bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer for the Film-Cooled Vane of a 1-1/2 Stage High-Pressure Transonic Turbine: Part II—Effect of Cooling Variation on the Vane Airfoil and Inner Endwall
Authors: Kahveci Harika S. , Haldeman Charles W. , Mathison Randall M. , Dunn Michael G.
Published: May 2012

The impact of film cooling on heat transfer is investigated for the high-pressure vane of a one-and-one-half stage high-pressure turbine operating at design corrected conditions. Cooling is supplied through three independently controllable circuits to holes in the inner and outer endwall, vane leading edge showerhead, and the pressure and suction surfaces of the airfoil in addition to vane trailing edge slots. Four different overall cooling flow rates are investigated and one cooling circuit is varied independently. All results reported in this part of the paper are for a radial inlet temperature profile, one of the four profiles reported in Part I of this paper. Part I describes the experimental setup, data quality, influence of inlet temperature profile, and influence of cooling when compared to a solid vane. This part of the paper shows that the addition of coolant reduces airfoil Stanton Number by up to 60%. The largest reductions due to cooling are observed close to the inner endwall because the coolant to the majority of the vane is supplied by a plenum at the inside diameter. While the introduction of cooling has a significant impact on Stanton Number, the impact of changing coolant flow rates is only observed for gauges near 5% span and on the inner endwall. This indicates that very little of the increased coolant mass flow reaches all the way to 90% span and the majority of the additional mass flow is injected into the core flow near the plenum. Turning off the vane outer cooling circuit that supplies coolant to the outer endwall holes, vane trailing edge slots, and three rows of holes on the pressure surface of the airfoil, has a local impact on Stanton Number. Changes downstream of the holes on the airfoil pressure surface indicate that internal heat transfer from the coolant flowing inside the vane is important to the external heat transfer, suggesting that a conjugate heat-transfer solution may be required to achieve good external heat-transfer predictions in this area. Measurements on the inner endwall show that temperature reduction in the vane wake due to the trailing edge cooling is important to many points downstream of the vane.
Energy Usage in Natural Gas Pipeline Applications
Authors: Garcia-Hernandez Augusto , Brun Klaus
Published: May 2012

Energy required to transport the fluid is an important parameter to be analyzed and minimized in pipeline applications. However, the pipeline system requirements and equipment could impose different constraints for operating pipelines in the best manner possible. One of the critical parameters that is looked at closely, is the machines’ efficiency to avoid unfavorable operating conditions and to save energy costs. However, a compression-transport system includes more than one machine and more than one station working together at different conditions. Therefore, a detailed analysis of the entire compression system should be conducted to obtain a real power usage optimization. This paper presents a case study that is focused on analyzing natural gas transport system flow maximization while optimizing the usage of the available compression power. Various operating scenarios and machine spare philosophies are considered to identify the most suitable conditions for an optimum operation of the entire system. Modeling of pipeline networks has increased in the past decade due to the use of powerful computational tools that provide good quality representation of the real pipeline conditions. Therefore, a computational pipeline model was developed and used to simulate the gas transmission system. All the compressors’ performance maps and their driver data such as heat rate curves for the fuel consumption, site data, and running speed correction curves for the power were loaded in the model for each machine. The pipeline system covers 218 miles of hilly terrain with two looped pipelines of 38″ and 36″ in diameter. The entire system includes three compressor stations along its path with different configurations and equipment. For the optimization, various factors such as good efficiency over a wide range of operating conditions, maximum flexibility of configuration, fuel consumption and high power available were analyzed. The flow rate was maximized by using instantaneous maximum compression capacity at each station while maintaining fixed boundary conditions. This paper presents typical parameters that affect the energy usage in natural gas pipeline applications and discusses a case study that covers an entire pipeline. A modeling approach and basic considerations are presented as well as the results obtained for the optimization.
Alternative Approach to Determining the Preferred Plant Size of Parabolic Trough CSP Power Plants
Authors: Sa´nchez D. , Frej H. , Mun˜oz de Escalona J. M. , Chacartegui R. , Sa´nchez T.
Published: May 2012

The share of Concentrated Solar Power plants in power generation has increased significantly in the last decade due to the need to develop and deploy clean technologies that help reduce the carbon footprint of the power generation industry and, at the same time, are less voracious in terms of fossil fuel consumption. As a governmental support to promote the installation of solar plants, different incentives are found in most countries: complementary rates to the market price of electricity (premium), tax credits, financial support, long term power purchase agreements and, in general, other mechanisms that are generally grouped in a “feed-in tariff” that should ideally be more demanding (stringent) over time. The objective of these measures is to make this technology competitive in the mid/long term. At the same time, and in order to distribute these economical resources as fairly as possible, governments have usually limited the power output of those power plants benefitting from these incentives, as a means to prevent oligopolies that would eventually stop technology evolution while concentrating on preserving market conditions. This has led to the common 50 and 80 MW limits that exist in Spain and the USA respectively. As a consequence, OEMs and EPCs have focused on developing reliable and cost-effective CSP plants of these sizes, especially 50 MW. This work is based on unrestrained regulatory or market scenarios, with the aim of finding out which plant size yields the best efficiency at the lowest cost of electricity (COE). In other words, the objective is to establish the plant size of interest for power producers and consumers, should CSP facilities compete in the same market conditions as conventional fossil-fuel plants. The work begins by reviewing briefly the origins of the usual constraints applied to CSP plants. Then, a survey of existing literature dealing with the issue of technical and economic CSP optimization is presented, with a special focus on the work by B. Kelly from Nexant Inc. Taking this work as reference, a model of performance of parabolic trough plants developed in Thermoflex environment to put forth strong project specific feature of CSP facilites. Thermal storage and natural gas hybridization are included among the key design parameters.
Experimental Study and Optimization of a 2.44 Meter Vertical Axis Wind Turbine
Authors: Nichols Brad , Dimond Timothy , Storer Josh , Allaire Paul
Published: May 2012

Vertical axis wind turbines (VAWTs) have long been considered a viable source for alternative energy; however, limited published research has contributed to limited technological advancement in these machines. Slower advancements are due, in part, to their complex aerodynamic models which include wake effects, vortex shedding, and cyclical blade angles of attack and Reynolds numbers. VAWTs are believed to hold several advantages over their more popular and better studied horizontal axis counterparts, including a simpler design and better efficiencies in lower wind speeds. They may have a unique niche in standalone applications at moderate wind speeds such as on an island, a remote military installation, or an inland farm. Currently, no published design standards or criteria exist for optimizing the physical properties of these turbines to maximize power output. A 2.44 m tall VAWT prototype with variable physical parameters was constructed for wind tunnel testing. The purpose of the experiment was to maximize the turbine’s power output by optimizing its physical configuration within the given parameters. These parameters included rotor radius, blade chord length, and pitch offset angle. The prototype was designed as a scaled-down model of a potential future VAWT unit that may be used to sustain a small farm or 2–4 houses. The wind tunnel consisted of a 2.74 m by 1.52 m cross section and could produce maximum wind speeds of 3.56 m/s. The turbine prototype consisted of three sets of interchangeable blades featuring two airfoils of varying chord length. Spokes of varying length allowed for rotor radii of 190.5, 317.5, and 444.5 mm. The pitch offset of the blades was varied from 0°–20° with a focus on the 10°–16° range as preliminary results suggested that this was the optimal range for this turbine. Ramp-up and steady-state rotational speeds were recorded as the blades were interchanged and the turbine radius was varied. A disk brake provided braking torque so that power coefficients could be estimated. This study successfully optimized the turbine’s power output within the given set of test parameters. The importance of finding an appropriate aspect ratio and pitch offset angle are clearly demonstrated in the results. A systematic approach to small scale wind tunnel testing prior to implementation is presented in this paper.
A Comparative Study on Accuracy and Efficiency of Metamodels for Large Industrial Datasets
Authors: Subramaniyan Arun K. , Wang Liping , Beeson Don , Nelson John , Berg Richard , Cepress Randall
Published: May 2012

This paper provides a comparative study on accuracy and efficiency of metamodels constructed from large datasets. Two examples inspired by large industrial applications are used to identify the best metamodeling technique. Artificial Neural Networks, Radial Basis Functions, Gaussian Process and Nonlinear regression are used to build metamodels. The examples used showcase a broad range of industrial applications in aircraft engines and gas turbines. Although Radial Basis Functions and Gaussian Process models are robust for small data sets, their high computational cost for large datasets reduces their practical application. ANN models are found to perform optimally when large number of training points are readily available and the accuracy requirements are high.
Overall and Adiabatic Effectiveness Values on a Scaled Up, Simulated Gas Turbine Vane: Part I—Experimental Measurements
Authors: Dees Jason E. , Bogard David G. , Ledezma Gustavo A. , Laskowski Gregory M.
Published: May 2012

Recent advances in computational power have made conjugate heat transfer simulations of fully conducting, film cooled turbine components feasible. However, experimental data available with which to validate conjugate heat transfer simulations is limited. This paper presents experimental measurements of external surface temperature on the suction side of a scaled up, fully conducting, cooled gas turbine vane. The experimental model utilizes the matched Bi method, which produces non-dimensional surface temperature measurements that are representative of engine conditions. Adiabatic effectiveness values were measured on an identical near adiabatic vane with an identical geometry and cooling configuration. In addition to providing a valuable data set for computational code validation, the data shows the effect of film cooling on the surface temperature of a film cooled part. As expected, in nearly all instances the addition of film cooling was seen to decrease the overall surface temperature. However, due to the effect of film injection causing early boundary layer transition, film cooling at a high momentum flux ratio was shown to actually increase surface temperature over 0.35 < s/C < 0.45.
Overall and Adiabatic Effectiveness Values on a Scaled Up, Simulated Gas Turbine Vane: Part II—Numerical Simulations
Authors: Ledezma Gustavo A. , Laskowski Gregory M. , Dees Jason E. , Bogard David G.
Published: May 2012

Conjugate heat transfer (CHT) calculation techniques for the heat transfer analysis of high-pressure turbines (HPT) have been developed during the past few years. Thus, it has become possible to take into account the coupling of the film, internal cooling, external gas flow and the metal diffusive heat transfer. The coupling problem may become extremely important in regions such as the airfoil leading edge and the vicinity of film hole breakout region where heat fluxes and thermal gradients are high. This article presents the results obtained using fully coupled 3D CHT simulations of a simplified film-cooled leading edge model and a NASA C3X vane with suction side film cooling. The results for the two cases are compared against experimental data obtained at University of Texas at Austin. The numerical simulations were conducted using the k-ω turbulence model. The leading edge model overall effectiveness predictions are in good agreement with the experiments, especially in the low blowing ratio range (1≤M≤2). For the C3X vane, the CHT results tend to underpredict the midspan and laterally averaged effectiveness due to film liftoff. However, the quantitative agreement is still reasonably good. The different levels of overall effectiveness agreement found between all cases are discussed.
Compressor Blade Modelling Under Highly Negative Incedence
Authors: Zachos Pavlos K. , Ruelke Cornelia , Pachidis Vassilios , Singh Riti
Published: May 2012

This paper investigates performance prediction techniques for compressor blades operating under highly negative incidence angle which is typical during engine groundstarts or windmilling relights. Although this is a very frequently occurring situation during the life of an aero engine, turbomachinery components are rarely tested under those conditions in the sake of resource saving. However, performance engineers require some knowledge of generic blade loss coefficients under those conditions for the preliminary estimation of the groundstart or relight capability of the engine which is also linked to design decisions such as the volume of the combustion chamber. A blade element concept is employed to break a 3D compressor blade design down to a number of 2D cross sections and study them separately using a CFD derived 2D blade loss coefficient database. Several different ways to synthesize the 3D blade out of the 2D sections are herein presented based on different expressions of blade aerodynamic coefficients. An investigation based on the expressions of the aerodynamic coefficients is conducted in order to justify the applicability of the blade element theory at such off-design conditions. The most suitable parameter set to represent a three dimensional blade design by a number of radially stacked two dimensional profiles is identified. The analysis shows that the approach based on pressure change and tangential force coefficients can more adequately approximate the performance of the 3D blade and therefore can be safely employed for a preliminary off-design blade performance studies.
Distributed Parameter Acoustic Modeling of a Perforation With Bias Flow
Authors: Mazdeh Alireza , Kashani Reza
Published: May 2012

Perforated acoustic liners (screech liners) with bias flow are commonly used for mitigation of thermoacoustic instabilities in augmentors. In addition to cooling the liner, the flow of air thru the liner perforation (dubbed ‘bias flow’) improves the damping effectiveness of the liner thru enhancing its energy dissipation. These liners are currently being designed using empirical design rules followed by build-test-improve steps, basically trial and error. The development of physics-based tools to assist in the design of such liners is of great interest to practitioners. In this paper, the existing work in developing analytical, semi-empirical, and numerical techniques such as Large-Eddy Simulations (LES) in exploring the damping effectiveness of an acoustic liner with bias flow are reviewed. The paper continues with presenting the research in progress that has been conducted by the authors in this area with the goal of expanding the numerical modeling work beyond the current state of the art by including the variables that were not incorporated in previous studies including, but not limited to, hole orientation, combined effect of tangential grazing flow and bias flow interaction with acoustics, and different flow characteristics (Mach and Reynolds number). In addition, the spatial distribution of pressure and velocity over the aperture area (instead of the current practice of averaging these variables) are being looked at.
Estimating the Probabilistic Size and Shape Distributions of 3D Anomalies From Sectioning Measurements Using the Stereological Unfolding Approach
Authors: Liang Wuwei , Enright Michael P.
Published: May 2012

The accuracy of probabilistic risk assessment of rotor disks is strongly dependent on the accurate description of the size and shape distributions of anomalies in alloys. These size-shape distributions of anomalies are often derived from planar sectioning data measurements using stereological unfolding algorithms. Since it is impossible to accurately predict the shape and orientation parameters of a general ellipsoid based on measurements obtained from two-dimensional sectioning data, the anomaly model should be limited to a spheroid. In this study, an unfolding algorithm was implemented and verified that can be used to estimate the probabilistic dimensions and orientations of 3D spheroids based on 2D section data. It is shown that the accuracy of the predicted spheroid model is dependent on the number of sections and the discretization of the mesh used to characterize the data.
Modeling of Biodiesel Fueled Micro Gas Turbine
Authors: Zabihian Farshid , Fung Alan S. , Chiang Hsiao-Wei D.
Published: May 2012

Biodiesel is an environmentally benign renewable alternative for conventional diesel fuel, and its utilization in macro gas turbines (MGT) is an interesting option for many applications. The objective of this work is to develop a steady-state model to evaluate the performance of a micro gas turbine fueled by the blends of biodiesel and petrodiesel. The concentration of inlet biodiesel to the model was 10%, 20%, and 30%. In order to validate the developed model, the results of modelling work were compared against the experimental data obtained from a micro gas turbine experimental unit. The engine was modified by mounting various sensors to monitor and record system performance parameters, such as pressure, temperatures, and flow rates at various locations as well as output power, and ambient conditions. The results indicate that most parameters are influenced, to some degree, by changes in the fuel composition. This indicates that although most MGTs can be potentially operated by a high concentration of biodiesel blends, before this fuel switching can be implemented, the system operational parameters should be evaluated by the system modeling to predict possible negative impacts of biodiesel in the inlet fuel on the engine.
Coal Ash Deposition on Nozzle Guide Vanes: Part II—Computational Modeling
Authors: Barker B. , Casaday B. , Shankara P. , Ameri A. , Bons J. P.
Published: May 2012

Coal ash deposition was numerically modeled on a GE-E3 high pressure turbine vane passage. A model was developed, in conjunction with Fluent™ software, to track individual particles through the turbine passage. Two sticking models were used to predict the rates of deposition which were subsequently compared to experimental trends. The strengths and limitations of the two sticking models, the critical viscosity model and the critical velocity model, are discussed. The former model ties deposition exclusively to particle temperature while the latter considers both the particle temperature and velocity. Both incorporate some level of empiricism, though the critical viscosity model has the potential to be more readily adaptable to different ash compositions. Experimental results show that both numerical models are reasonably accurate in predicting the initial stages of deposition. Beyond the initial stage of deposition, transient effects must be accounted for.
Real-Time Execution of a High Fidelity Aero-Thermodynamic Turbofan Engine Simulation
Authors: Fuksman Igor , Sirica Steven
Published: May 2012

In the past, a typical way of executing simulations in the real-time environment had been to use transfer function models, state-variable models or reduced-order aero-thermodynamic models. These models are typically not as accurate as the conventional full-fidelity aero-thermodynamic simulations used as basis for generation of the real-time models. Also, there is a cost associated with creation and maintenance of these derived real-time models. The ultimate goal is to use the high fidelity aero-thermodynamic simulation as the real-time model. However, execution of the high fidelity aero-thermodynamic simulation in a real-time environment is a challenging objective since accuracy of the simulation cannot be sacrificed to optimize execution speed, yet execution speed still has to be limited by some means to fit into real-time constraint. This paper discusses the methodology used to resolve this challenge, thereby enabling use of a contemporary turbofan engine high fidelity aero-thermodynamic simulation in the real-time environments.
Impact of Inter-Stage Dynamics on Stalling Stage Identification
Authors: Dhingra Manuj , Prasad J. V. R. , Tiwari Prashant , Nakano Tsuguji , Breeze-Stringfellow Andy
Published: May 2012

A key objective of compressor rig tests is the identification of compressor stall boundary. A complementary goal is the identification of the stalling stage based on test data. This serves two purposes: 1) Validate the pre-test prediction of the stage loading distribution, and 2) identify the weak stages, should improvements in operating range be desired in subsequent design iterations. Typically the pertinent test data is in the form of static pressure measurements. Many engineers believe that a stalling stage is accompanied by a transient upstream pressure rise coupled with a downstream pressure loss. However, inter-stage dynamics may cloud the identification of the stalling stage. To this end, an analysis of inter-stage dynamics, immediately preceding the stall event, could provide an alternate assessment of the stalling stage. This work reviews existing stall models for studying compressor dynamics. The main focus of this work is to develop ability to capture inter-stage dynamics. A 3-state equation lumped Moore-Greitzer (MG3) model is widely used to study the dynamic compressor response during surge and rotating stall transients. However the evolution of MG3 model may not provide a suitable framework for the investigation of inter-stage dynamics. On the other hand, an unsteady time marching 1-D fluid dynamic model (e.g. similar to the DynTECC formulation which includes body forces), while unable to capture the rotating stall dynamics, is sufficient for this purpose. A numerical simulation has been developed to investigate the impact of stage characteristics, as well as load distribution on the compression and expansion waves that develop prior to a surge event. Through a controlled weakening of selected stages, the time evolution of these waves is related back to the stalling stage. It is found that the weakened stage is not necessarily the stalling stage as identified via the pressure rise and downstream pressure drop pattern.
Low Emissions Power Generation Using Natural Gas Condensates
Authors: Joklik R. , Eskin L. , Klassen M. , Roby R. , Holton M. , Mallinson T.
Published: May 2012

A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed that converts liquid fuels into a substitute for natural gas. This fuel can then be burned with low emissions in virtually any combustion device in place of natural gas. This technology offers the possibility of using unprocessed oil-field Natural Gas Condensate (NGC) for local or export power generation using a DLN-equipped gas turbine rather than flaring, as is common practice in some regions. The ability to run a turbine on natural gas condensate with NOx and CO emissions comparable to those of natural gas has been demonstrated using a surrogate fuel made up from a mixture of naphtha (representing C4 and greater) and methane (representing <C4). The naphtha was vaporized using an LPP system, mixed with methane, and used to generate power in a 30kW Capstone C30 microturbine. The LPP Gas™ was tailored to match the modified Wobbe Index (MWI) of methane. NOx emissions in pre-mix mode on the surrogate NGC fuel were sub 5 ppm, indistinguishable from those when running on methane. CO emissions were sub 20 ppm, comparable to those on methane. At lower loads (in diffusion mode), NOx and CO emissions on surrogate NGC-based LPP Gas™ remain comparable to those on methane. No changes were required to the DLN gas turbine combustor hardware.
A Review of Mechanisms Controlling Bluff-Body Stabilized Flames With Closely-Coupled Fuel Injection
Authors: Lovett Jeffery A. , Cross Caleb , Lubarsky Eugene , Zinn Ben T.
Published: May 2012

The processes controlling bluff-body stabilized combustion have been extensively studied over the years because such stabilization approaches are commonly used in many practical systems. Much of the current understanding of this problem was attained in experimental and analytical studies of premixed combustion systems where the complexities introduced by fuel atomization, vaporization and mixing could be neglected. Yet, practical considerations often require fuel injection just upstream of the bluff-body stabilized combustion region. Consequently, it’s necessary to develop understanding of the fundamental processes in such non-premixed systems. Supplying fuel via the injection of discrete liquid fuel jets requires understanding of the complex physics of two-phase sprays and the transport to various regions within the combustor. This paper describes current understanding of the manner in which these processes affect flame stabilization in bluff-body combustion systems that employ close-coupled, liquid fuel injection. Specifically, the paper compares findings of premixed bluff-body flames with recent results obtained in studies using close-coupled fueling at Georgia Tech to support postulates of the processes controlling flame stabilization and flame structure. These findings are also used to propose a set of parameters that can be used to describe the combustion behavior and performance of such combustion systems.
Process Flow Model of Combined High Temperature Fuel Cell Operated With Mixture of Methane and Carbon Dioxide
Authors: Zabihian Farshid , Fung Alan S.
Published: May 2012

This paper investigates the impacts of carbon dioxide concentration in the inlet fuel on the performance of a hybrid tubular solid oxide fuel cell (SOFC) and gas turbine (GT) cycle with two configurations: system with and without anode exhaust recirculation. The reference case is introduced when the system is fueled by pure methane. Then, the performance of the hybrid SOFC-GT system is investigated when methane is partially replaced by CO2 from concentration of 0% to 90% with an increment of 5% at each step. The steady-state macro level model of the SOFC-GT hybrid system was developed in Aspen Plus® using built in and user-defined modules. The performance of the system was monitored by estimating and recording performance parameters, such as SOFC and system thermal efficiency; net and specific work of SOFC, GT, and cycle as a whole; air to fuel ratio; and mass and molar flow rate and temperature of various streams. The results demonstrate that the CO2 fraction in the inlet fuel has remarkable influences on the system’s operating parameters, such as efficiency and specific work.
Gas Turbines CHP for Bioethanol and Biodiesel Production Without Waste Streams
Authors: D’Alessandro Bruno , Bartocci Pietro , Fantozzi Francesco
Published: May 2012

In the context of the recent decision of the European Commission to incorporate a minimum of 10% biofuel by 2020 in total transport fuel use, the production of bioethanol and biodiesel will be boosted. When compared to fossil fuels this two biofuels have numerous advantages i.e. they are renewable, they run in conventional vehicles, they are not toxic, they are biodegradable, they show low particulate emissions and they are CO2 neutral. However they show some disadvantages such as the high energy demand of their production and the high yield of byproducts (i.e. glycerin for biodiesel and distiller’s waste for bioethanol), that require a dedicated marketing effort and supply chain. The energy demand required for the production of both biodiesel, through transesterification of vegetal oils, and bioethanol, through fermentation followed by distillation, is thermal and mechanical and can be satisfied by means of a CHP plant integrated in the production line fueled by its own byproducts. The paper analyzes the energy balances of two CHP plants fed with the above mentioned wastes (glycerin and wheat straw residues) and integrated in the biofuels (respectively biodiesel and bioethanol) production plants. The CHP plant considered are based on the IPRP (Integrated Pyrolysis Regenerated Plant) technology, meaning a gas turbine fed with syngas obtained from slow pyrolysis of the residues. Results show that in the case of biodiesel the production of glycerine is sufficient to satisfy the electricity demand of the plant that is lower than the heat demand, while the last cannot be completely covered because glycerine production is reduced respect to the input mass of vegetable oil and equal to 10% w/w. Concerning bioethanol, wheat straw residues are enough to cover heat demand that is the most important energy input of the process but they are not able to cover electricity input that is linked with the milling of the raw material. This is because of the reduced syngas yields and its lower energy content if compared with that obtained using glycerine.
Effect of Non-Uniform Blade Root Friction and Sticking on Disk Stresses
Authors: Simmons Harold R. , Iyengar Vishwas
Published: May 2012

Stress levels predicted by conventional disk modeling assumptions are lower than expected to cause conventional creep or fatigue damage consistent with slot failures experienced in some compressor and turbine disks. It was suspected that disparate slot to slot friction at the blade root surface will result in sticking of some blade roots as the turbine is shut down while adjacent blades slip; the un-resisted stuck root would pry the steeples apart causing additional bending stress. Testing of a blade root/disk slot pair in a load frame found that the blade root will stick in place as imposed radial loads decrease. Simulation of blade root movement during shutdown indicates peak stress can increase by 20% or more depending on geometric factors. The slot stress only rises above its maximum speed condition on shutdown (at 80% Max Speed in the example case). This brief stress rise will not cause significant creep damage, but can shorten disk life based on low cycle fatigue or hold time fatigue damage.
Development of an Open Rotor Cycle Model in NPSS Using a Multi-Design Point Approach
Authors: Hendricks Eric S.
Published: May 2012

NASA’s Environmentally Responsible Aviation Project and Subsonic Fixed Wing Project are focused on developing concepts and technologies which may enable dramatic reductions to the environmental impact of future generation subsonic aircraft [1][2]. The open rotor concept (also referred to as the Unducted Fan or advanced turboprop) may allow the achievement of this objective by reducing engine emissions and fuel consumption. To evaluate its potential impact, an open rotor cycle modeling capability is needed. This paper presents the initial development of an open rotor cycle model in the Numerical Propulsion System Simulation (NPSS) computer program which can then be used to evaluate the potential benefit of this engine. The development of this open rotor model necessitated addressing two modeling needs within NPSS. First, a method for evaluating the performance of counter-rotating propellers was needed. Therefore, a new counter-rotating propeller NPSS component was created. This component uses propeller performance maps developed from historic counter-rotating propeller experiments to determine the thrust delivered and power required. Second, several methods for modeling a counter-rotating power turbine within NPSS were explored. These techniques used several combinations of turbine components within NPSS to provide the necessary power to the propellers. Ultimately, a single turbine component with a conventional turbine map was selected. Using these modeling enhancements, an open rotor cycle model was developed in NPSS using a multi-design point approach. The multi-design point (MDP) approach improves the engine cycle analysis process by making it easier to properly size the engine to meet a variety of thrust targets throughout the flight envelope. A number of design points are considered including an aerodynamic design point, sea-level static, takeoff and top of climb. The development of this MDP model was also enabled by the selection of a simple power management scheme which schedules propeller blade angles with the freestream Mach number. Finally, sample open rotor performance results and areas for further model improvements are presented.
A Statistical Characterization of the Effects of Mistuning in Multi-Stage Bladed Disks
Authors: D’Souza Kiran X. , Epureanu Bogdan I.
Published: May 2012

A great deal of research has been conducted on the effects of small random variations in structural properties, known as mistuning, in single stage bladed disks. Due to the inherent randomness of mistuning and the large dimensionality of the models of industrial bladed disks, a reduced order modeling approach is required to understand the effects of mistuning on a particular bladed disk design. Component mode mistuning (CMM) is an efficient compact reduced order modeling method that was developed to handle this challenge in single stage bladed disks. In general, there are multiple stages in bladed disk assemblies, and it has been demonstrated that for certain frequency ranges accurate modeling of the entire bladed disk assembly is required because multi-stage modes exist. In this work, a statistical characterization of structural mistuning in multi-stage bladed disks is carried out. The results were obtained using CMM combined with a multi-stage modeling approach previously developed. In addition to the statistical characterization, a new efficient classification method is detailed for characterizing the properties of a mode. Also, the effects of structural mistuning on the characterization of the mode is explored.
Experimental Investigation of Disc Cavity Leakage Flow and Hub Endwall Contouring in a Linear Rotor Cascade
Authors: Erickson Ryan D. , Simon Terrence W. , Zhang Luzeng , Moon Hee-Koo
Published: May 2012

An experimental study is carried out in a stationary linear cascade which simulates a turbine rotor to compare the thermal performance of two new axisymmetric endwall contour geometries. Measurements of endwall adiabatic film cooling effectiveness and near-endwall passage temperature fields are made for this purpose. In addition to documenting endwall contouring effects, a range of disc cavity leakage flow rates is investigated. This information is meant to quantify, over the range tested, the benefits and penalties of introducing leakage flow into the passage using the designated endwall contouring. Special attention is paid to determine whether the endwall curvature has any effect on the interaction between mainstream and secondary flows within the passage. Results indicate improved thermal performance when strong endwall curvature exists near the blade leading edge. The strong curvature causes cavity leakage flow to remain closer to the endwall, thereby increasing cooling effectiveness.
Experimental Analysis of Simultaneous Non-Harmonically Related Unstable Modes in a Swirled Combustor
Authors: Lamraoui Ammar , Richecoeur Franck , Ducruix Se´bastien , Schuller Thierry
Published: May 2012

The present study investigates combustion instabilities generated in a turbulent swirled combustor featuring two non-harmonically related unstable modes. Sound pressure and chemiluminescence spectra show the presence of two peaks located around 180 Hz and 280 Hz during unstable operation. The low frequency acoustic response of the test-rig is then analyzed using a two-coupled-cavity model including a realistic impedance of the system at the premixer inlet. This analytical approach is used to link the two observed frequencies to the first chamber and premixer modes respectively. Analytical predictions are compared with acoustic pressure measurements to determine the structure of these modes. The Rayleigh source term in the energy balance is also computed and shows that the two modes feed acoustic energy simultaneously in the system. High-speed PIV data gathered under unstable operation are filtered around these two frequencies to obtain phase conditioned images. Results show that the unsteady flow in the flame region features distinct dynamics associated to a bulk longitudinal oscillation of the flow in the flame arms at 180 Hz and large wrinkles in the radial direction at 280 Hz.
Measurements of Adiabatic Film and Overall Cooling Effectiveness on a Turbine Vane Pressure Side With a Trench
Authors: Albert Jason E. , Bogard David G.
Published: May 2012

Film cooling performance is typically quantified by separating the external convective heat transfer from the other components of the conjugate heat transfer that occurs in turbine airfoils. However, it is also valuable to assess the conjugate heat transfer in terms of the overall cooling effectiveness, which is a parameter of importance to airfoil designers. In the current study, adiabatic film effectiveness and overall cooling effectiveness values were measured for the pressure side of a simplified turbine vane model with three rows of showerhead cooling at the leading edge and one row of body film cooling holes on the pressure side. This was done by utilizing two geometrically identical models made from different materials. Adiabatic film effectiveness was measured using a very low thermal conductivity material, and the overall cooling effectiveness was measured using a material with a higher thermal conductivity selected such that the Biot number of the model matched that of a turbine vane at engine conditions. The theoretical basis for this matched-Biot number modeling technique is discussed in some detail. Additionally, two designs of pressure side body film cooling holes were considered in this study: a standard design of straight, cylindrical holes and an advanced design of “trenched” cooling holes in which the hole exits were situated in a recessed, transverse trench. This study was performed using engine representative flow conditions, including a coolant-to-mainstream density ratio of DR = 1.4 and a mainstream turbulence intensity of Tu = 20%. The results of this study show that adiabatic film and overall cooling effectiveness increase with blowing ratio for the showerhead and pressure side trenched holes. Performance decreases with blowing ratio for the standard holes due to coolant jet separation from the surface. Both body film designs have similar performance at a lower blowing ratio when the standard hole coolant jets remain attached. Far downstream of the cooling holes both designs perform similarly because film effectiveness decays more rapidly for the trenched holes.
Integrating Oil Health and Vibration Diagnostics for Reliable Wind Turbine Health Predictions
Authors: Sheldon Jeremy S. , Watson Matthew J. , Byington Carl S.
Published: May 2012

The Department of Energy’s (DOE) goal for wind energy is that it comprise 20% of the nation’s energy by 2030. For this to be achieved, so called “distributed wind” and off-shore wind farms will be required. However, to date, operating & maintenance and unscheduled outage costs make such applications risky [1]. A potential risk mitigation strategy is implementation of Prognostics and Health Management (PHM). Prognostics promise great benefits to parts order/handling, logistic planning, maintenance scheduling, which ultimately reduces the cost of ownership/operation. Successful prognostics require that faults be detected at the earliest possible stage. However, to fully realize the benefit of the investment, PHM systems must provide early detection of precursors for failure modes. Incipient fault detection is critical to increasing reliability and lowering Operation and Maintenance (O&M) costs for wind turbine gearboxes. The combination of this critical incipient fault detection capability with prognostics will allow wind turbine owners to reap the promised PHM benefits. It is possible to generalize gearbox faults into two areas: mechanical and lubricant related faults. To provide adequate coverage to both generalized areas, the authors will show how two primary sensing technologies can be combined to provide the necessary detection horizon for wind turbine gearboxes. The authors will introduce a generalized PHM architecture that can be adapted for a broad range of mechanical systems, especially wind turbine gearboxes. Various sensors and diagnostic techniques that can be integrated into the architecture will be discussed. Finally, the authors will show how the architecture, sensors, and techniques can be applied to a subscale test, including example results.
Control of Fan Blade Vibrations Using Piezoelectrics and Bi-Directional Telemetry
Authors: Provenza Andrew J. , Morrison Carlos R.
Published: May 2012

A novel wireless device which transfers supply power through induction to rotating operational amplifiers and transmits low voltage AC signals to and from a rotating body by way of radio telemetry has been successfully demonstrated in the NASA Glenn Research Center (GRC) Dynamic Spin Test Facility. In the demonstration described herein, a rotating operational amplifier provides controllable AC power to a piezoelectric patch epoxied to the surface of a rotating Ti plate. The amplitude and phase of the sinusoidal voltage command signal, transmitted wirelessly to the amplifier, was tuned to completely suppress the 3rd bending resonant vibration of the plate. The plate’s 3rd bending resonance was excited using rotating magnetic bearing excitation while it spun at slow speed in a vacuum chamber. A second patch on the opposite side of the plate was used as a sensor. This paper discusses the characteristics of this novel device, the details of a spin test, results from a preliminary demonstration, and future plans.
Robust Post-Processing Procedure for Multi-Hole Pressure Probes
Authors: Yasa Tolga , Paniagua Guillermo
Published: May 2012

Aerodynamic probes have been extensively used in turbine performance measurements for over 60 years to provide flow direction and Mach numbers. In turbomachinery applications the absence of adequate optical access prevents the use of laser-Doppler-anemometry (LDA), laser-two-focus velocimetry, particle-image-velocimetry (PIV). Moreover, multi-hole pressure probes are more robust than hot-wire or hot-fiber probes, and less susceptible to gas contamination. The pressure readings are converted into flow direction using calibration maps. Some researchers tried to model theoretically or numerically the calibration map to speed up the process. Due to manufacturing abnormalities, experimental calibration is still essential. The calibration map is obtained in a wind tunnel varying the yaw and pitch angles, while recording the hole-pressures. With the advent of powerful computers, researchers introduced sophisticated techniques to process the calibration data. Depending on the geometry or manufacturing imperfections a conventional calibration map is distorted, with multiple crossings resulting in the inability to identify a unique flow direction. In the current paper, a new calibration and data processing procedure is introduced for multi-hole probe measurements. The new technique relies on a set of calibration data rather than a calibration map. The pressure readings from each hole are considered individually through a minimization algorithm. Hence, the new technique allows computing flow direction even when a hole is blocked during the test campaign. The new methodology is demonstrated in a five-hole probe including estimates on the uncertainty.
Two- and Three-Dimensional Prescribed Surface Curvature Distribution Blade Design (CIRCLE) Method for the Design of High Efficiency Turbines, Compressors, and Isolated Airfoils
Authors: Korakianitis T. , Hamakhan I. A. , Rezaienia M. A. , Wheeler A. P. S.
Published: May 2012

The prescribed surface curvature distribution blade design (CIRCLE) method is presented for the design of two-dimensional (2D) and three-dimensional (3D) blades for axial compressors and turbines, and isolated blades or airfoils. The original axial turbine blade design method is improved, allowing it to use any leading-edge (LE) and trailing-edge (TE) shapes, such as circles and ellipses. The method to connect these LE and TE shapes to the remaining blade surfaces with curvature and slope of curvature continuity everywhere along the streamwise blade length, while concurrently overcoming the “wiggle” problems of higher-order polynomials is presented. This allows smooth surface pressure distributions, and easy integration of the CIRCLE method in heuristic blade-optimization methods. The method is further extended to 2D and 3D compressor blades and isolated airfoil geometries providing smooth variation of key blade parameters such as inlet and outlet flow angles, stagger angle, throat diameter, LE and TE radii etc. from hub to tip. One sample 3D turbine blade geometry is presented. The efficacy of the method is examined by redesigning select blade geometries and numerically evaluating pressure-loss reduction at design and off-design conditions from the original blades: two typical 2D turbine blades; two typical 2D compressor blades; and one typical 2D isolated airfoil blade geometries are redesigned and evaluated with this method. Further extension of the method for centrifugal or mixed-flow impeller geometries is a coordinate transformation. It is concluded that the CIRCLE method is a robust tool for the design of high-efficiency turbomachinery blades.