bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Ingress on Turbine Discs
Authors: Cho GeonHwan , Sangan Carl M. , Owen J. Michael , Lock Gary D.
Published: August 2015

The ingress of hot gas through the rim seal of a gas turbine depends on the pressure difference between the mainstream flow in the turbine annulus and that in the wheel-space radially inward of the seal. This paper describes experimental measurements which quantify the effect of ingress on both the stator and rotor discs in a wheel-space pressurised by sealing flow. Infrared sensors were developed and calibrated to accurately measure the temperature history of the rotating disc surface during a transient experiment, leading to an adiabatic effectiveness. The performance of four generic (though engine-representative) single- and double-clearance seals was assessed in terms of the variation of adiabatic effectiveness with sealing flow rate. The measurements identify a so-called thermal buffering effect, where the boundary layer on the rotor protects the disc from the effects of ingress. It was shown that the effectiveness on the rotor was significantly higher than the equivalent stator effectiveness for all rim seals tested. Although the ingress through the rim seal is a consequence of an unsteady, three-dimensional flow field, and the cause-effect relationship between pressure and the sealing effectiveness is complex, the time-averaged experimental data is shown to be successfully predicted by relatively simple semi-empirical models, which are described in a separate paper. Of particular interest to the designer, significant ingress can enter the wheel-space before its effect is sensed by the rotor.
Regression-Based Modelling of a Fleet of Gas Turbine Engines for Performance Trending
Authors: Borguet S. , Léonard O. , Dewallef P.
Published: August 2015

Module performance analysis is a well-established framework to assess changes in the health condition of the components of the engine gas-path. The primary material of the technique is the so-called vector of residuals, which are built as the difference between actual measurement taken in the gas-path and values predicted by means of an engine model. Obviously, the quality of the assessment of the engine condition depends strongly on the accuracy of the engine model.

The present paper proposes a new approach for data-driven modelling of a fleet of engines of a given type. Such black-box models can be designed by operators such as airlines and third-party companies. The fleet-wide modelling process is formulated as a regression problem that provides a dedicated model for each engine in the fleet, while recognising that all engines are of the same type. The methodology is applied to a virtual fleet of engines generated within the ProDiMES environment. The set of models is assessed quantitatively through the coefficient of determination and is further used to perform anomaly detection.
Characteristics of a Spherical Seat TPJB With Four Methods of Directed Lubrication: Part 1 — Thermal and Static Performance
Authors: Coghlan David M. , Childs Dara W.
Published: August 2015

Static and thermal characteristics (measured and predicted) are presented for a 4-pad, spherical-seat, TPJB with 0.5 pivot offset, 0.6 L/D, 101.6 mm nominal diameter, and 0.3 preload in the load-between-pivots orientation. One bearing is tested four separate times in the following four different lubrication configurations: (1) flooded single-orifice (SO) at the bearing shell, (2) evacuated leading edge groove (LEG), (3) evacuated spray-bar blocker (SBB), and (4) evacuated spray-bar (SB). The LEG, SBB, and SB are all considered methods of “directed lubrication”. These methods rely on lubrication injected directly to the pad/rotor interface. The same set of pads is used for every test to maintain clearance and preload; each method of lubrication is added as an assembly to the bearing. Test conditions include surface speeds and unit loads up to 85 m/s and 2.9 MPa respectively. Static data includes rotor-bearing eccentricities, and attitude angles. Thermal data include measured temperatures from sixteen bearing thermocouples. Twelve of the bearing thermocouples are embedded in the babbitt layer of the pads while the remaining four are oriented at the leading and trailing edge of the loaded pads exposed to the lubricant. Bearing thermocouples provide a circumferential and axial temperature gradient. The pivot stiffness (pad and pivot in series) is measured and incorporated into predictions.
Characteristics of a Spherical Seat TPJB With Four Methods of Directed Lubrication: Part 2 — Rotordynamic Performance
Authors: Coghlan David M. , Childs Dara W.
Published: August 2015

Measured and predicted rotordynamic characteristics are presented for a 4-pad, spherical-seat, TPJB with 0.5 pivot offset, 0.6 L/D, 101.6 mm nominal diameter, and 0.3 preload in the load-between-pivots orientation. One bearing is tested four separate times in the following four different lubrication configurations: (1) flooded single-orifice (SO) at the bearing shell, (2) evacuated leading edge groove (LEG), (3) evacuated spray-bar blocker (SBB), and (4) evacuated spray-bar (SB). The same set of pads is used for every test to maintain clearance and preload; each method of lubrication is added as an assembly to the bearing. Test conditions include surface speeds and unit loads up to 85 m/s and 2.9 MPa respectively. Dynamic data includes four sets (one set for each bearing configuration) of direct and cross-coupled rotordynamic coefficients derived from measurements and fit to a frequency independent KCM model. The pivot stiffness (pad and pivot in series) is measured and incorporated into predictions.
An Assessment of Flamelet Generated Manifold Combustion Model for Predicting Combustor Performance
Authors: Rida Samir , Chakravorty Saugata , Basani Jaydeep , Orsino Stefano , Ansari Naseem
Published: August 2015

In Rich-Quench-Lean design of aircraft gas turbine combustors, primary zone mixing is critical for emissions, flame shape, and heat transfer. From a modeling perspective, the primary zone flow prediction is largely impacted by the fidelity of the mixing model and the type of combustion model used. The assumption that fuel spray burns in a diffusion flame or in a partially premixed flame has an impact on the combustor’s performance parameters. In this paper, we compare the non-premixed steady diffusion flamelet model with the partially premixed flamelet generated manifold model for several Honeywell combustors using the commercial CFD code ANSYS FLUENT. The validations are made in the context of Large Eddy Simulation and the time averaged CFD results are compared with rig data highlighting the impact of the combustion models on combustor performance. Results show that the flamelet generated manifold combustion model provides a more realistic lifted flame shape that is not in contact with the fuel nozzle.
Analytical Study on the Performance of Centrifugal Compressor Considering Running Tip Clearance
Authors: Kim Changhee , Yang Jangsik , Son Changmin , Lee Horim , Hwang Yoonjei , Jeong Jinhee
Published: August 2015

In this study, a series of aero-thermo-mechanical analyses were carried out to predict the running tip clearance and the effects of impeller deformation on the performance using two different centrifugal compressors (blade type A and B). In operation, impeller deformation due to the combination of centrifugal force, aerodynamic pressure and thermal load results in non-uniform tip clearance profile. The predicted running tip clearance leads to further findings of its impact on compressor performance. The prediction employs one-way fluid-structure interaction (FSI) method using CFX 14.5 and ANSYS. The results show that the maximum displacement occurs at the leading edge tip of the impeller blade but maximum stress takes place at the blade root of the impeller for these particular designs. The analysis also confirms the centrifugal force has dominant effect on impeller deformation at its operating condition. The predicted running tip clearance shows non-uniform profile over the entire flow passage. In particular, a significant reduction of the tip clearance height has occurred at the leading edge and the trailing edge of the impeller. Due to the reduction of the tip clearance, the tip leakage flow has decreased by 19.4% and 16.2% in the blade type A and B, respectively. Also, the polytropic efficiency of the blade type A and B at operating condition has increased by 0.72% and 1.81%, respectively. These findings confirm that the prediction of running tip clearance and its impact on compressor performance is important area for further investigation.
Numerical Investigation of Inlet Distortion for Different Rear Mounted Engine Installations at Taking-Off Conditions
Authors: Xie Hairun , Wu Yadong , Wang Anjenq , Ouyang Hua
Published: August 2015

Rear mounted engines are widely used in business jet and regional jet applications. It is a “clean wing” design. The engine is mounted behind the wing, so that the inlet/exhaust of nacelle has a minor influence on the flow over the wing. The engine thrust line is close to the fuselage axis. As a result, the asymmetric yaw moment will be smaller when single engine stall occurs.

Field experience and historical data have revealed that engine aerodynamic stability and fan aeromechanics are extremely sensitive to the uniformity and steadiness of inlet flow. Engine inlet flow could be distorted and separated at various operating conditions, such as, high ground crosswind, take off, and other high angle of attack (AOA) maneuvers. As a result, strict regulations and requirements were set by certification agencies to assess: i) aircraft maneuver capability, ii) engine operating characteristics, as well as iii) aerodynamics/aeromechanics behaviors and capability, with respect to flow field surrounding the entire propulsion system.

Due to the nature of complexity of the flow field at air intake, the inlet compatibility of fuselage mounted engines becomes one of the most complicated & challenged item to meet the FAR33 as well as the FAR25 certification requirements. This research paper discusses the inlet compatibility of rear-mounted aircraft engine with respect to AOA and crosswind under various operating conditions. Models of two installed configurations, which set by relative position of engine to fuselage and wing, were created. At each case, the engine inlet flow field was calculated at various AOA and crosswind conditions. Comparisons of total pressure contours at air intake were made to assess the likelihood of flow separation. The radial and circumferential inlet distortion levels were calculated at the assumed inlet AIP location for each operating condition and installed configuration. Assessments are made based on intensive usage of CFD analysis, and substantiated by test results. The flow field information obtained by CFD calculation reveals a close coupling phenomenon exist among engine installation, AOA and inlet capability. Analytical results were also checked, and the results agreed well with that of the compliant flight tests.
Numerical Study on Typical Wet Steam Flow Based on a New Two-Fluid Model
Authors: Cui Ke , Chen Huanlong , Song Yanping , Chen Fu
Published: August 2015

A new two-fluid model with the influence of inter-phase velocity-slip taken into account was proposed and a modified realizable k-ε turbulence model was put forward as well to make the equation set of two-fluid model closed. Based on this two-fluid model, numerical simulations were conducted on typical wet steam flow in different cases. The good consistency of numerical result and the experimental result infers that this two-fluid model is provided with high accuracy and wide applicability. The flow field analysis also shows that there exist several particular positions along the flow direction. These particular positions illustrate the development mechanism of nucleation and droplet growing. In addition, further discussion on the flow in cascade then indicates that the occurrence of condensation has strong impact on the flow while the impact of inter-phase velocity-slip is relatively weaker. The composition of total pressure loss is present here, the majority of total pressure loss brought by condensation is about 8.78% of inlet total pressure while the inter-phase velocity-slip just results in a small part of about 0.42% of inlet total pressure, the rest of the total pressure loss is caused by pneumatic factors and this part is about 3.95% of inlet total pressure. In addition, discussion about the turbulence then shows that the turbulence intensity in two-phase flow is higher than that in single-phase flow.
Time-Domain Implementation of Higher-Order Non-Reflecting Boundary Conditions for Turbomachinery Applications
Authors: Henninger Stefan , Jeschke Peter , Ashcroft Graham , Kügeler Edmund
Published: August 2015

The present paper demonstrates the time-domain implementation of arbitrary-order non-reflecting boundary conditions for a 3d non-linear time-accurate RANS solver for turbomachinery applications. The conditions are based on the 2d circumferential mode decomposition of the linearized Euler equations. The exact linearized conditions are non-local since they involve space-time Fourier/Laplace transforms. Time-local conditions of arbitrary order are obtained by approximation of the inverse Laplace transform Bessel function convolution kernel by sums of exponential functions. Likewise, this corresponds to a rational function approximation of the exact non-reflecting boundary kernel in the frequency-domain.

The boundary conditions are validated against two numerical test cases. The first test case mimics Tyler-Sofrin modes present in turbomachinery applications by prescribing 2d acoustic modes in a uniform flow. The second test case is concerned with the potential contamination of blade flutter analyses by spurious reflections on artificial boundaries. For the benchmark problem Standard Configuration 10, blade flutter with non-zero inter-blade phase angle, acoustic resonance generates spinning waves susceptible to reflection. Contrasting the results of non-reflecting boundary conditions of varying order of accuracy shows that low order conditions can fail for challenging cases, which emphasizes the need for an accurate non-reflecting boundary treatment.
On the Influence of Fuel Mixing and Flue Gas Recirculation on the Emissions of a Fuel Flexible Gas Turbine Combustor
Authors: Fischer Stefan , Kluß David , Joos Franz
Published: August 2015

The main benefits of operating a combustor under flue gas recirculation conditions are the increase in efficiency of the post combustion carbon capture and storage process and the potential to reduce NOX emissions while keeping the thermal load of the gas turbine constant. The latter is primarily caused by the change in thermodynamic properties of the combustive mixture with increasing vitiation. As a result, the dominant NOX formation pathways change with increasing FGR ratio.

In a partially premixed combustor, the formation of NOX emissions can also be influenced by the fuel mixing behavior. Different setups lead to combustive mixtures with different degrees of homogeneity as well as influencing the distribution of the mixture within the combustion chamber.

In this paper the combined effects of the variation of mixture homogeneity and the flue gas recirculation ratio on the NOX emissions and the stability range is experimentally investigated for different fuel gases. The experiments are performed on the atmospheric laboratory test rig, which is equipped with a partially premixed combustor. The burner is equipped with modular fuel gas nozzles allowing for the variation of the fuel mixing behavior. Exhaust gas measurements are performed to evaluate the influence of the parameters on the emissions profile of the combustor and to compare the results to a theoretical study.

The results of this study show that the level of nitric oxide emissions as well as the potential to decrease said emissions with FGR operation is dependent on the mixing behavior of the combustor. Furthermore, the combined effects of fuel gas nozzle and FGR operation lead to a proposal of an operational strategy for the combustor which combines the advantages of low nitric oxide emissions and a broad range of stability.
The Analyses for the Casing Improvements of the MPM-20 Engine
Authors: Ratkovská K. , Čerňan J. , Cúttová M. , Semrád K.
Published: August 2015

The operational issues of a small turbojet engine MPM – 20 are discussed. The engine was created by modifying the Soviet turbostarter TS – 20B/21 designed for short-term operation. It is necessary to make structural modifications that allow for the long-term operational premise of the engine. For this purpose, several analyses were focused on the thermally stressed parts. The first, a material analysis carried out on the outer casing of the combustion chamber and on the combustor liner reveals information about the mechanical properties of these structural nodes. It was necessary since there is no documentation of the engine with this information. Another analysis of the infrared emission spectra is important for monitoring operational conditions, especially from the temperature point of view. Subsequent stress analysis of the casing is based on results from previous analyses. It was used to observe the behaviour of the casing as operational conditions changed. This revealed a dangerous increase of thermally induced stress levels as temperature increased up to 150°C. Various structural modifications can be made in the future with these results, such as an application of a protective coating on the casing and combustor liner of the engine.
Optimisation of Support Fuel Consumption Burning Low Heat Value Gas Using Controlled Combustion Oscillations
Authors: Giuliani Fabrice , Moosbrugger Vanessa , Stuetz Markus , Leitgeb-Simandl Thomas
Published: August 2015

The purpose of this work is to develop a new combustion technology to reduce the operation costs of thermal systems that burn low heat value gases. Landfill methane emission is a greenhouse gas source which can be defined and reduced. Landfill managing companies in Austria have adapted the latest regulations on methane emissions primarily by collecting and flaring off landfill gas, sometimes with energy recovery. Their concern is related to long-term landfills where the methane concentration by volume falls well below 20%. The costs to flare-off these gases are mostly driven by the use of support fuel to ensure combustion. A technical solution using the programme MethaNull (to approach zero methane emissions) is proposed to extend the combustion domain of gases with low heat value so that the amount of support fuel can be significantly reduced. This solution should fit a large range of LHV gases, for combustion at ambient conditions as well as under pressure at elevated inlet temperature conditions. The process has similarities with pulse combustion, where the combustion process benefits from a higher energy density and better heat transfer rates. As the forced pulsation is generated by a separate module, the methodology can be easily adapted or retrofitted for existing facilities. This paper covers the MethaNull programme, the burner design, the flow pulsation technology and its operation. A systematic comparison between steady state and oscillating combustion is presented.
Experimental Characterization of a Swirl Stabilized MGT Combustor
Authors: Monz T. O. , Stöhr M. , O’Loughlin W. , Zanger J. , Hohloch M. , Aigner M.
Published: August 2015

A swirl stabilized MGT combustor (Turbec T100) was operated with natural gas and was experimentally characterized in two test rigs, a pressurized and optically accessible MGT test rig and an atmospheric combustor test rig. For the detailed characterization of the combustion processes, planar OH-PLIF and simultaneous 3D-stereo PIV measurements were performed in the atmospheric combustor test rig. Flow fields, reaction zones and exhaust gas emissions are reported for a range of pressure scaled MGT load points. Parameter studies on combustor inlet conditions (e.g. air preheating temperature, air and fuel mass flow rates and fuel split) were conducted in the atmospheric combustor test rig. From the parameters studies the fuel split between the pilot and the main stage and the air preheating temperature were found to have the biggest impact on the flame shape, flame stabilization and exhaust gas emissions. The measurements of the ATM test rig are compared with measurements of the pressurized MGT test rig with and without an optically accessible combustion chamber. Opened and closed conical flame and flow pattern were found in both test rigs. Reasons for the two flame and flow pattern are supposed to be the interaction of pilot stage combustion and flow field and the interaction of the dilution air with the combustion and the flow field. The results are discussed and compared with repect to a transferability of combustion characteristics from the ATM test rig to the MGT test rigs.
Calibration and Uncertainty Quantification of Gas Turbine Performance Models
Authors: Chao Manuel Arias , Lilley Darrel S. , Mathé Peter , Schloßhauer Volker
Published: August 2015

Calibration and uncertainty quantification for gas turbine (GT) performance models is a key activity for GT manufacturers. The adjustment between the numerical model and measured GT data is obtained with a calibration technique. Since both, the calibration parameters and the measurement data are uncertain the calibration process is intrinsically stochastic. Traditional approaches for calibration of a numerical GT model are deterministic. Therefore, quantification of the remaining uncertainty of the calibrated GT model is not clearly derived. However, there is the business need to provide the probability of the GT performance predictions at tested or untested conditions. Furthermore, a GT performance prediction might be required for a new GT model when no test data for this model are available yet. In this case, quantification of the uncertainty of the baseline GT, upon which the new development is based on, and propagation of the design uncertainty for the new GT is required for risk assessment and decision making reasons. By using as a benchmark a GT model, the calibration problem is discussed and several possible model calibration methodologies are presented. Uncertainty quantification based on both a conventional least squares method and a Bayesian approach will be presented and discussed. For the general nonlinear model a fully Bayesian approach is conducted, and the posterior of the calibration problem is computed based on a Markov Chain Monte Carlo simulation using a Metropolis-Hastings sampling scheme. When considering the calibration parameters dependent on operating conditions, a novel formulation of the GT calibration problem is presented in terms of a Gaussian process regression problem.
Numerical Modelling Techniques for Turbine Blade Internal Cooling Passages
Authors: Dhopade Priyanka , Capone Luigi , McGilvray Matthew , Gillespie David , Ireland Peter
Published: August 2015

Numerical modelling of internal cooling passages in gas turbine blades is a challenging task due to their physical characteristics, such as rounded duct corners, the presence of rib turbulators and their staggered locations between surfaces. This results in complex fluid dynamic phenomenon such as counter-rotating vortices and other secondary flow structures that can drive the heat transfer. Heat transfer mechanisms in such passages are inherently coupled with momentum transport and diffusion. Current industry practices for numerical modelling of such passages use unstructured mesh generation tools, steady Reynolds-averaged Navier-Stokes (RANS) equations and two-equation turbulence models such as k-ε and k-ω SST. This paper investigates two generic, engine-representative rib geometries using current numerical practices to determine their limitations. Three mesh generation tools and two turbulence models are compared across two rib geometries. The results are qualitatively and quantitatively compared to detailed experimental Nusselt numbers on the passage walls. It was found that as long as the rib geometry results in a secondary flow that directly impinges onto the wall, the meshing tools and turbulence models agree reasonably well with experiments. When the passage includes wall-wrapped ribs resulting in more complex secondary flows, this decreases the validity of the numerical tools, suggesting that more sophisticated modelling techniques are required as rib geometries continue to evolve.
Unsteady Measurements of Periodic Effects in a Transonic Compressor With Casing Treatments
Authors: Brandstetter Christoph , Wartzek Fabian , Werner Jan , Schiffer Heinz-Peter , Heinichen Frank
Published: August 2015

Application of non-axisymmetric Casing Treatments (CTs) can extend the operating range of a transonic compressor significantly. Recent CT designs have proven successful at achieving operating range extension without efficiency loss under design conditions. Two different CT designs were investigated on a high-speed one and a half stage test rig using extensive instrumentation. The stage setup is representative of the front stage of a modern high-pressure compressor.

Results of Particle Image Velocimetry (PIV) measurements taken in the blade tip region underneath the Casing Treatment show a significantly modified flow structure compared to the Smooth Casing reference case. Blockage zone, secondary flow and shock structures are affected by the CT, especially in highly throttled operating conditions.

The stall inception process of the system with Axial Slots shows unexpected behavior, with modal activities that are not observed without CT. These activities are resolved using unsteady wall pressure and Hot Wire measurements.
Transient Behavior in Axial Compressors in Event of Ice Shed
Authors: Saxena Swati , Singh Rajkeshar , Breeze-Stringfellow Andrew , Nakano Tsuguji
Published: August 2015

Incidents of partial or total thrust loss due to engine icing at cruise have been recorded over past several years. These events increase the demand for better understanding of compressor dynamics under such conditions. In the present study, physics based compressor blade row model (BRM) is used to evaluate the effect of booster ice-shed on axial high pressure compressor (HPC) at flight and approach idling conditions (65%–82% Nc). A representative aviation high-bypass turbofan engine HPC is used in this study. Transient behavior of compressor with varying ice ingestion conditions is compared and inter-stage dynamics is analyzed. Stage re-matching occurs due to heat exchange between air and ice which dictates the stall inception stage in the compressor. It is found that although T3 drop is closely related to compressor stall inception, the transient mechanism of ice-shed also plays an important role. Comparisons are made with steady energy balance equation to determine total water content (TWC) at HPC inlet to emphasize the importance of compressor transients. The ice amount, its ingestion duration and rate affect the onset of stall. HPC might sustain through a slower ice-shed while a faster ice-shed can lead to compressor stall with little or no chances of recovery. Understanding this transient behavior and inter-stage dynamics due to ice-shed will help in designing and implementing passive or active stall control mechanisms.
A Superposition Technique for Multiple-Row Film-Cooling for Calculation of 2-D Effectiveness and Heat Transfer Coefficients
Authors: Ingram Peter T. , Yavuzkurt Savas
Published: August 2015

A superposition technique for multiple-row film-cooling heat-transfer augmentation and effectiveness is investigated. The technique is developed for use with 2-D correlations of film-cooling properties such as film cooling effectiveness and heat transfer coefficients. The method proposed is for implementations with Iterative Conjugate Heat-Transfer using a Reduced Order Film Model (ICHT-ROFM). The superposition technique is used in conjunction with 2-D correlations developed in a previous study for single row of holes to obtain the heat transfer augmentation and film-cooling effectiveness for two staggered rows for dustpan shaped holes. The results are compared to data for multiple-row film-cooling. The results for effectiveness were within 15% of empirical data. The results obtained from using the current technique are compared to spanwise-averaged superposition techniques, which had errors nearing 50%, and it was found to be more accurate.
Heat Transfer in a Rib and Pin Roughened Rotating Multi-Pass Channel With Hub Turning Vane and Trailing-Edge Slot Ejection
Authors: Wu Hao-Wei , Zirakzadeh Hootan , Han Je-Chin , Zhang Luzeng , Moon Hee-Koo
Published: August 2015

A three-passage internal cooling test model with a 180° U-bend at the hub turn portion was used to perform the investigation. The flow is radially inward at the second passage, while it is radially outward at the third passage after the U-bend. Measurement was conducted at the second and the third passages. Aspect ratio of the second passage is 2:1 (AR=2), while the third passage is wedge-shaped with side wall slot ejections. The squared ribs with P/e = 8, e/Dh = 0.1, α = 45°, were configured on both leading and trailing surfaces along the second passage, and also the inner half of the third passage. Three rows of cylinder-shaped pin-fins with diameter of 3 mm were placed at both leading and trailing surfaces of the outer half of the third passage. The results showed that the rotating effects on radial inward flow and radial outward flow are consistent with previous studies. When there is no turning vane, heat transfer on the leading surface at hub turn region is increased by rotation, while it is decreased on the trailing surface. The presence of turning vane reduces the effect of rotation on hub turn portion. Ejection and pin-fin array enhance heat transfer at the third passage. Even though there is mass loss of cooling air along the third passage with side wall slot ejection, the heat transfer coefficient remains high until the end of the passage. Correlation between regional heat transfer coefficients and rotation numbers is presented for both cases of with and without turning vane.
The Low Reduced Frequency Limit of Vibrating Airfoils: Part I — Theoretical Analysis
Authors: Corral Roque , Vega Almudena
Published: August 2015

This paper studies the unsteady aerodynamics of vibrating airfoils in the low reduced frequency regime with special emphasis in its impact on the scaling of the work per cycle curves using an asymptotic approach (Part I) and numerical simulations (Part II). A perturbation analysis of the linearized Navier-Stokes equations for real modes at low reduced frequency is presented and some conclusions are drawn. The first important result is that the loading of the airfoil plays an essential role in the trends of the phase and modulus of the unsteady pressure caused by the vibration of the airfoil. For lightly loaded airfoils the unsteady pressure and the influence coefficients scale linearly with the reduced frequency whereas the phase departs from π/2 and changes linearly with the reduced frequency. As a consequence the work-per-cycle scales linearly with the reduced frequency for any inter-blade phase angle and it is independent of its sign. For highly loaded airfoils the unsteady pressure modulus is fairly constant exhibiting only a small correction with the reduced frequency, while the phase departs from zero and varies linearly with it. In this case only the mean value of the work-per-cycle scales linearly with the reduced frequency. This behavior is independent of the geometry of the airfoil and the modeshape in first approximation. For symmetric cascades the work-per-cycle scales linearly with the reduced frequency irrespectively of whether the airfoil is loaded or not. Simulations using a frequency domain linearized Navier-Stokes solver have been carried out on a low-pressure turbine airfoil section, the NACA0012 and NACA65 profiles and a flat plate to show the generality and correctness of the analytical conclusions (Part II of the corresponding paper). Both, the traveling-wave and influence coefficient formulations of the problem are used in combination to increase the understanding and explore the nature of the unsteady pressure perturbations.
Effects of Return Channel With Splitter Vanes on Performance of Multistage Centrifugal Compressor
Authors: Yagi Manabu , Nishioka Takahiro , Kobayashi Hiromi , Nishida Hideo , Yamamoto Satoru
Published: August 2015

The effects of a return channel with splitter vanes on the performance of a multistage centrifugal compressor were investigated. As a preliminary study, the optimum location of the splitter vanes was numerically examined with the aim of achieving high overall efficiency. The results indicated that the optimum location was the 30% of the normalized pitchwise distance from the suction side of the main vane, with the leading-edge located at a radius ratio to the main vane trailing-edge of 1.77. To investigate the effects of the return channel with and without the optimum splitter vanes on the overall performance, performance tests were carried out using a one-and-half-stage test rig. Three pre-swirl vanes, whose vane angles from the tangential direction at the trailing-edge were 20, 30 and 40° were used to simulate three operating conditions with low, design and high flow coefficients, respectively. The design flow coefficient of the downstream impeller was 0.073 and the peripheral Mach number was 0.87. The test results showed that the return channel with the optimum splitter vanes achieved 11.8% higher overall efficiency at the high flow coefficient with respect to the case without the splitter vanes while maintaining the same efficiency at both low and design flow coefficients. The return channel with the optimum splitter vanes was concluded to be effective for improving the efficiency of a multistage centrifugal compressor.
Experimental Study on Orifice Discharge Coefficients in Impingement Cooling With Confined Cross Flow
Authors: Schellenberg Andre , Kinell Mats , Eriksson Daniel
Published: August 2015

This work experimentally investigates the effects of confined cross flow and geometrical parameters in impingement flows on the jet discharge coefficient, Cd. Such cooling configurations are common in the gas turbine industry and all properties were chosen to be applicable in real applications.

The effect on Cd was studied for square edged orifices with thickness to diameter ratio l/d = 1 in the range of jet to cross flow mass velocity ratio 0 ≤ Gc/Gj ≤ 6 at a jet Reynolds number of 104. The distance between orifices in the span wise yn/d = 2.5–8 and stream wise xn/d = 2.5–7 directions as well as the spacing to the target plate z/d = 1–3 were investigated.

Generally, the conclusions from previous studies were confirmed. An exception to this was the observed increase of Cd with increasing Gc/Gj for Gc/Gj < 0.5.

A correlation was developed for the discharge coefficient with the new experimental data as function of z/d, yn/d and Gc/Gj. The resemblance to the measured data was excellent with a maximum deviation of 4%.
Evaluation of the Turbulence Radiation Interaction and the Validity of the Optically Thin Fluid Approximation in a High Turbulent Premixed Methane Flame
Authors: Eiberger Fabian , Habisreuther Peter , Zarzalis Nikolaos , Turrini Fabio
Published: August 2015

This paper presents the evaluation of the turbulence radiation interaction (TRI), which is usually neglected in Reynolds averaged simulations (RAS) of computational fluid dynamics (CFD) problems. As a result of neglecting this interaction, it is obtained that the radiative heat loss in the flame and the radiative thermal load on the combustor is too low. The TRI is evaluated using the optically thin fluctuation approximation (OTFA) in coupled (radiation and CFD) calculations in a highly turbulent lean premixed methane flame. The validity of the OTFA is investigated in terms of the resulting change in temperature and reaction progress. Two common absorption-emission models are used in Monte-Carlo radiation calculations: the weighted-sum-of-grey-gases (WSGG) and the statistical narrow band correlated-absorption coefficient (SNB-CK). Both models show that the radiative thermal load on walls is increased up to 27 % due to TRI. In contrast, the flame shape is not affected since local temperatures changes are less than 25 K.
CFD Investigation of a Lean Premixed Burner Redesign for High Hydrogen Content Syngas Operation
Authors: Bianchini C. , Da Soghe R. , Andreini A. , Anisimov V. , Bulli A. , Dacca’ F. , Rizzo S.
Published: August 2015

The continuous challenge to develop more efficient and cleaner combustion systems for energy production, promotes the exploitation of traditional fossil fuels in alternative energy cycles capable of abating pollutant emissions. Integrated coal gasification combined cycle (IGCC) technology for instance permits to convert standard coal and other carbon based fuels into hydrogen-rich syngas. These gases are generally used to fuel standard gas turbine engines typically designed for natural gas combustion. Due to the increased propensity to flashback with high hydrogen content, lean premixed burners usually need a specific redesign to ensure adequate flow velocity at the burner exit section so as to extend lean blow out limits.

However design practices for flashback prevention are far from being established especially for these unconventional fuels and it is therefore of interest to rely on CFD analysis to establish flame stabilization process and to predict incipient flashback. The purpose of this work is to assess the accuracy and reliability of a CFD methodology to describe the flame anchoring process and exhaust pollutant emissions in a high hydrogen syngas version of a standard swirled lean premixed burner which has been tested in a tubular test rig.

Considered numerical setup is based on the use of the Flamelet-Generated Manifolds (FGM) method which is a good choice to combine computational efficiency and detailed chemistry modelling. This work aims at providing a first assessment of the FGM model as implemented in Fluent v15 in the framework of RANS turbulence approach. Four different operating conditions at increasing pressure levels are tested and a detailed sensitivity analysis of the combustion model is provided exploring flamelet generation parameters, turbulence-chemistry interaction closures and methods to assign progress variable variance. A specifically developed detailed chemical mechanism for H2 was implemented and used to verify NOx emission predicting capabilities of three alternative methods: lookup table generated integrating with presumed PDF, automatic reactor network model based on CFD aero-thermal solution and Fluent native NOx model. Obtained results are validated against available experimental data.
Blade Resonant Forced Response Excited by Combustor Acoustic Eigenmodes
Authors: Beretta-Müller Arrigo , Szwedowicz Jaroslaw
Published: August 2015

In accordance with common engineering practice, the main source for forced response and subsequent high cycle fatigue problems in axial turbines is classical rotor-stator interaction. This criterion determines the excitability of a blade row for its relative circumferential motion with respect to upstream and downstream blade rows that generate time dependent pressure fields due to potential and viscous flow phenomena as well as possible shock waves.

This publication focuses on a less common source of blade vibration excitation induced by acoustic eigenmodes of a combustion chamber. The article gives an overview of a historical example where acoustic pulsations had the potential for exciting harmful vibration on the adjacent first rotating turbine blade row.

A 3D acoustic FEM analysis is performed to predict acoustic eigenmodes of the combustion cavity that could potentially excite vibration of the first turbine stage. Acoustic modes in the range of the critical frequencies from the point of view of resonance with structural eigenfrequencies of neighbouring components are identified and compared to engine measurements. The knowledge gained of the critical frequencies allows for mitigation of the excitation sources with Helmholtz dampers. This paper delivers an additional excitability criterion of rotating blades by acoustic pressure fluctuations in the combustor. Turbine blade excitation is currently assessed only by considering the number of burners in the combustor chamber.
CO2 Research Rig for Advanced Compressors (CORA)
Authors: Metz Kolja , Wacker Christian , Schildhauer Markus , Hylla Eike
Published: August 2015

This paper is giving an overview of advanced technology development for CO2 compression. CO2 has a long tradition in modern industrial processes and furthermore plays an increasing role in the present discussion of the world wide climate change. Today many industrial processes require CO2 not in a gaseous but in a compressed state at a specific pressure and temperature. Since commercially operated compressors are required to have certain safety margins, conservative design approaches are usually favoured from the thermodynamic point of view. Power reductions can be achieved with a more aggressive approach and improved stage components. The significant areas of necessary R&D are identified in the presentation. Development, design, assembly and initial commissioning of a high pressure CO2Research Rig for Advanced Compressors (CORA) are presented. The key features of this test rig are pointed out. The test rig contains two compressor stages with an integrally geared design in a high pressure closed loop. The compression system is designed for a suction pressure of up to 120 bar and a discharge pressure of up to 250 bar, driven by a variable speed driver and features a high pressure shell and tube heat exchanger. Possibilities for testing are explained for the various compression system components such as impellers, variable inlet guide vanes, compressor stage components, shaft seals, heat exchanger, instrumentation, recycle valves and gearbox.
Study of Effects of Rotor Tip Tailoring in Axial Flow Compressors
Authors: Halbe Chaitanya V. , Chati Yashovardhan S. , George Jubin Tom , Pradeep A. M. , Roy Bhaskar , Yu Hong , Townsend Peter
Published: August 2015

The performance of an axial compressor rotor is known to be affected by the variations in tip clearance during its operation. This effect is pronounced for the rear stages of a multistage compressor. This paper describes a novel design that is shown to aerodynamically desensitize the rotor tip to the tip clearance variations. The effect of tip clearance variations on the performance of a baseline low speed, high hub-to-tip ratio axial compressor rotor is studied using CFD. Based on the understanding developed from this flow analysis, the baseline rotor is redesigned by tailoring the tip and redistributing the blade loading over the span. The tip tailoring results in a blade with split dihedral, i.e. of applied dihedral variable from the leading edge to the trailing edge. CFD analysis of the tip tailored configuration shows lower pressure drop with increasing tip clearance as compared to the baseline design. The simulation results are validated through testing in a low speed axial compressor rig, thereby giving experimental support to the desensitization of the rotor to the studied tip clearance variations by tip tailoring.
Evaluation of Experimental Data From a Highly Loaded Transonic Compressor Stage to Determine Loss Sources
Authors: Lurie David P. , Breeze-Stringfellow Andrew
Published: August 2015

An advanced GE compressor design with high reaction and stage loading, demonstrated front stage efficiencies significantly lower than predicted by CFD calculations. The source of the efficiency miss has proven difficult to pinpoint with conventional inter-stage instrumentation. A test was performed in the NASA Glenn W7 facility with the compressor operating as both a single stage and a two stage machine allowing for the acquisition of detailed traverses at each station throughout the compressor.

This paper presents the data from this test and the GE interpretation of what the data implies, concentrating particularly on one operating point, the stage one peak efficiency point. Tracking of the calculated fluid entropy between the exit of the rotor and the exit of the stator leads to the conclusion that there is significant entropy increase in the freestream fluid outside the stator wakes and this loss is believed to be attributable to mixing loss in the rotor wakes. The loss due to wake mixing is largest, and may indeed be amplified, where the rotor wakes pile up on the pressure surface of the stator.
Bi-Stable Flame Behaviour of Heavy Duty Gas Turbine Burner: RANS, LES and Experiment Comparison
Authors: Anisimov Vyacheslav V. , Chiarioni Aldo , Rofi Luca , Ozzano Claudia , Hermeth Sebastian , Hannebique Gregory , Staffelbach Gabriel , Poinsot Thierry
Published: August 2015

VeLoNOx™ series (Very Low NOx) burners have been developed by Ansaldo Energia to satisfy the most restrictive emissions limits required by various countries. For these combustion systems the characterization of the field of stable operating conditions is a key design element. In particular, flame transition is of paramount importance for the stability of these combustion systems. Usually, this phenomenon occurs during load ramps and is characterized by a change of the flame shape, occurring in a well-defined load range. Proper flame shape control is essential to achieve more stable operating conditions up to base load.

At transition, experiments in a full scale pressure test-rig clearly show both a modification of the flame shape, a change of the measured air side burner effective area, and a reduction of the combustion chamber wall temperatures.

LES simulations were conducted using the same boundary conditions as RANS simulations discussed in a previous work [1]. In this paper, we show that both RANS and LES were able to correctly predict flame transition and a RANS-LES-Experiment comparison is performed.
Investigation of Conjugate Heat Transfer in Brush Seals Using Porous Media Approach Under Local Thermal Non-Equilibrium Conditions
Authors: Qiu Bo , Li Jun , Feng Zhenping
Published: August 2015

As a type of contacting seal technology, brush seals provide superior sealing performance and flexible behavior. Brush seals have found increasing application in more challenging high-temperature locations in recent years. Thus, the frictional heat generation between the seal bristles and mating surfaces is becoming another major concern for stable operation of brush seals. This study presents detailed investigations on the conjugate heat transfer behavior of brush seals using Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) approaches. A dual-energy equation was proposed to describe the conjugate heat transfer in the porous bristle pack region under local thermal non-equilibrium conditions. The heat transfer CFD model was established with consideration of anisotropic thermal conductivity and a radius-dependent porosity of the bristle pack. The frictional heat generation was calculated from the product of the bristle-rotor frictional force and sliding velocity. The bristle-rotor frictional force was obtained from the brush seal FEM model with consideration of internal friction and aerodynamic load on the bristles. The temperature distribution of the brush seal was predicted at various operational conditions using the iterative CFD and FEM brush seal model. The effects of pressure ratios and rotational speeds on the temperature distribution and bristle maximum temperature of the brush seal were investigated based on the developed numerical approach. The effect of frictional heat generation on brush seal leakage was also analyzed.