bluuebunny/crossref_metadata_2025 huggingface dataset:
Educational Software for Blade and Disk Design
Authors: Gutzwiller David P. , Turner Mark G. , Downing Michael J.
Published: February 2010

One problem with many introductory level turbomachinery courses is a lack of easy to use design and visualization tools. Oftentimes students will become too focused on the underlying math and never develop a good understanding of the physical systems they are working with. To combat this problem, a series of GUI based design and visualization codes have been created. The codes are intended primarily for educational purposes, but in many cases they are robust enough for actual design use. All of the new codes have been designed to complement and to a small extent connect to the existing T-Axi suite of codes. This paper will focus on two new freely available codes: T-Axi Blade and T-Axi Disk. T-Axi Blade was created to help visualize the key design features of a single rotor, with special emphasis on vector triangles, and the ability to design compressor, turbine, axial and centrifugal rotors with a universal approach. T-Axi Blade can also output files for use with T-Axi Disk, a code to aid in the design of a lightweight disk to support the blade row. This code allows the user to design a disk interactively with instantaneous feedback in the form of weights, stresses, and a series of 2D and 3D visualizations. Taken together these codes offer a simple introduction to multidisciplinary engineering. In this paper the structure of these codes and the numerical models are discussed. Ideas are presented of how these codes can be used as a classroom tool and as an actual design tool. An example analysis of the third stage GE EEE HPC axial rotor is presented to demonstrate the features of these codes.
Research and Development of Minitype Twin-Bladed Air Turbine
Authors: Wang Shih-Chun , Huang Kuang-Yuh
Published: February 2010

In order to improve the machining efficiency of ultra-precision and micro fabrication technology, a high speed spindle is essential for the minitype tools widely applied in systems such as PCB drilling machines, micro fabrication machines, dental handpieces, etc. To realize the high speed performance, the air driven turbine is verified to be more feasible than the electromagnetic actuator. Furthermore, the operational efficiency and quality of the high speed spindle are significantly influenced by the turbine blades and the bearings respectively. Through detailed configurational studies and performance analyses on diverse minitype turbine blades, we have derived the efficiency- and quality-influential parameters. And based on optimization results, we have developed a novel type of twin bladed air turbine (TB-air turbine), which consists of two parallel blades with an angular offset. The offseted twin blades can efficiently and smoothly transform pneumatic energy into rotational energy. Therefore, steady driving force and less dynamic unbalance are able to be easily achieved for reducing nervous disturbances such as vibration, noise, and wear. By applying finite element analytical method, the operational performances and quality of the new developed twin bladed air turbine such as rotational speed, torque, vibration and noise were analyzed for comprehending influences of the design parameters and the operational parameters. While the inlet angle, the blade shape and its geometric parameters are the dominant design parameters; the inlet pressure and mass flow rate, and the outlet pressure are the main operational parameters. Through the turbine blades, the pneumatic energy will be transformed into operational energy in form of the flow field and the pressure distribution and the energy loss in form of turbulence. Also by integrating knowledge of production technology, a neat design of the turbine blades suitable for automatic manufacturing process is developed. And furthermore, through an elaborate layout of the flow guiding, a minimum rotational runout can be effectively achieved without any complicate and costly dynamic balancing process. Consequently, it has significantly depressed the stream noise and raised the operation lifetime of bearings. According to our experimental verification, the vibration and the stream noise of our TB-air turbines are 60% and 50% lower than traditional counterparts respectively. Our developed minitype spindle with novel TB-air turbine can efficiently realize high speed rotation with high torque, less vibration and less noise.
Effect of Environmental Factors on the Performance Characteristics of an Oil Cooling System Designed for a Turbo-Shaft Engine
Authors: Mishra R. K. , Mishra A. K. , Gouda G.
Published: February 2010

High rotor speeds of turbo-shaft engines demand an efficient oil cooling system to keep the bearing temperature within the acceptable limit. This makes the oil cooling system to play an important part in engine lubrication circuit and any malfunction or inefficiency of the system will lead to rotor instability and seizure causing power loss and damage to the engine. An oil cooling system has been designed for a 900 kW class turbo-shaft engine. It has undergone system level tests to study the effect of various environmental conditions such as sand ingestion during desert operation, prolong exposure to high humidity and salt-laden atmosphere during marine/coastal area operation, and with growth of fungus on external surfaces, etc. The paper presents the tolerance of the oil cooling system to different adverse environmental factors and highlights their effect on the performance characteristics of the system.
Optimization of a Regenerative Gas Turbine Engine With Isothermal Heat Addition With the Genetic Algorithm
Authors: Haghighi E. , Borzou B. , Ghahremani Amir R. , Shafii M. Behshad
Published: February 2010

The use of advanced cycles to take advantage of the gas turbine’s thermodynamic characteristics has received increasing attention in recent years. These cycles have been developed for large scale power generation. Due to the powerful abilities of bio-inspired computing techniques such as Genetic Algorithm in locating the optimal (or near optimal) solutions to a given optimization problem, they are widely utilized for determining the parameters of different engineering systems in order to meet the specified performance objectives for a given problem. In order to illustrate the performance of one of these techniques, development and application of it for an engineering problem is presented. In this paper a regenerative gas turbine cycle, with isothermal heat addition has been analyzed. The optimization of system has been carried out numerically using the Genetic Algorithm method. Results show that the regenerative gas turbine engine, with isothermal heat addition, designed according to the optimum parameters condition gives the best performance and exhibits highest cycle efficiencies.
Coanda Surface Geometry Optimization for Multi-Directional Co-Flow Fluidic Thrust Vectoring
Authors: Saghafi Fariborz , Banazadeh Afshin
Published: February 2010

The performance of Co-flow fluidic thrust vectoring is a function of secondary flow characteristics and the fluidic nozzle geometry. In terms of nozzle geometry, wall shape and the secondary slot aspect ratio are the main parameters that control the vector angle. The present study aims to find a high quality wall shape to achieve the best thrust vectoring performance, which is characterized by the maximum thrust deflection angle with respect to the injected secondary air. A 3D computational fluid dynamics (CFD) model is employed to investigate the flow characteristics in thrust vectoring system. This model is validated using experimental data collected from the deflection of exhaust gases of a small jet-engine integrated with a multi-directional fluidic nozzle. The nozzle geometry is defined by the collar radius and its cutoff angle. In order to find the best value of these two parameters, Quasi-Newton optimization method is utilized for a constant relative jet momentum rate, a constant secondary slot height and insignificant step size. In this method, the performance index is described as a function of thrust deflection angle. Optimization parameters (wall geometric parameters) are estimated in the direction of gradient, with an appropriate step length, in every iteration process. A good guess of initial optimization parameters could lead to a rapid convergence towards an optimal geometry and hence maximum thrust deflection angle. Examination over a range of geometric parameters around the optimum point reveals that this method promises the best performance of the system and has potential to be employed for all the other affective factors.
Effects of Hot-Gas Composition on Temperature Distribution in a Flat Plate Cooled by Internal and Film Cooling
Authors: Na S. , Dennis R. A. , Alsup C. , Bryden K. M. , Shih T. I.-P.
Published: February 2010

Developing turbine technologies to operate on coal-derived synthesis gas (syngas) and hydrogen fuels is critical to the development of advanced power generation systems that can lead to the capture and separation of carbon dioxide (CO2). One issue that arises from burning such fuels is the change in the hot-gas constituents, which differ in specific heats, thermal conductivity, and molecular weight. Another issue is increased heat-transfer rate from the hot-gas side from increased volumetric flow rate. In this study, CFD simulations were performed to examine the heat transfer and temperature distributions in and about a flat plate with and without thermal-barrier coating that is cooled by internal and film cooling in which the hot-gas constituents are from the products of combustion of natural gas, syngas, hydrogen, and oxyfuel. Also examined is the effect of Biot number from negligible resistance by conduction heat transfer to when the resistance by conduction and convection is comparable. This computational study is based on the ensemble average continuity, species balance, compressible Navier-Stokes, and energy equations closed by the realizeable k-ε turbulence model (wall functions were not used) for the gas phase and the Fourier equations for conduction in the solid phase.
Blended Education in Turbomachinery and Fluid Dynamics
Authors: Backman Jari L. H. , Turunen-Saaresti Teemu , Jaatinen Ahti
Published: February 2010

The paper deals with blended education in turbomachinery and fluid dynamics courses in Finland. The teaching methodology of these courses has been developed to comply with the new challenges of the education in technology. Presently six of the courses in the curriculum are following the schemes explained in this presentation. The courses are studied in the last year of the Bachelor level and in the Masters level quantifying from 2 to 4 ECTS credits. Students get all the material from the teaching platform in the web, which can be accessed freely anytime and practically from anywhere. Before attending the teaching events, the students go through the study material, perform several exercises and take a quiz, which can give them extra points for the exam tally. The contact teaching of the course is divided into four Learning Sessions of four hours. The first half is reserved to deepen the acquired knowledge, and performed in a way to attract a more interactive atmosphere. In the second half the students are divided to groups, where they solve more difficult study exercises compared to those they already have trained on. As the students are expected to study with the material of blended learning in advance, the percentage of the contact hours has to be lowered in comparison to the traditional teaching in order to maintain a balance with the credits in the course. However, with the acquired knowledge, the students are more interactive with the teachers and the teaching becomes more efficient. The students have given positive feedback on the courses. The instructors have found that the blended learning is not necessary an easier task, although there are less contact hours with the student. The efficiency of teaching has increased and the teaching is more rewarding. Both the students and the teachers found that blended education suited best for student groups around 10 students.
Micro Jet Engine Oil Consumption Measurement Technique
Authors: Sandor Ivo , Staudacher Stephan , Hertweck Gernot
Published: February 2010

Oil consumption of micro gas turbine engines plays a significant role with regards to their practical application in aerospace. In this context an oil consumption measurement device has been developed on behalf of Daimler AG for the application to vehicle turbo chargers. This device has been used to measure the oil consumption of an own design micro jet engine of 400 N thrust. The design of the device is based on the principle of gravimetric weighting. In the past, volumetric principles have been applied to engine oil consumption measurements. Technical advances in the field of piezoelectricity have improved the accuracy of gravimetric weighting in such a way that today its accuracy is comparable to volumetric gauging. Moreover, unlike volumetric gauging gravimetric weighting is not influenced by the density or the amount of emulsified gas in the oil. Hence, application of gravimetric weighting represents a more robust and more efficient way to evaluate oil consumption in micro gas turbine engines. Unlike non-conventional measurement strategies like emission measurement and tracer techniques, gravimetric weighting allows very simple and convenient oil consumption measurements [3]. The device was validated using defined laboratory measurements. Experimental results are shown.
Pressure Dependence of the Stability Limits and the NOX Exhaust Gas Concentrations in Case of Swirl-Stabilized, Diffusion Flames Burning in a Lift-Off Regime
Authors: Kasabov Plamen , Zarzalis Nikolaos
Published: February 2010

The present study deals with confined, swirl-stabilized, diffusion flames burning in a lift-off regime and is meant to be a meaningful extension of our previous work [1]. The unique features of these hybrid flames originate from the presence of the so called lift-off zone located between the burner exit and the reaction zone. In the lift-off zone, surrounded by hot recirculating exhaust gases, the liquid fuel heats up and will reach a certain degree of prevaporation and premixing before entering the reaction zone. For that reason lifted flames posses some of the advantages of the premixed flames, for example in respect of emissions, but lack their major drawbacks, such as susceptibility to flashback and combustion noise. The investigations were motivated by the high NOX reduction potential of the lifted flames and the scarce information about their emission characteristics, flame behaviour and stability limits for gas turbine typical conditions especially when operated with liquid fuels. In order to gain a deeper understanding of the stabilization mechanism of lifted flames, several process parameters were varied within this study. The impact of the pressure (up to 18bar), of the air preheating and of the stoichiometry on the NOX emissions and on the lean blowout limits was investigated and discussed. The lift-off burning mode was achieved by utilizing a modified airblast nozzle and kerosene serving as a fuel. To acquire measurement data for a set of Reynolds numbers and residence times, four nozzles with similar geometries, but different scaling factors were employed. All main components of the exhaust gas were detected by means of conventional gas analysis. The NOX concentrations for the whole measured pressure range and for adiabatic flame temperatures up to 1800K does not exceed 20ppm normalized for 15% O2. The carbon monoxide concentration served as indicator for the presence of flame instabilities. The evaluation of the gathered data revealed some interesting phenomena. For example a sudden change in the nitrogen oxides concentration plotted over the equivalence ratio allows to distinguish between two burning modes: lift-off and detached flame. Another interesting finding is a maximum in the profile of the LBO limits as a function of the operational pressure, signifying a change in the predominant stabilization mechanism.
Effects of Height-to-Diameter Ratio of Pin Element on Heat Transfer From Staggered Pin-Fin Arrays
Authors: Chyu Minking K. , Siw Sean C. , Moon Hee Koo
Published: February 2010

A pin-fin array is a compact heat exchanger and widely used for cooling of turbine airfoils. This study is to experimentally examine the effects of pin height or height-to-diameter ratio (H/D) on the heat transfer from a pin-fin array. The test models are designed to facilitate three different H/D ratios, from 2 to 4, with a staggered pin-fin array of inter-pin spacing 2.5 times the pin diameter (S/D = X/D = 2.5) in both longitudinal and transverse directions. The Reynolds number ranges from 10,000 to 30,000. The experiment uses a hybrid technique based on the transient liquid-crystal imaging to obtain detailed local heat transfer coefficients over both the pin-fin surface and endwalls. Overall array-averaged heat transfer increases with the H/D value or pin height. Most of the heat transfer contribution for H/D>2 comes from the pins rather than the endwall. However, higher H/D leads to a greater pressure loss. As a measure of heat transfer enhancement per pressure loss, H/D = 2 leads to the highest performance index and H/D = 4 is the lowest.
An Experimental Investigation on Cooling Performance of a Laminated Configuration Using Infrared Thermal Image Technique
Authors: Wang Jianhua , Lv Xijia , Liu Qingdong , Wu Xiangyu
Published: February 2010

The performance of double-wall laminated film cooling configurations was studied by the experiments carried out in the hot gas wind tunnel of UTSC. Three devices with the true size of gas turbine components were employed as specimens. The specimens have different angles of film hole with mainstream direction and rib designs. The temperature distributions at the hot surface of the specimens were measured by an infrared thermal imaging system. An algorithm of digital imaging signal was used, and two-dimensional temperature drop from initial wall to cooled wall was directly obtained. By comparison of the temperature drop of the three devices, the influences of the columnar ribs and angle of film holes on cooling effectiveness were discussed. The experimental parameters of the wind tunnel were accurately dominated by two digital control systems for mainstream temperature and mass flow rate, average cooling effectiveness of the three specimens were measured. The correlations between the mainstream Reynolds number with the Nusselt number and the average effectiveness were quantitatively compared for the three specimens. The investigation indicates that the effect of the film holes’ angle on the overall cooling effectiveness is much marked than the rib effect.
Electrophoretic Deposition of Environmental Barrier Overlay Coatings for Yttria-Stabilized Zirconia Thermal Barrier Coatings
Authors: Mohan Prabhakar , Patterson Travis , Sohn Yongho
Published: February 2010

Thermal barrier coatings (TBCs) are increasingly susceptible to environmental degradation due to molten deposits of fuel impurities and air ingested sand. At elevated temperature, these deposits adhere, melt and degrade the TBCs via repeated freeze-thaw action and, to a certain extent, direct chemical reaction with TBC constituents. In order to protect TBCs from such melt ingression, a thin, dense and continuous environmental barrier overlay coating can be applied on the surface of TBCs. In this study, dense, continuous and crack-free overlay coatings of YSZ, Al2O3 and MgO were fabricated by electrophoretic deposition (EPD) on air-plasma sprayed (APS) YSZ. APS YSZ specimens of 300 μm thickness were prepared from 8YSZ powders on graphite substrates. A stable colloidal suspension of YSZ, Al2O3 and MgO powders in an organic solvent mixture of acetone and ethanol with Iodine additive was used for EPD. At a controlled applied DC voltage with deposition time within minutes, a crack-free green compact can be obtained. After drying and controlled sintering at high temperature, thin, dense, crack-free overlay coatings of controlled thickness on free-standing YSZ were produced. The coatings were characterized by x-ray diffraction and scanning electron microscopy. The degradation resistance of overlay coatings fabricated by EPD and sintering for YSZ TBCs against melt ingression of CMAS and V2O5 is highlighted.
The Thermal Impact of Using Syngas as Fuel in the Regenerator of Regenerative Gas Turbine Engine
Authors: Oliveira Luciana M. , Nascimento Marco A. R. , Menon Gene´sio J.
Published: February 2010

Environment and energy are driven force of human survival and development. Nowadays the use of primary energy comprises mostly mineral fuels, which have limited reserves and whose utilization may cause serious environmental impacts. Attention has been paid to discover clean and renewable resources such as syngas which is an important renewable source of energy and is environment friendly. The use of syngas from biomass gasification process as fuel in regenerative gas turbine causes an increase in turbine exhaust mass flow and a change in the gas composition due to a low heat value. As a result, the regenerator changes its size, thermal characteristics, weight and cost compared with the use of natural gas as fuel. The aim of this work is to assess the thermal performance, the size and the cost of the recuperator of 600 kW regenerative gas turbine engine when designed for syngas and natural gas. Two different types of surfaces, Cross-Corrugated and Undulated-Corrugated, are used for analysis. The results are shown, comparing heat transfer coefficient, effectiveness, pressure loss, size and cost for syngas and natural gas.
Numerical Simulation of Broadband Combustion Noise With the RPM-CN Approach
Authors: Mu¨hlbauer B. , Ewert R. , Kornow O. , Noll B. , Aigner M.
Published: February 2010

A new numerical approach called RPM-CN approach is applied to predict broadband combustion noise. This highly efficient hybrid CFD/CAA approach can rely on a reactive RANS simulation. The RPM method is used to reconstruct stochastic broadband combustion noise sources in the time domain based on statistical turbulence quantities. Subsequently, the propagation of the combustion noise is computed by solving the acoustic perturbation equations (APE-4). The accuracy of the RPM-CN approach will be demonstrated by a good agreement of the simulation results with acoustic measurements of the DLR-A flame. The high efficiency and therefore low computational costs enable the usage of this numerical approach in the design process.
Local Heat/Mass Transfer and Friction Loss Measurement in a Rotating Matrix Cooling Channel
Authors: Oh In Taek , Kim Kyung Min , Lee Dong Hyun , Park Jun Su , Cho Hyung Hee
Published: February 2010

The present investigation provides detailed local heat/mass transfer distribution and pressure drop characteristics in a matrix cooling channel under rotating conditions. The matrix channel has cooling sub-passages with crossing angle of 45 degrees. Detailed heat/mass transfer coefficients are measured using the naphthalene sublimation method. The pressure drops are also measured. The experiments were conducted under various Reynolds numbers (10,000 to 44,000) and rotation numbers (0.0 to 0.8). For the stationary case, the heat transfer characteristics are dominated by turning, impinging and swirling flow which are induced by the matrix channel geometry. Averaged heat/mass transfer coefficients on the leading and trailing surfaces in the stationary channel are approximately 2.1 times higher than those in a smooth channel. For the rotating cases, the effect of rotation on heat/mass transfer characteristics shows different tendency compared to typical rotating channels with radially outward flow. As the rotation number increases, the Sherwood number ratios increase on the leading surface, but changed slightly on the trailing surface. The thermal performance factors increases with increasing rotation numbers due to increased Sherwood number ratios and decreased friction factor ratios.
Heat Transfer Measurements on a Turbine Airfoil With Pressure Side Separation
Authors: Ladisch Helge , Schulz Achmed , Bauer Hans-Jo¨rg
Published: February 2010

Heat transfer measurements on a highly loaded low-pressure turbine airfoil with a separation bubble on the pressure surface are presented. The experiments were conducted in a linear cascade at various free-stream turbulence intensities (Tu1 = 1.6% to 10%) and Reynolds numbers of the inflow. The effect of both quantities on heat transfer, separation and laminar-turbulent transition is quantified. Particle-Image-Velocimetry has been performed to study the characteristics of the separation bubble. The results reveal a considerable influence of the boundary layer separation on the local heat transfer. The size of the separation region is strongly influenced by free-stream turbulence level and Reynolds number.
Experimental Investigation of Turning Flow Effects on Innovative Trailing Edge Cooling Configurations With Enlarged Pedestals and Square or Semicircular Ribs
Authors: Facchini Bruno , Simonetti Francesco , Tarchi Lorenzo
Published: February 2010

In this paper the experimental measurements concerning the heat transfer capabilities of several trailing edge (TE) cooling configurations that are based on the combination of enlarged pedestals and small rib turbulators are presented. The baseline geometry consists of a converging duct, reproducing the typical shape of a high pressure turbine blade TE, with two rows of enlarged pedestals. Three rows of square or semicircular turbulators were arranged in between the pedestals on the pressure side (PS) surface; the ribs height is e = 1 mm and the pitch is P/e = 10. The airflow pattern inside the test rig simulates the rotor blade cooling scheme with a 90deg turning flow from the hub inlet to the TE outlet. For each configuration heat transfer measurements were made keeping Mach number fixed at 0.3 and varying Reynolds number from 9000 to 27000 in the TE throat section. The effect of a varying tip massflow rate was tested considering 0%, 12.5% and 25% of the TE massflow. The detailed HTC maps were measured using the transient technique with TLC and a PMMA test article. As expected, by comparison with the baseline geometry, test results show that the HTC distribution and the average Nusselt number over the PS surface are affected by the presence of the ribs which promote the airstream turbulence. However, no remarkable difference between the results from different rib shapes can be highlighted. The tip massflow rate alters the HTC distribution in the radial direction over the whole TE. The results are compared with previous experiments, performed on the same geometries, but with an axial inlet.
Premixed Generated Manifolds for the Computation of Technical Combustion Systems
Authors: Ketelheun Anja , Olbricht Clemens , Hahn Frederik , Janicka Johannes
Published: February 2010

Large eddy simulations (LES) show a good prediction accuracy at a decent computational cost for the simulation of combustion processes in complex geometries. However, the large grids required make the direct solution of detailed reaction kinetics impracticable. Therefore, the chemical reactions can be tabulated in a pre-processing step using detailed chemistry with one-dimensional laminar steady flamelets. These flamelets can be either non-premixed or premixed and are stored based on controlling variables like mixture fraction and reaction progress parameter, for example. In this work, a progress variable approach (PVA) using premixed flamelets was adopted to generate a manifold defined by mixture fraction and reaction progress variable. Since the computation of the flamelets is only feasible between flammability limits, the data outside these limits has to be extrapolated to obtain the complete manifold for all chemical states. The extrapolation influences the stability of the LES and its prediction quality and so four different extrapolation schemes were studied. A probability density function (PDF) model was applied to account for subgrid scale variances. Two methods of modeling the joint PDF of mixture fraction and progress variable in terms of their statistical dependence were investigated. Some results of a bluff body configuration comparing the PDF modeling approaches are shown. The results demonstrated that a diffusion flame can be simulated with both the progress variable approach based on premixed flamelets and classic non-premixed flamelets without progress variable.
Gas Turbine Fault Identification by Fusing Vibration Trending and Gas Path Analysis
Authors: Kyriazis A. , Tsalavoutas A. , Mathioudakis K. , Bauer M. , Johanssen O.
Published: February 2010

A fusion method that utilizes performance data and vibration measurements for gas turbine component fault identification is presented. The proposed method operates during the diagnostic processing of available data (process level) and adopts the principles of certainty factors theory. Both performance and vibration measurements are analyzed separately, in a first step, and their results are transformed into a common form of probabilities. These forms are interweaved, in order to derive a set of possible faulty components prior to deriving a final diagnostic decision. Then, in the second step, a new diagnostic problem is formulated and a final set of faulty health parameters are defined with higher confidence. In the proposed method the non-linear gas path analysis is the core diagnostic method, while information provided by vibration measurements trends is used to narrow the domain of unknown health parameters and lead to a well defined solution. It is shown that the presented technique combines effectively different sources of information, by interpreting them into a common form and may lead to improved and safer diagnosis.
Optimization of the Part-Load Control Strategy for a Two-Shaft Microturbine With Intercooling, Reheat and Recuperation
Authors: Saari Jussi , Kaikko Juha , Backman Jari L. H. , Larjola Jaakko
Published: February 2010

Microturbines have become popular among small-scale distributed energy systems. This paper focuses on a two-shaft arrangement where high efficiency is obtained through intercooling, reheat and recuperation. An optimized method for controlling the part-load performance via variable speed control of the generator shaft in addition to the turbine inlet temperature reduction is presented. The studied methods to reduce the power output were variable speed control of the generator shaft in combination with independent turbine inlet temperature control of both turbines. Optimization was performed by using a differential evolutionary algorithm to find a sufficient number of points at steadily reducing power settings to determine the optimal control curves for the three control parameters. In the microturbine model the operating values of the engine were obtained by solving the system of nonlinear equations formed by the governing relations. As a result an optimal part-load control method was found which provides better part-load efficiency than any of the studied control methods alone or in simple combinations could have provided. The optimal control strategy and the relative change of part-load electric efficiency were shown to be fairly independent of the design-point specifications for the turbomachinery and recuperator.
Computational Study of the Heat Transfer of the Buoyancy-Driven Rotating Cavity With Axial Throughflow of Cooling Air
Authors: Dweik Zain , Briley Roger , Swafford Timothy , Hunt Barry
Published: February 2010

Buoyancy driven flows that occur in the inter-disk space of an axial compressor spool play a major role in projecting gas turbine engine life and performance. The Rayleigh-Benard-like flow structure developed under the influence of centrifugal buoyancy creates sharp temperature gradients at the rotating walls of the compressor hardware. These sharp temperature gradients greatly influence the running stresses inside the machine and therefore affecting its life. The objective of this work is to generate a complete set of computationally-derived Nusselt number correlations that will be used in conducting the conjugate heat transfer analyses. The impact of engine power condition (Idle, Highpower, and Shutdown) on the heat transfer of these rotating cavities is studied under the wide range of operating conditions encountered by realistic turbomachines. A computational analysis is performed using commercially available computational tools for grid generation (ICEM-CFD) and turbulent-flow simulation (CFX). A total of fifty steady CFD cases for two different cavity configurations were analyzed. The CFD computed results of these cases were used to generate a complete set of Nusselt number correlations for different cavity geometry (gap ratios), flow regimes (forced and free convection dominated regimes), and operating conditions (Rossby Number Ro, Rotational Rayleigh Number RaΩ, and axial Reynolds Number Rez). The CFD computed heat-transfer results revealed that, despite the complicated flow patterns inside these cavities, and despite the large variation in their geometry, the simple Nusselt number correlations for free convection from a vertical flat plate with constant temperature can be used to predict the global Nusselt number values for the buoyancy-dominated regime of all such cavities. Furthermore, the Nusselt number correlations for the laminar and turbulent forced convection over a flat plate can be used to predict the global Nusselt number values for the central-jet dominated regime.
Dynamics of Premixed H2/CH4 Flames Under Near-Blowoff Conditions
Authors: Zhang Qingguo , Shanbhogue Santosh J. , Lieuwen Tim
Published: February 2010

Swirling flows are widely used in industrial burners and gas turbine combustors for flame stabilization. Several prior studies have shown that these flames exhibit complex dynamics under near-blowoff conditions, associated with local flamelet extinction and alteration in the vortex breakdown flow structure. These extinction events are apparently due to the local strain rate irregularly oscillating above and below the extinction strain rate values near the attachment point. In this work, global, temporally resolved and detailed spatial measurements were obtained of hydrogen/methane flames. Supporting calculations of extinction strain rates were also performed using detailed kinetics. It is shown that flames become unsteady (or local extinctions happen) at a nearly constant extinction strain rate for different hydrogen/methane mixtures. Based upon analysis of these results, it is suggested that classic Damkohler number correlations of blowoff are, in fact, correlations for the onset of local-extinction events, not blowoff itself. Corresponding Mie scattering imaging of near-blowoff flames also was used to characterize the spatio-temporal dynamics of holes along the flame that are associated with local extinction.
A Load-Based Depth-Sensing Indentation Technique for Damage Assessment of Thermal Barrier Coatings
Authors: Kang B. S.-J. , Feng C. , Tannenbaum J. M. , Alvin M. A.
Published: February 2010

In this paper, we present a load-based micro-indentation technique for evaluating material mechanical property as well as degradation evaluation and debonding/spallation detection of thermal barrier coating (TBC) materials. Comparing to the current prevailing nano/micro-indentation methods, which require precise measurements of the indentation depth and load, the proposed technique only measures indentation load and the overall indentation displacement (i.e. including load-induced displacement of the loading apparatus). Coupled with a multiple-partial unloading procedure during the indentation process, this technique results in a load-depth sensing indentation system capable of determining Young’s modulus of metals, superalloys, and single crystal matrices, and stiffness of coated material systems with flat, tubular, or curved architectures. This micro-indentation technique can be viewed as a viable non-destructive evaluation (NDE) technique for determining as-manufactured and process-exposed metal, superalloy, single crystal, and TBC-coated material properties. This technique also shows promise for the development of a portable instrument for on-line, in-situ NDE and mechanical properties measurement of structural components.
Long-Term Oxidation Behavior of Various Chromia-Forming Alloys: Effect of Thermal Cycle Length
Authors: Deodeshmukh Vinay P. , Srivastava S. Krishna
Published: February 2010

Thermal cycle length can severely affect long-term oxidation behavior of high-temperature alloys. The present study is focused on the effect of thermal cycle length (twelve 30-day cycles versus six 60-day cycles) on the long-term (360 days) oxidation behavior of various chromia-forming alloys at 982°C, 1092°C, and 1149°C (1800°F, 2000°F, and 2100°F). The alloys included in this study are HAYNES® 230® alloy, 617 alloy, HR-160® alloy, HR-120® alloy, and 800HT® alloy. Alloy performances were assessed by analyzing the weight-change behavior and extent of attack as measured by metal loss and average internal penetration. The 230 and 617 alloys exhibited excellent oxidation resistance under both cycling conditions, presumably due to their ability to form and maintain adherent oxide scale. In particular, alloys with high Fe contents underwent accelerated oxidation attack. There was a significant increase in the extent of attack with increase in number of cycles (i.e. shorter cycle length). Moreover, the effect of cycle length was most pronounced at the highest test temperature (1149°C), and a strong correlation was found between oxidation kinetics and alloy composition as well as oxidation kinetics and the cycle length. HAYNES, 230, HR-160, HR-120 are registered trademarks of Haynes International, Inc. 800HT is a registered trademark of Special Metals Corporation.
Active Control of the Acoustic Boundary Conditions of Combustion Test Rigs: Extension to Actuators With Non-Linear Response
Authors: Bothien Mirko R. , Paschereit Christian Oliver
Published: February 2010

In the design process, new burners are generally tested in combustion test rigs. With these experiments, as well as with CFD, finite element calculations, and low-order network models, the burner’s performance in the full-scale engine is sought to be predicted. Especially, information about the thermoacoustic behaviour and the emissions is very important. As the thermoacoustics strongly depend on the acoustic boundary conditions of the system, it is obvious that test rig conditions should match or be close to those of the full-scale engine. This is, however, generally not the case. Hence, if the combustion process in the test rig is stable at certain operating conditions, it may show unfavourable dynamics at the same conditions in the engine. In previous works, the authors introduced an active control scheme which is able to mimic almost arbitrary acoustic boundary conditions. Thus, the test rig properties can be tuned to correspond to those of the full-scale engine. The acoustic boundary conditions were manipulated using woofers. In the present study, an actuator with higher control authority is investigated, which could be used to apply the control scheme in industrial test rigs. The actuator modulates an air mass flow to generate an acoustic excitation. However, in contrast to the woofers, it exhibits a strong non-linear response regarding amplitude and frequency. Thus, the control scheme is further developed to account for these non-linear transfer characteristics. This modified control scheme is then applied to change the acoustic boundary conditions of an atmospheric swirl-stabilized combustion test rig. Excellent results were obtained in terms of changing the reflection coefficient to different levels. By manipulating its phase, different resonance frequencies could be imposed without any hardware changes. The non-linear control approach is not restricted to the actuator used in this study and might therefore be of use for other actuators as well.
Waste Heat Recovery From Closed Brayton Cycle Using Organic Rankine Cycle: Thermodynamic Analysis
Authors: Yari Mortaza
Published: February 2010

This study examines the performance of a gas-cooled nuclear power plant with closed Brayton cycle (CBC) combined with an organic Rankine cycle (ORC) plant, as well as the irreversibility within the system. Individual models have been developed for each component, through applications of the first and second laws of thermodynamics. The overall system performance is then analyzed by employing individual models and further application of thermodynamic laws for the entire cycle, to evaluate the thermal efficiency and entropy production of the plant. The effects of the turbine inlet temperature, compressor pressure ratio, evaporator temperature, and temperature difference in the evaporator on the combined cycle first-law, second-law efficiency and exergy destruction rate are studied. Finally optimization of the combined cycle in a systematic way has been developed and discussed. It was found that the combined cycle first-law efficiency is about 9.5–10.1% higher than the simple CBC cycle. Also, the exergy destruction rate for the GT-MHR/ORC combined cycle, is about 6.5–8.3% lower than that of the GT-MHR cycle.
Investigation of Circular and Shaped Effusion Cooling Arrays for Combustor Liner Application—Part 1: Experimental Analysis
Authors: Facchini Bruno , Tarchi Lorenzo , Toni Lorenzo , Cinque Giuseppe , Colantuoni Salvatore
Published: February 2010

An experimental analysis of two different effusion cooled plates, with a feasible arrangement for combustor liner application, is presented in this paper. Though having the same porosity and very shallow injection angle (17 deg), the first configuration presents a “standard” circular drilling (D = 2.65 mm; L/D = 16.4), while the other has “shaped” holes with such an elliptical cross-section that leads to a circular imprint on the cooled surface (Dh = 3.39 mm; L/Dh = 12.8). Either geometry is to be studied on two different samples made of both an adiabatic and a high conductivity material. Tests performed on the adiabatic plates were required to obtain adiabatic effectiveness bidimensional distributions; a full 3D FEM post-processing procedure for the evaluation of the remnant and undesired heat fluxes across the surface was employed as well. Objective of the tests carried out on the conductive samples, having the same flow parameters as the adiabatic ones, was the estimation of overall efficiency, given by the combined effect of film protection and heat removal by convection inside the holes. Hot gas side heat transfer coefficient spanwise averaged values have been evaluated employing the outcome of both adiabatic and conductive tests. Experimental measurements were performed imposing two different coolant jet Reynolds numbers, 12500 and 20000, and varying blowing ratio from 5.0 to 9.0; effectiveness was evaluated with a steady-state technique, using TLC (Thermochromic Liquid Crystals) wide band formulation. Results reveal that the reduced coolant jet penetration achievable by means of shaped configuration leads to an increased wall protection in terms of both peak and spanwise averaged values, even if circular holes guarantee a more uniform effectiveness distribution.
Investigation of Circular and Shaped Effusion Cooling Arrays for Combustor Liner Application—Part 2: Numerical Analysis
Authors: Andreini A. , Bianchini C. , Ceccherini A. , Facchini B. , Mangani L. , Cinque G. , Colantuoni S.
Published: February 2010

A numerical analysis of two different effusion cooled plates, with a feasible arrangement for combustor liner application, is presented in this paper. Though having the same porosity and very shallow injection angle (17°), the first configuration presents a “conventional” circular drilling, while the other has “shaped” holes with such an elliptical cross-section that leads to a circular imprint on the cooled surface. Either geometries were the object of an experimental survey in which both adiabatic and overall effectiveness were measured. In order to compensate for the lack of detailed aerodynamic measurements, 3D CFD computations were performed for the two geometries. Steady state RANS calculations were carried out using a k–ε Two Layer turbulence model, both in the standard isotropic and in an algebraically corrected non isotropic version specifically tuned to better predict the lateral spreading of jets in a cross flow. Flow characteristic reproduce typical effusion cooled combustor liner conditions with blowing ratio of 5 and coolant jet Reynolds number of 12500. Even though good agreement could not be obtained comparing thermal adiabatic effectiveness with experiments, the findings of the experiments regarding the rating of the cooling efficiency of the two configurations were confirmed. Additionally, conjugate simulations were performed for the circular hole geometry in order to quantify heat transfer effects and to directly compare them with raw experimental overall effectiveness data.
High Power, High Pitch Velocity Gear Box Failures in Oil Production Fields
Authors: Ingistov S.
Published: February 2010

This Paper describes continuation of efforts to improve the low reliability of the high power, high pitch velocity gear boxes. These gear boxes are located in oil and gas production facilities (OAGPF) and serve to transmit the power from gas turbine drivers to large, two or three case turbo compressor trains. Life expectancy of these gear boxes did not meet predicted life expectancy of typical high speed, high energy gear boxes. This paper deals with various modifications of these gear boxes which were necessary to improve very low, initial 34% reliability. The series of modifications improved gear boxes life expectancies, however they never reached desired goal that is at least 10 years of continuous service without gear elements failures.