bluuebunny/crossref_metadata_2025 huggingface dataset:
Case History of Pad Fluttering in a Tilting-Pad Journal Bearing
Authors: Pennacchi Paolo , Vania Andrea , Chatterton Steven , Pesatori Emanuel
Published: January 2011

This paper describes in detail the case history of a steam turbine affected by very high level of vibrations. Spectral analysis showed that the turbine shaft exhibited high sub-synchronous harmonic components. The analysis of the machine dynamic behavior, fully described here, allowed excluding some causes of instability like steam whirl or oil whirl/whip. The cause of the abnormal vibration level was ascribed to fluttering phenomena that affected some shoes of one of the “load on pad-type” four-pad tilting-pad journal bearings on which the rotor was supported. This abnormal behaviour was caused by the assembling error of the bottom shoe. Moreover, when approaching the operating speed, it was rather difficult to obtain a suitable convergent oil-film on the lateral pads. This reason, as well as the periodic changes of the journal position inside the bearing caused by the shaft synchronous vibrations due to the turbine residual imbalance, generated the excitation of sub-synchronous vibrations of both pads and shaft.
Gas Turbine Power Augmentation Technologies: A Systematic Comparative Evaluation Approach
Authors: Bianchi M. , Branchini L. , De Pascale A. , Melino F. , Peretto A. , Bhargava R. K. , Chaker M. A.
Published: January 2011

Increasing electric rates in peak demand period, especially during summer months, are forcing power producers to look for gas turbine power augmentation technologies (PATs). One of the major undesirable features of all the gas turbines is that their power output and fuel efficiency decreases with increase in the ambient temperature resulting in significant loss in revenues particularly during peak hours. This paper presents a systematic comparative evaluation approach for various gas turbine power augmentation technologies (PATs) available in the market. The application of the discussed approach has been demonstrated by considering two commonly used gas turbine designs, namely, heavy-duty industrial and aeroderivative. The following PATs have been evaluated: inlet evaporative, inlet chilling, high pressure fogging, overspray, humid air injection and steam injection. The main emphasis of this paper is to provide a detailed comparative thermodynamic analysis of the considered PATs including the main variables, such as ambient temperature and relative humidity, which influence their performance in terms of power boost, heat rate reduction and auxiliary power consumption.
High Temperature Turbine First Stage Vane Wake to Stator Heat Shield Interaction on Outer Casing
Authors: Cochet Magali , Arzel Tanguy , Gritsch Michael , Stephan Bruno , Schnieder Martin
Published: January 2011

Emission reduction and efficiency increase are key targets for gas turbine design. One way to reduce emissions is to get a lower peak temperature, e.g. to replace a parabolic inlet temperature profile protecting edge areas (platforms, heatshields) by a flat temperature profile. Another possibility is to design compact turbines with smaller spacing between blade rows to reduce hot gas wetted areas. Both solutions result in higher thermal load on endwalls. At part interfaces, gaps need to be purged to prevent hot gas ingestion. Cooling air consumption leads to lower efficiencies. A better understanding of the thermal load on endwalls will offer cooling air reduction potential. This paper focuses on the purging gap between first stage vane and the downstream outer diameter heatshield. The requirements for the gap purge air depend on the vane wake. A generic, realistic geometry including the interfacial gap is studied. Computational fluid dynamic is used to understand the flow structure, the film cooling effectiveness and heat transfer coefficient. Film-cooling effectiveness are measured on a cascade bench by a steady-state thermochromic liquid crystal technique. Results are compared to CFD. A parametric study on the influence of blowing ratio is included.
Advanced Open Rotor Performance Modelling for Multidisciplinary Optimization Assessments
Authors: Bellocq Pablo , Sethi Vishal , Cerasi Luca , Ahlefelder Sebastian , Singh Riti , Tantot Nicolas
Published: January 2011

As a consequence of increased stringent engine emission regulations, in a highly competitive market, it has become necessary to explore innovative, economic and environmentally friendly cycles to sustain competitive advantages. Among these innovative cycles, both the geared and the direct drive counter-rotating open rotors, due to their relatively higher propulsive efficiency, have the potential to significantly reduce fuel consumption and emissions relative to conventional high bypass ratio turbofans. A detailed TERA (Technoeconomic Environmental Risk Analysis), multidisciplinary optimisation framework, can be used to optimise both engines and thereby assess their potential as well as quantify their risks on a formal and consistent basis. This technique is based on detailed and rigorous engine performance, aircraft performance, engine geometry, engine weight, noise, gaseous emissions and environmental impact simulation models. No specific performance simulation methodology for counter rotating open rotors is available in the public domain. An innovative technique is introduced, comprising novel models of: • Counter-rotating propellers (including their interaction); • Counter-rotating turbines; • Planetary differential gearboxes. A thorough description of the modelling methodology (with a justification of the main assumptions) of each of these three components is presented and an indication of work in progress is provided. These components are then used to develop direct drive and geared open rotor performance models. The results of steady state design point and off design performance simulations of these two engine models are subsequently presented via two case studies. Some of the differences in the performance of the low pressure system of geared and direct drive open rotors are highlighted. It was observed that the impact of the key OR performance DP parameters is different for the two engines. Consequently the optimal design and control strategies of theses two configurations will differ. The flexibility of the new simulation technique makes it a suitable candidate to perform multi-disciplinary TERA design space exploration and optimisation studies assess and optimise open rotor designs and control strategies in a multidisciplinary framework.
Effects of an Axisymmetric Contoured Endwall on a Nozzle Guide Vane: Adiabatic Effectiveness Measurements
Authors: Thrift A. A. , Thole K. A. , Hada S.
Published: January 2011

Gas turbine designs seek improved performance by modifying the endwalls of nozzle guide vanes in the engine hot section. Within the nozzle guide vanes these modifications can be in the form of an axisymmetric contour as the area contracts from the combustor to the turbine. This paper investigates the effect of axisymmetric endwall contouring on the cooling performance of a film cooled endwall. Adiabatic effectiveness measurements were performed in a planar passage for comparison to a contoured passage whereby the exit Reynolds numbers was matched. For the contoured passage, measurements were performed on both the flat endwall and on the contoured endwall. Fully expanded film cooling holes were distributed on the endwall surface preceded by a two-dimensional slot normal to the inlet axis. Results indicated that the coolant coverage from the upstream leakage slot was spread over a larger area of the contoured endwall in comparison to the flat endwall of the planar passage. Film cooling effectiveness on the flat endwall of the contoured passage showed minimal differences relative to the planar passage results. The contracting endwall of the contoured passage, however, showed a significant reduction with average film cooling effectiveness levels approximately 40% lower than the planar passage at low film cooling flow rates. In the case of all endwalls, increasing leakage and film cooling mass flow rates led to an increase in cooling effectiveness and coolant coverage.
The Impact of CO2 Compressor Characteristics and Integration in Post Combustion Carbon Sequestration Comparative Economic Analysis
Authors: Koopman Aaron A. , Bahr David A.
Published: January 2011

The objective of this paper is to better equip the reader with tools to make relative comparisons between different Carbon Capture and Sequestration (CCS) concepts including various CO2 compressor configurations with more confidence. Methods for analyzing comparative costs for CCS implementation in Coal plants, in terms of Levelized Cost of Electricity (LCOE) and cost per ton CO2 removed or avoided ($/tonCO2) are described. The contribution of compression to LCOE is significant and highly dependent on configuration. Critical inputs required for accurately calculating compressor power and some common errors that significantly impact the results of power consumption can increase the estimated power required by 40%. Sensitivity analyses for critical compressor characteristics are provided. In addition, the impact of energy (heat) integration on the overall economics of the plant can reduce the LCOE penalty. Finally, configuration parameters for systems meeting the national targets of 35% LCOE penalty for CCS costs are explored.
Geometrical Uncertainty and Film Cooling: Fillet Radii
Authors: Montomoli F. , Massini M. , Salvadori S. , Martelli F.
Published: January 2011

This study presents an investigation of the impact of filleted edges variations on heat transfer. In real gas turbines, sharp edges are an approximation, because of manufacturing tolerances and/or geometrical modifications occurring during operation. The value of fillet radius is not exactly known a priori. It can be assumed that a specific radius occurs with a probability following a probabilistic distribution. For this reason, the effect of variation of the filleted edge on internal channel of a film cooling configuration has been studied numerically using an in house solver. The hole exit is fan-shaped and the feeding duct axis and the main stream are perpendicular to each other. A response surface has been generated varying the internal Mach number of coolant and the pressure ratio range between coolant and main gas. Four fillets radii for the internal duct have been analysed, r/D = 0.0–5%. A Gaussian distribution for the fillet radius has been assumed. Using the over mentioned distributions it is possible to obtain the probabilistic functions of the corresponding discharge coefficient, Cd, and adiabatic effectiveness, η. The overall variation of Cd and η can be more than 10% the value without fillet. Furthermore the differences on Cd due to the uncertainties on fillet radius are bigger than those obtained modifying the exit duct shape (i.e. from cylindrical to fanshaped). This paper shows that the effect of variation of fillet radii must be included in numerical simulations. This has direct consequences on LES and DNS simulations, which normally include sharp corners or mean radii. A probabilistic approach must be included in the analysis of the results and the equivalent fillet radius assumed instead.
Computational Predictions of Heat Transfer and Film-Cooling for a Turbine Blade With Non-Axisymmetric Endwall Contouring
Authors: Lynch Stephen P. , Thole Karen A. , Kohli Atul , Lehane Christopher
Published: January 2011

Three-dimensional contouring of the compressor and turbine endwalls in a gas turbine engine has been shown to be an effective method of reducing aerodynamic losses by mitigating the strength of the complex vortical structures generated at the endwall. Reductions in endwall heat transfer in the turbine have been also previously measured and reported in the literature. In this study, computational fluid dynamics simulations of a turbine blade with and without non-axisymmetric endwall contouring were compared to experimental measurements of the exit flowfield, endwall heat transfer and endwall film-cooling. Secondary kinetic energy at the cascade exit was closely predicted with a simulation using the SST k-ω turbulence model. Endwall heat transfer was overpredicted in the passage for both the SST k-ω and realizable k-ε turbulence models, but heat transfer augmentation for a non-axisymmetric contour relative to a flat endwall showed fair agreement to the experiment. Measured and predicted film-cooling results indicated that the non-axisymmetric contouring limits the spread of film-cooling flow over the endwall depending upon the interaction of the film with the contour geometry.
Study of Flow and Convective Heat Transfer in a Simulated Scaled Up Low Emission Annular Combustor
Authors: Sedalor Teddy , Patil Sunil , Ekkad Srinath , Tafti Danesh , Kim Yong , Moon Hee-Koo , Srinivasan Ram
Published: January 2011

Modern Dry Low Emissions (DLE) combustors are characterized by highly swirling and expanding flows that makes the convective heat load on the gas side difficult to predict and estimate. A coupled experimental-numerical study of swirling flow inside a DLE annular combustor model is presented. A simulated scaled up annular combustor shell was designed with a generic fuel nozzle model to create the swirl in the flow. The experiment was simulated with a cold flow and heated combustor walls in a low speed wind tunnel. An infrared camera was used to obtain the temperature distribution along the liner wall. The experiment was conducted at various Reynolds numbers to investigate the effect on the convective heat transfer peak locations. A CFD study performed using FLUENT was used to get a better understanding of high swirl flow field and its effect on the heat transfer on liner walls. Results show that the heat transfer distributions in the annulus have slightly different characteristics for the concave and convex walls. Results also show a much slower drop in heat transfer coefficient enhancement with increasing Reynolds number compared to can combustor liner walls.
An Axial-Flow Compressor for Operation With Humid Air and Water Injection
Authors: Tomita Jesuino Takachi , Bontempo Luciano Porto , Barbosa Joa˜o Roberto
Published: January 2011

The first steps of the turbomachinery design usually rely on numerical tools based on inviscid formulation with corrections using loss models to account for viscous effects, secondary flows, tip clearances and shock waves. The viscous effects are accounted for using semi-empirical correlations specially assembled for the chosen airfoils and range of operating conditions. Fast convergence and good accuracy are required from such design procedures. There are successful models that produce very accurate performance prediction. Among the methodologies commonly used, the streamline curvature (SLC) is used, since those characteristics and the most important properties can be calculated reasonably well at any radial positions, assisting other more complex analysis programs. The SLC technique is, therefore, well suited for the design of axial flow compressors, for reasons like quick access to vital flow properties at the blade edges, from which actions may be taken to improve its performance at the design stage. This work reports the association of a SLC computer program and commercial software for comparison purposes, as well as for grid generation required by a full 3D, turbulent Navier-Stokes computer program, used for flow calculation in the blade passages. Application to a high performance 3-stage axial-flow compressor with Inlet Guide Vane (IGV) demonstrates the methodology adopted. The SLC program is also capable of calculating the compressor performance with humid air and water injection at any axial position along the compressor. The influence of water injection at different axial positions, water particle diameter, temperature of water particles were studied for different humid air conditions. The positions of the evaporating water particles were calculated using their thermo-physical and dynamic properties along the compressor.
Oxy-Fuel Gas Turbine, Gas Generator and Reheat Combustor Technology Development and Demonstration
Authors: Anderson Roger , Viteri Fermin , Hollis Rebecca , Keating Ashley , Shipper Jonathan , Merrill Gary , Schillig Cora , Shinde Sachin , Downs James , Davies Daniel , Harris Mark
Published: January 2011

Future fossil-fueled power generation systems will require carbon capture and sequestration to comply with government green house gas regulations. The three prime candidate technologies that capture carbon dioxide (CO2) are pre-combustion, post-combustion and oxy-fuel combustion techniques. Clean Energy Systems, Inc. (CES) has recently demonstrated oxy-fuel technology applicable to gas turbines, gas generators, and reheat combustors at their 50MWth research test facility located near Bakersfield, California. CES, in conjunction with Siemens Energy, Inc. and Florida Turbine Technologies, Inc. (FTT) have been working to develop and demonstrate turbomachinery systems that accommodate the inherent characteristics of oxy-fuel (O-F) working fluids. The team adopted an aggressive, but economical development approach to advance turbine technology towards early product realization; goals include incremental advances in power plant output and efficiency while minimizing capital costs and cost of electricity [1]. Proof-of-concept testing was completed via a 20MWth oxy-fuel combustor at CES’s Kimberlina prototype power plant. Operability and performance limits were explored by burning a variety of fuels, including natural gas and (simulated) synthesis gas, over a wide range of conditions to generate a steam/CO2 working fluid that was used to drive a turbo-generator. Successful demonstration led to the development of first generation zero-emission power plants (ZEPP). Fabrication and preliminary testing of 1st generation ZEPP equipment has been completed at Kimberlina power plant (KPP) including two main system components, a large combustor (170MWth) and a modified aeroderivative turbine (GE J79 turbine). Also, a reheat combustion system is being designed to improve plant efficiency. This will incorporate the combustion cans from the J79 engine, modified to accept the system’s steam/CO2 working fluid. A single-can reheat combustor has been designed and tested to verify the viability and performance of an O-F reheater can. After several successful tests of the 1st generation equipment, development started on 2nd generation power plant systems. In this program, a Siemens SGT-900 gas turbine engine will be modified and utilized in a 200MWe power plant. Like the 1st generation system, the expander section of the engine will be used as an advanced intermediate pressure turbine and the can-annular combustor will be modified into a O-F reheat combustor. Design studies are being performed to define the modifications necessary to adapt the hardware to the thermal and structural demands of a steam/CO2 drive gas including testing to characterize the materials behavior when exposed to the deleterious working environment. The results and challenges of 1st and 2nd generation oxy-fuel power plant system development are presented.
Evaluation of Alumina-Forming Austenitic Foil for Advanced Recuperators
Authors: Pint Bruce A. , Brady Michael P. , Yamamoto Yukinori , Santella Michael L. , Maziasz Philip J. , Matthews Wendy J.
Published: January 2011

A corrosion- and creep-resistant austenitic stainless steel has been developed for advanced recuperator applications. By optimizing the Al and Cr contents, the alloy is fully austenitic for creep strength while allowing the formation of a chemically-stable external alumina scale at temperatures up to 900°C. An alumina scale eliminates long-term problems with the formation of volatile Cr oxy-hydroxides in the presence of water vapor in exhaust gas. As a first step in producing foil for primary surface recuperators, three commercially cast heats have been rolled to ∼100μm thick foil in the laboratory to evaluate performance in creep and oxidation testing. Results from initial creep testing are presented at 675° and 750°C showing excellent creep strength compared to other candidate foil materials. Laboratory exposures in humid air at 650°-800°C have shown acceptable oxidation resistance. Similar oxidation behavior was observed for sheet specimens of these alloys exposed in a modified 65kW microturbine for 2,871h. One composition that showed superior creep and oxidation resistance has been selected for preparation of a commercial batch of foil.
High Temperature Performance of Cast CF8C-Plus Austenitic Stainless Steel
Authors: Maziasz Philip J. , Pint Bruce A.
Published: January 2011

Covers and casings of small to medium size gas turbines, can be made from cast austenitic stainless steels, including grades such as CF8C, CF3M, or CF10M. Oak Ridge National Laboratory (ORNL) and Caterpillar have developed a new cast austenitic stainless steel, CF8C-Plus, that is a fully-austenitic stainless steel, based on additions of Mn and N to the standard Nb-stabilized CF8C steel grade. The Mn addition improves castability, as well as increasing the alloy solubility for N, and both Mn and N act synergistically to boost mechanical properties. CF8C-Plus steel has outstanding creep-resistance at 600°–900°C, which compares well with Ni-based superalloys like alloys X, 625, 617 and 230. CF8C-Plus also has very good fatigue and thermal fatigue resistance. It is used in the as-cast condition, with no additional heat-treatments. While commercial success for CF8C-Plus has been mainly for diesel exhaust components, this steel can also be considered for gas-turbine and microturbine casings. The purpose of this paper is to demonstrate some of the mechanical properties and update the long-term creep-rupture data, and to present new data on the high-temperature oxidation behavior of these materials, particularly in the presence of water vapor.
Toward Developing a Probabilistic Methodology for Predicting High-Cycle Fretting Fatigue in Aero-Engines
Authors: Chan Kwai S. , Enright Michael P. , Simmons Harold R. , Golden Patrick J. , Chandra Ramesh , Pentz Alan C.
Published: January 2011

This paper reports the results of an investigation focused on identifying the necessary steps required to develop a probabilistic fracture mechanics-based methodology for treating high-cycle fretting fatigue in military engine disks. The current methodology based on finite-element method (FEM) modeling, analytical contact stress analysis, and probabilistic fracture mechanics for analyzing low-cycle fretting fatigue is highlighted first. Incorporation of high-frequency vibratory stress cycles into a composite mission profile containing mostly low-cycle stresses requires the use of the Campbell diagram and the need to identify the mode shape, frequency, and forcing function for blade excitation induced by stator wake, flutter or rotating stall. Forced response computation methods for addressing these phenomena in the literature are reviewed to assess their applicability for integration with a contact stress analysis and a probabilistic fracture mechanics life-prediction code. This overview identifies (1) a promising path for combining vibratory stress computation, FEM structural modeling, contact stress analysis, and probabilistic fracture mechanics for treating high-cycle fretting fatigue at the attachment region of engine disks, and (2) a new approach for treating high-cycle fretting fatigue due to vibratory stresses separately from low-cycle fretting fatigue at various positions of a fan-speed profile.
Momentum and Thermal Boundary Layer Development on an Internally Cooled Turbine Vane
Authors: Dees Jason E. , Bogard David G. , Ledezma Gustavo A. , Laskowski Gregory M. , Tolpadi Anil K.
Published: January 2011

Recent advances in computing power have made conjugate heat transfer simulations of turbine components increasingly popular; however, limited experimental data exists with which to evaluate these simulations. The primary parameter used to evaluate simulations is often the external surface temperature distribution, or overall effectiveness. In this paper, the overlying momentum and thermal boundary layers at various streamwise positions around a conducting, internally cooled simulated turbine vane were measured under low (Tu = 0.5%) and high (Tu = 20%) freestream turbulence conditions. Furthermore, experimental results were compared to computational predictions. In regions were a favorable pressure gradient existed, the thermal boundary layer was found to be significantly thicker than the accompanying momentum boundary layer. Elevated freestream turbulence had the effect of thickening the thermal boundary layer much more effectively than the momentum boundary layer over the entire vane. This data is valuable in understanding the conjugate heat transfer effects on the vane as well as serving as a tool for computational code evaluation.
Optimization of a Gas Turbine Engine Rotor Disc Using Case-Based Reasoning and the GATE Genetic Algorithm
Authors: Dominique S. , Tre´panier J.-Y.
Published: January 2011

The implementation of an automated decision support system in the field of structural design and optimization can give a significant advantage to any industry working on mechanical design. Such a system can reduce the project cycle time or allow more time to produce a better design by providing solution ideas to a designer or by upgrading existing design solutions while the designer is not at work. This paper presents an approach to automating the process of designing a gas turbine engine rotor disc using case-based reasoning (CBR), combined with a new genetic algorithm, the Genetic Algorithm with Territorial core Evolution (GATE). GATE was specifically created to solve problems in the mechanical structural design field, and is essentially a real number genetic algorithm that prevents new individuals from being born too close to previously evaluated solutions. The restricted area becomes smaller or larger during optimization to allow global or local searches when necessary. The CBR process uses a databank filled with every known solution to similar design problems. The closest solutions to the current problem in terms of specifications are selected, along with an estimated solution from an artificial neural network. Each solution selected by the CBR is then used to initialize the population of a GATE island. Our results show that CBR may significantly upgrade the performance of an optimization algorithm when sufficient preliminary information is known about the design problem. It provides an average solution 5.0% lighter than the average solution found using random initialization. The results are compared to other results obtained for the same problems by four optimization algorithms from the I-SIGHT 3.5 software: the sequential quadratic programming algorithm (SQP), the insular genetic algorithm (GA), the Hookes & Jeeves generalized pattern search (HJ) and POINTER. Results show that GATE can be a very good candidate for automating and accelerating the structural design of a gas turbine engine rotor disc, providing an average disc 18.9% lighter than SQP, 11.2% lighter than HJ, 23.9% lighter than GA and 4.3% lighter than POINTER, even when starting with the same solution set.
Thermodynamic Modeling and Optimization of Cogeneration Heat and Power System Using Evolutionary Algorithm (Genetic Algorithm)
Authors: Ebrahimi P. , Karrabi H. , Ghadami S. , Barzegar H. , Rasoulipour S. , Kebriyaie M.
Published: January 2011

A gas-turbine cogeneration system with a regenerative air preheater and a single-pressure exhaust gas boiler serves as an example for application of CHP Plant. This CHP plant which can provide 30 MW of electric power and 14kg/s saturated steam at 20 bars. The plant is comprised of a gas turbine, air compressor, combustion chamber, and air pre-heater as well as a heat recovery steam generator (HRSG). The design Parameters of the plant, were chosen as: compressor pressure ratio (rc), compressor isentropic efficiency (ηac), gas turbine isentropic efficiency (ηgt), combustion chamber inlet temperature (T3), and turbine inlet temperature (T4). In order to optimally find the design parameters a thermoeconomic approach has been followed. An objective function, representing the total cost of the plant in terms of dollar per second, was defined as the sum of the operating cost, related to the fuel consumption. Subsequently, different pars of objective function have been expressed in terms of decision variables. Finally, the optimal values of decision variables were obtained by minimizing the objective function using Evolutionary algorithm such as Genetic Algorithm. The influence of changes in the demanded power on the design parameters has been also studied for 30, 40 MW of net power output.
Destabilization of Forward Rub in Rotor Magnetic Bearing Systems Using Actively Controlled Auxiliary Bearings
Authors: Cade Iain S. , Sahinkaya M. Necip , Burrows Clifford R. , Keogh Patrick S.
Published: January 2011

During fault conditions, rotor displacements in magnetic bearing systems may potentially exceed safety/operating limits. Hence it is a common design feature to incorporate auxiliary bearings adjacent to the magnetic bearings for the prevention of rotor/stator contact. During fault conditions the rotor may come into contact with the auxiliary bearings, which may lead to continuous rub type orbit responses. In particular, forward rub responses may become persistent. This paper advances the methodology by considering an actively controlled auxiliary bearing system. An open-loop control strategy is adopted to provide auxiliary bearing displacements that destabilize established forward rub orbit responses. A theoretical approach is undertaken to identify auxiliary bearing motion limits at which forward rub responses become unstable. Experimental validation is then undertaken using a rotor/active magnetic bearing system with an actively controlled auxiliary bearing system under piezoelectric actuation. Two different operating speeds below the first bending mode of the rotor are considered and the applied harmonic displacements of the auxiliary bearing are shown to be effective in restoring contact free levitation.
The Experimental and Numerical Research for Linear Cascade Film Cooling With Different Hole Shapes
Authors: Lu Yi , Hong Yinyi , Lin Zhirong , Yuan Xin
Published: January 2011

Detailed film cooling effectiveness distributions were experimentally obtained on a turbine vane platform within a linear cascade. Testing was done in a large scale five-vane cascade with low freestream Renolds number condition 634,000 based on the axial chord length and the exit velocity. The detailed film-cooling effectiveness distributions on the platform were obtained using pressure sensitive paint technique. Two film-cooling hole configurations, cylindrical and fan-shaped, were used to cool the vane surface with two rows on pressure side, two rows on suction side and three rows on leading edge. For cylindrical holes, the blowing ratio of the coolant through the discrete cooling holes on pressure side and suction side ranged from 0.3 to 1.5 (based on the inlet mainstream velocity) while the blowing ratio ranging from 0.15 to 1.5 on leading edge; for fan-shaped holes, the four blowing ratios were 0.5, 1.0, 1.5 and 2.0. Results showed that average film-cooling effectiveness decreased with increasing blowing rate for the cylindrical holes, while the fan-shaped passage showed increased film-cooling effectiveness with increasing blowing ratio, indicating the fan-shaped cooling holes helped to improve film-cooling effectiveness by reducing overall jet liftoff. Fan-shaped holes improved average film-cooling effectiveness by 93.2%, 287.6% and 489.6% on pressure side, −4.1%, 27.9% and 78.2% on suction side over cylindrical holes at the blowing ratio of 0.5, 1.0 and 1.5 respectively. Numerical results were used to analyze the details of the flow and heat transfer on the cooling area with two turbulence models. Results demonstrated that tendency of the film cooling effectiveness distribution of numerical calculation and experimental measurement was generally consistent at different blowing ratio.
Influence of Flow Structure on Shaped Hole Film Cooling Performance
Authors: Laveau Benoit , Abhari Reza S.
Published: January 2011

Shaped holes are used on modern turbine blades for their higher performance and greater lateral coolant spreading compared to classic streamwise angled holes. This study incorporates measurements and observations from a shaped hole geometry undertaken at ETH Zurich in which a row of laterally expanded diffusely shaped holes is compared to the classic row of streamwise round holes. Infrared measurements provide high-resolution data of the adiabatic effectiveness and three dimensional velocity measurements are carried out through stereoscopic Particle Image Velocimetry. Both experiments are run for similar operating conditions allowing a comparison to be made between the flow structure and the thermal performance. The adiabatic effectiveness is seen to be higher for shaped holes compared to cylindrical holes: in particular the laterally averaged values are higher due to a larger lateral spreading of the coolant. The work presented here shows the first results on the limited influence of the density ratio on the thermal performance. The performance is also influenced by the vortical structure. The typical counter-rotating vortex pair which is completed by another pair of anti-kidney vortices is observed with their strength being clearly reduced compared to the example with cylindrical holes. The doubled structure and the reduced strength change the behavior of the jet, explaining the higher performance of a jet with shaped holes. The vertical motion leading to lift-off is reduced, so the jet remains close to the surface even at high blowing rates. The goal of this article is to present data for the thermal performance and flow field of shaped holes and then explain the relationship between the two.
Investigation of Microjet Injection for Reduction of Supersonic Jet Noise
Authors: Okada Ryuichi , Watanabe Toshinori , Uzawa Seiji , Himeno Takehiro , Oishi Tsutomu
Published: January 2011

Jet noise reduction is one of essential issues to realize environmentally-friendly and highly-efficient supersonic jet propulsion system. In the present study, experimental and numerical investigations were conducted in order to clarify the effect of microjet injection on supersonic jet noise. The experiments were focused on supersonic jet with Mach number up to 1.49, generated from a rectangular nozzle with high aspect ratio. The microjet injection angle was set to 90 degrees against the main jet axis. Far field measurements were conducted for the jet noise in the cases with and without microjet injection, and the noise reduction up to 7.5 dB was obtained. To study the mechanism of noise reduction, flow field visualization by schlieren technique and CFD analysis were conducted.
A Numerical Study on Ground-Based Vibration Response of a Spinning Cyclic Symmetric Rotor With Cracks
Authors: Shen I. Y.
Published: January 2011

This paper is to study how presence of cracks affects ground-based vibration response of a spinning cyclic symmetric rotor via a numerical simulation. A reference system used in this study is a spinning disk with four pairs of brackets, representing a 4-fold cyclic symmetric rotor. A crack with a variable depth is introduced at one of the eight disk-bracket interfaces. Both radial and circumferential cracks are simulated. The ground-based vibration response of the spinning disk-bracket system is simulated using an algorithm introduced by Shen and Kim [1]. Compared with a perfectly cyclic symmetric rotor, the crack introduces additional resonances when the crack size is large enough. Frequencies of these additional resonances can be predicted accurately and may be used as a way to detect presence of cracks. In addition, the additional resonances are more prominent for the circumferential crack than the radial crack.
Effect of Density Ratio on Flat Plate Film Cooling With Shaped Holes Using PSP
Authors: Wright Lesley M. , McClain Stephen T. , Clemenson Michael D.
Published: January 2011

Detailed film cooling effectiveness distributions are obtained on a flat plate using the pressure sensitive paint (PSP) technique. The applicability of the PSP technique is expanded to include a coolant-to-mainstream density ratio of 1.4. The effect of density ratio on the film cooling effectiveness is coupled with varying blowing ratio (M = 0.25–2.0), freestream turbulence intensity (Tu = 1%–12.5%), and film hole geometry. The effectiveness distributions are obtained on three separate flat plates containing either simple angle, cylindrical holes, simple angle, fanshaped holes (α = 10°), or simple angle, laidback, fanshaped holes (α = 10°, γ = 10°). In all three cases, the film cooling holes are angled at θ = 35° from the mainstream flow. Using the PSP technique, the combined effects of blowing ratio, turbulence intensity, and density ratio are captured for each film cooling geometry. The detailed film cooling effectiveness distributions, for cylindrical holes, clearly show the effectiveness at the lowest blowing ratio is enhanced at the lower density ratio (DR = 1). However, as the blowing ratio increases, a transition occurs, leading to increased effectiveness with the elevated density ratio (DR = 1.4). In addition, the PSP technique captures an upstream shift of the coolant jet reattachment point as the density ratio increases or the turbulence intensity increases (at moderate blowing ratios for cylindrical holes). With the decreased momentum of the shaped film cooling holes, the greatest film cooling effectiveness is obtained at the lower density ratio (DR = 1.0) over the entire range of blowing ratios considered. In all cases, as the freestream turbulence intensity increases, the film effectiveness decreases; this effect is reduced as the blowing ratio increases for all three film hole configurations.
Dynamics of Non-Premixed Bluff Body-Stabilized Flames in Heated Air Flow
Authors: Cross Caleb , Fricker Aimee , Shcherbik Dmitriy , Lubarsky Eugene , Zinn Ben T. , Lovett Jeffery A.
Published: January 2011

This paper describes a study of the fundamental flame dynamic processes that control bluff body-stabilized combustion of liquid fuel with low dilatation. Specifically, flame oscillations due to asymmetric vortex shedding downstream of a bluff body (i.e., the Be´nard/von-Ka´rma´n vortex street) were characterized in an effort to identify the fundamental processes that most affect the intensity of these oscillations. For this purpose, the spatial and temporal distributions of the combustion process heat release were characterized over a range of inlet velocities, temperatures, and overall fuel-air ratios in a single flame holder combustion channel with full optical access to the flame. A stream of hot preheated air was supplied to the bluff body using a preburner, and Jet-A fuel was injected across the heated gas stream from discrete fuel injectors integrated within the bluff body. The relative amplitudes, frequencies, and phase of the sinusoidal flame oscillations were characterized by Fourier analysis of high-speed movies of the flame. The amplitudes of the flame oscillations were generally found to increase with global equivalence ratio, reaching a maximum just before rich blowout. Comparison of the flame dynamics to the time-averaged spatial heat release distribution revealed that the intensity of the vortex shedding decreased as a larger fraction of the combustion process heat release occurred in the shear layers surrounding the recirculation zone of the bluff body. Furthermore, a complete transition of the vortex shedding and consequent flame stabilization from asymmetric to symmetric modes was clearly observed when the inlet temperature was reduced from 850°C to 400°C (and hence, significantly increasing the flame dilatation ratio from Tb/Tu ∼ 2.3 to 3.7).
Maximum Amplification of Blade Response in Mistuned Multi Stage Assemblies
Authors: Avalos Javier , Mignolet Marc P.
Published: January 2011

This paper focuses on the determination of the maximum amplification of blade response due to mistuning in multi stage assemblies. The modal optimization strategy developed earlier in connection with single stage models is extended here to multi stage configurations. Theoretical developments are carried out first and lead to the new upper limit of (1+N1+N2(g2/g1)+…)/2, where Ni are the number of blades on the stages and gi = FiTMi−1Fi with Fi the force vector applied on a sector of stage i and Mi its mass matrix. For identical stages, this maximum equals the Whitehead limit observed with single stages but with the number of blades equal to sum of the numbers of blades of the coupled stages. A computational validation of the theoretical results is achieved next on both a single degree of freedom per blade model and a reduced order model of a blisk. These numerical optimization efforts confirm the theoretical developments and demonstrate that such high amplification factors can indeed be achieved with small levels of mistuning. The effects of the number of blades on the different stages, damping in the system, stage coupling strength, etc are discussed in details.
Experimental Study of Effects of Grooved Tip Clearances on the Flow Field in a Compressor Cascade Passage
Authors: Ma Hongwei , Zhang Jun , Zhang Jinghui , Yuan Zhou
Published: January 2011

This paper presents an experimental investigation of effects of grooved tip clearances on the flow field of a compressor cascade. The tests were performed in a low-speed large-scale cascade respectively with two tip clearance configurations, including flat tip and grooved tip with a chordwise channel on the blade top. The flow field at 10% chord downstream from the cascade trailing edge was measured at four incidence angles using a mini five-hole pressure probe. The static pressure distribution was measured on the tip endwall. The results show that the pressure gradient from the pressure side to the suction side on the blade tip is reduced due to the existence of the channel. As a result, the leakage flow is weakened. The high-blockage and high-loss region caused by the leakage flow is narrower with the grooved tip. In the meantime, the leakage flow migrates to lower spanwise position. The combined result is that the flow capacity in the tip region is improved at the incidence angles of 0° and 5° with the grooved tip. However, the loss is slightly greater than that with the flat tip at all the incidence angles.
Experimental Flow Visualization Study in a Trapezoidal Duct With Impingement Jets and Cross Flow Near the Leading Edge
Authors: Liu Haiyong , Liu Songling , Qiang Hongfu , Liu Cunliang
Published: January 2011

An enlarged model of trapezoidal duct in leading-edge with impingement jets, swirl, cross flow and effusion was built up. Experiments were performed to measure flow fields in the confined passage and exit holes on one of its side walls. A row of staggered circular impingement holes were arranged on the opposite side wall. Cross flow and effusion flow was induced in the channel by the outflow of exit hole and film cooling hole, which were oriented on one end wall and bottom wall of the passage. Detailed flow structures were measured for two impingement angles of 35° and 45° with 6 combinations of out flow ratios. Results showed that the small jets impinged the target wall effectively while the large jets contributed to inducing and impelling a strong counter-clockwise vortex in the upper part of the passage. Cross flow had significant effect on the flow structures in the passage and exit holes. It deflected the jets, enhanced swirl and deteriorated side exit conditions. Impingement angle also had important influence on flow fields and its effect revealed more evidently with cross flow. Within the present test conditions, the mass flow rates and outflow positions of film cooling holes had no distinct effect on the main flow structures. These data were helpful for the design and optimization of internal cooling structures in gas turbine airfoils.
A New Finite Element Approach to Biaxial Fatigue Life Prediction in Gas Turbine Engine
Authors: Tarar Wasim , Shen M.-H. Herman
Published: January 2011

High cycle fatigue is the most common cause of failure in gas turbine engines. Different design tools have been developed to predict number of cycles to failure for a component subjected to fatigue loads. An energy-based fatigue life prediction framework was previously developed in recent research for prediction of axial and bending fatigue life at various stress ratios. The framework for the prediction of fatigue life via energy analysis was based on a new constitutive law, which states the following: the amount of energy required to fracture a material is constant. A finite element approach for uniaxial and bending fatigue was developed by authors based on this constitutive law. In this study, the energy expressions that construct the new constitutive law are integrated into minimum potential energy formulation to develop a new QUAD-4 finite element for fatigue life prediction. The newly developed QUAD-4 element is further modified to obtain a plate element. The Plate element can be used to model plates subjected to biaxial fatigue including bending loads. The new QUAD-4 element is benchmarked with previously developed uniaxial tension/compression finite element. The comparison of Finite element method (FEM) results to existing experimental fatigue data, verifies the new finite element development for fatigue life prediction. The final output of this finite element analysis is in the form of number of cycles to failure for each element in ascending or descending order. Therefore, the new finite element framework can predict the number of cycles to failure at each location in gas turbine engine structural components. The new finite element provides a very useful tool for fatigue life prediction in gas turbine engine components. The performance of the fatigue finite element is demonstrated by the fatigue life predictions from Al6061-T6 aluminum and Ti-6Al-4V. Results are compared with experimental results and analytical predictions.
Aerodynamic Analysis of a Micro Turbine Centrifugal Compressor
Authors: Olivero Mattia , Javed Adeel , van Buijtenen Jos P.
Published: January 2011

Micro turbine technology has developed rapidly during the last two decades. Major research issues related to this technology are the scale effects on aerodynamic turbomachinery performance, which include relatively high viscous losses due to the low Reynolds number of the flow through the cascades and also to the relative magnitude of size-independent losses. Micro Turbine Technology B.V. is developing a micro turbine for domestic combined heat and power units and combined auxiliary power unit/parking heaters for trucks. This paper describes the analysis of the micro turbine single stage centrifugal compressor by means of a numerical steady-state model, which approximates the real, time-dependent flow physics with satisfactory results and shorter computational time with respect to an unsteady approach. A commercial three-dimensional (3D) Reynolds-averaged Navier-Stokes computational fluid dynamics (CFD) code is adopted for this study. The simulations allow to understand the most significant flow phenomena of the 3D compressor flow field and to solidify the role of CFD as a consistent analysis tool, especially when accurate measurements are impossible to perform. The numerical results are compared with experimental data and the flow field analysis highlights some critical flow phenomena such as relative Mach number higher than unity in the inducer and secondary flow structures with their associated losses in the impeller.