bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Re-Attachment Along the Surface of a Low Pressure Turbine Blade
Authors: Schobeiri M. T. , O¨ztu¨rk B.
Published: November 2008

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.
A Selective Assembly Method to Reduce the Impact of Blade Flow Variability on Turbine Life
Authors: Sidwell Vince , Darmofal David
Published: November 2008

A selective assembly method is proposed that decreases the impact of blade passage manufacturing variability on the life of a row of cooled turbine blades. The method classifies turbine blades into groups based on the effective flow areas of the blade passages, then a row of blades is assembled exclusively from blades of a single group. A simplified classification is considered in which blades are divided into low-flow, nominal-flow, and high-flow groups. For rows assembled from the low-flow class, the blade plenum pressure will tend to rise and the individual blade flows will be closer to the design intent than for a single low-flow blade in a randomly-assembled row. Since the blade metal temperature is strongly dependent on the blade flow, selective assembly can lower the metal temperature of the lowest-flowing blades and increase the life of a turbine row beyond what is possible from a randomly-assembled row. Furthermore, the life of a nominal-flow or high-flow row will be significantly increased (relative to a randomly-assembled row) since the life-limiting low-flow blades would not be included in these higher-flowing rows. The impact of selective assembly is estimated using a model of the first turbine rotor of an existing high-bypass turbofan. The oxidation lives of the nominal-flow and high-flow blade rows are estimated to increase approximately 50% and 100% compared to randomly-assembled rows, while the life of the low-flow rows are the same as the randomly-assembled rows. Alternatively, selective assembly can be used to increase turbine inlet temperature while maintaining the maximum blade metal temperatures at random-assembly levels. For the nominal-flow and high-flow classes, turbine inlet temperature increases are estimated to be equivalent to the turbine inlet temperature increases observed over several years of gas turbine technology development.
Leakage and Power Loss Test Results for Competing Turbine Engine Seals
Authors: Proctor Margaret P. , Delgado Irebert R.
Published: November 2008

Advanced brush and finger seal technologies offer reduced leakage rates over conventional labyrinth seals used in gas turbine engines. To address engine manufactures’ concerns about the heat generation and power loss from these contacting seals, brush, finger, and labyrinth seals were tested in the NASA High Speed, High Temperature Turbine Seal Test Rig. Leakage and power loss test results are compared for these competing seals for operating conditions up to 922 K (1200 °F) inlet air temperature, 517 KPa (75 psid) across the seal, and surface velocities up to 366 m/s (1200 ft/s).
Investigation of Three-Dimensional Stress Fields and Slip Systems for FCC Single Crystal Superalloy Notched Specimens
Authors: Arakere Nagaraj K. , Siddiqui Shadab , Magnan Shannon , Ebrahimi Fereshteh , Forero Luis E.
Published: November 2008

Metals and their alloys, except for a few intermetallics, are inherently ductile, i.e. plastic deformation precedes fracture in these materials. Therefore, resistance to fracture is directly related to the development of the plastic zone at the crack tip. Recent studies indicate that the fracture toughness of single crystals depends on the crystallographic orientation of the notch as well as the loading direction. In general, the dependence of crack propagation resistance on crystallographic orientation arises from the anisotropy of (i) elastic constants, (ii) plastic deformation (or slip), and (iii) the weakest fracture planes (e.g. cleavage planes). Because of the triaxial stress state at the notch tips, many slip systems that otherwise would not be activated during uniaxial testing, become operational. The plastic zone formation in single crystals has been tackled theoretically by Rice and his co-workers [10–14] and only limited experimental work has been conducted in this area. The study of the stresses and strains in the vicinity of a FCC single crystal notch tip is of relatively recent origin. We present experimental and numerical investigation of 3D stress fields and evolution of slip sector boundaries near notches in FCC single crystal PWA1480 tension test specimens, and demonstrate that a 3D linear elastic finite element model that includes the effect of material anisotropy is shown to predict active slip planes and sectors accurately. The slip sector boundaries are shown to have complex curved shapes with several slip systems active simultaneously near the notch. Results are presented for surface and mid-plane of the specimens. The results demonstrate that accounting for 3D elastic anisotropy is very important for accurate prediction of slip activation near FCC single crystal notches loaded in tension. Results from the study will help establish guidelines for fatigue damage near single crystal notches.
Strain-Life Assessment of Grainex Mar-M 247 for NASA’s Turbine Seal Test Facility
Authors: Delgado Irebert R. , Halford Gary R. , Steinetz Bruce M. , Rimnac Clare M.
Published: November 2008

NASA’s Turbine Seal Test Facility is used to test air-to-air seals for use primarily in advanced jet engine applications. Combinations of high temperature, high speed, and high pressure limit the disk life, due to the concern of crack initiation in the bolt holes of the Grainex Mar-M 247 disk. The primary purpose of this current work is to determine an inspection interval to ensure safe operation. The current work presents high temperature fatigue strain-life data for test specimens cut from an actual Grainex Mar-M 247 disk. Several different strain-life models were compared to the experimental data including the Manson-Hirschberg Method of Universal Slopes, the Halford-Nachtigall Mean Stress Method, and the Modified Morrow Method. The Halford-Nachtigall Method resulted in only an 18% difference between predicted and experimental results. Using the experimental data at a −99.95% prediction level and the presence of 6 bolt holes it was found that the disk should be inspected after 665 cycles based on a total strain of 0.5% at 649°C.
Thermoacoustic Stability of Quasi-One-Dimensional Flows: Part I — Analytical and Numerical Formulation
Authors: Prasad Dilip , Feng Jinzhang
Published: November 2008

A numerical method is developed for transient linear analysis of quasi-one-dimensional thermoacoustic systems, with emphasis on stability properties. This approach incorporates the effects of mean flow variation as well as self-excited sources such as the unsteady heat release across a flame. Working in the frequency domain, the perturbation field is represented as a superposition of local wave modes, which enables the linearized equations to be integrated in space. The problem formulation is completed by specifying appropriate boundary conditions. Here, we consider impedance boundary conditions as well as those relevant to choked and shocked flows. For choked flows, the boundary condition follows from the requirement that perturbations remain regular at the sonic point, while the boundary conditions applicable at a normal shock are obtained from the shock jump conditions. The numerical implementation of the proposed formulation is described for the system eigenvalue problem, where the natural modes are sought. The scheme is validated by comparison with analytical and numerical solutions.
Turbine Heat Transfer and Aerodynamic Measurements and Predictions for a 1.5 Stage Configuration
Authors: Chana Kam S. , Singh Udai K. , Povey Thomas
Published: November 2008

This paper considers the surface heat transfer rate to, and aerodynamics of, a 1.5 stage turbine — a high pressure (HP) turbine stage followed by an intermediate pressure (IP) vane. Unsteady interactions arising from the relative motions of vane/blade rows are examined. The IP vane was of structural type, and was designed with a vane count of 26. Measurements of time-mean heat transfer and aerodynamics are seldom performed in 1.5 stage turbines, because of the necessary complexity of the experimental setup required for such investigations. This paper presents both steady and unsteady measurements conducted in an engine-size research turbine, operated at engine-representative non-dimensional conditions. Measurements are compared to the predictions from a three-dimensional, viscous, non-linear, time accurate flow solver. An unstructured grid was used, and, by using the Erdos direct storage technique, the code was extended to allow for non-integer vane/blade pitch ratios. A prediction was performed in which all three vane/blade rows were simultaneously modelled. The measured and predicted unsteady surface heat transfer rates for the IP vane and HP rotor blade were in good agreement, and demonstrated that the interactive effects arising from the relative motion of these components were significant.
Application of a Split-Fiber Probe to Velocity Measurement in the NASA Research Compressor
Authors: Lepicovsky J.
Published: November 2008

A split-fiber probe was used to acquire unsteady data in a research compressor. The probe has two thin films deposited on a quartz cylinder 200 μm in diameter. A split-fiber probe allows simultaneous measurement of velocity magnitude and direction in a plane that is perpendicular to the sensing cylinder. A calibration method was devised for a split-fiber probe, and a new algorithm was developed to decompose split-fiber probe signals into velocity magnitude and direction. The algorithm is based on the minimum value of a merit function that is built over the entire range of flow velocities for which the probe was calibrated. The new decomposition scheme is fast and robust. The split-fiber probe performance and signal decomposition was first verified in a free-jet facility by comparing the data from three thermo-anemometric probes, namely a single-wire, a single-fiber, and the split-fiber probe. The wire and single-fiber probe diameters are 5 μm and 70 μm, respectively. All three probes performed extremely well as far as the velocity magnitude was concerned. However, there are differences in the peak values of measured velocity unsteadiness in the jet shear layer. The single-wire probe indicates the highest unsteadiness level, followed closely by the split-fiber probe. The single-fiber probe indicates a noticeably lower level of velocity unsteadiness. Experiments in the NASA Low Speed Axial Compressor facility revealed similar results. The mean velocities agree within 2% of the measured velocity magnitude. The differences in the measured velocity unsteadiness are similar to the case of a free jet. A reason for these discrepancies is in the different frequency response characteristics of probes used. It follows that the single-fiber probe has the slowest frequency response. In summary, the split-fiber probe worked reliably during the entire program. The acquired data averaged in time followed closely data acquired by conventional pneumatic probes. Despite small differences among all probes used, that still need to be explained, it is believed that data acquired by the split-fiber probe can be used reliably to analyze unsteady flow phenomena in the NASA Low Speed Axial Compressor.
Multi-Fidelity Simulation of a Turbofan Engine With Results Zoomed Into Mini-Maps for a Zero-D Cycle Simulation
Authors: Turner Mark G. , Reed John A. , Ryder Robert , Veres Joseph P.
Published: November 2008

A Zero-D cycle simulation of the GE90-94B high bypass turbofan engine has been achieved utilizing mini-maps generated from a high-fidelity simulation. The simulation utilizes the Numerical Propulsion System Simulation (NPSS) thermodynamic cycle modeling system coupled to a high-fidelity full-engine model represented by a set of coupled 3D computational fluid dynamic (CFD) component models. Boundary conditions from the balanced, steady-state cycle model are used to define component boundary conditions in the full-engine model. Operating characteristics of the 3D component models are integrated into the cycle model via partial performance maps generated from the CFD flow solutions using one-dimensional meanline turbomachinery programs. This paper high-lights the generation of the highpressure compressor, booster, and fan partial performance maps, as well as turbine maps for the high pressure and low pressure turbine. These are actually “mini-maps” in the sense that they are developed only for a narrow operating range of the component. Results are compared between actual cycle data at a take-off condition and the comparable condition utilizing these mini-maps. The mini-maps are also presented with comparison to actual component data where possible.
Aerodynamic-Aeroacoustic Investigation of Rotating Stall in Conventional and Skewed Rotors
Authors: Cai N. , Benaissa A. , Allan W. D.
Published: November 2008

An experimental investigation and a numerical simulation of aerodynamic-aeroacoustic performance of an axial-flow fan at the rotating stall condition are reported in this paper. The wake profiles of rotors were measured using two-channel, hot wire probes. The Reynolds-averaged Navier-Stokes equations of the flow field were numerically solved. The two rotors studied included a conventional and a skewed-swept rotor with the objective being to determine the influence of skew and sweep on the sound levels and rotating stall characteristic. In both cases, a single stall cell was observed in fully developed stall conditions. The experimental results showed a significant difference in stall cell hysteresis, size, circumference and spanwise position, and cell propagation velocity between the two rotors. The stall cell in the skewed rotor propagated faster than the one in the conventional rotor. A fully developed stall cell was observed near the mid-span in the skewed rotor whereas it was situated near the hub in the conventional rotor. The noise level in the skewed rotor at the stall condition was more than 2 dBA lower than in the conventional rotor. Sound frequency spectra were obtained and analyzed in the near and far fields between the skewed and conventional radial rotors at rotating stall point and at design point. Significant differences in the sound directivity between the two types of rotors at steady and unsteady operating conditions were observed throughout the measured sound region. Results showed that the numerical models predicted at the rotating stall condition with good accuracy.
Probabilistic Analysis of Geometric Uncertainty Effects on Blade-Alone Forced Response
Authors: Brown Jeffrey M. , Grandhi Ramana V.
Published: November 2008

This paper investigates the effect of manufacturing variations on the blade-alone forced response of a transonic low aspect ratio fan. A simulated set of coordinate measurement machine measurements from a single rotor, representative of actual manufacturing variations, are used to investigate geometric effects. A reduced order model is developed to rapidly solve for the forced response and is based on eigensensitivity analysis and dynamic response mode superposition. An approximation error analysis is conducted to quantify accuracy of the new tool and errors between approximate and full finite element analysis solutions are shown to be small for low order modes with some high order modes having moderate error. A study of the simulated measured blade results show a significant amount of forced response variation along the leading edge of the airfoil. Statistics from this simulated measured rotor are used with Monte Carlo sampling to generate random blades realizations that are solved with the reduced order model. This procedure allows the prediction of the variation across an entire fleet of blades from a small sample of blades. The large variations predicted, up to 40%, could have a significant impact of the blade design process including the procedures to account for foreign object damage damage tolerance, how non-intrusive stress measurement systems are used, and how mistuning prediction algorithms are validated.
An Experimental Investigation of Contoured Leading Edges for Secondary Flow Loss Reduction
Authors: Becz Sandor , Majewski Mark S. , Langston Lee S.
Published: November 2008

Experimental results are presented which provide mass averaged total pressure loss coefficient measurements for three different turbine airfoil leading edge configurations. A baseline (Langston) configuration, a leading edge bulb, and a leading edge fillet were tested in a large-scale, low aspect ratio, high turning linear cascade. Results show that while the fillet geometry reduced overall loss by approximately 7%, the bulb did not exhibit a loss reduction. For the fillet, overall turning was slightly reduced, while for the bulb turning increased slightly. Thus, the bulb shows potential for increasing airfoil loading without an associated loss penalty. Contour plots of total pressure loss coefficient and vorticity are presented for all geometries and the major differences between each are discussed. Through investigation of pitch averaged loss profiles it is found that the area of greatest reduction differs between the bulb and fillet, leading to the possibility that the mechanisms through which each is affecting the flow may be different. This provides hope that the best features of each may potentially be combined to determine an optimum shape for secondary flow loss reduction.
Introduction of Residual Stresses to Enhance Fatigue Performance in the Initial Design
Authors: Preve´y Paul , Jayaraman N. , Ravindranath Ravi
Published: November 2008

High cycle fatigue (HCF) performance of turbine engine components has been known for decades to benefit from compressive surface residual stresses introduced through shot peening. However, credit for the fatigue benefits of shot peening has not been taken into account in the design of components. Rather shot peening has been used primarily to safe guard against HCF damage initiation. Recently, laser shock processing (LSP) and low plasticity burnishing (LPB) have been shown to provide spectacular fatigue and damage tolerance improvement by introducing deep (through-thickness) compression in critical areas. Until now, the fatigue benefits of these new surface treatments have been introduced during repair to improve an existing design. The present paper describes a design methodology and testing protocol* to take appropriate credit for the introduction of beneficial residual stresses into a component design to achieve optimal fatigue performance. A detailed design protocol has been developed that relates the introduction of a residual stress distribution using LPB for targeted HCF performance. This design protocol is applied to feature specimens designed to simulate the fatigue conditions at the trailing edge of a 1st stage low pressure compressor vane to provide optimal trailing edge damage tolerance. The use of finite element modeling, linear elastic fracture mechanics, and x-ray diffraction documentation of the residual stress field to develop LPB processing parameters is described. A novel adaptation of the traditional Haigh diagram to estimate the compressive residual stress magnitude and distribution to achieve optimal fatigue performance is described. Fatigue results on vane-edge feature samples are compared with analytical predictions provided by the design methodology. The potential for designing reduced section thickness of structural components leading to weight savings is discussed.
Ceramic Matrix Composite Vane Subelement Fabrication
Authors: Calomino Anthony , Verrilli M.
Published: November 2008

Vane subelements were fabricated from a silicon carbide fiber reinforced silicon carbide matrix (SiC/SiC) composite and were coated with an environmental barrier coating (EBC). In order to address realistic critical design features of a turbine airfoil, the vane subelement cross section was derived from an existing production aircraft engine vane. A new fabrication technique has been developed at NASA Glenn Research Center that enables ceramic composite vanes to be constructed using stoichiometric SiC fiber in the form of a two dimensional cloth. A unique woven cloth configuration was used to provide a sharp trailing edge with continuous fiber reinforcement. Fabrication of vanes with a sharp trailing edge was considered to be one of the more challenging features for fabricating a ceramic composite vane. The vanes were densified through the chemical vapor infiltration/slurry cast/silicon melt-infiltration process. Both NDE inspection and metallographic examinations revealed that the final as-fabricated composite quality of the vanes was consistent with that typically obtained for the same composite material fabricated into flat panels. Two vane configurations were fabricated. One consisted of a thin wall (1.5 mm) shell with a continuously reinforced sharp trailing edge. The second vane configuration included a reinforcing web bridging the pressure and suction-side vane walls and the same reinforced sharp trailing edge. This paper will discuss the vane fabrication and characterization efforts.
Experimental Reduction of Transonic Fan Forced Response by IGV Flow Control
Authors: Bailie S. Todd , Ng Wing F. , Copenhaver William W.
Published: November 2008

The main contributor to the high-cycle fatigue of compressor blades is the response to aerodynamic forcing functions generated by an upstream row of stators or inlet guide vanes. Resonant response to engine order excitation at certain rotor speeds can be especially damaging. Studies have shown that flow control by trailing edge blowing (TEB) can reduce stator wake strength and the amplitude of the downstream rotor blade vibrations generated by the unsteady stator-rotor interaction. In the present study, the effectiveness of TEB to reduce forced fan blade vibrations was evaluated in a modern single-stage transonic fan rig. Data was collected for multiple uniform full-span TEB conditions over a range of rotor speed including multiple modal resonance crossings. Resonant response sensitivity was generally characterized by a robust region of strong attenuation. The baseline resonant amplitude of the first torsion mode, which exceeded the endurance limit on the critical blade, was reduced by more than 80% with TEB at 1.0% of the total rig flow. The technique was also found to be modally robust; similar reductions were achieved for all tested modal crossings, including more than 90% reduction of the second LE bending response using 0.7% of the rig flow.
Inlet Air Salt Concentration Detection on U.S. Navy Ship Service Gas Turbine Generator Sets
Authors: Caguiat Daniel E. , Connor Jennifer , Duckless Edward , DeCorso Richard J.
Published: November 2008

The Naval Surface Warfare Center, Carderock Division (NSWCCD) Gas Turbine Emerging Technologies Code 9334 has been working, in conjunction with Vibro-Meter Incorporated, to evaluate and further develop the Vibro-Meter Flame Contaminant Detector (FCD). This device has been used on various commercial gas turbine platforms to quantify the level of sodium entrained in fuel. The FCD consists of a spectrometer device, fiber optic cabling, and a lens assembly, which is mounted in an open combustor port. The combustion flame is continuously monitored for sodium wavelength intensity during gas turbine operation. The FCD was initially of interest to NSWCCD for use in fuel filtration system health monitoring. However, based on known Ship Service Gas Turbine Generator (SSGTG) hot section corrosion issues, it was believed that the FCD would also serve as useful tool for quantifying inlet air salt concentration. Testing was performed at the Philadelphia Land Based Engineering Site in 2003. It was determined that the FCD was able to detect salt concentrations as low as 0.003 parts per million. Initial indications are that airborne salt can be differentiated from fuel entrained salt based on continuous vs. intermittent sodium levels. Continuing efforts are centered on optimizing the existing FCD algorithm to properly differentiate between and quantify inlet air and fuel-entrained salt concentration.
Cumulative Damage Mechanics: Characterization, Modeling, and Interpretation of Progressive Failure in Ceramics and Composites
Authors: Jenkins Michael G. , Labossie`re Paul E. , Salem Jonathan A.
Published: November 2008

Ceramic matrix composites (CMCs) have evolved to exhibit inherent damage tolerance through nonlinear energy absorption mechanisms while retaining the desirable attributes of their monolithic structural ceramic counterparts. Mathematical (analytic and numeric) models together with experimental measurements of this damage absorption have aided in understanding the thermomechanical behavior of CMCs. This understanding has led to improved test methods, better predictive modeling of material behavior, appropriate processing methods, and finally novel design methodologies for implementing CMCs. In this paper, background on CMC damage is presented, damage measurement and damage models are discussed and finally probabilistic aspects of constituent materials that can be used to illustrate the cumulative damage behavior of CMCs are described.
Effects of Hot Streaks on Adiabatic Effectiveness for a Film Cooled Turbine Vane
Authors: Varadarajan Krishnakumar , Bogard David G.
Published: November 2008

Turbine guide vanes in gas turbine engines are typically subjected to localized “hot streaks” emanating from the combustor. This experimental program examined how these hot streaks affect the film cooling performance for these vanes. Adiabatic effectiveness tests were conducted on the showerhead and suction side regions of the vane. Particular attention was placed on how to scale that adiabatic effectiveness data obtained with a hot streak to correctly predict the adiabatic effectiveness. Thermal field measurements were made to determine the temperature gradients for the hot streak near the wall. These experiments showed that the effect of the hot streak on the adiabatic effectiveness could be accounted for by using an “adjusted” mainstream temperature equal to the hot streak temperature at the wall of the vane.
Wet Compression System Stability Analysis: Part II — Simulations and Bifurcation Analysis
Authors: Zheng Qun , Li Minghong
Published: November 2008

In this part, wet compression system stability performances are theoretical analyzed with bifurcation theory, and a basic wet compression system stability bifurcation model is established. Numerical simulations are carried out with MATLAB SIMULINK to verify the wet compression effects on the stabilities of compression system. The results indicate that wet compression can not only restrain the rotating stall, but also can diminish the surge, except for some extreme mismatching cases. Therefore, wet compression can be another useful method to help improving the stability performance and increase the stable working range of gas turbine.
Calculation of the Mixed-Out State in Turbomachine Flows
Authors: Prasad Anil
Published: November 2008

A systematic and rational methodology for the calculation of an equilibrium state from an initial non-uniform flow field, is presented with particular emphasis on the underlying assumptions and their attendant justifications. The imposed conservation criteria that are used to define a final state from the initial one depend on the coordinate system and flow configuration being analyzed. The imposition of these criteria for flow in parallel-walled annular ducts defines a state of complete (mechanical and thermal) equilibrium, for which radial profiles of the velocity components, static pressure and temperature assume a specific form for a perfect gas. A robust method for solving the system of equations that define the state of complete equilibrium (or mixed-out state) is presented using an effcient algorithm. The procedure is applied to the swirling flow exiting an isolated transonic compressor, and comparisons are made with other available methods of averaging flow fields.
Improving Rough Cutting Efficiency for Machining of Impellers
Authors: Tsay Der-Min , Chen Chien-Wen
Published: November 2008

A procedure that can be used to generate rough cutting tool paths with minimized variations of material removal rates (MRRs) is developed for 5-axis ball end milling of centrifugal compressor impellers. Based on the geometric model of impellers, the detailed processes in finding the cutter contact (CC) points with equal spacing for step interval between two adjacent tool paths and a constant depth between two neighboring cutting layers are presented. The developed system can considerably improve productivity and lower production costs in rough machining since the time required can be reduced by minimizing the waste tool paths. Simulation and machining tests by a 5-axis computer numerically controlled (CNC) milling machine are performed to illustrate the procedure and its advantages.
Maximum Amplification of Blade Response Due to Mistuning in Multi-Degree-of-Freedom Blade Models
Authors: Xiao Bing , Rivas-Guerra Alejandro J. , Mignolet Marc P.
Published: November 2008

This paper focuses on the determination and study of the maximum amplification of the steady state forced response of bladed disks due to mistuning. A general multi-degree-of-freedom dynamic model is adopted for each blade/disk sector and optimization techniques are used to maximize a weighted quadratic norm of the response of the degrees-of-freedom of blade 1 (overall response of blade 1). First, a mathematical optimization effort is conducted in which the resonant mistuned mode shape(s) (1 for engine orders 0 and N/2 where N is the number of blades, 2 otherwise) is selected to maximize the overall response of blade 1. The form of these optimum mode shapes is derived for all weighting matrices. The specific mode shapes are also derived for two particular weights the first one of which depends on the tuned bladed disk mass matrix and for which the overall response is akin to the kinetic energy. A closed form solution is also derived when the analysis focuses solely on the response of a specific degree-of-freedom or a specific stress component. In these cases, the ratio of the corresponding overall response to its tuned counterpart, i.e. the amplification factor, is found to be the product of two terms. The first one is an amplification obtained by tuned variations of the blade properties/mode shapes and thus is referred to as the modal amplification factor. The second term is an amplification obtained by proper mistuning. Interestingly, the modal amplification factor may take on very large values while a representative value of the largest mistuned factor is often the Whitehead limit of (1+N)/2 as in the single-degree-of-freedom per blade model. The above formulation and results are readily extended to the optimization of the blade alone response (as opposed to blade and disk sector). Numerical optimization efforts were also undertaken on both a two-degree-of-freedom per blade disk model and a 24-blade blisk reduced order model. The results of these computational efforts not only confirm the assumptions and findings of the theoretical developments but also demonstrate that substantially larger amplification factors can be obtained with a general natural frequency mistuning as opposed to Young’s modulus mistuning. Finally, an amplification due to mistuning (no tuned amplification) slightly larger than the Whitehead limit was obtained with relative variations in blade alone frequencies less than 0.5%.
Fuel Injection and Emissions Characteristics of a Commercial Microturbine Generator
Authors: Phi V. M. , Mauzey J. L. , McDonell V. G. , Samuelsen G. S.
Published: November 2008

Microturbine generators (MTGs) offer an attractive alternative for addressing future demand for electrical power. However, increasingly stringent emission regulations such as those found in California pose a major technical challenge that these devices must overcome if they are to make significant market penetrations. In the context of these regulations, the present study characterizes the exhaust emissions and mixing capability of a commercial MTG and assesses (1) the ability of this device to meet future emissions regulatory requirement and (2) the extent to which mixing can be used to reduce emissions. The results establish that, for this MTG, both NOx and CO are minimized for 80–100% load. Kinetics and CFD analysis illustrate how NOx emissions are affected by local equivalence ratios and how fuel staging and local quenching impact CO emissions. Measured injector premixing levels indicate a standard deviation of less than 4% relative to the mean. Subsequent analysis using a well-stirred reactor approach suggests a maximum of a 10% reduction in NOx could be achieved with further improved premixing.
An Impact of Environmental Disturbances on Combined Cycle Power Plant Control
Authors: Domachowski Zygfryd , Dzida Marek
Published: November 2008

Combined cycle power plants operate at thermal efficiency approaching 60 percent. In the same time their performance presents several problems that have to be addressed. E.g. gas turbines are very sensitive to backpressure exerted on them by the heat recovery steam generators as well as to ambient pressure and temperature.
Understanding Royal Navy Gas Turbine Sea Water Lubricating Oil Cooler Failures When Caused by Microbial Induced Corrosion (‘SRB’)
Authors: Bolwell Richard
Published: November 2008

A managed programme to review engine failures and take necessary preventative measures has been in place successfully in the Royal Navy since the introduction of gas turbines into service in the 1970’s. One of the more prominent failure mechanisms with the Tyne RM1C and Spey SM1A engines has been the degradation of main line bearings accounting for 25 percent of all engines rejected. Historically, since the first recorded incident in March 1987, the failures pointed to poor performance of the bearings themselves. However, maintenance studies and recent analysis indicates that a vast proportion have occurred through previously unidentified chloride corrosion as a result of contamination of the lubricating oil system with salt water from the seawater lubricating oil cooler (SWLO cooler). Despite joint ownership of both engine variants with the Royal Netherlands Navy, there was no clear evidence until about five years ago to suggest why tube perforation was occurring. Indeed, the fact that failures have only occurred in Royal Navy service is an interesting twist to the problem. This paper summarises the phenomenon of SWLO cooler corrosion caused by Microbial Induced Corrosion (principally Sulphate Reducing Bacteria – SRB). It highlights the conditions in which SRB occurs along with demonstrated prevention in Royal Navy gas turbine service through the combined efforts of maintenance and development of a new titanium tubestack. The fault finding and remedial recovery experience may well be of interest to operators of marine gas turbines, both naval and commercial, who use tube type heat exchangers, especially when operating or undertaking work in estuarial waters and non tidal basins or when undertaking littoral duties. This is a practical view of the issue from an operators perspective and whilst utilising a wealth of research and technical data available on the subject, it relates the issues at hand to the particular corrosion problem and is not intended as an introduction into organic chemistry.
Monitoring the Approach to the Surge Line of a 4-Stage Transonic Compressor Based on Cepstral-Analysis
Authors: Methling Frank-O. , Kuss Jens
Published: November 2008

Current research concerned with the aerodynamic instability of compressors aims at an extension of the operating range of the compressor towards decreased mass flow. In practice a safety margin is maintained between operating point and surge line to prevent the compressor from going into stall and surge. In this paper the behavior of a 4-stage transonic axial compressor before entering aerodynamic instability is investigated using the well-known Fourier-Transform as well as the Cepstral-Analysis. All results are based on measurements of the unsteady static wall pressure of only one sensor in front of the first rotor. The analysis of the static pressure signals using the Fast Fourier Transform shows for this compressor, that peripheral disturbances (modal waves) prior to aerodynamic instability can only be identified in a small speed range close to nominal speed (at 95%). At lower speeds (50% to 80% of nominal speed) the investigated compressor flow enters instability by spike-type stall. The intensity of rotating disturbances did not indicate unambiguously the approach to the surge line. As modal waves occurred only in the range of high compressor speed before entering aerodynamic instability, the intensity of rotating disturbances increased only in the said speed range. The Cepstral-Analysis shows that the quefrency band (computed cepstral time range) corresponding to the blade passing frequency and their higher harmonics decreases when approaching the surge line. On the basis of these results a parameter based on high-speed measurements is presented which is an indicator for the current compressor operating point. A compressor monitoring based on this parameter is able to cover the entire speed range as well as the entire mass flow range of the compressor. The method works reliably and independent of the mechanism of stall inception i.e. for spike-type stall as well as for modal waves.
Thermal Performance of Angled, V-Shaped, and W-Shaped Rib Turbulators in Rotating Rectangular Cooling Channels (AR = 4:1)
Authors: Wright Lesley M. , Fu Wen-Lung , Han Je-Chin
Published: November 2008

An experimental study was performed to measure the heat transfer distributions and frictional losses in rotating ribbed channels with an aspect ratio of 4:1. Angled, discrete angled, V-shaped, and discrete V-shaped ribs were investigated, as well as the newly proposed W-shaped and discrete W-shaped ribs. In all cases, the ribs are placed on both the leading and trailing surfaces of the channel, and they are oriented 45° to the mainstream flow. The rib height-to-hydraulic diameter ratio (e/D) is 0.078, and the rib pitch-to-height ratio (P/e) is 10. The channel orientation with respect to the direction of rotation is 135°. The range of flow parameters includes Reynolds number (Re = 10000–40000), rotation number (Ro = 0.0–0.15), and inlet coolant-to-wall density ratio (Δρ/ρ = 0.12). Both heat transfer and pressure measurements were taken, so the overall performance of each rib configuration could be evaluated. It was determined that the W-shaped and discrete W-shaped ribs had the superior heat transfer performance in both non-rotating and rotating channels. However, these two configurations also incurred the greatest frictional losses while the discrete V-shaped and discrete angled ribs resulted in the lowest pressure drop. Based on the heat transfer enhancement and the pressure drop penalty, the discrete V-shaped ribs and the discrete W-shaped ribs exhibit the best overall thermal performance in both rotating and non-rotating channels. These configurations are followed closely by the W-shaped ribs. The angled rib configuration resulted in the worst performance of the six configurations of the present study.
Analysis of Sludge and Coal Co-Gasification Power Plant
Authors: Wang Xun , Xiao Yunhan
Published: November 2008

Co-gasification of sludge with coal provides a prospective way to sludge to power generation. Sludge without moisture removed will be mixed directly with coal and then the mixture is fed to gasifier. Moisture in sludge acts as the role of gasification agent. There is no need to inject steam into gasifier. Both the thermal efficiency and economics of power output could be improved. In the present work, we analyzed the influence of mixing ratio of sludge and sludge moisture on syngas composition, power generation capability and efficiency. These works provided preliminary information about sludge and coal co-gasification power plant.
Sensor Validation and Recovery for Combustion Turbines in Electrical Power Generation
Authors: Schoeller Michael H. , Orsagh Rolf , Roemer Michael , Angello Leonard C.
Published: November 2008

Development of a comprehensive combustion turbine health management system will play a critical role in reducing the cost of electricity by improving reliability, availability, and maintainability. The real-time health management technologies under development use a combination of probabilistic and artificial intelligence-based tools to assess both thermodynamic and mechanical health of combustion turbines. These technologies include sensor validation, performance diagnostics and prognostics, vibration diagnostics, and critical component remaining useful life assessments. Sensor validation is an important front-end of the health management system that checks the integrity of sensed data before it is passed to the diagnostic and prognostic modules. The sensor validation software utilizes a combination or fusion of neural network model-based and generic signal-processing based approaches to ensure the highest possible sensor fault detection confidence with minimal false alarms. In the event that a gas path sensor fault is detected, neural network models are used to calculate proxy or “recovered” signal values that allow diagnostic and component life assessments until the fault is corrected. The sensor validation and recovery module is demonstrated on a GE Frame 7FA application.
Simulation of the Break-Up of a Liquid Jet in Crossflow at Atmospheric Conditions
Authors: Madabhushi Ravi K. , Leong May Y. , Hautman Donald J.
Published: November 2008

The break-up of a liquid jet in crossflowing air-stream has been numerically simulated at atmospheric pressure and temperature conditions using a Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) code. The break-up model simulates the effects of jet bending, flattening and penetration prior to column fracture, droplet secondary break-up due to aerodynamic forces, changes in droplet drag due to distortion, and droplet dispersion due to gas phase turbulence and break-up process. Results from the calculations are compared with the PDI (Phase Doppler Interfometry) measured near-field data (e.g., volumetric flux, droplet size, velocity etc.) for different momentum flux ratios, orifice sizes and crossflow velocities. The agreement between computed results and measured data is generally good, considering the complex physics involved in the atomization process and the interaction between the liquid jet and air.
Thermodynamic Analysis of Intercooled Gas-Steam Combined and Steam Injected Gas Turbine Power Plants
Authors: Yadav R. , Jumhare Sunil Kumar , Kumar Pradeep , Saraswati Samir
Published: November 2008

The current emphasis on the development of gas turbine related power plants such as combined and steam injected is on increasing the plant efficiency and specific work while minimizing the cost of power production per kW and emission. The present work deals with the thermodynamic analysis of intercooled (both surface and evaporative) gas/steam combined and steam injected cycle power plants. The intercooling has a beneficial effect on both plant efficiency and specific work if the optimum intercooling pressure is chosen between 3 and 4. The evaporative intercooler is superior to surface type with reference to plant efficiency and specific work.
Numerical Study of Unsteady Flow in a Centrifugal Pump
Authors: Majidi Kitano
Published: November 2008

Computational Fluid Dynamics analysis has been used to solve the unsteady three-dimensional viscous flow in the entire impeller and volute casing of a centrifugal pump. The results of the calculations are used to predict the impeller/volute interaction and to obtain the unsteady pressure distribution in the impeller and volute casing. The calculated unsteady pressure distribution is used to determine the unsteady blade loading. The calculations at the design point and at two off-design points are carried out with a multiple frame of reference and a sliding mesh technique is applied to consider the impeller/volute interaction. The results obtained show that the flow in the impeller and volute casing is periodically unsteady and confirm the circumferential distortion of the pressure distribution at the impeller outlet and in the volute casing. Due to the interaction between impeller blades and the tongue of the volute casing the flow is characterized by pressure fluctuations, which are strong at the impeller outlet and in the vicinity of the tongue. These pressure fluctuations are died away in the casing as the advancement angle increases. These reduced pressure fluctuations are spread to the discharge nozzle; the pressure fluctuations are also reflected to the impeller inlet and they affect the mass flow rate through the blade passages.