bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Evaluation of Slotted Pocket Gas Damper Seals on a Rotating Test Rig
Authors: Li Jiming , Kushner Frank , De Choudhury Pranabesh
Published: February 2009

A slotted pocket gas damper seal has been experimentally evaluated on a flexible rotor test rig for rotor vibration reduction properties. For unbalance response tests, the experiments were conducted at several seal inlet pressures out to 14.5 bar (210 psia), and the rotor speed ranged up to 8,000 rpm, which was well above the damped first critical speed of the flexible rotor. The influence of gas pre-swirl and seal eccentricity on the seal dynamic performance was investigated in the tests. Experimental results showed that the slotted pocket damper seal provided high positive damping and small positive stiffness in the tested pressure range. Comparisons of seal dynamic characteristics and leakage were made between the slotted pocket damper seal and a conventional pocket damper seal tested previously on the same test stand. The stability characteristics of the slotted pocket gas damper seal were also experimentally evaluated at 12,000 rpm, the maximum operating speed of this test rig. Test conditions involved three inlet pressures up to 20.7 bar (300 psia) and intentional pre-swirl gas flows. Experimental results demonstrated that the slotted pocket damper seal was rotordynamically stable at high speeds without any subsynchronous vibration in the frequency spectrum measured using proximity probes for the test rotor.
Modeling Finite Squeeze Film Dampers
Authors: El-Shafei A.
Published: February 2009

Most closed form solutions of Reynolds’ equation assume either a short bearing approximation or a long bearing approximation. These closed form approximations are used in rotordynamic simulation applications, otherwise a Finite Difference solution of Reynolds’ equation would be prohibitively time consuming. Recently, there have been proposed series solutions for Reynolds’ equation for special cases. In this paper, a perturbation solution to the governing equations is proposed to obtain a closed form solution of Reynolds’ equation for a finite squeeze film damper executing a circular centered orbit. The pressure field and velocity profiles are obtained. It is shown that in the limit the finite damper solution approaches either the appropriate short or long damper. This perturbation solution can be used with appropriate boundary conditions, for various damper sealing configurations, and provides insight into the damper performance.
The Experimental Researches on Improving Operating Stability of a Single Stage Transonic Fan
Authors: Yu Qing , Li Qiushi , Li Ling
Published: February 2009

High thrust-weight ratio aircraft engine means high single stage load and high tangential speed of the rotor blade, while strong shock waves, secondary flow, boundary layer development and mutual interaction among shock, boundary layer and leakage flow occur in the rotor tip region. All of these have great influence on the performance of compressor and decrease operating stability of compressor. Casing treatment is a practical technique that is often used to enlarge compressor stable operating region, but normally this benefit is achieved at the sacrifice of efficiency of the compressor. In this paper, three kinds of casing treatment have been tested on a high pressure-ratio, high through-flow single-stage transonic fan. The performances of the transonic axial fan have been measured with and without casing treatments at different operating speeds. It is obvious that the three types of casing treatments — Reversed Vortex Style Casing Treatment (RVSCT), Axial Slope Slot Casing Treatment (ASSCT) and Arc-Curve Skewed Slot Casing Treatment (ACSSCT), are not same effective on the operating stability and efficiency. It is very exciting that the peak efficiency of the single-stage transonic fan was improved as well as the stable operating range was increased with ACSSCT about 1% at low operating speeds. Unfortunately at the design speed the stall margin was increased but the adibatic efficiency was decreased 2% compared with the original fan in this case. In order to get detailed understanding of the flow structure with casing treatments near the end wall, three-dimensional velocity was measured using a small five-hole probe at outlet of the rotor passage at the lower operating speeds. The results indicated that the casing treatments with plenum chamber delayed the formation of rotating stall and improved the flow near the end wall region. That means at these lower operating speeds the boundary layer of the end wall was decreased and the efficiency of the fan was increased.
Application of Casing Circumferential Grooves for Improved Stall Margin in a Transonic Axial Compressor
Authors: Rabe D. C. , Hah C.
Published: February 2009

Experimental and numerical investigations were conducted to study the fundamental flow mechanisms of circumferential grooves in the casing of a transonic compressor and their influence on compressor stall margin. Three different groove configurations were tested in a highly loaded transonic compressor. Experimental results show that circumferential grooves increase the stall margin of the compressor at the tested operating condition. Grooves with a much smaller depth than conventional designs are shown to be similarly effective in increasing the stall margin. Steady-state Navier-Stokes analyses were performed to study flow structures associated with each casing treatment. The numerical procedure calculates the overall effects of the circumferential grooves correctly. Detailed investigation of calculated flow fields indicates that losses are generated by interaction between the main passage flow and flow exiting the grooves. The grooves increase the stall margin by reducing the flow incidence angle on the pressure side of the leading edge, despite an overall increase in the endwall boundary layer thickness. This is due to complex interaction of the main passage flow with the additional radial and tangential flows created by the grooves.
3-D Digital PIV Measurements of the Tip Clearance Flow in an Axial Compressor
Authors: Wernet Mark P. , Van Zante Dale , Strazisar Tony J. , John W. Trevor , Prahst P. Susan
Published: February 2009

The accurate characterization and simulation of rotor tip clearance flows has received much attention in recent years due to their impact on compressor-performance and stability. At NASA Glenn the first known three dimensional Digital Particle Image Velocimetry (DPIV) measurements of the tip region of a low speed compressor rotor have been acquired to characterize the behavior of the rotor tip clearance flow. The measurements were acquired phase-locked to the rotor position so that changes in the tip clearance vortex position relative to the rotor blade can be seen. The DPIV technique allows the magnitude and relative contributions of both the asynchronous motions of a coherent structure and the temporal unsteadiness to be evaluated. Comparison of measurements taken at the peak efficiency and at near stall operating conditions characterizes the mean position of the clearance vortex and the changes in the unsteady behavior of the vortex with blade loading. Comparisons of the 3-D DPIV measurements at the compressor design point to a 3D steady N-S solution are also done to assess the fidelity of steady, single-passage simulations to model an unsteady flow field.
Numerical Simulation of the Axial Fan Performance Degradation Due to Sand Ingestion
Authors: Ghenaiet A. , Tan S. C. , Elder R. L.
Published: February 2009

This paper presents a method based on Lieblein and Koch correlations for assessing the performance degradation of an axial fan due to sand ingestion. The method is based on mean line analysis, and predicted aerodynamic performance includes the adiabatic efficiency, pressure rise coefficient and stall margin. Changes to the blade geometry which affect the fan aerodynamic performance are mainly due to erosion which reduces the blade chord and increases the tip clearance and surface roughness. Erosion damage has a significant effect on the aerodynamic lift coefficient, which is related to the static pressure distribution. An in-house developed trajectory code, combined with restitution factors and an erosion model (applicable for cast aluminium alloy and stainless steel), was used to predict particle trajectories and the amount of material removed. The method was applied successfully to a contra-whirl axial fan where reasonably good agreement was found between predicted and experimental results. Tests were conducted with MIL-E 5007E sand particle sizes of between 0.0 and 1000.0 microns. A method for predicting life expectancy of the fan is also presented. The methodology shows that critical blade parameters necessary for performance degradation simulation can be successfully obtained in this way.
Nondestructive Characterization of Enviromental Barrier Coatings Applied to Monolithic Ceramics
Authors: Ellingson W. A. , Deemer C. , Erdman S. , Parikh A.
Published: February 2009

Full-size silicon nitride gas-turbine vanes coated with an environmental barrier coating (EBC) were evaluated in an exploratory way by two nondestructive methods: polarized elastic optical scattering and infrared thermal imaging. Initial test results indicate that the laser scatter data correlate with EBC thickness. A description of the methods and results of recent tests are presented.
Feasibility and Performance of an Ambient Pressure MCFC Combined With a Commercial Gas Turbine
Authors: Desideri Umberto , Lunghi Piero , Ubertini Stefano
Published: February 2009

Fuel cells have resulted to be very attractive power generation systems, promising highly efficient electricity generation with very low environmental impact. Although still in embryonic infancy high-temperature fuel cells, the very high energetic efficiency can be further increased by their integration in hybrid cycles. While a wide variety of potential bottoming technologies for exploiting the high temperature exhaust gases waste heat is available, a lot of research effort is needed to determine the optimal integration of well established technologies with these very novel conversion devices. This work, using results from previous works, in which a MCFC/Gas Turbine hybrid plant was defined and the working parameters optimised both with a GT simple cycle and with steam injection and post combustion, starts from choosing an existing gas turbine technology with suitable working parameters to perform a system evaluation and integration. Since the gas turbine nominal maximum temperature cannot be reached by the only means of heat exchange from the MCFC plant section, post combustion has been considered and the turbine has been simulated both in nominal and in off design conditions in order to find an optimal solution. The work takes into consideration not only the main plants modifications of the existing components to allow for system integration but also the most relevant issues connected with altered working conditions.
Simplified Versus Detailed SOFC Reactor Models and Influence on the Simulation of the Design Point Performance of Hybrid Systems
Authors: Magistri Loredana , Bozzo Riccardo , Costamagna Paola , Massardo Aristide F.
Published: February 2009

High efficiency Hybrid Systems (HS) based on the coupling of Solid Oxide Fuel Cells (SOFCs) and Gas Turbines (GT) are analysed in this paper through the use of two different approaches: simplified and detailed SOFC models. The simplified model, already presented by the Authors1, is very useful for HS design and off-design analysis. The detailed model, developed by the Authors2 and verified through the use of available experimental data, allows the complete description of the SOFC reactor’s internal behaviour to be obtained. The detailed model can also be utilised for HS modelling. Both models are presented and discussed in this paper, and they are compared to each other. The results obtained for the stand-alone SOFC reactor, and the HS design point configuration are presented and carefully discussed, also taking into account the non linear SOFC response.
Inlet-Temperature Suppression of Inlet Air for Gas-Turbine Compressors by Evaporative Cooling of Water Spray
Authors: Trewin Richard R.
Published: February 2009

An evaporative cooling system for lowering the inlet temperature of a gas-turbine compressor is described. This system uses the latent enthalpy of evaporation for injected water droplets to decrease the enthalpy of the air. The requirements for compatible operation between this system and the compressor are given.
Viscoplastic Modelling for Industrial Gas Turbine (IGT) Application With Emphasis on the Sheet Material Haynes 230
Authors: Hasselqvist Magnus
Published: February 2009

The need for high quality simulation to support cyclic life estimation of IGT hot parts is obvious. With increasing computational resources it is now feasible to perform fully 3D simulations using viscoplastic models. The superalloy Haynes 230 has been analyzed and modelled to support design against excessive deformation and Thermo Mechanical Fatigue (TMF). This requires a model which can accurately predict the stress corresponding to 1% creep after 40000h and the inelastic strain range in the stabilized loop. The one most important aspect of the modelling was identified as ‘how to predict the low temperature yield strength in the stabilized loop’, i.e. after TMF cycling with long holding times at service temperature. Haynes 230 is delivered in an unstable solutioned state and precipitates secondary carbides in service. The resulting carbide morphology, and therefore the mechanical properties, depends on the strain range and the service temperature. The dense distribution of fine carbides after cycling at 600°C, and the corresponding very high cyclic hardening, indicates that TMF cycling with a service temperature of 600 °C results in a corresponding increase in the low temperature yield strength. If the service temperature is high, over ageing will occur and the low temperature yield strength will decrease instead. This has been taken into account in a novel ‘crude but useful’ model containing a stabilized yield strength which depends explicitly on the service temperature. The modelling has been backed by case specific testing and SEM/TEM studies. The model has been implemented in ABAQUS and is being used. Further analysis will refine the model through improved understanding of the precipitation and ageing process, and also extend it to similar materials such as Hastelloy-X, 800H, 253MA and Haynes HR-120.
The Effect of Molybdenum on the Creep Behavior of Orthorhombic Titanium Aluminides
Authors: Shepherd Dominique A. , Vasudevan Vijay K.
Published: February 2009

The effect of molybdenum additions on the creep properties of two orthorhombic titanium aluminide materials, Ti-22Al-26Nb and Ti-22Al-24.5Nb-1.5Mo (% atomic fraction), has been investigated. Heat treatments below the beta transus temperature followed by a 16-hour ageing treatment produced similar microstructures. Using the similar microstructures (consisting of O laths in a B2 matrix with α2 dispersed at B2 grain boundaries) for the two compositions, tensile creep testing was conducted under stresses of 68 MPa, 160 MPa, and 197 MPa at temperatures of 590 °C and 760 °C. The creep results demonstrated the favorable effects of Mo on creep resistance in these orthorhombic titanium aluminides. Due to similar microstructures, results also suggested that improvements have been substructural, rather than purely microstructural, in nature.
Selection of Overlays for Single Crystal Shrouded Turbine Blades
Authors: Nava Irene , Nagy Douglas
Published: February 2009

Solar Turbines Incorporated (Solar) is investigating innovative turbine designs that will allow higher electrical efficiency and output power. Liburdi Engineering Limited (Liburdi) and Solar have evaluated the application of a powder metallurgy process based upon the Liburdi Powder Metallurgy (LPM™) repair process. The technique applies a chrome carbide and nickel-chrome alloy composite hardfacing onto a turbine blade’s Z-notches. Processing techniques (such as material form, alloy-hardface ratio optimization, binder ratio and heat treatment cycles) were investigated (some of the details developed at Liburdi are proprietary). Metallurgical, mechanical and short-term oxidation properties of the composite have been studied and defined by Solar. The LPM process was found to be feasible and practical to be applied on CMSX-4 single-cystal Z-notches of shrouded blades.
Experimental Investigation of Unsteady Flow Field Within a Two Stage Axial Turbomachine Using Particle Image Velocimetry
Authors: Uzol Oguz , Chow Yi-Chih , Katz Joseph , Meneveau Charles
Published: February 2009

Detailed measurements of the flow field within the entire 2nd stage of a two stage axial turbomachine are performed using Particle Image Velocimetry. The experiments are performed in a facility that allows unobstructed view on the entire flow field, facilitated using transparent rotor and stator and a fluid that has the same optical index of refraction as the blades. The entire flow field is composed of a “lattice of wakes”, and the resulting wake-wake and wake-blade interactions cause major flow and turbulence non-uniformities. The paper presents data on the phase averaged velocity and turbulent kinetic energy distributions, as well as the average-passage velocity and deterministic stresses. The phase-dependent turbulence parameters are determined from the difference between instantaneous and the phase-averaged data. The distributions of average-passage flow field over the entire stage in both the stator and rotor frames of reference are calculated by averaging the phase-averaged data. The deterministic stresses are calculated from the difference between the phase-averaged and average-passage velocity distributions. Clearly, wake-wake and wake-blade interactions are the dominant contributors to generation of high deterministic stresses and tangential non-uniformities, in the rotor-stator gap, near the blades and in the wakes behind them. The turbulent kinetic energy levels are generally higher than the deterministic kinetic energy levels, whereas the shear stress levels are comparable, both in the rotor and stator frames of references. At certain locations the deterministic shear stresses are substantially higher than the turbulent shear stresses, such as close to the stator blade in the rotor frame of reference. The non-uniformities in the lateral velocity component due to the interaction of the rotor blade with the 1st stage rotor-stator wakes, result in 13% variations in the specific work input of the rotor. Thus, in spite of the relatively large blade row spacings in the present turbomachine, the non-uniformities in flow structure have significant effects on the overall performance of the system.
Power Plant System Configurations for the 21st Century
Authors: Rao A. D. , Samuelsen G. S. , Robson F. L. , Geisbrecht R. A.
Published: February 2009

Under the sponsorship of the U.S. Department of Energy/National Energy Technology Laboratory, a multi-disciplinary team led by the Advanced Power and Energy Program of the University of California at Irvine is defining the system engineering issues associated with the integration of key components and subsystems into power plant systems that meet performance and emission goals of the Vision 21 program. The myriad of fuel processing, power generation, and emission control technologies are narrowed down to selected scenarios in order to identify those combinations that have the potential to achieve the Vision 21 program goals of high efficiency and minimized environmental impact while using fossil fuels. The technology levels considered are based on projected technical and manufacturing advances being made in industry and on advances identified in current and future government supported research. Examples of systems included in these advanced cycles are solid oxide and molten carbonate fuel cells, advanced gas turbines, ion transport membrane separation and hydrogen-oxygen combustion.
The Design and Layout of the Propulsion Plant of the RNLN Air Defence and Command Frigate (ADCF)
Authors: Broekhaus K. O. , Rand M. J.
Published: February 2009

The first section of this paper will discuss the aimed mission and need for the latest Royal Netherlands Navy’s (RNLN) ship class, the Luchtverdedigings en Commando Fregat (LCF) and its derived requirements for the propulsion plant. The choice of a CODOG (Combined Diesel or Gas) propulsion installation as opposed to COGOG (Combined Gas or Gas) or CODLAG (Combined Diesel Electric and Gas), will be explained. The difficult choice between the Rolls Royce Spey SM1C and the General Electric LM2500 gas turbines for the boost role will be explained showing how history largely shaped the choice. The second section of the paper will deal with the challenges of the Spey gas turbine installation, the development of a digital fuel control system, the problems encountered and the challenges yet to be resolved. Discussions on the provisioning and support arrangements will also be made. The last part of the paper will make a short reconnaissance in the near future of gas turbine ship propulsion and the broad thoughts that are shaping the RNLNs thinking.
Numerical Investigation of Vortex Reducer Flows in the High Pressure Compressor of Modern Aeroengines
Authors: Peitsch Dieter , Stein Manuela , Hein Stefan , Niehuis Reinhard , Reinmo¨ller Ulf
Published: February 2009

Modern jet engines require very high cycle temperatures for efficient operation. In turn, cooling air is needed for the turbine, since the materials are not yet capable of taking these temperatures. Air is taken from the compressor for the purpose of cooling and turbine rim sealing, bypassing the main combustion circuit. Since this affects the efficiency of the engine in a negative manner, measures are taken to reduce the amount of air to an absolute minimum. These measures include the investigation of reducing pressure losses within the involved subsystems. One of these subsystems in the BR700 aeroengine series of Rolls-Royce is the vortex reducer device, which delivers bleed air to the secondary air system of the engine. The German government has set up a research project, aiming for an overall improvement of aeroengines. This program, Engine 3E, where 3E reflects Efficiency, Economy and Environment, concentrates on the main components of gas turbines. Programmes for the high pressure turbine and for the combustion chamber have been set up. The high pressure compressor has been identified as key component as well. A new 9-stage compressor is being developed at Rolls-Royce Deutschland to adress the respective needs. From the point of view of the secondary air system, the vortex reducer in this component plays a major role with respect to the efficient use of cooling and sealing air. Rolls-Royce Deutschland has performed CFD studies on the performance of different vortex reducer geometries, which currently are considered for incorporation into the future engine. The results of these investigations wil be converted into more simple design rules for proper reflection of the behaviour of this system for future designs. The paper presents the set up of the geometries, the applied boundary conditions as well as the final results. To tackle the difference between a high pressure compressor rig and a typical two-shaft engine, a dedicated investigation to assess the difference between a pure high pressure core without an internal shaft and a realistic high/low pressure shaft configuration has been carried out and is included in the paper. Recommendations to improve the design with respect to minimized pressure losses will be shown as well.
Integration of Condition Based Maintenance Technologies Into U.S. Navy Gas Turbine Engines
Authors: McGroarty Jack J. , Scharschan John W. , Eghtessad John M.
Published: February 2009

The benefits of utilizing Condition Based Maintenance (CBM) over a time based preventative approach to reduce life cycle costs has been well documented over the years. The U.S. Navy has been working through several separate programs, such as Smartship, Integrated Condition Assessment System (ICAS), Accelerated Capabilities Initiative (ACI), to develop this technology for use in the fleet. Recently, an effort was initiated to coordinate these programs in an application on marine gas turbines. This paper describes the phased process of CBM implementation on marine gas turbines and the resulting benefits of reduced life cycle costs and condition based engineering plant alignment.
Computational Modeling of Vortex Generators for Turbomachinery
Authors: Chima R. V.
Published: February 2009

In this work computational models were developed and used to investigate applications of vortex generators (VGs) to turbomachinery. The work was aimed at increasing the efficiency of compressor components designed for the NASA Ultra Efficient Engine Technology (UEET) program. Initial calculations were used to investigate the physical behavior of VGs. A parametric study of the effects of VG height was done using 3-D calculations of isolated VGs. A body force model was developed to simulate the effects of VGs without requiring complicated grids. The model was calibrated using 2-D calculations of the VG vanes and was validated using the 3-D results. Then three applications of VGs to a compressor rotor and stator were investigated: 1. The results of the 3-D calculations were used to simulate the use of small casing VGs used to generate rotor preswirl or counterswirl. Computed performance maps were used to evaluate the effects of VGs. 2. The body force model was used to simulate large partspan splitters on the casing ahead of the stator. Computed loss buckets showed the effects of the VGs. 3. The body force model was also used to investigate the use of tiny VGs on the stator suction surface for controlling secondary flows. Near-surface particle traces and exit loss profiles were used to evaluate the effects of the VGs.
Performance Evaluation of an Internal Flow Navier-Stokes Solver for Compressible Viscous Flow Simulations
Authors: Tınaztepe H. Tug˘rul , U¨c¸er Ahmet S¸. , Akamandor I˙. Sinan
Published: February 2009

A three-dimensional compressible full Navier-Stokes solver is developed for the analysis of the flow field inside turbomachinary cascades. The solver uses an explicit second order accurate (cell-vertex) finite volume Lax-Wendroff scheme over hexahedral cells. The viscous and heat conduction terms are discretized in conservative form at the cell center. Second and fourth order numerical smoothing terms are added with local scaling factors. Eddy viscosity is calculated by the Baldwin-Lomax model and is adapted to the pointered cell based algorithm. Turbulent viscosity is blended by inverse distance square weighting functions near corners. Characteristic boundary conditions are used. A computational analysis has been carried out to present the capability of the solver in capturing secondary velocity patterns, flow angles and total pressure loss distributions inside a linear high turning turbine cascade. A controlled diffusion compressor cascade at high incidence has been analyzed. Main features of the flow field in this compressor cascade were resolved (secondary and end wall flows and leading edge laminar separation bubble) as in the experimental data. The main aim of the work is to demonstrate the performance of the code in capturing the details of the complicated flow fields using grids that can be regarded as coarse.
Economic Assessment of Evaporative Gas Turbine Cycles With Optimized Part Flow Humidification Systems
Authors: Jonsson Maria , Yan Jinyue
Published: February 2009

This study is an economic assessment of evaporative and steam-injected cycles based on three gas turbines (Trent, GTX100 and Cyclone). The evaporative cycles included part or full flow humidification and steam injection. For the Trent and GTX100, part flow cases had the lowest costs of electricity (32.6 mills/kWh and 30.9 mills/kWh, respectively), while a full flow case had the lowest cost of electricity (35.3 mills/kWh) for the Cyclone. However, the cost variations between different cycles were small: below 1% (0.4 mills/kWh) for the GTX100 and Cyclone cases and below 3% (0.9 mills/kWh) for the Trent cases. The specific investment costs were lower for part flow evaporative cycles than for full flow cycles, while steam-injected cycles had the lowest specific investment costs. The Trent and GTX100 evaporative cycles had significantly lower total and specific investment costs than combined cycles, while the costs of electricity were approximately the same.
Maximizing Asset Value of Combustion Turbines
Authors: Hoffman John S. , Kopko William L.
Published: February 2009

An, improved gas-turbine supercharging technology [1–3], newly patented, uses variable supercharging with enhanced fogging or evaporative cooling (enhanced supercharging) to sustain mass density through a turbine system at maximum allowable level for the supercharged turbine, allowing output similar to that available normally at cold weather and sea level conditions all year long. Using variable pitch fans to modulate pressure increases, enhanced supercharging increases pressures to restore mass flow levels as high as possible without surpassing torque limits on the shaft or other constraining factors, such as generator capacity. Increased fogging then removes sensible heat added by the fan, essentially straight lining output throughout the year at the maximum output for which the turbine system has been designed. Largest increases in output occur on the hottest days, but significant increases also occur at ISO conditions and below. Achievable increments of net output on a peak summer day can be nine times higher than fogging alone, the currently preferred augmentation mode for combustion turbines. Enhanced supercharging increases shareholder value by maximizing the increase in economic value added (EVA) for combustion turbine assets [4]. Under EVA, an investment that returns 9% when the cost of capital is 9% would be counted as adding no increment of profit or value to a company. Whether a combustion turbine has an augmentation system or has none, enhanced supercharging almost always adds significant EVA. The EVA for enhanced supercharging often exceeds other options by an order of magnitude. Enhanced supercharging produces greatest profits on combined-cycle plants, although it will also produce additional EVA on many simple-cycle engines. As the power industry struggles to return to profitability, enhanced supercharging offers a simple and straightforward means to increase shareholder value, returning on average 15 times the economic value added of investments in base power plants. For new plants, the increment of value may be sufficient to turn a “no-go” into a “go” decision. For existing plants enhanced supercharging can to turn a lackluster financial year into a profitable one.
The High-Pressure Combustion Facility at the NASA Glenn Research Center
Authors: Penko Paul F. , Fraser Bryan , Adkins Susan E. , Wey Changlie
Published: February 2009

A combustion test facility at the NASA Glenn Research Center is described that has the test-section capability of 60 bars in pressure, 970 K in air temperature, and air flow rate to 23 kg/s. Included in the description are the facility operating map; services such as fuel, cooling air and water; instrumentation for temperature, pressure and flow rate measurements; and gaseous-emissions and laser-measurement capabilities.
Computation of Heat Transfer for Two Discs Rotating at Different Speeds
Authors: Kilic Muhsin , Owen J. Michael
Published: February 2009

Computations have been conducted for the case where one rotating disc is heated and the other surfaces are adiabatic. Discs rotating at different speeds are found in the internal cooling-air systems of engines, and it is convenient to define Γ as the ratio of the angular speed of the slower (adiabatic) disc to that of the faster (heated) disc. A finite-volume, axisymmetric, elliptic, multigrid solver, employing a low-Reynolds-number k-ε turbulence model, previously used for a complementary study of the flow structure, has been validated using available heat transfer measurements for Γ = −1, 0 and +1. The effect of Γ (for the range −1 ≤ Γ ≤ +1) on heat transfer is then considered for a generic case in which the rotational Reynolds number, Reφ, is 1.25 × 106. (Although this is much lower than the values found in practice, the magnitude of the coolant flow rate was chosen to produce an engine-representative flow structure.) Theoretical values of the adiabatic-disc temperature are in reasonable agreement with computed values for Γ > 0. In the source region, at the smaller radii, there is no effect of Γ on the local Nusselt numbers, Nu, which are consistent with a free-disc correlation. For the average Nusselt numbers, Nuav, the Reynolds analogy shows that the ratio of Nuav/ReφCm, where Cm is the moment coefficient, should be equal to a constant value of 0.259. For Γ ≥ 0, the computed value of this “constant” is within 7% of the theoretical value.
New Free-Piston Topping Cycle for Gas-Turbine Power Plants
Authors: Kopko William L. , Hoffman John S.
Published: February 2009

A proposed topping cycle inserts a free-piston internal-combustion engine between the compressor and the combustor of a combustion turbine. The topping cycle diverts air from the compressor to supercharge the free-piston engine. Because the free-piston engine uses gas bearings to support the piston and is built of high-temperature materials, the engine can increase the pressure and temperature of the gas, exhausting it to a small expander that produces power. The exhaust from the topping-cycle expander is at a pressure that can be re-introduced to the main turbine, allowing almost complete recovery of waste heat. A capacity increase exceeding 35% is possible, and overall cycle efficiency can approach 70% when incorporated into a state-of-the-art combined-cycle plant. The cost of per incremental kW of the topping cycle can be dramatically lower than that of the base turbine because of the high power density and simplicity of the engine. Building on decades of progress in combustion turbines systems, the new cycle promises high performance without the engineering risks of manufacturing a completely new cycle.
Modelling NO-NO2 Conversion in Counter-Flow Diffusion Flames
Authors: Kyne A. G. , Pourkashanian M. , Wilson C. W. , Williams A.
Published: February 2009

As emission regulations become more stringent there is increasing interest in the formation of NO2 in combustion products where it is in higher concentration than if slowly formed from NO in the atmosphere. It is common knowledge that NO2 is significantly more toxic than NO. The chemistry of NO2 formation in combustion processes is simple in comparison to that of NO. Indeed, all NO2 is formed from oxidation of NO mainly by reaction with HO2 radicals with its conversion back to NO resulting from reactions involving O and H atoms. Since consumption and formation of NO2 always occur simultaneously, although with unbalanced kinetic rates leading to local super-equilibrium concentrations, parameters such as temperature, velocity and species concentrations fields can drastically affect the degree of conversion of NO to NO2 in combustion applications. It is not well known what these conditions are and in certain circumstances, such as aircraft engine reheat systems, the emission of NO2 is clearly visible under the form of brown fumes. A comprehensive numerical simulation was undertaken to investigate the NO-NO2 relationship in a counter-flow diffusion flame. The CHEMKIN II suite of software (Kee et al., 1989) in conjunction with the opposed diffusion flame code OPPDIF (Lutz et al, 1997) was run using the Gas Research Institute’s (GRI’s) methane reaction mechanism v.3.0. A number of different strain rates using boundary conditions typical in a gas turbine exhaust were investigated. A rate of production and sensitivity analysis was made in determining which reactions were important in the NO-NO2 conversion process.
On Compressor Station Layout
Authors: Kurz Rainer , Ohanian Sebouh , Lubomirsky Matt
Published: February 2009

This paper discusses issues that influence the decision on the arrangement of compressors and the type of equipment in gas pipeline compressor stations. Different concepts such as multiple small units versus single large units are considered, both regarding their impact on the individual station and the overall pipeline. The necessity of standby units is discussed. Various concepts for drivers (gas turbine, gas motor and electric motor) and compressors (centrifugal and reciprocating) are analyzed. The importance of considering all possible operating conditions is stressed. With the wide range of possible operating conditions for the pipeline in mind, the discussion will be brought into the general context of operational flexibility, availability, reliability, installation issues, remote control, and operability of gas turbine driven centrifugal compressors compared to other solutions such as electric motor driven compressors or gas engine driven reciprocating compressors. The impact of different concepts on emissions and fuel cost is discussed. Among the assumptions in this paper are the performance characteristics of the compressor. It will be outlined how these performance characteristics influence the conclusions.
A Numerical Study on the Influence of Vane-Blade Spacing on a Compressor Stage at Sub- and Transonic Operating Conditions
Authors: Zachcial Andreas , Nu¨rnberger Dirk
Published: February 2009

A detailed numerical investigation into the influence of the axial gap between the blade rows of a stator/rotor compressor configuration is presented. Unsteady, two-dimensional simulations at both subsonic and transonic operating points have been performed for several axial spacings. From time-averaged data, the influence of the axial gap setting on stage efficiency at the subsonic operating point was found to be opposite to that at the transonic operating point. By examining the passage losses, a correlation between the trends in stage performance and rotor losses as a function of the axial spacing was found. At maximum efficiency, the unsteady flow fields at both operating points show similar vortex patterns. These vortices are rotating clockwise and are located near the suction side of the rotor profile. It was found that these vortices affect the boundary layer behaviour of the rotor and lead to a gain in performance due to a reduction of the rotor losses. This process depends on the operating point and the axial spacing between the rows. Through a detailed analysis of the time-averaged and instantaneous data, the influence of the upstream wake on the stage performance is assessed and discussed in the context of future designs.
Research on Sound-Vortex Resonance in Enhancing Performance of an Annular Cascade
Authors: Qiu Yaxi , Ge Jingdong , Lu Yajun , Zhou Sheng , Li Qiushi
Published: February 2009

This paper presents an experimental investigation on the effects of internal acoustic excitation on enhancing performance of an annular cascade. Based on the research on the shedding frequency characteristics of the annular cascade, the mechanism of interaction between the unsteady fluctuation and the separated flow in the annular cascade was systematically investigated by means of unsteady acoustic excitation. The experimental results reveal that the aerodynamic performance of turbomachinery would be improved amazingly if the unsteady interferences in the flow field could be reasonably organized. In experiment, the loss in one cascade passage could be reduced by nearly 30 perents. The optimal effect of the acoustic excitation was studied at different frequencies, intensities and positions of the excitation as well as at different flow incidence angles.
Interaction of Shroud Leakage Flow and Main Flow in a Three-Stage LP Turbine
Authors: Gier Jochen , Stubert Bertram , Brouillet Bernard , de Vito Laurent
Published: February 2009

Endwall losses significantly contribute to the overall losses in modern turbomachinery, especially when aerodynamic airfoil load and pressure ratios are increased. In turbines with shrouded airfoils a large portion of these losses are generated by the leakage flow across the shroud clearance. Generally the related losses can be grouped into losses of the leakage flow itself and losses caused by the interaction with the main flow in subsequent airfoil rows. In order to reduce the impact of the leakage flow and shroud design related losses a thorough understanding of the leakage losses and especially of the losses connected to enhancing secondary flows and other main flow interactions has to be understood. Therefore, a three stage LP turbine typical for jet engines is being investigated. For the three-stage test turbine 3D Navier-Stokes computations are performed simulating the turbine including the entire shroud cavity geometry in comparison with computations in the ideal flow path. Numerical results compare favourably against measurements carried out at the high altitude test facility at Stuttgart University. The differences of the simulations with and without shroud cavities are analysed for several points of operation and a very detailed quantitative loss breakdown is presented.
The Characteristics of Radial Turbines for Small Gas Turbines
Authors: Rodgers C.
Published: February 2009

Inward flow radial and mixed flow turbines are effectively utilized in both small gas turbine auxiliary power units (APU’s) and turbochargers, where moderately high levels of efficiency can be readily attained with simple cast components, less sensitive to blade end-gap clearances than axial turbines. This paper provides an overview of radial turbine performance characteristics for small gas turbine applications as basically influenced by specific speed, velocity ratio, exit flow coefficient, and rotor tip to exducer root mean square (RMS) diameter ratio. Since turbine rotor mass and inertia play important roles in structural integrity and engine acceleration characteristics, the importance of turbine velocity ratio selection upon rotor tip diameter, and cycle performance are discussed. The effects of rotor reaction on radial turbine flow versus pressure characteristics are examined pertinent to engine matching requirements. Engine transient performance is addressed, as influenced by turbine operation towards and beyond runaway conditions.
Some Effects of Size on the Performances of Small Gas Turbines
Authors: Rodgers C.
Published: February 2009

By the new millennia gas turbine technology standards the size of the first gas turbines of Von Ohain and Whittle would be considered small. Since those first pioneer achievements the sizes of gas turbines have diverged to unbelievable extremes. Large aircraft turbofans delivering the equivalent of 150 megawatts, and research micro engines designed for 20 watts. Microturbine generator sets rated from 2 to 200kW are penetrating the market to satisfy a rapid expansion use of electronic equipment. Tiny turbojets the size of a coca cola can are being flown in model aircraft applications. Shirt button sized gas turbines are now being researched intended to develop output powers below 0.5kW at rotational speeds in excess of 200 Krpm, where it is discussed that parasitic frictional drag and component heat transfer effects can significantly impact cycle performance. The demarcation zone between small and large gas turbines arbitrarily chosen in this treatise is rotational speeds of the order 100 Krpm, and above. This resurgence of impetus in the small gas turbine, beyond that witnessed some forty years ago for potential automobile applications, fostered this timely review of the small gas turbine, and a re-address of the question, what are the effects of size and clearances gaps on the performances of small gas turbines?. The possible resolution of this question lies in autopsy of the many small gas turbine component design constraints, aided by lessons learned in small engine performance development, which are the major topics of this paper.
Research on Application of Melt-Growth Composite Ceramics to Gas Turbines
Authors: Fujiwara Kenji , Nakagawa Narihito , Kobayashi Kenji , Yokoi Shinya , Kihara Tsutomu , Takamatsu Hideaki
Published: February 2009

An unique ceramic material produced through unidirectional solidification with eutectic composition of two-phase oxides was introduced recently. This composite material has the microstructure of coupled networks of two single crystals interpenetrate each other without grain boundaries. Depending on this microstructure this material, called Melt Growth Composite (MGC), can sustain its room temperature strength up to 1,700 (near its melting point) and offer strong oxidization-resistant ability, making its characteristics quite ideal for the gas turbine application. Our research project on MGC started in 2001 with the objective of establishing component technologies for MGC application to the high temperature components of the gas turbine engine. This paper outlines the results of our research so far at the early stage of the project.
Relative Cooling System: Design and Efficiency
Authors: Constantin Sandu , Brasoveanu Dan
Published: February 2009

Cooling systems with liquid for gas turbines that use the relative motion of engine stator with respect to rotor have been called relative cooling systems. This motion actuates the pump for liquid recirculation and the system is encapsulated within the engine rotor. In this manner, the difficult problem of sealing stator/rotor interfaces at high temperature, pressure and relative velocity is circumvented. A first generation of such systems could be manufactured using existing technologies and would boost thermal efficiency of gas turbines by more than 3% compared to the most advanced air-cooling engines. In the end, relative systems would boost temperatures at turbine inlet to stoichiometric levels and therefore increase thermal efficiency of gas turbines by about 8%. Such systems would recover most heat extracted from turbine for cooling and increase the power to size and power to weight ratio of all gas turbines. The appreciated high reliability of this cooling relies on encapsulation within the rotor and will allow widespread use in both ground and aerospace applications.
Experimental Results on Humidification of Compressed Air in a Tubular Humidifier for Evaporative Cycles
Authors: Dalili Farnosh , Westermark Mats
Published: February 2009

The evaporative gas turbine (EvGT), also known as the humid air turbine (HAT) has the potential to compete with diesel engines and combined cycles in small and intermediate sizes. Most EvGT concepts include a packed bed tower for humidification; however, an alternative is a tubular humidifier unit. A tubular humidifier test rig was designed and constructed at the Royal Institute of Technology in Stockholm. A thorough investigation of the humidifier’s performance and characteristics at different pressures was conducted in 1998. The humidifier consists of a single vertical surface-extended tube and shell. The water and the compressed air are brought into countercurrent contact inside the tube, resulting in evaporation of the water film in the compressed air. The heat required for the evaporation comes mainly from the exhaust gas cooling on the shell side. Experimental results show that the tubular humidifier operates satisfactorily. The exhaust gas heat is recovered to significantly low temperatures. The temperature and the humidity ratio of the compressed air are promising for EvGT applications. The flooding velocity and the wetting limit were also examined. In most cases an inner tube diameter of approximately 50 mm and a tube length of 9 m are considered suitable for this type of application.