bluuebunny/crossref_metadata_2025 huggingface dataset:
Bump and Trench Modifications to Film-Cooling Holes at the Vane Endwall Junction
Authors: Sundaram N. , Thole K. A.
Published: March 2009

The endwall of a first stage vane experiences high heat transfer and low adiabatic effectiveness levels because of high turbine operating temperatures and formation of leading edge vortices. These vortices lift the coolant off the endwall and pull the hot mainstream gases towards it. The region of focus for this study is the vane-endwall junction region near the stagnation location where cooling is very difficult. Two different film-cooling hole modifications, namely trenches and bumps, were evaluated to improve the cooling in the leading edge region. This study uses a large-scale turbine vane cascade with a single row of axial film-cooling holes at the leading edge of the vane endwall. Individual hole trenches and row trenches were placed along the complete row of film-cooling holes. Two-dimensional semi-elliptically shaped bumps were also evaluated by placing the bumps upstream and downstream of the film-cooling row. Tests were carried out for different trench depths and bump heights under varying blowing ratios. The results indicated that a row trench placed along the row of film-cooling holes showed a greater enhancement in adiabatic effectiveness levels when compared to individual hole trenches and bumps. All geometries considered produced an overall improvement to adiabatic effectiveness levels.
Kinetics of Gas Turbine Liquid Fuels Combustion: Jet-A1 and Bio-Kerosene
Authors: Dagaut Philippe , Gai¨l Sandro
Published: March 2009

The oxidation of kerosene and bio-kerosene (kerosene-rapeseed oil methyl esters 80/20 in mole) was studied experimentally in a jet-stirred reactor at 10 atm and constant residence time, over the high temperature range 740-1200 K, and for variable equivalence ratios in the range 0.5–1.5. Concentration profiles of reactants, stable intermediates, and final products were obtained by probe sampling followed by on-line and off-line GC analyses. The oxidation of these fuels in these conditions was modeled using a detailed kinetic reaction mechanism consisting of 2027 reversible reactions and 263 species. The surrogate bio-kerosene model-fuel used consisted of a mixture of n-hexadecane, n-propylcyclohexane, n-propylbenzene, and n-decane. For bio-kerosene, the methyl ester fraction was simply represented by n-hexadecane. The proposed kinetic reaction mechanism used in the modeling yielded a good representation of the kinetics of oxidation of kerosene and bio-kerosene under JSR conditions. The data and the model showed the bio-kerosene (Jet A-1/RME mixture) has a slightly higher reactivity than Jet A-1 whereas not major modification of the products distribution was observed besides the formation of small methyl esters from RME’s oxidation.
Impact of Radiation on the Wall Heat Load at a Test Bench Gas Turbine Combustion Chamber: Measurements and CFD Simulation
Authors: Dannecker R. , Schildmacher K.-U. , Noll B. , Koch R. , Hase M. , Krebs W. , Aigner M.
Published: March 2009

Experimental and numerical work has been carried out to determine the wall heat load at the liner structure of a model gas turbine combustion chamber. Measured cross-sectional profiles of the velocity and temperature field inside the chamber could be used to validate various CFD calculations of the combustion flow. It turned out that only a special treatment of the thermal boundary conditions at all liner walls would actually lead to appropriate values of the wall heat flux. Radiation modeling included two radiative properties models (SG single gray gas and WSSG weighted sum of gray gases) and three radiation transport models (P1, DT discrete transfer, MC Monte Carlo). The performance of the WSGG model has been assessed with charts and the impact of the radiation on the liner wall temperature distribution has been studied. The experimental values are matched within 3% deviation with the best combination of transport and radiation property models. The radiation contributes to 20-30% of the total wall heat flux. The present approach enables Siemens PG to access the thermal design of combustors more precisely.
Migration of Combustor Exit Profiles Through High Pressure Turbine Vanes
Authors: Barringer M. D. , Polanka M. D. , Clark J. P. , Koch P. J. , Thole K. A.
Published: March 2009

The high pressure turbine stage within gas turbine engines is exposed to combustor exit flows that are nonuniform in both stagnation pressure and temperature. These highly turbulent flows typically enter the first stage vanes with significant spatial gradients near the inner and outer diameter endwalls. These gradients can result in secondary flow development within the vane passage that is different than what classical secondary flow models predict. The heat transfer between the working fluid and the turbine vane surface and endwalls is directly related to the secondary flows. The goal of the current study was to examine the migration of different inlet radial temperature and pressure profiles through the high turbine vane of a modern turbine engine. The tests were performed using an inlet profile generator located in the Turbine Research Facility (TRF) at the Air Force Research Laboratory (AFRL). Comparisons of area-averaged radial exit profiles are reported as well as profiles at three vane pitch locations to document the circumferential variation in the profiles. The results show that the shape of the total pressure profile near the endwalls at the inlet of the vane can alter the redistribution of stagnation enthalpy through the airfoil passage significantly. Total pressure loss and exit flow angle variations are also examined for the different inlet profiles.
Numerical Simulation of Partial Flame Failure in Gas Turbine Engine
Authors: Panov V. , Smith M. K. D.
Published: March 2009

A mathematical model for the simulation of engine start-up thermodynamics has been developed and validated against engine test data. This numerical model has been validated using engine test results for both single and multiple combustor flameouts, and reasonable agreement between test and simulation data has been observed. Numerical simulations have then been generated for flameout cases that have not been available from engine tests, such as flame failure in different combinations of combustors, and at different engine operating conditions. The mathematical model features object modeling of engine components with three gas compositions, being air, fuel, and combustion products. The combustion system has been represented by six combustors, and the gas stream from each combustor has been divided according to the number of the gas path thermocouples downstream from the combustion system. The effects of heat transfer within the combustors and turbine have been modeled. Two sets of thermocouples have been considered, the first being thermocouples installed in multiple combustor burners, and the second being an array of thermocouple probes which are circumferentially positioned in the engine hot gas path. All thermocouples have been modeled as first order dynamic systems. The numerical simulations have been successfully used to support development of a new partial flame failure detection method, which is based on the combined measurements from both sets of thermocouples. A range of numerical simulations have been conducted in order to assess the ability of this new detection algorithm to detect different partial flame failure scenarios, and to examine the sensitivity of the detection algorithm with respect to thermocouples faults.
Axial Compressor Performance Map Prediction Using Artificial Neural Network
Authors: Ghorbanian Kaveh , Gholamrezaei Mohammad
Published: March 2009

The application of artificial neural network to compressor performance map prediction is investigated. Different types of artificial neural network such as multilayer perceptron network, radial basis function network, general regression neural network, and a rotated general regression neural network proposed by the authors are considered. Two different models are utilized in simulating the performance map. The results indicate that while the rotated general regression neural network has the least mean error and best agreement to the experimental data, it is however limited to curve fitting application. On the other hand, if one considers a tool for curve fitting as well as for interpolation and extrapolation applications, multilayer perceptron network technique is the most powerful candidate. Further, the compressor efficiency based on the multilayer perceptron network technique is determined. Excellent agreement between the predictions and the experimental data is obtained.
Heat/Mass Transfer Characteristics in Angled Ribbed Channels With Various Bleed Ratios and Rotation Numbers
Authors: Kim Kyung Min , Park Suk Hwan , Jeon Yun Heung , Lee Dong Hyun , Cho Hyung Hee
Published: March 2009

The present study investigates the effects of secondary flow due to angled rib turbulators on the heat/mass transfer in the square channels with channel rotation and bleed flow. The angle of attack of the angled ribs was 45°. The bleed holes were located between the rib turbulators on either the leading or trailing surface. The tests were conducted under the conditions corresponding to various bleed ratios (BR = 0.0, 0.2 and 0.4) and rotation numbers (Ro = 0.0, 0.2 and 0.4) at Re = 10,000. The results suggest that the heat/mass transfer characteristics were influenced by the Coriolis force, the decrement of the main flow rate and the secondary flow. In the 90° angled ribbed channel, the heat/mass transfer reduced on the leading surface with an increment in the rotation number, but it increased on the trailing surface. However, it decreased on both surfaces in the 45° angled ribbed channel. As the bleed ratio increased, the Sherwood number ratios decreased on both the bleeding and non-bleeding surfaces for the 45° angled ribs, but increased on the bleeding surface for the 90° angled ribs.
An Experimental and Numerical Study of Heat Transfer and Pressure Losses of V- and W-Shaped Ribs at High Reynolds Numbers
Authors: Maurer Michael , von Wolfersdorf Jens , Gritsch Michael
Published: March 2009

An experimental and numerical investigation was conducted to assess the thermal performance of V- and W-shaped ribs in a rectangular channel. The ribs were located on one channel sidewall in order to simulate a typical combustor liner cooling. The cross section of the channel had an aspect ratio of 2:1. Local heat transfer coefficients were measured using the transient thermochromic liquid crystal technique. Pressure taps along the channel sidewall were used to obtain the periodic pressure losses. The rib height-to-hydraulic diameter ratio (e/Dh) was set to 0.02, and the rib pitch-to-height ratios (P/e) were 5 and 10. The Reynolds numbers investigated varied from 80,000 to 500,000. All rib configurations were additionally investigated numerically and the obtained computational results were compared with experimental data. For all computations the commercial software FLUENT™ was used with a two-layer k-ε turbulence model. It could be demonstrated that applying W-shaped ribs instead of V-shaped ribs has the advantage of an increased heat transfer enhancement, but is accompanied by a rise in pressure loss. Reducing the rib pitch-to-height ratio from 10 to 5 decreases the heat transfer enhancement, but results in a significantly reduced pressure loss. Finally, the best thermal performance was found for W-shaped ribs with a pitch-to-height ratio of 10, having a slightly increased pressure loss but with considerable rise in heat transfer enhancement compared to V-shaped ribs.
Evaluation of Different Alternatives of Power Augmentation for an Existing Combined Cycle Power Plant in Brazil
Authors: Celis Ce´sar , de Avellar Vinicius P. , Ferreira Sandro B. , Braga Sergio L.
Published: March 2009

Not only in simple cycle power plants, but also in combined cycle power plants based on gas turbines, the power output is considerably reduced with the increase of the ambient temperature. Many technologies for power augmentation of gas turbines have been proposed along the last decades, and several systems have already been applied in real plants. Power augmentation techniques are concentrated on the philosophy of increasing the mass flow rate going through the gas turbine. The goal of this paper is to review the state-of-the-art of the different technologies of power augmentation available today for gas turbines, as well as to evaluate and to select the best alternative of power augmentation for an existing combined cycle power plant in Brazil. The calculations are carried out using an in-house computer program, called the Power Augmentation Technologies (PAT) model, developed for thermal performance modeling and financial analysis. In order to validate the computational model developed, the authors carried out comparisons between the results obtained with this model and data obtained from literature. For the specific combined cycle power plant analyzed in this work, and considering the internal rate of return and the pay-back period as the main investment economic indicators determining the implementation of a project developed for increasing the plant power output, the results show that the power augmentation systems based on evaporative coolers are the most suitable for this plant.
Fundamental Mechanism of Entropy Noise in Aero-Engines: Numerical Simulation
Authors: Mu¨hlbauer Bernd , Widenhorn Axel , Liu Martin , Noll Berthold , Aigner Manfred
Published: March 2009

Entropy noise is generated by entropy non-uniformities being accelerated for example in the turbine section downstream of gas-turbine combustion chambers. The entropy noise was experimentally investigated in the test facility Entropy Wave Generator (EWG) [1, 2]. The EWG induces entropy waves by supplying energy pulses to a tube flow. The air stream is accelerated in a convergent-divergent nozzle where entropy noise is excited. In order to investigate entropy noise generation mechanism the numerical simulation of thermo-acoustics was done. This paper shows results concerning the numerical simulation of a reference test case of the EWG applying a compressible URANS approach. The simulations indicate that both fully reflective and non-reflective boundary conditions are inappropriate for modeling of the propagation of entropy noise in this case. The change of cross sectional area in the downstream tube section at a certain position requires the application of a partially reflective boundary condition in the numerical simulation. The variation of the length of the tube section upstream the nozzle proves the existence of entropy noise. Changing the tube length downstream the nozzle results in a phase shift of the superposed downstream and partially reflected upstream propagating pressure fluctuations. Furthermore, the influence of the amount of energy supplied to the system on the generated entropy noise is shown. All numerical results show a good agreement with experimental data.
An Experimental Study of the Inception of Rotating Stall in a Single-Stage Low-Speed Axial Compressor
Authors: Simpson Alexander K. , Longley John P.
Published: March 2009

There are two established mechanisms, spike and modal inception, by which rotating stall is initiated in an axial flow compressor. Whilst the “Critical incidence hypothesis” and the “Zero slope criterion” are useful ideas in explaining the different stability boundaries for spikes and modes they do not provide the designer with a predictive tool. A detailed experimental investigation utilising a single-stage low-speed compressor is presented in which the aerodynamic environment of a rotor blade row is changed (rotor geometry is held fixed) so that it exhibited both spike and modal inception upon throttling into stall. The dominant mechanism of stall inception was found to be dependent on both the inlet flowfield and the downstream stator. The measurements are analysed and show that the meridional acceleration across the tip region of the rotor influences the mechanism by which rotating stall is incepted. This research is presented as a contribution towards the prediction of the stall inception mechanism.
Robust Strategies for Forced Response Reduction of Bladed Discs Based on Large Mistuning Concept
Authors: Nikolic M. , Petrov E. P. , Ewins D. J.
Published: March 2009

In this paper, robust maximum forced response reduction strategies based on a “large mistuning” concept are introduced, including both (i) probabilistic and (ii) deterministic approaches. An industrial bladed fan disc serves as an application example for a reliability assessment of the aforementioned strategies using two well-established tools for uncertainty analysis: (i) statistics and (ii) sensitivity and robustness. The feasibility and other practical aspects of implementing large mistuning as a means of preventing excessive forced response levels caused by random mistuning and ensuring the predictability of the response are discussed.
Evaluation of Two-Equation Models of Turbulence in Predicting Film Cooling Performance Under High Free Stream Turbulence
Authors: Yavuzkurt Savas , Hassan Jawad S.
Published: March 2009

The capabilities of four two-equation turbulence models in predicting film cooling effectiveness under high free stream turbulence (FST) intensity (Tu = 10%) were investigated and their performance are presented and discussed. The four turbulence models are: the standard k-ε, RNG, and realizable k-ε models as well as the standard k-ω model all four found in the FLUENT CFD code. In all models, the enhanced wall treatment has been used to resolve the flow near solid boundaries. A systematic approach has been followed in the computational setup to insure grid-independence and accurate solution that reflects the true capabilities of these models. Exact geometrical and flow-field replicas of an experimental study on discrete hole film cooling were generated and used in FLUENT. A pitch-to-diameter ratio of 3.04, injection tube length-to-diameter ratio of 4.6 and density ratios of 0.92 and 0.97 were some of the parameters used in the film cooling analysis. The study covered two levels of blowing ratios (M = 0.5 and 1.5) at an environment of what is defined as high initial free-stream turbulence intensity (Tu = 10%). Performance of these models under a very low initial FST were presented in a paper by the authors in Turbo Expo 2006. In that case, the standard k-ε model had the most consistent performance among all considered turbulence models and the best centerline film cooling effectiveness predictions under very low FST. However, after the addition of high FST in the free-stream, even the standard k-ε model started to deviate greatly from the experimental data (up to 200% over-prediction) under high blowing ratios (M = 1.5). The model which performed the best under high FST but low blowing ratios (M = 0.5) is still the standard k-ε model. In all cases only standard k-ε model results match the trends of data for both cases. It can be said that under high FST with high M all the models do not do a good job of predicting the data. It was concluded that these deviations resulted from the effects of both high FST and high M. Under high M, near the injection holes deviations could result from the limitations of Boussinesq hypothesis relating the direction of Reynolds stress to the mean strain rate. Also, it seems like all models have trouble including the effects of high FST by not being able to take into account high levels of diffusion of turbulence from the free stream. However, standard k-ε model still looks like the best candidate for further improvement with the addition of new diffusion model for TKE under high FST.
Numerical Analysis of the Vaned Diffuser of a Transonic Centrifugal Compressor
Authors: Marconcini Michele , Rubechini Filippo , Arnone Andrea , Ibaraki Seiichi
Published: March 2009

A three-dimensional Navier-Stokes solver is used to investigate the flow field of a high pressure ratio centrifugal compressor for turbocharger applications. Such a compressor consists of a double-splitter impeller followed by a vaned diffuser. Particular attention is focused on the analysis of the vaned diffuser, designed for high subsonic inlet conditions. The diffuser is characterized by a complex three-dimensional flow field, and influenced by the unsteady interaction with the impeller. Detailed Particle Image Velocimetry (PIV) flow measurements within the diffuser are available for comparison purposes.
Impact of Inlet Swirl on High-Speed High-Flow Centrifugal Stage Performance
Authors: Grimaldi Angelo , Tapinassi Libero , Bernocchi Andrea , Biagi Fernando Roberto , Guenard Denis , Michelassi Vittorio
Published: March 2009

Cooling cycle in applications such as Liquefied Natural Gas makes use of centrifugal impellers associated with heavy gas. Increasing projects handled flow leads compressor manufacturers to try to increase flow coefficient and peripheral Mach Number of those stages to limit compressor size. As a consequence, severe aerodynamic problems linked to the blade aspect ratio, meridional channel curvature and inlet tip relative Mach number arise. Of the three, the onset of transonic or supersonic inlet conditions at tip is a matter of concern since it can significantly reduce stage range and performance. Very aggressive blade redesign is often not possible due to mechanical limitations. An accurate coupling of the impeller with the upstream stator parts may partly overcome the problem. The paper summarizes the design activity of a centrifugal stage designed for inlet pre-rotation, covering the most significant considerations made during its design, starting from 1D preliminary design until three dimensional CFD verifications. Finally, the paper draws conclusions on comparison with the results of an experimental campaign the purpose of which was to evaluate the benefits brought about by the new impeller design and different inlet configurations. The new impeller design allowed to reach still acceptable operating range even with relative Mach Number of 1.05 but with a noticeable efficiency decay. Use of Inlet Guide Vane with prewhirl, to bring Mach down to lower value, allowed to recover efficiency values without any further gain of operating range.
Pseudo-ARMA Model for Meta-Modeling Extrapolation
Authors: Luo Huageng , Wang Liping , Beeson Don , Wiggs Gene
Published: March 2009

In spite of exponential growth in computing power, the enormous computational cost of complex and large-scale engineering design problems make it impractical to rely exclusively on original high fidelity simulation codes. Therefore, there has been an increasing interest in the use of fast executing meta-models to alleviate the computational cost required by slow and expensive simulation models — especially for optimization and probabilistic design. However, many state-of-the-art meta-modeling techniques, such as Radial Basis Function (RBF), Gaussian Process (GP), and Kriging can only make good predictions in the case of interpolation. Their ability for extrapolation is not impressive since the models are mathematically constructed for interpolations. Although Multivariate Adaptive Regression Splines (MARS) and Artificial Neural Network (ANN) have been tried for extrapolation problems (forecasting), the results do not always meet accuracy requirements. The autoregressive moving-average (ARMA) model is a popular time series modeling and forecasting tool. It has been widely used in many engineering applications in which all the inputs and outputs are time dependent. Many researchers have tried to extend the time series ARMA modeling technique into so-called spatial ARMA modeling or time-space ARMA modeling. However, the time-space ARMA modeling requires extensive computation in grid data generation as well as in model building, particularly for high dimensional problems. In this paper, a pseudo-ARMA approach is proposed to strengthen meta-modeling extrapolation capability. Each input is randomly sampled at a given mean value and distribution range to form a pseudo-time series. The output variables are evaluated based on input variables, which formulate output variable pseudo time series. The pseudo-ARMA model is built based on the pseudo input and output time series. Using the constructed pseudo-ARMA model, and new input variables generated with extended distribution parameters, such as distribution means and distribution ranges, the output variables can be evaluated to achieve extrapolations. Several numerical examples are presented to demonstrate the proposed approach. The results are compared with Radial Basis Function (RBF) meta-modeling results for both interpolation and extrapolation.
Periodical Unsteady Flow Within a Rotor Blade Row of an Axial Compressor: Part II — Wake–Tip Clearance Vortex Interaction
Authors: Mailach Ronald , Lehmann Ingolf , Vogeler Konrad
Published: March 2009

In this two-part paper results of the periodical unsteady flow field within the third rotor blade row of the four-stage Dresden Low-Speed Research Compressor are presented. The main part of the experimental investigations was performed using Laser-Doppler-Anemometry. Results of the flow field at several spanwise positions between midspan and rotor blade tip will be discussed. In addition time-resolving pressure sensors at midspan of the rotor blades provide information about the unsteady profile pressure distribution. In part II of the paper the flow field in the rotor blade tip region will be discussed. The experimental results reveal a strong periodical interaction of the incoming stator wakes and the rotor blade tip clearance vortices. Consequently, in the rotor frame of reference the tip clearance vortices are periodical with the stator blade passing frequency. Due to the wakes the tip clearance vortices are separated into different segments. Along the mean vortex trajectory these parts can be characterised by alternating patches of higher and lower velocity and flow turning or subsequent counterrotating vortex pairs. These flow patterns move downstream along the tip clearance vortex path in time. As a result of the wake influence the orientation and extension of the tip clearance vortices as well as the flow blockage periodically vary in time.
Gas Turbines in Alternative Fuel Applications: Biodiesel Field Test
Authors: Molie`re Michel , Panarotto Elvio , Aboujaib Maher , Bisseaud Jean Michel , Campbell Anthony , Citeno Joseph , Maire Pierre-Andre´ , Ducrest Laurent
Published: March 2009

As fuel candidates for power generation are mushrooming worldwide, there is presently a surge of interest around liquid biofuels that form a large and contrasting family. Among biofuels, biodiesels are natural candidates due to their compatibility with gasoil and their increasing use in the transportation sector. While biodiesels are similar to gasoils in terms of physical data, both their chemical properties and combustion behavior can be markedly different. In the framework of a development program devoted to biofuels and in collaboration with the Swiss power producer Groupe E, GE Energy has carried out a preliminary characterization of the combustion and emissions of a FAME (fatty acid methyl ester) at the Cornaux power plant, canton of Neuchaˆtel. This Field Test has been performed in a Frame 6B equipped with standard combustors and involved both a pure FAME consisting of RME (rapeseed methyl ester) and FAME co-fired with natural gas.
Labyrinth Seal Leakage Tests: Tooth Profile, Tooth Thickness, and Eccentricity Effects
Authors: Gamal Ahmed M. , Vance John M.
Published: March 2009

The effects of two seal design parameters, namely blade (tooth) thickness and blade profile, on labyrinth seal leakage, as well as the effect of operating a seal in an off-center position, were examined through a series of non-rotating tests. Two reconfigurable seal designs were used, which enabled testing of two- four-, and six-bladed see-through labyrinth seals with different geometries using the same sets of seal blades. Leakage and cavity pressure measurements were made on each of twenty-three seal configurations with a four inch (101.6 mm) diameter journal. Tests were carried out with air as the working fluid at supply pressures of up to 100 psi-a (6.89 bar-a). Experimental results showed that doubling the thickness of the labyrinth blades significantly influenced leakage, reducing the flow-rate through the seals by up to 20%. Tests to determine the effect of blade-tip profile produced more equivocal results, with the results of experiments using each of the two test seal designs contradicting each other. Tests on one set of hardware indicated that beveling blades on the downstream side was most effective in limiting leakage whereas tests on newer hardware with tighter clearances indicated that seals with flat-tipped blades were superior. The test results illustrated that both blade profile and blade thickness could be manipulated so as to reduce seal leakage. However, an examination of the effects of both factors together indicated that the influence of one of these parameters can, to some extent, negate the influence of the other (especially in cases with tighter clearances). Lastly, for all configurations tested, results showed that leakage through a seal increases with increased eccentricity and that this phenomenon was considerably more pronounced at lower supply pressures.
Performance Evaluation for the Application of Variable Turbine-Cooling-Bleeds in Civil Turbofans
Authors: Kyritsis Vasileios E. , Pilidis Pericles
Published: March 2009

Frequently, the mechanical integrity of gas turbine components is designed for a hot day, sea level take-off, where the maximum values are encountered for critical temperatures, such as the ones at the compressor and combustor outlet and the turbine rotor inlet stations. Turbine cooling flow rates are then defined taking into consideration maximum allowable metal temperatures, stresses, component life expectancy and heat transfer technology. Remaining unchanged as a percent of the core engine mass flow through the rest of the flight envelope, excessive cooling mass flows are actually being used during the cruise and the descent segment, since these operating points are characterized by significantly reduced temperatures. The main objective of the current work is the preliminary evaluation of the performance benefits, which can be achieved during a long range civil flight when decreasing the cooling bleed fraction during cruise. This is considered an essential step before any study concerning the consequences upon lifing is conducted. A conventional engine is optimized to meet the respective flight requirements, operating under constant cooling fraction throughout the mission. Reduction in cooling mass flow is applied, changing in such a way its off-design performance. Changes in typical engine parameters are identified and are graphically presented versus bleed flow reduction. Moreover, making use of a model providing for the drag polar of an airframe, while taking into account of the continuous weight reduction due to fuel burn, the variation of fuel consumption during cruise is also calculated. Fuel benefits are identified; a 40% reduction of the cooling fraction results in cruise fuel dropping by 0.75%. This can be justified on the basis of decreasing the cooling of the mainstream and increasing the mass flow, which is expanded through the turbine stages upstream. Although a metal temperature increase is also expected, it is accompanied by a Combustor Outlet and Turbine Entry temperature reduction.
Analysis of Indirectly Fired Gas Turbine Power Systems
Authors: Gauthier J. E. Donald
Published: March 2009

This paper describes the results of modelling the performance of several indirectly fired gas turbine (IFGT) power generation system configurations based on four gas turbine class sizes, namely 5 kW, 50 kW, 5 MW and 100 MW. These class sizes were selected to cover a wide range of installations in residential, commercial, industrial and large utility power generation installations. Because the IFGT configurations modelled consist of a gas turbine engine, one or two recuperators and a furnace; for comparison purpose this study also included simulations of simple cycle and recuperated gas turbine engines. Part-load, synchronous-speed simulations were carried out with generic compressor and turbine maps scaled for each engine design point conditions. The turbine inlet temperature (TIT) was varied from the design specification to a practical value for a metallic high-temperature heat exchanger in an IFGT system. As expected, the results showed that the reduced TIT can have dramatic impact on the power output and thermal efficiency when compared to that in conventional gas turbines. However, the simulations also indicated that several configurations can lead to higher performance, even with the reduced TIT. Although the focus of the study is on evaluation of thermodynamic performance, the implications of varying configurations on cost and durability are also discussed.
CFD Study of HPT Blade Cooling Flow Supply Systems
Authors: El-Sadi Haifa , Guevremont Grant , Marini Remo , Girgis Sami
Published: March 2009

This work summarizes the results of the CFD analyses to investigate the effect of the geometrical parameters for a typical coverplate-disk cavity and blade broach system also known as the blade cooling flow supply system. A turbofan high pressure turbine was used as the test vehicle for this investigation. The main objective was to explore potential improvements in engine SFC (aerodynamic performance) by reducing the parasitic work while minimizing the impact on the factors that affect the durability of the turbine blades; feed pressure, temperature, and mass flow. Various tangential on-board injection (TOBI) blade cooling flow supply systems were considered: i) Phase 1 compared the radial TOBI and axial TOBI, ii) Phase 2 compared coverplate-disk cavity shapes, and iii) Phase 3 compared blade broach shapes. The in-house CFD code NS3D was used for the analyses. Compared to the radial TOBI, the axial TOBI has a positive impact on the parasitic work (lower) and blade feed temperature (lower) while it has a negative impact on the blade feed pressure (lower). Further, the coverplate-disk cavity shapes investigated had no significant impact on the parasitic work, blade feed pressure, and blade feed temperature. The CFD solutions show that the major portion of the parasitic work is due to flow turning at the broach entrance. Finally, reducing the blade broach cross-section by sloping up the lower wall has no significant impact on the parasitic work and blade feed temperature but a negative impact on the blade feed pressure and mass flow. Modifying the broach pressure side wall shape is preferred among the blade broach geometries investigated. Future work to improve the CFD analysis consists of performing unsteady analyses to better capture the vortex flow in the blade broach, and including upstream stationary components with either iterative boundary condition modeling or an unsteady multi-stage approach.
Comparative Study of Two Low CO2 Emission Cycle Options With Natural Gas Reforming
Authors: Zhang Na
Published: March 2009

Two power plant schemes with natural gas reforming and CO2 emission reduction were analyzed and discussed. The first one integrates natural gas reforming technology with an oxy-fuel combined power cycle (OXYF-REF), with water as the main work fluid. The reforming heat is obtained from the available turbine exhaust heat, and the produced syngas is used as fuel with oxygen as the oxidizer. The turbine working fluid can expand down to a vacuum, producing a high pressure ratio. The second system adopts pre-combustion decarbonization and a chemical absorption technology for CO2 removal (PCD-REF). The gas turbine is the conventional air based one with compressor intercooling. Supplementary combustion is adopted to elevate the turbine exhaust temperature and thus achieve a much higher methane conversion rate (∼95%). Both cycles involve internal heat recuperation from gas turbine exhausts, and particular attention has been put on the integration of heat recovery chain to reduce the related exergy destruction. The systems are simulated and compared in terms of both thermal efficiency and CO2 removal. The OXYF-REF cycle has shown better performance with higher levels of CO2 removal and energy efficiency of 52%. The PCD-REF cycle showed a thermal efficiency of 43% and CO2 specific emission of 55.5 g/kWh.
Effect of Clocking on the Unsteady Rotor Blade Loading in a 1.5-Stage Low-Speed Axial Compressor
Authors: Jia Huixia , Vogeler Konrad
Published: March 2009

This paper presents the effect of clocking on the unsteady loading of the rotor blades in the first stage with an inlet guide vane row (IGV) of the Dresden Low-Speed Research Compressor (LSRC). The unsteady flow field of the Dresden LSRC at 10 IGV clocking positions for the design point was investigated using a 3D time-accurate viscous solver. The time-averaged pressure distributions on the pressure side (PS) and the suction side (SS) of the rotor blades at midspan (MS) are presented for different clocking positions. The effect of the clocking on the time-averaged Root Mean Square-value (RMS) of the unsteady pressure fluctuations of the rotor blades at MS is investigated. The unsteady pressure fluctuations on the PS and the SS of the rotor blades at MS for different clocking positions are presented and discussed. The unsteady blade pressure forces on the rotor blades, which are calculated from the profile pressure distributions, are presented and analysed for different clocking positions. The maximal fluctuation amplitude of the unsteady pressure forces on the rotor blades, which fluctuate around the nearly identical mean values for different clocking positions, can be reduced about 60 percent with the IGV clocking for the design point in the investigated configuration. The effect of the clocking on the time-resolved inlet- and outlet flow fields of the rotor blades is investigated and discussed.
Improvements to the Analysis of Gas Foil Bearings: Integration of Top Foil 1D and 2D Structural Models
Authors: San Andre´s Luis , Kim Tae Ho
Published: March 2009

Gas foil bearings (GFBs) find widespread usage in oil-free turbo expanders, APUs and micro gas turbines for distributed power due to their low drag friction and ability to tolerate high level vibrations, including transient rubs and shaft misalignment, static and dynamic. The static load capacity and dynamic forced performance of GFBs depends largely on the material properties of the support elastic structure, i.e. a smooth foil on top of bump strips. Conventional models include only the bumps as an equivalent stiffness uniformly distributed around the bearing circumference. More complex models couple directly the elastic deformations of the top foil to the bump underlying structure as well as to the hydrodynamics of the gas film. This paper details two FE models for the top foil supported on bump strips, one considers a 2D shell anisotropic structure and the other a 1D beam-like structure. The Cholesky decomposition of the stiffness matrix representing the top foil and bump strips is performed off-line prior to computations coupling it to the gas film analysis governed by Reynolds equation. The procedure greatly enhances the computational efficiency of the numerical scheme. Predictions of journal attitude angle and minimum film thickness for increasing static loads and two journal speeds are obtained for a GFB tested decades ago. 2D FE model predictions overestimate the minimum film thickness at the bearing centerline, while underestimating it at the bearing edges. Predictions from the 1D FE model compare best to the limited tests data; reproducing closely the experimental circumferential wavy-like minimum film thickness profile. The 1D top foil model is recommended due to its low computational cost. Predicted stiffness and damping coefficients versus excitation frequency show that the two FE top foil structural models result in slightly lower direct stiffness and damping coefficients than those from the simple elastic foundation model.
Acoustic Pyrometry for Harsh, Chemically Reacting Environments
Authors: Norris William , Bauer Candice
Published: March 2009

The objective of this research is to demonstrate the feasibility of using acoustic pyrometry methods to take measurements in harsh, chemically reacting flow such as gas turbine engine combustion chambers. Conventional methods utilize flow invasive devices, have line of sight requirements, or use exterior parameters to measure the internal temperatures of a combustion chamber. Acoustic pyrometry methods can avoid many of these compromises and have been applied to a wide variety of industrial systems including the measurement of furnace exit gas temperatures, waste-to-energy boilers, cement kilns, metal treatment furnaces, and many other applications. The passive system works on the concept that temperature affects the speed of sound through a fluid. This work establishes that passive acoustic pyrometry is a viable option for determining combustor performance and for measuring fuel-to-air ratios and temperatures from acoustic resonances in an engine. The results include the ability to monitor temperature distributions and develop algorithms to obtain several other data sets. The work detailed includes research performed and compared with results obtained using conventional methods at NASA Glenn Research Center and Rolls Royce.
Effect of Rotation on Heat/Mass Transfer for an Impingement/Effusion Cooling System
Authors: Hong Sung Kook , Cho Hyung Hee
Published: March 2009

The purpose of this study is to investigate the effect of rotation on the heat/mass transfer in an impingement/effusion cooling system. To simulate the rotating impingement/effusion system, a test duct with injection and effusion holes is installed on the rotating system. The jet Reynolds number based on the hole diameter is fixed to 3,000 and the Rotation number is set to 0.032. The experiments are carried out for various parameters such as the plate spacing to hole diameter ratio (H/d), orientation of the jet relative to the rotating axis and the tests for the array jet cooling are performed together. The naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. The local heat/mass transfer distributions are altered by the rotation. For the impingement/effusion cooling with orthogonal orientation, the low and non-uniform heat/mass transfer occurs between the effusion holes because the impinging jet is deflected by the Coriolis force. At a small H/d, the rotation enhances the heat/mass transfer in the stagnation region due to an increase in flow mixing. The impingement/effusion cooling with H/d = 2 shows the most efficient cooling performance and it is confirmed that the crossflow and H/d affect the averaged Sh value significantly under rotating conditions.
Validation of Advanced Computational Methods for Determining Flame Transfer Functions in Gas Turbine Combustion Systems
Authors: Kostrzewa Krzysztof , Noll Berthold , Aigner Manfred , Lepers Joachim , Krebs Werner , Prade Bend , Huth Michael
Published: March 2009

The operation envelope of modern gas turbines is affected by thermoacoustically induced combustion oscillations. The understanding and development of active and passive means for their suppression is crucial for the design process and field introduction of new gas turbine combustion systems. Whereas the propagation of acoustic sound waves in gas turbine combustion systems has been well understood, the flame induced acoustic source terms are still a major topic of investigation. The dynamics of combustion processes can be analyzed by means of flame transfer functions which relate heat release fluctuations to velocity fluctuations caused by a flame. The purpose of this paper is to introduce and to validate a novel computational approach to reconstruct flame transfer functions based on unsteady excited RANS simulations and system identification. Resulting time series of velocity and heat release are then used to reconstruct the flame transfer function by application of a system identification method based on Wiener-Hopf formulation. CFD/SI approach has been applied to a typical gas turbine burner. 3D unsteady simulations have been performed and the flame transfer results have been validated by comparison to experimental data. In addition the method has been benchmarked to results obtained from sinusoidal excitations.
Axis-Asymmetric Profiled Endwall Design by Using Multiobjective Optimisation Linked With 3D RANS-Flow-Simulations
Authors: Dorfner Christian , Nicke Eberhard , Voss Christian
Published: March 2009

Secondary flow loss in modern axial compressors is considered to be the prime reason for the reduction of overall isentropic efficiency in these engine components. This paper presents a new methodology to diminish blade secondary loss and endwall loss by an axis-asymmetric modification of endwalls using an automated multiobjective optimizer in conjunction with 3D-RANS-flow-simulations. In order to obtain a favorable design for a wide operating range, the most important operating-points are considered in the optimization process. The existing multiobjective optimization package is enhanced by implementation of DLR’s in-house 3D-flow-solver TRACE. A straightforward stator optimization was performed for a 3D-process-chain test run. Finally, the novel endwall design technique is introduced and the first optimization results and further studies are discussed.
Flow and Mixing in a Model GT Combustor Investigated by LES and Monte-Carlo Filtered PDF Methods
Authors: Olbricht Clemens , Hahn Frederik , Ku¨hne Jens , Sadiki Amsini , Janicka Johannes , Bake Friedrich , Ro¨hle Ingo
Published: March 2009

In advanced gas turbines prediction and understanding of mixing and combustion dynamics become increasingly important to achieve higher efficiency and lower emissions. Therefore suitable information on the small scales is required due to their influence on a vast number of process factors such as micromixing efficiency, chemical reaction rate, turbulence-chemistry interaction, etc.. Here the subgrid probability density function (pdf) of a transported scalar is obtained by an Eulerian Monte-Carlo approach. In this context the evolution of the pdf is represented by ensembles of stochastic particles. The macromixing is provided by LES resolving the large scales. Dealing with confined configurations, the ability of LES to enable accurate temporal and spatial analysis of flow and mixing process is first demonstrated within a swirl stabilized model gas turbine combustor. Then LES is coupled to the Eulerian Monte Carlo method to provide an extensive study of multi-scale mixing processes. Therefore a feature of realistic combustors is investigated by means of two opposite rows of jets penetrating a cross flow. It turns out that the hybrid LES-MC method is a reliable tool for this purpose.