bluuebunny/crossref_metadata_2025 huggingface dataset:
Features of a Cooling System Simulation Tool Used in Industrial Preliminary Design Stage
Authors: Zecchi Stefano , Arcangeli Lorenzo , Facchini Bruno , Coutandin Daniele
Published: November 2008

Due to expected increases in gas turbine performance, strictly related to firing temperature, heat transfer is a major issue in design processes. To keep components temperature levels below design requirements, cooling systems are commonly used. Nowadays, nozzle and blade cooling systems have reached a high degree of complexity. In a preliminary design stage, both experimental and 3D numerical analyses are usually not very suitable to define geometry, coolant mass flow rate or cooling system typology. This is mainly due to the uncertainty on several parameters, i.e. pressure distributions and materials properties, and their undefined interaction. This work presents a simulation tool useful to provide system cooling development with qualitative and quantitative information about metal temperature, coolant mass flow rate, heat transfer and much more. This tool couples energy, momentum and mass flow conservation equations together with experimental correlations for heat transfer and pressure losses. Metal conduction is solved by two dimensional calculations for several blade to blade sections. This methodology allows to investigate several cooling system configurations and compare them in a relatively short time. Main features of this simulation tool are shown comparing obtained results with experimental data.
The Transient Liquid Crystal Technique: Influence of Surface Curvature and Finite Wall Thickness
Authors: Wagner G. , Kotulla M. , Ott P. , Weigand B. , von Wolfersdorf J.
Published: November 2008

The transient liquid crystal technique is nowadays widely used for measuring the heat transfer characteristics in gas turbine applications. Usually, the assumption is made that the wall of the test model can be treated as a flat and semi-infinite solid. This assumption is correct as long as the penetration depth of the heat compared to the thickness of the wall and to the radius of curvature is small. However, those two assumptions are not always respected for measurements near the leading edge of a blade. This paper presents a rigorous treatment of the curvature and finite wall thickness effects. The unsteady heat transfer for a hollow cylinder has been investigated analytically and a data reduction method taking into account curvature and finite wall thickness effects has been developed. Experimental tests made on hollow cylinder models have been evaluated using the new reduction method as well as the traditional semi-infinite flat plate approach and a third method that approximately accounts for curvature effects. It has been found that curvature and finite thickness of the wall have in some cases a significant influence on the obtained heat transfer coefficient. The parameters influencing the accuracy of the semi-infinite flat plate model and the approximate curvature correction are determined and the domains of validity are represented.
The Measurement of Turbomachinery Blade Vibration Through Tip Timing With Capacitance Tip Clearance Probes
Authors: Lawson Craig , Ivey Paul C.
Published: November 2008

Turbomachinery blade vibrations can cause High Cycle Fatigue, which reduces blade life. In order to observe this vibration a non-intrusive monitoring system is sought. The vibration can be detected by measuring blade tip timing since in the presence of vibration the blade timing will differ slightly from the passing time calculated from rotor speed. Much research and development has gone into investigating the ability of optical probes to achieve this. However, this paper looks at the potential for a dual use capacitance probe sensor to measure both tip timing and tip clearance. This paper provides new insights into the ability of a commercially available capacitance probe tip clearance measurement system for application as a non-intrusive turbomachinery blade tip timing measurement device. This is done by correlating capacitance probe tip timing results with simultaneously measured blade-mounted strain gauge vibration results and precise rotational speeds. Thus the characterisation of the performance of the capacitance probe system when measuring blade vibration on a full-sized low-speed research compressor is analysed and reported.
Gas Turbine Diagnosis Using a Fault Isolation Enhanced GPA
Authors: Li Y. G.
Published: November 2008

Gas Path Analysis (GPA) and its different derivatives have been developed for more than thirty years and used widely and successfully by many gas turbine manufacturers and operators. In gas turbine gas path component diagnosis, it has been recognized for a long time that GPA would be more successful if degraded components could be located. Unfortunately, only the deviation of measurable parameters is monitored in operation and information about the degraded components is normally not available. In this research, a two-step diagnostic approach is introduced, where a pattern matching method is used first and further developed to isolate degraded components; then Gas Path Analysis is applied to assess the quantity of degradation. A gas turbine performance simulation program, Cranfield University TURBOMATCH, has been modified to simulate the diagnostic process. A model gas turbine engine similar to Rolls-Royce aero AVON is used to test the effectiveness of the approach. It is found that the developed fault isolation method can isolate degraded components accurately and enhance the effectiveness of the quantitative assessment of the degradation with Gas Path Analysis (GPA) in gas turbine diagnostics.
Evaluation of Predicted Heat Transfer on a Transonic Blade Using v2-f Models
Authors: Ameri Ali A. , Ajmani Kumud
Published: November 2008

The v2–f models of Durbin and the new v2–f model of Jones et al. were used to compute the blade heat transfer for the transonic cascade of Giel et al.. Three different experimental cases were considered. Calculations were performed using the Glenn-HT code modified so that it solves these turbulence model equations using an implicit scheme. An iterative matrix solver, namely GMRES was used for this purpose. Comparisons were made with previously published results using the SST model and a simple algebraic model modified for the stagnation heat transfer effects and transition effects. The results, albeit limited to the present case, show that the v2–f model of Durbin provides good predictions on the pressure surface. But there is some discrepancy between the suction surface heat transfer predictions and experimental measurements. The newer model of Jones et al. requires further modification before it can be routinely used for blade heat transfer.
Advanced Transmission and Oil System Concepts for Modern Aero-Engines
Authors: Klingsporn M.
Published: November 2008

For better efficiency of modern gas turbine aero-engines, higher compressor pressure ratios, operating temperatures and shaft speeds are proposed which lead to increased demands also on transmission and oil system components. As a response to these demands, the European research project “Advanced Transmission and Oil System Concepts” (ATOS) was established to develop innovative transmission and oil system concepts in commercial gas turbines. The present paper, written by the project co-ordinator, discusses the design trends and objectives of recent research work. Furthermore, the main results of experimental and theoretical work on hybrid (ceramic) bearings, two-phase flow visualization and heat generation in bearing chambers, auto ignition temperature of oils for oil fire prevention, air/oil separation, novel electrically driven oil pumps, shaft buckling as well as dual-alloy shaft technology are presented. Special emphasis will be on two-phase flow aspects related to bearing chambers in aero engines.
Aerodynamic and Mechanical Vibration Analysis of a Compressor Blisk at Surge
Authors: Scho¨nenborn Harald , Breuer Thomas
Published: November 2008

Typically surge events in compressors are investigated only from the aerodynamic point of view (aerodynamic instability or lack of surge margin). For this assessment various methods exist during the design phase. For the analysis of the structural impact of surge in this phase the situation is more challenging, because an analytical prediction of the blade loading during surge is difficult to obtain. In this paper a combined analysis of aerodynamic and structural aspects of surge in compressor rotor blades of advanced axial flow compressors with state-of-the-art numerical procedures is presented and compared to extensive strain-gauge measurements. The unsteady aerodynamic excitation of a compressor rotor blade during surge is determined with a numerical procedure which allows calculating the unsteady flow field in a compression system. Blade rows of the compressor are simulated by appropriate loss/deviation characteristics covering both the normal and the unstable operating regime of the compressor, including reversed flow conditions. Elements adjacent to the compressor such as inlet pipes, exit volumes and throttles are modeled as required to include their impact on the systems dynamic behavior. The unsteady flow field within the system is determined by solving the unsteady conservation laws for compressible, inviscid flow. Blade forces are determined from the change of aerodynamic momentum across a blade row. The resulting forces in axial and circumferential direction are used as an input for a direct transient Finite-Element stress analysis. The resulting forces are applied to the blades. The results of the Finite-Element analysis are compared with experimental results from a compressor test rig. Stress is measured by strain-gauges in various positions on the blades. In addition, transient pressure is recorded. Measurements are taken during normal operation of the compressor as well as during surge. It is shown that the procedure is able to predict the vibration stress level of the blades satisfactorily.
Noise Computation of a Turbo-Engine Jet Exhaust Based on LES and Lighthill’s Acoustic Analogy
Authors: Mihaˇescu Mihai , Sza´sz Ro´bert-Zolta´n , Fuchs Laszlo
Published: November 2008

Increasing noise regulations at urban airports force jet engine manufactures to develop and build more quiet engines. Over recent years, a significant reduction in fan and mechanical noise has been achieved. However, the jet exhaust is the principal source of noise. The acoustical field that is generated by a turbo-engine jet exhaust running near the ground level is considered. The full equations of motion for compressible and unsteady flows describe both flow field and sound generation. The flow variables are decomposed into semi-compressible components and inviscid, irrotational acoustical components. The turbulent flow and mixing are computed using Large Eddy Simulation (LES). The radiated acoustical field is computed using the Lighthill’s acoustic analogy with acoustic sources provided by instantaneous LES data.
On the Aerodynamic Design of Compressor Airfoils for Robustness Under Geometric Uncertainty
Authors: Garzon Victor E. , Darmofal David L.
Published: November 2008

This paper considers the aerodynamic design of compressor blade sections for improved performance robustness in the face of geometric uncertainty caused by noisy manufacturing processes. A probabilistic, gradient-based optimization method was used to redesign subsonic and transonic compressor airfoils subjected to geometric variability. Three different design goals were considered: Minimizing the deterministic profile total pressure loss coefficient, minimizing the mean value of loss coefficient, and minimizing the loss variability. In both transonic and subsonic applications, deterministic minimization of loss coefficient produced essentially the same airfoils as the probabilistic minimization of mean loss. However probabilistic minimization of loss variability produced clearly different airfoils which achieved reductions of 20% or more in standard deviation of loss compared to the minimum-loss designs. For the subsonic application, the improved robustness of the minimum variability design was achieved through a reduction in diffusion immediately downstream of the leading edge on the pressure side. This reduction in diffusion resulted in less sensitivity of the boundary layer to geometric variability in the leading edge region. For the transonic application, the robustness improvement was achieved by redesigning the suction side to produce a constant pressure region immediately downstream of the passage shock, which had the effect of desensitizing the boundary layer to variability in shock strength and position. A meanline model was used to assess the impact of probabilistic airfoil section optimization on overall compressor performance. While the mean efficiency was found to be nearly the same for all designs, the robust blade designs produced a decrease in compressor efficiency variability of 50% compared to the minimum-loss designs.
Production of Hydrogen-Rich Gas Through Pyrolysis of Biomass in a Two-Stage Reactor
Authors: Chen Guanyi , Li Qiang , Lv Xiaoyang , Deng Na , Jiao Lifei
Published: November 2008

Biomass is quite abundant in the world, particularly in some countries like China. China has large quantities of straw and/or stalk-origin biomass resources and the attention is currently being paid to the exploitation of these resources to produce energy products via different technical solutions, among of which pyrolysis of biomass to produce hydrogen-rich gas is very promising as hydrogen is a very clear energy carrier. In this work, pyrolysis of rice straw, corn stalk and sawdust was carried out in a two-stage reactor (the first-stage reactor is a conventional fixed-bed pyrolyser, and the second-stage reactor is a catalytic fixed bed) to produce hydrogen-rich gas. The effect of catalytic bed on the pyrolysis behaviour have been investigated, with the emphasis on final product particularly hydrogen. The operation of the catalytic reactor appears significant in promoting biomass pyrolysis towards the production of gaseous products, especially hydrogen. At 750°C of the pyrolyser with rice straw as fuel, the use of the catalytic bed leads to the increases of gas yield from 0.41 Nm3/kg to 0.50 Nm3/kg, approximately 22% increase, and of H2 concentration from 33.79% to 50.80% in volume, approximately 50.3% increase, respectively. Compared with calcined dolomite, fresh nickel-based catalyst shows stronger catalytic effect on the pyrolysis of rice straw as its use in the catalytic bed results in the increase of gas yield from 0.41 Nm3/kg to 0.56 Nm3/kg, approximately 36.6% increase, and the increase of H2 concentration from 33.79% to 59.55% in volume, approximately 76.2% increase. Furthermore, two catalysts follow the same trend for the pyrolysis of corn stalk and sawdust. At temperature of 815°C, catalysts also follow the same trend. Catalytic bed can significantly reduce the level of tar which is carried out with the producer gas, to less than 1% of original level. Catalyst load or gas space velocity (hourly) has the influence on the gas yield and H2 concentration. 30% of load, i.e. gas space velocity (hourly) 0.9 × 104 h−1, appears reasonable. Beyond that, gas yield and H2 concentration remain almost unchanged.
Optimization of Microturbine Aerodynamics Using CFD, Inverse Design and FEM Structural Analysis: 2nd Report — Turbine Design
Authors: Watanabe Hiroyoshi , Okamoto Hidenobu , Guo Shijie , Goto Akira , Zangeneh Mehrdad
Published: November 2008

In this second report, a new aerodynamic design is presented for a radial turbine stage of a microturbine engine. To optimize three-dimensional (3-D) flows, an inverse design method, in which 3-D blade geometry is numerically obtained for specified blade loading distribution, has been applied together with numerical assessment using CFD (Computational Fluid Dynamics) and FEM (Finite Element Method). The runner blade profile along the hub surface was modified to attain nearly radially arranged blade elements especially at the exducer part of the radial turbine in order to achieve required structural strength. Also the blade thickness distribution was optimized to avoid vibration resonance and to meet creep strength requirements. The blade profile along the shroud surface was optimized via 3-D inverse design and CFD. CFD predicted aerodynamic performance of the modified turbine runner was confirmed to be similar to that of the fully 3-D blade shape, while maintaining structural reliability. The turbine nozzle also has been re-designed by using the inverse design method, with stage performance improvements confirmed by stage calculations using CFD.
The Effectiveness of Passive Combustion Control Methods
Authors: Paschereit Christian Oliver , Gutmark Ephraim
Published: November 2008

Flame stabilization in a swirl-stabilized combustor occurs in an aerodynamically generated recirculation region which is a result of vortex breakdown. The characteristics of the recirculating flow are dependent on the swirl number and on axial pressure gradients. Coupling to downstream pressure pulsations is also possible. Control methods of unstable thermoacoustic modes and reduction of NOx and CO emissions were investigated in a low-emission swirl-stabilized industrial combustor. Several axisymmetric and helical unstable modes were identified for fully premixed and diffusion type combustion. In addition to mode variation, the instabilities spanned a wide range of frequencies. The unstable modes that were associated with flow instabilities of the wake-like region on the combustor axis due to vortex breakdown (VBD), shear layer instabilities at the sudden expansion (dump plane) and equivalence ratio fluctuations were in a range of normalized frequency St = 0.5–1.1. Other unstable modes at higher frequencies of St = 7.77, were excited by the Kelvin-Helmholtz vortices shed at the burner’s exit. The combustion structures associated with the different unstable modes were visualized using phase locked images of OH chemiluminescence and analyzed using cross-correlations between OH detecting fiberoptics. After identifying the structure of the instabilities and determining their source, different geometrical changes were applied to disrupt their formation or vary their characteristics. These modifications reduced the periodic heat release and enabled decoupling of the heat from acoustic modes that led to thermoacoustic instabilities. The passive control techniques that will be described in this paper were effective in suppressing the thermoacoustic pressure oscillations and also reduced NOx and CO emissions.
A Comparative Study of Genetic Algorithms and Gradient Methods for RM12 Turbofan Engine Diagnostics and Performance Estimation
Authors: Gro¨nstedt Tomas , Wallin Markus
Published: November 2008

Recent work on gas turbine diagnostics based on optimisation techniques advocates two different approaches: 1) Stochastic optimisation, including Genetic Algorithm techniques, for its robustness when optimising objective functions with many local optima and 2) Gradient based methods mainly for their computational efficiency. For smooth and single optimum functions, gradient methods are known to provide superior numerical performance. This paper addresses the key issue for method selection, i.e. whether multiple local optima may occur when the optimisation approach is applied to real engine testing. Two performance test data sets for the RM12 low bypass ratio turbofan engine, powering the Swedish Fighter Gripen, have been analysed. One set of data was recorded during performance testing of a highly degraded engine. This engine has been subjected to Accelerated Mission Testing (AMT) cycles corresponding to more than 4000 hours of run time. The other data set was recorded for a development engine with less than 200 hours of operation. The search for multiple optima was performed starting from more than 100 extreme points. Not a single case of multi-modality was encountered, i.e. one unique solution for each of the two data sets was consistently obtained. The RM12 engine cycle is typical for a modern fighter engine, implying that the obtained results can be transferred to, at least, most low bypass ratio turbofan engines. The paper goes on to describe the numerical difficulties that had to be resolved to obtain efficient and robust performance by the gradient solvers. Ill conditioning and noise may, as illustrated on a model problem, introduce local optima without a correspondence in the gas turbine physics. Numerical methods exploiting the special problem structure represented by a non-linear least squares formulation is given special attention. Finally, a mixed norm allowing for both robustness and numerical efficiency is suggested.
Performance-Based Geometric Tolerancing of Compressor Blades
Authors: Lamb Caroline Twomey , Darmofal David L.
Published: November 2008

The relationship between statically measured geometric parameters (tolerances) and the aerodynamic performance of an airfoil are investigated in this paper. The goal is to determine which geometric parameters are critical to control during manufacturing, such that a blade will have acceptable aerodynamic performance. A probabilistic model of geometric variability for a three-dimensional blade is derived. Using this geometric model, probabilistic aerodynamic simulations are conducted to analyze the variability in aerodynamic performance. Tolerance optimization is then applied in which tolerance ranges are modified to best sort blades according to some arbitrary performance limit. The optimization is performed for several limits, expressed as a percent of nominal performance, to observe both which parameters best predict performance and the accuracy of that prediction at each limit. Two blade cases are considered, both based on the same compressor blade: the base compressor blade with nominal manufacturing noise; and a probabilistic redesign of the blade geometry designed to minimize the impact of manufacturing noise, also analyzed with nominal manufacturing noise. Results show the best static indicators of meanline performance are parameters concerning the LE of the airfoil, and the effectiveness of these parameters vary greatly depending on the chosen performance limit. In addition, it was shown that the optimized tolerances for the redesigned blade were consistently looser, or less restrictive, than those for the original blade population for a given performance limit. The differences in observed optimized tolerance ranges are small for less restrictive performance limits but at more aggressive performance limits, there is a 20–30% increase in tolerance range for the redesigned blade population.
Multistage Aspects and Unsteady Effects of Stator and Rotor Clocking in an Axial Turbine With Low Aspect Ratio Blading
Authors: Behr T. , Porreca L. , Mokulys T. , Kalfas A. I. , Abhari R. S.
Published: November 2008

This paper presents the outcome of a recent study in clocking-related flow features and multistage effects occurring in high-pressure turbine blade geometries. The current investigation deals with an experimentally based systematic analysis of the effects of both stator-stator and rotor-rotor clocking. Due to the low aspect ratio of the turbine geometry, the flow field is strongly three-dimensional and is dominated by secondary flow structures. The investigation aims to identify the flow interactions involved and the associated effects on performance improvement or degradation. Consequently a three-dimensional numerical analysis has been undertaken to provide the numerical background to the test case considered. The experimental studies were performed in a two-stage axial research turbine facility. The turbine provides a realistic multi-stage environment, in which both stator blade rows and the two rotors can be clocked relative to each other. All blade rows have the same blade number count, which tends to amplify clocking effects. Unsteady and steady measurements were obtained in the second stage using fast response aerodynamic probes (FRAP) and miniature pneumatic 5-hole probes. The current comprehensive investigation has shown that multistage and unsteady flow effects of stator and rotor clocking in low aspect ratio turbines are combined in a nonlinear fashion caused by axial and radial redistribution of low energy fluid. The integral result of clocking on stage efficiency is compensated by competing loss generating mechanisms across the span.
Three-Dimensional Separations in Axial Compressors
Authors: Gbadebo Semiu A. , Cumpsty Nicholas A. , Hynes Tom P.
Published: November 2008

Flow separations in the corner regions of blade passages are common. The separations are three dimensional and have quite different properties from the two-dimensional separations that are considered in elementary courses of fluid mechanics. In particular the consequences for the flow may be less severe than the two-dimensional separation. This paper describes the nature of three-dimensional separation and addresses the way in which topological rules, based on a linear treatment of the Navier-Stokes equations, can predict properties of the limiting streamlines, including the singularities which form. The paper shows measurements of the flow field in a linear cascade of compressor blades and compares these with the results of 3D CFD. For corners without tip clearance, the presence of three-dimensional separation appears to be universal and the challenge for the designer is to limit the loss and blockage produced. The CFD appears capable of predicting this.
Turbine Fuel Ignition and Combustion Facility for Extremely Low Temperature Conditions
Authors: Pucher G. , Allan W. D.
Published: November 2008

As the temperature of combustion air and fuels are reduced, the ability to achieve ignition within gas turbine engines becomes increasingly difficult. Several factors share responsibility, related largely to the physical characteristics of fuel emerging from nozzles, whereby an increasing fuel viscosity with temperature reduction results in larger average fuel droplets. The ensuing reduced surface area hinders fuel evaporation within an environment where evaporation is already impeded by low partial pressures due to low ambient temperature conditions and/or depending on the mode of operation, due to a high altitude environment. To study the effects of extremely low air and fuel temperatures on gas turbine fuel ignition performance, a dual mode (namely for cold start and altitude relight) test rig has been designed and commissioned. Its main components include a turbo-jet combustion chamber section, fuel system, ignition system, fuel/air cooling systems, and data acquisition/instrumentation. For airflow within the combustion chamber, two alternate sources are used, depending on the mode of operation. As such, this rig allows key parameters related to gas turbine ignition, such as fuel flow, fuel viscosity, ignition characteristics, airflow, and pressure conditions to be monitored and recorded. Highlights of this test rig include a General Electric J-85 combustion chamber section with quartz windows, fuel and air cooling via cryogenic liquids (LN2 for the fuel, LN2 and LOx for air), fuel and air closed loop temperature control, high speed data acquisition, a gas turbine exciter or, as selected, a custom programmable ignition system. Airflow is provided either by twin 11 HP blowers providing up to 0.5 kg/s of airflow to simulate sea level start conditions, or through the entrainment of high velocity air to simulate relight conditions at up to 21000 feet altitude. This rig is capable of achieving minimum inlet air temperatures and fuel temperatures lower than −45°C. A series of commissioning tests was undertaken with the rig in both ground start and altitude (low pressure) configurations. In order to study viscosity effects on ignition performance, two common gas turbine fuels were utilized, namely JP-4 (F-40) and JP-8 (F-34). Ignition fuel flows as well as lean blowout flows for a stock injector design are presented for these fuels across a matrix of fuel and air temperatures. Conclusions are drawn and future developments are described.
Rotordynamic Performance of Flexure Pivot Hydrostatic Gas Bearings for Oil-Free Turbomachinery
Authors: Zhu Xuehua , San Andre´s Luis
Published: November 2008

Micro-turbomachinery demands gas bearings to ensure compactness, lightweight and extreme temperature operation. Gas bearings with large stiffness and damping, and preferably of low cost, will enable successful commercial applications. Presently, tests conducted on a small rotor supported on flexure pivot–hydrostatic pad gas bearings (FPTPBs) demonstrate stable rotordynamic responses up to 100,000 rpm (limit of the drive motor). Test rotor responses show the feed pressure raises the system critical speed (increase in bearing direct stiffness) while the viscous damping ratio decreases. Predictions correlate favorably with experimentally identified (synchronous) direct stiffness bearing force coefficients. Identified experimental gas bearing synchronous damping coefficients are 50% or less of the predicted magnitudes, though remaining relatively constant as the rotor speed increases. Tests without feed pressure show the rotor becomes unstable at ∼ 81 krpm with a whirl frequency ratio of 20%. FPTPBs are mechanically complex and more expensive than cylindrical plain bearings. However, their enhanced stability characteristics and predictable rotordynamic performance makes them desirable for the envisioned oil-free applications in high speed micro turbomachinery.
Preliminary Study of a Novel R718 Turbo-Compression Cycle Using a 3-Port Condensing Wave Rotor
Authors: Kharazi Amir A. , Akbari Pezhman , Mu¨ller Norbert
Published: November 2008

Using a novel 3-port condensing wave rotor enhancing the turbo-compression in a R718 refrigeration cycle, which uses only water as a refrigerant, has been introduced. The wave-rotor implementation can increase efficiency and reduce size and cost of R718 units. The condensing wave rotor employs pressurized water to pressurize, desuperheat, and condense the refrigerant vapor — all in one dynamic process. The underlying phenomena of flash evaporation, shock wave compression, desuperheating, and condensation inside the wave rotor channels are described in a wave and phase-change diagram. The thermodynamic process is shown in pressure-enthalpy and temperature-entropy diagrams. A computer program based on a thermodynamic model was generated to evaluate the performance of R718 baseline and wave-rotor-enhanced cycles. The effect of some key parameters on the performance enhancement is demonstrated as an aid for optimization. A performance map summarizes the findings. It shows optimum wave rotor pressure ratio and maximum relative performance improvement of R718 cycles by using the 3-port condensing wave rotor.
An Integrated Design System for Fans, Compressors, and Turbines: Part 3 — Fan and Compressor Airfoil Geometry Generators
Authors: Durschmidt Don F. , Medlock Allen , Miller Max J.
Published: November 2008

A new aerodynamic design system has been developed that includes geometry generators for fans, axial compressors, and centrifugal compressors. This paper describes geometry generators for both arbitrary and flank-milled airfoils in axial, radial and mixed gas paths. Both geometry generators have the special feature that airfoil sections are constructed on construction curves, not on flow paths or streamlines. Construction curves are independent of flow path curves and streamlines, but can be defined to coincide with them. This makes high-flowing and low-flowing designs very easy. A special feature specific to the flank milled airfoil geometry generator is an undercutting analysis to reveal any unwanted contact with the conical cutter. This special feature and others have provided major savings from productivity improvements and reductions in design cycle time.
Evaluation of an Enhanced Bank of Kalman Filters for In-Flight Aircraft Engine Sensor Fault Diagnostics
Authors: Kobayashi Takahisa , Simon Donald L.
Published: November 2008

In this paper, an approach for in-flight fault detection and isolation (FDI) of aircraft engine sensors based on a bank of Kalman filters is developed. This approach utilizes multiple Kalman filters, each of which is designed based on a specific fault hypothesis. When the propulsion system experiences a fault, only one Kalman filter with the correct hypothesis is able to maintain the nominal estimation performance. Based on this knowledge, the isolation of faults is achieved. Since the propulsion system may experience component and actuator faults as well, a sensor FDI system must be robust in terms of avoiding misclassifications of any anomalies. The proposed approach utilizes a bank of (m+1) Kalman filters where m is the number of sensors being monitored. One Kalman filter is used for the detection of component and actuator faults while each of the other m filters detects a fault in a specific sensor. With this setup, the overall robustness of the sensor FDI system to anomalies is enhanced. Moreover, numerous component fault events can be accounted for by the FDI system. The sensor FDI system is applied to a commercial aircraft engine simulation, and its performance is evaluated at multiple power settings at a cruise operating point using various fault scenarios.
Some Experiments on Oil Whirl and Oil Whip
Authors: El-Shafei A. , Tawfick S. H. , Raafat M. S. , Aziz G. M.
Published: November 2008

The oil whirl and oil whip phenomena are well known since the early twentieth century. However, there is a lot of confusion on the parameters that affect the onset of instability. In this study, we investigate the onset of instability on a flexible rotor mounted on two plain cylindrical journal bearings. The rotor is run through the first critical speed, the instability, and the second critical speed. Tests are conducted at various unbalance levels, pressures, and misalignment conditions on the coupling. It is shown that, by far, the misalignment of the coupling is the parameter that is most effective on the onset of instability. In particular angular misalignment resulted in the smoothest rotor response.
Turbine Engine Modeling Using Temporal Neural Networks for Incipient Fault Detection and Diagnosis
Authors: Menon Sunil , Uluyol O¨nder , Gupta Deepanker
Published: November 2008

We present a method of fault detection and diagnosis in turbine engines using temporal neural networks. Temporal neural networks allow us to represent the complete engine operating range by complementing the first-principle models which are usually restricted to takeoff and cruise phases. Because faults that are manifest only in particular phases can be detected, complete coverage leads to more accurate anomaly detection and fault diagnosis systems. The time series sensor data from the engine is collected during particular aircraft flight phases such as startup, takeoff, cruise, and shutdown. We use the echo state network to develop an incipient fault detection and diagnosis system. Echo state networks have several advantages over conventional types of temporal neural networks, including accuracy and ease of training. We demonstrate the efficacy of using the echo state networks to focus on flight phases that are difficult to model. We present results of our fault detection and diagnosis method with actual propulsion engine transient flight data.
CFD Heat Transfer Predictions for a High-Pressure Turbine Stage
Authors: Tallman James A.
Published: November 2008

Computational Fluid Dynamics (CFD) was used to predict the turbine airfoil heat transfer for the high-pressure vane and high-pressure blade of a modern, one and one half stage turbine at its correct scale. Airfoil pressure and heat transfer measurements were recently obtained for the turbine in a transient shock tunnel facility, which allows for the replication of the actual engine turbine’s design corrected speed, pressure ratio, and gas-to-metal temperature ratio. A 3-D, compressible, Reynolds-averaged Navier-Stokes CFD solver with k-ω turbulence modeling was used for the CFD predictions. The turbulence model’s implementation into the numerical procedure was modified slightly, in order to better capture the model’s intended near-wall behavior and resolve the heat transfer prediction. Both the high-pressure vane and high-pressure blade were computed as steady-state flows and for two different turbine Reynolds number settings. Overall, the predictions compare very favorably with the measurement for both pressure and heat transfer at the mid-span location. A discussion of the features of the airfoil heat transfer distribution is included.
Flow Characteristics Within and Downstream of Spherical and Cylindrical Dimple on a Flat Plate at Low Reynolds Numbers
Authors: Khalatov A. , Byerley A. , Ochoa D. , Min Seong-Ki
Published: November 2008

A comprehensive experimental study has been performed in the U.S. Air Force Academy water tunnel to obtain a better understanding of the complicated flow patterns in shallow dimple configurations (h/D ≤ 0.1), including single cylindrical and spherical dimples, as well as single spanwise rows of dimples. The flow patterns, in-dimple separation zone extent, and bulk flow oscillation frequencies have been measured at low Reynolds number conditions. Three different single dimples and two single rows of dimples have been tested over a range of Reynolds numbers ReD of 3,170 to 23,590 including laminar and turbulent flow patterns downstream of a dimple. To visualize the fine flow features, five different colors of dye were injected through five cylindrical ports machined at locations upstream and inside the dimples. The measured results revealed unsteady and three-dimensional flow features inside and downstream of the dimple. The Reynolds number, dimple shape and the presence of adjacent dimples all play important roles in determining the nature of the flow pattern formation. Some preliminary conclusions regarding the laminar-turbulent flow transition after a dimple are presented.
Pressure Driven Temperature Field in a Combustion Chamber
Authors: Sierra Fernando Z. , Kubiak Janusz , Urquiza Gustavo
Published: November 2008

In this work numerical computation has been applied to investigate the temperature field in a gas turbine combustion chamber. The simulation considered pressure imbalance conditions of air flow between primary and secondary inlets. The combustion chamber under study is part of a 70 MW gas turbine from an operating combined cycle power plant. The combustion was simulated with proper fuel-air flow rate assuming stoichiometric conditions. Characteristic temperature and pressure fields were obtained under constant boundary conditions of air inlet. However, with pressure distribution imbalances of the order of 3 kPa between primary and secondary air inlets, excessive heating in regions other than the combustion chamber core were obtained. Over heating in these regions helped to explain what was observed to produce permanent damage to auxiliary equipment surrounding the combustion chamber core, like the cross flame pipes. It is observed that high temperatures which normally develop in the central region of the combustion chamber may reach other surrounding upstream regions by modifying slightly the air pressure. Scanning microscope examination of the damaged material confirmed that it was exposed to high temperatures such as predicted through the numerical computation.
Operation of a Circulating Fluidised Bed Biomass Gasifier
Authors: Chen Guanyi , Li Gang , Glazer Michel P. , Zhang Chunlei , Andries J.
Published: November 2008

Energy generation from the use of biomass is gaining an increasing attention. Gasification of biomass at present, is widely accepted as a popular technical route to produce fuel gas for the application in boilers, engine, gas/micro turbine or fuel cell. Up to now, most of researchers have focused their attentions only on fixed-bed gasification and fluidised bed gasification under air-blown conditions. In that case, the producer gas is contaminated by high tar contents and particles which could lead to the corrosion and wear of blades of turbine. Furthermore, both the technologies, particularly fixed bed gasification, are not flexible for using multiple biomass-fuel types and also not feasible economically and environmentally for large scale application up to 10∼50 MWth. An innovative circulating fluidised bed concept has been considered in our laboratory for biomass gasification thereby overcoming these challenges. The concept combines and integrates partial oxidation, fast pyrolysis (with an instantaneous drying), gasification, and tar cracking, as well as a shift reaction, with the purpose of producing a high quality of gas, in terms of low tar level and particulates carried out in the producer gas, and overall emissions reduction associated with the combustion of producer gas. This paper describes our innovative concept and presents some experimental results. The results indicate that the gas yield can be above 1.80Nm3/kg with the calorific value of 4.5–5.0MJ/Nm3, and the fluctuation of the gas yield during the period of operation is 3.3%–3.5% for the temperature of 750–800 °C. In genera, the results achieved support our concept as a promising alternative for the gasifier coupled with micro/gas turbine to generate electricity.
Improving Stall Margin by Using an Air-Separator for a Variable-Pitch Axial-Flow Fan
Authors: Nishioka Takahiro , Kuroda Shuuji , Kozu Tadashi
Published: November 2008

An air-separator for extending the operating range of a variable-pitch axial-flow fan has been developed. It has a circular-are outer casing, a part of which forms the guide vane at the inlet of the air-separator. To obtain a wide operating range and to minimize penalties in terms of efficiency and noise, the influence of exposure and clearance ratios at various stagger-angle settings for rotor blades in low-speed and high-speed axial flow fans was experimentally investigated. Flow distributions and pressure fluctuations downstream of the rotor were also measured in order to investigate the influence of the air-separator on rotating stall. The distributions and fluctuations suggested that the air-separator decreased the blockage effect near the rotor tip and suppressed the rotating stall. Moreover, stall-margin and pressure-rise improvements were independent of the clearance ratio. These improvements depended on the exposure ratio and stagger-angle settings for the rotor blades. The fan efficiency for the air-separator also depended on the exposure ratio. In addition, the efficiency had the opposite tendency to the stall-margin and pressure-rise improvements. In contrast, the noise for the air-separator was independent of the exposure ratio and decreased as the clearance ratio increased. For the optimum combination of the exposure and clearance ratios, the stall-margin and pressure-rise were improved by over 20% with minimized penalties in terms of efficiency and noise. It is concluded from these results that the developed air-separator can provide a wide operating range for a variable-pitch axial-flow fan.
Heat Transfer and Pressure Drop Characteristics of Finned Tube Banks in Heat Exchanger for Gas Turbine
Authors: Kawaguchi K. , Okui K. , Hasegawa Y.
Published: November 2008

In recent years the requirement for reduction of energy consumption has been increasing to solve the problems of the global warming and the shortage of petroleum resources. For example in the power generation field, as the thermal power generation occupied 60% of the power generation demand, the improvement of the thermal efficiency is required considerably. This paper described the heat transfer and pressure drop characteristics of the finned tube banks used for the heat exchanger in the thermal power generation. The characteristics were clarified by testing the serrated finned tubes banks for improvement of higher heat transfer and the conventional spiral finned tube banks under the same test conditions. The equations to predict heat transfer coefficient and pressure drop which are necessary on design of the heat exchanger were proposed.
Boundary-Layer Transition Over Rough Surfaces With Elevated Free-Stream Turbulence
Authors: Roberts S. K. , Yaras M. I.
Published: November 2008

This paper presents experimental results documenting the combined effects of surface roughness and free-stream turbulence level on boundary-layer transition. The experiments were conducted on a flat surface, upon which a pressure distribution similar to those prevailing on the suction side of turbine blades was imposed. The test matrix consists of four variations in the roughness conditions, at each of three free-stream turbulence levels and two flow Reynolds numbers. The ranges of these parameters considered in the study, which are typical of low-pressure turbines, resulted in both attached-flow and separation-bubble transition. The experimental results show that the transition inception location remains sensitive to surface roughness with increasing free-stream turbulence. Through spectral analysis of the velocity signals, this is shown to be due to earlier appearance and larger amplitude of Tollmien-Schlichting instability waves in both attached-flow and separation-bubble transition. In the test cases in which a separation-bubble is present, the rate of transition is seen to be insensitive to surface roughness, and only mildly sensitive to free-stream turbulence.
Large Eddy Simulation of Flow and Heat Transfer in a Rectangular Channel With Crossed Angled Ribs
Authors: Takahashi Toshihiko , Watanabe Kazunori
Published: November 2008

Characteristics of fully developed flow and heat transfer in stationary rectangular channels with two opposite ribbed walls, adopted for internal cooling of a gas turbine blade, were investigated by using Large Eddy Simulation (LES). Effect of aspect ratio of the channel cross section on the flow and thermal fields in the channels with crossed, 60-deg. angle ribs was studied. The thermo-flow field in the stationary rectangular channels with the crossed angled ribs has a single secondary swirl in the cross sections, which exhibits a basic pattern for convection in the channels with the angled ribs. The aspect ratio was varied from 0.5 to 2.0. The rib height-to-hydraulic diameter and the rib pitch-to-height ratio were kept at 0.075 and 11.547, respectively. Calculations were conducted for Reynolds number based on the hydraulic diameter at around 50,000 and 120,000. The present calculations showed that formation of rib induced separation vortex varies with the channel aspect ratio. The change in the vortex formation has an influence on augmentation of friction and heat transfer. Current correlations for friction and heat transfer agreed reasonably with previous experiments.