bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation on the Leakage Flow, Windage Heating and Swirl Development of Rotating Labyrinth Seal in a Compressor Stator Well
Authors: Kong Xiaozhi , Liu Gaowen , Liu Yuxin , Feng Qing 
Published: September 2016

What make the labyrinth seal in a compressor stator well different from the normal labyrinth seal are the inlet and outlet rotor-stator disc cavities. Due to the presence of rotating disc cavities, the windage heating and the swirl development are remarkable, which can have a great influence on the leakage characteristic. Besides, when compressor operates at different speeds, the rotor and stator grow differently owing to centrifugal expansion and thermal expansion. Hence the tip clearance which determines the leakage mass flow changes with the varying of rotational speed and temperature in the stator well.
A rotating test rig with rotational speed 8100rpm and pressure ratio range 1.05∼1.3 was designed for the test of labyrinth seal in a compressor stator well. A cantilevered structure was used to entirely collect the mass flow for an accurate measurement. To know the working tip clearance precisely, the set up tip clearance was measured with plug gauges, while the radial displacements of rotating disc and stationary casing were measured separately with two high precision laser distance sensors. The total temperatures of airflow in the stator well were measured with thermocouples to analyze the proportion of windage heating among the inlet rotating disc cavity, outlet rotating disc cavity, and labyrinth seal segment. The disc and stator casing were manufactured with non-metallic materials to reduce heat dissipation. Furthermore, the circumferential velocity of the leakage flow was measured using probes to reveal the swirl development.
Two-dimensional, axisymmetric swirl flow numerical simulations were carried out to provide insight into the flow field details, total temperature variation and swirl flow development in the stator well. The numerical results of discharge coefficient, windage heating and swirl ratio were compared with the experimental data. Of particular note is, the tip clearance of numerical model at a specific rotating speed was set to be the same with the actual working clearance which was measured in the experiment. The inlet and outlet parameters corresponded with the experimental conditions also.
Large Eddy Simulation of a Reacting Jet in Cross Flow With NOx Prediction
Authors: Weinzierl Johannes , Kolb Michael , Ahrens Denise , Hirsch Christoph , Sattelmayer Thomas 
Published: September 2016

The reduction of full and part load emissions and the increase of the turndown ratio are important goals for gas turbine combustor development. Combustion techniques, which generate lower NOx emissions than unstaged premixed combustion in the full load range, and which have the potential of reducing minimum load while complying with emission legislation, are of high technical interest. Therefore axial staged combustion systems have been designed, either with or without expansion in a turbine stage between both stages. In its simpler form without intermediate expansion stage a flow of hot combustion products is generated in the first stage of the premixed combustor, which interacts with the jets of premixed gas injected into the second stage.
The level of NOx formation during combustion of the premixed jets in the hot cross flow determines the advantage of axially staged combustion regarding full load NOx emission reduction. Employing Large Eddy Simulation in OpenFOAM, a tool has been developed, which allows to investigate staged combustion systems including not only temperature distribution but also NOx emissions under engine conditions. To be able to compute NOx formation correctly the combustion process has to be captured with sufficient level of accuracy. This is achieved by the partially stirred reactor model. It is combined with a newly developed NOx model, which is a combination of a tabulation technique for the NOx source term based on mixture fraction and progress variable and a partial equilibrium approach. The NOx model is successfully validated with generic burner stabilized flame data and with measurements from a large scale reacting jet in cross flow experiment. The new NOx model is finally used to compute a reacting jet in cross flow under engine conditions to investigate the NOx formation of staged combustion in detail. The comparison between the atmospheric and the pressurized configuration gives valuable insight in the NOx formation process. It can be shown that the NOx formation within a reacting jet in cross flow configuration is reduced and not only diluted.
Numerical Study of Purge and Secondary Flows in a Low Pressure Turbine
Authors: Cui J. , Tucker P. G. 
Published: September 2016

The secondary flow increases the loss and changes the flow incidence in the downstream blade row. To prevent hot gases from entering disk cavities, purge flows are injected into the mainstream in a real aero-engine. The interaction between purge flows and the mainstream usually induces aerodynamic losses. The endwall loss is also affected by shedding wakes and secondary flow from upstream rows. Using a series of eddy-resolving simulations, this paper aims to improve the understanding of the interaction between purge flows, incoming secondary flows along with shedding wakes and mainstream flows on the endwall within a stator passage.
It is found that for a blade with an aspect ratio of 2.2, a purge flow with a 1% leakage rate increases loss generation within the blade passage by around 10%. The incoming wakes and secondary flows increase the loss generation further by around 20%. The purge flow pushes the passage vortex further away from the endwall and increases the exit flow angle deviation. However, the maximum exit flow angle deviation is reduced after introducing incoming wakes and secondary flows. The loss generation rate is calculated using the mean flow kinetic energy equation. Two regions with high loss generation rate are identified within the blade passage: the corner region and the region where passage vortex interacts with the boundary layer on the suction surface. Loss generation rate increases dramatically after the separated boundary layer transitions. Since the endwall flow energizes the boundary layer and triggers earlier transition on the suction surface, the loss generation rate close to the endwall at the trailing edge is suppressed.
Experimental Investigation of Effects of Rim Sealing Flow on the Flow Field in a Turbine Cascade Passage With Different Rim Seal Configurations
Authors: Wang Lixiang , Ma Hongwei , Zhang Jinghui 
Published: September 2016

The hot gas in mainstream can ingest into the stator-rotor wheel space through the working clearance between the rotating and stationary parts of a turbo machine. To avoid ingestion, a certain amount of compressor air is injected into the cavity. On one hand, it can lead to a significant loss of engine efficiency, so the injected air coming from the compressor should be as little as possible. On another hand, when the rim sealing flow enters the passage, strong interaction happens between the rim sealing flow and the secondary flow structures. The rim sealing flow adversely affects the aerodynamics of the mainstream flow.
The authors have designed a contoured slot seal (CSS) configuration and found this configuration has better sealing performance than uniform slot seal (USS) configuration. However, the effects of rim sealing flow on the flow field in the turbine blade passage with a contoured slot seal (CSS) configuration is unknown. Hence an experimental study is carried out to investigate the effects of rim sealing flow on the performance of a turbine cascade passage with different kinds of rim seal configurations and some suggestions about rim seal design are put forward.
The tests were performed in a linear turbine cascade in Beihang University. The flow field at 10% chord downstream from the turbine blade trailing edge was measured by a mini five-hole probe. Three different rim seal configurations are investigated: (1) uniform slot seal (USS) configuration, (2) contoured slot seal configuration with small seal clearance at the leading edge of the blade (CSS_S), and (3) contoured slot seal configuration with large seal clearance at the leading edge of the blade (CSS_L). The configuration without cavity is studied as the baseline case. This experiment investigated the effects of the rim sealing flow on the flow field of the linear cascade at four different rim sealing flow rates.
Results show that when there is no rim sealing flow, the existence of seal clearance makes the passage vortex in the blade root weaker for USS and CSS_L than that for the configuration without cavity. With the increasing of the rim sealing flow, the passage vortex is enhanced and moves towards the middle span for USS and CSS_S. For all of the rim sealing flow, the passage vortex intensity of CSS_L is weaker than that of USS and CSS_S. The rim sealing flow has the smallest effect on the performance of the turbine cascade for CSS_L. Based on the better feature of CSS_L, a new CSS configuration is proposed.
An Acoustic Excitation System for the Generation of Turbomachinery Specific Sound Fields: Part II — Experimental Verification
Authors: Hurfar C. Mandanna , Keller Christian , Mumcu Akif , Seume Joerg R. 
Published: September 2016

A detailed understanding of the sound propagation and transmission within the engine and adjacent ducts is mandatory for the development of efficient noise reduction techniques for the tonal sound field produced by the turbomachinery components of aircraft engines. For this purpose, experimental acoustic investigations are needed. In the first part of this paper, an acoustic excitation system for the generation of acoustic spinning modes with circumferential mode order one and varying radial mode order, as well as a microphone array optimized for a radial decomposition of the sound field have been systematically designed.
To verify the excitation method and the design of the excitation system, corresponding experimental measurements are carried out in an acoustic wind tunnel. Amongst others, the sound power of the specific excited acoustic modes of order (1,0) and (1,1) are compared with the respective powers achieved with a non-specific sound field excitation. To test the range of flexible use of the sound generator, measurements are carried out over a wide frequency range. It is shown that the intended modes can be controlled at the design frequency of the sound generator as well as off-design frequencies. However, the dominance of the excited modes strongly depends on the number of cut-on modes and the excitation frequency as non-linear resonance effects may interfere. Furthermore, the benefit of an increased number of loudspeaker rows for stable mode excitation is discussed. The experimental results are supported by numerical simulations.
Understanding of Secondary Loss Structures in a Multi-Stage Transonic Compressor Using DES
Authors: Kim Donghyun , Son Changmin , Kim Kuisoon 
Published: September 2016

In the present study, a multi-stage transonic compressor has been analyzed to investigate secondary loss structures and flow interactions in the corner region where the hub endwall and blade suction surface meet. The Detached Eddy Simulation (DES) approach is used successfully with the Shear Stress Transport (SST) turbulence model to directly resolve the eddy structure in the separated region. The SST-DES results for a transonic three stage axial compressor are compared with a RANS analysis obtained using ANSYS CFX.
The present analysis indicates that the DES is better in simulating secondary losses and vortex structures than the RANS. With the DES, a large three-dimensional separation is predicted in the stator suction surface and hub endwall compared to the RANS prediction. The flow separation affects adversely the loss characteristics such as increases in the entropy and total pressure loss. The DES analysis indicates that the secondary flow phenomenon of the stator rows is apparent in all stages. It is observed to predict two distinct vortices induced by a three dimensional flow separation in the region adjacent to the suction surface and trailing edge of the last stage stator near the hub endwall. For the front two stages, the DES also predicts strong vortices and flow separation in the same corner region while the RANS analysis fails to predict them clearly.
The total pressure loss prediction is concerned, the DES analysis predicts significantly larger than the RANS analysis in the region where the hub corner separation occurs. The DES is also found to predict a periodic fluctuations in the entropy, leading to the instantaneous efficiency variations with maximum differences of about 10% compared with the RANS solutions.
Chemical Kinetic Models for Enhancing Gas Turbine Flexibility: Model Validation and Application
Authors: Güthe Felix , Gassner Martin , Bernero Stefano , Meeuwissen Thiemo , Wind Torsten 
Published: September 2016

In recent years, market trends towards higher power generation flexibility are driving gas turbine requirements of operation at stable conditions and below environmental emission guarantees over a wide range of operating conditions, such as load, and for changing fuels. In order to achieve these targets, engine components and operation concept need to be optimized to minimise emissions (e.g. CO, NOx) and combustion instabilities, as well as to maximize component lifetime. Therefore the combination of field experience, experimental studies and theoretical modelling of flames with state of the art tools play a key role in enabling the development of such solutions.
For many applications the relative changes of reactivity due to changes in operation conditions are important thus in this report a few examples are shown, where chemical kinetics simulations are used to determine the reactivity and to predict engine behaviour. The predicted trends are validated by correlating them to validation data from high pressure test rigs and real gas turbine operational data. With this approach the full operational range from highest reactivity (flashback) to lowest reactivity (blow out or CO emission increase) are covered. The study is focused on the sequential combustor (SEV) of reheat engines and addresses both the safety margins with respect to highly reactive fuels and achievable load flexibility with respect to part load CO emissions.
The analysis shows that it is necessary to utilize updated kinetic mechanisms since older schemes have proved to be inaccurate. A version of the mechanism developed at NUI Galway in cooperation with Alstom and Texas A&M was used and the results are encouraging, since they are well in line with experimental test data and can be matched to GT conditions to determine, predict, and optimize their operational range.
This example demonstrates nicely how a development over several years starting from fundamental basic research over experimental validation finally delivers a product for power plants. This report therefore validates the kinetic model in combination with the approach to use modelling for guidance of the GT development and extending it fuel capabilities.
The GT24 / GT26 can not only be operated with H2 containing fuels, but also at very low part load conditions and with the integration of H2 from electrolysis (∼power to gas ∼PTG) the turndown capability can even be further improved. In this way the energy converted at low electricity prices can be stored and utilised at later times when it is advantageous to run the GT at lower loads increasing the overall flexibility. This development is well suited to integrate renewable energy at highly fluctuating availability and price to the energy provisioning by co-firing with conventional fuels.
Optimization of Robust Transonic Compressor Blades
Authors: Lejon Marcus , Andersson Niklas , Grönstedt Tomas , Ellbrant Lars , Mårtensson Hans 
Published: September 2016

Surface degradation in an axial compressor during its lifetime can have a considerable adverse effect on its performance. The present study investigates how the optimized design of compressor blades in a single compressor stage is affected by considering a high level of surface roughness on a level representative of a long period of in-service use. It is shown that including surface roughness in the optimization process is of relatively little importance, however, matching of compressor stages is shown to require consideration as the rotational speed must be increased to reach the design point as surface quality decrease. An increased surface roughness in itself is shown to have a large effect on performance.
Two optimization approaches are compared. The first approach considers the compressor blades to be hydraulically smooth. The designs obtained from this approach are subsequently degraded by increasing the level of surface roughness. The compressor blades from the first approach are compared to designs obtained from a second optimization approach, which considers a high level of surface roughness from the outset.
The degraded compressor stages from the first approach are shown to be among the best performing designs in terms of polytropic efficiency and stability when compared to designs obtained with the second approach.
Numerical Investigation of Three-Dimensional Separation in an Axial Flow Compressor: The Influence of Free-Stream Turbulence Intensity and Endwall Boundary Layer State
Authors: Scillitoe Ashley D. , Tucker Paul G. , Adami Paolo 
Published: September 2016

Regions of three-dimensional separations are an inherent flow feature of the suction surface - endwall corner in axial compressors. These corner separations can cause a significant total pressure loss and reduce the compressor’s efficiency. This paper uses wall-resolved LES to investigate the loss sources in a corner separation, and examines the influence of the inflow turbulence on these sources.
Different subgrid scale (SGS) models are tested and the choice of model is found to be important. The σ SGS model, which performed well, is then used to perform LES of a compressor endwall flow. The time-averaged data is in good agreement with measurements. The viscous and turbulent dissipation are used to highlight the sources of loss, with the latter being dominant. The key loss sources are seen to be the 2D laminar separation bubble and trailing edge wake, and the 3D flow region near the endwall.
Increasing the free-stream turbulence intensity (FST) changes the suction surface boundary layer transition mode from separation induced to bypass. However, it doesn’t significantly alter the transition location and therefore the corner separation size. Additionally, the FST doesn’t noticeably interact with the corner separation itself, meaning that in this case the corner separation is relatively insensitive to the FST.
The endwall boundary layer state is found to be significant. A laminar endwall boundary layer separates much earlier leading to a larger passage vortex. This significantly alters the endwall flow and loss. Hence, the need for accurate boundary measurements is clear.
Parasitic Loss due to Leading Edge Instrumentation on a Low Pressure Turbine Blade
Authors: Ng Henry C.-H. , Coull John D. 
Published: September 2016

During the testing of development engines and components, intrusive instrumentation such as Kiel head Pitot probes and shrouded thermocouples are used to evaluate gas properties and performance. The size of these instruments can be significant relative to the blades and their impact on aerodynamic efficiency must be considered when analysing the test data. This paper reports on such parasitic losses for instruments mounted on the leading edge of a stator in a low pressure turbine, with particular emphasis on understanding the impact of probe geometry on the induced loss.
The instrumentation and turbine blades have been modeled in a low Mach number cascade facility with an upstream turbulence grid. The cascade was designed so that the leading edge probes were interchangeable in-situ, allowing for rapid testing of differing probe geometries. RANS calculations were performed to complement the experiments and gain more understanding about the flow behaviour.
A horseshoe vortex-like system forms at the join of the probe body and blade leading edge, generating pairs of streamwise vortices which convect over the blade pressure and suction surfaces. These vortices promote mixing between the freestream and boundary layer fluid, and promote the transition of the boundary layer from laminar to turbulent flow.
The size and shape of the leading edge probes relative to the blade varies significantly between applications. Tests with realistic probe geometries demonstrate that the detailed design of the shroud bleed system can impact the loss. A study of idealised cylinders is performed to isolate the impact of probe diameter, aspect ratio and incidence.
Effect of Rib Density on Flow and Heat Transfer in an Internal Cooling Passage
Authors: Hagari Tomoko , Ishida Katsuhiko , Takeishi Kenichiro , Komiyama Masaharu , Oda Yutaka 
Published: September 2016

Effect of rib density on mechanism of flow and heat transfer enhancement in an internally-cooled channel with rib turbulators have been investigated numerically. Based on the experimental setup in the previous study [32], flowfield and heat transfer coefficient distributions were predicted with LES approach. The rib pitch-to-height ratios were 3 and 11, and Reynolds number based on the channel hydraulic diameter and bulk velocity was set at 30,000. Comparison of time-averaged flow and heat transfer characteristics between numerical and experimental results showed that prediction accuracy of the present numerical setup was reasonable.
The previous study [33] suggested that, for higher rib density, low-frequency velocity fluctuation characterizes heat transfer. To investigate its flow and heat transfer mechanism, instantaneous velocity and temperature fields were compared. For smaller rib density, small vortices constantly occurred from each rib and were dissipated into the mainstream before reaching the next rib. On the other hand, for higher rib density, relatively large vortex occurs above the ribs in addition to smaller vortices inside the cavity between the ribs. The large vortex occurs intermittently behind the second rib of the channel, and increases its size by interacting with smaller vortex downstream. For each rib pitch, similar trend was observed in the measured result obtained using Particle Image Velocimetry. This unsteady vortex structure would contribute to enhancing the heat transfer of a cooling channel with densely-arranged rib turbulators.