bluuebunny/crossref_metadata_2025 huggingface dataset:
Key Parameters for the Performance of Impaction-Pin Nozzles Used in Inlet Fogging of Gas Turbine Engines
Authors: Chaker Mustapha A.
Published: November 2008

Application of inlet air fogging to gas turbine engines for power augmentation, has become common practice, with more than a 1000 installations worldwide including a large number of advanced gas turbines. In this paper an experimental investigation and empirical analysis of key operating parameters on the performance of impaction pin nozzles will be investigated. To this date no such correlation is available for impaction pin nozzles, which are currently used in about 75% of this type of applications. The correlations are developed from a series of experiments conducted in a wind tunnel equipped with the Malvern Spraytec droplet size measurement system. The conducted analysis covered a wide range of the relevant parameters. Mainly the water flow rate from the nozzle orifice was (0.00126 1.s−1 to 0.00063 1.s−1: 0.02 gpm to 0.1 gpm), the operating pressure was (34.5 bars to 204.1 bars: 500 psi to 3000 psi), the airflow velocity was (1.5 m.s−1 to 15.2 m.s−1: 295 fpm to 3000 fpm), the distance between the nozzle orifice and the location of measurement was (0.0127m to 0.508 m: 0.5” to 20”). Other parameters such as the plume spray one angle and the surrounding ambient psychrometric conditions, which may affect the droplet size for impaction pin nozzles is also discussed.
Conceptual Design of a Supersonic CO2 Compressor
Authors: Lawlor Shawn P. , Baldwin Peter
Published: November 2008

Ramgen Power Systems, Inc. (RPS) is developing a family of high performance supersonic compressors that combine many of the aspects of shock compression systems commonly used in supersonic flight inlets with turbo-machinery design practices employed in conventional axial and centrifugal compressor design. The result is a high efficiency compressor that is capable of single stage pressure ratios in excess of those available in existing axial or centrifugal compressors. A variety of design configurations for land-based compressors utilizing this system have been explored. A proof-of-concept system has been designed to demonstrate the basic operational characteristics of this family of compressors when operating on air. The test unit was designed to process ∼1.43 kg/s and produce a pressure ratio across the supersonic rotor of 2.41:1. Based on the results from that effort a compressor specifically designed for the high pressure ratios required to support CO2 liquification has been proposed. The basic theory of operation of this new family of compressors will be reviewed along with the performance characteristics and conceptual design features of the proposed CO2 compressor systems.
Study on Biomass Pyrolysis Kinetics
Authors: Zhang Xiaodong , Xu Min , Sun Rongfeng , Sun Li
Published: November 2008

Pyrolysis is the most fundamental process in thermal chemical conversion of biomass, and pyrolysis kinetic analysis is valuable for the in-depth explore of process mechanism. On the basis of thermal gravity analysis of different kinds of biomass feedstock, thermal kinetics analysis was performed to analyze the pyrolysis behavior of biomass. With the apparent kinetic parameters derived, kinetic model was proposed for the main reaction section of biomass pyrolysis process. The pyrolysis characteristics of three kinds of biomass material were compared in view of corresponding biochemical constitution. Through model simulation of different pyrolysis process, the diversity in pyrolysis behavior of different kinds of biomass feedstock was analyzed, and pyrolysis mechanism discussed. The results derived are useful for the development and optimization of biomass thermal chemical conversion technology.
Cycle Optimization and High Performance Analysis of Gas Engine-Gas Turbine Combined Cycles
Authors: Tsuji Tadashi
Published: November 2008

The reciprocating engine operates with a maximum pressure and temperature in its cylinders that is higher than that in conventional gas turbines. When a gas engine is integrated with a gas turbine instead of a turbocharger, it is an ETCS (Engine-Turbo Compound System). We have developed the concept of a compound system with ERGT (Engine Reheat Gas Turbine) and propose it as a system with potentially high thermal efficiency. A natural gas firing gas turbine combined cycle (CC) is selected as the standard system for a thermal power plant. A higher TIT (Turbine Inlet Temperature) of gas turbine usually enables higher power generation efficiency. Focusing on the effect of engine exhaust temperature, we found that the ETCS cycle with a ERGT has the potential to achieve higher thermal efficiency than that of a gas turbine combined cycle, with no change in TIT. An engine exhaust temperature of 1173K increases the system power generation efficiency from 46 to 50%LHV (TIT 1150°C) and 54 to 57%LHV (TIT 1350°C), respectively. The gas engine–gas turbine combined cycle has the potential to achieve a significant efficiency increase of +4.1%LHV (TIT 1150°C) and +2.8%LHV (TIT 1350°C), making it a promising system for future power plants. Efficiency is expected to be improved by +8.7% (TIT 1150°C) and +5.6% (TIT 1350°C), relatively.
NOx Emissions Reduction in an Innovative Industrial Gas Turbine Combustor (GE10 Machine): A Numerical Study of the Benefits of a New Pilot-System on Flame Structure and Emissions
Authors: Andreini Antonio , Facchini Bruno , Mangani Luca , Asti Antonio , Ceccherini Gianni , Modi Roberto
Published: November 2008

One of the driving requirements in gas turbine design is emissions reduction. In the mature markets (especially the North America), permits to install new gas turbines are granted provided emissions meet more and more restrictive requirements, in a wide range of ambient temperatures and loads. To meet such requirements, design techniques have to take advantage also of the most recent CFD tools. As a successful example of this, this paper reports the results of a reactive 3D numerical study of a single-can combustor for the GE10 machine, recently updated by GE-Energy. This work aims to evaluate the benefits on the flame shape and on NOx emissions of a new pilot-system located on the upper part of the liner. The former GE10 combustor is equipped with fuel-injecting-holes realizing purely diffusive pilot-flames. To reduce NOx emissions from the current 25 ppmvd@15%O2 to less than 15 ppmvd@15%O2 (in the ambient temperature range from −28.9°C to +37.8°C and in the load range from 50% and 100%), the new version of the combustor is equipped with 4 swirler-burners realizing lean-premixed pilot flames; these flames in turn are stabilized by a minimal amount of lean-diffusive sub-pilot-fuel. The overall goal of this new configuration is the reduction of the fraction of fuel burnt in diffusive flames, lowering peak temperatures and therefore NOx emissions. To analyse the new flame structure and to check the emissions reduction, a reactive RANS study was performed using STAR-CD™ package. A user-defined combustion model was used, while to estimate NOx emissions a specific scheme was also developed. Three different ambient temperatures (ISO, −28.9°C and 37.8°C) were simulated. Results were then compared with experimental measurements (taken both from the engine and from the rig), resulting in reasonable agreement. Finally, an additional simulation with an advanced combustion model, based on the laminar flamelet approach, was performed. The model is based on the G-Equation scheme but was modified to study partially premixed flames. A geometric procedure to solve G-Equation was implemented as add-on in STAR-CD™.
Influence of the Interaction of Equivalence Ratio and Mass Flow Fluctuations on Flame Dynamics
Authors: Auer M. P. , Hirsch C. , Sattelmayer T.
Published: November 2008

Modern lean combustion systems are often prone to combustion instabilities — an interaction of acoustic waves, fluid dynamics and heat release oscillations. Mass flow oscillations are one important part of the feedback loop of combustion instabilities. Therefore, modulated mass flows of fuel or/and combustion air are main objectives in many studies on combustion instabilities and their active control (AIC, Active Instability Control). Flame response and flame transfer matrices are often determined by excitation of combustion air at various frequencies by sirens or loudspeakers. For the purpose of active control modulated secondary fuel is usually injected to the mass flow to dampen heat release fluctuations of the flame in order to de-couple the thermoacoustic feedback loop. This paper demonstrates the influence of modulated mass flows on the flame dynamics in an atmospheric test rig with a natural gas fired swirl burner. In the investigated cases the modulation of combustion air also result in equivalence ratio fluctuations due to choked main fuel injection. This combination has a tremendous effect on the flame dynamics. A model was developed to describe the interaction of equivalence ratio fluctuations and total mass flow oscillations and their influence on combustion instabilities. In experiments these equivalence ratio fluctuations were generated by injecting modulated secondary fuel. The derived model provides a deep insight into the driving mechanisms of combustion instabilities.
Microturbine Performance Improvement Through the Implementation of Inlet Air Cooling
Authors: Williamson Toussaint , Luker Mike , Hack R. L.
Published: November 2008

Microturbines have permeated the power generation infrastructure owing to their low cost, simple installation, and relatively low maintenance operation as compared to larger gas turbines. However, microturbines are susceptible to dramatic output power loss and efficiency degradation when the ambient temperature increases. To counteract the effect of increased inlet air temperatures, large scale turbines have utilized inlet air misting and fogging with water to reduce the temperature and increase density through evaporative cooling and ultimately increasing power output. Such a cooling scheme has not found wide spread utilization with microturbines possibly due to cost, complexity and/or implementation issues. This paper describes a simple, low cost system employed for cooling inlet air to a microturbine and the results of a testing program to characterize the improvements in performance. The system, integrated on a pair of Capstone C60 microturbines, has provided measured improvements in output power of approximately 25% as compared to the non-cooled operation. Specifically, at ambient temperatures between 32 C and 41 C, increases in output power from 9 kW to 12 kW have been observed. Improvements in efficiency have also been observed.
Axial Compressor Overhaul: GE-Made GT, Frame 7, Model EA
Authors: Ingistov Steve
Published: November 2008

This Paper contains technical and procedural information related to the overhauling of axial compressor being integral part of GE-built Frame No. 7, model EA CGT. Four CGT-driven electric generators are in operation in Watson Cogeneration Company (WCC), Carson, California, USA. CGT units were commissioned during fall of 1987 and winter of 1988 and have been operating under the base load since. Original overhauls of CGT rotors were performed by GE. Later on a decision was made to include third Parties capable to overhaul axial compressor and GT rotors. Overhaul Specifications (1) were generated in 1998 and were included into the Bid Packages. These specifications were intended to be used as a guide line only. The particular axial compressor overhaul efforts described in this Paper were the third since the commissioning. Step-by-step overhaul efforts of axial compressor assembly are described in order to understand the complexities and risks associated with the repair procedures.
An Evaluation of the Geometry and Weight of a Mixed Flow Low Bypass Ratio Turbofan Engine With an Intermediate Turbine Burner
Authors: Chen Chorng-Yow , Waters Mark H. , Mavris Dimitri
Published: November 2008

Turbofan engines are designed with two or even three spools of fan- compressor and turbine combinations. This arrangement allows the possibility of increased power output by placing a second combustor between turbine spools. Such a combustor is called an “Intermediate Turbine Burner, ITB,” and in a twin spool turbofan engine the combustor would be placed between the discharge of the high pressure turbine and the entrance of the low pressure turbine. An evaluation of the mechanical design of an ITB integrated into a low bypass ratio mixed flow turbofan is the subject of this paper. It is well known that an engine with an ITB has increased specific thrust but at the expense of increased specific fuel consumption. To take advantage of the ITB potential, the choice of cycle parameters — fan pressure ratio, overall pressure ratio and bypass ratio must be evaluated, and recent studies have demonstrated that the turbofan cycle with an ITB should have increased fan and overall pressure ratios to maximize performance. However, little has been done to estimate the weight and dimensions of an ITB integrated engine including the weight, flow path area and length of the ITB. Of particular concern are the volume and resulting flow path area and length required for the ITB.
Intake Air Aerodynamic Silencer Design and Fabrication: GE Frame 7, Model EA GT
Authors: Ingistov Steve
Published: November 2008

This Paper describes aerodynamic silencer that is presently installed in one GT Unit in Watson Cogeneration Company, Carson, California, USA. The silencer, made from three sections, was fit into existing Intake Air Duct System (IADS) during March, 2004 Major Inspection (MI). The purpose for original silencer replacement was to reduce IA pressure drops and to minimize continuous dirt carry-over from the old silencer panels into the compressor suction. GT is very sensitive to IA pressure drops and this sensitivity is manifested in GT power output reduction. IA pressure drop reduction alone justified expenditures in replacing the old silencer by new, aerodynamic silencer. Simplified EA presented in this Paper demonstrates good profit in replacing the old silencer with the new, redesigned silencer. In addition to improvements of IA aerodynamics, silencer was designed to capture IA cooling water that did not evaporate and to drain the collected water to designated locations. This Paper also incorporates field test data results, completed by others.
Development of an Aero-Thermodynamics Course to Aid an Undergraduate Propulsion Track
Authors: Boyer Keith M. , Rouser Kurt P. , Lawrence Timothy J.
Published: November 2008

This paper describes the development and assessment of a sophomore-level, aero-thermodynamics class structured to meet the needs of both the Department of Aeronautics and Department of Astronautics at the United States Air Force Academy. The course was developed following ABET EC2000 guidelines. Because of the large core class requirement placed on students at the USAF Academy, this single course was developed as an alternative to students taking traditional separate thermodynamics and gas dynamics courses. Benefits and tradeoffs of this approach are presented. The general philosophy in developing the course was to provide solid foundations in thermodynamics and compressible gas dynamics while motivating and inspiring students to their chosen engineering profession. To that end, the course is loaded with practical applications and hands-on laboratories. Engineering rigor was maintained by inclusion of an unsteady, three-dimensional control volume formulation of the governing equations, emphasizing assumptions and their implications, and enforcing engineering analysis methods. Quantitative assessment of specific performance criteria demonstrates achievement of educational outcomes. Student course critique scores provided additional quantitative data. Finally, an initial assessment of course impact on two different undergraduate propulsion classes demonstrates the intended result — improved understanding of fundamentals allowing for expanded coverage in other areas. In short, the propulsion tracks in both departments appear to be improved.
Structural Stiffness, Dry-Friction Coefficient and Equivalent Viscous Damping in a Bump-Type Foil Gas Bearing
Authors: Rubio Dario , San Andre´s Luis
Published: November 2008

High performance oil-free turbomachinery implements gas foil bearings (FBs) to improve mechanical efficiency in compact units. FB design, however, is still largely empirical due to their mechanical complexity. The paper provides test results for the structural parameters in a bump-type foil bearing. The stiffness and damping (Coulomb or viscous type) coefficients characterize the bearing compliant structure. The test bearing, 38.1 mm in diameter and length, consists of a thin top foil supported on bump-foil strips. A prior investigation identified the stiffness due to static loads. Presently, the test FB is mounted on a non-rotating stiff shaft and a shaker exerts single frequency loads on the bearing. The dynamic tests are conducted at shaft surface temperatures from 25 °C to 75°C. Time and frequency domain methods are implemented to determine the FB parameters from the recorded periodic load and bearing motions. Both methods deliver identical parameters. The dry friction coefficient ranges from 0.05 to 0.20, increasing as the amplitude of load increases. The recorded motions evidence a resonance at the system natural frequency, i.e. null damping. The test derived equivalent viscous damping is inversely proportional to the motion amplitude and excitation frequency. The characteristic stick-slip of dry friction is dominant at small amplitude dynamic loads leading to a hardening effect (stiffening) of the FB structure. The operating temperature produces shaft growth generating a bearing preload. However, the temperature does not affect significantly the identified FB parameters, albeit the experimental range was too small considering the bearings intended use in industry.
Thermoeconomic Analysis and Optimization of a Gas Turbine Cogeneration Unit by a Systems Approach
Authors: Yokoyama Ryohei , Takeuchi Shinsuke , Ito Koichi
Published: November 2008

It is important to design and operate energy conversion systems such as gas turbine cogeneration ones optimally from the thermoeconomic viewpoint. However, an energy conversion system has a complex network structure, and it takes much time to create its model for the thermoeconomic analysis and optimization. In this paper, a systems approach is presented for the performance analysis and optimization of mechanical systems with network structures, and it is applied to the thermoeconomic analysis and optimization of a gas turbine cogeneration unit. The system modeling for the performance analysis is conducted by a building block approach. Static and dynamic problems for the performance analysis are formulated as sets of nonlinear algebraic and differential algebraic equations, and are solved by the Newton-Raphson method and a hierarchical combination of the Runge-Kutta and Newton-Raphson methods, respectively. The performance optimization is conducted to determine design and operation conditions which optimize performance criteria. This problem is formulated as a nonlinear programming one and is solved by a global optimization method. In the application, the cycle analysis is conducted to determine mass flow rates, pressures, and temperatures, which is followed by the exergy and cost analyses to determine exergy flow rates and efficiencies, and capital costs, respectively. In addition, design and operation conditions are determined to maximize the exergy efficiency or minimize the annual total cost based on the results of the cycle, exergy, and cost analyses. Through a numerical study, it turns out that the proposed systems approach enables one to conduct the thermoeconomic analysis and optimization efficiently.
Thermoacoustic Analysis of Gas Turbine Combustion Systems Using Unsteady CFD
Authors: Schuermans Bruno , Luebcke Holger , Bajusz Denis , Flohr Peter
Published: November 2008

Unsteady Computational Fluid Dynamics (CFD) has been used to predict thermoacoustic interaction processes in an industrial gas turbine burner. Because detailed unsteady simulation of an entire gas turbine combustion system is forbiddingly expensive, two different approaches have been applied to overcome this problem. In the first approach, time-domain acoustic boundary conditions are applied to the computational domain of the CFD. The idea is to model in CFD only that part of the problem that cannot be represented by low order (acoustic) models. The advantage is not only that the method is much faster; it also allows changes in acoustic boundary conditions without a need to make a new mesh for the problem. This method introduced here is novel and can be used to apply any (causal) acoustic impedance matrix to a CFD computation. The desired impedance can either be obtained analytically, from an acoustic network model or from an acoustic finite element code. The method has been tested on various test cases and proved to be accurate and robust. First, a simple duct with non reactive flow has been simulated. A non refelecting boundary condition for plane waves has been applied. In a further step the methodology was implemented on a gas turbine burner with combustion. The measured acoustic boundary conditions of a single burner test facility have been applied. The predicted pressure spectra are in reasonable agreement with measured pulsation spectra of a full-scale gas turbine burner in an atmospheric combustion test facility. In the second approach a system identification technique is used in a post-processing step of the CFD results. In this way the transfer function relating the acoustic quantities on both sides of the flame is obtained. This transfer function can then be applied to an acoustic network model of the system. The advantage of this method is that once the transfer matrix of the combustion zone is obtained, the influence of combustion system geometry can be investigated in the low order model, which is very fast. This method has been compared with measured transfer matrices of a full-scale swirl stabilized gas turbine burner and proved to be in good agreement.
Power Management and Controls of a Propulsion System for a Lighter Than Air High Altitude Platform
Authors: Kotulla Michael , Staudacher Stephan
Published: November 2008

A possible propulsion system concept for a stratospheric multi-body airship has been investigated. It features distributed propulsion to fulfill thrust and stabilization demands of the airship. In the frame of this research a simulation model for the propulsion system has been developed in Matlab/Simulink. The propulsion system’s main components are propellers, which are driven by electro motors, back-up batteries and gas turbine power plants to supply the necessary electric energy. All components have been adapted to work in ambient conditions at an altitude of 20km. The investigations have demonstrated adequate system dynamics and confirmed the sizing of power plants and back-up batteries. The control system has shown adequate stability and, therefore, guarantees the provision of the demanded thrusts and powers.
Analytical and Experimental Study of Hydroinertia Gas Bearings for Micromachine Gas Turbines
Authors: Isomura Kousuke , Togo Shin-ichi , Hikichi Kousuke , Goto Satoshi , Tanaka Shuji
Published: November 2008

Hydro-inertia gas bearing is a type of static air bearing, which supports the rotor by suction force generated by supersonic flow in large bearing clearance [1]. A tool to analyze the flow inside the clearance of hydroinertia gas bearings have been developed, and validated by experiment. A tool to estimate the load capacity and the bearing stiffness of the hydroinertia gas bearing based on experimental data has also been developed. A micro spinner test rig has been fabricated to test an hydroinertia gas bearings designed by the developed tools, and stable operation of 4mm diameter shaft at 1,200,000 rpm has successfully been achieved. A micro-high-speed bearing test rig to test a rotor for micromachine gas turbine has been designed and fabricated. Current micromachine gas turbine’s configuration requires a rotor with 10mm diameter compressor and turbine impellers on each end of 4mm diameter shaft to operate stably at 870,000rpm. Based on the achievement of stable operation at the high-speed of 1,200,000 rpm, hydro-inertia gas bearing has been selected as a candidate for both the bearings for micromachine gas turbine. Currently, the rotor speed as high as 770,000rpm has been achieved in this test rig.
Turbulence Modeling in a Model Combustor
Authors: Jiang Lei-Yong , Campbell Ian
Published: November 2008

The flow field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically investigated. Solutions obtained from four turbulence models together with a laminar flamelet combustion model, discrete ordinates radiation model and enhanced wall treatment are presented and discussed. The numerical results are compared, in detail, with a comprehensive database obtained from a series of experimental measurements. It is found that the Reynolds stress model (RSM), a second moment closure, illustrates superior performance over three popular two-equation eddy-viscosity models. Although the main flow features are captured by all four turbulence models, only the RSM is able to successfully predict the lengths of both recirculation zones and the turbulence kinetic energy distribution in the combustor chamber. In addition, it provides fairly good predictions for all Reynolds stress components, except for the circumferential normal stress at downstream sections. However, the superiority of the RSM is not so obvious for the temperature and species predictions in comparison with eddy-viscosity models, except for the standard k-ε model. This suggests that coupling between the RSM and combustion models needs to be further improved in order to enhance its applications in practical combustion systems.
Reduced Order Thrust Estimation for a Jet Engine
Authors: Henriksson Mattias , Gro¨nstedt Tomas
Published: November 2008

A reduced order thrust estimation filter is derived, based on a linearized process model and a low order disturbance description. The reduced filter is obtained by ignoring the measurement error on the two spool speeds. Robustness to engine to engine variability is evaluated by Monte Carlo simulations by use of a nonlinear RM12 jet engine model. Both measurement and process disturbance models are presented and used in the filter design. The difference between the reduced order filter and full order filter is negligible. The Monte Carlo simulations clearly show that Kalman based thrust estimation filters are sensitive to parameter variations caused by engine degradation or engine to engine variation.
Ceramic Matrix Composite Combustor Liners: A Summary of Field Evaluations
Authors: van Roode Mark , Price Jeff , Kimmel Josh , Miriyala Naren , Leroux Don , Fahme Anthony , Smith Kenneth
Published: November 2008

Solar Turbines Incorporated (Solar) under U.S. government sponsored programs has been evaluating ceramic matrix composite (CMC) combustor liners in test rigs and Solar Centaur® 50S engines since 1992. The objective was to evaluate and improve the performance and durability of CMCs as high temperature materials for advanced low emissions combustors. Field testing of CMC combustor liners started in May 1997 and by the end of 2004, over 67,000 operating hours have been accumulated on SiC/SiC and oxide/oxide CMC liners. NOx and CO emissions measured were < 15 ppmv and < 10 ppmv, respectively. Long test durations of 15,144 hrs and 13,937 hrs have been logged for SiC/SiC liners with protective environmental barrier coatings (EBCs). An oxide/oxide CMC liner with a Friable Graded Insulation (FGI) coating has been tested for 12,582 hrs. It was observed that EBCs significantly improve SiC/SiC CMC liner life. The basic three-layer EBC consists of consecutive layers of Si, mullite, and barium strontium aluminum silicate (BSAS). The durability of the baseline EBC can be improved by mixing in BSAS with mullite in the intermediate coating layer. The efficacy of replacing BSAS with SAS has not been demonstrated yet. Heavy degradation was observed for two-layer Si/BSAS and Si/SAS EBCs, indicating that the elimination of the intermediate layer is detrimental to EBC durability. Equivalent performance was observed when the Hi-Nicalon fiber reinforcement was replaced with Tyranno ZM or ZMI fiber. Melt infiltrated (MI) SiC/SiC CMCs have improved durability compared to SiC/SiC CMCs fabricated by Chemical Vapor Infiltration (CVI) of the matrix, in the absence of an EBC. However, the presence of an EBC results in roughly equivalent service life for MI and CVI CMCs. Early results indicate that oxide/oxide CMCs with protective FGI show relatively minor degradation under Centaur 50S engine operating conditions. The results of and lessons learned from CMC combustor liner engine field testing, conducted through 2004, have been summarized.
A Retrofit Integration of an Absorption Chiller With a Microturbine Array
Authors: Williamson Toussaint , Luker Mike , Hack R. L.
Published: November 2008

The overall system efficiency of a microturbine generator system, and hence the economic viability, are greatly enhanced through co-generation. The utilization of the exhaust energy for heating needs is well understood and has been extensively implemented. Potentially more desirable but having found far less implementation is the integration of microturbines with absorption chillers to generate cold water. Long recognized as a tremendous opportunity in HVAC systems, the integration of a microturbine with an absorption chiller is complicated by the relatively low quality and quantity of heat available from the traditionally recuperated microturbine system. This paper address the design process and the issues encountered in developing a 160 ton absorption chiller system integrated with an array of eight, 60-kW Capstone microturbines. The designed system is not a pre-packaged turbine/chiller system but rather a system that integrates a mix of existing and new microturbines with a commercial gas-to-liquid heat exchanger and a commercial single effect Li-Br absorption chiller. The goal of the effort is demonstrate a cost effective retrofit installation of an absorption chiller with existing microturbines to effectively provide base load chilling for the building’s HVAC needs.
A New Calculation Approach to the Energy Balance of a Gas Turbine Including a Study of the Impact of the Uncertainty of Measured Parameters
Authors: Andersen Helmer G. , Chen Pen-Chung
Published: November 2008

Computing the solution to the energy balance around a gas turbine in order to calculate the intake mass flow and the turbine inlet temperature requires several iterations. This makes hand calculations very difficult and, depending on the software used, even causes significant calculation times on PCs. While this may not seem all that important considering the power of today’s personal computers, the approach described in this paper presents a new way of looking at the gas turbine process and the resulting simplifications in the calculations. This paper offers a new approach to compute the energy balance around a gas turbine. The energy balance requires that all energy flows going into and out of the control volume be accounted for. The difficulty of the energy balance equation around a gas turbine lies in the fact that the exhaust gas composition is unknown as long as the intake flow is unknown. Thus, a composition needs to be assumed when computing the exhaust gas enthalpy. This allows the calculation of the intake flow, which in turn provides a new exhaust gas composition, and so forth. By viewing the exhaust gas as a flow consisting of ambient air and combusted fuel, the described iteration can be avoided. The study presents the formulation of the energy balance applying this approach and looks at the accuracy of the result as a function of the inaccuracy of the input parameters. Furthermore, solutions of the energy balance are presented for various process scenarios, and the impact of the uncertainty of key process parameter is analyzed.
Investigation of Design Parameters and Failure Criteria of O-Ring Seal Structure
Authors: Hu Dianyin , Wang Rongqiao , Ren Quanbin , Hong Jie
Published: November 2008

First, this paper established the seal structural 2D axisymmetric model of a certain Solid Rocket Booster (SRB) and calculated the deformation and stresses at ignition through a large displacement, incompressible, contact finite element analysis. The results show that the maximum contact stress appears at the contact area and the maximum shear stress at groove notch. Then, some typical parameters of the seal structure which might have the impact on the sealing performance, such as the gap breadth, initial compressibility, fillets of the groove notch and bottom, groove width, were analyzed. We can find that the gap breadth and initial compressibility do great contributions to the maximum contact normal stress, and the groove notch and bottom fillets act upon the maximum shear stress obviously. In order to verify the validity of the 2D axisymmetric model, 3D structural finite element analysis of the structure was conducted, and the results indicate that in service, the upper flange is inclined relative to the nether flange, which seems to mean that the gap breadth can not be considered as a constant during the 2D axisymmetric analysis. However further calculations say that if using the minimum gap breadth gotten in 3D analysis as its constant gap value, the above 2D axisymmetric model can rationally take the place of 3D model to analyze the sealing performance. Finally, the failure modes & criteria of the O-ring seals based on the maximum contact normal stress and shear stress were determined to ensure the reliability of this structure.
Impact of Compressor Protection System on Rundown Characteristics
Authors: Tveit Gisle B. , Bjo̸rge Tor , Bakken Lars E.
Published: November 2008

Knowledge of compressor system behaviour during trip is essential to obtain reliable operation. Experience at Troll Kollsnes gas treatment plant has shown that the compressor can suffer from surge and rotating stall in situations with voltage drops in the electricity grid. The electric motor driven compressor and the protection valves and piping has been modelled and dynamic simulations has been done to reveal the transient response. An elaborate plant model has been created with the dynamic simulation tool OTISS by AspenTech and tuned to represent the plant. The paper focuses on the impact of different compressor discharge volumes, dimensions of the recycle piping as well as the sizing, characteristics and trip signal delay of the recycle protection valve(s). Sensitivity analyses for the actual plant reveal the response and protection during compressor driver trip.
Practical Use of Unsteady CFD and FEM Forced Response Calculation in the Design of Axial Turbocharger Turbines
Authors: Filsinger D. , Frank Ch. , Scha¨fer O.
Published: November 2008

One of the challenges in the design of rotating machinery is the issue of vibrations. The structure, no matter if talking about compressors or turbines, is subject to various sources of excitation that lead to vibrations under resonance conditions. This paper deals with the question of turbine blade vibrations. It describes practical examples of the implementation of unsteady computational fluid dynamics (CFD) and forced response calculation by means of finite element methods (FEM) applied to the design and development procedure of axial turbocharger turbines. The four examples deal with various questions which rise at different stages in the development process of turbines. One example concerns to the expected excitation of the rotor due to the stator. It demonstrates the advantages of using CFD in the prediction of this kind of excitation. Another one deals with an engine application, for which the influence of the inlet housing on the blade excitation had to be assessed. Both examples rely on the comparison of calculated excitation to the corresponding experimental strain gauge measurement for a reference case. This reference case can be used for calibration. A further case study concerns to blade vibrations in pulse charging systems. It was the intention not only to determine a spatial resolution of the excitation, but also to calculate true stresses by means of forced response calculations with FEM. In this example first bending mode shapes of the turbine blade of a rather simple type were investigated. Higher, more complex mode shapes were also investigated to prove the method. In this example, dynamic stresses were also estimated, using calculated excitation as input for forced response calculations. The results show that the use of modern numerical methods reduces cost and required time in the design of axial turbocharger turbines. They help to substantially reduce the experimental effort, while even more complete information concerning excitation and response of the structure is made available for the designer.
Onset of Combustion Instabilities During Transition to Supercritical Fuel Injection in High Pressure Combustor
Authors: Lubarsky E. , Shcherbik D. , Scarborough D. , Bibik O. , Zinn B. T.
Published: November 2008

This paper describes a study of the onset of severe combustion instabilities (i.e., with peak to peak amplitudes of up to 0.97MPa) in a high pressure (PC>500psia or 3.45MPa) air breathing combustor as the inlet temperature of the injected liquid fuel (n-heptane - C7H16) was varied over the 20–335°C range, achieving supercritical conditions when the temperature exceeded 300°C. The attainment of supercritical operation was determined by a specially developed probe that illuminated the liquid spray with a laser beam and collected the light scattered off the spray. As the temperature of the fuel was increased, the spray disappeared when the fuel attained a supercritical state and the scattered signal could be no longer detected. Two different unstable modes (i.e., ∼100 and ∼400Hz) were excited in the combustor as the fuel temperature was increased from low to supercritical conditions and then cooled again. The lower frequency instability (∼100Hz) was excited and then disappeared when the fuel temperature was well below supercritical values (i.e., TFUEL<200°C) whereas the higher frequency mode (∼400Hz) was typically excited at sub- and super- critical conditions (i.e., TFUEL>250°C). It’s shown that the dynamics of the excitation and disappearance of these modes as well as their limit cycle amplitudes strongly depend upon the direction in which fuel temperature varies and also upon the temperature of the combustion air. Significantly, the results of this study strongly suggest that combustion instabilities may be excited in future high performance aircraft combustor that will operate at very high-pressures and with supercritical fuel injection.
Performance Evaluation of a Small Size Cogenerative System Based on a PEM Fuel Cell Stack
Authors: Bagnoli M. , De Pascale A.
Published: November 2008

The use of fuel cell systems for distributed generation represents an interesting option due to the intrinsic high efficiency and the potential to reduce the environmental impact of power supply in comparison with thermoelectric plants. In this paper the study of a cogenerative energy system based on a Proton Exchange Membrane fuel cell stack, that should satisfy a small electric utility, is reported; the capability of this cogenerative system to supply electrical and thermal power demand of a civil user has been investigated. In this research the electric efficiency has been calculated as net electric power on chemical power given to the system and the thermal efficiency as thermal power given to user on chemical power in input. Moreover, an energy saving index has been introduced to assess the cogenerative performance of this energy system. The investigation has been developed by experimenting an existing stack of fuel cell and studying its behaviour with a variable power demand. In particular, all the input and output mass flows have been evaluated to have parameters through which the operation of the whole cogenerative system, made by fuel cell stack and all the auxiliaries like compressor and pumps, could be simulated.
Modeling and Control of Combustion Oscillations
Authors: Dowling Ann P.
Published: November 2008

Clean combustion, with low levels of pollutants, can be achieved by burning lean and premixed. Unfortunately, these are just the conditions that cause self-excited oscillations which can become so intense that they break the combustor. Many gas-fuelled power stations have suffered damage in this way and been unable to achieve their designed power and low-emission levels. Self-excited oscillations are also being experienced in the development of the next generation of aeroengines as they strive to achieve lower emissions. These instabilities occur due to the interaction between sound and flames: the unsteady combustion generates acoustic waves and these in turn alter the inlet flow rates of fuel and air and lead to further unsteady combustion. An overview of the recent research in this area at the University of Cambridge is presented. Emphasis is placed on the physics of the interaction between sound and flames investigated through experiment and computer modeling. The elements needed for effective prediction and modeling are discussed, together with the potential of ‘anti-sound’ and passive acoustic absorbers to eliminate the instability.
Assessment of a 3D Linear Euler Flutter Prediction Tool Using Sector Cascade Test Data
Authors: Ma˚rtensson Hans , Vogt Damian M. , Fransson Torsten H.
Published: November 2008

An assessment and validation of a numerical prediction tool for flutter are made using new experimental data from experiments on turbine blades in a sector cascade. The 3D geometry is that of a low-pressure (LP) turbine blade with twist and a profile that changes along span in an annular sector cascade. The numerical model is a linear harmonic Euler equation solver. Rig results are obtained for the blade by oscillating 1 blade out of 7 in the annular sector cascade. The blade is oscillated in the rig using a mechanical type of actuator to control the mode. The mode shapes in the rig consist of torsion and bending modes around a pivot mechanism fixed inside the hub end wall. The frequencies obtained in the rig are in the range up to 219 Hz, or reduced frequency based on full chord k = 0.5, which covers the range of useful reduced frequencies typically found in turbine designs. Under reference running conditions the unsteady pressure responses are found qualitatively in line with the experiment. The test case is shown to be challenging to the numerical tool in terms of effects of tip clearance as well as off-design effects. In order to improve results tip clearance modeling and inclusion of viscous terms are identified as key factors.
A Fully Integrated Approach to Component Zooming Using Computational Fluid Dynamics
Authors: Pachidis Vassilios , Pilidis Pericles , Talhouarn Fabien , Kalfas Anestis , Templalexis Ioannis
Published: November 2008

This study focuses on a simulation strategy that will allow the performance characteristics of an isolated gas turbine engine component, resolved from a detailed, high-fidelity analysis, to be transferred to an engine system analysis carried out at a lower level of resolution. This work will enable component-level, complex physical processes to be captured and analyzed in the context of the whole engine performance, at an affordable computing resource and time. The technique described in this paper utilizes an object-oriented, zero-dimensional (0-D) gas turbine modeling and performance simulation system and a high-fidelity, three-dimensional (3-D) computational fluid dynamics (CFD) component model. The work investigates relative changes in the simulated engine performance after coupling the 3-D CFD component to the 0-D engine analysis system. For the purposes of this preliminary investigation, the high-fidelity component communicates with the lower fidelity cycle via an iterative, semi-manual process for the determination of the correct operating point. This technique has the potential to become fully automated, can be applied to all engine components and does not involve the generation of a component characteristic map. This paper demonstrates the potentials of the ‘fully integrated’ approach to component zooming by using a 3-D CFD intake model of a high by-pass ratio (HBR) turbofan as a case study. The CFD model is based on the geometry of the intake of the CFM56-5B2 engine. The high-fidelity model can fully define the characteristic of the intake at several operating condition and is subsequently used in the 0-D cycle analysis to provide a more accurate, physics-based estimate of intake performance (i.e. pressure recovery) and hence, engine performance, replacing the default, empirical values. A detailed comparison between the baseline engine performance (empirical pressure recovery) and the engine performance obtained after using the coupled, high-fidelity component is presented in this paper. The analysis carried out by this study, demonstrates relative changes in the simulated engine performance larger than 1%.
A Transient Model of a Hybrid Fuel Cell/Gas Turbine Test Facility Using Simulink
Authors: Shelton Michael , Celik Ismail , Liese Eric , Tucker David , Lawson Larry
Published: November 2008

The National Energy Technology Laboratory (NETL, U.S., D.O.E.) in Morgantown, West Virginia has successfully designed and is operating a fuel cell/turbine hybrid test facility. With the successful operation of this test facility, it is now possible to model, test and evaluate the effect of pressure and temperature transients important to the design and operation of a fuel cell/gas turbine hybrid system and provide a means of quantifying mitigation methods to address adverse impacts of such transients to the operation, safety and efficiency of these systems. This paper deals exclusively with the Simulink, lumped parameter model and its relationship to controls development. Presented in detail are the development, structure and methodology of this Simulink process model as related to the Hybrid Performance (Hyper) test facility in use at NETL. Thus far the model simulates only the test facility, which presently does not have a fuel cell, but a large plenum is used to represent the cathode air volume. Future work will insert fuel cell models developed by NETL. Components of the model are presented and described in detail. Two case studies are presented based on the effect of load shed transients on system performance. These case studies are 1.) Speed controlled load shedding, 2.) Speed set point changing.
A Numerical Capability to Analyze the Effects of Water Ingestion on Compression System Performance and Operability
Authors: Hale Alan , Klepper Jason , Hurwitz Wayne
Published: November 2008

A modeling and simulation technique has been developed to use a one-dimensional (1-D) multiphase code and a 1-D compressor meanline code to investigate the effects of water ingestion. The multiphase code primarily accounts for the heat transfer associated with the phase change of water, and the meanline code uses the heat transfer and gas properties to model the flow properties through a compression system. Validation of the combined codes is performed with fogging water experimental data along with cycle code information from a ground-based Industrial Gas Turbine, FT8. A parametric study is then conducted with a modern fan and core compressor to determine the performance trend changes caused by the ingestion of liquid and/or vapor water such as might be present during steam ingestion from a carrier-lauched aircraft.