames (TMTF) in the two-stage two-spool test turbine located at the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) of Graz University of Technology. The facility is a continuously operating cold-flow open-circuit plant which is driven by pressurized air. The flow path consists of a transonic turbine stage (HP) followed by a low pressure turbine stage made of a turning mid turbine frame (TMTF) and a counter-rotating low pressure rotor. Downstream of the low pressure turbine a measurement section is instrumented with acoustic sensors.
Three TMTF setups have been investigated at engine like flow conditions. The first configuration (C1) consists of 16 highly 3D-shaped turning struts. The goal of the second design (C2) was to reduce the length of the TMTF by 10% without increasing the losses and providing comparable inflow to the LP turbine rotor. This was achieved by applying 3D-contoured endwalls at the hub. The third one (C3) is a new embedded concept for the turning mid turbine frame with two zero-lift splitters placed into the strut passages. In total 48 vanes (16 struts plus 32 splitter vanes) guide the flow from the HP rotor to the LP rotor.
The comparison in terms of noise generation and propagation of the turbines is done by the microphones signal spectra, the emitted sound pressure and sound power level of each TMTF setup. Therefore the acoustic field is characterized by azimuthal and radial modes by means of a microphone array at the outer casing traversed over 360 degrees.
By comparing the first two setups (C1 and C2) in terms of noise generation the propagating modes due to the HP turbine were found to be the same, while a difference of 5 dB in amplitude of the modes related to the LP turbine was found due to the different axial spacing between both setups. In the multi-splitter configuration (C3), the overall sound power level depending on the blade passing frequency (BPF) of the HP turbine is reduced by 7 dB and depending on the BPF of the LP turbine by 4 dB compared to C1, respectively. The overall effect is a reduction of the noise emission for the HP turbine due to the embedded design as well as for the LP turbine due to increasing the axial spacing between the TMTF Vanes and LP Blades on the one hand and considerably due to the embedded design on the other hand.
Evaluation of Compressor Bleed Air Transients in a Fuel Cell Gas Turbine Hybrid System Using Hardware Simulation
Authors: Zhou Nana , Yang Chen , Tucker David 
Published: August 2015

Thermal management in the fuel cell component was a critical issue in the operation of a solid oxide fuel cell gas turbine (SOFC/GT) hybrid system. The effective management of fuel cell cathode air mass flow was thought to be a potential method to improve the thermal management during transients.
The U.S. Department of Energy, National Energy Technology Laboratory (NETL) designed and built a hybrid performance (HyPer) facility by interfacing a real time solid oxide fuel cell system numerical model through hardware with a physical gas turbine system. Perturbations were accomplished by diverting part of the compressor discharge directly to atmosphere through the manipulation of a bleed-air bypass valve in open loop experiments using the HyPer facility. Two tests were performed: the fuel cell numerical simulation model was both decoupled and fully coupled with the gas turbine hardware component.
The responses of both physical subsystem and virtual subsystem to the disturbances were evaluated in this paper. Distributed temperatures and current densities along the fuel cell were evaluated. Turbine speed and system pressures were analyzed. The application of bleed-air bypass valve was shown to have a minimal impact on cathode airflow, but a significant effect on turbine speed. Thus, the manipulation of compressor bleed was expected to be an effective means to mitigate the impact of a sudden increase in turbine speed, such as fuel cell load reductions or load trips.
Parametric Analysis of Flashback Propensity With Various Fuel Compositions and Burner Materials
Authors: Duan Zhixuan , Kalantari Alireza , McDonell Vincent 
Published: August 2015

Flashback is a key operability issue for low NOx premixed combustion of hydrogen enriched fuels. Previous work has systematically investigated the impact of fuel composition on flashback propensity and noted the coupling of flashback with burner tip temperature. It led to models for critical velocity gradient as an indicator of flashback propensity as a function of parameters studied, such as fuel composition, burner tip temperature and laminar flame speed, etc. The present work further analyzes existing data and develops an empirical physical model for flashback propensity as a function of dimensionless groups. A comprehensive parameter screening is conducted and the potential variables determining flashback behavior are catalogued into five types: operational parameters, unburnt conditions, ambient conditions, rig properties and others. The objective of the analysis is to predict the critical operational parameters with given unburnt conditions which are generally known to the hardware designer. Other factors, such as ambient conditions and rig properties might also affect the prediction performance. To account for such factors, a dimensional analysis is conducted based on Buckingham Pi theorem. The critical Damköhler number is selected as the indicator of flashback propensity and a model is developed suggesting the significance of preferential diffusion (Le), heat loss (TuT0), thermal coupling effect (TtipTu) and flame Péclet number (Pef) as follows:
Da = Const. · Le -6.12 · T u T 0 -1.71 · T tip T u -3.69 Pe f 1.89 · f 1 θ ′ d · f 2 P u P 0
Finally, preliminary results for pressure effects are presented.