bluuebunny/crossref_metadata_2025 huggingface dataset:
Contra-Rotating Open Rotor Operation for Improved Aerodynamics and Noise at Takeoff
Authors: Zachariadis Alexios , Hall Cesare A. , Parry Anthony B.
Published: May 2012

The contra-rotating open rotor is, once again, being considered as an alternative to the advanced turbofan to address the growing pressure to cut aviation fuel consumption and carbon dioxide emissions. One of the key challenges is meeting community noise targets at takeoff. Previous open rotor designs are subject to poor efficiency at takeoff due to the presence of large regions of separated flow on the blades as a result of the high incidence needed to achieve the required thrust. This is a consequence of the fixed rotor rotational speed constraint typical of variable pitch propellers. Within the study described in this paper, an improved operation is proposed to improve performance and reduce rotor-rotor interaction noise at takeoff. Three-dimensional computational fluid dynamics (CFD) calculations have been performed on an open rotor rig at a range of takeoff operating conditions. These have been complemented by analytical tone noise predictions to quantify the noise benefits of the approach. The results presented show that for a given thrust, a combination of reduced rotor pitch and increased rotor rotational speed can be used to reduce the incidence onto the front rotor blades. This is shown to eliminate regions of flow separation, reduce the front rotor tip loss and reduce the downstream stream tube contraction. The wakes from the front rotor are also made wider with lower velocity defect, which is found to lead to reduced interaction tone noise. Unfortunately, the necessary increase in blade speed leads to higher relative Mach numbers, which can increase rotor alone noise. In summary, the combined CFD and aero-acoustic analysis in this paper shows how careful operation of an open rotor at takeoff, with moderate levels of re-pitch and speed increase, can lead to improved front rotor efficiency as well as appreciably lower overall noise across all directivities.
Measured Static and Rotordynamic Coefficient Results for a Rocker-Pivot, Tilting-Pad Bearing With 50 and 60% Offsets
Authors: Kulhanek Chris D. , Childs Dara W.
Published: May 2012

Static and rotordynamic coefficients are measured for a rocker-pivot, tilting-pad journal bearing (TPJB) with 50 and 60% offset pads in a load-between-pad (LBP) configuration. The bearing uses leading-edge-groove direct lubrication and has the following characteristics: 5-pads, 101.6 mm (4.0 in) nominal diameter, .0814–.0837 mm (.0032–.0033 in) radial bearing clearance, .25 to .27 preload, and 60.325 mm (2.375 in) axial pad length. Tests were performed on a floating bearing test rig with unit loads from 0 to 3101 kPa (450 psi) and speeds from 7 to 16 krpm. Dynamic tests were conducted over a range of frequencies (20 to 320 Hz) to obtain complex dynamic stiffness coefficients as functions of excitation frequency. For most test conditions, the real dynamic stiffness functions were well fitted with a quadratic function with respect to frequency. This curve fit allowed for the stiffness frequency dependency to be captured by including an added mass matrix [M] to a conventional [K][C] model, yielding a frequency independent [K][C][M] model. The imaginary dynamic stiffness coefficients increased linearly with frequency, producing frequency-independent direct damping coefficients. Direct stiffness coefficients were larger for the 60% offset bearing at light unit loads. At high loads, the 50% offset configuration had a larger stiffness in the loaded direction, while the unloaded direct stiffness was approximately the same for both pivot offsets. Cross-coupled stiffness coefficients were positive and significantly smaller than direct stiffness coefficients. Negative direct added-mass coefficients were obtained for both offsets, especially in the unloaded direction. Cross-coupled added-mass coefficients are generally positive and of the same sign. Direct damping coefficients were mostly independent of load and speed, showing no appreciable difference between pivot offsets. Cross-coupled damping coefficients had the same sign and were much smaller than direct coefficients. Measured static eccentricities suggested cross-coupling stiffness exists for both pivot offsets, agreeing with dynamic measurements. Static stiffness measurements showed good agreement with the loaded, direct dynamic stiffness coefficients.
Near and Far-Field Investigations of Supersonic Jet Noise Predictions Using a Coupled LES and FW-H Equation Method
Authors: Erwin James P. , Sinha Neeraj
Published: May 2012

The hot supersonic exhausts of gas turbine engines on military aircraft generate dangerously high noise levels. The noise levels associated with operating these engines are harmful to aircraft carrier deck personnel as well as detrimental to ship and aircraft structures. In this paper, the supersonic jet exhaust is simulated using Large Eddy Simulation (LES), and the Ffowcs Williams and Hawkings (FW-H) equation transforms the LES solution to an acoustic solution in the far-field. A Mach 1.5 laboratory jet test at United Technologies Research Center - Acoustics Research Tunnel is used as validation for the LES/FW-H method. A grid refinement study was performed with the objective of determining the requirements for accurate noise predictions. The finest grid resolution yields the best near and far-field acoustic prediction. A second LES/FW-H validation case is shown for a twin jet experiment that was performed in the anechoic chamber at University of Mississippi’s National Center for Physical Acoustics (NCPA). The LES/FW-H method is applied to the higher complexity heated twin jet with faceted nozzle profiles, demonstrating the applicability of the method over a wider range of flow regimes. The far-field noise prediction agrees very well with the NCPA experiment, including the prediction of broadband shock associated noise and jet screech.
Experimental and Analytical Leakage Characterization of Annular Gas Seals: Honeycomb, Labyrinth and Pocket Damper Seals
Authors: Sheng Nuo , Ruggiero Eric J. , Devi Ravindra , Guo Jianping , Cirri Massimiliano
Published: May 2012

Modern day turbomachinery requires the use of annular gas seals to provide flow restriction from high pressure to low pressure regions within the machine. These flow restrictions are critical design points in the overall performance of the machine and directly impact the system-level efficiency. Consequently, understanding the leakage performance of a given seal element as a function of operating pressure, rotor speed, and rotor offset is critical to the successful design of the turbomachine. In the present work, three annular gas seals are experimentally tested on a leakage test rig at GE Global Research (Niskayuna, New York). The test rig is capable of high-speed, high-pressure flow testing and has a radial degree of freedom that enables non-concentric leakage characterization. The leakage performances of a labyrinth, honeycomb and pocket damper seals are compared over a range of inlet pressures and pressure ratios. Analytical tools, including a CFD model and a Bulk Flow Code, are developed to provide leakage prediction and to establish understanding of underlying flow mechanisms. Predictions of the seal leakage are found to be in good agreement with experimental data.
Performance Modeling of Unfired Steam Cycle Using Single and Dual Pressure Once-Through Steam Generator
Authors: Hamid Emad , Newby Mike , Pilidis Pericles
Published: May 2012

The high thermal efficiency and the use of low carbon content fuel (e.g., natural gas) have made the Combined Cycle Power Plant (CCPP) one of the best choices for power generation due to its benefits associate with low cost and low environmental impact. The performance of Unfired Steam Cycle (USC) as a part of the CCPP has significant impact on the performance of the whole power plant as it provides the CCPP with around one third of the total useful power. An accurate performance simulation of the USC is therefore necessary to analyze the effects of various operating parameters on the performance of combined cycle power plant. In this paper, a performance simulation approach for an unfired steam cycle using single and dual pressure-level of an OTSG is presented. The developed modeling method has been applied to the performance simulation of an existing unfired steam cycle power generation unit installed at Manx Electricity Authority and the results are promising. A comparison between simulated and actual performance at design and off design operating conditions of the same USC has shown a remarkable agreement with errors values below 1%.
Further Characterization of the Disturbance Field in a Transversely Excited Swirl-Stabilized Flame
Authors: O’Connor Jacqueline , Lieuwen Tim
Published: May 2012

Transverse instabilities in annular gas turbine combustors are an important problem for both power generation and aircraft applications. These instabilities, also found in afterburners and rocket engines, are manifested as strong acoustic field fluctuations perpendicular to the flow direction. Transverse acoustic waves not only directly perturb the flame, but also couple with nozzle acoustics and inherent fluid mechanic instabilities. As such, the unsteady flow field that disturbs the flame is a complex superposition of transverse and longitudinal disturbances associated with both acoustic and vortical waves. This study closely follows prior work of the authors, which overviewed the disturbance field characteristics of a transversely forced, swirling nozzle flow. Velocity data from a transversely forced, swirl-stabilized flame was taken using high-speed particle image velocimetry (PIV). The topology of the velocity and vorticity field is compared between the inphase and out-of-phase forcing cases using both filtered and instantaneous data. These data also show that the acoustic and vortical disturbances are comparable in amplitude and, because they propagate at very different speeds, their superposition leads to prominent interference patterns in the fluctuating velocity. Data from both non-reacting and reacting test cases are presented to show that many features of the unsteady shear layers are quite similar.
Effect of the Axial Spacing Between Vanes and Blades on the Performance of a Transonic Axial Turbine
Authors: Chang Dongil , Tavoularis Stavros
Published: May 2012

Unsteady numerical simulations have been conducted to investigate the effect of axial spacing between the stator vanes and the rotor blades on the performance of a transonic, single-stage, high-pressure, axial turbine. Three cases were considered, the reference case, which is based on the geometry of a commercial jet engine and has an axial spacing at 50% blade span equal to 42% of the vane axial chord, as well as two other cases with axial spacings equal to 31 and 52% vane axial chords, respectively. Present interest has focused on the effect of axial gap size on the instantaneous and time-averaged flows as well as on the blade loading and the turbine performance. Decreasing the gap size reduced the pressure and increased the Mach number in the core flows in the gap region. However, the flows near the two endwalls did not follow monotonic trends with the gap size change; instead, the Mach numbers for both the small gap and the large gap cases were lower than that for the reference case. This Mach number decrease was attributed to increased turbulence due to the increased wake strength for the small gap case and the increased wake width for the large gap case. In all considered cases, large pressure fluctuations were observed in the front region of the blade suction sides. These pressure fluctuations were strongest for the smaller spacing. The turbine efficiencies of the cases with the larger and smaller spacings were essentially the same, but both were lower than that of the reference case. The stator loss for the smaller spacing case was lower than the one for the larger spacing case, whereas the opposite was true for the rotor loss.
Forced Combustion Experiments on Aero Combustors
Authors: Pilatis Nick , Whiteman Michael , Madden Paul , Macquisten Michael A. , Moran A. John
Published: May 2012

In the world of gas turbine combustion there is always the spectre of thermo-acoustic instability. Over the past few decades there has been significant effort afforded to researching the phenomenon of thermo-acoustics. The results of the research have produced numerous mathematical models and at system level these models have been used to predict and postdict where noise is likely to occur in a given system. The models also allow the combustion system to be numerically tested through the flight or operational envelope to identify areas where instability may occur before testing is carried out, thus reducing the risk of unexpected noise occurring. The weakness of many of these models is that they require, what is known as a flame transfer function. The flame transfer function is normally measured after the combustor has been fully designed and at a high TRL (Technology Readiness Level) so significant investment in time and money are already baked into the design. Remedial action if required can result in a significant loss of time and money in the development of the combustor. This paper describes the design and use of a test rig that allows combustion systems to be tested at much lower TRL. A ‘siren’ rig has been developed and used to identify what particular design changes in either combustor flow field or fuel delivery systems have effects on the thermo-acoustics. The exit boundary of the unit has a representative choked end point. This end point has the ability to be modulated in time, thus forcing the whole system. How the system reacts to the forcing is measured over a range of frequencies. The rig has been successfully used to influence design changes required to avoid combustion driven oscillations within the next generation of aero gas turbine combustors. The rig is not a representation of a complete 360 degree annular combustor system, but of a smaller sector. The objective is to isolate the Fuel Spray Nozzle (FSN) and corresponding combustor sector from acoustic resonances and derive functions expressing the relationship between unsteady heat release rate and unsteady aerodynamics for a range of operating conditions by controlling the modulation of air mass flow rate. Such functions can be used in conjunction with acoustic linear theory to predict wave modes and growth rates in combustor geometries.
Analysis of NOX Formation in an Axially Staged Combustion System at Elevated Pressure Conditions
Authors: Chockalingam Prathap , Galeazzo Flavio Cesar Cunha , Kasabov Plamen , Habisreuther Peter , Zarzalis Nikolaos , Beck Christian , Krebs Werner , Wegner Bernhard
Published: May 2012

The objective of this investigation was to study the effect of axially staged injection of methane in the vitiated air cross flow in a two stage combustion chamber on the formation of NOX for different momentum flux ratios. The primary cylindrical combustor equipped with a low swirl air blast nozzle operating with Jet-A liquid fuel generates vitiated air in the temperature range of 1473–1673 K at pressures of 5–8 bar. A methane injector was flush mounted to the inner surface of the secondary combustor at an angle of 30°. Oil cooled movable and static gas probes were used to collect the gas samples. The mole fractions of NO, NO2, CO, CO2 and O2 in the collected exhaust gas samples were measured using gas analyzers. For all the investigated operating conditions, the change in the mole fraction of NOX due to the injection of methane (ΔNOX) corrected to 15% O2 and measured in dry mode was less than 15 ppm. The mole fraction of ΔNOX increased with an increase in mass flow rate of methane and it was not affected by a change in the momentum flux ratio. The penetration depth of the methane jet was estimated from the profiles of mole fraction of O2 obtained from the samples collected using the movable gas probe. For the investigated momentum flux ratios, the penetration depth observed was 15 mm at 5 bar and 5 mm at 6.5 and 8 bar. The results obtained from the simulations of the secondary combustor using a RANS turbulence model were also presented. Reaction modeling of the jet flame present in a vitiated air cross flow posed a significant challenge as it was embedded in a high turbulent flow and burns in partial premixed mode. The applicability of two different reaction models has been investigated. The first approach employed a combination of the eddy dissipation and the finite rate chemistry models to determine the reaction rate, while the presumed JPDF model was used in the further investigations. Predictions were in closer agreement to the measurements while employing the presumed JPDF model; this model was also able to predict some key features of the flow as the change of penetration depth with the pressure.
Experimental and Numerical Investigation of the Unsteady Flow Field and Tone Generation in an Isolated Centrifugal Fan Impeller
Authors: Wolfram Daniel , Carolus Thomas H.
Published: May 2012

In spite of low circumferential Mach number the sound of isolated centrifugal fan impellers is sometimes dominated by distinctive tones at blade passing frequency (BPF) and integer multiples. This paper reports on an experimental and numerical investigation intended to unveil the tone generating mechanism. The sound spectra from three impellers operating at a large range of speed were measured and decomposed into Strouhal and Helmholtz number dependent functions. This led to the preliminary conclusion that the BPF related tones are exclusively flow-induced. Based on hot-wire and blade pressure fluctuation measurements and a subsequent correlation analysis, coherent flow structures different from the one associated with the principal azimuthal flow pattern due to the blades were detected. Eventually, numerical three-dimensional unsteady flow simulation and experimental flow visualization revealed an inlet vortex. It takes on a helical form, with the vortex core slowly varying its position with respect to the impeller center. As the blades cut through that quasi-stationary helical vortex they encounter blade force fluctuations producing the BPF tones. The slow spin of the vortex core and the slow variation of vortex strength were identified as the reason for the amplitude modulation of the BPF tone.
Validation of a First Vane Platform Cooling Design
Authors: Krueckels Joerg , Colban William , Gritsch Michael , Schnieder Martin
Published: May 2012

Low emission requirements for large industrial gas turbines can be achieved with flat combustor temperature profiles reducing the combustor peak temperature. As a result the heat load on the first stage vane platforms increases and platform film cooling is an important requirement. Furthermore, high lift airfoils generate stronger secondary flows including complex vortex flows over the platforms, which impacts heat transfer coefficients and film cooling. Cascade tests have been performed on a high lift profile with a platform film configuration and will be presented. The linear cascade was operated at engine representative Mach numbers. Pressure measurements are compared to design data to ensure correct operating conditions and periodicity of the cascade. The thermochromic liquid crystal measurement technique is used to obtain adiabatic film cooling effectiveness. The upstream gap (corresponding to the gap between the combustor and turbine) and the purge air exiting this gap are included in the investigations. The effect of the purge air on the recovery temperature is very strong and needs to be taken into account for the layout of the cooling scheme. The heat transfer coefficient distribution on the platform is obtained for an uncooled configuration using a transient infrared imaging technique with heat flux reconstruction. Computational fluid dynamics (CFD) assessments are used to support the validation results. Heat transfer coefficients and the effect of the purge air on adiabatic wall temperatures are compared with experimental results.
Detailed Heat Transfer Distributions in Engine Similar Cooling Channels for a Turbine Rotor Blade With Different Rib Orientations
Authors: LeBlanc Christopher , Ekkad Srinath V. , Lambert Tony , Rajendran Veera
Published: May 2012

Detailed Nusselt number distributions are presented for a gas turbine engine similar internal channel geometry used for cooling a modern first stage rotor blade. The cooling design has one leading edge channel and a three-pass channel that covers the rest of the blade. The simulated model, generated from the midspan section of an actual cooling circuit, was studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The model wall inner surfaces were sprayed with thermochromic liquid crystals, and a transient test was used to obtain the local heat transfer coefficients from the measured color change. Results are presented for a nominal channel inlet leading edge channel Reynolds number of 10700 and a channel inlet three-pass channel Reynolds number of 25500. Detailed heat transfer measurements are presented for the simulated leading edge, first pass, second pass and third pass interior walls for different rib configurations. The channels were studied for smooth, 90° ribs, and angled ribs geometries in addition to ribs on the divider walls between adjacent passages. Overall pressure drop measurements were also obtained for each passage. Some of these results are compared with the predicted heat transfer from standard correlations used in design practices. Results show very complicated heat transfer behavior in these realistic channels compared to results obtained in simplistic geometry channels from published studies. In some cases, the Nusselt numbers predicted by correlations are 50–60% higher than obtained from the current experiments.
A Low-Order Modelling of Ducted Flames With Temporally Varying Equivalence Ratio in Realistic Geometries
Authors: Graham Owen S. , Dowling Ann P.
Published: May 2012

The interaction between unsteady heat release and acoustic pressure oscillations in gas turbines results in self-excited combustion oscillations which can potentially be strong enough to cause significant structural damage to the combustor. Correctly predicting the interaction of these processes, and anticipating the onset of these oscillations can be difficult. In recent years much research effort has focused on the response of premixed flames to velocity and equivalence ratio perturbations. In this paper, we develop a flame model based on the so-called G-Equation, which captures the kinematic evolution of the flame surfaces, under the assumptions of axisymmetry, and ignoring vorticity and compressibility. This builds on previous work by Dowling [1], Schuller et al. [2], Cho & Lieuwen [3], among many others, and extends the model to a realistic geometry, with two intersecting flame surfaces within a non-uniform velocity field. The inputs to the model are the free-stream velocity perturbations, and the associated equivalence ratio perturbations. The model also proposes a time-delay calculation wherein the time delay for the fuel convection varies both spatially and temporally. The flame response from this model was compared with experiments conducted by Balachandran [4, 5], and found to show promising agreement with experimental forced case. To address the primary industrial interest of predicting self-excited limit cycles, the model has then been linked with an acoustic network model to simulate the closed-loop interaction between the combustion and acoustic processes. This has been done both linearly and nonlinearly. The nonlinear analysis is achieved by applying a describing function analysis in the frequency domain to predict the limit cycle, and also through a time domain simulation. In the latter case, the acoustic field is assumed to remain linear, with the nonlinearity in the response of the combustion to flow and equivalence ratio perturbations. A transfer function from unsteady heat release to unsteady pressure is obtained from a linear acoustic network model, and the corresponding Green function is used to provide the input to the flame model as it evolves in the time domain. The predicted unstable frequency and limit cycle are in good agreement with experiment, demonstrating the potential of this approach to predict instabilities, and as a test bench for developing control strategies.
Intercooled-Recuperated Gas-Turbine-Cycle Engine Coupled With Pneumatic Motor With Quasi-Isothermal Heat Addition
Authors: Stankovic Branko
Published: May 2012

A hybrid energy system has been proposed, consisting of an intercooled-recuperated gas-turbine-cycle engine coupled with a pneumatic motor (compressed-air engine), using reciprocating linear motion of a piston or a rotary vane motor, with quasi-isothermal heat addition process. Both gas-turbine (GT) engine and pneumatic motor have their own and separate combustion processes, occurring serially one after another, owing to the fact that in the GT engine exhaust gas there is still enough oxygen needed for combustion of fuel (liquid or gaseous) in an internal combustion engine. The quasi-isothermal nature of the heat addition process within the pneumatic motor is a result of averaging of the two thermodynamic processes, simultaneously interconnected within a cylinder-piston motor: isobaric heat addition and adiabatic gas expansion. The final expansion pressure at the end of the pneumatic-motor quasi-isothermal heat addition/expansion process is considered to correspond to the initial specific volume of inlet ambient air. Three (3) possible configurations of such a hybrid energy system were analyzed, differing only in the sequence of equipment connecting in the direction of air/working-gas flow (GT-cycle combustor, GT, pneumatic motor with combustor and recuperator). The results showed that the most efficient cycle configuration is No. 2, in which quasi-isothermal heat addition / gas expansion in the pneumatic motor occurs right after the GT-cycle heat addition in the associated GT-cycle combustor, then the partly expanded combustion gas first cools down in the GT-cycle recuperator, prior to its final expansion in the GT and exhaust to atmosphere. Estimated overall cycle thermal efficiency for the system configuration #2 ranges from ∼62% for a maximum GT/pneumatic motor inlet temperature of 1500 K (1227°C or 2240°F) to ∼66% for a maximum GT/pneumatic motor inlet temperature of 1700 K (1427°C or 2600°F), assuming a purely isothermal heat addition/expansion process in the pneumatic-motor cylinder. This is likely due to the fact that there is no necessity to cool the low-temperature GT of this configuration. Overall cycle thermal efficiency increases with the ambient temperature decrease for any cycle configuration.
An Energy-Based Axial Isothermal-Mechanical Lifing Procedure
Authors: Wertz John , Shen M.-H. Herman , Scott-Emuakpor Onome , George Tommy , Cross Charles
Published: May 2012

An energy-based fatigue lifing procedure for the determination of fatigue life and critical life of in-service structures subjected to axial isothermal-mechanical fatigue (IMF) has been developed. The foundation of this procedure is the energy-based axial room-temperature fatigue model, which states: the total strain energy density accumulated during both a monotonic fracture event and a fatigue process is the same material property. The energy-based axial IMF lifing framework is composed of the following entities: (1) the development of an axial IMF testing capability; (2) the creation of a testing procedure capable of assessing the strain energy accrued during both a monotonic fracture process and a fatigue process at various elevated temperatures; and (3), the incorporation of the effect of temperature into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed in conjunction with the monotonic fracture curve testing procedure to produce eight fracture curves at three operating temperatures. The strain energy densities for these fracture curves were compared, leading to the assumption of constant monotonic fracture energy at operating temperatures below the creep activation temperature.
Measurement of a Benchmarking Jet in Crossflow Configuration Under Highly Turbulent Conditions
Authors: Ca´rdenas Camilo , Sedlmaier Julia , Zarzalis Nikolaos , Valdes Richard J. , Krebs Werner
Published: May 2012

The configuration of a jet in crossflow appears in many practical applications such as combustion and mixing processes in the chemical industry. This kind of flow is particularly complex due to the presence of various interacting vortex systems and it is widely studied in literature both experimentally and numerically. In addition to the physical interest, this flow configuration serves as a benchmark for numerical methods such as Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) because of its prototypic nature. The present work aims at generating benchmark data for a jet in crossflow configuration under highly turbulent conditions. In this context, the investigated operating conditions were chosen carefully to match the conditions existing in gas turbines and hence the experiments were carried out for two different Reynolds-numbers of the crossflow, Re∞ = 60000 and 40000. Keeping the flow rate of the jet flow constant, two different velocity ratios between jet and crossflow of r = 4.15 and 6.25 result. The measurements were performed in an appropriate air channel, which was built with the objective to obtain accurately controlled flow conditions at the measurement section. Two-dimensional laser induced fluorescence (2d-LIF) combined with particle imaging velocimetry (PIV) was used for the measurements of simultaneous scalar concentration and velocity fields and the experimental acquisition of Reynolds-fluxes and -stresses. The knowledge of Reynolds-fluxes and -stresses is of fundamental concern not only for the understanding of the mechanisms which are responsible for the formation of the vortex-structures in a jet in crossflow, but also for the development and validation of turbulence- and mixing-models.
Rotordynamic Force Coefficients of Bubbly Mixture Annular Pressure Seals
Authors: San Andre´s Luis
Published: May 2012

As oil fields deplete, in particular in deep sea reservoirs, pump and compression systems work under more strenuous conditions with gas in liquid and liquid in gas mixtures, mostly inhomogeneous. Off-design operation affects system overall efficiency and reliability, including penalties in leakage and rotordynamic performance of secondary flow components, namely seals. The paper details a bulk-flow model for annular damper seals operating with gas in liquid mixtures. The analysis encompasses all-liquid and all-gas seals, as well as seals lubricated with homogenous (bubbly) mixtures, and predicts the static and dynamic force response of mixture lubricated seals; namely: leakage, power loss, reaction forces and rotordynamic force coefficients, etc., as a function of the mixture volume fraction (βS), supply and discharge pressures, rotor speed, whirl frequency, etc. A seal example with a Nitrogen gas mixed with light oil is analyzed. The large pressure drop (70 bar) causes a large expansion of the gas within the seal even for (very) small gas volume fractions (βS). Predictions show leakage and power loss decrease as β → 1; albeit at low βS (<0.3) (re)laminarization of the flow and an apparent increase in mixture viscosity, produce a hump in power loss. Cross-coupled stiffnesses and direct damping coefficients decrease steadily with increases in the gas volume fraction; however some anomalies are apparent when the flow turns laminar. Mixture lubricated seals show frequency dependent force coefficients. The equivalent damping decreases above and below βS∼0.10. The direct stiffness coefficients show atypical behavior: a low βS = 0.1 produces stiffness hardening as the excitation frequency increases. Recall that an all liquid seal has a dynamic stiffness softening as frequency increases due to the apparent fluid mass. The predictions call for an experimental program to quantify the static and dynamic forced performance of annular seals operating with (bubbly) mixtures and to validate the current predictive model results.
Computational Study of Micro-Jet Impingement Heat Transfer in a High Pressure Turbine Vane
Authors: Anand Karan , Jubran B. A.
Published: May 2012

The purpose of this numerical investigation is to study the micro-jet impingement heat transfer characteristics and hydromechanics in a 3-D, actual-shaped turbine vane geometry. No concession is made on either the skewness or curvature profile of the airfoil in the streamwise direction, nor to the lean, airfoil twist or tapering of the vane in the spanwise direction. The problem on hand consists of a constant property flow of air via an array of 42 round micro jets impinging onto the inner surface of the airfoil. For simplicity, validation and better understanding of the nature of impingement heat transfer, the airfoil surfaces are provided with a constant temperature boundary condition. Validation is performed against existing numerical results on a simplified model with no spanwise tapering or twisting. The modeled volume spans a total of 12D and consists of three rows of jets; each row contains 14 inline jets. Governing equations are solved using a finite volume method in FLUENT. Effects of jet inclination (+45° and −45° inclinations) and decrease in nozzle diameter (0.51, 0.25 and 0.125 mm) are studied. Inclination of −45° produced enhanced mixing and secondary peaks with marginal decrease in stagnation values. The effect of reducing the diameter of the jets yielded positive results; the tapering effect too enhanced the local heat transfer values, which is attributed to the increase in local velocities at jet exit.
A Computational Study of Hydrogen Substitution Effects on the Combustion Performance for a Micro Gas Turbine
Authors: Shih Hsin-Yi , Liu Chi-Rong
Published: May 2012

The effects of hydrogen substitution on methane/air combustion in a micro gas turbine were studied in this work. The combustion performance and emission characteristics of a can type combustor were investigated with model simulations using the commercial code STAR-CD, in which the three-dimension compressible k-ε turbulent flow mode and presumed probability density function for chemical reaction between methane/hydrogen/air mixtures were used. With hydrogen being the substituent, not a supplement to methane, the detailed flame structures, distributions of flame temperature and flow velocity, and gas emissions were presented and compared by using a fraction of hydrogen to substitute methane in the combustor. For the scenarios from pure methane to pure hydrogen, results show the flame temperature and exit gas temperature increase when only 10% methane is substituted. But as hydrogen substitution percentage increases, the flame temperature and exit gas temperature decrease because of a power shortage caused by lower mass flow rate and heating value of the resulting blended fuels, although the pattern factor drops drastically compared to that of pure methane. As the fuel inlet velocity decreases from 100 m/s to 20 m/s, the high temperature region shifts to the side of the combustor due to the high diffusivity of hydrogen. Increasing hydrogen substitution percentage at a fixed fuel injection velocity reduces NOx emission due to lower flame temperature, but CO emissions increase continually with increasing hydrogen substitution percentage because oxygen depletion for methane/air combustion. Before hydrogen blended fuels or pure hydrogen are used as an alternative fuel for the micro gas turbine, further experimental testing are needed as the CFD modeling results provide a guidance for the improved designs of the combustor.
Numerical Comparison of Heat Transfer and Pressure Drop in Gas Turbine Blade Cooling Channels With Dimples and Rib-Turbulators
Authors: Amano R. S. , Guntur Krishna S. , Kumar Sourabh , Lucci Jose Martinez
Published: May 2012

In order to enhance the performance of a gas turbine and to maintain the blade material within operating temperature range, cooling channels are made within the blade materials that extract the heat. The walls of these cooling channels are usually enhanced with some sort of turbulence generators — ribs and dimples being the most common. While both the geometries provide improvement in enhancing the heat transfer, dimples usually have a lower pressure drop. It is essential to improve the heat transfer rate with a minimal pressure loss. In this study, the heat transfer and pressure loss are determined numerically and combined to show the effect of both in channels with ribs and dimples on one wall of the channel. Similar geometric and boundary conditions are used for both the turbulators. Reynolds numbers of 12,500 and 28,500, based on the hydraulic diameter are used for the study. The Reynolds-Stress Model was used for all the computations as a turbulence model by employing Fluent.
Frequency Clustering in Cyclic Symmetric Rotors Considering Geometry Nonlinearity
Authors: Chang Jen-Yuan James , Brown Jeffrey M. , Cross Charles J.
Published: May 2012

Motivated by finite element results of a bladed disk model, a discrete model and numerical analysis are developed and presented in this paper with view toward understanding effect of large geometric design factors on the vibrations of a cyclic symmetric integrally bladed rotor (IBR). It is found that nonlinear eigenvalue-loci crossing for split frequency doublet modes and eigenvalue-loci veering for repeated frequency modes having the same wavenumber content can occur when large blade span distribution and blade to disk inertia ratio are considered in the discrete IBR model. Clustering of eigen-loci is found and characterized in blade span parameter study when blade’s inertia is significant large. These three findings are new to the literature and have engineering implications on structure design and vibration control of engine components in turbine and automobile applications.
Investigation of Unsteady Compressor Flow Structure With Tip Injection Using Particle Image Velocimetry
Authors: Matzgeller Roland , Voges Melanie , Schroll Michael
Published: May 2012

Fluid injection at the tip of highly loaded compressor rotors is known to be very effective in suppressing the onset of rotating stall and eventually compressor instability. To understand the effects of tip injection, the flow field at the tip region of a transonic compressor rotor with and without fluid injection was investigated in this paper. Using results acquired by phase-locked PIV measurements as well as the static pressure field obtained by fast response pressure transducers, the unsteady interaction between the injection jet and the rotor could be described thoroughly. Both, an influence of the rotor’s flow field on the jet as well of the jet on the rotor was clearly visible. Since unsteady inflow conditions to the front rotor in the relative frame of reference were imposed by the injection jets, the rotor’s unsteady response was investigated by inspection of the position of the tip leakage vortex trajectory. It could be shown that due to a short time for the flow to adapt at the rotor’s leading edge, its position didn’t change distinctly. Because a significantly longer time was needed for the overall passage flow to adapt, it was concluded that this causes the beneficial effect of tip injection.
Numerical Study on Flow and Heat Transfer Characteristics of Jet Impingement
Authors: Wang Xinjun , Liu Rui , Bai Xiaowei , Yao Jinling
Published: May 2012

A mathematical model used for studying jet impingement cooling characteristics is established, and the rationality of the calculation model and method is confirmed by the experimental data. The CFX software is used to numerically simulate the jet impingement cooling characteristics on a gas turbine blade. The effects of various parameters, such as the arrays of impinging nozzles, the jet Reynolds number, the jet-to-jet distance, the ratio of nozzle-to-surface spacing to jet diameter H/d, and the radius of curvature of the target surface, on the flow and heat transfer characteristics of a impingement cooling process are studied. The results indicate that the impingement jets can make complex vortex in the cooling channel, the flow boundary layer is extremely thin and highly turbulent. Underneath each impingement nozzle, there will appear a low temperature area and a peak of Nusselt number on the impingement target surface, the distribution of temperature and Nusselt number on the target surface are associated with arrangement of impingement nozzles. The average Nusselt number of the in-line arrangement nozzles is higher than that of the staggered arrangement ones. With the increasing of jet Reynolds number, the velocity impinging on the target surface and Nusselt number increase. However, heat transfer of impingement cooling on target surface is not sensitive to the jet nozzles distance; the velocity impinging on the target surface and Nusselt number decrease with the increasing of the H/d value. For the curved target surface cases, the average Nusselt number of the target surface and the effect of heat transfer decreased with the increasing of curvature radius R.
Effects of Multiple-Injection-Burner Configurations on Combustion Characteristics for Dry Low-NOx Combustion of Hydrogen-Rich Fuels
Authors: Asai Tomohiro , Dodo Satoschi , Koizumi Hiromi , Takahashi Hirokazu , Yoshida Shouhei , Inoue Hiroshi
Published: May 2012

The successful combination of coal-based integrated gasification combined cycle (IGCC) technology with carbon dioxide (CO2) capture and storage (CCS) requires gas turbines that can achieve dry low-NOx combustion of hydrogen-rich syngas with a wide range of hydrogen concentrations for lower emissions and higher plant efficiency. The authors have been developing a “multiple-injection burner” to achieve dry low-NOx combustion of such hydrogen-rich fuels. The purpose of this paper is to experimentally investigate the combustion characteristics of a multiple-injection burner with a convex perforated plate in order to determine its effectiveness in suppressing combustion oscillation. The experiments were conducted at atmospheric pressure. Three kinds of fuel with hydrogen concentrations ranging from 40 to 84% were tested. The temperature of the combustion gas at the burner exit was 1775 K. The experimental results show that the convex burner was effective in suppressing combustion oscillation: it achieved stable low-NOx emissions of less than 10 ppm for all the test fuels. These findings demonstrate that the convex burner can achieve stable low-NOx combustion of hydrogen-rich fuels with a wide range of hydrogen concentrations by suppressing combustion oscillation.
Characteristics of an Ultra-Lean Swirl Combustor Flow by LES and Comparison to Measurements
Authors: Kern Matthias , Marinov Svetoslav , Habisreuther Peter , Zarzalis Nikolaos , Peschiulli Antonio , Turrini Fabio
Published: May 2012

The lean combustion process is one of the most promising methods for reducing NOx emissions of jet engines. Since the risk of flash back is major for premixed concepts a diffusion flame concept is applied. In order to realize the lean condition in this concept the percentage of air flowing through the injection system and combustor dome has to be drastically increased. This leads to nozzles with a high effective area and to high volume flux in the primary zone of the combustor chamber. Such an injection system demands a particular focus towards flame stability at low load. Hence, it is essential to gain information on characteristics such as vortex breakdown, turbulent mixing and coherent structures (e.g. PVC) of the flow by means of numerical simulations. In the paper it is reported on the flow characteristics of the PERM injection system, which equips the AVIO annular combustor designed and developed within NEWAC, an integrated project co-funded by the European Commission. For this injections system RANS and LES simulations have been performed to investigate the isothermal flow field. The results are compared to detailed field measurements of velocity components and Reynolds stresses.
Compressible and Incompressible Large Eddy Simulation of a Premixed Dump Combustor
Authors: Ma Terence , Kempf Andreas M.
Published: May 2012

Premixed combustion in the ORACLES dump combustor is investigated by Large-Eddy Simulation. The results are compared with experimental measurements of mean and fluctuating velocities at various points inside the combustor. The LES is performed with the in-house PsiPhi code, which has been modified to account for compressibility so that flame-acoustic interactions can be studied. The modifications include the use of proper boundary conditions that are based on the Navier-Stokes Characteristic Boundary Conditions (NSCBC) [1]. A fixed velocity and temperature inlet as well as a partially reflecting outlet are selected. The reaction rate is modelled using algebraic expressions for the generalised flame surface density (FSD) Σgen. A selection of FSD models [2] were previously tested using the incompressible version of PsiPhi and this work examines three additional models. Previous incompressible works [2, 3] on this setup emulated the effect of acoustic oscillations by introducing sinusoidal pulsations at the inlet with a frequency of 50Hz. We apply the same technique for the simulations and match the results with those from the modified compressible version, albeit for a compact domain which cannot be expected to capture the lowest acoustic frequencies. Apart from assessing performance, we also make comparisons of the simulation cost and stability to gain a better perspective of whether new FSD models and the compressible description are favorable.
Experimental Measurements of Ingestion Through Turbine Rim Seals: Part 2—Rotationally-Induced Ingress
Authors: Sangan Carl M. , Zhou Kunyuan , Owen J. Michael , Pountney Oliver J. , Wilson Mike , Lock Gary D.
Published: May 2012

Part 1 of this two-part paper presented experimental results for externally-induced (EI) ingress, where the ingestion of hot gas through the rim seal into the wheel-space of a gas turbine is controlled by the circumferential variation of pressure in the external annulus. In Part 2, experimental results are presented for rotationally-induced (RI) ingress, where the ingestion is controlled by the pressure generated by the rotating fluid in the wheel-space. Although EI ingress is the common form of ingestion through turbine rim seals, RI ingress or combined ingress (where EI and RI ingress are both significant) is particularly important for double seals, where the pressure asymmetries are attenuated in the annular space between the inner and outer seals. In this paper, the sealing effectiveness was determined from concentration measurements, and the variation of effectiveness with sealing flow rate was compared with theoretical curves for RI ingress obtained from an orifice model. Using a nondimensional sealing parameter, Φ0, the data could be collapsed onto a single curve, and the theoretical variation of effectiveness with Φ0 was in very good agreement with the data for a wide range of flow rates and rotational speeds. It was shown that the sealing flow required to prevent RI ingress was much less than that needed for EI ingress, and it was also shown that the effectiveness of a radial-clearance seal is significantly better than that for an axial-clearance seal for both EI and RI ingress.