bluuebunny/crossref_metadata_2025 huggingface dataset:
Feasibility Study on Oil Droplet Flow Investigations Inside Aero Engine Bearing Chambers—PDPA Techniques in Combination With Numerical Approaches
Authors: Glahn A. , Kurreck M. , Willmann M. , Wittig S.
Published: February 2008

The present paper deals with oil droplet flow phenomena in aero engine bearing chambers. An experimental investigation of droplet sizes and velocities utilizing a Phase Doppler Particle Analyzer (PDPA) has been performed for the first time in bearing chamber atmospheres under real engine conditions. Influences of high rotational speeds are discussed for individual droplet size classes. Although this is an important contribution to a better understanding of the droplet flow impact on secondary air/oil system performance, an analysis of the droplet flow behavior requires an incorporation of numerical methods because detailed measurements as performed here suffer from both strong spatial limitations with respect to the optical accessibility in real engine applications and constraints due to the extremely time-consuming nature of an experimental flow field analysis. Therefore, further analysis is based on numerical methods. Droplets characterized within the experiments are exposed to the flow field of the gaseous phase predicted by use of our well-known CFD code EPOS. The droplet trajectories and velocities are calculated within a Lagrangian frame of reference by forward numerical integration of the particle momentum equation. This paper has been initiated rather to show a successful method of bearing chamber droplet flow analysis by a combination of droplet sizing techniques and numerical approaches than to present field values as a function of all operating parameters. However, a first insight into the complex droplet flow phenomena is given and specific problems in bearing chamber heat transfer are related to the droplet flow.
Exergy Analysis for a Gas Turbine Cogeneration System
Authors: Oh Si-Doek , Pang Hyo-Sun , Kim Si-Moon , Kwak Ho-Young
Published: February 2008

A general exergy balance equation that is applicable to any component of thermal systems has been formulated in this study. One of distinct features of this formulation is that the exergy involved in the component of any thermal system can be decomposed into exergy flows, entropy production flows, and the appropriate exergy rate terms such as fuel and available work. The exergy analysis based on this equation permits one to predict the thermal efficiency of the system, the exergy destruction in each component as well as the mass flow rate, the composition, and the temperature of the exhaust gases. We have examined the performance of a 1000 kW gas turbine cogeneration system when it is operated at part and full-load conditions through this analysis. We have also tested the effect of the inlet air temperature and the relative humidity of the inlet air on the performance of the system. The predicted values of the performances for the system have been compared with the actual performance data provided by the gas turbine manufacturer. It has been found that the measured data of net power and the properties of exhaust gases are in good agreement with calculation ones, differing by less than 3 percent. The exergy balance equation may be utilized in the exergoeconomic analysis to estimate the production costs depending on various input costs in a gas turbine cogeneration system.
Thermal Cycle Analysis and Component Aerodesign for Gas Turbine Concept in Low-Range Cogenerating Systems
Authors: Bozza F. , Senatore A. , Tuccillo R.
Published: February 2008

The authors link together their previous experiences in gas turbine plant analysis and aerodynamic design of radial flow compressors. In recent papers they have introduced a method for the performance estimation of gas turbine engines, based on the prediction of the matching conditions among the several components in the whole operating range. On the other hand they have expressly paid attention to the problem of optimal design of radial flow compressors for satisfactory operation within an assigned operating range. In this paper, the authors present an integrated method, which aims to define the optimal characteristics of a low-power gas turbine engine (i.e., in the range 500–2000 kW). In this case, the radial compressor performance plays an important role as regards gas turbine operation for both power generation and cogeneration applications. The analysis proceeds with the optimization of rotating components (i.e., radial compressor and axial flow turbine) for given thermal cycle parameters. The prescribed objectives of the optimizing procedure are related to performance levels not only at the reference design conditions but also throughout the operating field. A particular emphasis is given to the extension of the field of satisfactory performance for cogeneration applications, with best fitting of mechanical and thermal power requirements. The aerodynamic design of radial flow compressor utilizes a method based on genetic algorithms.
Aerodynamic Loading and Magnetic Bearing Controller Robustness Using a Gain-Scheduled Kalman Filter
Authors: Smith R. D. , Weldon W. F. , Traver A. E.
Published: February 2008

Modeling or predicting aerodynamic loading effects on rotating equipment has been a source of concern to those who wish to examine stability or response of critical components. The rotordynamic model of the system employed for such examination assumes greater importance for active bearings than for passive ones, if only because of the additional potential for instability introduced by the controller. For many systems, aerodynamic loading may vary widely over the range of operation of the bearings, and may depend on extended system variables. Thus, potential controllers for active magnetic bearings require sufficient robustness or adaptation to changes in critical aerodynamic loading parameters, as might be embodied in cross-coupled stiffness terms for compressor impellers. Furthermore, the presence of plant or measurement noise provides additional sources of complication. Here, the previous development of a nonlinear controller for a hypothetical single-stage centrifugal gas compressor is extended by comparing the compensator performance using a multivariable Luenberger observer against that of a stationary Kalman filter, both gain-scheduled for rotational speed. For the postulated system, it was found that the slower poles of the Kalman filter did not observably detract from controller convergence and stability, while predictably smoothing out the simulated sensor noise.
The Development of Life Prediction Techniques for Structural Ceramics
Authors: Khandelwal P. K. , Provenzano N. J. , Schneider W. E.
Published: February 2008

One of the major challenges involved in the use of ceramic materials in advanced vehicular heat engines is ensuring adequate strength and durability. This Department of Energy supported activity has developed methodologies to predict the structural behavior of ceramic components. The effort involved the characterization of injection-molded and hot isostatic pressed PY6 silicon nitride and the development of analytical life prediction techniques. Three failure modes are addressed: fast fracture, slow crack growth, and creep rupture. The technique deals with surface as well as internal component failures. The life prediction methodologies for fast fracture and slow crack growth have been verified using two types of confirmatory specimens: (1) flat circular disks subjected to bending stresses, and (2) high-speed rotating spin disks. Correlation was achieved for a variety of test conditions and failure mechanisms. The predictions associated with surface failures proved to be optimistic, requiring re-evaluation of the components’ initial fast fracture strength. Correlation was achieved for the spin disks that failed in fast fracture from internal flaws. Time-dependent, elevated-temperature spin disk failures were also successfully predicted.
Computer-Aided Simulation of Piston and Piston Ring Dynamics
Authors: Knoll G. , Peeken H. , Lechtape-Gru¨ter R. , Lang J.
Published: February 2008

A numerical computer simulation program was developed, aiding in finding optimum design parameters in the multibody-system piston, piston-rings, and cylinder with respect to optimum sealing, minimal friction, and minimum noise stimulation (impact impulse). In the simulation of piston secondary movement and piston ring motion, forces arising from the combustion process, subsonic/supersonic gas flow between the combustion chamber and the crank case, inertial forces and forces resulting from the hydrodynamic lubrication between cylinder liner and piston shaft and piston rings and between piston ring flanks and piston grooves are considered. In addition it is possible to account for effects of global, three-dimensional ring deformation as well as local piston deformation, roughness effects in lubricated contacts, and variable viscosity and variable oil supply. The governing differential equations for the pressure as well as the deformation are solved via finite element techniques, while initial value problems are solved by efficient implicit time integration schemes. The application of the developed computer code is presented in examples.
Fatigue Strength as a Function of Preloading in Dynamic Fatigue Testing of Glass and Ceramics
Authors: Choi S. R. , Gyekenyesi J. P.
Published: February 2008

The solution of fatigue strength as a function of preloading in dynamic fatigue (constant stress-rate) testing was obtained analytically and numerically. The effect of preloading on dynamic fatigue strength decreases with increasing fatigue parameter (n), and for n ≥ 20 the effect is negligible up to a preloading of 90 percent. The solution was verified by dynamic fatigue experiments conducted with soda-lime glass and alumina specimens in room-temperature distilled water. This result showed that one can apply a preloading corresponding up to 90 percent of fatigue strength for most glass and ceramic materials, resulting in a dramatic saving of testing time in dynamic fatigue testing. The key feature that makes this technique feasible is that most of the slow crack growth under dynamic fatigue loading occurs close to failure time where the dynamic fatigue strength is defined.
Coupled Lagrangian Monte Carlo PDF–CFD Computation of Gas Turbine Combustor Flowfields With Finite-Rate Chemistry
Authors: Tolpadi A. K. , Hu I. Z. , Correa S. M. , Burrus D. L.
Published: February 2008

A coupled Lagrangian Monte Carlo Probability Density Function (PDF)-Eulerian Computational Fluid Dynamics (CFD) technique is presented for calculating steady three-dimensional turbulent reacting flow in a gas turbine combustor. PDF transport methods model turbulence-combustion interactions more accurately than conventional turbulence models with an assumed shape PDF. The PDF transport equation was solved using a Lagrangian particle tracking Monte Carlo (MC) method. The PDF modeled was over composition only. This MC module has been coupled with CONCERT, which is a fully elliptic three-dimensional body-fitted CFD code based on pressure correction techniques. In an earlier paper (Tolpadi et al., 1995), this computational approach was described, but only fast chemistry calculations were presented in a typical aircraft engine combustor. In the present paper, reduced chemistry schemes were incorporated into the MC module that enabled the modeling of finite rate effects in gas turbine flames and therefore the prediction of CO and NOx emissions. With the inclusion of these finite rate effects, the gas temperatures obtained were also more realistic. Initially, a two scalar scheme was implemented that allowed validation against Raman data taken in a recirculating bluff body stabilized CO/H2/N2-air flame. Good agreement of the temperature and major species were obtained. Next, finite rate computations were performed in a single annular aircraft engine combustor by incorporating a simple three scalar reduced chemistry scheme for Jet A fuel. This three scalar scheme was an extension of the two scalar scheme for CO/H2/N2 fuel. The solutions obtained using the present approach were compared with those obtained using the fast chemistry PDF transport approach (Tolpadi et al., 1995) as well as the presumed shape PDF method. The calculated exhaust gas temperature using the finite rate model showed the best agreement with measurements made by a thermocouple rake. In addition, the CO and NOx emission indices were also computed and compared with corresponding data.
Anchored CCD for Gas Turbine Combustor Design and Data Correlation
Authors: Danis A. M. , Burrus D. L. , Mongia H. C.
Published: February 2008

Correlations based on design database, combined with multidimensional computational combustion dynamics (CCD) models are used in the combustion design process. However, because of limitations in the current turbulent combustion models, numerics, and boundary conditions, CCD has provided mainly qualitative trends for aerothermal performance, emissions, and liner wall temperature levels and gradients. To overcome these deficiencies, hybrid modeling approaches have been proposed to analyze existing combustors. A typical hybrid modeling approach combines empirical and semianalytical correlations with CCD to give quantitatively accurate predictions of NOx, CO, HC, smoke, lean blowout, ignition, pattern factor, and liner wall temperatures. An alternate approach, anchored CCD, is described in this paper. First, the models were anchored with one of the five modern turbopropulsion engine combustors. The anchored models were then run for the other four combustors. The predicted results correlated well with measured NOx, CO, HC, LEO, and exit temperature quality data, demonstrating a broader applicability of the anchored method. The models were also used for designing a new combustion concept. The pretest prediction agreed well with sector rig data from development hardware, showing the feasibility of using the anchored methodology as a design tool.
Preliminary Gas Turbine Combustor Design Using a Network Approach
Authors: Stuttaford P. J. , Rubini P. A.
Published: February 2008

The preliminary design process of a gas turbine combustor often involves the use of cumbersome, geometry restrictive semi-empirical models. The objective of this analysis is the development of a versatile design tool for gas turbine combustors, able to model all conceivable combustor types. A network approach is developed that divides the flow into a number of independent semi-empirical subflows. A pressure-correction methodology solves the continuity equation and a pressure-drop/flow rate relationship. The development of a full conjugate heat transfer model allows the calculation of flame tube heat loss in the presence of cooling films, annulus heat addition, and flame tube feature heat pick-up. A constrained equilibrium calculation, incorporating mixing and recirculation models, simulates combustion processes. Comparison of airflow results to a well-validated combustor design code showed close agreement. The versatility of the network solver is illustrated with comparisons to experimental data from a reverse flow combustor.
The Prediction of Laminar Flame Speeds for Weak Mixtures
Authors: Kretschmer D. , Odgers J.
Published: February 2008

In a recent publication [3], the authors tentatively explored the prediction of propane flame speeds using the calculated burned gas temperature (Tb) and the predicted flame extinction temperature (Ti). A formula was developed that utilized these temperatures together with correction factors for inlet temperature and the oxygen/inert ratio. The present paper has extended this technique so that data from 20 different fuels have been examined over a range of conditions, which include significant variations of both inlet temperature and pressure. Limitations of the technique are discussed, as are possible related applications to other premixed systems such as laminar flames and well-stirred reactors.
Aircraft Gas Turbine Engine Fuel Pumping Systems in the 21st Century
Authors: Hansen L. D. , Kucera G. D. , Clemons J. S. , Lee J.
Published: February 2008

Since their introduction, main engine fuel pumping systems for aircraft gas turbine engines have remained relatively unchanged. The main engine fuel pump has been an engine accessory gearbox driven, positive displacement pump (except for the Concorde), until recently when centrifugal pumps were introduced on Pratt-Whitney and General Electric military engines. This paper describes some of the issues that must be addressed as pumping system technology moves into the 21st century and gives a description of two programs that address these issues.
A Semiclosed-Cycle Gas Turbine With Carbon Dioxide–Argon as Working Fluid
Authors: Ulizar I. , Pilidis P.
Published: February 2008

This paper describes the performance analysis of a semiclosed-cycle gas turbine. The working fluid is carbon dioxide and the fuel is low heating value gas synthesized from coal. The objective of the machine is to produce clean electricity with the smallest efficiency penalty. First, the thermodynamic properties of the gases in the cycle were obtained as a function of temperature and pressure. Then two performance simulation codes were developed. These have the ability of simulating different configurations of open, closed, and semiclosed cycles. The first code was used for cycle optimization and the second for off-design studies. The design and off-design performances of the machine are predicted. The production of clean electricity will be at the expense of a lower efficiency compared with current equipment. Finally, some critical issues for the development of such a gas turbine are identified.
Design and Test of a New Axial Compressor for the Nuovo Pignone Heavy-Duty Gas Turbines
Authors: Benvenuti Erio
Published: February 2008

This axial compressor design was primarily focused to increase the power rating of the current Nuovo Pignone PGT10 Heavy-Duty gas turbine by 10 percent. In addition, the new 11-stage design favorably compares with the existing 17-stage compressor in terms of simplicity and cost. By scaling the flowpath and blade geometry, the new aerodynamic design can be applied to gas turbines with different power ratings as well. The reduction in the stage number was achieved primarily through the meridional flowpath redesign. The resulting higher blade peripheral speeds achieve larger stage pressure ratios without increasing the aerodynamic loadings. Wide chord blades keep the overall length unchanged thus assuring easy integration with other existing components. The compressor performance map was extensively checked over the speed range required for two-shaft gas turbines. The prototype unit was installed on a special PGT10 gas turbine setup, that permitted the control of pressure ratio independently from the turbine matching requirements. The flowpath instrumentation included strain gages, dynamic pressure transducers, and stator vane leading edge aerodynamic probes to determine individual stage characteristics. The general blading vibratory behavior was proved fully satisfactory. With minor adjustments to the variable stator settings, the front stage aerodynamic matching was optimized and the design performance was achieved.
A Normalized Modal Eigenvalue Approach for Resolving Modal Interaction
Authors: Yang M.-T. , Griffin J. H.
Published: February 2008

Modal interaction refers to the way that the modes of a structure interact when its geometry and material properties are perturbed. The amount of interaction between the neighboring modes depends on the closeness of the natural frequencies, the mode shapes, and the magnitude and distribution of the perturbation. By formulating the structural eigenvalue problem as a normalized modal eigenvalue problem, it is shown that the amount of interaction in two modes can be simply characterized by six normalized modal parameters and the difference between the normalized frequencies. In this paper, the statistical behaviors of the normalized frequencies and modes are investigated based on a perturbation analysis. The results are independently verified by Monte Carlo simulations.
Multidimensional Modeling of Combustion for a Six-Mode Emissions Test Cycle on a DI Diesel Engine
Authors: Xin J. , Montgomery D. , Han Z. , Reitz R. D.
Published: February 2008

Numerical simulations of direct injection (DI) heavy-duty diesel engine combustion over the entire engine operating range were conducted using the KIVA code, with modifications to the spray, combustion, turbulence, and heat transfer models. In this work, the effect of the rates of species conversion from reactants to products in the combustion model was investigated, and a characteristic time combustion model was formulated to allow consideration of multiple characteristic time scales for the major chemical species. In addition, the effect of engine operating conditions on the model formulation was assessed, and correlations were introduced into the combustion model to account for the effects of residual gas and Exhaust Gas Recirculation (EGR). The predictions were compared with extensive engine test data. The calculation results, had good overall agreement with the experimental cylinder pressure and heat release results, and the multiple-time-scale combustion model is shown to give improved emissions predictions compared to a previous single-time-scale model. Overall, the NOx predictions are in good agreement with the experiments. The soot predictions are also in reasonable agreement with the measured particulates at medium and high loads. However, at light loads, the agreement deteriorates, possibly due to the neglect of the contribution of SOF in the soot model predictions.
Nonlinear Valve Train Dynamics Simulation With a Distributed Parameter Model of Valve Springs
Authors: Lee J. , Patterson D. J.
Published: February 2008

A simulation model of valve train dynamics was developed in order to investigate the vibrational behavior of a valve train under heavy normal load, especially for heavy-duty diesel engines. The nonlinear multi-degree-of-freedom model developed for this study uses input data resulting from the kinematic analysis. The valve spring was modeled as a distributed parameter system rather than a lumped mass system. The stiffness constants of each valve train component were theoretically obtained as nonlinear values. The partial differential equation describing the motion of the spring and the ordinary differential equations for other components, which were considered as a lumped mass system, were solved simultaneously without any iterations by using the numerical “Time Marching Step” method. The results of this simulation, which treated the elastic characteristics of each component as nonlinear, were more accurate than the previous studies that used simple linear elastic models.
Prediction of Flow and Erosion in Power Utility Boilers and Comparison With Measurement
Authors: Tu J. Y. , Fletcher C. A. J. , Behnia M. , Reizes J. A. , Owens D. , Jones P.
Published: February 2008

Multidimensional simulations of both flue gas and fly ash (solid particle) flows with application to erosion prediction in the economisers of coal-fired power utility boilers are reported. A computer code specifically designed for power utility boilers, DS4PUB (Design Software for Power Utility Boilers), was used for the calculations. The major area of erosion often occurs at the economizer of the boiler and depends on the particulate velocity and concentration so that computational results include the economizer inlet distribution of the mean flue gas and particulate velocities, and fly ash concentration. The computer code was validated by comparisons with previously available experimental data and recently performed measurements for flue gas flow velocity, dust burden, and erosion rates at the inlet of economizers in large operating power stations. The results of the multidimensional simulations agreed reasonably well with the experimental measurements. An important finding of this study is that the transverse location of maximum erosion in the economizer tube bank strongly depends on the upstream geometric design of the boiler. For boilers with a shorter turning flow path, the maximum erosion is found to be close to the rear wall of the economizer because both the maximum particulate velocity and concentration occur in this region. For configurations with a long flow path, which includes a splitter plate, the maximum erosion region was found to be closer to the front wall of the economizer, mainly due to the high flow velocity in this region. A relatively high erosion area close to the side and rear wall was also found because of the high concentration of large fly ash particles in this area. Interesting feature of fly ash flow in multidimensional complex boiler geometries such as concentration distributions for different fly ash particle sizes are also discussed.
Receptance Method for the Sensitivity Analysis of Critical Speeds to Rotor Support Stiffness
Authors: Su Chen-Kai , Huang Shyh-Chin
Published: February 2008

A rotor system can be studied via various approaches, e.g., FEM, the transfer matrix method, etc. The receptance method has been one of the methods used for frequency analysis of rotors. The authors, herein, have shown an application of the receptance matrix for sensitivity analysis. Examples of critical speed sensitivity to support stiffness were illustrated and a computing algorithm was developed. Numerical examples proved the approach to be valuable for rotor engineers in quick evaluation and understanding of the support effects.
Flutter and Resonant Vibration Characteristics of Engine Blades
Authors: Srinivasan A. V.
Published: February 2008

This paper presents an in-depth study of blade vibration problems that seriously impact development of advanced gas turbine configurations. The motivation for this study arises from the author’s conviction that structural integrity of power plants is the dominant factor that influences the quality, reliability, and marketability of the product. Implications of this study in the context of potential R&D challenges and opportunities of interest to industry, governments, and academia are discussed.
Ceramic Matrix Composites Application in Automotive Gas Turbines
Authors: Izumi Takao , Kaya Hiroshi
Published: February 2008

We are conducting the development of ceramic matrix composites (CMC) and components made of CMC for a 100 kW automotive ceramic gas turbine (CGT) as shown in Fig. 1. When compared to monolithic ceramics (MC), CMC that we have developed demonstrate superior strength characteristics in terms of resistance to particle impact and thermal shock. We have conducted evaluation tests on the strength of CMC components in which MC such as silicon nitride and silicon carbide were used as a reference for comparison with CMC in the same testing process as employed for components made of MC such as silicon nitride and silicon carbide. It was confirmed that actual components made of CMC realized approximately the same strength as the test pieces. Furthermore, some CMC components have already passed screening tests that evaluated the strength of the components. It was therefore confirmed that the potential exists for the possibility of testing these components in high-temperature assembly tests and engine tests.
Experimental Studies of Air Extraction for Cooling and/or Gasification in Gas Turbine Applications
Authors: Kapat J. S. , Wang T. , Ryan W. R. , Diakunchak I. S. , Bannister R. L.
Published: February 2008

This paper describes an experimental study on how the flow field inside the dump diffuser of an industrial gas turbine is affected by air extraction through a single port on the shell around the dump diffuser. A subscale, 360 deg model of the diffuser-combustor section of an advanced developmental industrial gas turbine was used in this study. The experiments were performed under cold flow conditions, which can be scaled to actual machine operation. Three different conditions were experimentally studied: 0, 5, and 20 percent air extraction. It was found that air extraction, especially extraction at the 20 percent rate, introduced flow asymmetry inside the dump diffuser and, in some locations, increased the local flow recirculations. This indicated that when air was extracted through a single port on the shell, the performance of the dump diffuser was adversely affected with an approximate 7.6 percent increase of the total pressure loss, and the air flow into the combustors did not remain uniform. The global flow distribution was shown to be approximately 35 percent nonuniform diametrically across the dump diffuser. Although a specific geometry was selected, the results provide sufficient generality for improving understanding of the complex flow behavior in the reverse flow diffuser-combustor sections of gas turbines under the influence of various air extractions.
The Effects of Dissolved Oxygen Concentration, Fractional Oxygen Consumption, and Additives on JP-8 Thermal Stability
Authors: Ervin J. S. , Williams T. F. , Heneghan S. P. , Zabarnick S.
Published: February 2008

Since dissolved oxygen participates in fuel deposit formation, knowledge of the effects of dissolved oxygen concentration on fuel thermal stability is critical for fuel system design. In this work, the combined effects of dissolved oxygen availability and additives on jet fuel thermal stability are studied. Experiments with JP-8 jet fuel were conducted in a three-part heat exchanger that simulated a complex thermal and flow environment. The dissolved oxygen content at the flow inlet was varied, and deposition was studied under conditions of either fractional or complete oxygen consumption. The effects of a thermal stability additive package were also studied. An intriguing result found with JP-8 fuels is an increase in deposits formed in heated regions for decreased oxygen consumption, but inverse behavior with the additive package.
Development of a Catalytic Combustor for a Heavy-Duty Utility Gas Turbine
Authors: Dalla Betta R. A. , Schlatter J. C. , Nickolas S. G. , Cutrone M. B. , Beebe K. W. , Furuse Y. , Tsuchiya T.
Published: February 2008

The most effective technologies currently available for controlling NOx emissions from heavy-duty industrial gas turbines are diluent injection in the combustor reaction zone, and lean premixed Dry Low NOx (DLN) combustion. For ultralow emissions requirements, these must be combined with selective catalytic reduction (SCR) DeNOx systems in the gas turbine exhaust. An alternative technology for achieving comparable emissions levels with the potential for lower capital investment and operating cost is catalytic combustion of lean premixed fuel and air within the gas turbine. The design of a catalytic combustion system using natural gas fuel has been prepared for the GE model MS9OO1E gas turbine. This machine has a turbine inlet temperature to the first rotating stage of over 1100°C and produces approximately 105 MW electrical output in simple cycle operation. The 508-mm-dia catalytic combustor designed for this gas turbine was operated at full-scale conditions in tests conducted in 1992 and 1994. The combustor was operated for twelve hours during the 1994 test and demonstrated very low NOx emissions from the catalytic reactor. The total exhaust NOx level was approximately 12–15 ppmv and was produced almost entirely in the preburner ahead of the reactor. A small quantity of steam injected into the preburner reduced the NOx emissions to 5–6 ppmv. Development of the combustion system has continued with the objectives of reducing CO and UHC emissions, understanding the parameters affecting reactor stability and spatial nonuniformities that were observed at low inlet temperature, and improving the structural integrity of the reactor system to a level required for commercial operation of gas turbines. Design modifications were completed and combustion hardware was fabricated for additional full-scale tests of the catalytic combustion system in March 1995 and January 1996. This paper presents a discussion of the combustor design, the catalytic reactor design, and the results of full-scale testing of the improved combustor at MS9OO1E cycle conditions in the March 1995 and January 1996 tests. Major improvements in performance were achieved with CO and UHC emissions of 10 ppmv and 0 ppmv at baseload conditions. This ongoing program will lead to two additional full-scale combustion system tests in 1996. The results of these tests will be available for discussion at the June 1996 Conference in Birmingham.
Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part I—Cylindrical Duct
Authors: Holdeman J. D. , Liscinsky D. S. , Oechsle V. L. , Samuelsen G. S. , Smith C. E.
Published: February 2008

This paper summarizes NASA-supported experimental and computational results on the mixing of a row of jets with a confined subsonic crossflow in a cylindrical duct. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observations were that the momentum-flux ratio and the number of orifices were significant variables. Jet penetration was critical, and jet penetration decreased as either the number of orifices increased or the momentum-flux ratio decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the number of orifices was proportional to the square root of the momentum-flux ratio. In the cylindrical geometry, planar variances are very sensitive to events in the near-wall region, so planar averages must be considered in context with the distributions. The mass-flow ratios and orifices investigated were often very large (mass-flow ratio >1 and ratio of orifice area-to-mainstream cross-sectional area up to 0.5), and the axial planes of interest were sometimes near the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations. The results shown also seem to indicate that nonreacting dimensionless scalar profiles can emulate the reacting flow equivalence ratio distribution reasonably well. The results cited suggest that further study may not necessarily lead to a universal “rule of thumb” for mixer design for lowest emissions, because optimization will likely require an assessment for a specific application.
Wavelet Analysis for Gas Turbine Fault Diagnostics
Authors: Aretakis N. , Mathioudakis K.
Published: February 2008

The application of wavelet analysis to diagnosing faults in gas turbines is examined in the present paper. Applying the wavelet transform to time signals obtained from sensors placed on an engine gives information in correspondence to their Fourier transform. Diagnostic techniques based on Fourier analysis of signals can therefore be transposed to the wavelet analysis. In the paper the basic properties of wavelets, in relation to the nature of turbomachinery signals, are discussed. The possibilities for extracting diagnostic information by means of wavelets are examined, by studying the applicability to existing data from vibration, unsteady pressure, and acoustic measurements. Advantages offered, with respect to existing methods based on harmonic analysis, are discussed as well as particular requirements related to practical application.
Capacitive Measurement of Compressor and Turbine Blade Tip to Casing Running Clearance
Authors: Mu¨ller D. , Sheard A. G. , Mozumdar S. , Johann E.
Published: February 2008

It is an established fact that the efficiency of a gas turbine engine has an inverse relationship with the clearance between the rotor blades and the casing (Tip Clearance, or TC). TC is an essential measurement during the testing of development engines. While commercial TC measurement systems are available, their applicability to an engine is dictated by engine size, geometry, physical accessibility, and temperature distribution around the measurement region. This paper describes the development of a TC measurement system, based on the capacitive measurement principle, which was undertaken to satisfy the application requirements of a specific class of gas turbine engines. The requirements included a relatively long and flexible cable to route the electrical signals out of the engine. The TC measurement system was successfully used during engine testing and valuable data were obtained.
Structural Integrity of a Gas Turbine Combustion System Subjected to Increased Dynamic Pressure
Authors: Barnes J. E.
Published: February 2008

The effect of combustion dynamic pressure oscillations on the structural integrity of the MS 7001F dry low NOx2 (DLN 2) combustion system has been evaluated using ANSYS [1] finite element analyses and high cycle fatigue material data. Analytical results were validated with laboratory measurements on the combustion system subjected to combustion dynamic pressure at actual gas turbine temperature and pressure operating conditions. The combustion liner, transition piece, impingement sleeve, and supports were proven to have excellent durability when subjected to dynamic loads. No risk of structural failure exists at anticipated dynamic pressures using assumptions shown to be conservative.
Experience in Full-Load Testing of Natural Gas Centrifugal Compressors for Rotordynamics Improvements
Authors: Gelin A. , Pugnet J.-M. , Bolusset D. , Friez P.
Published: February 2008

During full-load shop tests under natural gas, two multistage centrifugal compressors exhibited subsynchronous vibrations. Both of them are low-flow, high-pressure, high rotational speed compressors, and are fitted with tilting pad bearings and dry gas seals. A rotating stall problem was first eliminated by a modification of the diffuser geometry. Then, aerodynamic excitations caused the rotors to operate at their stability limit, and high vibration levels were observed at the first natural frequency. A complete rotordynamics analysis was performed in order to model precisely all the fluid–structure interactions. Modifications of the rotor designs were implemented, consisting in optimizing conveniently the bearing pads, replacing the toothed labyrinth seals of the balance pistons by damping honeycomb seals, fitting them with improved shunt hole systems. In addition, the dry gas seals were found to have been damaged, due to thermal effects, and further modifications were implemented to eliminate this problem. Final full load tests demonstrated a satisfactory behavior of both centrifugal compressors.
Modeling of Friction Contact and Its Application to the Design of Shroud Contact
Authors: Yang B.-D. , Menq C.-H.
Published: February 2008

Designers of aircraft engines frequently employ shrouds in turbine design. In this paper, a variable normal load friction force model is proposed to investigate the influence of shroudlike contact kinematics on the forced response of frictionally constrained turbine blades. Analytical criteria are formulated to predict the transitions between stick, slip, and separation of the interface so as to assess the induced friction forces. When considering cyclic loading, the induced friction forces are combined with the variable normal load so as to determine the effective stiffness and damping of the friction joint over a cycle of motion. The harmonic balance method is then used to impose the effective stiffness and damping of the friction joint on the linear structure. The solution procedure for the nonlinear response of a two-degree-of-freedom oscillator is demonstrated. As an application, this procedure is used to study the coupling effect of two constrained forces, friction force and variable normal load, on the optimization of the shroud contact design.
A New Experimental Method to Study Combined Fatigue of Actual Turbine Disk Mortise Teeth at Elevated Temperatures
Authors: Wang Rongqiao , Nie Jingxu
Published: February 2008

This paper presents a new experimental system to study the L-HCCF of an actual turbine disk mortise teeth at elevated temperature, using an actual disk as experimental component. This system ingeniously achieves combined loading (simulating low cycle radial centrifugal force and high cycle crosswise vibration of blade), high-frequency induction local heating (550°C constant temperature), control of high cycle vibrating frequency and amplitude, and crack real-time detection. The experimental result is identical with the practical flight failure. This method can be easily popularized to study the L-HCCF of many components.
Limitations of Rigid Body Descriptions for Heavy-Duty Diesel Engine Vibration
Authors: Hoffman D. M. W. , Dowling D. R.
Published: February 2008

Internal combustion engine vibration modeling commonly relies on assuming the engine is a linearly reacting rigid body, thereby ignoring rotating, reciprocating, and nonsolid engine components. Limitations of this approach are identified from a series of experiments on a heavy-duty in-line six-cylinder Diesel engine typical of Class VIII trucks. Measurement of all three orthogonal vibration force components were made at each of three engine mounts during standard impact-excitation modal identification tests on the quiescent engine and during engine operation. The running-engine vibration forces, measured throughout the test engine load and speed operating envelope, were projected onto the quiescent-engine rigid body modes to determine the modal content and residual vibration as a function of frequency. Modal decomposition results for the running engine show that the quiescent-engine rigid body modes, with modal frequencies between 5.6 and 26.3 Hz, account for 80 percent or more of the measured engine vibration forces for all engine speeds and loads in a bandwidth from zero to 200 Hz. The likely origins of the residual vibration within this bandwidth are discussed.
A Contribution to the Analysis of Turbulence Anisotropy and Nonhomogeneity in an Open-Chamber Diesel Engine
Authors: Spessa E.
Published: February 2008

Further investigation of the turbulence time-frequency spectral structure and its anisotropy and nonhomogeneity has been carried out in the combustion chamber of an automotive diesel engine with a high-squish reentrant in-piston-bowl and a helical intake port. An advanced HWA technique was applied for turbulence measurements along the injector axis, under motored engine conditions in the speed range of 600–3000 rpm. Autospectral density functions of each fluctuating velocity component, as was determined by a specific sensor-wire orientation, were evaluated in consecutive crank-angle correlation intervals during the induction, compression, and early expansion strokes. In order to study the speed dependence of the turbulence-structure anisotropy and nonhomogeneity in different portions of the engine cycle, time-scales of cycle-resolved and conventional turbulent fluctuations were analyzed as functions of the engine speed for different wire orientations, measurement locations, and correlation intervals. Anisotropy and nonhomogeneity were generally significant at low engine speeds, whereas a tendency towards isotropy and homogeneity was found by increasing the speed. With specific reference to the bowl-generated turbulence, spectral anisotropy was remarkable at all speeds in the reverse-squish flow, close to the cylinder-head wall. However, spectral nonhomogeneity was the main feature of the direct-squish flow at low engine speeds.
Computation of Three-Dimensional Compressible Flow From a Rectangular Nozzle With Delta Tabs
Authors: Reddy D. R. , Steffen C. J. , Zaman K. B. M. Q.
Published: February 2008

A three-dimensional viscous flow analysis is performed using a time-marching Reynolds-averaged Navier-Stokes code for a 3:1 rectangular nozzle with two delta tabs located at the nozzle exit plane to enhance mixing. Two flow configurations, a subsonic jet case and a supersonic jet case using the same tab configuration, which were previously studied experimentally, are computed and compared with the experimental data. The experimental data include streamwise velocity and vorticity distributions for the subsonic case, and Mach number distributions for the supersonic case, at various axial locations downstream of the nozzle exit. The computational results show very good agreement with the experimental data. In addition, the effect of compressibility on vorticity dynamics is examined by comparing the vorticity contours of the subsonic jet case with those of the supersonic jet case which were not measured in the experiment.
New Nondimensional Parameters in Fluid Mechanics and Their Application to Turbine Flowmeter Data Analysis
Authors: Mozumdar S. , Islam O.
Published: February 2008

Dimensional analysis has been used in experimental fluid mechanics for over a hundred years. Controllable and uncontrollable variables in an experiment can be efficiently organized into nondimensional groups or parameters. Such nondimensional parameters are used for geometric scaling, and for developing dynamic similitude in experimental processes. Commonly used nondimensional parameters in fluid mechanics include Reynolds number, Mach number, Froude number, Weber number, Strouhal number, etc. Most modern text books and technical papers discuss the use of Buckingham Pi theorem for developing the nondimensionalization process. An often ignored and somewhat older technique is the Rayleigh method. Both the Pi theorem and the Rayleigh method are founded on the principle of dimensional homogeneity, and require some experience in the grouping of physical variables. The present paper uses the Rayleigh method to develop two new nondimensional parameters. A discussion is presented about the use of the parameters in the application of turbine flowmeter calibration and test data analysis. It is shown that data analysis for turbine flowmeters is considerably simplified by the use of the new parameters.
Assessment of Combustion Modes for Internal Combustion Wave Rotors
Authors: Nalim M. R.
Published: February 2008

Combustion within the channels of a wave rotor is examined as a means of obtaining pressure gain during heat addition in a gas turbine engine. Three modes of combustion are assessed: premixed autoignition (detonation), premixed deflagration, and non-premixed autoignition. The last two will require strong turbulence for completion of combustion in a reasonable time in the wave rotor. The autoignition modes will require inlet temperatures in excess of 800 K for reliable ignition with most hydrocarbon fuels. Examples of combustion mode selection are presented for two engine applications.
Active Control of Combustion Instability in a Liquid-Fueled Low-NOx Combustor
Authors: Cohen J. M. , Rey N. M. , Jacobson C. A. , Anderson T. J.
Published: February 2008

A practical active control system for the mitigation of combustion instability has been designed and demonstrated in a lean, premixed, single-nozzle combustor at realistic engine operating conditions. A full-scale engine fuel nozzle was modified to incorporate a simple fuel flow actuator. Results indicate that the system was capable of reducing pressure fluctuations by 82 percent (15 dB or 5.6×) while maintaining or reducing NOx and CO emissions levels.