bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Tip Leakage Vortex Breakdown in Flow Fields and Aerodynamic Characteristics of Transonic Centrifugal Compressor Impellers
Authors: Yamada Kazutoyo , Furukawa Masato , Fukushima Hisataka , Ibaraki Seiichi , Tomita Isao
Published: May 2012

This paper describes the experimental and numerical investigations on unsteady three-dimensional flow fields in two types of transonic centrifugal compressor impellers with different aerodynamic characteristics. In the experimental results, the frequency spectra of the pressure fluctuations, which were measured with the high-response pressure transducers mounted on the casing wall just upstream of the impeller, turned out to be quite different between the compressor impellers at stall condition. The simulation results also showed different stall pattern for each compressor impeller. In the compressor impeller with a better performance at off-design condition, the stall cell was never formed despite decreasing flow rate and instead all the passages were covered with a reverse flow near the tip, where the vortex breakdown happened in the tip leakage vortex of full blade and led to the unsteadiness in the impeller. The vortex breakdown happened in all the passages prior to the stall and generated a blockage near the tip. This means that even with the advent of rotating stall the flow could not return to a normal undistorted condition in unstalled region, because all the passages are already occupied by the blockage due to the vortex breakdown. As a result, the rotating stall cell could not appear in the impeller. In the other compressor impeller, the rotating stall cell was formed at stall inception without the vortex breakdown in the tip leakage vortex of full blade, and developed with decreased flow rate.
Suppression of NOx Emission of a Lean Staged Combustor for an Aircraft Engine
Authors: Fujiwara H. , Matsuura K. , Shimodaira K. , Hayashi S. , Kobayashi M. , Oda T. , Horikawa A. , Matsuyama R. , Ogata H. , Kinoshita Y.
Published: May 2012

Due to the increasing demands for environment protection, the regulation of NOx emissions from aircraft engines specified by ICAO have become more stringent year by year. A combustor with lean staged fuel injectors is one of the effective methods to reduce NOx emissions. Kawasaki heavy industries Ltd GTBC and Japan Aerospace Exploration Agency (JAXA) have been conducting joint research on a lean staged concentric fuel nozzle for a high pressure ratio aero engine. High pressure combustion tests were performed to clarify the effect of the contour of the air flow passage of the main premix duct, the arrangement of the swilers and the fuel injection position on the NOx emission especially at high power. Visualization of the fuel spray at elevated pressure inside of the premix duct using a model with transparent walls and a laser diagnostics technique showed clear relationship between the distribution of the fuel spray and the NOx emission.
Aerodynamic Redesigning of an Industrial Gas Turbine
Authors: Rubechini Filippo , Schneider Andrea , Arnone Andrea , Dacca` Federico , Canelli Claudio , Garibaldi Pietro
Published: May 2012

This paper deals with the aerodynamic redesigning of a four-stage heavy-duty gas turbine. Traditional design tools, such as through-flow methods, as well as more sophisticated tools, such as three-dimensional RANS computations, were applied in subsequent steps according to a given hierarchical criterion. Each design or analysis tool was coupled with modern optimization techniques, and the overall redesign procedure relies on a neural-network-based approach aimed at maximizing the turbine’s power output while satisfying geometrical and mechanical constraints. A detailed description of the redesign procedure is provided, and the aerodynamic characteristics of the optimized geometry are discussed and compared to the original ones.
Optimal Operation of a Gas Turbine Cogeneration Plant in Consideration of Equipment Minimum Up and Down Times
Authors: Yokoyama Ryohei
Published: May 2012

It has become important for operators to determine operational strategies of energy supply plants appropriately corresponding to energy demands varying with season and time from the viewpoints of economics, energy saving, and recently reduction in CO2 emission. Especially, cogeneration plants produce heat and power simultaneously, which increases alternatives for operational strategies. This makes it more important for operators to determine operational strategies of cogeneration plants appropriately. In this paper, for the purpose of assisting operators or operating plants automatically, an optimal operational planning method based on the mixed-integer linear programming is developed to determine the operational strategy of equipment so as to minimize the operational cost, in consideration of equipment minimum up and down times for each piece of equipment to be operated with appropriate numbers of startups and shutdowns. In the numerical study, the proposed method is applied to the daily operational planning of a gas turbine cogeneration plant for district energy supply. It is clarified how the constraints for minimum up and down times affect the operational strategy and cost. Through the study, the validity and effectiveness of the proposed method is ascertained.
Numerical Simulations of Turbulent Mixing and Autoignition of Hydrogen Fuel at Reheat Combustor Operating Conditions
Authors: Ivanova Elizaveta , Noll Berthold , Griebel Peter , Aigner Manfred , Syed Khawar
Published: May 2012

Turbulent mixing and autoignition of H2-rich fuels at relevant reheat combustor operating conditions are investigated in the present numerical study. The flow configuration under consideration is a fuel jet perpendicularly injected into a crossflow of hot flue gas (T > 1000K, p = 15bar). Based on the results of the experimental study for the same flow configuration and operating conditions two different fuel blends are chosen for the numerical simulations. The first fuel blend is a H2/natural gas/N2 mixture at which no autoignition events were observed in the experiments. The second fuel blend is a H2/N2 mixture at which autoignition in the mixing section occurred. First, the non-reacting flow simulations are performed for the H2/natural gas/N2 mixture in order to compare the accuracy of different turbulence modeling methods. Here the steady-state Reynolds-averaged Navier-Stokes (RANS) as well as the unsteady scale-adaptive simulation (SAS) turbulence modeling methods are applied. The velocity fields obtained in both simulations are directly validated against experimental data. The SAS method shows better agreement with the experimental results. In the second part of the present work the autoignition of the H2/N2 mixture is numerically studied using the 9-species 21-steps reaction mechanism of O’Conaire et al. [1]. As in the reference experiments, autoignition can be observed in the simulations. Influences of the turbulence modeling as well as of the hot flue gas temperature are investigated. The onset and the propagation of the ignition kernels are studied based on the SAS modeling results. The obtained numerical results are discussed and compared with data from experimental autoignition studies.
Computational Study on the Effect of Local Expansion and Contraction Upon Surface Deposition in a Heated Fuel Injector
Authors: Alborzi Ehsan , Piazzolla Renato , Wilson Christopher
Published: May 2012

A preliminary numerical analysis was carried out to examine the effect of local expansion and contraction on surface deposition rate for two series of geometries. These geometries correspond to the new geometrical features found in jet fuel injection system. For this simulation, commercial computational fluid dynamic package, Fluent 6.3.26, was used. Fluid flow, energy, and turbulence equations were solved coupled with a pseudo-detailed chemical kinetic model for jet fuel thermal degradation and the subsequent surface deposition sub model. The model results indicate that the highest deposition rates occur at intermediate expansion ratios and for a bigger inlet diameter due to a lower convective heat transfer. It was also shown that high expansion ratios are recommended to be used for short injector lengths. These simulated results are used for the experimental work in progress. The most susceptible locations to surface deposition are those with the highest rates; these are the best indicative points for data sampling.
Performance Analysis of a 565 MW Steam Power Plant
Authors: Chacartegui R. , Sa´nchez D. , Becerra J. A. , Mun˜oz A. , Sa´nchez T.
Published: May 2012

In this work, a tool to predict the performance of fossil fuel steam power plants under variable operating conditions or under maintenance operations has been developed. This tool is based on the Spencer-Cotton-Cannon method for large steam turbine generator units. The tool has been validated by comparing the predicted results at different loads with real operating data of a 565 MW steam power plant, located in Southern Spain. The results obtained from the model show a good agreement with most of the power plant parameters. The simulation tool has been then used to predict the performance of a steam power plant in different operating conditions such as variable terminal temperature difference or drain cooler approach of the feed-water heaters, or under maintenance conditions like a feed-water heater out of service.
Application of MCFC in Coal Gasification Plants for High Efficiency CO2 Capture
Authors: Spallina Vincenzo , Romano Matteo C. , Campanari Stefano , Lozza Giovanni
Published: May 2012

Integrated gasification combined cycles (IGCCs) are considered the reference technology for high efficiency and low emission power generation from coal. In recent years, several theoretical and experimental studies in this field have been oriented towards capturing CO2 from IGCCs through the integration of Solid Oxide Fuel Cells (SOFC) for coal-syngas oxidation, investigating the so-called Integrated Gasification Fuel Cell cycles (IGFC). However, Molten Carbonate Fuel Cells (MCFC) can also be a promising technology in IGFCs. After a rather comprehensive research carried out by the authors on modeling and simulation of SOFC-based IGFC plants, an interesting IGFC cycle based on MCFC is assessed in this work, where plant layout is designed to exploit the capability of MCFCs of transferring CO2 and O2 from the oxidant side to the fuel side. Syngas produced in a high efficiency Shell gasifier is cleaned and mainly burned in a combustion turbine as in conventional IGCCs. Turbine flue gas, rich of oxygen and carbon dioxide, are then used as oxidant stream for the fuel cell at the cathode side, while the remaining clean syngas is oxidized at the anode side. In this way the MCFC, while efficiently producing electricity, separates CO2 from the gas turbine flue gas as in a post-combustion configuration; oxygen is also transported towards the anode side, oxidizing the remaining syngas as in an oxy-combustion mode. A CO2-rich stream is hence obtained at anode outlet, which can be cooled and compressed for long term storage. This configuration allows to produce power from coal with high efficiency and low emission. In addition, as already highlighted in a previous study where a similar concept has been applied to natural gas-fired combined cycles, a limited fraction of the power output is generated by the fuel cell (the most expensive component), highlighting its potential also from an economic point of view. Detailed results are presented in terms of energy and material balances of the proposed cycle.
Comparison Between a CFD Code and a Three-Control-Volume Model for Labyrinth Seal Flutter Predictions
Authors: Phibel R. , di Mare L.
Published: May 2012

Labyrinth seals are extensively used in turbomachinery to control flow leakage in secondary air systems. While a large number a studies have been performed to investigate the leakage and rotordynamics characteristics of these seals, the studies on their aeroelastic stability remain scarce. Little is known about this phenomenon and the design methods are limited to a stability criterion which does not take into account many of the parameters which are known to influence labyrinth seal aeroelastic stability. As a consequence the criterion can be unreliable or overly pessimistic. The alternative to this criterion is the use of CFD methods which, although reliable, are computationally expensive. This paper presents a three-control-volume (3CV) bulk-flow model specifically developed for flutter calculations in labyrinth seals. The model is applied to a turbine labyrinth seal of a large diameter aero-engine and the results are compared to those of a CFD analysis. Conclusions are drawn on the potential of this 3CV model for design purposes.
Experimental and Numerical Investigation of Mistuned Aerodynamic Influence Coefficients in an Oscillating LPT Cascade
Authors: Glodic Nenad , Vogt Damian , Fransson Torsten
Published: May 2012

The effect of aerodynamic mistuning on the aerodynamic damping in an oscillating Low-Pressure Turbine (LPT) cascade is investigated. The considered aerodynamic mistuning is caused by blade-to-blade stagger angle variations. The study is carried out experimentally and numerically by employing the influence coefficient method. On the experimental side a sector cascade is used where one of the blades is made oscillating in three orthogonal modes. The unsteady blade surface pressure is acquired on the oscillating blade and two neighbour blades and reduced to aeroelastic stability data. By gradually de-staggering the oscillating blade, aerodynamically mistuned influence coefficients are acquired. On the numerical side full-scale time-marching RANS CFD simulations are performed using nominal and de-staggered blades. The study shows that variations in blade-to-blade stagger angle affect the aerodynamic influence coefficients and as a consequence overall aeroelastic stability. Whereas discrepancies are found in the exact prediction of mistuned influence coefficients compared to measured, the overall magnitude and trends are well captured.
The Influence of Shrouded Stator Cavity Flows on the Aerodynamic Performance of a High-Speed Multistage Axial-Flow Compressor
Authors: Kato Dai , Yamagami Mai , Tsuchiya Naoki , Kodama Hidekazu
Published: May 2012

This paper investigates numerically the effects of shrouded stator seal cavity flows on a high-speed, six-stage, advanced axial-flow compressor performance. Two cases of fully three-dimensional unsteady Reynolds-averaged Navier-Stokes simulations are performed. The first case includes only the main flow path without cavities, while the second case takes into account the effect of cavities by fully meshing and solving the seal cavity flows under each of the stator vanes. Both simulations included rotor blade tip clearances. The latter case showed 1.7 point degradation in efficiency from the first case. Contributors to the overall performance degradation, such as windage heating, mixing loss due to seal leakage flow with the main flow, and additional loss of the rotors and stators due to alteration in velocity triangles, are identified by comparing the two simulation results. Compared to theoretical or semi-empirical leakage and windage models, higher loss production and temperature rise are found especially in mid to rear stages. Unsteady effects for such differences are discussed.
Optimization of Wind Energy Capture Using BET
Authors: Perez-Blanco H.
Published: May 2012

The Blade Element Theory (BET) has been used to predict performance of wind turbines, and to optimize energy extraction from the wind. A literature search shows that the number of parameters that can be varied to attempt optimization within BET varies for different authors. However, a repeated assumption is that the BE should be operating at the incidence angle resulting in maximum lift to drag ratio. In the present work, the incidence angle is one of the parameters varied for optimization, along with five others: the two induction factors, the chord, and the flow and setting angles. The optimization satisfies five equality constraints and three inequality constraints. The optimizer uses Levenberg-Marquardt, Conjugate Gradient or Quasi-Newton methods to maximize the power extracted. The equations adopted employ the Prandtl tip loss and require specification of the airfoil for the section, the radius of the turbine, the wind speed and the radial distribution of solidity. Up to twenty five elements can be specified for each turbine. The influence of airfoils on power coefficients is shown, and deviations from the expected maximum lift to drag positions noted. Comparisons to the performance of small wind turbines from the commercial and open literature are attempted. Whereas such comparisons are difficult in that airfoils and solidities are not often specified, they yield a baseline for establishing the validity of the optimization procedure.
Assessment of Numerical Tools for the Evaluation of the Acoustic Impedance of Multi-Perforated Plates
Authors: Andreini A. , Bianchini C. , Facchini B. , Simonetti F. , Peschiulli A.
Published: May 2012

Multi-perforated liners, commonly employed in Gas Turbine combustors as cooling devices to control metal temperature, are recognized as very effective sound absorbers. Thus, in the innovative lean combustion technology, where the onset of thermoacoustic instabilities represents one of the most important issue, the multi-perforated plates can be exploited both for wall cooling and damping combustion instabilities. As a first step of a large experimental and numerical research program regarding multi-perforated liners, an investigation of different numerical methodologies to analyze acoustic damping is here reported. In particular three different numerical techniques to evaluate planar waves sound absorption of perforated plates are presented and validated with literature test cases. A quasi 1-D code, implementing the wall compliance concept, provides results for a large set of geometric and fluidynamic conditions. A large test matrix was investigated varying perforation hole angle and diameter with different overall porosities. The effect of bias and grazing flows Mach number was tested as well. A subset of considered geometries were then supported by a full reconstruction of the unsteady pressure field by means of a Large Eddy Simulation computed with an open-source code. Non-reflective boundaries with forcing term provide the wave to acoustically excite the perforated plate. Multi-microphone postprocessing technique allowed the reconstruction of a progressive and regressive planar wave to compute the reflection coefficient. All results were cross-checked with a Finite Element Model, able to solve the wave equation in the frequency domain with a background velocity field.
A Low Pressure Turbine With Profiled End Walls and Purge Flow Operating With a Pressure Side Bubble
Authors: Jenny P. , Abhari R. S. , Rose M. G. , Brettschneider M. , Gier J.
Published: May 2012

This paper presents an experimental and computational study of non-axisymmetric rotor end wall profiling in a low pressure turbine. End wall profiling has been proven to be an effective technique to reduce both turbine blade row losses and the required purge flow. For this work a rotor with profiled end walls on both hub and shroud is considered. The rotor tip and hub end walls have been designed using an automatic numerical optimisation that is implemented in an in-house MTU code. The end wall shape is modified up to the platform leading edge. Several levels of purge flow are considered in order to analyze the combined effects of end wall profiling and purge flow. The non-dimensional parameters match real engine conditions. The 2-sensor Fast Response Aerodynamic Probe (FRAP) technique system developed at ETH Zurich is used in this experimental campaign. Time-resolved measurements of the unsteady pressure, temperature and entropy fields between the rotor and stator blade rows are made. For the operating point under investigation the turbine rotor blades have pressure side separations. The unsteady behavior of the pressure side bubble is studied. Furthermore, the results of unsteady RANS simulations are compared to the measurements and the computations are also used to detail the flow field with particular emphasis on the unsteady purge flow migration and transport mechanisms in the turbine main flow containing a rotor pressure side separation. The profiled end walls show the beneficial effects of improved measured efficiency at this operating point, together with a reduced sensitivity to purge flow.
Laminar Flame Velocity of Components of Natural Gas
Authors: Dirrenberger P. , Glaude P. A. , Le Gall H. , Bounaceur R. , Herbinet O. , Battin-Leclerc F. , Konnov A. A.
Published: May 2012

Laminar burning velocities are important parameters in many areas of combustion science such as the design of burners or engines and for the prediction of explosions. They play an essential role in the combustion in gas turbines for the optimization of the nozzles and of the combustion chamber. Adiabatic laminar flame velocities are usually investigated in three types of apparatus which are currently available for that type of measurements: constant volume bombs in which the propagation of a flame is initiated by two electrodes and followed by shadowgraphy, counterflow-flame burners with axial velocity profiles determined by Particle Imaging Velocimetry, and flat flame adiabatic burners which consist of a heated burner head mounted on a plenum chamber with the radial temperature distribution measurement made by a series of thermocouples (used in this work). This last method is based on a balance between the heat loss from the flame to the burner required for the flame stabilization and the convective heat flux from the burner surface to the flame front. It was demonstrated that this heat flux method is suitable for the determination of the adiabatic flame temperature and flame burning velocity. The main hydrocarbon in natural gas is methane, with smaller amounts of heavier compounds, mainly species from C2 to C4. New experimental measurements have been performed by the heat flux method using a newly built flat flame adiabatic burner at atmospheric pressure. These measurements of laminar flame speeds are presented for components of natural gas, methane, ethane, propane and n-butane, as well as for binary and tertiary mixtures of these compounds representative of different natural gases available in the world. Results for pure alkanes were compared successfully to the literature. The composition of the investigated air/hydrocarbon mixtures covers a wide range of equivalence ratios, from 0.6 to 2.1 when it is possible to sufficiently stabilize the flame. Empirical correlations have been derived in order to predict accurately the flame velocity of a natural gas containing C1 up to C4 alkanes as a function of its composition and the equivalence ratio.
Correlation Measure-Based Stall Margin Estimation for a Single-Stage Axial Compressor
Authors: Liu Yuan , Dhingra Manuj , Prasad J. V. R.
Published: May 2012

This paper presents a method for estimating compressor stall margin and the results of applying the estimation technique to an axial compressor rig. Stall margin estimation is accomplished through the use of a compressor stability detection parameter called the “correlation measure.” The correlation measure captures the periodicity of the pressure in the rotor tip region of the compressor. The downcrossing frequency of the correlation measure across some preset threshold is measured while operating the compressor rig at various steady-state points along the design speed characteristic line. These measurements are used to generate a relationship with stall margin as a function of downcrossing frequency. The estimation technique is evaluated by applying it while dynamically ramping the operating point of the compressor up the design speed line towards surge. A brief investigation on the effects of inlet distortions on the correlation measure-based estimation system is also given.
An Investigation of Reynolds Lapse Rate for Highly Loaded Low Pressure Turbine Airfoils With Forward and Aft Loading
Authors: Lyall M. Eric , King Paul I. , Sondergaard Rolf , Clark John P. , McQuilling Mark W.
Published: May 2012

This paper presents an experimental and computational study of the midspan low Reynolds number loss behavior for two highly loaded low pressure turbine airfoils, designated L2F and L2A, which are forward and aft loaded, respectively. Both airfoils were designed with incompressible Zweifel loading coefficients of 1.59. Computational predictions are provided using two codes, Fluent (with k-k1-ω model) and AFRL’s Turbine Design and Analysis System (TDAAS), each with a different eddy-viscosity RANS based turbulence model with transition capability. Experiments were conducted in a low speed wind tunnel to provide transition models for computational comparisons. The Reynolds number range based on axial chord and inlet velocity was 20,000 < Re < 100,000 with an inlet turbulence intensity of 3.1%. Predictions using TDAAS agreed well with the measured Reynolds lapse rate. Computations using Fluent however, predicted stall to occur at significantly higher Reynolds numbers as compared to experiment. Based on triple sensor hot-film measurements, Fluent’s premature stall behavior is likely the result of the eddy-viscosity hypothesis inadequately capturing anisotropic freestream turbulence effects. Furthermore, rapid distortion theory is considered as a possible analytical tool for studying freestream turbulence that influences transition near the suction surface of LPT airfoils. Comparisons with triple sensor hot-film measurements indicate that the technique is promising but more research is required to confirm its utility.
Modeling of the Heat Flux for Multi-Hole Cooling Applications
Authors: Cottin Guillaume , Laroche Emmanuel , Savary Nicolas , Millan Pierre
Published: May 2012

The aims of this work are to achieve a better understanding of thermal fluxes around a multi-perforated plate and obtain correlations for heat transfer coefficient on the hot as well as cold side and in a perforation. A 3-dimensional, RANS, conjugate simulation and an adiabatic one are performed for different aerothermal conditions already studied experimentally. Convective heat flux, wall temperature and adiabatic temperature are averaged on a periodic pattern around each hole. A mean heat transfer coefficient is calculated based on these quantities and correlations are deduced for this coefficient. Such results as fluid temperature rise in a perforation or the contribution of flux in the perforations to the whole cooling flux are also given in this article.
Experimental and Numerical Investigation of a Combustor Model
Authors: Barhaghi Darioush G. , Janczewski Jacek , Larsson Thomas
Published: May 2012

Fluid flow behaviour is studied both experimentally and numerically in a combustor model which is recently designed at Siemens Turbomachinery AB at Finspong. The model consists of a full size combustor sector that is surrounded by two half size combustor sectors. The half size sectors provide the pressure drop equal to a full scale combustor sector to guarantee the correct air mass flow distribution through the system. Measurements are performed at atmospheric condition and therefore the boundary conditions are scaled based on the Mach number. This means that the Mach number in different parts of the combustor under the test condition is equal to the Mach number of the flow at full load condition. Pitot tubes and pressure taps are employed to measure the dynamic and static pressures at different cross sections of the model. From the measured pressure, the velocity is calculated. The pressure distributions along the diffusers are compared and the pressure recovery factor is calculated for different cases. The computations are performed using RANS (SST k-ω model) and LES (Smagorinsky sub-grid scale model) methods. The computed and measured results show similar trends although there are rather large discrepancies between the results.
An Investigation of Stall Inception in Centrifugal Compressor Vaned Diffusers
Authors: Everitt J. N. , Spakovszky Z. S.
Published: May 2012

In compression systems the stable operating range is limited by rotating stall and/or surge. Two distinct types of stall precursors can be observed prior to full scale instability: the development of long-wavelength modal waves or a short-wavelength, three-dimensional flow breakdown (so-called “spike” stall inception). The cause of the latter is not well understood; in axial machines it has been suggested that rotor blade-tip leakage flow plays an important role, but spikes have recently been observed in shrouded vaned diffusers of centrifugal compressors where these leakage flows are not present, suggesting an alternative mechanism may be at play. This paper investigates the onset of instability in a shrouded vaned diffuser from a highly loaded turbocharger centrifugal compressor and discusses the mechanisms thought to be responsible for the development of short-wavelength stall precursors. The approach combines unsteady 3D RANS simulations of an isolated vaned diffuser with previously obtained experimental results. The unsteady flow field simulation begins at the impeller exit radius, where flow is specified by a spanwise profile of flow angle and stagnation properties, derived from single-passage stage calculations but with flow pitchwise mixed. Through comparison with performance data from previous experiments and unsteady full-wheel simulations, it is shown that the diffuser is accurately matched to the impeller and the relevant flow features are well captured. Numerical forced response experiments are carried out to determine the diffuser dynamic behavior and point of instability onset. The unsteady simulations demonstrate the growth of short-wavelength precursors; the flow coefficient at which these occur, the rotation rate and circumferential extent agree with experimental measurements. Although the computational setup and domain limitations do not allow simulation of the fully developed spike nor full-scale instability, the model is sufficient to capture the onset of instability and allows the postulation of the following necessary conditions: (i) flow separation at the diffuser vane leading edge near the shroud endwall; (ii) radially reversed flow allowing vorticity shed from the leading edge to convect back into the vaneless space; and (iii) recirculation and accumulation of low stagnation pressure fluid in the vaneless space, increasing diffuser inlet blockage and leading to instability. Similarity exists with axial machines, where blade-tip leakage sets up endwall flow in the circumferential direction leading to flow breakdown and the inception of rotating stall. Rather than the tip leakage flows, the cause for circumferential endwall flow in the vaned diffuser is the combination of high swirl and the highly non-uniform spanwise flow profile at the impeller exit.
Heat Transfer in a Channel Under Effects of a Shallow-Angle Jet Impingement and a Rib
Authors: Wang Lei , Sunde´n Bengt , Borg Andreas , Abrahamsson Hans
Published: May 2012

Experimental studies are carried out to investigate the heat transfer characteristics involving an impinging jet with a shallow-angle in a crossflow. A rib is applied to control the jet impingement heat transfer. Liquid crystal technique is employed to measure the wall temperature and obtain the heat transfer coefficients. In the study, the Reynolds number for the crossflow is 80,000 and the Reynolds number for the jet ranges from 20,000 to 40,000. This gives rise to the jet-to-crossflow velocity ratio varying from 1.4 to 2.8. For all the tested cases, it is found that the presence of rib makes the Nusselt number profiles across the stagnation point change from a classical bell-shaped profile to a plateau-like pattern, indicating the enhanced heat transfer region expands more as the rib is present. In particular, the presence of rib has a more pronounced effect on the enhancement of heat transfer at lower velocity ratio (R = 1.4). However, in such case, the local heat transfer in the rib corner region deteriorates. At higher velocity ratio, especially at R = 2.8, the presence of rib makes the heat transfer rate more uniform, but meanwhile, it is found that the impinging jet effect tends to be weaker.
Determination of the Wake Frequency Contents for a Twin Shaft Gas Turbine Variable Nozzle Guided Vane
Authors: Grimaldi Antonio Maria , Colantoni Simone , Melani Antonio , Manenc Pierre
Published: May 2012

This paper focuses on improving maintenance techniques for GE twin shaft gas turbines equipped with variable Nozzle Guided Vanes (NGVs) by enhancing the ability to predict potentially harmful stimuli due to NGV misalignment. NGV, by varying the geometry, controls the energy split between the high-pressure turbine and power turbine, allowing higher operational flexibility and higher efficiency at partial load/speed. This flexibility is a requirement for GT mechanical drive applications. The alignment of the NGV according to specification is part of the GE procedure to guarantee reliable operation of the turbine. The orientation of the vanes is checked and guaranteed via the measurement of the S/T ratio (throat opening/pitch). The S/T distribution potentially affects the downstream buckets in terms of harmonic stimuli for natural frequencies that could result in bucket HCF failures. The scope of this work is to develop a Fourier series-based tool that, for any statistically possible distribution of S/T ratios, automatically computes the Fourier Coefficients of the corresponding wake pattern and scales each harmonic magnitude with respect to the maximum harmonic magnitude of the symmetric wake pattern. This tool has been specifically developed to drive field operations when some of the NGVs in the row must be replaced. It allows the detection of harmonic stimuli that could potentially increase downstream bucket resonance without making S/T measurements, reducing the forced outage cycle time and saving maintenance costs.
Application of Artificial Neural Network for the Heat Transfer Investigation Around a High-Pressure Gas Turbine Rotor Blade
Authors: Eryilmaz Ibrahim , Inanli Sinan , Gumusel Baris , Toprak Suha , Camci Cengiz
Published: May 2012

This paper presents the preliminary results of using artificial neural networks in the prediction of gas side convective heat transfer coefficients on a high pressure turbine blade. The artificial neural network approach which has three hidden layers was developed and trained by nine inputs and it generates one output. Input and output data were taken from an experimental research program performed at the von Karman Institute for Fluid Dynamics by Camci and Arts [5,6] and Camci [7]. Inlet total pressure, inlet total temperature, inlet turbulence intensity, inlet and exit Mach numbers, blade wall temperature, incidence angle, specific location of measurement and suction/pressure side specification of the blade were used as input parameters and calculated heat transfer coefficient around a rotor blade used as output. After the network is trained with experimental data, heat transfer coefficients are interpolated for similar experimental conditions and compared with both experimental measurements and CFD solutions. CFD analysis was carried out to validate the algorithm and to determine heat transfer coefficients for a closely related test case. Good agreement was obtained between CFD results and neural network predictions.
Comparative Validation Study on Identification of Premixed Flame Transfer Function
Authors: Tay-Wo-Chong Luis , Bomberg Sebastian , Ulhaq Ahtsham , Komarek Thomas , Polifke Wolfgang
Published: May 2012

The flame transfer function (FTF) of a premixed swirl burner was identified from time series generated with CFD simulation of compressible, turbulent, reacting flow at non-adiabatic conditions. Results were validated against experimental data. For large eddy simulation (LES), the Dynamically Thickened Flame combustion model with one step kinetics was used. For unsteady simulation in a Reynolds-averaged Navier-Stokes framework (URANS), the Turbulent Flame Closure model was employed. The FTF identified from LES shows quantitative agreement with experiment for amplitude and phase, especially for frequencies below 200 Hz. At higher frequencies, the gain of the FTF is underpredicted. URANS results show good qualitative agreement, capturing the main features of the flame response. However, the maximum amplitude and the phase lag of the FTF are underpredicted. Using a low-order network model of the test rig, the impact of the discrepancies in predicted FTFs on frequencies and growth rates of the lowest order eigenmodes were assessed. Small differences in predicted FTFs were found to have a significant impact on stability limits. Stability behavior in agreement with experimental data was achieved only with the LES-based flame transfer function.
Accurate Calculation of the Slip Factor of Axial Cascades and Impellers for Arbitrary Blade Shapes
Authors: Smith Henrik , Semel Matthias , Epple Philipp , Miclea-Bleiziffer Mihai , Delgado Antonio
Published: May 2012

Nowadays, design, redraft and optimisation strategies of axial fans often still rely on the one dimensional mean line theory. However, as it is well known, it is based on a number of assumptions that do not apply to real flow behaviour so that various deviations can be observed. In the present paper, the plane potential theory is used to examine and calculate these deviations. The behaviour of axial cascades is analysed in general and a slip factor is computed. On this basis a quasi-3D calculation method is developed. It is applied to an exemplary impeller and the results are compared with 3D CFD computations. The main characteristic figures are presented and different angle correction and angle exaggeration methods are investigated and compared. Finally, the applicability of the presented method to a precise axial fan design process is illustrated.
Aerodynamic Design, Analysis, Integration, and Optimization Tool for Centrifugal Compressor OEM
Authors: Biba Yuri , Maier Julie A.
Published: May 2012

While three-dimensional techniques are widely used in the turbomachinery industry, a mean-line approach remains at the core of multidisciplinary design and analysis. Combining rules of design, conservation laws, and experience permits narrowing down design options, outlining geometry, and evaluating results in an effective and consistent manner. This paper reports on a project initiated by the original equipment manufacturer (OEM) to develop a versatile close-coupled stage design system for centrifugal compressor stages. This mean-line design suite is based on flexible system architecture including a combination of in-house and commercial analysis and design software modules. Inter-code data transfer and user interfacing are facilitated through a master spreadsheet and a commercial director integration program. Significant outputs available from this design system include rule-based solid models and selective flow path component optimization. Examples of both are presented in this paper. This work was done as part of an undergraduate cooperative work-study program. The cooperative education program offers value to both industry and academia. The educational and commercial implications of this project are discussed.
Aerodynamic Improvement of a Transonic Fan Outlet Guide Vane Using 3D Design Optimization
Authors: Endicott Giles , Sonoda Toyotaka , Olhofer Markus , Arima Toshiyuki
Published: May 2012

In this paper we follow the process of rapid design improvement for the fan outlet guide vane for a turbofan powering a very light jet. The small size of such engines leads to a low Reynolds number, resulting in flow-fields prone to boundary layer separation, causing significant losses in efficiency. This paper studies experimental testing in a scale rig, and numerical simulation using CFD, leading to the comparison of the two datasets and hence assessment of the numerical technique. The mesh employed by the CFD simulation was modified using Free Form Deformation to create different geometric designs, and hence an optimization scheme was subsequently utilized to find the deformation of 28 variables which maximized aerodynamic performance. The final optimized design displayed a novel oscillatory casing profile, while the blade shape had increased camber relative to the baseline. The improvement in pressure loss was approximately 20% across the range of operating conditions studied.
Experimental Investigation of the Influence of Water Injection on Acoustic Properties of the Exhaust System of a Gas Turbine Combustion Test Rig
Authors: Schmid Martin , Trott Natalie , Kathan Robert , Fanaca Dan , Sattelmayer Thomas
Published: May 2012

It is a known phenomenon that single can combustion test rigs and gas turbines have a different stability behavior. Real gas turbines are often more stable than their test rigs. One main difference between test rigs and real engines is the injection of cooling water into the test rigs to reduce the temperature of the exhaust gas and thus to protect the exhaust valve. A literature survey showed that the presence of a two phase flow can drastically reduce the sonic velocity and consequently change the acoustic properties of a system. The aim of this project is to study the influence of water injection on the acoustic properties of a test rig representing the exhaust system of a gas turbine. The experimental results clearly show that the sonic velocity does not change in the present test rig because the droplets are too big to follow the acoustic fluctuations. The critical dimension-less number in this context is the Stokes number, which is mainly determined by the droplet diameter and the acoustic frequency. Furthermore, the experimental results point out that the injected water increases the acoustic damping. It can be concluded from this study that the influence of water injection on the acoustic properties and therefore on the stability behavior is very sensitive to the injection conditions, especially the droplet diameter.
Simulation of Unsteady Turbomachinery Flows Using an Implicitly Coupled Nonlinear Harmonic Balance Method
Authors: Weiss Jonathan M. , Subramanian Venkataramanan , Hall Kenneth C.
Published: May 2012

A nonlinear harmonic balance method for the simulation of turbomachinery flows is presented. The method is based on representing an unsteady, time periodic flow by a Fourier series in time and then solving a set of mathematically steady-state equations to obtain the Fourier coefficients. The steady-state solutions are stored at discrete time levels distributed throughout one period of unsteadiness and are coupled via the physical time derivative and at periodic boundaries. Implicit coupling between time levels is achieved in a computationally efficient manner through approximate factorization of the linear system that results from the discretized equations. Unsteady, rotor-stator interactions are performed to validate the implementation. Results based on the harmonic balance method are compared against those obtained using a full unsteady, time-accurate calculation using moving meshes. The implicitly coupled nonlinear harmonic balance method is shown to produce a solution of reasonable accuracy compared to the full unsteady approach but with significantly less computational cost.
Performance Analysis of a Microturbine Centrifugal Compressor From a Manufacturing Perspective
Authors: Javed A. , Olivero M. , Pecnik R. , van Buijtenen J. P.
Published: May 2012

Gasturbine part manufacturers are often not involved in the design process. This means opportunities to optimize the design including manufacturing issues are missed. This paper presents a performance analysis of a microturbine centrifugal compressor from a manufacturer’s perspective. A one-dimensional (1D) performance modeling tool has been devised to predict the design and off-design performance by sequentially calculating the processes in the impeller, vaneless diffuser and scroll. Part drawings have been used to obtain the geometric information. Comprehensive two-zone modeling has been applied along with a set of meanline empirical loss models integrated in the secondary zone to estimate the entropy gain. This novel methodology has allowed the calculation of individual impeller loss mechanisms instead of predicting them as bulk. Computational Fluid Dynamics (CFD) has also been used to quantify the secondary flow properties and improve the 1D model. The results have been validated through a comparison with the microturbine test data. A sensitivity analysis has been performed to investigate the influence of geometric changes upon compressor performance. The study is important to develop design for manufacturing capability and optimize the designs for cost-effective manufacturing.
Implementation of a Multi Zone Radiation Method in a Low NOx Gas Turbine Combustion Chamber Conceptual Simulator
Authors: Arima Marcos N. , de Sousa Francisco D. A. , da Silva Guilherme A. L. , Branco Natashe N. , Spode Cleber , Leal Elisangela M. , Choze Sergio B.
Published: May 2012

A Multi-Zone Radiation method was employed in a conceptual simulator of gas turbine combustion chamber, which is configured as tubular, reverse flow and no film cooling, and equiped with a lean, premixed, low swirl and low Nox burner. Such simplified simulator is typically used for conceptual trade-off and optimization studies during the pre-design phase, when there is no experimental data available and when the number of runs can reach the order of hundreds or more. In the standard procedure, the convection heat fluxes of the annulus passage and combustion chamber liner are approximated by semi-empirical correlations; the thermal radiation flux is estimated by use of viewing factors between adjacent zones only; the heat conduction is estimated by a one-dimensional model. However, the present paper introduces a more accurate and theoretically rigorous estimation of the radiative heat transfer by adopting a Multi-Zone Method. The numerical code inputs are: the geometry; the flame burnout profile at the combustion region; and the mass fluxes through the dilution holes and the burner. The main outputs of the simulator are the average temperature and heat fluxes by conduction, radiation and convection of each zone. The present modeling strategy enabled the authors to assess the basic design characteristics of a conceptual model of combustion chamber, such as its length, its inlet air temperature, its combustion region equivalence ratio, its flame burnout profile, and its wall emissivities. Finally, it has advantages over the simplified radiation models because it takes into account the effects of temperature, burn-out and composition variations of all zones on each zone and vice-versa.