bluuebunny/crossref_metadata_2025 huggingface dataset:
Applicability of a Multiple-Injection Burner to Dry Low-NOx Combustion of Hydrogen-Rich Fuels
Authors: Asai Tomohiro , Koizumi Hiromi , Dodo Satoschi , Takahashi Hirokazu , Yoshida Shouhei , Inoue Hiroshi
Published: January 2011

To demonstrate the applicability of a “multiple-injection burner” to dry low-NOx combustion of hydrogen-rich fuels, the combustion characteristics of a burner were experimentally investigated. The experimental results show that a burner with a flame lift-off length of 5 mm and a fuel-injection-hole diameter of 1.5 mm achieves low NOx concentration of less than 6 ppm for hydrogen-rich fuels with a wide range of hydrogen concentrations. This finding demonstrates that the burner achieves dry low-NOx combustion of these hydrogen-rich fuels without need for any modification of the burner’s configuration. Moreover, it was found that fuel distribution, fuel composition, flame lift-off length, and fuel-jet velocity have significant effects on the burners’ combustion characteristics.
Ethanol as an Alternative Fuel in Gas Turbines: Combustion and Oxidation Kinetics
Authors: Glaude Pierre A. , Fournet Rene´ , Bounaceur Roda , Molie`re Michel
Published: January 2011

Some research is currently carried out in order to limit CO2 emissions in power generation. Among alternative fuels to natural gas and gasoil in gas turbines, ethanol offers some advantages. However, while the studies dealing with the combustion of methanol are numerous, the research devoted to ethanol flames is rather scarce, in particular with regard to the use in gas turbines. The combustion of ethanol has been theoretically studied by means of a detailed kinetic model well validated in flame conditions. Thanks to quantum chemistry calculations, the reactions necessary to represent low temperature oxidation have been identified and incorporated in the mechanism and their rate parameters have been determined. Several key parameters, such as auto-ignition temperature (AIT), ignition delay times, laminar burning velocities of premixed flames, adiabatic flame temperatures, and formation of pollutants such as CO and NOx have been investigated in an effort to covers gas turbine applications. One has also explored conditions close to ambient in order to address the related safety aspects (leakages of ethanol). To take into account the potential presence of water in ethanol based fuels, similar studies have been performed for ethanol-water-air mixtures. At last, the data have been compared with those calculated for methane combustion. In the low pressure range, the calculated minimum ignition temperatures have been found to be very sensitive to the pressure and the equivalence ratio for lean mixtures. For pressures above 5 bar and moderately lean or rich mixtures, AITs tend to remain close to 440K. Ignition delay times have been calculated in adiabatic conditions at constant pressure. Surprisingly the addition of limited water contents has a very low influence on these results. The addition of water in the ethanol-air mixture decreases slightly the flame temperatures. In the low temperature range, water increases slightly the auto ignition delay times whereas an opposite effect is observed at high temperature. Calculated flame speed has been compared to that deduced from empirical relations found in the literature and the agreement is satisfactory. The formation of CO in pure ethanol flame was always higher than in methane flame while NO formation showed no difference between the amount calculated in ethanol flame and in methane flame. This result is consistent with the slight difference observed between the adiabatic flame temperatures for the two fuels. When increasing the water content up to 10% in ethanol, the laminar velocities become close to those calculated for methane.
Parametric Single Gap Turbine Rim Seal Model With Boundary Generation for Asymmetric External Flow
Authors: Hu¨ning M.
Published: January 2011

In an effort to provide predictions for hot annulus ingestion flows across turbine rim seals into rotor-stator wheel-space cavities, this paper describes a parametric single gap turbine rim seal model, which contains of several different sub- or part-models. Annulus pressure variations are the underlying mechanism driving ingestion. Some of the sub-models are matched to published experimental results. The model results are compared with measurements from different test rigs. The proposed model calculates the annulus boundary conditions based on geometric, mean turbine aerodynamic and performance parameters for the rim seal under consideration. Special attention is paid to the modelling of the flow stagnation upstream of airfoils as a row of half-bodies and the local seal gap discharge coefficient in order to assess the flow distribution through the rim seal. Mixing zones are accounted by a mixing cascade modelling. The peak pressure attenuation behaviour around the seal is considered. Sensitivity studies, e.g. for the impact of annulus boundary layer thickness, are performed.
Towards Cooled Turbine Preliminary Life Prediction via Concurrent Aerodynamic, Thermal and Material Stress Simulations on Conjugate Meshes
Authors: Dawes W. N. , Kellar W. P. , Harvey S. A.
Published: January 2011

An important aspect of the successful design of a cooled turbine blade is trading off performance over a range of disciplines and over a range of conflicting criteria. This in turn implies a need for a speedy & integrated analysis system. The main novelties of the present work are to show: firstly, how the aero, thermal and material stress equations can be conveniently solved on a unified mesh; and secondly, how a very simple but fully integrated process can be constructed for conjugate analysis. As an example of the potential value of this approach, some indicative life predictions for a cooled turbine blade and a shrouded rotor blade will be presented.
Visualization of the Lean Blowout Process in a Model Combustor With a Swirl Cup
Authors: Xie Fa , Huang Yong , Wang Fang , Hu Bin
Published: January 2011

Lean blowout (LBO) limit is an important parameter for aero-engine combustors. There are some LBO correlations used by designers to estimate the LBO fuel/air ratio (FAR). Among these correlations, Lefebvre’s model is employed extensively. In his model, the parameters Vc and m˙A are the combustor volume and inlet air mass flowrate. However, it is argued that the flame volume near LBO is not the whole combustor volume (Vc), and the air involved in combustion near LBO is not the entire inlet air mass flowrate. To find out the mechanisms behind LBO for combustors with swirl cups, a visualization window was designed in a single dome rectangular model combustor with a dual-radial swirl cup, and flame images of the LBO process were recorded. In the experiments, three configurations of dual-radial swirl cups were employed, the differences among them were the variations of the flow areas of the primary and secondary swirlers. The air mass flowrate was about 0.6kg/s. The pressure in the combustor was kept 220KPa under each operation condition. Different flame shapes, flame colors, and flame anchoring locations were observed and recorded, while the LBO fuel/air ratios were also measured. It is found that the visualization window causes the combustor LBO limit to occur at a higher FAR by 8% (i.e. less stability). The flame images indicate that the flame only exists in a small space of the primary zone instead of the whole combustor near LBO. Moreover, the flow area of the primary swirler has the great effect on the LBO FAR. It is confirmed that the air involved in combustion mainly comes from the primary swirler while approaching to LBO condition. Furthermore, a correlation between LBO equivalence ratio and flame area is obtained. If the flame area is correlated to other geometrical and conditional parameters, the accuracy of Lefebvre’s LBO model will be improved further.
Experimental Study on the Influence of Pressure and Temperature on the Burning Velocity and Markstein Number of Jet A-1 Kerosene
Authors: Vukadinovic Vlade , Habisreuther Peter , Zarzalis Nikolaos
Published: January 2011

For accurate prediction of the laminar flame front propagation the influence of the stretch effect on the burning velocity has to be considered. Thus, only burning velocity and Markstein number together give complete information about the laminar flame front behavior. The Markstein number quantifies the influence of the stretch effect on the burning velocity and accordingly, indicates the flame front stability. Due to the analogy between the laminar and the turbulent flames these two parameters, laminar burning velocity and Markstein number must be also considered as essential for describing the turbulent flame front stability [1]. Nevertheless, the experimental data of commercial liquid fuels regarding these parameters are scarce, especially at elevated pressure. Combustion characteristics (laminar burning velocity and Markstein number) of Kerosene Jet A-1 are investigated experimentally in an explosion bomb vessel. For this purpose an optical laser method is employed based on the Mie-scattering of the laser light by smoke particles. Unlike analogous experiments conducted with gaseous fuels [1], the major challenge connected with the present experiments arises from the liquid state of the investigated fuel at ambient condition. Thus, a main difficulty in the present experiments is pre-evaporation of the fuel and achieving of homogeneous gaseous fuel/air mixture prior to ignition. This is solved by mounting a heating system into the walls of the bomb vessel that provides a homogeneous temperature distribution in the vessel and therewith of the mixture itself. The experimental investigation is practically done through the following steps: heating the vessel up to the requested temperature; filling the vessel with an appropriate mixture by the partial pressure method (providing a fuel in gaseous state through the liquid fuel injection and its instantaneous evaporation due to the elevated temperature); attaining an uniform mixture by means of fans; ignition and acquisition of the data; post-processing and data analyses. Within the experimental study influence on the burning velocity and Markstein number of three crucial parameters — initial temperature, initial pressure and mixture composition — are investigated. Observed results for the burning velocity and Markstein number follow the theoretically expected tendencies resulting from the variation of the initial parameters in almost all cases. Where that was not the case the reasons for discrepancies are discussed. Impact of the results on emissions influenced by different operating modes of jet turbines is considered. Due to the common substitution of the kerosene with n-decane in numerical simulations their burning velocities are compared.
Non-Linear Flutter in Fan Stator Vanes With Time Dependent Fixity
Authors: Srivastava R. , Panovsky J. , Kielb R. , Virgin L. , Ekici K.
Published: January 2011

A new mechanism for fan stator vane failure in turbofan engines at high speed and high loading has been identified and reported in this paper. Highly destructive vane failures have been encountered at Honeywell in one of the development fans with composite stator vanes. Measured data indicated nonlinear high amplitude vibratory response in fan stator vanes on stall side of the fan map at high speeds. Analysis showed that under certain vane steady loading vane fixity at hub could change, significantly reducing the vane natural frequency. At lower natural frequency the vane was found to be aeroelastically unstable and calculated response exhibited behavior observed during failure. An engine test was conducted to validate the role of hub fixity in vane failures. Test results showed failure to be a self-excited phenomenon and not driven by an external source of excitation. It was also shown that failures occur in vanes that are not rigidly fixed, validating the role of hub fixity in vane failures. Test results along with the analysis confirm the role of time dependent hub fixity leading to the highly destructive flutter responsible for vane failures.
Study of the Flow in a Vaneless Diffuser at Part Speed Operating Conditions
Authors: Hazby Hamid R. , Xu Liping , Schleer Matthias
Published: January 2011

The aim of the current paper is to investigate the evolution of the flow in the vaneless diffuser of a scaled-up turbocharger compressor, using the steady-state viscous calculations. First, the predicted flow patterns are compared with the detailed LDA and probe measurements, acquired at different operating conditions. Then, the numerical results are analyzed further to understand the origins of the flow features, observed in the measurements. It is shown that despite the complexity of the flow, the main flow features in the vaneless diffuser can be predicted at different operating conditions, using a simple mixing length turbulence model. It is also demonstrated that in the compressor studied, a vortical flow feature develops near the diffuser shroud at high flow coefficients. This flow feature is generated by strong pressure variations downstream of the impeller trailing edge, and disappears at low flow coefficients, where the static pressure gradient becomes almost radial in the vaneless diffuser.
Effect of Cooling Liner on Acoustic Energy Absorption and Flame Response
Authors: Bhayaraju Umesh , Schmidt Johannes , Kashinath Karthik , Hochgreb Simone
Published: January 2011

Gas turbine combustors with lean combustion injectors are prone to thermo-acoustic/combustion instabilities. Several passive techniques have been developed to control combustion instabilities, such as using Helmholtz resonators or viscous dampers using perforated liners that have potential for broadband acoustic damping. In this paper the role of single-walled cooling liners is considered in the damping of acoustic waves and on the flame transfer function in a sample bluff-body burner. Three liner geometries are considered: no bias flow (solid liner), normal effusion holes, and grazing effusion holes at 25° inclination. Cold flow experiments with speaker forcing are carried out to characterise the absorption properties of the liner and compared with an acoustic network model. The results show that whereas the bulk of the acoustic losses is due to the vortex recirculation zones, the liners contribute significantly to the absorption over a wide area of the frequency range. The flame transfer function gain is measured as a function of bias flow for a given operating condition of the burner. The experiments show that for the geometry considered, the global flame transfer function is little affected by cooling except in the case of the normal flow holes. Further analysis shows that whereas the total flame transfer function is not affected, the flame heat release becomes more spatially distributed along the axial length, and a 1D flame response shows distinct modes corresponding to the modal heat release locations.
Identification of Flame Transfer Functions From LES of a Premixed Swirl Burner
Authors: Tay Wo Chong Luis , Komarek Thomas , Kaess Roland , Fo¨ller Stephan , Polifke Wolfgang
Published: January 2011

Large eddy simulations of compressible, turbulent, reacting flow were carried out in order to identify the Flame Transfer Function (FTF) of a premixed swirl burner at different power ratings. The Thickened Flame model with one step kinetics was used to model combustion. Time-averaged simulation results for inert and reacting flow cases were compared with experimental data for velocity and heat release distribution with good agreement. Heat losses at the combustor walls were found to have a strong influence on computed flame shapes and spatial distributions of heat release. For identification of the FTF with correlation analysis, broadband excitation was imposed at the inlet. At low power rating (30 kW), measured and computed FTFs agree very well at low frequencies (corresponding to Strouhal numbers St < 4), showing a pronounced maximum of the gain at St ≈ 2. At higher frequencies, where the flame response weakens, the agreement between experiment and computation deteriorates, presumably due to decreasing signal-to-noise ratio. At higher thermal power (50 kW), a high-frequency instability developed during the simulation runs, resulting in poor overall signal-to-noise ratio and thus to unsatisfactory prediction of the gain of the flame transfer function. The phase of the FTF, on the other hand, was predicted with good accuracy up to St < 5. An analytical expression for the FTF, which models the flame dynamics as a superposition of time-delayed responses to perturbations of mass flow rate and swirl number, respectively, was found to match the experimental results.
A Data Filter for Identifying Steady-State Operating Points in Engine Flight Data for Condition Monitoring Applications
Authors: Simon Donald L. , Litt Jonathan S.
Published: January 2011

This paper presents an algorithm that automatically identifies and extracts steady-state engine operating points from engine flight data. It calculates the mean and standard deviation of select parameters contained in the incoming flight data stream. If the standard deviation of the data falls below defined constraints, the engine is assumed to be at a steady-state operating point, and the mean measurement data at that point are archived for subsequent condition monitoring purposes. The fundamental design of the steady-state data filter is completely generic and applicable for any dynamic system. Additional domain-specific logic constraints are applied to reduce data outliers and variance within the collected steady-state data. The filter is designed for on-line real-time processing of streaming data as opposed to post-processing of the data in batch mode. Results of applying the steady-state data filter to recorded helicopter engine flight data are shown, demonstrating its utility for engine condition monitoring applications.
Flow-Field and Flame Dynamics of a Gas Turbine Model Combustor During Transition Between Thermo-Acoustically Stable and Unstable States
Authors: Arndt Christoph M. , Steinberg Adam M. , Boxx Isaac G. , Meier Wolfgang , Aigner Manfred , Carter Campbell D.
Published: January 2011

Laser-based and optical measurements of a gas turbine (GT) model combustor undergoing transitions between a thermo-acoustically stable and unstable state are presented. Planar laser-induced fluorescence of the OH radical, OH chemiluminescence and the planar three-component velocity field were simultaneously measured at a sustained repetition rate of 5 kHz. The combustor was operated with a lean, technically premixed CH4/air flame at ambient pressure that transitioned unpredictably between a thermo-acoustically unstable (‘noisy’) state and a state without pulsations (‘quiet’ state). The transition from the noisy to the quiet state was correlated with the lift-off of the flame from the burner nozzle and a subsequent stabilization of the flame above the nozzle. During the transition from the quiet to the noisy state, the flame reattached to the nozzle. It was observed that the transitions occurred consistently at a particular phase of the thermo-acoustic cycle. The axial velocity fields indicated that the reattachment of the flame was assisted by an increase of the backflow velocity in the inner recirculation zone.
Extended Instrumentation and Model Calibration for a Small Micro-Turbine
Authors: Bakalis Diamandis P. , Stamatis Anastassios G.
Published: January 2011

In this paper the calibration of a model representing a real small turbojet engine is presented. The development of the model was based on a modular general approach using adaptive modeling principles. Calibration of the model was implemented by exploiting its adaptive features and using part of the extended measurement set provided for the engine instrumentation. Certain problems regarding data acquisition were pointed out and the source for their existence was discussed. Validation of the model was performed through comparison of predicted and experimental data. Although initial results of the simulation may be considered promising it became evident the need for further model refinements. The instrumented engine as well as the simulation model developed will be valuable educational tools for the students in our department.
Uncertainty Analysis for Large-Scale Industrial Radial Compressors
Authors: Bu¨che Dirk , Beetz Michael , Ribi Beat
Published: January 2011

This paper analyzes the influence of uncertainties on large-scale industrial radial compressors. The goal is to verify the robustness of new compressor designs towards operational and geometrical uncertainties. Key uncertainties for compressors are identified. Detailed measurements are conducted and modeled by probability distributions. These models then serve as input for the uncertainty analysis. For the uncertainty analysis different techniques are compared. The focus is on computationally efficient techniques, i.e., the required number of CFD simulations for the uncertainty analysis should be minimal. Promising methods are the Probabilistic Collocation Method and techniques that use response surface models in combination with the i-optimal design approach for generating sample points. Pure Monte Carlo simulations are not practical as they are too time-consuming. The key uncertainty considered here is the surface roughness. The effect is modeled with a commercial CFD RANS solver. The uncertainty analyzes show a performance decrease and variation for roughness values above the limit of hydraulically smooth surfaces.
Towards Investigation of Combustor Turbine Interaction in an Integrated Simulation
Authors: Klapdor E. Verena , Pyliouras Stavros , Eggels Ruud L. G. M. , Janicka Johannes
Published: January 2011

Modelling combustor turbine interaction is to be performed in an integrated simulation of a combustion chamber and the nozzle guide vane of a jet engine. Starting with an incompressible pressure based combustion CFD code, two steps are required to obtain a code that is suitable for performing such calculations. Firstly, the SIMPLE algorithm needs to be extended to all-Mach-number flows. Secondly the solution algorithm needs to be modified to deal with combustion. This paper presents the first of these steps. A solver has been developed which is capable of computing both incompressible and transonic flows. Validation of modelling compressible viscous flow is performed using experimental data. The suitability of the algorithm to highly complex geometry is demonstrated on real engine nozzle guide vane geometry and results are compared to the results of other solvers.
Film Cooling Calculations With an Iterative Conjugate Heat Transfer Approach Using Empirical Heat Transfer Coefficient Corrections
Authors: Dhiman Sushant , Yavuzkurt Savas
Published: January 2011

An iterative conjugate heat transfer technique has been developed to predict the temperatures on film cooled surfaces such as flat plates and turbine blades. Conventional approaches using a constant wall temperature to calculate heat transfer coefficient and applying it to solid as a boundary condition can result in errors around 14% in uncooled blade temperatures. This indicates a need for conjugate heat transfer calculation techniques. However, full conjugate calculations also suffer from inability to correctly predict heat transfer coefficients in the near field of film cooling holes and require high computational cost making them impractical for component design in industrial applications. Iterative conjugate heat transfer (ICHT) analysis is a compromise between these two techniques where the external flow convection and internal blade conduction are loosely coupled. The solution obtained from solving one domain is used as boundary condition for the other. This process is iterated until convergence. Flow and heat transfer over a film cooled blade is not solved directly and instead convective heat transfer coefficients resulting from external convection on a similar blade without film cooling and under the same flow conditions are corrected by use of experimental data to incorporate the effect of film cooling in the heat transfer coefficients. The effect of conjugate heat transfer is taken into account by using this iterative technique. Unlike full conjugate heat transfer (CHT) the ICHT analysis doesn’t require solving a large number of linear algebraic equations at once. It uses two separate meshes for external convection and blade conduction and thus problem can be solved in lesser time using less computational resources. A demonstration of this technique using a commercial CFD solver FLUENT is presented for simulations of film cooling on flat plates. Results are presented in form of film cooling heat transfer coefficients and surface temperature distribution which are compared with results obtained from conventional approach. For uncooled surfaces, the deviations were as high as 3.5% between conjugate and conventional technique results for the wall temperature. For film cooling simulations on a flat plate using the ICHT approach showed deviations up to 10% in surface temperature compared to constant wall temperature technique for a high temperature difference case and 3% for a low temperature difference case, since surface temperature is not constant over the surface when conjugate heat transfer is considered. Results show that conjugate heat transfer effect is significant for film cooling flows involving high temperature differences for the current blade materials and application of film cooling correction obtained from experimental data is very useful in obtaining realistic blade temperatures.
Experimental and Numerical Study of Steady and Modulated Transverse Jets at Low Blowing Ratios
Authors: Bidan Guillaume , Bouladoux Pierre-Emmanuel , Oertling Jeremiah E. , Nikitopoulos Dimitris E.
Published: January 2011

The effects of jet flow pulsation were investigated in the case of a fully modulated vertical jet in crossflow over a flat plate using Mie scattering visualizations, hotwire anemometry and Large Eddy Simulations (LES). A preliminary steady state study was conducted over a wide range of blowing ratios to provide a baseline comparison to pulsed results in terms of vortical structures and performance. Based on observation of the vortical structures and hotwire signatures, two distinct regimes were identified separated by a transitional region. LES using the dynamic Smagorinsky sub-grid model were carried out to provide additional insights on vortical structures formation mechanisms and their effect on heat transfer results, showing good agreement with the experimental observations and measurements. The influence of the pulsing parameters such as mean, high and low blowing ratios, forcing frequency and duty cycle was explored in terms of jet coverage metrics and spanwise adiabatic effectiveness. Average blowing ratios of 0.250, 0.350 and 0.450, duty cycles of 25, 50 and 70% and forcing frequencies of St∞ = 0.008, 0.016, 0.079, and 0.159 were investigated. While in most of the cases, forced jets show a decrease in average performance compared to steady state configurations, some improvement was found in part of the forcing cycle. Vortical structures formed at the jet onset are consistent with the classification given by previous studies in terms of stroke-ratio and high blowing ratio over an overlapping range of conditions. The dynamics of the vortical structures formed at the pulse rise are highly responsible for the decrease in performance observed under forced conditions.
The Impact of Density Ratio on the Primary Atomization of a Turbulent Liquid Jet in Crossflow
Authors: Herrmann Marcus , Arienti Marco , Soteriou Marios
Published: January 2011

Atomizing liquids by injecting them into crossflows is a common approach in gas turbines and augmentors. Much of our current understanding of the processes resulting in atomization of the jets, the resulting jet penetration and spray drop size distribution have been obtained by performing laboratory experiments at ambient conditions. Yet, operating conditions under which jets in crossflows atomize can be far different from ambient. Hence, several dimensionless groups have been identified that are believed to determine jet penetration and resulting drop size distribution. These are usually the jet and crossflow Weber and Reynolds numbers and the momentum flux ratio. In this paper we aim to answer the question of whether an additional dimensionless group, the liquid to gas density ratio must be matched. To answer this question, we perform detailed simulations of the primary atomization region using the Refined Level Set Grid (RLSG) method to track the motion of the liquid/gas phase interface. We employ a balanced force, interface projected curvature method to ensure high accuracy of the surface tension forces, use a multi-scale approach to transfer broken off, small scale nearly spherical drops into a Lagrangian point particle description allowing for full two-way coupling and continued secondary atomization, and employ a dynamic Smagorinsky large eddy simulation (LES) approach in the single phase regions of the flow to describe turbulence. We present simulation results for a turbulent liquid jet (q = 6.6, We = 330, Re = 14,000) injected into a gaseous crossflow (Re = 740,000) analyzed under ambient conditions (density ratio 816) experimentally by Brown and McDonnel (2006). We compare simulation results obtained using a liquid to gas density ratio of 10 to those obtained using a density ratio of 100, a value typical for gas turbine combustors. The results show that the increase in density ratio results in a notice-able increase in liquid core penetration with reduced bending in the crossflow and spreading in the transverse directions. The post-primary atomization spray, however, penetrates further in both the jet and transverse direction. Results further show that penetration correlations for the windward side trajectory commonly reported in the literature strongly depend on the value of threshold probability used to identify the leading edge. Correlations based on the penetration of the jet’s liquid core center of mass, on the other hand, can provide a less ambiguous measure of jet penetration. Finally, the increase in density ratio results in a decrease in wavelength of the most dominant feature associated with a traveling wave along the jet as determined by proper orthogonal decomposition.
Novel IGV Designs for Centrifugal Compressors and Their Interaction With the Impeller
Authors: Mohseni Arman , Goldhahn Erik , Van den Braembussche Rene´ A. , Seume Joerg R.
Published: January 2011

In centrifugal compressors, variable inlet guide vanes (IGVs) are used to control the mass flow rate with negligible change in pressure ratio and shaft speed. The efficient operation of IGVs is limited to the range of aerodynamic stability of their vane profiles. Thin symmetric profiles, which are usually used, tend to exhibit flow separation already at low setting angles, resulting in a rapid decrease of the global efficiency. Three different guide vane profiles including a symmetric reference, a two-piece tandem profile with variable angle, and an s-cambered, together with two auxiliary profiles were considered. These variants were numerically and experimentally investigated at different setting angles, covering negative and positive inlet swirl and at different operating points. The results show that tandem and s-cambered vanes have superior aerodynamic performance in comparison with the symmetric reference profile and extend the operating range of the compressor over which the efficiency remains high. The tandem profile shows better aerodynamic performance than the s-cambered profile at negative inlet swirl, while the asymmetric s-cambered profile offers an extended range of high efficiency at positive preswirl. Considering manufacturing requirements and cost, the s-cambered profile is preferred for applications with positive preswirl.
Numerical Investigation on the Labyrinth Seal Design for a Low Flow Coefficient Centrifugal Compressor
Authors: Wang Zhiheng , Xu Liqun , Xi Guang
Published: January 2011

The leakage flow across the shroud of a centrifugal compressor impeller has an important effect on the compressor’s performance, in particular, in the low flow coefficient compressor. This paper presents the three-dimensional CFD simulations and the Radial Basis Function (RBF) model to investigate the aerodynamic performance of the labyrinth seal as well as the low flow coefficient centrifugal impeller. The CFD simulations are performed on the computational domain consisting of the labyrinth seal and the impeller. The relationship between the leakage loss coefficient and the isentropic efficiency is indicated. With the application of the RBF model, the global sensitivity analysis to the seal geometric design parameters is carried out, and the geometry of the labyrinth seal is optimized. The leakage of the optimized labyrinth seal is reduced remarkably and the impeller’s isentropic efficiency improved by 2% in a wide operating range.
Theoretical and Experimental Study on Stability of Rotor System With Cylindrical Bearing and Elliptical Bearing
Authors: Wang Yongliang , Liu Zhansheng , Zhang Guanghui , Sun Liquan
Published: January 2011

Dynamic characteristics of a 600MW steam turbine rotor model supported by cylindrical bearings and elliptical bearings were investigated respectively. Differences between the linear and nonlinear characteristics of rotor-bearing systems were studied by numerical simulations, and the performances of rotor systems using different bearings were also presented. Dynamic tests were performed on the 600MW turbine generator group model test rig, while sustained by different types of bearings, to study the oil whirl and whip phenomenon. Comparisons of the numerical results with experimental data show that the nonlinear model is more accurate than the linear model, and the elliptical bearing has the advantage of better dynamic stability over cylindrical bearings.
Numerical Study of the Stagger Angle Effects in Forward Swept Axial Compressor Rotor Passages
Authors: Ramakrishna P. V. , Govardhan M.
Published: January 2011

In the present numerical work, an axial compressor rotorstator stage is studied for three rotor sweep configurations (Unswept, 20° Tip chordline swept and 20° Axially swept) and for three stagger configurations (0°, + 3° and +5°). CFD results with the unswept rotor and the 20° TCS rotor are well validated with the experiments for the designed stagger angle case. Results show that sections near the tip are subjected to lower incidences and the opposite effect is observed with increasing the stagger angle. The included sweep and dihedral schemes in axial sweeping resulted in the AXS rotor to undergo high degree of variations in the performance with stagger angle. TCS passages are subjected to low loss levels when compared with the UNS rotor at the designed stagger. This ability is found to diminish with increase in the stagger angle. AXS rotor passages are subjected to the low loss levels always. The idea of employing positive dihedral in addition to forward sweeping is thus thoughtful with regard to the stagger variations as well. As the stagger angle is increased, the tipward centrifugation of the boundary layer fluid is reduced, but the hub endwall boundary layer migration is observed to increase towards the suction side corner for some rotors resulting in corner vortex like structure towards the hub trailing edge. These secondary flows are less with the true sweeping. The separation point is shifted to upstream locations on the blade at higher stagger angles due to low streamwise velocities and higher adverse pressure gradients.
A Computational Study on the Effect of Angles of Attack on a Double-Cone Type Supersonic Inlet With Bleeding System
Authors: Ryu Kyung Jin , Lim Seol , Kim Sang Dug , Song Dong Joo
Published: January 2011

The flow characteristics on a supersonic inlet with bleeding system at various angles of attack are studied by using computational 3D turbulent flow analysis. A turbulent CSCM compressible upwind flux difference splitting Navier-Stokes method with k-w turbulence model is used to compute the inlet flowfields. MPICH-2.0 library and PC-cluster system are used to reduce computational times. Distortion and average of total pressure recovery at the AIP (aerodynamic interface plane) are used as evaluation criteria of inlet performance. The flow characteristics at zero of angle of attack of double-cone type supersonic inlet without and with bleeding system have been compared. Without bleeding system inlet with the strong SBLI (shock/boundary-layer interaction) induces slow flow recovery near the throat and produces very thick boundary layer downstream. But the bleeding system successfully removes the low energy flow from the boundary layer near the throat. As the angle of attack at the AIP because large, we can see more non-uniform flow field, and the non-uniform flow field is the major aggravating factor of inlet performance.
Heat Transfer and Pressure Drop in Combustor Cooling Channels With Combinations of Geometrical Elements
Authors: Kunstmann Se´bastien , von Wolfersdorf Jens , Ruedel Uwe
Published: January 2011

An investigation was conducted to assess the thermal performance of 90° ribs, low and high W-shaped ribs, and combinations of low W-shaped ribs with high W-shaped ribs and with dimples in a rectangular channel with an aspect ratio (W/H) of 2:1. The blockage ratios (e/Dh) were 0.02 with the 90° ribs and the low W-shaped ribs and 0.06 with high W-shaped ribs. The rib pitch-to-height ratio (P/e) were 10 and 20. The channel height-to-dimple diameter (H/D) was 16.67; the dimple depth-to-dimple diameter (δ/D) was 0.3. The ribs and the dimples were located on one channel wall (side W). Furthermore, W-shaped ribs and 90° ribs with e/Dh = 0.027 and P/e = 10 were also individually investigated in a test channel with 1/4 of its cross section blocked. The Reynolds numbers investigated (Re > 100k) are typical for combustor liner cooling configurations in gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The different configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement rates are obtained by a combination of W-shaped ribs with P/e = 10 and e/Dh = 0.06 and W-shaped ribs with P/e = 10 and e/Dh = 0.02. The best thermal performance is achieved by regularly spaced lower W-shaped ribs and by a compound roughness of regularly spaced W-shaped ribs and dimples at Re below and above 300,000, respectively.
Conjugate Heat Transfer Numerical Validation and PSE Analysis of Transonic Internally-Cooled Turbine Cascade
Authors: Yan Peigang , Wang Zhenfeng , Han Wanjin
Published: January 2011

Conjugate heat transfer numerical simulation of a transonic internal cooled turbine vane is carried out with a third-order accuracy TVD (Total Variation Diminishing) scheme and multi-block structured grids using the code developed in this paper. Comparison between results of commercial CFD codes with several turbulence models and those of this code show that it is incorrect of computational codes to predict the thermal boundary layer with traditional turbulence models, and that the turbulence models considering transitional phenomenon is able to acquire better accurate heat transfer in thermal boundary layer despite of certain deficiencies yet. The predicted distributions of aerodynamic parameters agree well with the experiments except for the temperature and heat transfer coefficient over the profile surface, which are largely different from the measured data. Results by Star-CD with V2-F model meet the same problem. Results by the code of this paper are close to those by CFX with K-ω-SST-ML transition model. Adopting transition model of Menter & Langtry (Shear-Stess-Transition model) gives the best results by adjusting the transition onset momentum thickness Reynolds number and the inlet viscosity ratio, especially for the mid part of the suction side where the validation accuracy is of a serious shortage by traditional turbulence model. It is proved in this paper that commercial codes have the ability to simulate transition process and thermal boundary layer accurately, but the designer’s experience is of utmost importance. Robust transition turbulence model should be developed further. PSE stability analysis equation and e-N prediction method are both integrated in this paper. It is concluded that boundary layer stability analysis by PSE method can be applied to the prediction of the transition onset without too many experiences and is able to define the empirical turbulence parameters for the accurate simulation of thermal boundary layer for any airfoil, such as the very important transition onset momentum thickness Reynolds number.
A Finite Element Approach of Turbines in Contact Following a Shaft Failure Event
Authors: Capozzi P. , Psarra A. , Pachidis V. , Pilidis P.
Published: January 2011

The shaft failure of a gas turbine engine can be considered as a potentially hazardous event. Since the turbine rotor becomes suddenly decoupled from the compressor, it will rapidly accelerate and disc bursting or blade shedding may be possible outcomes. Blade tangling occurring between the turbine blades and the downstream NGV stator vanes can be an effective mean to prevent dangerous over-speed conditions. Since experimental test arrangements are considered to be time and cost in-effective, impact simulations can aid the understanding of the main phenomena involved in the event and help the designer in reducing the possibility of dangerous over-speed conditions. This paper represents a first attempt to model the impact between turbines following a shaft failure event. The contribution of this paper is the modeling approach of turbines in contact after a shaft failure. The results of the impact simulation in terms of rotational speed, frictional torque and frictional energy are presented, while some basic checks of the FEA model are carried out to assess the plausibility of the derived results.
Enhancement of a Detailed Mechanism of Propene
Authors: Braun-Unkhoff Marina , Slavinskaya Nadezhda , Aigner Manfred
Published: January 2011

Propene (C3H6) is an important constituent of practical hydrocarbons fuels and an important intermediate in the combustion of these fuels. Furthermore, synthetic gases such as biogenic gas mixtures not only consist of hydrogen, methane, and carbon monoxide, but also of small amounts of higher hydrocarbons, in different proportions, including propene. In the present work, a detailed propene sub-model was constructed starting from an in-house reaction model (DLR-LS) shown previously to describe major combustion properties including PAH and soot formation for several different fuel air flames. The predictive capability of the detailed propene submodel concerning laminar flame speed and ignition delay time of different propene-oxygen mixtures will be discussed. These data are needed to describe the heat release and to predict the possibility of a flashback. From these comparisons, it is concluded that the extended propene sub-model is capable to predict combustion properties of propene-oxygen gas mixtures.
Nonlinear Dynamic Analysis of a Flexible Rod Fastening Rotor Bearing System
Authors: Liu Heng , Li Chen , Wang Weimin , Qi Xiaobin , Jing Minqing
Published: January 2011

This paper is concerned the stability and bifurcation of a flexible rod-fastening rotor bearing system (FRRBS). Here the shaft is considered as an integral or continuous structure and be modeled by using Timoshenko beam-shaft element which can take the effects of axial load into consideration. And using Hamilton’s principle, model tie rods distributed along the circumference as a constant stiffness matrix and an add-moment which caused by unbalanced pre-tightening forces. Then the model is reduced by a component mode synthesis method, which can conveniently account for nonlinear oil film forces of the bearing. This study focuses on the influence of nonlinearities on the stability and bifurcation of T periodic motion of the FRRBS subjected to the influence of mass eccentricity. The periodic motions and their stability margin are obtained by shooting method and path-following technique. The local stability and bifurcation behaviors of periodic motions are obtained by Floquet theory. The results indicate that mass eccentricity and unbalanced pre-tightening forces of tie rods have great influence on nonlinear stability and bifurcation of the T periodic motion of system, cause the spillover of system nonlinear dynamics and degradation of stability and bifurcation of T periodic motion.
Combustion Under Flue Gas Recirculation Conditions in a Gas Turbine Lean Premix Burner
Authors: Burdet Andre´ , Lachaux Thierry , de la Cruz Garci´a Marta , Winkler Dieter
Published: January 2011

An EV burner as installed in Alstom’s dry low NOx gas turbines was experimentally investigated under different Flue Gas Recirculation (FGR) and engine conditions. FGR enables the reduction of the high exhaust volume flow while significantly increasing the exhaust CO2 concentration. This may substantially improve the post-combustion capture of CO2. However, FGR introduces consequent changes in the gas turbine combustion process mainly because of the oxygen depletion and CO2 increase within the oxidizer. N2 and CO2 were mixed with air in order to obtain at the burner inlet a synthetic oxidizer mixture reproducing O2 and CO2 levels spanning different FGR levels of interest for engine operation. In addition, various degrees of unmixedness of the reactive mixture were investigated by varying the ratio of fuel injected at different port locations in the investigated burner set. Stable operation was achieved in all tested conditions. The lean premix flame shifts downstream when O2 is depleted due to the decrease of the reactivity, although it always stays well within the combustion chamber. The potential for NOx reduction when using FGR is demonstrated. Changes of the NOx formation mechanism are described and compared to the experimental data for validation. Unmixedness appears to be less detrimental to NOx emission when under high FGR ratio. However, CO emission is shown to increase when FGR ratio is increased. Meanwhile, with the present gas turbine combustor, the CO emission follows the equilibrium limit even at high FGR ratio. Interestingly, it is observed that when the burner inlet pressure is increased (and consequently the inlet burner temperature), the increase of CO emission due to FGR is lowered while the NOx emission stays at a very low level. This present an argument for using a higher cycle pressure in gas turbines optimized for FGR operation.