bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Staggered and In-Line V-Shaped Dimple Arrays Using S-PIV
Authors: Brown Charles P. , Wright Lesley M. , McClain Stephen T.
Published: August 2015

As a result of the reduced pressure loss relative to ribs, recessed dimples have the potential to increase the thermal performance of internal cooling passages. In this experimental investigation, a Stereo-Particle Image Velocimetry (S-PIV) technique is used to characterize the three-dimensional, internal flow field over V-shaped dimple arrays. These flowfield measurements are combined with surface heat transfer measurements to fully characterize the performance of the proposed V-shaped dimples. This study compares the performance of two arrays. Both a staggered array and an in-line array of V-shaped dimples are considered. The layout of these V-shaped dimples is derived from a traditional, staggered hemispherical dimple array. The individual V-shaped dimples follow the same geometry, with depths of δ / D = 0.30. In the case of the in-line pattern, the spacing between the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. For the staggered pattern, a spacing of 3.2D in the spanwise direction and 1.6D in the streamwise direction is examined. Each of these patterns was tested on one wide wall of a 3:1 rectangular channel. The Reynolds numbers examined range from 10000 to 37000. S-PIV results show that as the Reynolds numbers increase, the strength of the secondary flows induced by the in-line array increases, enhancing the heat transfer from the surface, without dramatically increasing the measured pressure drop. As a result of a minimal increase in pressure drop, the overall thermal performance of the channel increases as the Reynolds number increases (up to the maximum Reynolds number of 37000).
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.
Solution Strategies for Thin Film Rimming Flow Modelling
Authors: Kakimpa B. , Morvan H. P. , Hibberd S.
Published: August 2015

This paper explores the role of surface tension, grid resolution, inertia term representation and temporal discretisation scheme in the numerical simulation of shear-driven thin-film rimming flows. An ideal film formulation and solution strategy, suitable for the simulation of smooth, shock and pool solutions is presented. Shock and pool solution stability is shown to be dependent on the provision of sufficient grid refinement to resolve key flow features present in the solution such as steep fronts and small wavelength capillary waves. A minimum grid refinement criterion is proposed based on the findings from a parametric study. A previously established dependence of solution stability on surface tension is shown to be linked to the sensitivity of the wavelengths of disturbances in the capillary zone on the surface tension coefficient. Solution strategies utilising un-physically high surface tension values to guarantee stability, are explored and shown to enhance stability by modifying the solution in the capillary zone to one that is resolvable on the available grid. The role of inertia in solution stability is also investigated and simplified inertia representations are shown to primarily affect accuracy but not stability.
Considerations for Measuring Compressor Aerodynamic Excitations Including Rotor Wakes and Tip Leakage Flows
Authors: Smith Natalie R. , Murray William L. , Key Nicole L.
Published: August 2015

The unsteady flow field generated by the rotor provides unsteady aerodynamic excitations to the downstream stator, which can result in vibrations such as forced response. In this paper, measurements of the rotor wake and rotor tip leakage flow from an embedded rotor in a multistage axial compressor are presented. A unique feature of this work is the pitchwise traverse of the flow field used to highlight the changes in the rotor exit flow field with respect to the position of the surrounding vane rows. Results acquired at mid-span focus on characterizing an average rotor wake, including the effects on the frequency spectrum, from a forced response perspective. While many analyses use an average rotor wake to characterize the aerodynamic forcing function to the downstream stator, this study explores the factors that influence changes in the rotor wake shape and the resulting impact on the spectrum. Additionally, this paper investigates the flow near the endwall where the tip leakage vortex is an important contributor to the aerodynamic excitations for the downstream vane. For the first time, experimental data are presented at the rotor exit, which show the modulation in size and radial penetration of the tip leakage vortex as the rotor passes through the upstream vane wake. As computational models become more advanced, the ability to incorporate these aerodynamic excitation effects should be considered to provide better predictions for vane vibratory response.
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.
Estimating Over Temperature and its Duration in a Flat Plate With Sudden Changes in Heating and Cooling
Authors: Lee C.-S. , Shih T. I-P. , Bryden K. M.
Published: August 2015

When the operating condition of a gas-turbine engine changes from one steady state to another, the cooling must ensure that the solid’s temperatures to never exceed the maximum allowable throughout the transient process. Exceeding the maximum allowable temperature is possible even though cooling is increased to compensate for the increase in heating because there is a time lag in how the solid responds to sudden changes in its convective heating and cooling environments. In this paper, a closed-form integral solution (referred to as the 1-D model) is generated to study the unsteady heat transfer in a flat plate subjected to sudden changes in convective heating and cooling. Comparison with the exact solution shows the 1-D model to be accurate within 0.1%. The 1-D model can be used to estimate the over temperature and its duration in a flat plate subjected to sudden changes in heating and cooling rates. For a given change in heating rate, the 1-D model can also be used to estimate the minimum cooling needed to ensure the new steady-state temperature will not exceed the maximum allowable. In addition, this model can estimate the precooled wall temperature needed before imposing a sudden increase in heat load to ensure no over temperature. This 1-D model was generalized for application to problems in multidimensions. The generalized model was used to estimate the duration of over temperature in a two-dimensional problem involving a step change in the heat-transfer coefficient on cooled side of a flat plate and provided results that match the exact solution within 5%.
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.
Beyond Life: Including Risk and Consequence in Maintenance Planning
Authors: Slottner Pontus
Published: August 2015

Adequate and timely maintenance is a tool to improve the value of equipment by ensuring that potential risks are mitigated in a timely and efficient manner thereby increasing the return on investment of the equipment. In practice, this means that every maintenance activity needs to eliminate a known or predicted future cost of maintenance, loss of production, other consequence costs of failures or any combination of the above that is more expensive than the maintenance action itself. Different approaches to this optimization problem have been suggested over the years including model based physical as well as purely numerical and hybrid approaches. This paper discusses an attempt to combine failure consequence analysis methods and probabilistic methods with classical prognostics methods for a gas turbine blade where the life time show high sensitivity to operation conditions and multiple failure modes are active. Applications of the results are discussed. The conclusions indicate that the shape of failure data can be a strong indicator on the relative sensitivity of reliability to changes in quality of parts and workmanship, overall plant design and gas turbine maintenance.
Deposition on a Cooled Nozzle Guide Vane With Non-Uniform Inlet Temperatures
Authors: Prenter Robin , Ameri Ali , Bons Jeffrey P.
Published: August 2015

External deposition on a slot film cooled nozzle guide vane, subjected to non-uniform inlet temperatures, was investigated experimentally and computationally. Experiments were conducted using a four-vane cascade, operating at temperatures up to 1353 K and inlet Mach number of approximately 0.1. Surveys of temperature at the inlet and exit planes were acquired to characterize the form and migration of the hot streak. Film cooling was achieved on one of the vanes using a single span-wise slot. Deposition was produced by injecting sub-bituminous ash particles with a median diameter of 6.48μm upstream of the vane passage. Several deposition tests were conducted, including a baseline case, a hot streak only case, and a hot streak and film cooled case. Results indicate that capture efficiency is strongly related to both the inlet temperature profiles and film cooling. Deposit distribution patterns are also affected by changes in vane surface temperatures. A computational model was developed to simulate the external and internal flow, conjugate heat transfer, and deposition. Temperature profiles measured experimentally at the inlet were applied as thermal boundary conditions to the simulation. For deposition modeling, an Eulerian-Lagrangian particle tracking model was utilized to track the ash particles through the flow. An experimentally tuned version of the critical viscosity sticking model was implemented, with predicted deposition rates matching experimental results well. Comparing overall deposition rates to results from previous studies indicate that the combined effect of non-uniform inlet temperatures and film cooling cannot be accurately simulated by simple superposition of the two independent effects, thus inclusion of both conditions in experiments is necessary for realistic simulation of external deposition.
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.
Simulations of Friction Damping on Laboratory-Test-Rigs of Rotors and Stators of an Axial Compressor
Authors: Miyakozawa Tomokazu , Peng Caetano , Andrews Stuart , Brace Mark , Schroeter Thomas , Rose Martin
Published: August 2015

This paper presents comparisons of the non-linear behaviours and the damping characteristics of rotors and stators. It assesses the differences between the linear FE predicted modeshapes and the measured operating deflection shapes (ODS) of rotors and stators of an axial compressor. The comparisons are between the experimental results obtained from the laboratory rig damping tests and the numerical nonlinear forced response analyses. The damping tests are performed using an experimental rig apparatus driven by piezoelectric and electromagnetic shakers. The forced response analyses are performed on the finite element (FE) models that simulate the laboratory rig configurations using in-house multi-harmonic balance non-linear forced response code named FORSE.

Firstly, the measured resonant frequencies and ODS are compared against the predicted results. Moreover, some comparisons of the damping characteristics and local interactions at friction interfaces are discussed. Then, the FORSE predicted instantaneous displacements are examined to understand possible changes in ODS using the Modal Assurance Criterion (MAC) technique. It was found that the instantaneous displacements predicted by FORSE are significantly different from the modeshapes predicted by the linear FE tool. These results suggest that the experimentally measured ODS of the components may also differ from linear FE results. The predicted normalised maximum alternating stresses are also shown to be different from the standard linear FE results due to the modal coupling effects between the neighbouring modes. These findings should alert the engineers about the possibilities of misinterpreting component vibration responses due to the changes in ODS.
CFD Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions
Authors: Doğu Yahya , Sertçakan Mustafa C. , Bahar Ahmet S. , Pişkin Altuğ , Arıcan Ercan , Kocagül Mustafa
Published: August 2015

Brush seals require custom design and tailoring due to their behavior driven by flow dynamic, which has many interacting design parameters, as well as their location in challenging regions of turbomachinery. Therefore, brush seal technology has not reached a conventional level across the board standard. However, brush seal geometry generally has a somewhat consistent form. Since this consistent form does exist, knowledge of the leakage performance of brush seals depending on specific geometric dimensions and operating conditions is critical and predictable information in the design phase. However, even though there are common facts for some geometric dimensions available to designers, open literature has inadequate quantified information about the effect of brush seal geometric dimensions on leakage.

This paper presents a detailed CFD investigation quantifying the leakage values for some geometric variables of common brush seal forms functioning in some operating conditions. Analyzed parameters are grouped as follows; axial dimensions, radial dimensions and operating conditions.

The axial dimensions and their ranges are front plate thickness (z1=0.040–0.150in.), distance between front plate and bristle pack (z2=0.010–0.050in.), bristle pack thickness (z3=0.020–0.100in.), and backing plate thickness (z4=0.040–0.150in.).

The radial dimensions are backing plate fence height (r1=0.020–0.100in.), front plate fence height (r2=0.060–0.400in.), and bristle free height (r3=0.300–0.500in.).

The operating conditions are chosen as clearance (r0=0.000–0.020in.), pressure ratio (Rp=1.5–3.5), and rotor speed (n=0–40krpm).

CFD analysis was carried out by employing compressible turbulent flow in 2-D axi-symmetric coordinate system. The bristle pack was treated as a porous medium for which flow resistance coefficients were calibrated by using literature based test data.

Selected dimensional and operational parameters for a common brush seal form were investigated, and their effects on leakage performance were quantified. CFD results show that, in terms of leakage, the dominant geometric dimensions were found to be the bristle pack thickness and the backing plate fence height. It is also clear that physical clearance dominates leakage performance, when compared to the effects of other geometric dimensions. The effects of other parameters on brush seal leakage were also analyzed in a comparative manner.
Analysis of Bifurcations in Multiharmonic Analysis of Nonlinear Forced Vibrations of Gas-Turbine Engine Structures With Friction and Gaps
Authors: Petrov E. P.
Published: August 2015

An efficient frequency-domain method has been developed to analyse the forced response of large-scale nonlinear gas-turbine structures with bifurcations. The method allows: detection and localization of the design and operating conditions sets where bifurcations occur; calculation of tangents to the solution trajectory and continuation of solutions under parameter variation for structures with bifurcations.

The method is aimed at calculation of steady-state periodic solution and multiharmonic representation of the variation of displacements in time is used. The possibility of bifurcations in realistic gas-turbine structures with friction contacts and with cubic nonlinearity has been shown.
Noise Generation in Hot Nozzle Flow
Authors: Knobloch Karsten , Werner Tiago , Bake Friedrich
Published: August 2015

Noise originating from the unsteady heat-release during the combustion process in the combustor of a gas turbine is well known. However, an effect known as indirect combustion noise has received considerable interest only recently. Indirect combustion noise will be generated, when entropy or vorticity fluctuations will be subject to a strong velocity gradient like in nozzle guide vane of the high pressure turbine. First experimental proof of this phenomenon could be obtained some years ago in a dedicated small-scale laboratory experiment. Recent experiments performed in the Hot Acoustic Test rig (HAT) by the German Aerospace Center (DLR) aim at further understanding of this phenomenon by investigating the sound propagation through a nozzle and sound generation when cold air spots are injected into a hot mean flow. The nozzle Mach number was varied from subsonic to sonic conditions. First results based on propagation time analysis reveal noise generation at the location of the nozzle. Parameter studies of nozzle Mach number, temperature of the cold streaks, and the way the cold air is injected (radial/axial blowing) have been performed.
Investigation of Flow Aerodynamics for Optimal Fuel Placement and Mixing in the Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustion Chamber
Authors: Agbonzikilo Festus Eghe , Owen Ieuan , Sadasivuni Suresh Kumar , Bickerton Ronald A.
Published: August 2015

This paper presents the results of a detailed investigation of the fuel-air mixing processes that take place within the radial swirler slot of a dry low emission combustion system. The aerodynamics of the flow within the slot is complex and this, together with the placement of the fuel holes with cross injection, controls the mixing of the fuel and air. Computational fluid dynamics (CFD) with the Shear Stress Transport (k-ω) turbulence model was used for flow and mixing predictions within the radial swirler slot and for conducting a CFD-based Design of Experiments (DOE) optimisation study, in which different parameters related to the fuel injection holes were varied. The optimisation study was comprised of 25 orthogonal design configurations in a Taguchi L25 orthogonal array. The test domain for the CFD, and its experimental validation, was a large-scale representation of a swirler slot from a Siemens proprietary DLE combustion system. The DOE study showed that the number of fuel holes, injection hole diameter and inter-hole distance are the most influential parameters for determining optimal fuel mixing.

Consequently, the optimised mixing configuration obtained from the above study was experimentally tested on an atmospheric test facility. The mixing patterns from experiments at various axial locations across the slot are in good agreement with the mixing predictions from the optimal CFD model. The optimised fuel injection design improved mixing compared with the original design by about 60%.
Thrust Measurement Model-Based Correction System for Turbine Engine Test Cell Dynamic Data
Authors: Palmer Carl , Hettler Eric
Published: August 2015

This paper describes a turbine engine thrust estimator that computes “virtual measurements” of dynamic engine thrust and other parameters of interest from test cell data in a very short amount of time. The system ‘tunes’ a user’s engine model, as developed in the commonly used Numerical Propulsion System Simulation (NPSS), by optimizing system biases and health parameters to match the sensor outputs of a set of steady state data points across the operating range. The tuned model is then used to create a constant gain extended Kalman filter that is added directly within the NPSS model code. The results, including thrust, from this NPSS model with Kalman filter are then presented as the ‘actual’ corrected data.

Key aspects of the system include:

• Utilization of and tight integration with NPSS. This ensures that the results always preserve mass and energy, and are realistic from an engine performance point of view.

• Flexibility; any NPSS model for any gas turbine engine can be used.

• The ability for the whole tuning process to ‘correct’ not just noisy test data, but also performance parameters within the user’s actual NPSS model.

• A GUI that leads the user through each step of the process, such as matching NPSS variable names to signals in the actual test cell data files, and selection of ‘tuners’ (performance parameters, sensor errors) and Kalman filter variables.

The system has been tested both on a simulated two spool turbojet engine, plus an actual two spool turbojet engine, with recorded test cell data.
Characterization of Spray Formed by Liquid Jet Injected Into Oscillating Air Crossflow
Authors: Song Jinkwan , Lee Jong Guen
Published: August 2015

This paper presents experimental results on the characteristics of spray formed by a liquid (Jet-A) jet injected into an oscillating air crossflow. Ambient air pressure is raised up to 15.86 bar, and the corresponding aerodynamic Weber number and liquid-air momentum flux ratio are up to 1000 and 25, respectively. The level of modulated crossflow velocity is kept up to 20% of its mean value. For limited cases, the air crossflow is preheated. Planar Mie-scattering measurements are utilized to visualize changes of the spray penetration and cross-sectional spray area in the oscillating air crossflow, and PDPA measurements are used to measure the mean drop size and drop size distribution. Phase-synchronized PDPA measurement of droplet size under the modulation of crossflow shows that the modulating crossflow results in preferentially larger amount of smaller and bigger droplets than average-sized droplets. Global spray response of spray to modulating crossflow is characterized by using proper orthogonal decomposition (POD) analysis of Mie-scattering images and collecting (and hence determining gain of) Mie-scattering intensity of droplets at a fixed downstream distance. It is found that the dominant behavior of the spray is convective oscillation in the axial direction and the change of vertical penetration of the spray is almost negligible for the level of crossflow velocity modulation up to 20%. The gain of Mie-scattering intensity with respect to crossflow velocity modulation level gradually decreases as liquid-air momentum flux ratio increases. Also, per given momentum flux ratio and Weber number, the gain hardly varies with respect to crossflow modulation level, suggesting the response of spray increases in proportion to crossflow velocity modulation level.
Requirements and Limitations of Controlling Turbine Tip Shroud Cavity Flow Mixing With Bladelets on Rotating Shroud
Authors: Palmer Timothy R. , Tan Choon S. , Montgomery Matthew , Malandra Anthony , Little David , Zuniga Humberto , Zhou Kunyuan
Published: August 2015

A potential means of significantly reducing the cavity exit mixing loss, a dominant primary loss mechanism in turbine tip shroud cavity flow, is assessed. The operational constraints on the turbine stage dictate that losses may only be mitigated through configuration changes within the cavity. A configuration, known herein as the Hybrid Blade, features a shrouded main blade with a row of high aspect ratio bladelets affixed to the rotating shroud is formulated and shown to nearly eliminate the cavity exit mixing loss. However the Hybrid Blade configuration incurs a penalty associated with bladelet low Reynolds number effects, cavity inlet flow asymmetry introduced by the scalloped shroud, and a resulting mismatch with the upstream vane as well as downstream diffuser. This penalty offsets the efficiency gain from mitigating cavity exit mixing loss. For the Hybrid Blade system, it can thus be inferred that the turbine stage and the diffuser need to be reconfigured to accommodate the modified tip shroud, and the bladelets redesigned for low Reynolds number operation and cavity inlet flow asymmetry to achieve an overall benefit.
Low Cycle Fatigue Model Selection by Performance Analysis
Authors: Riva Andrea , Vacchieri Erica , Poggio Eleonora , Merckling Gunther
Published: August 2015

A reliable low cycle fatigue (LCF) model requires the selection of appropriate damage mechanism components necessary to accurately approximate experimental life data. In particular, two fundamental tasks have to be performed: firstly, identify the most appropriate model among those available in literature, and secondly, verify that the model is appropriate in relation to the operational conditions of the component whose life is under evaluation (e.g., check if the model accounts for all the relevant damage mechanisms and phenomena).

The European Creep Collaborative Committee (ECCC) developed a procedure that supports the researcher in evaluating performances and reliability of creep models, known as Post Assessment Tests (PATs). At the moment, there is no equivalent procedure for low cycle fatigue and ECCC work may provide the LCF researcher with useful guidelines.

This paper is intended to investigate, compare and suggest which kind of verification is appropriate to identify any possible misbehavior in a fatigue model or in the LCF tests that supported the model. This procedure involves an analysis of the model performances in terms of comparison with the experimental population, supported by a deep knowledge of the damage mechanisms of the given material. Particular attention will be paid to materials with a particularly high dispersion, such as cast nickel-based superalloys.

This paper is also meant to stimulate the fatigue data user community to propose and share methodologies in the perspective of the creation of a recommendation code, similar to what has been done by ECCC for creep.
Experimental and Numerical Investigation of Labyrinth Seal Clearance Impact on Centrifugal Impeller Performance
Authors: Marechale Russell , Ji Min , Cave Michael
Published: August 2015

Labyrinth seals are widely used in industrial multistage centrifugal compressors to reduce internal leakage and maintain compressor performance for a prolonged operation time. The leakage flow across the shroud seal of covered impellers and the hub seal of the rotating shaft has an important effect on the compressor performance. The amount of leakage flow is primarily a function of seal running clearances, which is typically designed based on the compressor working environment, such as pressure and temperature conditions. The present paper discusses the experimental and numerical studies of seal clearance impact on the performance and operation of a single stage centrifugal compressor.

Two experimental campaigns of running a medium-flow coefficient impeller and a low-flow coefficient impeller with various radial clearances of the impeller shroud and the hub labyrinth seal were conducted based on the configuration of the impeller and the return channel system in a closed-loop compressor test rig. The experimental investigation consists of both the overall stage performance test and the traverse test of the flow field downstream of the impeller using three-hole Cobra probes. Static pressure taps were arranged in the impeller shroud cavity in order to obtain the stream-wise pressure distribution. CFD simulations were then performed to compare with the test results. The paper presents the analysis of test data and simulation results of five arrangements of the impeller shroud and the hub seal radial clearances. The impacts of seal clearance height on stage efficiency and head are quantitatively evaluated. The impact on impeller internal flow field and cavity pressure distributions and swirl angle are discussed.

Findings from this study are that efficiency reduction with increased seal clearance was as expected, but impeller Euler work was significantly reduced. CFD simulation was validated as a tool for predicting these effects and provides some understanding of the flow mechanisms.
Unsteady Flow Dynamics Within an Inertial Particle Separator
Authors: Snyder Philip H. , Barone Dominic , Loth Eric
Published: August 2015

Inertial Particle Separators are utilized in the inlet of a gas turbine engine to remove a significant fraction of the damaging sand and dust particulate ingested by the engine. In gas turbine propulsion applications these devices have pressure loss, space claim, and maintainability characteristics that are more favorable than other types of particle separating devices. Maximizing the particle separation efficient of such devices is the subject of continuing importance. A more complete understanding of the underlying fluid and particulate flow mechanisms present has been undertaken. This study focuses on the how particulate is affected by the unsteady flow dynamics within the inertial particle separator (IPS). The work utilized a particle separator test rig with flow path scale and airflow velocities relevant to that used in current production designs. The techniques of surface flow visualization, net separation efficiency measurement, specific geometry changes, traditional Particle Image Velocimetry (PIV), Multi-Phase PIV (MP-PIV), and high speed video were each applied to examine the fundamental flow physics of the fluid flow field and the particle motion created by the IPS geometries.
LES Simulation of an Enclosed Turbulent Reacting Methane Jet With the Tabulated Premixed CMC Method
Authors: Velez Carlos , Martin Scott , Jemcov Aleksander , Vasu Subith
Published: August 2015

The Tabulated Premixed Conditional Moment Closure Method (T-PCMC) has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in a RANS environment [1]. Here the premixed conditional moment closure method is extended to Large Eddy Simulation. The new model is validated with the turbulent, enclosed reacting methane backward facing step data from El Banhawy [2]. The experimental data has a rectangular test section at atmospheric pressure and temperature with an inlet velocity of 10.5 m/s and an equivalence ratio of 0.9 for two different step heights. Contours of major species, velocity and temperature are provided.

The T-PCMC model falls into the class of table lookup turbulent combustion models where the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the CFD code using three controlling variables; the reaction progress variable, variance and local scalar dissipation rate. The local scalar dissipation is used to account for the affects of the small scale mixing on the reaction rates. A presumed shape beta function PDF is used to account for the effects of large scale turbulence on the reactions. Sub-grid scale models are incorporated for the scalar dissipation and variance. The open source CFD code OpenFOAM is used with the compressible Smagorinsky LES model. Velocity, temperature and major species are compared to the experimental data. Once validated, this “low runtime” CFD turbulent combustion model will have great utility for designing the next generation of lean premixed gas turbine combustors.
Preliminary Design Assessments of Pusher Geared Counter-Rotating Open Rotors: Part I — Low Pressure System Design Choices, Engine Preliminary Design Philosophy and Modelling Methodology
Authors: Bellocq Pablo , Garmendia Iñaki , Sethi Vishal
Published: August 2015

In this 2-part publication, the impact of the main low pressure system parameters of a pusher counter rotating Geared Open Rotor (GOR) on mission fuel burn, certification noise and emissions is presented for a 160 PAX medium haul class aircraft.

Due to their high propulsive efficiency, GORs have the potential to significantly reduce fuel consumption and emissions relative to conventional high bypass ratio turbofans. However, this novel engine architecture presents many design and operational challenges both at engine and aircraft level.

The assessment of the impact of the main low pressure preliminary design parameters of GORs on mission fuel burn, certification noise and emissions is necessary at preliminary design stages in order to identify optimum design regions. These assessments may also aid the development process when compromises need to be performed as a consequence of design, operational or regulatory constraints.

Part I of this two-part publication describes the main low pressure (LP) system design choices for a GOR as well as the preliminary design philosophy and simulation framework developed for the assessments. Part II presents the assessment studies. The simulation framework described in this paper comprises the following models: engine and aircraft performance, engine mechanical design and weight, engine certification noise and emissions.

A novel aspect of the presented simulation framework is that the design point efficiency and the design feasibility of the low pressure components are calculated for each engine design.