bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comprehensive Fuel Spray Model for High Pressure Fuel Injectors
Authors: Micklow Gerald J. , Ankem Krishna , Abdel-Salam Tarek
Published: August 2009

Understanding the physics and chemistry involved in spray combustion, with its transient effects and the inhomogeneity of the spray is quite challenging. For efficient operation of both internal combustion and gas turbine engines, great insight into the physics of the problem can be obtained when a computational analysis is used in conjunction with either an experimental program or through published experimental data. The main area to be investigated to obtain good combustion begins with the fuel injection process and an accurate description of the mean diameter of the fuel particle, injection pressure, drag coefficient, rate shaping etc must be defined correctly. This work presents a methodology to perform the task set out in the previous paragraph and uses experimental data obtained from available literature to construct a semi-empirical numerical model for high pressure fuel injectors. A modified version of a multidimensional computer code called KIVA3V was used for the computations, with improved sub-models for mean droplet diameter, injection pressure, injection velocity, and drop distortion and drag. The results achieved show good agreement with the published in-cylinder experimental data for a Volkswagen 1.9 L turbo-charged direct injection internal combustion engine under actual operating conditions. It is crucial to model the spray distribution accurately, as the combustion process and the resulting temperature distribution and pollutant emission formation is intimately tied to the in-cylinder fuel distribution. The present scheme has achieved excellent agreement with published experimental data and will make an important contribution to the numerical simulation of the combustion process and pollutant emission formation in compression ignition direct injection engines and gas turbine engines.
Predictions of Thermal and Hydrodynamic Characteristics of a Single Circular Micro-Jet Impinging on a Flat Plate
Authors: Le´on De Paz Marcel , Jubran B. A.
Published: August 2009

Jet impingement cooling remains one of the key methods in various high-end cooling applications as it can induce higher heat transfer rates. The objective of this preliminary investigation is to shed some light on micro-impingement cooling and assess the accuracy for a future 3-dimensional turbine blade model. For the purpose of this study, several micro-jet impingement cases are modeled in Gambit and iterated with Fluent. The reference model consists of a single 500μm cylindrical nozzle impinging on a constant temperature flat plate. Conducive results were found on the effects of turbulence model, Reynolds number, and H/D ratio for the Nusselt distribution on the flat plate. The Reynolds numbers iterated were: 2000, 3000, 4000, 5000, and 6000. The different H/D ratios modeled were: 6, 5, 4, 3, 2, 1. In general, it was observed that a higher Reynolds number increased the heat transfer on the plate, but the jet to target spacing had no significant impact on it. All results were validated via comparison with several published experimental data, the deviation margins indicated a good agreement.
Influence of Stator-Rotor Interaction on the Aerothermal Performance of Recess Blade Tips
Authors: Mischo Bob , Burdet Andre´ , Abhari Reza S.
Published: August 2009

This paper investigates the influence of stator-rotor interaction on the stage performance of three blade tip geometries. A reference flat tip is used to assess two different recess blade geometries. The study is made in the context of the realistic turbine stage configuration provided by the ETHZ 1.5 stage LISA turbine research facility. This numerical investigation describes the details of unsteady recess cavity flow structure and confirms the beneficial effects of the improved recess geometry over the flat tip and the nominal recess design both in terms of stage efficiency and tip heat load. The tip flow field obtained from the improved recess design combines the advantages of a nominal recess design (aerodynamic sealing) and the flat tip configuration. The turbine stage capacity is almost unchanged between the flat tip and the improved recess tip cases, which simplifies the design procedure when using the improved recess design. Overall heat load in the improved recess case is reduced by 26% compared to the flat tip and by 12% compared to the nominal recess. A key finding of this study is the difference in effects of the upstream stator wake on the recess cavity flow. Where cavity flow in the nominal design is only moderately influenced, the improved recess cavity flow shows enhanced flow unsteadiness. The tip Nusselt number from a purely steady state prediction in the nominal recess case is nearly identical to the time-average prediction. The improved design shows a 6% difference between steady state and time average tip Nusselt number. This is due to the strong influence of the wake passing on the recess cavity flow. In fact, the wake enhances a small flow difference at the leading edge of the recess cavity between the nominal and improved recess cavities, which results in a completely different flow field further downstream in the recess cavity.
Turbulence Model Assessment for Conjugate Heat Transfer in a High Pressure Turbine Vane Model
Authors: Ledezma Gustavo A. , Laskowski Gregory M. , Tolpadi Anil K.
Published: August 2009

An assessment of steady state Reynolds Averaged Navier-Stokes (RANS) models has been undertaken for conjugate heat transfer of an internally cooled high-pressure turbine vane with and without film cooling. The assessment includes near wall treatment and different 2-equation Eddy Viscosity Models (EVM) and 6-equation Reynolds Stress Models (RSM) models. The present study was conducted using CFX v11.0 with unstructured tetrahedral meshes with near wall prism layers. The validation cases are the 1983 NASA C3X internally cooled vane and the 1988 NASA C3X internally and film cooled vane. Internal cooling for both cases is achieved with ten radial cooling channels of constant cross-sectional area. Film cooling is achieved for the same airfoil geometry but with three separately fed upstream plenums feeding various rows of film cooling holes. Predictions obtained with the different modeling strategies are compared to documented metal surface pressures and temperatures and the differences are discussed. A conjugate heat transfer assessment is made using the vane Biot number. In general good agreement with experimental data is obtained for wall integration meshes with the k-ω and SST turbulence models.
Effects of Combustor Geometry on the Flowfields and Flame Properties of a Low-Swirl Injector
Authors: Cheng R. K. , Littlejohn D.
Published: August 2009

The Low-swirl injector (LSI) is a novel dry-low NOx combustion method that is being developed for gas turbines to burn a variety of gaseous fuels including natural gas, low-Btu fuels, syngases and hydrogen. Its basic principle is described by a top level analytical model that relates the flame position to the flowfield similarity parameters and the turbulent flame speed correlation. The model was based on experimental measurements in open laboratory flames. It has been useful for guiding hardware development. As the LSI is being adapted to different engine configurations, one open question is how the combustor geometry and size affect its basic operating principle. The objective of this paper is to investigate these effects by conducting Particle Image Velocimetry (PIV) measurements in open and enclosed flames produced by a 6.35 cm diameter LSI using two quartz cylinders of 15.5 and 20 cm diameter to simulate the combustor casing. Results from 18 methane-air flames show that the enclosures do not alter the flame properties or the nearfield flow structures. The differences occur mostly in the farfield where the tighter enclosure deters the formation of a weak recirculation zone. The enclosure effects on hydrogen and hydrogen-methane flames were studies using the 20 cm cylinder. The results show that the outer recirculation zone generated at the corner of the dump plane promotes the formation of attached flames. However, the properties and nearfield flow features of the attached flames are similar to those of the lifted flames. At higher stoichiometries, the attached flame collapses to form a compact disc shaped flame that has very different flowfield structures. These results show that the enclosure effects on the LSI are strongly coupled to the fuel type and dump plane geometry but are less dependent on the enclosure size. These observations will provide the basis for developing computational methods that can be used as design tools for LSI adaptation.
Application of a 3D Blade Design Method for Supersonic Vaneless Contra-Rotating Turbine
Authors: Fang Xiang-Jun , Liu Si-Yong , Wang Ping , Zhang Wei-Jun
Published: August 2009

A new 3D blade design method basing on S1 surface, which is approximate the true three-dimensional flows in machinery, is presented in the paper to design the rotor blades of supersonic highly loaded vaneless contra-rotating turbine (abbr. VCRT) with large meridian passage divergence angle. The basic principle of 3D profile design is introduced. The high pressure rotor of highly loaded VCRT was designed with exit Mach number 1.33 and meridian channel divergence angle 37.3°. The results of 3D numerical simulation indicated that the distributions of dynamics parameters are well-proportioned and there are few separated flows in VCRT. Its stagnation efficiency reaches 92.3%. The results of CRT design showed that the 3D profile design method is more precise and effective than the conventional 2D cylinder method for turbine blades with large meridian expansion passage and sophisticated streamlines because the 3D features of flows are appropriately considered.
Axial Turbine Blade Aerodynamic Optimization Using a Novel Multi-Level Genetic Algorithm
Authors: O¨ksu¨z O¨zhan , Akmandor I˙brahim Sinan
Published: August 2009

In this paper, a new multiploid genetic optimization method handling surrogate models of the CFD solutions is presented and applied for single objective turbine blade aerodynamic optimization problem. A fast, efficient, robust, and automated design method is developed to aerodynamically optimize 3D gas turbine blades. The design objectives are selected as maximizing the adiabatic efficiency and torque so as to reduce the weight, size and cost of the gas turbine engine. A 3-Dimensional steady Reynolds Averaged Navier Stokes solver is coupled with an automated unstructured grid generation tool. The solver is verified using two well known test cases. Blade geometry is modeled by 36 design variables plus the number of blades variable in a row. Fine and coarse grid solutions are respected as high and low fidelity models, respectively. One of the test cases is selected as the baseline and is modified by the design process. It was found that the multiploid genetic algorithm successfully accelerates the optimization at the initial generations for both optimization problems, while preventing converging to local optimums.
Flow Field and Combustion Characterization of Premixed Gas Turbine Flames by Planar Laser Techniques
Authors: Stopper Ulrich , Aigner Manfred , Meier Wolfgang , Sadanandan Rajesh , Sto¨hr Michael , Kim Ik Soo
Published: August 2009

Lean premixed natural gas/air flames produced by an industrial gas turbine burner were analyzed using laser diagnostic methods. For this purpose, the burner was equipped with an optical combustion chamber and operated with preheated air at various thermal powers P, equivalence ratios Φ, and pressures up to p = 6 bar. For the visualization of the flame emissions OH* chemiluminescence imaging was applied. Absolute flow velocities were measured using particle image velocimetry (PIV), and the reaction zones as well as regions of burnt gas were characterized by planar laser induced fluorescence (PLIF) of OH. Using these techniques, the combustion behavior was characterized in detail. The mean flow field could be divided into different regimes: the inflow, a central and an outer recirculation zone, and the outgoing exhaust flow. Single-shot PIV images demonstrated that the instantaneous flow field was composed of small and medium sized vortices, mainly located along the shear layers. The chemiluminescence images reflected the regions of heat release. From the PLIF images it was seen that the primary reactions are located in the shear layers between the inflow and the recirculation zones and that the appearance of the reaction zones changed with flame parameters.
Multi Objective Aerodynamic Optimization of Axial Turbine Blades Using a Novel Multi-Level Genetic Algorithm
Authors: O¨ksu¨z O¨zhan , Akmandor I˙brahim Sinan
Published: August 2009

In this paper, a new multiploid genetic optimization method handling surrogate models of the CFD solutions is presented and applied for multi objective turbine blade aerodynamic optimization problem. A fast, efficient, robust, and automated design method is developed to aerodynamically optimize 3D gas turbine blades. The design objectives are selected as maximizing the adiabatic efficiency and torque so as to reduce the weight, size and cost of the gas turbine engine. A 3-Dimensional steady Reynolds Averaged Navier Stokes solver is coupled with an automated unstructured grid generation tool. The solver is verified using two well known test cases. Blade geometry is modeled by 36 design variables plus the number of blades variable in a row. Fine and coarse grid solutions are respected as high and low fidelity models, respectively. One of the test cases is selected as the baseline and is modified by the design process. It was found that the multiploid multi-objective genetic algorithm successfully accelerates the optimization, and prevents converging to local optimums.
Preliminary Design and Projected Performance for Intercooled-Recuperated Microturbine
Authors: Wolf Thomas L. , Kesseli James B. , Nash James S.
Published: August 2009

The Inter-Cooled-Recuperated (ICR) cycle is recognized for its high efficiency potential in gas-turbine applications. This paper reports on a proposed implementation of the ICR cycle in a microturbine setting, using a three-spool configuration incorporating a variable-geometry nozzle on the low-pressure ‘free’ power turbine. Hardware specified for the high-pressure turbine is an existing ceramic rotor fabricated and spin-tested in connection with a prior DOE-sponsored program. Rated engine design-point power and efficiency are projected at 378kWe and 39.5% (net LHV), under realistic prescriptions for component efficiencies and parasitic losses, and with TIT = 1366K (2000°F) specified for the ceramic rotor. Detailed off-design performance projections are carried out, demonstrating exceptional range and part-load efficiency. A key attraction of the ICR compared to a non-intercooled recuperated cycle is its compatibility with high cycle pressure ratio, making for dramatic size and cost reductions for high-pressure components, most importantly the recuperator. A related advantage is reduced ceramic-turbine rotor diameter for a given power level, extending the applicability of ceramic components under conservative manufacturability limits. Engine layout and preliminary mechanical designs for the major subassemblies are developed for application to a forty-foot transport bus with hybrid-electric drive. Further applications under evaluation for the proposed microturbine are stationary power generation, and in a hybrid powerplant setting using a solid-oxide fuel cell.
Analysis of Cooling Effectiveness and Heat Transfer Variations on the End Wall of a Nozzle Guide Vane Caused by Turbine Leakage Flows
Authors: Dannhauer Axel
Published: August 2009

Extensive thermodynamic measurements were carried out on a vane endwall to investigate the interaction with the upstream rotor leakage flow. The experiments were performed at the low speed cascade wind tunnel (NGG) of the German Aerospace Centre (DLR), Go¨ttingen. The investigated cascade consists of three large nozzle guide vanes. The effect of tip leakage flow was simulated by blow-off air. This was ejected through a leakage gap in the side wall closely upstream of the cascade. To investigate the different, possible constructive solutions of tip clearances, at least two different blowing directions were investigated: tangential and perpendicular to the mainstream at three different mass flow ratios. The influence of inlet turbulence was investigated too, applying an active turbulence grid in the intake. To get a realistic temperature gradient the leakage air was cooled down by a heat exchanger to adjust a distinctive temperature difference to the mainstream. The surface temperatures were detected by an infrared camera. Heat flux measurements assisted the interpretation of the resulting distributions of film-cooling effectiveness. It appeared that even for perpendicular injection a large amount of leakage air is distributed to the front area of the end wall although the secondary flow structure is amplified. The leakage air for mass flow ratios until 1.0% is visible between the 3D-separation lines of the horseshow vortices. With tangential ejection an adiabatic effectiveness of ηaw = 0.2 at the cascade outlet was detectable. For both investigated injection directions it was possible to weaken the three dimensional vortex structures. For a further increase in resolution of the adiabatic effectiveness some examinations applying the so-called superposition method were performed.
An Optimization Technique for Radial Compressor Impellers
Authors: Casey Michael , Gersbach Frank , Robinson Chris
Published: August 2009

A software tool has been created to aid in automated impeller design within an integrated design system for radial flow impellers. The design tool takes the results from the 1D preliminary design process and uses these to define a parameterized blade geometry, which incorporates features that are required for low mechanical stresses and simple manufacturing. This geometry is then adjusted to minimize a global objective function using a throughflow computation. The adjustment is based on selection with a breeder genetic algorithm. The initial population includes “elite” designs from a database of earlier well-proven experience, and the final design is honed to perfection with a hill-climbing method. With the help of a suitable global objective function incorporating mechanical and aerodynamic criteria, and taking into account wide experience with the design of impellers, the tool provides a fast screening of various design possibilities to produce a geometrical input for more advanced computational fluid dynamic and mechanical analysis. This is demonstrated through the redesign of an impeller previously designed by conventional methods. Comparisons of the results of the CFD analysis of the new impeller with that of the earlier design demonstrate that the tool can rapidly produce nearly optimal designs as an excellent basis for further refinement by the more complex analysis methods.
Leading Edge Cooling Performance of an Integrated Cooling Configuration
Authors: Bamba Takahiro , Kumagai Takao , Mimura Fujio , Yamane Takashi , Fukuyama Yoshitaka , Usui Taiki , Yoshida Toyoaki
Published: August 2009

This paper presents the experimental work on the leading edge cooling performance of an integrated impingement and pin-fin cooling configuration. Experiments are conducted for seven different spatial geometries under the simulated condition of 1400 degree Celsius-class actual turbine vane leading edge with the temperature ratio of 2.1. The Reynolds number of the hot gas side was 91000 and the cooling air Reynolds number was varied in the range of 5900–47000. The test piece surface temperature distributions were measured using an infrared camera with the correction by a thermocouple embedded on the test piece surface. The cooling effectiveness obtained from the experiments showed the superior cooling performance by the pin-fin integration. The effect of the cooling effectiveness enhancement was more than the cooling surface area increment. The detailed analyses of the cooling performance and the pressure loss characteristics are discussed.
State-of-the-Art Combustor Design Utilizing the Preliminary Combustor Design System PRECODES
Authors: Pegemanyfar Nima , Pfitzner Michael
Published: August 2009

Advanced state-of-the-art gas turbine combustion chamber design requires a multitude of design rules and parameters using a large number of empirical correlations. In order to allow for a more effective use of this knowledge, the preliminary combustor design system PRECODES was developed in the framework of the European research project INTELLECT D.M. (INTEgrated Lean Low Emission CombusTor Design Methodology). The development of PRECODES has already been described by the authors in previous ASME papers [1], [2]. This paper is focused on the results achieved by the application of the system and the demonstration of its potential regarding an automated combustion chamber design. Since the preliminary design of the combustor is performed and optimized fully automatically by the system, the evaluation and comparison of a much higher number of combustor configurations is possible compared to using a manual design process. Moreover detailed CFD analysis is no more limited to the final design phase, but can now be performed early during the preliminary design phase. The CFD results allow for a detailed postprocessing, to check whether all requirements, as derived from the design rules by correlations are satisfied by the configuration (e.g. zonal air/fuel ratios, residence times). The iterative combustor design process loop, as described by the authors in the previous papers [1], [2] has been closed. New, improved combustor design rules have been derived providing a sophisticated combustor design. Different preliminary combustor configurations are produced by the system on the basis of varying performance parameters and geometric requirements, resulting in a variation of the combustor volume, mixing holes sizes and application of different types of mixing holes required to meet the zonal stoichiometries. Some of the configurations have been analysed and compared more specifically using the detailed post-processing capability. An overview of this detailed post-processing analysis and of the data comparison is given in the paper. A promising configuration has been obtained with respect to NOx and CO emissions, at the same time ensuring sufficient residence times for both relight and combustion efficiency requirements.
Error Evaluation in Metal Surface Temperature Prediction Due to Non-Simulation of the Effect of Water Impingement and Runback Water on an Anti-Iced Turboprop Engine Inlet Guide Vane Structure
Authors: Castillo Javier , Ortega Gema
Published: August 2009

During the optimization of the TP400D6 engine (powering the A400M military transport aircraft), the mechanical design of the Front Bearing Structure has proven to be one of the most challenging topics in the engine development programme. One of the leading technical subjects has been the design and optimization of the thermal anti-icing system of the component. When non-specific icing simulation software tools are available, the effect of the water impingement and runback water is difficult to simulate. The objective of this paper is to show one particular aspect learnt during the design and development phase of the project: the evaluation of the error obtained in the calculation of metal temperatures on an antiiced airfoil surface due to the effect of water impingement and runback water. TP400D6 engine front end arrangement consists of a single radial structure after the engine air intake performing both the structural and aerodynamic function, transmitting bearing and high propeller loads and being the compressor IGVs. The anti-icing system employs hot compressor bleed air circulating internally in the component through a series of internal channels and passages and exiting the airfoil through trailing edge holes. Due to airfoil aerodynamic constraints and material selection, it was realised in the earlier stages of the project that it was not possible to heat the whole vane profile up to the trailing edge. In consequence, the effects of the impingement water and runback of non-evaporated water from the intake and the IGV leading edge itself, play a key role on the determination of the airfoil surface temperature and potential ice accretion. Because of not having a specific icing simulation software, water impingement and runback water effects cannot be predicted with sufficient accuracy. During the engine programme’s development phase, a dedicated component antiicing rig test was conducted in order to evaluate and obtain a closer approximation of the real behaviour of the system. The scope of this paper is to go through the details of the aforementioned effect of icing water on airfoil surface temperature, focusing on the discrepancies between predicted temperatures and test rig measured temperatures. Typical thermal modelling is used, which incorporates the best possible understanding of the water particle impingement pattern onto the airfoils and flow lines distribution around the IGV profiles. Results from the rig test have been applied to the traditional thermal model in order to improve the thermal prediction simulation and understanding of the component.
Advanced Reconditioning Technologies for Turbine Blading at Alstom
Authors: Summerside Ian , Kurtz Rainer , van der Meij Richard
Published: August 2009

The demand for increased availability, reliability and performance combined with reduced maintenance costs are key factors for the success of gas turbine users. Advanced hot gas path components, such as SX and DS base materials, thin walled components with sophisticated cooling techniques and high strength structural brazing, therefore play a major role in today’s state-of-the art heavy-duty gas turbines. Reconditioning of these components calls for advanced technologies, reflecting recovery of structural integrity, component functionality and possible component improvements for the next service interval at lowest cost, all to the benefit of the customer. This paper provides an overview of Alstom’s reconditioning capabilities focussing on production experience of several advanced technologies for the analysis, reconditioning, modification and improvement of hot gas path components. Several process development programs are discussed, in particular the reopening of (fan shaped) cooling air holes and laser metal forming as required for advanced GT turbine components such as GT24 and GT26.
Comparison of Experimental and Numerical Results Concerning the Damping of Perforated Liners With Bias Flow
Authors: Heuwinkel Claus , Enghard Lars , Ro¨hle Ingo , Mu¨hlbauer Bernd , Noll Berthold , Aigner Manfred , Busse Stefan
Published: August 2009

Perforated liners with bias flow are integrated in the wall of gas turbine combustors to suppress thermoacoustic instabilities. The suppression of these unstable pressure oscillations is a requirement for the safe and stable operation of a gas turbine while applying new combustion concepts concerning more efficiency and cleanliness. Previous experiments have shown the high potential of perforated liners absorbing sound energy and therefore minimize combustion instabilities. In this collaborative work, the absorption properties of a liner are determined from both experimental measurements and numerical simulations. In both cases the analysis is based on acoustic pressure data recorded at several axial positions upstream and downstream of the liner. In the experiments this data is acquired by microphone measurements and in the simulation it is numerically calculated applying a three dimensional compressible URANS approach. The dissipation coefficient of the liner is identified for plane wave propagation at ambient conditions while a grazing flow is present in the duct. Parameters are the bias flow velocity and the amplitude of the incident sound wave. Comparing the results of the highly accurate experiments and the simulation reveals the abilities and limits of the numerical approach to model the absorption effect. The results are in very good agreement for the case without bias flow. However, the discrepancy between the experimental and numerical results is increasing while a bias flow is present.
Property Risk Assessment for Combined Cycle Power Plants
Authors: Orme G. J. , Venturini M.
Published: August 2009

In the paper, a procedure for Property Risk Assessment is presented and discussed. The procedure is applied to some combined cycle power plants and the most common sources of loss are identified. The impact on operational costs is evaluated through the determination of two indices of risk. First, their dependence on combined cycle configuration and electric power output is established. Second, a sample analysis for risk/benefit evaluation is carried out to estimate whether the adoption of risk assessment procedures allows an actual profit for plant owners. Finally, customer feedback is also discussed.
Velocity Distributions for Low Pressure Turbines
Authors: Coull John D. , Thomas Richard L. , Hodson Howard P.
Published: August 2009

A parametric set of velocity distributions has been investigated using a flat plate experiment. Three different diffusion factors and peak velocity locations were tested. These were designed to mimic the suction surfaces of Low Pressure (LP) turbine blades. Unsteady wakes, inherent in real turbomachinery flows, were generated using a moving bar mechanism. A turbulence grid generated a freestream turbulence level that is believed to be typical of LP turbines. Measurements were taken across a Reynolds number range of 50,000–220,000 at three reduced frequencies (0.314, 0.628, 0.942). Boundary layer traverses were performed at the nominal trailing edge using a Laser Doppler Anemometry system and hot-films were used to examine the boundary layer behaviour along the surface. For every velocity distribution tested, the boundary layer separated in the diffusing flow downstream of the peak velocity. The loss production is dominated by the mixing in the reattachment process, mixing in the turbulent boundary layer downstream of reattachment and the effects of the unsteady interaction between the wakes and the boundary layer. A sensitive balance governs the optimal location of peak velocity on the surface. Moving the velocity peak forwards on the blade was found to be increasingly beneficial when bubble-generated losses are high, i.e. at low Reynolds number, at low reduced frequency and at high levels of diffusion.
Time Resolved Simulation and Experimental Validation of the Flow in Axial Slot Casing Treatments for Transonic Axial Compressors
Authors: Brignole Giovanni A. , Danner Florian C. T. , Kau Hans-Peter
Published: August 2009

Building on the experience of previous investigations, a casing treatment was developed and applied to an axial transonic compressor stage, in literature referred to as Darmstadt Rotor 1. The aerodynamics of the experimental compressor stage was improved by applying axially orientated semicircular slots to the original plain casing, which both enhanced the operating range and design point efficiency. A gain in total pressure ratio along the entire design speed line was also observed. Within the scope of this study four different axial casing treatments were designed. Their effect on the flow in a transonic axial compressor stage was investigated parametrically using time-resolved 3D-FANS simulations with a mesh of approximately 4.8 · 106 grid points. This research aims to identify correlations between the geometrical cavity design and the changed channel flow. The findings help to formulate parameters for evaluating the performance of casing treatments. These criteria can further be used as target functions in the design optimisation process. The predicted behaviour of the transonic compressor was validated against experiments as well as an alternative numerical model, the non-linear harmonic method. Both confirmed the effect of the slots in raising efficiency as well as moving the design speed line towards higher pressure ratios. In the experiments, the addition of the slots increased the total pressure ratio at stall conditions by more than 5% and reduced mass flow from 87.5% of the design mass flow to less than 77.5% compared to the original geometry.
Unsteady 3-D Conjugated Heat Transfer Simulation of a Thermal Barrier Coated Gas Turbine Bucket
Authors: Herna´ndez Rossette Alejandro , Mazur C. Zdzislaw , Bautista P. Eder A. , Demeulenaere Alain , Lo´pez Hernandez J. A. Roque
Published: August 2009

The unsteady aerodynamic and aero-thermal performance of a first stage gas turbine bucket with thermal barrier coating (TBC) and internal cooling configuration were investigated by application of a three dimensional Navier-Stokes commercial turbomachinery oriented CFD-code. Convection and conduction were modeled for a super alloy blade with TBC. The CFD simulations were configured with a mesh domain including the nozzle and bucket inter-stage in order to accurately predict the fluid parameters at inlet and outlet of bucket. Comparisons to the gas turbine manufacturer data have permitted to validate the flow conditions at the inlet of the rotor. The effects of blade TBC surface temperature changes during a start-up cycle were simulated by means of an unsteady simulation, with unsteady inlet/outlet boundary conditions specified according to test data. The calculations include not only the fluid but also the solving of conduction within the blade, allowing for a correct modeling of the large difference of thermal inertia between the fluid and solid. The role of thermal barrier coatings (TBC) is, as their name suggests, providing thermal insulation of the blade. A coating of about 100–400 μm can reduce the temperature by up to 200°C. A TBC can be used either to reduce the need for blade cooling (by about 36%) increasing the turbine efficiency, while maintaining identical creep life of the substrate; or to increase considerably the creep life of the blade while maintaining level of blade cooling (and therefore allowing the blade to operate at lower temperature for an identical turbine inlet temperature).
The Analytical Approach to the Temperature Prediction of Steam Turbine Shells Based on the Thermocouple Temperature Measurements at a Few Points
Authors: Ekbote Ajit B. , Brilliant Howard M.
Published: August 2009

The performance and efficiency of a steam turbine does depend upon the clearances during the hot conditions. The reliability and accuracy of the clearance calculations is based upon how good are the temperature predictions of the local zones at the secondary steam leakage path. Especially during the transients of the start-up and shutdown of a turbine, the temperature gradients result in the differential expansions of the shell at the top and bottom. This causes the humping or sagging of the shell. Along with the shell, the stationary parts fixed to the shell, such as diaphragms also move up or down. This increases the probability of interference and rubs. These transient gradients are not, in general, captured in the conventional analyses owing to a plethora of reasons. The methods described in this paper are applicable to any section of a steam turbine, as well as a gas turbine. The authors have considered the double flow low pressure (LP) steam turbine inner casing, for which the field data in terms of the metal temperature measurement was compiled and made available. The LP section of a turbine with bottom condenser has, generally double flow arrangement. The thermocouples put on the geometrically symmetrical points indicated difference in temperature and thus the circumferential variation. The paper describes how a few temperature measurements on the shell using thermocouples can be effectively utilized to calculate the temperature as a boundary condition at all the nodes of the finite element (FE) model by means of shape function interpolation. The results based on this technique give a continuous temperature distribution. The thermocouple based shell temperature measurements in the field are used for the calculations of the temperature at each point and the structural analysis was carried out. The analysis did indicate the sagging & humping of the shell. Plans for future improvements will be presented. Temperature and deflection profiles and transient errors are shown to be representative of observed behavior.
Temporal Structure of the Boundary Layer in Low Reynolds Number, Low Pressure Turbine Profiles
Authors: Lazaro Benigno J. , Gonzalez Ezequiel , Vazquez Raul
Published: August 2009

Viscous effects in the suction side of low pressure turbines account for about 1/2 of the total turbine losses. Modern design practices simultaneously include decreasing the profiles’ Reynolds number and increasing their aerodynamic load, thereby compromising the suction side boundary layer flow. The objective of the present investigation is to experimentally elucidate the spatial and temporal structure of the suction side boundary layer in the low Reynolds number regime. Under steady state approaching flow conditions, the boundary layer undergoes laminar separation shortly after the external flow velocity peak is reached. The separation produces a low kinetic energy, uniform pressure fluid region. Between this and the external flow, a laminar shear layer develops. The laminar shear layer undergoes a sudden, non linear instability process when its distance to the suction side wall is compatible with the shear layer most unstable scale. This instability promotes the formation of large scale vortices that reattach the flow to the suction side wall. When the approaching flow includes moving wakes that simulate the previous turbine stage, the above description is modified. The laminar shear layer undergoes a global instability triggered by the passing wakes’ perturbation field. Later on the viscous layer reattaches as the wakes’ perturbation field accelerates the fluid. After each wake passage there is a transient, relaxation period characterized by the growth of the low energy, recirculating fluid region and the simultaneous lift of the shear layer away from the suction side wall. The measurements conducted allow the identification of flow regions, as well as temporal and spatial scales that account for the downstream evolution of the viscous layer integral parameters.
Emulation of Hybrid System Start-Up and Shutdown Phases With a Micro Gas Turbine Based Test Rig
Authors: Ferrari Mario L. , Pascenti Matteo , Magistri Loredana , Massardo Aristide F.
Published: August 2009

The aim of this work, focused on natural gas fired distributed power systems, is the experimental analysis of the start-up and shutdown for high temperature fuel cell hybrid systems. These critical phases have been emulated using the micro gas turbine test rig developed by TPG at the University of Genoa, Italy. The rig is based on the coupling of a modified commercial 100 kWe recuperated gas turbine with a modular volume designed to emulate fuel cell stacks of different dimensions. It is essential to test the dynamic interaction between the machine and the fuel cell, and to develop different operative procedures and control systems without any risk to the expensive stack. This paper shows the preliminary experimental results obtained with the machine connected to the volume. The attention is mainly focused on avoiding surge and excessive stress on the machine components during the tests. Finally, after the presentation of the valve control system, this paper reports the emulation of the hybrid system start-up and shutdown phases. They have been performed to produce a gradual heating up and cooling down of the fuel cell volume, using the cold bypass line, three high temperature valves, and the machine load control system. This approach is necessary to avoid high thermal stress on the cell material, extremely dangerous for the plant life.
Further Effects of Water Ingestion on Axial Flow Compressors and Aeroengines at Part Speed
Authors: Williams John
Published: August 2009

Further experimental work is reported on the effects of water ingestion on the performance of an axial flow compressor. The background to the work is the effect that heavy rain has on a high bypass ratio aeroengine compressor when operating at “descent idle” power, i.e., when the compressor is operating at part speed and when the aero-mechanical effects of water ingestion are more important than the thermodynamic effects. The current work presents direct measurements on a low-speed four stage laboratory compressor and shows how the surge line is only adversely affected by water ingestion when the stall initiating stage is adversely affected. For a compressor operating at part speed, it is generally the first stage that initiates stall, and the laboratory compressor was consistent with this. When water was injected into the laboratory compressor inlet from straight jet or low fan angle nozzles at mid-span, the first stage performance (unlike later stage performance) was scarcely different from under dry conditions. With water-to-air mass flowrate ratios of up to 20% at the stall point, the overall total-to-static pressure rise was reduced but the stall point remained on the throttle line passing through the stall point of the dry characteristic. This implies no movement of the surge line and results from the near-casing region of the first stage remaining relatively dry, due to the high axial momentum of the water taking it through the rotor blade row without being centrifuged to the casing. In contrast, tests with atomising nozzles producing low axial momentum fine droplets over the whole inlet area, and tests spraying water directly onto the compressor casing ahead of the inlet showed significant adverse effects on both stage one (and later stage) performance and the compressor surge line. The similarity between these latter two sets of test results is consistent with the known dominance of the near-casing region in determining compressor performance with water ingestion. The tests with the atomising nozzles, i.e. all stages affected by water, are most engine-representative. By combining the measured movements of the surge line with the measured increases in driving torque, and considering choked HP and IP turbines, the results are applied to a generic high bypass ratio engine with four stage HP compressor operating at idle speed. The HP compressor is predicted to stall with a core water-to-air mass flowrate ratio of just 2.5%.
Numerical Modelling of Flow and Heat Transfer From an Array of Jets Impinging Onto a Concave Surface Under Stationary and Rotating Conditions
Authors: Craft Tim J. , Iacovides Hector , Mostafa Nor A.
Published: August 2009

The paper reports computations of the flow and heat-transfer from an array of five round jets impinging onto a concave semi-circular surface, under both stationary and rotating conditions. The geometry is designed to reproduce important flow features found in internal turbine blade cooling applications. Linear and non-linear eddy-viscosity models are applied, with wall-functions to cover the near-wall layer, and are shown to capture many of the overall flow characteristics under stationary conditions, although greater discrepancies are found in rotating cases. The standard, log-law based, form of wall-function is found to be inadequate in predicting the heat-transfer, and a more advanced form developed at Manchester (the AWF) is also tested, and shown to lead to better heat transfer results.
Aero-Thermal Study of the Unsteady Flow Field in a Transonic Gas Turbine With Inlet Temperature Distortions
Authors: Martelli Francesco , Adami Paolo , Salvadori Simone , Chana Kam S. , Castillon Lionel
Published: August 2009

CFD prediction of the unsteady aero-thermal interaction in the HP turbine stage, with inlet temperature non-uniformity, requires appropriate unsteady modelling and a low diffusive numerical scheme coupled with suitable turbulence models. This maybe referred to as high fidelity CFD. A numerical study has been conducted by the University of Florence in collaboration with ONERA to compare capabilities and limitations of their CFD codes for such flows. The test vehicle used for the investigation is a turbine stage of three-dimensional design from the QinetiQ turbine facility known as MT1. This stage is a high pressure (HP) transonic stage that has an un-shrouded rotor, configured un-cooled with 32 stators and 60 rotor blades. Two different CFD solvers are compared that use different unsteady treatment of the interaction. A reduced count ratio technique has been used by the University of Florence with its code HybFlow, while a phase lag model has been used by ONERA in their code, elsA. Four different inlet conditions have been simulated and compared with a focus on the experimental values provided by QinetiQ in the frame of TATEF and TATEF2 EU 6th Framework projects. The differences in terms of performance parameters and hot fluid redistribution, as well as the time- and pitch-averaged radial distributions on a plane downstream of the rotor blade, have been underlined. Special attention was given to the predictions of rotor blade unsteady pressure and heat transfer rates.
LCAC Main Engine Installed Performance
Authors: Canilang Benjamin , Zipkin David
Published: August 2009

This paper investigates the installed performance of the ETF40B marine gas turbine engine (MGTE) on SLEP LCAC. Historical estimates of intake and uptake losses for SLEP LCAC have proven inaccurate, resulting in loss of available power for hump transition. A recent computational fluid dynamic (CFD) analysis of the uptakes revealed a possible 1000% increase in actual uptake losses. NSWCCD was tasked to evaluate and correct these detrimental deficiencies. This paper documents the development of the performance testing and results. Specifically, NSWCCD performed CFD analyses of the uptake configuration, designed pressure/temperature rakes, developed a unique DAQ schema, and statistical analysis of the average engine based upon acceptance test procedures (ATP), and generation of new torque tables based upon the LCAC drive train limits.
CO2 Capture and Sequestration Options: Impact on Turbo-Machinery Design
Authors: Zachary Justin , Titus Sara
Published: August 2009

In the present climate of uncertainty about CO2 emissions legislation, owners and power plant planners are looking into the possibility of accommodating “add on” carbon capture and sequestration (CCS) solutions in their current plant designs. The variety of CCS technologies currently under development makes it a very challenging task. This paper initially discusses the more mature post-combustion CCS technologies, such as chemical absorption, and the associated equipment requirements in terms of layout, integration within the generating plant, and auxiliary power consumption. The analysis addresses both supercritical coal-fired as well as combined cycle plants. Plant configuration details and various operational scenarios are evaluated. The issues related to balance-of-plant systems, including water treatment, availability and redundancy criteria, are also offered. Continuing the paper presents a number of options for pre-combustion processes such as oxy-fuel combustion and integrated gasification combined cycle (IGCC) water-shift CO conversion to CO2. The impacts of several processes that only partially capture carbon are also evaluated from an engineering, procurement, and construction (EPC) contractor’s perspective as plant designer and integrator. Finally, the paper presents several examples of studies in development by Bechtel where a neutral but proactive technical approach was applied to achieve the best and most cost-effective solution.