bluuebunny/crossref_metadata_2025 huggingface dataset:
Computation of Ingestion Through Gas Turbine Rim Seals
Authors: Zhou Kunyuan , Wilson Mike , Owen J. Michael , Lock Gary
Published: May 2012

Three-dimensional unsteady computational fluid dynamics (CFD) is applied to the ingestion of fluid from a non-uniform mainstream annulus flow via a rim-seal into a rotor-stator wheel-space. The results provide understanding of the complex flow and information for the development of more efficient computational models and analytical ‘orifice models’. The commercial CFD code CFX has been used to carry out unsteady RANS computations with an SST turbulence model. A scalar equation is employed to represent the seeded tracer gas that can be used in experiments to determine sealing effectiveness, and the variation of effectiveness with sealing flow rate is determined for a simple axial clearance seal and one combination of axial and rotational Reynolds numbers. The computational domain comprises one pitch in a row of stator vanes and rotor blades The rotating blade is accounted for by a sliding interface between the stationary and rotating sections of the model, located downstream of the seal clearance. The unsteady computations confirm that the magnitude of the peak-to-trough pressure difference in the annulus is the principal driving mechanism for ingestion (or ingress) into the wheel-space. This pressure difference is used in orifice models to predict sealing effectiveness; its magnitude however depends on the locations in the annulus and the wheel-space that are chosen for its evaluation as well as the sealing flow rate. The CFD is used to investigate the appropriateness of the locations that are often used to determine the pressure difference. It is shown that maximum ingestion occurs when the static pressure peak produced by the vane combines with that produced by the blade, and that highly swirled ingrested flow could contact both the stator and rotor disk when little sealing flow is provided. The relationships between the unsteady simulations and simplified, more computationally efficient steady computations are also investigated. For the system considered here, ingress is found to be dictated principally by the pressure distribution caused by the vane. The effect of the rotating blade on the pressure distribution in the annulus is investigated by comparing the unsteady results with those for steady models that do not involve a blade. It is found that the presence of the blade increases the pressure asymmetry in the annulus. Although the pressure asymmetry predicted by unsteady and steady models have a similar magnitude, the sealing effectiveness is over-predicted considerably for the corresponding steady model. If a “thin seal” geometric approximation is used in the steady model, however, similar effectiveness results compared with the unsteady model may be obtained much more economically.
Mildly-Compressible Pressure-Based CFD Methodology for Acoustic Propagation and Absorption Prediction
Authors: Gunasekaran B. , McGuirk J. J.
Published: May 2012

A modified pressure-based CFD methodology — as commonly used for analysis/design of low Mach number gas turbine combustor flows — is described, which can accurately resolve acoustic wave propagation and absorption. The computational algorithm is based on the classical pressure-correction approach. This is modified to achieve (i) better capture of acoustic waves at reduced number of grid points per wavelength for low dispersion performance, and (ii) incorporation of characteristic boundary conditions to enable accurate representation of acoustic excitation (e.g. via a loudspeaker or siren), as well as acoustic reflection and transmission characteristics. The methodology is first validated against simple test cases demonstrating good numerical accuracy, then compared against classical linear acoustic analysis of acoustic and entropy waves in quasi-1D variable area duct flows. Finally, it is applied to the prediction of experimental measurements of the acoustic absorption coefficient for an orifice flow. Excellent agreement with experimental data is obtained for both linear and non-linear characteristics.
Unsteady Wetness Effects in LP Steam Turbines
Authors: Chandler Kane D. , White Alexander J. , Young John B.
Published: May 2012

One of the unresolved issues for condensing flow in large steam turbines is correct prediction of the droplet size distribution. Optical measurements taken in the later stages of LP steam turbines have shown that the time-averaged droplet size spectra are much broader with larger average diameters than predicted by most theoretical and computational methods. Previous work has suggested that the broad distributions might stem from unsteadiness created by the interaction between successive blade rows — the so-called ‘wake-chopping’ effect. The current paper presents preliminary results of multi-stage CFD calculations aimed at investigating the impact of such unsteadiness on the condensation process. A method for calculating unsteady, viscous, condensing flows in multi-stage steam turbines is first outlined. This is based on an established single-phase flow solver with nucleation and droplet growth incorporated via moment evolution equations for the polydispersed liquid phase. The method can be used to compute two- and three-dimensional steady and unsteady flows, time accuracy being preserved for unsteady calculations by means of the dual time-stepping technique. Comparison between computed results and experimental data is presented for nozzle and cascade flows for the purpose of validation. Finally, results are presented for a two-dimensional unsteady multi-stage calculation, highlighting the impact of wake-chopping and related unsteady phenomena on the droplet spectra.
Remaining Life Assessment Technology Applied to Steam Turbines and Hot Gas Expanders
Authors: Dowson Phillip , Dowson David
Published: May 2012

In today’s market place, a large percentage of oil refinery, petrochemical, and power generation plants throughout the world have been trying to reduce their operation cost by extending the service life of their critical machines, such as steam turbines, beyond the design life criteria. The key ingredient in plant life extension is Remaining Life Assessment Technology. This paper will outline the Remaining Life Assessment procedures, and review the various damage mechanisms such as creep, fatigue, creep-fatigue and various embrittlement mechanisms that can occur in these machines. Also highlighted will be the various testing methods for determining remaining life or life extension of components such as high precision STR (Stress Relaxation Test), which determines creep strength, and CDR (Constant Displacement Rate) Test, which evaluates fracture resistance. Other tests such as replication/microstructure analysis and toughness tests will also be reviewed for calculating the remaining life or life extension of the components. Use of the latest computer software will also be highlighted showing how creep-life, fatigue-life and creep/fatigue-life calculations can be performed. Also shown will be an actual life extension example of a hot gas expander performed in the field.
Convective and Absolute Instabilities in Reacting Bluff Body Wakes
Authors: Emerson Benjamin , Lundrigan Julia , O’Connor Jacqueline , Noble David , Lieuwen Tim
Published: May 2012

This paper describes the variation of bluff body wake structure with flame density ratio. It is known that the bluff body flow structure at “high” and “low” flame density ratios is fundamentally different, being dominated by the convectively unstable shear layers or absolutely unstable Von Karman vortex street, respectively. This paper characterizes the aforementioned transition and shows that the bifurcation in flow behavior does not occur abruptly at some ρu/ρb value. Rather, there exists a range of transitional density ratios at which the flow exists intermittently in both flow states, abruptly shifting back and forth between the two. The fraction of time that the flow spends in either state is a monotonic function of ρu/ρb. This behavior is to be contrasted with lower Reynolds number, laminar flow problems where the convective/absolute instability transition occurs at a well defined value of bifurcation parameter. With this distinction in mind, however, this paper also shows that local parallel stability analyses developed for laminar base wake flows can capture many of the observed flow dependencies. These results have important implications on the dynamics of high Reynolds number, vitiated flows, where typical parameter values fall into the highly intermittent flow regime characterized in this study. This suggests that such flows exhibit two co-existing dynamical states, intermittently jumping between the two.
Development of GUI Type On-Line Condition Monitoring Program for a Turboprop Engine Using LabVIEW®
Authors: Kong Changduk , Kim Keonwoo , Kim Jihyun
Published: May 2012

Recently, the health monitoring system has been developed for precaution and maintenance action against faults or performance degradations of the advanced propulsion system which may be occurred in severe environments such as high altitude, foreign object damage particles, hot and heavy rain and snowy atmospheric conditions. However to establish this health monitoring system, the on-line condition monitoring program is firstly required, and the program must monitor the engine performance trend through comparison between measuring engine performance data and base performance results calculated by base engine performance model. This work aims to develop a GUI type on-line condition monitoring program for the PT6A-67 turboprop engine of a high altitude and long endurance operation UAV using LabVIEW. The base engine performance of the on-line condition monitoring program is simulated using component maps inversely generated from the limited performance deck data provided by engine manufacturer. The base engine performance simulation program is evaluated because analysis results by this program are well agreed with the performance deck data. The proposed on-line condition program can monitor the real engine performance as well as the trend through precise comparison between clean engine performance results calculated by the base performance simulation program and measuring engine performance signals. In the development phase of this monitoring system, a signal generation module is proposed to evaluate the proposed on-line monitoring system. For user friendly purpose, all monitoring program are coded by LabVIEW, and monitoring examples are demonstrated using the proposed GUI type on-condition monitoring program.
Rotor-Tip Flow Fields Near Inception Point of Rotating Instability in an Axial-Flow Fan
Authors: Nishioka Takahiro , Kanno Toshio , Hiradate Kiyotaka
Published: May 2012

Stall inception patterns at three stagger-angle settings for the highly loaded rotor blades were experimentally investigated in a low-speed axial-flow fan. Rotor-tip flow fields were also numerically investigated to clarify the mechanism behind the stall inception from a rotating instability. The rotating instability is confirmed near stall condition at the high stagger-angle settings for the highly loaded rotor blades as same as that for the moderate loaded rotor blades. The rotating instability is induced by an interaction between the incoming flow, the reversed tip-leakage flow, and the end-wall backflow from the trailing edge. At the high stagger-angle settings for the rotor blades, the interface between the incoming flow and the reversed tip leakage flow becomes parallel to the leading edge plane near and at the stall condition. Moreover, the tip leakage flow spills from the leading edge of the adjacent blade at the stall condition. The changes in the end-wall flow at the rotor tip are consistent with the criteria for the spike initiation suggested by Vo et al. and Hah et al. However, the short length-scale stall cell is not observed at the high stagger-angle settings. The tip-leakage vortex breakdown is confirmed at the three stagger-angle settings. The end-wall blockage induced by the tip-leakage vortex breakdown influences the development of the stall cell. Moreover, the development of the three-dimensional separation vortex induced by the tip-leakage vortex breakdown seems to be one of the criteria for spike-type stall inception.
Construction of Shock Response Map for a Flexible Rotor-Bearing System With Mount System to Base Excitations Using the FE Transient Analysis Method
Authors: Lee An Sung , Kim Byung Ok
Published: May 2012

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems such as warships, submarines and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect the machines from such excessive shock forces, one may need to accurately analyze transient responses of rotors earlier on in their design stages, considering the dynamics of mount designs to be applied with. In this study, utilizing the generalized FE transient response analysis method of a flexible rotor-bearing system with a mount system to base-transferred shock forces, constructions of the shock response and static deflection maps of turbine rotor-bearing and mount system are devised, introducing the mount mass, resilient support stiffness and damping ratios to the counterpart rotor mass, bearing stiffness and damping and the mount system natural frequency. For the given turbine rotor system design a best available mount system design, composed of a mount plate and resilient support, can be readily selected from the constructed maps to meet the rotor’s shock response and mount’s static design limits. The shock response maps also show that for the same shock the FE flexible rotor model used herein yield a more compact light-weighed mount system design than the conventional simple rigid rotor model. Therefore, the shock response map approach in conjunction with the more complicated FE flexible rotor transient response analysis method is justified.
Design and Test of a Highly Loaded Single-Stage High Pressure Turbine
Authors: Wolf T. , Janke E. , Benton R. , Kost F. , Haselbach F. , Gegg S.
Published: May 2012

For the small to medium thrust range of modern aero engines, highly loaded single-stage HP turbines facilitate an attractive alternative to a more conventional 2-stage HPT architecture. Within the German government funded LUFO-3 programme “Transonic Single Stage High-Pressure Turbine”, a substantial activity towards the development and test of supersonic aerodynamic technology for single stage turbines was launched in 2003. This paper describes fundamental aerodynamic concept studies and related cascade experiments in support of a future highly loaded high-pressure turbine architecture. Details of the first out of two builds featuring an engine representative single-stage HPT is described in detail. Focus will be on instrumentation design, selected results from performance, area traverse and unsteady blade surface pressure measurements and the comparison of experiments with numerical simulations. The successfully completed test campaign confirms the existence of an aerodynamically efficient design of a highly loaded HPT, thereby enabling a competitive building block for a small to medium size engine concept.
Study on Compensatory Magnitude of Axial Misalignment for Flexible Couplings Assembled by Interference Fit
Authors: Wang Guoping , Chen Hualing , Qi Shemiao , Wu Jiuhui , Yu Lie
Published: May 2012

In general, there are three kinds of common metal flexible couplings, such as diaphragm coupling, disc coupling and gear coupling. Gear couplings, compared with diaphragm couplings and disc couplings, usually have a little ability in compensating misalignments. Diaphragm couplings have nice compensatory ability in radial, angular and axial directions, especially muti-diaphragm couplings have better compensatory ability than disc couplings. Diaphragm couplings are also suitable for higher rotating speed than disc couplings. They are high technology products, are widely used in micro gas turbine. Joint way of a diaphragm coupling with a shaft usually uses bolts and interference fit. In this article, a flexible diaphragm coupling assembled by interference fit was taken as research object. By comparing three kinds of interference assembly forms of the coupling, a most reasonable form was chosen and its axial compensatory ability was treated as main research content. An idea that “established process of balances is the varied process of misalignment magnitude” was presented. Combining the idea and the characters of interference fit, new boundary conditions were confirmed via bringing assumed shearing forces, and then the physical model was established based on the new boundary conditions mentioned above. Two-step method, based on the physical model, was presented to solve the axial compensatory magnitude. Meanwhile centrifugal stress and torsional shearing stress of diaphragms of the coupling were also considered in the process of calculation. Finally an example was done to support the method. Some important conclusions were acquired by calculating, and they are significant for design of the flexible diaphragm couplings.
Effects of Surface Geometry on Film Cooling Performance at Airfoil Trailing Edge
Authors: Murata Akira , Nishida Satomi , Saito Hiroshi , Iwamoto Kaoru , Okita Yoji , Nakamata Chiyuki
Published: May 2012

Cooling at trailing edge of gas turbine airfoil is one of the most difficult problems because of its thin shape: high thermal load from both surfaces, hard-to-cool geometry of narrow passages, and at the same time demand for structural strength. In this study, heat transfer coefficient and film cooling effectiveness on pressure-side cutback surface was measured by a transient infrared thermography method. Four different cutback geometries were examined: two smooth cutback surfaces with constant-width and converging lands (base and diffuser cases) and two roughened cutback surfaces with transverse ribs and spherical dimples. The Reynolds number of main flow defined by the mean velocity and two times of channel height was 20,000 and the blowing ratio was varied among 0.5, 1.0, 1.5, and 2.0. The experimental results clearly showed spatial variation of the heat transfer coefficient and the film cooling effectiveness on the cutback and land top surfaces. The cutback surface results clearly showed periodically enhanced heat transfer due to the periodical surface geometry of ribs and dimples. Generally, the increase of blowing ratio increased both the heat transfer coefficient and the film cooling effectiveness. Within the present experimental range, the dimple surface was a favorable cutback-surface geometry, because it gave the enhanced heat transfer without deterioration of the high film cooling effectiveness.
Validation of Conjugate Heat Transfer Predictions on Labyrinth Seals and Novel Designs for Improved Component Lifetime
Authors: Born Dominik , Heiniger Kurt , Zanazzi Giorgio , Mokulys Thomas , Grossmann Patrick , Ripamonti Luca , Sell Michael
Published: May 2012

Cyclic lifetime assessment of steam turbine components has become increasingly important for several reasons. In the last years and decades the nominal steam temperatures and pressures were further increased to improve cycle efficiency. In addition, the market constantly demands increased flexibility and reliability for given lifetime exploiting the limits of the existing materials. A number of components in a steam turbine are critical in the focus of lifetime predictions such as the rotor and front stage blades, the inner casing and the area of labyrinth seals connected to the life steam. For this reason, it becomes extremely important to rely on accurate predictions of local temperatures and heat-transfer-coefficients of components in the steam path. The content of this paper aims on the validation of the numerical tools based on CHT (conjugate heat transfer) approach against experimental data of a labyrinth seal regarding discharge coefficients and measured heat transfer coefficients. Furthermore, a real steam turbine application has been optimized in design and operation to improve lifetime. The improved prediction of temperature and heat transfer allowed novel designs of labyrinth seals of a single flow high-pressure turbine and a combined intermediate and low-pressure turbine, which helped to strongly increase the component lifetime of a steam turbine rotor by more than 100%.
Effect of Recirculation Device With Counter Swirl Vane on Performance of High Pressure Ratio Centrifugal Compressor
Authors: Tamaki Hideaki
Published: May 2012

Centrifugal compressors used for turbochargers need to achieve a wide operating range. The author has developed a high pressure ratio centrifugal compressor with pressure ratio 5.7 for a marine use turbocharger. In order to enhance operating range, two different types of recirculation devices were applied. One is a conventional recirculation device. The other is a new one. The conventional recirculation device consists of an upstream slot, bleed slot and the annular cavity which connects both slots. The new recirculation device has vanes installed in the cavity. These vanes were designed to provide recirculation flow with negative preswirl at the impeller inlet, a swirl counterwise to the impeller rotational direction. The benefits of the application of both of the recirculation devices were ensured. The new device in particular, shifted surge line to a lower flow rate compared to the conventional device. This paper discusses how the new recirculation device affects the flow field in the above transonic centrifugal compressor by using steady 3-D calculations. Since the conventional recirculation device injects the flow with positive preswirl at the impeller inlet, the major difference between the conventional and new recirculation device is the direction of preswirl that the recirculation flow brings to the impeller inlet. This study focuses on two effects which preswirl of the recirculation flow will generate. (1) Additional work transfer from impeller to fluid. (2) Increase or decrease of relative Mach number. Negative preswirl increases work transfer from the impeller to fluid as the flow rate reduces. It increases negative slope on pressure ratio characteristics. Hence the recirculation flow with negative preswirl will contribute to stability of the compressor. Negative preswirl also increases the relative Mach number at the impeller inlet. It moves shock downstream compared to the conventional recirculation device. It leads to the suppression of the extension of blockage due to the interaction of shock with tip leakage flow.
Experimental Investigation of Turbulent Boundary Layer Flashback Limits for Premixed Hydrogen-Air Flames Confined in Ducts
Authors: Eichler Christian , Baumgartner Georg , Sattelmayer Thomas
Published: May 2012

The design of flashback-resistant premixed burners for hydrogen-rich fuels is strongly dependent on reliable turbulent boundary layer flashback limits, since this process can be the dominant failure type for mixtures with high burning velocities. So far, the flashback data published in literature is based on tube burner experiments with unconfined flames. However, this flame configuration may not be representative for the most critical design case, which is a flame being already present inside the duct geometry. In order to shed light on this potential misconception, boundary layer flashback limits have been measured for unconfined and confined flames in fully premixed hydrogen-air mixtures at atmospheric conditions. Two duct geometries were considered, a tube burner and a quasi-2D turbulent channel flow. Furthermore, two confined flame holding configurations were realized, a small backward-facing step inside the duct and a ceramic tile at high temperature, which was mounted flush with the duct wall. While the measured flashback limits for unconfined tube burner flames compare well with literature results, a confinement of the stable flame leads to a shift of the flashback limits towards higher critical velocity gradients, which are in good agreement between the tube burner and the quasi-2D channel setup. The underestimation of flashback propensity resulting from unconfined tube burner experiments emerges from the physical situation at the burner rim. Heat loss from the flame to the wall results in a quenching gap, which causes a radial leakage flow of fresh gases. This flow in turn tends to increase the quenching distance, since it constitutes an additional convective heat loss. On the one hand, the quenching gap reduces the local adverse pressure gradient on the boundary layer. On the other hand, the flame base is pushed outward, which deters the flame from entering the boundary layer region inside the duct. The flashback limits of confined flames stabilized at backward-facing steps followed this interpretation, and experiments with a flush ceramic flame holder constituted the upper limit of flashback propensity. It is concluded that the distribution of the flame backpressure and the flame position itself are key parameters for the determination of meaningful turbulent boundary layer flashback limits. For a conservative design path, the present results obtained from confined flames should be considered instead of unconfined tube burner values.
Ultra High Bypass Ratio Engine Sizing and Cycle Selection Study for a Subsonic Commercial Aircraft in the N+2 Timeframe
Authors: Kestner Brian K. , Schutte Jeff S. , Gladin Jonathan C. , Mavris Dimitri N.
Published: May 2012

This paper presents an engine sizing and cycle selection study of ultra high bypass ratio engines applied to a subsonic commercial aircraft in the N+2 (2020) timeframe. NASA has created the Environmentally Responsible Aviation (ERA) project to serve as a technology transition bridge between fundamental research (TRL 1–4) and potential users (TRL 7). Specifically, ERA is focused on subsonic transport technologies that could reach TRL 6 by 2020 and are capable of integration into an advanced vehicle concept that simultaneously meets the ERA project metrics for noise, emissions, and fuel burn. An important variable in exploring the trade space is the selection of the optimal engine cycle for use on the advanced aircraft. In this paper, two specific ultra high bypass engine cycle options will be explored: advanced direct drive and geared turbofan. The advanced direct drive turbofan is an improved version of conventional turbofans. In terms of both bypass ratio and overall pressure ratio, the advanced direct turbofan benefits from improvements in aerodynamic design of its components, as well as material stress and temperature properties. By putting a gear between the fan and the low pressure turbine, a geared turbo fan allows both components to operate at optimal speeds, thus further improving overall cycle efficiency relative to a conventional turbofan. In this study, sensitivity of cycle design with level of technology will be explored, in terms of both cycle parameters (such as specific thrust consumption (TSFC) and bypass ratio) and aircraft mission parameters (such as fuel burn and noise). To demonstrate this sensitivity, engines will be sized for optimal performance on a 300 passenger class aircraft for a 2010 level technology tube and wing airframe, a N+2 level technology tube and wing air-frame, and finally on a N+2 level technology blended wing body airframe with and without boundary layer ingestion (BLI) engines.
An Analytical Approach to Gas Turbine Engine Model Linearization
Authors: Chung Gi-Yun , Dhingra Manuj , Prasad J. V. R. , Meisner Richard , Sirica Steven
Published: May 2012

This paper presents analytical linearization schemes of a reduced order aero-thermodynamic model of the generic back end of a turbofan engine. The proposed linearization scheme has advantages of flexibility and reusability over the commonly used linearization method based on the numerical perturbation scheme. Also, a blending algorithm employing the distance to the boundary as the weight has been incorporated into the linearization scheme to capture the change of the flow behaviour near bifurcating boundaries. The proposed linearization scheme is developed and applied to a back end model of a generic turbofan engine with bifurcations corresponding to choked/unchoked boundaries. This model is also used for proof of concept validation test.
Assessment of Gas Turbine and Combined Cycle Power Plant Performance Degradation
Authors: Hepperle Nina , Therkorn Dirk , Schneider Ernst , Staudacher Stephan
Published: May 2012

Recoverable and non-recoverable performance degradation has a significant impact on power plant revenues. A more in depth understanding and quantification of recoverable degradation enables operators to optimize plant operation. OEM degradation curves represent usually non-recoverable degradation, but actual power output and heat rate is affected by both, recoverable and non-recoverable degradation. This paper presents an empirical method to correct longterm performance data of gas turbine and combined cycle power plants for recoverable degradation. Performance degradation can be assessed with standard plant instrumentation data, which has to be systematically stored, reduced, corrected and analyzed. Recoverable degradation includes mainly compressor and air inlet filter fouling, but also instrumentation degradation such as condensate in pressure sensing lines, condenser or bypass valve leakages. The presented correction method includes corrections of these effects for gas turbine and water steam cycle components. Applying the corrections on longterm operating data enables staff to assess the non-recoverable performance degradation any time. It can also be used to predict recovery potential of maintenance activities like compressor washings, instrumentation calibration or leakage repair. The presented correction methods are validated with long-term performance data of several power plants. It is shown that the degradation rate is site-specific and influenced by boundary conditions, which have to be considered for degradation assessments.
Experimental Investigation Into the Impact of Crossflow on the Coherent Unsteadiness Within Film Cooling Flows
Authors: Fawcett Richard J. , Wheeler Andrew P. S. , He Li , Taylor Rupert
Published: May 2012

It is known that the mixing of a film cooling flow with the main turbine passage flow is an unsteady process, with coherent unsteady features occurring across a range of blowing ratios. Upon an aero engine the cooling holes on a turbine blade commonly have a crossflow at the hole inlet. Previous work has shown that crossflow at the hole inlet modifies the time-mean flowfield downstream of a cooling hole compared to the case without crossflow. The current paper investigates the impact of spanwise orientated crossflow on the coherent unsteadiness within film cooling flows. Both cylindrical and fan-shaped holes, located on a blade pressure surface, are studied. The range of blowing ratios considered is 0.7 to 1.8 and the crossflow velocity is up to 0.8 times the bulk jet velocity. High Speed Photography and Hot Wire Anemometry are used to observe the presence of coherent unsteadiness, both immediately downstream of the hole exit and within the cooling hole tube. The results show that the coherent unsteadiness downstream of the hole exit is persistent and its occurrence is not significantly affected by the magnitude of spanwise crossflow. Within the cooling hole tube the existence of coherent unsteadiness is presented for the first time, inside both cylindrical and fan-shaped holes, with a Strouhal number of 0.6 to 0.8. The pattern of this in-hole coherent unsteadiness is seen to change with increasing the crossflow velocity.
Flue Gas Recirculation of the Alstom Sequential Gas Turbine Combustor Tested at High Pressure
Authors: Guethe Felix , Stankovic Dragan , Genin Franklin , Syed Khawar , Winkler Dieter
Published: May 2012

Concerning the efforts in reducing the impact of fossil fuel combustion on climate change for power production utilizing gas turbine engines Flue Gas Recirculation (FGR) in combination with post combustion carbon capture and storage (CCS) is one promising approach. In this technique part of the flue gas is recirculated and introduced back into the compressor inlet reducing the flue gas flow (to the CCS) and increasing CO2 concentrations. Therefore FGR has a direct impact on the efficiency and size of the CO2 capture plant, with significant impact on the total cost. However, operating a GT under depleted O2 and increased CO2 conditions extends the range of normal combustor experience into a new regime. High pressure combustion tests were performed on a full scale single burner reheat combustor high-pressure test rig. The impact of FGR on NOx and CO emissions is analyzed and discussed in this paper. While NOx emissions are reduced by FGR, CO emissions increase due to decreasing O2 content although the SEV reheat combustor could be operated without problem over a wide range of operating conditions and FGR. A mechanism uncommon for GTs is identified whereby CO emissions increase at very high FGR ratios as stoichiometric conditions are approached. The feasibility to operate Alstom’s reheat engine (GT24/GT26) under FGR conditions up to high FGR ratios is demonstrated. FGR can be seen as continuation of the sequential combustion system which already uses a combustor operating in vitiated air conditions. Particularly promising is the increased flexibility of the sequential combustion system allowing to address the limiting factors for FGR operation (stability and CO emissions) through separated combustion chambers.
Reduced Order Model of a Bladed Rotor With Geometric Mistuning: Comparison Between Modified Modal Domain Analysis and Frequency Mistuning Approach
Authors: Bhartiya Yasharth , Sinha Alok
Published: May 2012

Mistuning has traditionally been modeled through the changes in Young’s moduli of blades, or equivalently through perturbations in the stiffness matrices associated with blades’ degrees of freedom. Such a mistuning is termed as Frequency Mistuning because it alters the blade alone frequencies without altering the mode shapes component associated with the blades. Many reduced order models have been developed for frequency mistuning [1–7]. Although frequency mistuning has been developed for Young’s Modulus mistuning, it is applied to geometric mistuning in the literature. In this paper frequency mistuning is applied to a geometrically mistuned system and the results from Subset of Nominal Modes (SNM) [5] technique, a reduced order model based on frequency mistuning, are compared with those from Modified Modal Domain Analysis (MMDA). It is shown that frequency mistuning analysis is unable to capture the effects of geometric mistuning in general, whereas MMDA provides accurate estimates of natural frequencies, mode shapes and forced response.
Experimental and Computational Results of Distributed Combustion for Application in Current Gas Turbine Engine Combustor Architectures
Authors: Overman Nick , Ryon Jason
Published: May 2012

Current development and testing has lead to a fuel/air injection system for application in gas turbine engines that produces ultra low emissions and stable, lean combustion. The system is designed to operate with current combustor architectures similar to existing gas turbine engines. This paper presents both experimental and numerical test results demonstrating the benefits of such technology including extremely low emissions of NOx, CO, and un-burned hydrocarbons (UHC). Primary focus is on experimental results demonstrating reaction distribution and emissions. Numerical confirmation of flow field dynamics was used to develop an understanding of the re-circulation rates within the combustor and impact on reaction behavior. Several design configurations were tested to investigate the effects of aerodynamic stagnation point and fuel placement with respect to the aerodynamic shear layer produced by the swirling flow field. Test conditions were varied, including inlet air temperature and injector pressure drop for monitoring effects on the operating envelope of distributed reaction and on lean blow out limit. Results demonstrate the improved performance of a system capable of operating in a flameless or distributed reaction mode over that of a typical lean burn system.
Experimental Comparison of DBD Plasma Acuators for Low Reynolds Number Separation Control
Authors: Marks Christopher , Sondergaard Rolf , Wolff Mitch , Anthony Rich
Published: May 2012

This paper presents experimental work comparing several Dielectric Barrier Discharge (DBD) plasma actuator configurations for low Reynolds number separation control. Actuators studied here are being investigated for use in a closed loop separation control system. The plasma actuators were fabricated in the U. S. Air Force Research Laboratory Propulsion Directorate’s thin film laboratory and applied to a low Reynolds number airfoil that exhibits similar suction surface behavior to those observed on Low Pressure (LP) Turbine blades. In addition to typical asymmetric arrangements producing downstream jets, one electrode configurations was designed to produce an array of off axis jets, and one produced a spanwise array of linear vertical jets in order to generate vorticity and improved boundary layer to freestream mixing. The actuators were installed on an airfoil and their performance compared by flow visualization, surface stress sensitive film (S3F), and drag measurements. The experimental data provides a clear picture of the potential utility of each design. Experiments were carried out at four Reynolds numbers, 1.4×105, 1.0 × 105, 6.0 × 104, and 5.0 × 104 at a −1.54° angle of attack. Data was taken at the AFRL Propulsion Directorate’s Low Speed Wind Tunnel (LSWT) facility.
Stiffness Measurement for Pressure-Loaded Brush Seals
Authors: Bidkar Rahul A. , Zheng Xiaoqing , Demiroglu Mehmet , Turnquist Norman
Published: May 2012

Brush seals are widely used as flexible seals for rotor-stator and stator-stator gaps in power generation turbo-machinery like steam turbines, gas turbines, generators and aircraft engines. Understanding the force interactions between a brush seal bristle pack and the rotor is important for avoiding overheating and rotor dynamic instabilities caused by excessive brush seal forces. Brush seal stiffness (i.e. brush seal force per unit circumferential length per unit incursion of the rotor) is usually measured and characterized at atmospheric pressure conditions. However, the inter-bristle forces, the blow-down forces and the friction forces between the backplate and the bristle pack change in the presence of a pressure loading, thereby changing the stiffness of the brush seal in the presence of this pressure loading. Furthermore, brush seals exhibit different hysteresis behavior under different pressure loading conditions. Understanding the increased brush seal stiffness and the increased hysteresis behavior of brush seals in the presence of a pressure loading is important for designing brush seals for higher pressure applications. In this article, we present the development of a test fixture for measuring the stiffness of brush seals subjected to a pressure loading. The fixture allows for measurement of the bristle pack forces in the presence of a pressure loading on the seal while the rotor is incrementally pushed (radially) into the bristle pack. Following the development of this test fixture, we present representative test results on three sample seals to show the trends in brush seal stiffness as the pressure loading is increased. Specifically, we study the effect of different brush seal design parameters on the stiffness of brush seals over a wide range of pressure loadings. These test data can be used for developing predictive models for brush seal stiffness under pressure loading. Furthermore, we demonstrate the utility of this fixture in studying the hysteresis exhibited by brush seals along with the importance of the backplate pressure balance feature present in several brush seal designs. The test results validate the bilinear force-displacement curves previously reported in the literature.
Multi-Objective Optimization of Film-Cooling Holes Considering Heat Transfer and Aerodynamic Loss
Authors: Lee Ki-Don , Kim Sun-Min , Kim Kwang-Yong
Published: May 2012

In the present work, multi-objective shape optimization of a row of laidback fan shaped film cooling holes has been performed using a hybrid multi-objective evolutionary approach in order to achieve an acceptable compromise between two competing objectives, i.e., enhancement of the film cooling effectiveness and reduction of the aerodynamic loss. In order to perform comprehensive optimization of film-cooling hole shape, the injection angle of the hole, the lateral expansion angle of the diffuser, the forward expansion angle of the hole and the pitch to hole diameter ratio, are chosen as design variables. Forty experimental designs within design spaces are selected by Latin hypercube sampling method. The response surface approximation method is used to construct the surrogate with objective function values for the experimental designs calculated through Reynolds-averaged Navier-Stokes analysis. The shear stress transport turbulence model is used as a turbulence closure. The optimization results are processed by the Pareto-optimal method. The Pareto optimal solutions are obtained using a combination of the evolutionary algorithm NSGA-II and a local search method. The optimum designs are grouped by k-means clustering technique and the six optimal points selected in the Pareto optimal solutions are evaluated by numerical analysis. The different trends in the variations of the design variables for each blowing ratios were found, and the optimum designs show enhanced objective function values.
Predictions of Effusion Cooling With Conjugate Heat Transfer
Authors: Oguntade Habeeb Idowu , Andrews Gordon E. , Burns Alan , Ingham Derek , Pourkashanian Mohammed
Published: May 2012

This work involves CFD conjugate heat transfer modelling of the geometrical design influence on effusion cooling. Experimental data was modelled for the overall effusion film cooling effectiveness using Nimonic 75 walls with imbedded thermocouples. The Fluent CFD code was used to investigate the experimental configuration for a 10×10 square array of holes with a 90° injection angle. In the computational predictions, 10000ppm of methane tracer gas was added to the coolant and the concentration at the wall allowed the adiabatic cooling effectiveness of the effusion film cooling to be predicted separately from the overall wall cooling effectiveness. The predicted overall cooling effectiveness results show that the wall was locally at a uniform temperature, but the axial development of the cooling film does result in a gradual reduction of the wall temperature with axial distance. The predictions show that the heating of the coolant by the hot wall was equally split between the hole approach flow on the backside of the wall and inside the film cooling holes. This heating changed the conditions in the film cooling layer from those of the equivalent adiabatic wall. There was good agreement between the conjugate heat transfer predictions of the overall cooling effectiveness with the experimental data.
Axial Swirler Design Influences on NOx Emissions for Premixed Combustion in Gas Turbine Combustors With all the Combustor Air Flow Passing Through the Swirler
Authors: Andrews Gordon E. , Ahmad Nasser T.
Published: May 2012

This work investigates a single axial swirler combustor using flat bladed axial swirlers at atmospheric pressure, 600K preheat, with premixed propane and air. The aim was to investigate the axial swirler design influences on flame stability and NOx emissions, for fully premixed combustion in a single swirler cylindrical combustor configuration. A reference Mach number of 0.05 at 600K was used, which represents all the combustion air passing through the swirler. This maximum swirler airflow is required for the highest turbine entry temperatures with low NOx emissions. The axial swirler design had only a small influence on the weak extinction, but it had a greater influence on NOx. The swirlers with a large central hub had greater NOx emissions, as this created a larger central recirculation zone and greater residence time of the hottest part of the flame. It was preferable to stabilise the flame with an outer expansion shear layer as this minimised the size of the inner recirculation zone and this minimised the NOx. The influence of the swirl angle, 30, 45 or 60° for the same flow capacity was that the swirler had to be a larger diameter as the vane angle was increased, to keep the blockage and pressure loss the same. This removed the possibility of having either an inner or outer flow expansion for the 60° swirler, but the flow expansions were maximised for the 30° swirler. The effect of the swirl vane angle on NOx was mainly due to the associated changes in the flow expansion. 45° swirlers with no central hub and a large outer expansion were the best design for the lowest NOx emissions and could achieve 15ppm NOx at 15% oxygen at 2000K.
The Effect of Inlet Flow Distortion on the Performance of Centrifugal Fans for Utility Applications
Authors: Greenzweig Jim , Henry Ray , Holm Ted
Published: May 2012

This paper provides an overview of published literature on the effect of inlet Flow Distortion on the performance of centrifugal fans, with an emphasis on a recently completed testing program [8] on the effect of inlet distortion on the performance of airfoil bladed Centrifugal fans, at various inlet vane positions. The results of this testing program [8] show that a model fan, when equipped with variable inlet vanes, is generally subject to lower levels of performance degradation, for a given level of inlet distortion, than the same model when the variable inlet vanes are not present. This indicates that the variable inlet vanes are acting to condition the distorted flow prior to entry into the fan wheel in a beneficial manner. The reduction in performance degradation seems to occur when the variable inlet vanes are wide open (parallel to the fan shaft axis), and does not seem to improve with closure of the variable inlet vanes. The maximum reduction in Total Pressure development and Total Efficiency measured for fans without variable inlet vanes in this test was −8.4% and −6.1% respectively. The maximum reduction in Total Pressure development and Total Efficiency measured for fans with variable inlet vanes in the wide open position was reduced to −2.9% and −3.5% respectively. In fact, the beneficial effects of the variable inlet vanes appear to be greater with the vanes in the wide open position, and are possibly less beneficial when the inlet vanes are partially closed. (The maximum reduction in Total Pressure development and Total Efficiency measured for fans with variable inlet vanes in a partially open position was −2.5% and −4.1% respectively.) Refer to Table 2 for a summary of the Maximum Distortion Observed for the testing program. An unanticipated result of the tests conducted [8] is the discovery that the effects of distortion seem to vary with the position of the rating point along the fan curve, with distortion effects being greater at higher flow conditions and lower at lower flow conditions. An actual field case study on the negative effects of inlet distortion on a centrifugal Induced Draft (ID) fan is also presented. Recommended steps to take in designing a fan system to minimize the potential for any negative effects on fan performance from inlet distortion are also presented. The conclusion compares the results of previously conducted tests [1, 2] and recently conducted tests [8], and concludes that the recent tests do not support many of the earlier findings. This leads to authors to believe that the actual impact of inlet distortion is highly dependent on the specific geometry of the airfoil-bladed centrifugal fan involved, and the relationship to various fan design parameters is not currently well understood.