bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation of Unsteady Boundary Layer Transition Induced by Periodically Passing Wakes With an Intermittency Transport Equation
Authors: Pecnik Rene , Sanz Wolfgang , Pieringer Paul
Published: November 2008

A numerical study was performed to investigate unsteady flow transition under the effect of periodically passing wakes on a highly loaded low-pressure turbine cascade. The simulation was done by a time-accurate 2D Navier-Stokes solver, which was developed at the Institute for Thermal Turbo-machinery and Machine Dynamics. The transition process was modeled by coupling a baseline two-equation k-ω turbulence model with an intermittency transport equation via the turbulence production term. The experimental investigations on the highly loaded low-pressure turbine cascade, called T106D-EIZ were carried out at the Institut fu¨r Strahlantriebe der Universita¨t der Bundeswehr Mu¨nchen (Germany). The available experimental data contains three test cases by varying the isentropic exit Reynolds number from 200.000 to 60.000. The objective of this paper is to show the ability of an intermittency transport equation to model unsteady wake induced transition and separation mechanisms. The numerical results are compared by the pressure distribution, shape factor and loss behavior to the experiments.
Buoyancy-Induced Flow in a Heated Rotating Cavity
Authors: Owen J. Michael , Powell Jonathan
Published: November 2008

Experimental measurements were made in a rotating-cavity rig with an axial throughflow of cooling air at the centre of the cavity, simulating the conditions that occur between corotating compressor discs of a gas-turbine engine. One of the discs in the rig was heated, and the other rotating surfaces were quasi-adiabatic; the temperature difference, between the heated disc and the cooling air was between 40 and 100 °C. Tests were conducted for axial Reynolds numbers, Rez, of the cooling air between 1.4 × 103 and 5 × 104, and for rotational Reynolds numbers, Reφ, between 4 × 105 and 3.2 × 106. Velocity measurements inside the rotating cavity were made using LDA, and temperatures and heat flux measurements on the heated disc were made using thermocouples and fluxmeters. The velocity measurements were consistent with a 3D, unsteady, buoyancy-induced flow in which there was a multicell structure comprising one, two or three pairs of cyclonic and anti-cyclonic vortices. The core of fluid between the boundary layers on the discs rotated at a slower speed than the discs, as found by other experimenters. At the smaller values of Rez, the radial distribution and magnitude of the local Nusselt numbers, Nu, were consistent with buoyancy-induced flow. At the larger values of Rez, the distribution of Nu changed, and its magnitude increased, suggesting the dominance of the axial throughflow.
Investigation on the Influence of a Core Chevron Nozzle on the Performance of a Modern Bypass Engine
Authors: Weißschuh Matthias , Staudacher Stephan
Published: November 2008

In light of intensifying environmental concerns, the noise in aircraft gas turbine engines needs to be reduced significantly. Considerable work has been conducted to reduce jet noise produced by the mixing of high velocity gas streams with ambient air. Various nozzle designs such as lobed nozzles, serrated nozzles or chevron nozzles have been used and proposed to control and modify the velocity pattern of exhaust gas streams. This paper presents investigations on the influence of a core chevron nozzle on the performance of a modern bypass engine. The characteristic discharge, velocity and specific thrust coefficients of the chevron and non-chevron nozzles are determined by numerical calculations and are verified with experimental data. The nozzle coefficients form the basis for an engine performance comparison between the two hot nozzle configurations of the bypass engine. The effect of the nozzle configuration on overall engine performance and component working points has been investigated by applying an engine performance synthesis tool. The thrust loss and the corresponding SFC increase which has been observed by using the chevron nozzle have been related to engine internal rematching and changes in nozzle performance.
A Low Speed Axial Compressor With a Cascade of Magnus Rotors to Replace the Aerofoils of the Stator
Authors: Rose M. G.
Published: November 2008

The low speed axial research compressor ‘Rheinfall’ in the Turbomachinery Labs at ETH Zu¨rich has been modified to include a novel stator row. The conventional stator’s vanes have been replaced with a cascade of rotating cylinders or ‘Magnus Rotors’. The initial aim was to demonstrate that such a cascade could reproduce the effect of the aerofoils. This paper gives an overview of the design, experimental results and conclusions drawn from simple modeling of the experiment. The behaviour of the compressor is essentially preserved; the conventional rotor stalls at a slightly higher flow coefficient (φ = 0.4). The pressure rise across the compressor is a function of the cylinder rotational speed. The pressure recovery coefficient Cpr across the stator can be increased by up to 60% compared to the conventional aerofoils with high rotational speed. The stator pressure rise is maintained at much lower flow coefficient (φ = 0.23). Lift coefficients of up to 7.0 have been stably demonstrated. The stator is capable of very high turning (>60°), to axial and beyond. From simple flow modeling the aerodynamic efficiency appears to be about the same as the conventional machine. However, the parasitic losses in the high-speed Magnus spindles double the power absorbed. The recorded characteristics show strong hysteresis across the whole flow range.
Computational Parametric Study of Fuel Distribution in an Experimental Trapped Vortex Combustor Sector Rig
Authors: Hendricks R. C. , Ryder R. C. , Brankovic A. , Shouse D. T. , Roquemore W. M. , Liu N.-S.
Published: November 2008

Numerical simulations are performed to predict the flow properties in a liquid spray droplets fueled Trapped Vortex Combustor (TVC) sector rig. The quantities studied include aerodynamics, pressure drop, spray droplets trajectories, evaporation, mixing and combustion, and combustor exit temperature distributions. Previous numerical simulations of this TVC configuration have identified basic flow patterns and performance characteristics, and were generally in good agreement with experimental data. In the current effort, more detailed investigations were performed to understand the sensitivity of the TVC combustor to variations in the liquid fuel injection parameters. The computational model is described, including combustor geometry, boundary conditions for all combustion and cooling air injections, and spray droplets inlet conditions. A key finding is that liquid fuel injection boundary conditions for different types of downstream flows (cavity, high velocity cross flow) require different treatments, even though similar fuel injectors are used. This is evident in the large differences observed in the combustor exit plane pattern factor due to only minor differences in the fueling schemes. Combustor exit temperature profile strongly affects the design for turbine durability. With small changes in the temperature distribution, design modifications for the first turbine vane cooling schemes are required.
High Coverage Blade Tip Film Cooling
Authors: Kuwabara M. , Tsukagoshi Keizo , Arts T.
Published: November 2008

More sophisticated cooling schemes are required for the turbine blade due to the demand of increased turbine temperature for improved performance. Although the tip portion of a turbine blade is one of the most critical portions in a gas turbine, there are few studies on cooling this portion compared to those for airfoil, especially film cooling strategies. Industrial gas turbines have a more uniform gas temperature profile than aero engines. For these applications, it is more important to understand the characteristics of tip film cooling to improve the blade durability and gas turbine performance by reducing cooling air. A numerical and experimental program was initiated to study film cooling effectiveness on a flat blade tip as a function of tip gap and mass flux ratios. Flow visualization tests were conducted with and without film cooling to verify the numerical CFD findings. The predictions and visualization results showed that a separation bubble forms at the pressure side edge that increases with tip gap. Film effectiveness measurements were carried out on a 1.3X scale blade model in a low speed test while simulating the normalized pressure distribution typical of an engine design. The engine density ratio of the coolant to mainstream was replicated in the film cooling tests to provide the best simulation of the engine. Two rows of holes were placed near the tip of the blade to provide high film coverage prior to the flowing over the tip. The data shows that film effectiveness increases with decreasing tip clearance. Blowing ratio provides an improvement due to the added mass flow, which was shown by a non-dimensionalized correlation.
A Study of Parameters Affecting the Combustion Stability and Emissions Behavior of Alstom Heavy-Duty Gas Turbines
Authors: Nord Lars O. , Andersen Helmer G.
Published: November 2008

A number of factors can influence the combustion instability region and emission behavior of a heavy-duty gas turbine. Changes in the composition of the natural gas supplied have an impact that was studied in a prior investigation, which focused on parameters such as fuel temperature and composition. To further investigate the fuel sensitivity additional plants were included in this study. In addition to the fuel properties the distribution of the fuel inside the combustor was examined. To expand the fuel properties study, additional parameters were examined. Ambient conditions were paid special interest, specifically ambient temperature and humidity. Included in this study was also the effect on combustion of changes in compressor discharge pressure. With the growing interest in inlet chilling a pulsation/emission study was included to specifically look for NOx and combustion instability effects due to inlet chilling. Also, influences from special occurrences such as on-line compressor washing were examined. The turbines in this study utilize a silo-type combustor with either the DLN [Dry Low NOx] EV [EnVironmental] burners or with single diffusion burners using water or steam as NOx reduction medium. The rated power output of the gas turbines was in the range of 50–120 MW. The data acquired included frequency-analyzed combustion instabilities, various process data, as well as ambient conditions and fuel composition. The collected data shows the magnitude of the changes in the emissions and combustion noise with changes in the parameters studied. The conclusion is that some key parameters are very important for both the pulsations and the emissions, whereas others can be neglected. Some parameters affect the combustion instabilities only, without noticeable effect on emissions, and vice versa.
The Effect of Freestream Turbulence on Film Cooling Heat Transfer Coefficient and Adiabatic Effectiveness Using Compound Angle Holes
Authors: Mayhew James E. , Baughn James W. , Byerley Aaron R.
Published: November 2008

The film-cooling performance of a flat plate in the presence of low and high freestream turbulence is investigated using thermochromic liquid crystal thermography. Distributions of the convective heat transfer coefficient and adiabatic effectiveness are determined over the film-cooled surface of the flat plate. Three blowing rates are investigated for a model with one hole oriented at a compound angle of 45° and with an injection angle of 30° from the flat plate surface. An increase in heat transfer coefficient due to mass injection is clearly observed in the images and is quantitatively determined for both the low and high freestream turbulence cases. The increase in heat transfer coefficient is greater than in previously published research, possibly due to the use of different, more representative thermal boundary conditions upstream of the injection location. At low blowing ratio, freestream turbulence is shown to reduce the adiabatic effectiveness due to increased mixing between the cooling air and the main flow. However, at high blowing ratio, when much of the jet has lifted off in the low turbulence case, high freestream turbulence turns its increased mixing into an asset, entraining some of the coolant that penetrates into the main flow and mixing it with the air near the surface. This paper also contributes high-resolution contour plots that show the wider spreading of cooling air over the film-cooled surface as a result of high turbulence, and the asymmetric regions of high heat transfer.
Ignition Characteristics on the Annular Combustor With Rotating Fuel Injection System
Authors: Lee Kang Yeop , Choi Seong Man , Han Yeoung-Min , Park Jeong-Bae
Published: November 2008

An experimental study was performed to investigate the ignition characteristics on the annular combustor with rotating fuel injection system. The combustor was tested in KARI (Korea Aerospace Research Institute) combustor test facility. As the results of the test, equivalence ratio of lean ignition limit is 0.15 at 7,300 rpm and 0.08 at 10,400 rpm respectively. Combustion efficiency is gradually increased from 99.1% to 99.62% with increasing shaft speed from 15,000 rpm to 30,000 rpm. Over than 30,000 rpm, the combustion efficiency is not changed and kept constant. From the ignition and combustion test, ignition process of this annular combustor is mainly governed by the shaft speed. To understand the relationship between the spray characteristics and shaft speed, droplet size was measured by using PDPA system. In this spray test, Sauter mean diameter (SMD) largely depends on the shaft speed. SMD is changed from 73 μm to 42 μm with increasing the shaft speed from 5,000 rpm to 20,000 rpm.
The Influence of Compressor Aerodynamics on Pressure Probes: Part I — In Rig Calibrations
Authors: Coldrick S. , Ivey P. C. , Wells R. G.
Published: November 2008

Steady state flow measurements as obtained by multi hole pneumatic pressure probes are relevant to the current design process. These probes are calibrated in a uniform flow in a wind tunnel prior to their application in the test compressor. It is known that the probes do not behave in the same way in the test compressor as in the wind tunnel, one of the factors is that the flow in the compressor is fluctuating and this is thought to influence the probe’s operation. This two part paper investigates the influence of unsteady effects on probe operation. Part one covers an experimental investigation in which two pneumatic probes were calibrated firstly in a wind tunnel, then in low and high speed compressors. The probe that was used for the low speed compressor was scaled up from its high speed counterpart due to the increased size of the machine. The calibration graphs obtained by yawing the probe in the wind tunnel were reproduced with good accuracy when the same process was performed in the compressors. Whereas for the low speed compressor, the probe Reynolds number was the same as in the wind tunnel, the high speed compressor operated at a much larger Reynolds number.
The Influence of Compressor Aerodynamics on Pressure Probes: Part 2 — Numerical Models
Authors: Coldrick S. , Ivey P. C. , Wells R. G.
Published: November 2008

This paper presents the second part of an investigation into the influences of the aerodynamics of compressor blade rows on measurements made using steady state pneumatic pressure probes. In part one, the in rig calibrations of the probes in the low and high speed compressors showed that the wind tunnel derived calibration in yaw could be reproduced with good accuracy in the compressor, despite the flow in the compressor being unsteady, and in the case of the high speed compressor, of a different Reynolds number. In this part, CFD simulations of the flow about a probe, both within a low speed compressor and a steady, uniform flowfield are presented. The influence of the pressure gradient existing within the stators in which the probe is positioned was found to be small, as was the effects of unsteady flow. The major contribution to measurement errors appears to lie within the probe blockage effect.
A Non-Coupled CFD-FE Procedure to Evaluate Windage and Heat Transfer in Rotor-Stator Cavities
Authors: Lewis Leo V. , Provins James I.
Published: November 2008

A combined CFD and FE method, which could be applied to a wide range of internal air system rotor-stator cavities and which overcomes the disadvantages of many non-coupled approaches, is presented. It is used to predict windage and heat transfer in the HP compressor rear cone outer cavity of a service aeroengine. From the CFD it is shown that rotor wall torque, and hence windage, decreases as cavity throughflow increases, and that the data from several engine cavities can be reduced to a single characteristic of windage versus mass flow. Stator wall torque is also presented. A comparison with engine thermocouple data shows that further development of the modelling is required before engine testing could be replaced.
Film-Cooling Effectiveness on a Gas Turbine Blade Tip Using Pressure Sensitive Paint
Authors: Ahn Jaeyong , Mhetras Shantanu , Han Je-Chin
Published: November 2008

Effects of the presence of squealer, the locations of the film cooling holes, and the tip gap clearance on the film cooling effectiveness were studied and compared to plane tip. The film cooling effectiveness distributions were measured on the blade tip using Pressure Sensitive Paint technique. Air and nitrogen gas were used as the film cooling gases and the oxygen concentration distribution for each case was measured. The film cooling effectiveness information was obtained from the difference of the oxygen concentration between air and nitrogen gas cases by applying the mass transfer analogy. Plane tip and squealer tip blades were used while the film cooling holes were located (a) along the camber line on the tip or (b) along the span of the pressure side. The average blowing ratio of the cooling gas was controlled to be 0.5, 1.0, and 2.0. Tests were conducted in a five-bladed linear cascade with a blow down facility. The free stream Reynolds number, based on the axial chord length and the exit velocity, was 1,100,000 and the inlet and the exit Mach number were 0.25 and 0.59, respectively. Turbulence intensity level at the cascade inlet was 9.7%. All measurements were made at three different tip gap clearances of 1%, 1.5%, and 2.5% of blade span. Results show that the locations of the film cooling holes and the presence of squealer have significant effects on surface static pressure and film-cooling effectiveness.
Measured Adiabatic Effectiveness and Heat Transfer for Blowing From the Tip of a Turbine Blade
Authors: Christophel J. , Couch E. , Thole K. A. , Cunha F. J.
Published: November 2008

The clearance gap between the tip of a turbine blade and the shroud has an inherent leakage flow from the pressure side to the suction side of the blade. This leakage flow of combustion gas and air mixtures leads to severe heat transfer rates on the blade tip of the high pressure turbine. As the thermal load to the blade increases, blade alloy oxidation and erosion rates increase thereby adversely affecting component life. The subject of this paper is the cooling effectiveness levels and heat transfer coefficients that result from blowing through two holes placed in the forward region of a blade tip. These holes are referred to as dirt purge holes and are generally required for manufacturing purposes and expelling dirt from the coolant flow when operating in sandy environments. Experiments were performed in a linear blade cascade for two tip gap heights over a range of blowing ratios. Results indicated that the cooling effectiveness was highly dependent upon the tip gap clearance with better cooling achieved at smaller clearances. Also, heat transfer was found to increase with blowing. In considering an overall benefit of cooling from the dirt purge blowing, a large benefit was realized for a smaller tip gap as compared with a larger tip gap.
Axial Turbine Tip Desensitization by Injection From a Tip Trench: Part 1 — Effect of Injection Mass Flow Rate
Authors: Rao Nikhil M. , Camci Cengiz
Published: November 2008

An experimental study of a turbine tip desensitization method based on tip coolant injection was conducted in a large-scale rotating turbine rig. One of twenty-nine rotor blades was modified and instrumented to have a tip trench with discrete injection holes directed towards the pressure side. Time accurate absolute total pressure was measured 0.3 chord lengths downstream of the rotor exit plane using a fast response dynamic pressure sensor in a phase-locked manner. The test cases presented include results for tip gap heights of 1.40% and 0.72% of the blade height, and coolant injection rates of 0.41%, 0.52%, 0.63%, and 0.72% core mass flow rate. At a gap height of 1.40% the leakage vortex is large, occupying about 15% blade span. A reduction in gap height causes the leakage vortex to reduce in size and move towards the blade suction side. The minimum total pressure measured, for the reduced gap, in the leakage vortex is about 4% greater. Coolant injection from the tip trench is successful in filling in the total pressure defect originally resulting from the leakage vortex without injection. At the higher tip injection rates the leakage vortex is also seen to have moved towards the blade tip. The high momentum associated with the tip jets affects the total pressure distributions in the neighboring passages.
Axial Turbine Tip Desensitization by Injection From a Tip Trench: Part 2 — Leakage Flow Sensitivity to Injection Location
Authors: Rao Nikhil M. , Camci Cengiz
Published: November 2008

In Part 1 of this paper it was shown that discrete jets issuing from a tip platform trench were successful in reducing the total pressure deficit due to tip leakage flow. The specific tip cooling system used in Part 1 had all four injection locations active. This paper examines the effect of the individual location of the injection hole on the tip leakage flow. The investigation was carried out in a large-scale rotating rig. Total pressure downstream of the rotor exit was measured using a Kulite sensor. The measurements were phase-locked and ensemble averaged over 200 rotor revolutions. The injection holes are located at 61%, 71%, 81%, and 91% blade axial chord, in the tip trench of a single blade with a clearance of 1.40% blade height. Individual injection at 61% and 71% chord reduced the leakage vortex size. Coolant injection at 81% chord was the most successful in reducing the total pressure deficit in the leakage vortex. Injection from 91% chord had no effect on the leakage vortex. Injection from combinations of holes had greater effect in reducing the leakage vortex size and the total pressure deficit associated with the vortex. It can be concluded that the individual jets most likely turn the leakage flow towards the trailing edge. Most of the leakage flow that is responsible for the greatest total pressure deficit occurs around 80% chord.
Gas Turbines in Alternative Fuel Applications: The Utilization of Highly Aromatic Fuels in Power Generation
Authors: Moliere Michel , Geiger Frederic
Published: November 2008

Heavy Duty Gas Turbines enjoy a wide fuel capability that makes them increasingly popular power generation tools in several branches of the industry. Among Alternative Fuels for gas turbines is a group of “Aromatic Fuels”. These fuels are presently virtually unknown but they offer interesting prospects namely for captive power in the refining and petrochemistry. Until now there has been a limited awareness of the combustion issues posed by Aromatic Fuels especially in the high temperature, medium pressure conditions of gas turbine combustors. This apparent disinterest is tied to various issues namely: - smoke problems faced by the aviation sector during the 70’s that were caused by “aromatic jet fuels”; - the supremacy of natural gas that monopolizes R&D combustion efforts for power applications. The success of light aromatics in spark engines as substitutes for lead-based RON improvers has been stopped by the ban of aromatics in car fuels. Toxicity is thus another blemish of aromatic fuels. Chemically, aromatic fuels involve a wide diversity of molecules in structure and size, ranging from simple mono-aromatics (one benzene ring) to poly-aromatics (up to 3 condensed benzene rings). The general combustion problem posed by aromatic fuels lies in the high thermal stability of the benzene ring in oxidative conditions and its propensity to condense on itself and to form soot particles. In addition, the high Auto Ignition Temperature and Delay of Aromatic Fuels make them improper for combustion in Diesel engines and require large residence time in atmospheric flames. Interestingly, it appears that, with their hot and lean diffusion flames and relatively oxidizing combustion zones, Heavy Duty Gas Turbines exhibit a remarkable ability to break and cleanly burn out these molecules. The paper presents this new class of gas turbine fuels, outlines their market rationale and offers key combustion considerations to ensure clean utilization. It also summarizes the experience gathered by a gas turbine manufacturer in the combustion of BTX, C9+ and LCO type fuels. It also outlines the chemical mechanisms that underlie the clean combustion of aromatic fuels in gas turbine chambers.
Unconventional Fuels Experimental Campaigns in Gas Turbine Combustor at ENEL Sesta Facility
Authors: Balestri M. , Cecchini D. , Cinti V.
Published: November 2008

In 1991 ENEL started a research program on gas turbine problems, an important activity which contributed to the realisation of the ENEL Sesta Gas Turbine Test Facility located in Radicondoli, Siena, Italy [1]. The aim of this program was to increase ENEL’s competitiveness in the liberalised energy market dominated by the increasing application of gas turbines in combined cycles and re-powered power stations due to lower costs and the higher performances. The first testing campaigns carried out in Sesta were conducted with conventional fuels such as natural gas and diesel oil. In 1998, ENEL built a specific plant able to simulate alternative fuels by mixing different pure components. Pure gases that can be added to the NG to simulate the syngas are: H2, CO, CO2, N2, steam and ammonia (NH3). Throughout the years, many test campaigns have been conducted at ENEL using industrial gas turbine combustion systems, as well as using a wide variety of fuels and technologies. These tests were carried out for ENEL purpose or for external industrial customers. This paper describes the main characteristics of the ENEL Sesta facility with particular reference to the alternative fuels plants. Two tests carried out at the Sesta facility by ENEL using different industrial combustion systems and non-conventional fuels are also described. The first one refers to the use of H2/CH4 mixtures in a diffusion flame gas turbine combustor. The second one concerns the co-combustion of methane and syngas from biomass in a modified DLN gas turbine combustor.
Wear Prediction of Strip Seals Through Conductance
Authors: Ghasripoor Farshad , Turnquist Norman A. , Kowalczyk Mark , Couture Bernard
Published: November 2008

Labyrinth seal assemblies are often used to reduce gas and/or steam leakage in turbines. Caulked-in continuous strip seals are one of the common forms of seals employed on both the rotating and stationary components of turbines. Labyrinth seals perform best when minimum clearances are achieved during the steady state operation of the turbine. However, the design of the turbine and its operation during transient periods of start-up, shut-down and hot re-start often result in interference between the seal components. In the case of the strip seals, this leads primarily to wear of the strip, which in effect adds to leakage. The aim of this paper is to show that strip tip heating and melting during the rub is the main mechanism of wear in the strip. Hence thermal conductivity through the strip and into the body mass in which it is caulked is the primary controlling factor in seal wear. This paper will discuss the use of thermal conductivity and geometry of the strip in predicting wear during high speed rubs against a proprietary material. A close correlation between calculated and experimental strip seal wear data with a number of seal alloys will be demonstrated. Test data will indicate that material properties such as tensile strength and hardness have a minor effect on the wear behavior of continuous seal elements during high-speed rubs.
Studies on Bypass Transition of a Boundary Layer Subjected to Localized Periodic External Disturbances
Authors: Funazaki K. , Wakita Y. , Otsuki T.
Published: November 2008

This study aims at clarification of wake-induced bypass transition process of a boundary layer on a flat plate with no pressure gradient. Special attention is paid to inception as well as growth of a turbulent spot created by the incoming wake as an external disturbance. To meet this goal a unique wake generator is invented to create an isolated turbulent spot. A multi-probe sensor with seven single-hot-wire probes is used to measure wake-affected boundary layer. The wake generator consists of a disk, pillars and a very thin wire with a small sphere on it. The sphere on the wire generates periodic wakes behind it when it passes across the main flow in front of the test flat plate. These sphere wakes impinge the flat plate in a spatially and timewisely localized manner so that the wakes periodically leave narrow affected zones inside the boundary layer. The observations confirm that an isolated turbulence spot emerges from each of those wake-affected zones. It is also found that the turbulent spot observed in this study bears a close resemblance to the conventional turbulent spot that takes a shape of arrowhead pointing downstream.
Surface Roughness Effects on Turbine Blade Aerodynamics
Authors: Hummel Frank , Lo¨tzerich Michael , Cardamone Pasquale , Fottner Leonhard
Published: November 2008

The aerodynamic performance of a turbine blade was evaluated via total pressure loss measurements on a linear cascade. The Reynolds number was varied from 600,000 to 1,200,000 to capture the operating regime for heavy-duty gas turbines. Four different types of surface roughness on the same profile were tested in the High Speed Cascade Wind Tunnel of the University of the German Armed Forces Munich and evaluated against a hydraulically smooth reference blade. The ratios of surface roughness to chord length for the test blade surfaces are in the range of Ra/c = 7.6×10−06 – 7.9×10−05. The total pressure losses were evaluated from wake traverse measurements. The loss increase due to surface roughness was found to increase with increasing Reynolds number. For the maximum tested Reynolds number of Re = 1,200,000 the increase in total pressure loss for the highest analysed surface roughness value of Ra = 11.8 μm was found to be 40% compared to a hydraulically smooth surface. The results of the measurements were compared to a correlation from literature as well as to well-documented measurements in literature. Good agreement was found for high Reynolds numbers between the correlation and the test results presented in this paper and the data available from literature.
Asymmetrical Underplatform Dampers in Gas Turbine Bladings: Theory and Application
Authors: Panning Lars , Popp Karl , Sextro Walter , Go¨tting Florian , Kayser Andreas , Wolter Ivo
Published: November 2008

During operation, the rotating blades of a gas turbine are subjected to centrifugal forces as well as fluctuating gas forces, resulting in blade vibrations. In addition to material damping, aerodynamical and blade root damping, underplatform dampers are widely used to increase the amount of damping and to decrease blade vibration amplitudes. The friction forces generated by the relative displacements between the underplatform damper and the blade platforms provide a significant amount of energy dissipation. In practice, a number of different underplatform damper designs are applied. Basically, these are wedge dampers with flat contact areas, cylindrical dampers with curved surfaces or asymmetrical dampers with both flat contact surfaces on one side and curved contact surfaces on the other. The latter damper type combines the advantages of both the wedge and the cylindrical damper by preventing the damper from pure rolling on the one hand as it has been observed for cylindrical dampers and on the other hand, avoiding a diverged plane area contact in case of a wedge damper, causing a damper lift-off. This paper will focus on the investigation of cylindrical and asymmetrical underplatform dampers. A comparison between measurements of rotating assemblies in Siemens PG gas turbines (V84.2, V64.3A and V94.3A(2)) under test and real operating conditions with cylindrical and asymmetrical underplatform dampers and the predictions of the developed theoretical model are presented. Special attention is paid to the frequency shift due to the application of an underplatform damper, since in particular for stationary gas turbines, in addition to the amplitude reduction, the accurate prediction of the resonance frequency is of major interest.
The Effect of Water Injection on Multi-Spool Gas Turbine Behaviour
Authors: Meacock A. J. , White A. J.
Published: November 2008

The injection of water droplets into industrial gas turbines is now common place and is central to several proposed advanced cycles. These cycles benefit from the subsequent reduction in compressor work, the increase in turbine work, and (in the case of recuperated cycles) reduction in compressor delivery temperature, which all act to increase the efficiency and power output. An investigation is presented here into the effect such water droplets will have on the operating point and flow characteristics of an aero-derivative gas turbine cycle. The paper first describes the development of a computer program to study the effects of water injection in multi-spool industrial gas turbines. The program can operate in two modes: the first uses pre-determined non-dimensional wet compressor maps to match the components and is instructive and fast but limited in scope; the second uses the compressor geometries as input and calculates the wet compressor operating conditions as and when required. As a result, it is more computationally demanding, but can cope with a wider range of circumstances. In both cases the compressor characteristics are calculated from a mean-line analysis using suitable loss, deviation and blockage models, coupled with Lagrangian-style droplet evaporation calculations. The program has been applied to a three-spool machine to address issues such as the effects of water-injection on power output and overall efficiency, and the off-design nature of the compressor operation.
Development of an Experimental Capability to Produce Controlled Blade Tip/Shroud Rubs at Engine Speed
Authors: Padova Corso , Barton Jeffery , Dunn Michael G. , Manwaring Steve , Young Gamaliel , Adams Maurice , Adams Michael
Published: November 2008

Development of an in-ground spin-pit facility specifically designed to investigate aeromechanic phenomena for engine hardware rotating at design speed is reported in this paper. The purpose of this paper is to describe the facility design and operation and to demonstrate utility by providing typical results from a recently completed measurement program. The facility is designed to allow insertion of a segment of engine casing into the path of single-bladed or multiple-bladed disks. In the current configuration, a 90-degree sector of a representative engine casing is forced to rub the tip of a single-bladed compressor disk with predetermined blade incursion into the casing for rotational speeds in the vicinity of 20,000 rpm.
Simulated Land-Based Turbine Deposits Generated in an Accelerated Deposition Facility
Authors: Jensen Jared W. , Squire Sean W. , Bons Jeffrey P. , Fletcher Thomas H.
Published: November 2008

This report presents a validation of the design and operation of an accelerated testing facility for the study of foreign deposit layers typical to the operation of land-based gas turbines. This facility was designed to produce turbine deposits in a 4-hour test that would simulate 10,000 hours of turbine operation. This is accomplished by matching the net foreign particulate throughput of an actual gas turbine. Flow Mach number, temperature and particulate impingement angle are also matched. Validation tests were conducted to model the ingestion of foreign particulate typically found in the urban environment. The majority of this particulate is ceramic in nature and smaller than 10 microns in size, but varies up to 80 microns. Deposits were formed for flow Mach number and temperature of 0.4 and 1150degC respectively, using air plasma sprayed (APS) TBC material coupons donated from industry. Investigations over a range of impingement angles yielded samples with deposit thicknesses from 20 to 100 microns in 4-hour, accelerated-service simulations. Above a threshold temperature, deposit thickness was dependent on impingement angle and particle concentration. Test validation was achieved using direct comparison with deposits from service hardware. Deposit characteristics affecting blade heat transfer via convection and conduction were assessed. Surface topography analysis indicated that the surface structure of the generated deposits were similar to those found on actual turbine blades. Scanning electron microscope (SEM) and x-ray spectroscopy analyses indicated that the deposit microstructures and chemical compositions were comparable to turbine blade deposit samples obtained from industry.
Aerodynamic Design and Testing of Three Low Solidity Steam Turbine Nozzle Cascades
Authors: Song Bo , Ng Wing F. , Cotroneo Joseph A. , Hofer Douglas C. , Siden Gunnar
Published: November 2008

Three sets of low solidity steam turbine nozzle cascades were designed and tested. The objective was to reduce cost through a reduction in parts count while maintaining or improving performance. The primary application is for steam turbine high pressure sections where Mach numbers are subsonic and high levels of unguided turning can be tolerated. The baseline Design A has a ratio of pitch to axial chord of 1.2. This is the pitch diameter section of a 50% reaction stage that has been verified by multistage testing on steam to have a high level of efficiency. Designs B and C have ratios of pitch to axial chord of 1.5 and 1.8 respectively. All three designs satisfy the same inlet and exit vector diagrams. Analytical surface Mach number distributions and boundary layer transition predictions are presented. Extensive cascade test measurements were carried out for a broad incidence range from −60 to +35 degrees. At each incidence, four outlet Mach numbers were tested, ranging from 0.2 to 0.8, with the corresponding Reynolds number variation from 1.8×105 to 9.0×105. Experimental results of loss coefficient and blade surface Mach number are presented and compared for the three cascades. The experimental results have demonstrated low losses over the tested Mach number range for a wide range of incidence from −45 to 15 degrees. Designs B and C have lower profile losses than Design A. The associated flow physics is interpreted using the results of wake profile, blade surface Mach number distribution and blade surface oil flow visualization, with the emphasis placed on the loss mechanisms for different flow conditions and the loss reduction mechanism with lower solidity. The effect of the higher profile loading of the lower solidity designs on increased end wall losses induced by increased secondary flow, especially on low aspect ratio designs, is the subject of ongoing studies.
Combined Fatigue Life Test and Extrapolation of Turbine Disc Mortise at Elevated Temperature
Authors: Wang Rongqiao , Cho Chongdu , Nie Jingxu
Published: November 2008

To investigate the crack failure of a certain turbine disc mortise, a test system with a new low- and high-cycle non-interfering loading scheme was established to study the Low- and High-Cycle Combined Fatigue (L-HCCF) of fir-tree mortise at elevated temperature. Then, for 50Hz and 100Hz vibrations with constant stress amplitude superimposed on the same low cycle loading respectively, the contrast L-HCCF life tests of light- and serious-corrosive disc mortises were carried out. Through real-time crack detection of the first teeth, the crack propagation rule of fir-tree mortise, a typical multiple load path structure, was obtained. Finally, a new method, two-frequency-ratio method, was presented to relate the load and life of laboratory test to the equivalent those of service in order to help the definition of the failure criteria for serious-corrosive discs in actual practice. The extrapolative results show that the life policies in use for light-corrosive turbine disc can not applied to serious-corrosive disc directly because its reliable life is greatly less than an overhaul schedule, and it is urgent to establish criteria for withdrawal from service of the serious-corrosive discs so as to assure the structural integrity of this aeroengine.
Inherently Safe Nuclear Power Generation With Electrically Coupled Compressor and Turbo Expander(s)
Authors: Crommelin Gulian A. K. , Crommelin Walter F.
Published: November 2008

Gas turbines in combination with a nuclear heat source have been subject for study for some years. This paper is a logical follow up on previous papers regarding small scale nuclear power generation using gas turbines with a well-proven, inherently safe nuclear heat source. In the Netherlands the NEREUS project has been working on this concept since 1993. The acronym NEREUS describes very well the goals of this project. (Ref 1, 2, 3, 4, 5). NEREUS stands for: a Natural safe, Efficient, Reactor, Easy to operate, Ultimately simple and Small. Current studies focus on the gas turbine part of the installation. After three years of studying the possibilities of the closed cycle helium gas turbine, the NEREUS project returned in 2000 to its original thought of using an existing open-cycle gas turbine or components of such an engine, as energy conversion unit. The paper starts with an introduction on why nuclear power should get more attention, basically explaining “the reasons why” of the NEREUS project. Secondly the paper gives an overview of the main characteristics of the nuclear heat source. Thirdly the paper will discuss the current study to determine the specifications of an open-cycle gas turbine for the NEREUS installation. Attention is given to the way such an open-cycle gas turbine can be controlled. The nuclear heat source is controlled by the laws of physics and it is not recommended to intervene under any circumstances with this very important safety feature.
Auto-Ignition and Heat Release in a Gas Turbine Burner at Elevated Temperature
Authors: Ivancic Blazenko , Flohr Peter , Paikert Bettina , Brandt Martin , Polifke Wolfgang
Published: November 2008

This paper reports on the validation of an advanced model for ignition and heat release of natural gas at elevated pressures and temperatures. The model comprises two sub-models: one for the auto-ignition process and the other to consider heat release. To describe the ignition process efficiently the model uses an intermediate species to represent the evolution of the radical pool. Once the radical pool has reached a critical concentration, the subsequent heat release process starts. Rates for both processes are determined by use of detailed chemistry; hence the model can also take into account effects of higher hydro-carbons without use of a tuning parameter. Turbulence-chemistry interactions are considered with a new Monte-Carlo formulation for the joint probability distribution. This approach is based on the description of the mixture statistics via particle ensembles and not via a function as traditional presumed PDF (Probability Density Function) methods do. The particle ensembles are generated for given means and (co-) variances of mixture fractions in a pre-processing step. To get information about the statistics in the CFD (Computed Fluid Dynamics) simulation, transport equations for means and variances are solved. Since the computation of turbulent mean reaction and heat release rates is performed in a pre-processing step, this approach is very efficient. Experimental results from a full-size burner of an industrial reheat gas turbine at atmospheric pressure was used as data for the model validation. It was found that this approach made possible the calculation of important physical characteristics, e.g. flame position and thickness for a wide range of operating conditions and burner geometries, with satisfying accuracy. Finally, it will be demonstrated how this numerical model is complementary to experimental development procedures and can be used as a burner design tool.
Development of an Ultra-Low NOx LP(P) Burner
Authors: v. d. Bank Ralf , Schilling Thomas
Published: November 2008

Within the EC framework 5 programme LOPOCOTEP Rolls-Royce Deutschland (RRD) continues to develop Lean Premix (Partially Pre-vaporized) (LP(P)) combustion systems to implement the ACARE goals to achieve further NOx reductions compared with the best combustor technology currently available. The results from the previous EC framework 4 programme LowNOx III had been used to calculate DpNOx/Foo values for an ICAO LTO cycle. The result showed that 40% from the CAEP II limit can be achieved for a medium size fan engine. Cycle and mission calculations have risen the hope that total NOx emissions can be reduced by more than 70% for a 800 NM medium range flight. The objective of the current programme is to further reduce the NOx emissions (30% CAEP II) for a more severe engine cycle and therefore a larger burner size compared to the LowNOx III programme. Flash-back and auto-ignition under all operation conditions have to be prevented. A scaling law was derived from the existing database and applied on an LP(P) module which was then tested at pressures of up to 35 bar and temperatures of up to 900 K in a single sector test rig. The applicability of the scaling laws was confirmed. Testing at take-off conditions showed single digit EINOx between 2 and 4 g/kg depending on the actual swirl-generator configuration. However, poor weak extinction was observed and gave concern regarding operability. The decision was taken to redirect the development efforts to improve operability and to increase the lean blow out (LBO) air-fuel-ratio (AFR). This led to the integration of an internal, centrally arranged pressure-swirl atomizer as pilot diffusion burner into the LP(P) burners. Due to an optimization of the aerodynamics of the LP(P) module which was performed at the same time the dimensions of the burner could be reduced while the effective area was kept constant. This burner was then initially tested at atmospheric conditions to address ignition and LBO limit. This burner showed excellent ground ignition capability at air temperatures as low as 350 K. In the best configuration one spark was sufficient. The testing of the lean extinction limit was repeatedly verified. At 350 K the LBO was always in the range between 110–130 OAFR. More detailed investigations on emissions, flash-back and auto-ignition characteristics will be performed at ONERA and Lund University.