bluuebunny/crossref_metadata_2025 huggingface dataset:
Static and Dynamic Characteristics of Air Foil Thrust Bearing Considering Tilting Pad Condition
Authors: Park Dong-Jin , Lee Yong-Bok , Kim Chang-Ho , Jang Gun-Hee
Published: March 2009

The thrust pad of the rotor is used to sustain the axial force generated due to the pressure difference between the compressor and turbine sides of turbomachinery such as the gas turbines and turbochargers. Furthermore, this thrust pad has a role to maintain and determines the attitude of the rotor. In a real system, it also helps reinforce the stiffness and damping of the journal bearing. This study was performed for the purpose of analyzing the characteristics of the air foil thrust bearing. The model for the air foil thrust bearing used in this study is composed of two parts: one is an inclined plane, which plays a role to increase the load carrying capacity using the physical wedge effect, and the other is a flat plane. This study mainly consists of three parts. First, the static characteristics were obtained over the region of the thin air film using the finite difference method (FDM) and the bump foil characteristics using the finite element method (FEM). Second, the analysis of the dynamic characteristics was conducted by perturbation method. For more exact calculation, the rarefaction gas coefficients perturbed about the pressure and film thickness were taken into consideration. At last, the static and dynamic characteristics of the tilting condition of the thrust pad were obtained. Furthermore, the load carrying capacity and torque were calculated for both tilting and not-tilting conditions. From this study, several results were presented: 1) the stiffness and damping of the bump foil under the condition of the various bump parameters, 2) the load carrying capacity and bearing torque at the tilting state, 3) the bearing performance under various bearing parameters, 4) the effects considering the rarefaction gas coefficients.
Prediction and Mitigation of Thermally Induced Creep Distortion in Gas Turbine Combustors
Authors: Rizkalla Hany , Strohl Page , Stuttaford Peter
Published: March 2009

In an effort to maximize efficiency and decrease emissions, modern gas turbine combustors are exposed to extreme operating conditions which if not accounted for during the design process, can lead to premature failure of the combustion components. Of interest to this article are some operating conditions that, in many instances can expose the gas turbine combustion chambers (liners) to asymmetric thermal loads. Highly asymmetric thermal loads at high temperatures can inflict severe distress on combustion liners attributing to thermal creep distortion and Thermo-Mechanical Fatigue (TMF). Modern low emission pre-mix combustion systems such as the Dry Low NOx (DLN) 2.6 in the GE F Class machines and PSM’s FlameSheet combustor employ firing curves that involve “staging” when the gas turbine is ramping up or down in load or is simply operating in part-load condition. During such staging process, the flame resides in only certain sectors of each combustor while the other sectors are cold, these part load conditions can cause high thermal gradients leading to high thermally induced stresses in the liners. High thermal stresses at high metal temperatures can induce severe visco-plastic (creep) geometric distortion in liners upon prolonged exposure to such conditions. Extreme thermally induced creep distortion can eventually lead to liners’ catastrophic failures due to buckling and/or rupture. Under mild circumstances permanent creep distortion of liners can lead to non-optimal combustion and hence attributing to non optimal operation of the gas turbine. Several means can be employed during the design process to avoid and/or account for creep distortion, some of which are discussed in this article. Although linear elastic analysis is usually used by design engineers to predict liner thermal deflection under part load conditions, it is important to note that even though the resulting stresses may be within the material’s elastic range, creep relaxation leading to permanent liner deformation may still occur over time causing non-optimal base load operation and degradation to the gas turbine efficiency. In most cases predicting thermally induced creep distortion over time can only be done using iterative numerical techniques such as FEA coupled with the material specimen creep testing. A case study involving a F class FlameSheet liner will be discussed and used for illustrative purposes. ANSYS non-linear creep FEA modeling was used to predict the creep deformation results over time using Haynes 230 specimen test data. The predicted numerical analytical results matched well with actual hardware characterized data, thus validating the analytical technique.
Identifying Areas Prone to Dusty Winds for Gas Turbine Inlet Specification
Authors: Brake Charles
Published: March 2009

The role and geographical spread of gas turbines is increasing. Because of this, there are more situations where the operator is likely to experience problems with high concentrations of dust overloading the intake system. This work summarizes the causes of dusty winds, areas where they are found, and offers recommendations to assist the inlet specifier. The causes of dusty winds are identified and discussed including desertification, small-scale local factors and meteorological conditions. Areas of the world where dust originates from and areas to which it can be carried are identified. In conclusion, the combinations of these factors are then offered as recommendations for the inlet specifier, to assist in choosing the correct type of filtration for inlets for areas likely to be affected by dust, and identify risk factors with specific types of inlet filter systems in these locations.
Turbulence Model Dependencies on Conjugate Simulation of Flow and Heat Conduction
Authors: Bamba Takahiro , Yamane Takashi , Fukuyama Yoshitaka
Published: March 2009

This paper discusses the influences of the turbulence model selection on the heat transfer prediction in the conjugate simulation of flow and heat conduction. It is known that the heat transfer prediction by the flow simulation based on RANS is dependent upon the turbulence model. Common difficulties are the anomalous production of turbulent kinetic energy in a flow with large rates of strain and the laminar-turbulent transition, both of which are persistent aspects in typical turbine cascade flow. Similar and possibly greater impact is expected when these turbulence models are applied to the conjugate simulation of flow and heat conduction. An anomaly treatment called a time-scale bound is applied to the low Reynolds number k-ω and the SST turbulence models installed in the common CFD platform UPACS. The turbulence model dependencies on the conjugate simulation of flow and heat conduction are investigated in an axisymmetric turbulent jet impingement and the 2D turbine cascade vanes.
Design of a Solid Propellant Air Turbo Rocket for a Tactical Air-Launched Missile
Authors: Haglind Fredrik , Edefur Henrik , Olsson Stefan
Published: March 2009

Traditionally, air-launched missiles are powered by a turbojet engine, rocket motor or a ramjet engine. A novel concept that may offer advantages over these concepts is the Air Turbo Rocket (ATR), which is a combined cycle engine, featuring a cycle where the turbine is isolated from the core engine flow entirely and powered by a separate gas generator. This paper is aimed at assessing the suitability of the solid propellant ATR as power source for a tactical air-launched missile. The ATR cycle is designed to achieve optimum performance, and a suitable solid propellant is selected. In addition, a turbojet and a solid rocket motor are designed for the same requirements, and the performances of these three engine concepts are compared. The ATR offers high thrust to weight and thrust to frontal area weight ratios, throttleability, and a wide speed-altitude operating envelope. The calculations suggest that, provided that the afterburning cooling issues can be solved, it would be reasonable to design the ATR such that a stoichiometric fuel/air mixture is obtained in the afterburner. For the Mach number range evaluated here, the ATR may offer advantages over the turbojet and the solid propellant rocket motor.
Preliminary Study on CO2 Processing in CO2 Capture From Oxy-Fuel Combustion
Authors: Li H. , Yan J.
Published: March 2009

Oxy-fuel combustion is one of promising technologies for CO2 capture, which uses simple flue gas processing normally including compression, dehydration and purification/liquefaction (non-condensable gas separation). However relatively high levels of impurities in the flu gas present more challenges for the gas processing procedure. This paper studied the sensitivity of operating parameters to inlet composition, the effects of impurities on energy consumption, and the relationship between energy consumption and operating parameters. Results show that comparatively the total compression work is more sensitive to the composition of SO2 if the total mass flow is constant; while the operating temperature of purification is more sensitive to N2. To pursue the minimum energy consumption, from the viewpoint of impurity, the content of O2, N2, Ar and H2O should be lowered as much as possible, which means the amount of air leakage into the system and excess oxygen should be controlled at a low level in the combustion; as to SO2, if it is possible to co-deposit with CO2, its existence may be helpful to decrease compression work. From the viewpoint of operating parameters, low intermediate pressure, high intercooling temperature and high outlet pressure are favorable to achieve high energy utilization, if heat recovery is considered.
Effect of a Bend on the Performance of an Oblong Ejector
Authors: Maqsood Asim , Birk A. M.
Published: March 2009

This paper presents the results of an experimental study on the performance of oblong ejectors with a bend in the mixing tube. In the aerospace industry, space limitations can lead to the design of exhaust ducts of oblong cross section. These ducts can also include ejectors for engine space ventilation or exhaust cooling or infrared signature suppression. In some cases these systems require bends after the primary driving nozzle. Each ejector consisted of a nozzle and a constant area mixing tube. A series of bent mixing tubes with the same radius of curvature was tested and the results were compared with the baseline straight ejector. A hot flow wind tunnel was used to provide the primary air flow at temperatures up to 450°C and mass flow rates up to 2 kg/s. Ambient air from the surroundings was allowed to enter the mixing tubes and mix with the primary air issuing from the primary nozzle. Velocity, pressure and temperature measurements were taken upstream of the nozzle, at the mixing tube inlet and at the exit of the mixing tube. Seven-hole probes were used to resolve the velocity vector at the exit of the mixing tube to identify large-scale flow structures. Mass flow ratio, temperature distribution and the losses in the different ejectors were compared to estimate the degradation of ejector performance with the degree of bend. Significant reduction in the performance was observed with the degree of bend in the ejector.
Case-Based Reasoning Approaches for Gas Turbine Trip Diagnosis
Authors: Graichen Catherine M. , Cheetham William E.
Published: March 2009

Effective maintenance, repair and design improvements of gas turbines require the classification of turbine automatic shutdown events into actionable categories. In particular, analysis is required at two distinct points in the life cycle of a shutdown event. The first evaluation is at the time of the shutdown when an initial assessment of the cause and the appropriate action must be decided as quickly as possible to return the turbine to service. At the time of the event, the primary sources of data are information collected from the sensors and control system. A second assessment is often performed as a post-event evaluation using additional information to validate the cause. General Electric created Case-Based Reasoning (CBR) tools to perform these classifications automatically. The first CBR tool, which works at the time of the event, was deployed in 2004. The second CBR tool was placed in operation in 2006.
The Development of Low-NOx CLEAN Combustor in the Frame of EEFAE Research Program
Authors: Colantuoni Salvatore , Di Martino Pasquale , Cinque Giuseppe , Terlizzi Alessandro
Published: March 2009

In the frame of the European Research Program EEFAE (Efficient and Environmentally Friendly Aero-Engine) successfully completed in five years (2000-2005), an advanced low-NOx combustor has been designed and validated for the CLEAN (Component vaLidator for Environmentally-friendly Aero-eNgine) demonstrator. The objectives of the paper are to show an overview of the CLEAN combustor development, such as combustor design, manufacturing and test rig results, and to provide first comparison between a-posteriori CFD analysis Vs. Rig experimental data, useful for a more comprehensive understanding of combustion performance.
Fuel Injection Scheme for a Compact Afterburner Without Flameholders
Authors: Birmaher Shai , Zeller Philipp W. , Wirfalt Peter , Neumeier Yedidia , Zinn Ben T.
Published: March 2009

State of the art afterburner combustion employs spray bars and flameholders in a long cavity, which adds significant length and weight to the engine and increases its observability. This paper presents a feasibility study for the development of a compact “prime and trigger” afterburner that eliminates the flameholders and reduces the length of the engine. In this concept, fuel is injected just upstream or in between the turbine stages in such a manner that upon exiting the turbine the fuel has evaporated and premixed with the flow without significant combustion, a process referred to as “priming”. Downstream of the turbine, combustion is initiated either through autoignition or by using a low power plasma radical generator being developed in a parallel investigation to “trigger” the combustion process. The prime and trigger injection and ignition scheme has been investigated using an experimental setup that simulates the operating conditions in a typical gas turbine engine. For this investigation, a trigger is not used, and combustion of the fuel occurs through autoignition. A physics-based theoretical model was developed to predict the location of autoignition for given flow and spray properties and injection locations. The theoretical predictions and the experimental results obtained using thermocouple measurements and CH* chemiluminescence confirm the feasibility of the prime and trigger concept by demonstrating the predictable and controlled autoignition of the afterburner fuel.
High Inlet Relative Mach Number Centrifugal Compressor Impeller Design
Authors: Sorokes James M. , Kopko Jason A.
Published: March 2009

This document presents an overview of impeller inlet relative Mach number, how the parameter is calculated, and its importance as an indicator of impeller performance. Comments are also offered regarding the comparison of inlet relative Mach numbers obtained from different compressor vendors. A sample impeller is used to illustrate the various methods used to calculate the inlet relative Mach number. Test data for that impeller is also offered to indicate the performance map achievable with high Mach number designs. Please note that this document is not intended to be an all-inclusive treatment of the subject; rather, it summarizes the OEM’s methodologies and perspective.
Flashback Detection Sensor for Hydrogen Augmented Natural Gas Combustion
Authors: Thornton Jimmy D. , Chorpening B. T. , Sidwell Todd G. , Strakey Peter A. , Huckaby E. D. , Benson K. J.
Published: March 2009

The use of hydrogen augmented fuel is being investigated by various researchers as a method to extend the lean operating limit, and potentially reduce thermal NOx formation in natural gas fired lean premixed (LPM) combustion systems. The resulting increase in flame speed during hydrogen augmentation, however, increases the propensity for flashback in LPM systems. Real-time in-situ monitoring of flashback is important for the development of control strategies for use of hydrogen augmented fuel in state-of-the-art combustion systems, and for the development of advanced hydrogen combustion systems. The National Energy Technology Laboratory (NETL) and Woodward are developing a combustion control and diagnostics sensor (CCADS), which has already been demonstrated as a useful sensor for in-situ monitoring of natural gas combustion, including detection of important combustion events such as flashback and lean blowoff. Since CCADS is a flame ionization sensor technique, the low ion concentration produced in pure hydrogen combustion raises concerns of whether CCADS can be used to monitor flashback in hydrogen augmented combustion. This paper discusses CCADS tests conducted at 0.2-0.6 MPa (2–6 atm), demonstrating flashback detection with fuel compositions up to 80% hydrogen (by volume) mixed with natural gas. NETL’s Simulation Validation (SimVal) combustor offers full optical access to pressurized combustion during these tests. The CCADS data and high-speed video show the reaction zone moves upstream into the nozzle as the hydrogen fuel concentration increases, as is expected with the increased flame speed of the mixture. The CCADS data and video also demonstrate the opportunity for using CCADS to provide the necessary in-situ monitor to control flashback and lean blowoff in hydrogen augmented combustion applications.
Evaporative Cooling of Gas Turbine Engines: Climatic Analysis and Application in High Humidity Regions
Authors: Chaker Mustapha , Meher-Homji Cyrus B.
Published: March 2009

There are numerous power generation and mechanical drive gas turbine applications where the power drop caused by high ambient temperatures has a very detrimental effect on the production of power or process throughput. Media evaporative cooling and inlet fogging are common low cost power augmentation techniques applied to reduce these losses. Several misconceptions exist regarding the applicability of evaporative cooling to what are often called “high humidity” regions. There is a sizable evaporative cooling potential in most locations when climatic data is evaluated based on an analysis of coincident wet bulb and dry bulb data. This data is not readily available to plant users and designers. This paper provides a detailed treatment of available climatic data bases and presents actual climatic data from several world wide locations to show that considerable cooling potential actually exists even in high humidity regions. It is hoped that this paper will be of value to plant designers, engineering and operating companies that are considering the use of evaporative cooling for power augmentation.
The Effect of Combustor-Turbine Interface Gap Leakage on the Endwall Heat Transfer for a Nozzle Guide Vane
Authors: Lynch S. P. , Thole K. A.
Published: March 2009

To enable turbine components to withstand high combustion temperatures, they are cooled by air routed from the compressor, which can leak through gaps between components. These gaps vary in size from thermal expansions that take place. The leakage flow between the interface of the combustor and the turbine, in particular, interacts with the flowfield along the endwall. This study presents measurements of adiabatic cooling effectiveness and heat transfer coefficients on the endwall of a first vane, with the presence of leakage flow through a flush slot upstream of the vane. The effect of axial contraction of the slot width due to thermal expansion of the engine was tested for two blowing rates. Contracting the slot width, while maintaining the slot mass flow, resulted in a larger coolant coverage area and higher effectiveness values, as well as slightly lower heat transfer coefficients. Matching the momentum flux ratio of the leakage flow from the nominal and contracted slot widths lowered both cooling effectiveness and heat transfer coefficients for the contracted slot flow. Comparison of the coolant coverage pattern to the measured endwall shear stress topology indicated that the trajectory of the slot coolant was dictated by the complex endwall flow.
Advanced Hydrogen Gas Turbine Development Program
Authors: Bancalari Ed , Chan Pedy , Diakunchak Ihor S.
Published: March 2009

The U.S. Department of Energy (DOE) has awarded Siemens Power Generation the first two phases for the Advanced Hydrogen Turbine Development Program. The 3-phase, multi-year program goals are to develop an advanced syngas, hydrogen and natural gas fired gas turbine fully integrated into coal-based Integrated Gasification Combined Cycle (IGCC) plants. The Program objectives are to demonstrate 3–5 percentage points efficiency improvement over current state of the art, less than 2 ppm NOx @ 15% O2 and reduction in plant capital cost. An additional objective is to show how the advanced gas turbine – IGCC plant can be configured for CO2 sequestration readiness. These objectives represent the overall DOE Advanced Power System goal to conduct Research and Development necessary to produce fuel flexible, CO2 sequestration ready advanced IGCC power systems for FutureGen type applications. Phase 1 entails advanced technologies identification, research and development Implementation Plan preparation and new gas turbine component conceptual designs. Phase 2 focuses on novel technologies development, validation, down selection and advanced gas turbine detail design. Phase 3 involves advanced gas turbine and IGCC plant construction and validation testing to demonstrate that efficiency, emissions and cost goals will be achieved and to prove the system’s commercial viability. The end objective is to validate the advanced gas turbine technology by 2015. The SGT6-6000G was selected as the basis for this development effort, due to its high firing temperature, output power and efficiency, as well as its advanced secondary air and steam cooling systems. It will be adapted for operation on coal, refinery residue and biomass derived hydrogen and syngas fuels, as well as natural gas, while achieving high performance levels and reduced plant capital costs in $/kW. New or enhanced technologies required to achieve high plant efficiency, while minimizing emissions and capital cost, will be developed and gas turbine design changes needed for optimum integration into the IGCC plant will be carried out. The main development thrust will be in the combustion, turbine cooling, materials/coating technologies and engine integration/operational flexibility. Several combustion systems will be investigated and the most successful candidate down selected. To minimize cooling air consumption, novel cooling concepts will be investigated, and validated in rig tests. Advanced bond coats, thermal barrier coatings, superalloys and airfoil architectures will be developed to minimize cooling air use. This paper describes the first year’s Phase 1 activities in advanced concepts, technologies identification and development, plant thermal performance evaluation, gas turbine IGCC plant integration studies and new gas turbine component conceptual designs.
Blowout Margin Estimation Based on Two Precursor Types
Authors: Prakash Shashvat , Neumeier Yedidia , Zinn Ben T.
Published: March 2009

Lean, premixed combustion has been aggressively pursued in recent years because it offers a practical approach for reducing emissions of nitrogen oxides (NOx) from gas turbines. However, lean premixed flames pose a greater risk of blowout. Studies on swirl and dump stabilized flames have shown that as a flame approaches blowout, distinctive precursors occur, such as pockets of localized extinctions and brief flame shape transitions to a thin ‘tornado’ configuration. For this study, both precursor types are detected using separate, dedicated optical sensors. Observations indicate that the tornado mode is part of the blowout process in a 127 mm long combustor and that a localized extinction precursor immediately precedes the tornado mode transition. Despite the causality, the statistics of tornado bursts and localized extinctions suggest a ‘memoryless’ Poisson process, where the occurrence of one event type does not influence the time until the next event of the same type. Localized extinctions have been used previously for blowout margin estimation, and are well suited for the purpose because the occurrence frequency increases with diminishing margin. However, the signals commonly used to detect localized extinction events are noisy due to the nature of the flame; thus, detection is prone to false alarms. Detecting tornado bursts, by comparison, is less ambiguous but such events occur too rarely for blowout mitigation applications. The shortcomings of both precursor detection methods can be addressed by combining observations of both precursor types in a meaningful manner. The presence of tornado bursts indicates that the flame is near blowout; this fact can be used to calibrate margin estimation routines based upon localized extinction. However, this approach would require two sensors since any one optical sensor cannot directly differentiate both precursor types. A single sensor approach can be developed whereby the causal relationship between the two precursor types is exploited. Local extinctions with longer duration times can potentially perturb the flame into an alternate flow configuration. The presence of these tornado ‘triggers’ manifest as an increase in the low frequency content of the chemiluminescence signal. A low pass filter with the appropriate cutoff frequency can differentiate between the tornado-triggering and benign, inconsequential localized extinctions. Therefore, the same signal that detects localized extinctions can be filtered to capably predict tornado mode shifts. This scheme will enable robust margin detection and minimize sensitivity to noise.
Prediction of High Cycle Fatigue Life of Steam Turbine Blading Based on Unsteady CFD and FEM Forced Response Calculation
Authors: Misek Tomas , Tetiva Antonin , Prchlik Lubos , Duchek Karel
Published: March 2009

This paper presents the high cycle fatigue life prediction of a shrouded packet blade row for a large high pressure steam turbine. The fatigue life assessment was based on a loosely coupled CFD and FEM calculations supported by the direct cyclic mechanical testing of a full scale model of the blade root attachment. In the first stage, potentially dangerous vibration modes were identified from the linear finite element analyses and verified by testing. Aerodynamic forces acting on rotating blades were obtained from an unsteady sliding mesh CFD calculation based on a viscous unsteady compressible turbulent flow. A forced vibration analysis was then performed for critical resonance frequencies close to nozzle passing frequency considering only the inherent material damping. The calculated alternating stress in the blade root attachment was used to estimate the safety against the high cycle fatigue failure. Fatigue life was evaluated for current and new design of stationary vanes. In the new design the number of vanes was increased and their full 3D shape was optimized. Both changes reduced the excitation forces by more then an order of magnitude. The final evaluation showed that the vibratory stresses for the new design were well below the actual fatigue limit of the blade root attachment.
Evaluation of Energy Efficiency for a CCHP System With Available Microturbine
Authors: Liang H. X. , Wang Q. W.
Published: March 2009

This paper deals with the problem of energy utilization efficiency evaluation of a microturbine system for Combined Cooling, Heating and Power production (CCHP). The CCHP system integrates power generation, cooling and heating, which is a type of total energy system on the basis of energy cascade utilization principle, and has a large potential of energy saving and economical efficiency. A typical CCHP system has several options to fulfill energy requirements of its application, the electrical energy can be produced by a gas turbine, the heat can be generated by the waste heat of a gas turbine, and the cooling load can be satisfied by an absorption chiller driven by the waste heat of a gas turbine. The energy problem of the CCHP system is so large and complex that the existing engineering cannot provide satisfactory solutions. The decisive values for energetic efficiency evaluation of such systems are the primary energy generation cost. In this paper, in order to reveal internal essence of CCHP, we have analyzed typical CCHP systems and compared them with individual systems. The optimal operation of this system is dependent upon load conditions to be satisfied. The results indicate that CCHP brings 38.7 percent decrease in energy consumption comparing with the individual systems. A CCHP system saves fuel resources and has the assurance of economic benefits. Moreover, two basic CCHP models are presented for determining the optimum energy combination for the CCHP system with 100kW microturbine, and the more practical performances of various units are introduced, then Primary Energy Ratio (PER) and exergy efficiency (α) of various types and sizes systems are analyzed. Through exergy comparison performed for two kinds of CCHP systems, we have identified the essential principle for high performance of the CCHP system, and consequently pointed out the promising features for further development.
Application of a 1-D Predicting Tool to the Analysis of Pressure Oscillations in an Industrial Gas Turbine Combustor: GE10 Machine
Authors: Asti Antonio , Mangani Luca , Andreini Antonio
Published: March 2009

The development of current industrial gas turbines is strictly constrained by legislative requirements for low polluting emissions. Lean Premixed combustion technology has become through the years the necessary standard to meet such requirements. Premixed technology introduces a new range of problems: combustion instabilities in many operating conditions. Specifically, lean premixed flames pose the threat of pressure oscillations. This phenomenon is the effect of the strong interaction between combustion heat-release and fluid dynamics aspects. The prediction of acoustic oscillations and combustion instabilities is generally difficult because of the complexity of real combustor geometries. As a result, the design phase is usually performed as a trial-and-error task: a specific design is constructed, tested and modified, in a process that continues until acceptable results are found. A specific tool was developed by GE Energy to help predicting the acoustic behaviour of newly designed partially-premixed combustors, avoiding the traditional trial-and-error process: the tool allows the designer to analyze the problem of combustion instabilities since the early design phase, limiting subsequent testing efforts. A mono-dimensional tool based on the 1-D acoustic model was developed by GE Energy and was applied to the single-can combustor of the GE10 machine (a gas turbine in the 10MW class). All the main geometrical features of the GE10 machine, including fuel line geometry, were considered and modeled in a one-dimensional scheme, in order to build an equivalent model for the linear tool analysis. The main frequencies, measured during tests on the GE10 machine, were compared to the numerical results of the tool, showing good agreement between numerical and experimental results and confirming the predictive capability. This good agreement demonstrates that the model can be used for predicting the effects of design changes, with a reduced need of tests.
Helicopter Structural Life Modeling: Flight Regime and Gross Weight Estimation
Authors: Grabill Paul , Jacobs Jerry , Johnson Tom , Brotherton Tom , Keller Jon
Published: March 2009

Accurate usage information collected by Health and Usage Monitoring Systems (HUMS) coupled with improved structural fatigue life calculation methodologies promise to reduce helicopter operational and support costs while maintaining current flight safety levels. Current fatigue life calculations assume worst-case flight profiles in determining component life. This approach may be outdated or not reflective of actual aircraft usage. On a small business innovative research (SBIR) contract the Intelligent Automation Corporation (IAC) has developed processing to include a low cost regime recognition and aircraft gross weight estimation capability as an extension to the US Army’s Vibration Management Enhancement Program (VMEP). IAC’s approach relies on multi-sensor data fusion technology and flight parameters collected by VMEP to provide an accurate flight regime calculation. Recording time in particular flight regimes has the potential of extending aircraft component life without changing proven lifing models. The regime recognition system has been implemented with the current release of IAC’s VMEP systems. Presented here are the methodology, development and visualization tools developed on the SBIR as well as results for using the system on AH-64 aircraft in follow-on work.
Performance Evaluation of Gas Turbine Labyrinth Seals Using Computational Fluid Dynamics
Authors: Soemarwoto Bambang I. , Kok Johan C. , de Cock Koen M. J. , Kloosterman Arjen B. , Kool Gerrit A. , Versluis Joris F. A.
Published: March 2009

The paper presents an investigation on the characteristics of flow through labyrinth seals. The focus of the paper lies in the application of the Computational Fluid Dynamics (CFD) methodology. The Reynolds-Averaged Navier-Stokes equations are employed as the flow governing equations. Turbulence is incorporated through a variant of the two-equation k-ω turbulence model. Three test cases are considered. The first test case concerns a labyrinth seal configuration with a honeycomb land. The computational results are compared to those obtained from seal test rig measurements. The second test case addresses the same labyrinth seal where the honeycomb land is replaced by a solid smooth land. The third test case addresses the flow through a labyrinth seal with canted knives. The CFD method is considered as an analysis tool complementary to rig-testing and enables investigating the effect of new seal design features. Additionally CFD is seen as a tool to support the correct representation of test-data in semiempirical engineering models for seal design. An industrial perspective is presented towards the exploitation of these modeling capabilities for real-life design of seals.
Small Recuperated Gas Turbine APU Concept to Abate Concern About Emissions, High Fuel Cost, and Noise
Authors: Rodgers Colin , McDonald Colin F.
Published: March 2009

During the last decade microturbines in the 30 to 250 kW power range have been in service, but they have not been produced in significant enough quantities to impact the DG market due to a combination of factors including their high cost, modest efficiency, utility institutional concerns, and low interest in CHP use in the USA, although the latter could change as a result of fuel cost escalation. Very small gas turbines (ie. less than 10 kW) have been investigated periodically over the years, mainly for potential military use, but to date have not found a niche. This could well change with over 20 states now having instigated idling regulations that limit or prohibit heavy duty truck diesel engine idling. With emphasis on reducing emissions and noise levels this essentially implies that in the future a small APU will be required to provide the truck’s stationary electrical needs and cabin climate control. While there will be several power source types vying for this potentially large market, a small gas turbine APU is viewed as having attractive features which include low emissions, low acoustic signature, vibration-free operation, compact and light weight package, obviates the need for oil lubrication and liquid coolant systems, ease of cold weather starting, immediate response, and the use of fuel from the truck tank. In this paper a small recuperated gas turbine APU concept rated at 5kW is discussed including component design considerations, layout features, engine performance, and target cost. The conservative design of the APU is based on the use of existing materials and state-of-the-art gas turbine technology, and is amenable to high volume automated manufacturing processes. A competitive cost is projected if the proposed APU of modular construction was fabricated in large quantities like the production of vehicular turbochargers in Europe.
Combined Effects of Wakes and Jet Pulsing on Film Cooling
Authors: Womack Kristofer M. , Volino Ralph J. , Schultz Michael P.
Published: March 2009

Pulsed film cooling jets subject to periodic wakes were studied experimentally. The wakes were generated with a spoked wheel upstream of a flat plate. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface were considered at blowing ratios, B, of 0.50, and 1.0 with jet pulsing and wake Strouhal numbers of 0.15, 0.30, and 0.60. Wake timing was varied with respect to the pulsing. Temperature measurements were made using an infrared camera, thermocouples, and constant current (cold wire) anemometry. The local film cooling effectiveness and heat transfer coefficient were determined from the measured temperatures. Phase locked flow temperature fields were determined from cold wire surveys. With B = 0.5, wakes and pulsing both lead to a reduction in film cooling effectiveness, and the reduction is larger when wakes and pulsing are combined. With B = 1.0, pulsing again causes a reduction in effectiveness, but wakes tend to counteract this effect somewhat by reducing jet liftoff. At low Strouhal numbers, wake timing had a significant effect on the instantaneous film cooling effectiveness, but wakes in general had very little effect on the time averaged effectiveness. At high Strouhal numbers, the wake effect was stronger, but the wake timing was less important. Wakes increased the heat transfer coefficient strongly and similarly in cases with and without film cooling, regardless of wake timing. Heat transfer coefficient ratios, like the time averaged film cooling effectiveness, did not depend strongly on wake timing for the cases considered.
Vortex Breakdown in Swirling Fuel Injector Flows
Authors: Midgley Kris , Spencer Adrian , McGuirk James J.
Published: March 2009

It is well known that the process of vortex breakdown plays an important role in establishing the near-field aerodynamic characteristics of fuel injectors, influencing fuel/air mixing and flame stability. The precise nature of the vortex breakdown can take on several forms, which have been shown in previous papers to include both a precessing vortex core (PVC) and the appearance of multiple helical vortices formed in the swirl stream shear layer. The unsteady dynamics of these particular features can play an important role in combustion induced oscillations. The present paper reports an experimental investigation, using PIV and hot-wire-anemometry, to document variations in the relative strength of PVC and helical vortex patterns as the configuration of a generic fuel injector is altered. Examples of geometric changes which have been investigated include: • The combination of an annular swirl stream with and without a central jet; • variation in geometric details of the swirler passage, e.g. alteration in the swirler entry slots to change swirl number, and variations in the area ratio of the swirler passage. The results show that these geometric variations can influence: • the axial location of the origin of the helical vortices (from inside to outside the fuel injector); • the strength of the PVC. For example, in a configuration with no central jet (swirl number S = 0.72) the helical vortex pattern was much less coherent, but the PVC was much stronger than when a central jet was present. These changes modify the magnitude of the turbulence energy in the fuel injector near field dramatically, and hence have an important influence on fuel air mixing patterns.
Pre-Stall Behavior of a Transonic Axial Compressor Stage via Time-Accurate Numerical Simulation
Authors: Chen Jen-Ping , Hathaway Michael D. , Herrick Gregory P.
Published: March 2009

CFD calculations using high-performance parallel computing were conducted to simulate the pre-stall flow of a transonic compressor stage, NASA compressor Stage 35. The simulations were run with a full-annulus grid that models the 3-D, viscous, unsteady blade row interaction without the need for an artificial inlet distortion to induce stall. The simulation demonstrates the development of the rotating stall from the growth of instabilities. Pressure-rise performance and pressure traces are compared with published experimental data before launching a detailed study of the flow evolution prior to the rotating stall. Spatial FFT analysis of the flow indicates a rotating long-length disturbance of one rotor circumference, which is followed by a spike-type breakdown. The analysis also links the long-length wave disturbance with the initiation of the spike inception. The spike instabilities occur when the trajectory of the tip clearance flow becomes vertical to the axial direction. When approaching to stall, the passage shock changes from a single oblique shock to a dual-shock, which distorts the vertical trajectory of the tip clearance vortex but shows no evidence to cause flow separation that may contribute to stall.
Experimental Characterization of the Damping of Fuel-Air Ratio Fluctuations Using Transfer Function Analysis
Authors: Chishty Wajid A. , Bourque Gilles , Furi Marc , Yimer Ibrahim
Published: March 2009

This paper presents the theoretical and experimental framework used to characterize the capability of premixers used in Dry Low Emission (DLE) gas turbines to dampen fuel-to-air ratio (FAR) oscillations and thus serve as a passive control device for combustion noise. Based on a convection-diffusion volume model, transfer function analysis in the frequency-domain was used to describe the interaction between convection and turbulent diffusion mechanisms. The study showed that the best achievable damping was obtained when the ratio of convection to turbulent diffusion effects (expressed in terms of Peclet number) was unity. For this particular condition, the spreading of Residence Time Distribution (RTD) is optimal hence decreasing the coherence between incoming and outgoing perturbations. For large Peclet numbers, mixing mechanisms are not sufficient to dampen incoming FAR fluctuations and for very small Peclet numbers FAR perturbations can be communicated almost instantaneously to the premixer outlet, without attenuation.
Early Detection of Lubrication Anomalies in Oil-Lubricated Bearings
Authors: Iyer Naresh S. , Qiu Hai , Yan Weizhong , Loparo Kenneth A.
Published: March 2009

Condition monitoring of roller element bearings is of considerable interest to many industries since faulty roller element bearings are known to cause the majority of problems in rotating machinery. The class of failure modes in roller bearings that has received the most attention include spalling or localized defect in one or more of the bearing components. This refers to dislodgement of a portion of the contact surface in one or more of the bearing components in the presence of various kinds of stresses like rotor imbalance, speed, bad lubrication, heavy radial and axial loads. Whereas substantial work has been done in the detection of spalls in bearing components, studies show that one of the primary root causes of spalls in a bearing tends to be ineffective lubrication resulting either from lack of lubrication conditions or the presence of contaminants in the lubricant. Leading bearing companies have indicated that incorrect lubrication can account for more than 90% of bearing failures because of which lubrication can be a key influence that can make or break bearing service and life. This emphasizes the need to develop techniques to sense lubrication anomalies as well as provide information needed to act upon them. In other words, monitoring the health and effectiveness of the bearing lubricant should be at the forefront of a condition-monitoring program for bearings. In this paper, we describe experiments, analyses and results obtained for monitoring and detecting anomalies in bearing lubrication for oil-lubricated bearings. More specifically, we consider two kinds of lubrication anomalies: lack of lubrication and contamination of lubrication. Our work involves the use of techniques in sensing and analyses of acoustic emissions from the bearing housing for detection of anomalous lubrication conditions of the above classes. We explore these techniques by conducting controlled experiments where, conditions equivalent to the appropriate fault condition are simulated in a test rig and AE readings are recorded; as a baseline, we also record vibration readings using traditional accelerometers. Our analyses will consist of extracting features from the AE signal that can suitably distinguish between normal and abnormal lubrication conditions. Additional analyses that can potentially be used to understand the degree of severity of the abnormality will also be presented.
Aero-Thermal Investigations of Tip Leakage Flow In Axial Flow Turbines: Part I — Effect of Tip Geometry and Tip Clearance Gap
Authors: Krishnababu S. K. , Newton P. J. , Dawes W. N. , Lock G. D. , Hodson H. P. , Hannis J. , Whitney C.
Published: March 2009

A numerical study has been performed to investigate the effect of tip geometry on the tip leakage flow and heat transfer characteristics in unshrouded axial flow turbines. Baseline flat tip geometry and squealer type geometries namely double squealer or cavity and suction side squealer were considered. The performances of the squealer geometries, in terms of the leakage mass flow and heat transfer to the tip, were compared with the flat tip at two different tip clearance gaps. The computations were performed using a single blade with periodic boundary conditions imposed along the boundaries in the pitchwise direction. Turbulence was modelled using three different models namely standard k-ε, low Re k-ω and SST k-ω, in order to assess the capability of the models in correctly predicting the blade heat transfer. The heat transfer and static pressure distributions obtained using the SST k-ω model was found to be in close agreement with the experimental data. It was observed that compared to the other two geometries considered, the cavity tip is advantageous both from the aerodynamic and from the heat transfer perspectives by providing a decrease in the amount of leakage, and hence losses, and average heat transfer to the tip. In general, for a given geometry, the leakage mass flow and the heat transfer to the tip increased with increase in tip clearance gap. Part II of this paper examines the effect of relative casing motion on the flow and heat transfer characteristics of tip leakage flow. In Part III of this paper the effect of coolant injection on the flow and heat transfer characteristics of tip leakage flow is presented.