bluuebunny/crossref_metadata_2025 huggingface dataset:
Prediction of Ingress Through Turbine Rim Seals: Part 2—Combined Ingress
Authors: Owen J. Michael , Pountney Oliver , Lock Gary
Published: January 2011

In Part1 of this two-part paper, the orifice equations were solved for the case of externally-induced ingress, where the effects of rotational speed are negligible. In Part 2, the equations are solved, analytically and numerically, for combined ingress (CI) where the effects of both rotational speed and external flow are significant. For the CI case, the orifice model requires the calculation of three empirical constants, including Cd,e,RI and Cd,e,EI, the discharge coefficients for rotationally-induced (RI) and externally-induced (EI) ingress. For the analytical solutions, the external distribution of pressure is approximated by a linear saw-tooth model; for the numerical solutions, a fit to the measured pressures is used. It is shown that, although the values of the empirical constants depend on the shape of the pressure distribution used in the model, the theoretical variation of Cw,min (the minimum nondimensional sealing flow rate needed to prevent ingress) depends principally on the magnitude of the peak-to-trough pressure difference in the external annulus. The solutions of the orifice model for Cw,min are compared with published measurements, which were made over a wide range of rotational speeds and external flow rates. As predicted by the model, the experimental values of Cw,min could be collapsed onto a single curve, which connects the asymptotes for RI and EI ingress at the respective smaller and larger external flow rates. At the smaller flow rates, the experimental data exhibit a minimum value of Cw,min, which undershoots the RI asymptote. Using an empirical correlation for Cd,e, the model is able to predict this undershoot, albeit smaller in magnitude than the one exhibited by the experimental data. The limit of the EI asymptote is quantified, and it is suggested how the orifice model could be used to extrapolate effectiveness data obtained from an experimental rig to engine-operating conditions.
Chemical Kinetic Modeling in Coal Gasification Processes: An Overview
Authors: Slavinskaya N. A.
Published: January 2011

Coal is the fuel most able to cover world deficiencies in oil and natural gas. This motivates the development of new and more effective technologies for coal conversion into other fuels. Such technologies are focused on coal gasification with production of syngas or gaseous hydrocarbon fuels, as well as on direct coal liquefaction with production of liquid fuels. The benefits of plasma application in these technologies is based on the high selectivity of the plasma chemical processes, the high efficiency of conversion of different types of coal including those of low quality, relative simplicity of the process control, and significant reduction in the production of ashes, sulphur, and nitrogen oxides. In the coal gasifier, two-phase turbulent flow is coupled with heating and evaporation of coal particles, devolatilization of volatile material, the char combustion (heterogeneous/porous oxidation) or gasification, the gas phase reaction/oxidation (homogeneous oxidation) of gaseous products from coal particles. The present work reviews literature data concerning modelling of coal gasification. Current state of related kinetic models for coal particle gasification, plasma chemistry and CFD tools is reviewed.
Characteristics of Preheated Bio-Oil Sprays Produced by an Air-Blast Injector
Authors: Panchasara Heena V. , Agrawal Ajay K.
Published: January 2011

In this study the vegetable oil (VO) is preheated to reduce the kinematic viscosity, and thus, improve atomization. A commercial air-blast atomizer is used to produce the VO spray at ambient conditions of temperature and pressure. Characteristics of the resulting spray are measured using a laser sheet visualization system and a Phase Doppler Particle Analyzer system. Experiments are conducted for VO temperatures varying from 40 C to 100 C and air to liquid mass ratio (ALR) of 2.0 and 4.0. Results show a decrease in Sauter Mean Diameter with an increase in VO temperature, regardless of the ALR. Radial profiles show larger droplets migrating towards the edge of the spray and smaller droplets in the interior spray region. Results show a significant difference in distributions of mean and root mean square axial velocity profiles as the VO inlet temperature is increased for a fixed ALR. Higher VO inlet temperature and higher ALR produced a narrower spray with smaller diameter droplets and higher peak axial velocities. Overall, this study has shown that preheating VO improves atomization by producing spray with smaller diameter droplets.
Hybrid LES Approach for Practical Turbomachinery Flows: Part 1—Hierarchy and Example Simulations
Authors: Tucker Paul , Eastwood Simon , Klostermeier Christian , Jefferson-Loveday Richard , Tyacke James , Liu Yan
Published: January 2011

Unlike Reynolds Averaged Navier Stokes (RANS) models which need calibration for different flow classes, LES (where larger turbulent structures are resolved by the grid and smaller modeled in a fashion reminiscent of RANS) offers the opportunity to resolve geometry dependent turbulence as found in complex internal flows — albeit at substantially higher computational cost. Based on the results for a broad range of studies involving different numerical schemes, LES models and grid topologies an LES hierarchy and hybrid LES related approach is proposed. With the latter, away from walls, no LES model is used, giving what can be termed Numerical LES (NLES). This is relatively computationally efficient and makes use of the dissipation present in practical industrial CFD programs. Near walls, RANS modeling is used to cover over numerous small structures, the LES resolution of which is generally intractable with current computational power. The linking of the RANS and NLES zones through a Hamilton-Jacobi equation is advocated. The RANS-NLES hybridization makes further sense for compressible flow solvers, where, as the Mach number tends to zero at walls, excessive dissipation can occur. The hybrid strategy is used to predict flow over a rib roughened surface and a jet impinging on a convex surface. These cases are important for blade cooling and show encouraging results. Further results are presented in a companion paper.
U.S. Navy TF Series Engine Commonality and Reutilization Supporting Condition Based Maintenance
Authors: Ranero Joseph
Published: January 2011

This paper discusses the evolution of marine gas turbine (MGT) maintenance practices on the US Navy landing craft, air cushion (LCAC). This includes the progression from the philosophy of remove, replace and depot repair of engine modules, to a more condition based maintenance (CBM) practice. Included is the original concept of reusing all common TF40B parts, allowing the ETF40B to be created from a kit. The TF40B engine is being retired while the LCAC Service Life Extension Program (SLEP) is implemented. The propulsion part of the SLEP includes an ETF40B engine. Historically, the TF40B engine would be returned to a depot for repair. Supporting this in the past has relied on a costly and time consuming depot repair methodology. This paper will explore repair and overhaul approaches associated with the evolution of the US Navy’s philosophy. It will show the benefits of applying more on-condition type repairs, which will lead into a conditioned based overhaul (CBO) concept. There are discussions of the CBM concept that supports the current fleet. It delivers a large reduction in support costs and time consumption at a time of budget cuts and increased repair turn-around times from industry reductions in available parts and labor.
The Development and Testing of a Gas Turbine Engine Foreign Object Damage (FOD) Detection System
Authors: Cardwell D. N. , Chana K. S. , Gilboy M. T.
Published: January 2011

This paper details the development of a prototype in-flight foreign object damage (FOD) detection system through various stages, resulting in a system capable of detecting objects as small as one gram (1g) mass. The system comprises an eddy current sensor based tip timing system and acoustic emissions vibration sensors controlled through a digital signal processor (DSP). QinetiQ have developed light weight, contamination-immune eddy current tip timing sensors for use in engine health management. Engine tests confirmed these sensors’ potential for detecting FOD events. FOD detection algorithms were developed and implemented in a prototype DSP that was built and tested on an uninstalled gas turbine engine. The trials showed that the prototype DSP FOD detection system could detect dynamic FOD events at full engine speed. Further work was carried out to enhance the FOD detection system, overcoming limitations in the previous system through the implementation of enhanced algorithms and its extension to accept four eddy current sensor inputs as well as a vibration signal input from an acoustic emissions (AE) sensor. An algorithm that computes engine speed from the tip timing data was also implemented to alleviate the need for a separate 1/rev signal. A number of engine trials were successfully completed in order to validate the system. The speed algorithm has been successfully validated on engine trials and comparisons with a conventional optical based 1/rev showed the DSP-generated 1/rev signals to be almost identical to the conventional system. Typically, the error was in the region of 0.03% speed. The investigations culminated in a test series designed to ascertain the system’s sensitivity to foreign object impacts. These demonstrated that the system was capable of detecting objects down to one gram (1g) mass introduced at low speed into the engine intake.
The Challenges of High Altitude Gas Turbine Engine Cycles
Authors: Van Treuren Kenneth W. , McClain Stephen T.
Published: January 2011

High altitude flight, approaching 65,000 ft and above, is becoming increasingly important for various types of aircraft missions. Unmanned Aerial Vehicles (UAV), either for military reconnaissance or commercial/scientific study, are leading the way. For the military commander, high altitude, long endurance (HALE) flight for UAVs provides a good field of view for a long period of time and provides reasonable safety of flight. The upper atmosphere also provides the possibility for uncrowded, direct commercial flights. In addition, supersonic business jets are looking for a flight regime that also could be in the upper atmosphere. Typically, commercial, off-the-shelf engines are adapted for use in high altitude aircraft. While this has provided some success, the engine performance is marginal and the cycles are not optimized for this high altitude environment. Aircraft such as the Predator C and the Global Hawk are already operating in the high altitude environment with turbofan engines. More study is needed to determine what engine cycle is best suited to high altitudes. The smaller engines currently used in HALE UAVs carry a unique set of challenges which constrain the problem of high altitude propulsion hardware choices. Turbine engines have the most promise, especially turbofans, because of the higher speeds that are possible for the aircraft. Preliminary turbofan cycle analysis indicates that higher bypass-ratios and high compressor pressure ratios will be needed requiring more power output from the turbine however, high altitude limits how large these values can and should be. High altitude flight drives the cycle to be designed and sized at the high cruise altitude resulting in considerable impact on the off-design engine performance. Small gas turbine engine technology predictions show that fan pressure ratios of 1.76, compressor pressure ratios of 16.6, bypass ratios of 4.54, and a thrust specific fuel consumption of 0.393 /hr are possible in the near future (sea level reference). The cycle studied found a fan pressure ratio of 1.57, compressor pressure ratio of 16.7, bypass ratio of 5.45, and a thrust specific fuel consumption of 0.436 /hr (sea level reference) to be typical for a small gas turbine engine designed to fly at 65,000 ft. High altitude flight also brings other issues. Environmental impact must be considered in any high altitude application. High altitude reconnaissance aircraft often carry an increased sensor array adding more electric power requirements to the cycle. Long endurance means the engine cycle must be extremely fuel efficient. If stealth considerations are to be incorporated in the aircraft design, then the engine must be embedded in the fuselage limiting engine cross-section. Last, engine operational control will be a key technology for high altitude, low Reynolds number conditions.
Thermoacoustic Instabilities in an Annular Rijke Tube
Authors: Moeck Jonas P. , Paul Markus , Paschereit Christian Oliver
Published: January 2011

Thermoacoustic instabilities are a major concern in the design of gas turbine combustors. Most modern combustion chambers have an annular shape with multiple circumferentially arranged burners and, accordingly, suffer often from azimuthal instability modes. However, due to the complexity of a full annular system with a large number of burners, most experimental and numerical studies focus on single burner systems with essentially purely longitudinal acoustics. In the present work, we therefore introduce a thermoacoustic surrogate system — an annular Rijke tube — which, albeit its simplicity, possesses the basic mechanisms to feature unstable azimuthal modes. As in a conventional Rijke tube, the sources of mean and unsteady heat release in our set-up are electrically driven heating grids. Different azimuthal instability modes are observed in the experiment, and the effect of two types of circumferential variations of the power input is investigated. A full suppression of the unstable modes is achieved by the application of an elementary feedback controller. The experimental investigations are accompanied by corresponding calculations with a low-order system model. Theoretical and experimental results are found to agree well.
USN Marine Gas Turbine Development Initiatives: Part I—Advanced High Temperature Materials
Authors: Shifler David , Hoffman Donald , Hartranft John , Grala Carl , Aprigliano Louis , Groghan Dan
Published: January 2011

In the 1950’s and 1960’s, the United States Navy (USN) embarked on an ambitious program to convert surface combatants from steam to gas turbine power. Navy unique engines were developed and commercial industrial engines were modified to meet the strenuous environments encountered by surface Navy ships. Ultimately, the best engines were found to be those developed from the aero-industry. However, those aero-derivative engines lacked shock hardness, vibration treatment and most importantly, they lacked the ability to survive long hours of operation in a heavy salt environment burning diesel and other poorer fuels. Those poorer fuels contained higher levels of sulfur and other chemical compounds that created a challenging environment for the aircraft engines. The aircraft engines were designed to burn much cleaner fuel with virtually no sea salt. As a result, early applications of those engines to Navy ships were disappointing. However, through aggressive materials development programs and extended endurance tests in a marine-like environment, engines including the Pratt and Whitney FT-4A and the General Electric LM2500 demonstrated themselves to be superior replacements for traditional Navy steam propulsion plants. The LM2500 eventually became the workhorse of the USN surface fleet and has proven to be an excellent engine. Nevertheless, as fuels become more costly and quality sometimes questionable, the Navy is interested in another leap forward. This leap is anticipated to again be based on aero-derivative engines, but will be focused on smaller, lighter, and more fuel efficient engines that will have the capability of burning the alternative fuels of the future. The Office of Naval Research (ONR) is contemplating a comprehensive program of materials developments, Phase I, which will facilitate the marinization of the highly efficient gas turbine engines being developed in various Air Force and commercial engine development programs. Marinization issues could include improving the performance of ceramic matrix composites in a marine environment and minimizing the affects of higher temperatures on disc corrosion in the final stages of the compressor and in the hot-section. A Phase II program is also contemplated that will then develop a series of engines for various future USN applications based on the results of the Phase I Program. This paper will describe the programs that are being contemplated.
On Forced Response of a Rotating Integrally Bladed Disk: Predictions and Experiments
Authors: Gibert Claude , Kharyton Vsevolod , Thouverez Fabrice , Jean Pierrick
Published: January 2011

An experimental setup is described which permits to rotate a bladed disk in vacuum and to measure its dynamic response to excitations provided by some embedded piezoelectric actuators. A particular spatial placement of actuators associated with phase-shifting electronic circuits is set for simulating travelling wave excitations with respect to the rotating frame. The system is demonstrated on an actual high-pressure compressor (HCP) integrally bladed disk. The dynamic response of the blisk is analyzed experimentally and results are correlated with those obtained from a simplified finite elements model taking into account Coriolis effect. The paper focuses on the influence of the latter which is most of the time neglected and its implication on the forced response levels is studied into two situations without or with mistuning.
Heat Transfer Investigation of an Aggressive Intermediate Turbine Duct: Part 1—Experimental Investigation
Authors: Arroyo Osso Carlos , Johansson T. Gunnar , Wallin Fredrik
Published: January 2011

In most designs of two-spool turbofan engines, intermediate turbine duct (ITD’s) are used to connect the high-pressure turbine (HPT) with the low-pressure turbine (LPT). Demands for more efficient engines with reduced emissions require more “aggressive ducts”, ducts which provide both a higher radial offset and a larger area ratio in the shortest possible length, while maintaining low pressure losses and avoiding non-uniformities in the outlet flow that might affect the performance of the downstream LPT. The work presented in this paper is part of a more comprehensive experimental and computational study of the flowfield and the heat transfer in an aggressive ITD. The main objectives of the study were to obtain an understanding of the mechanisms governing the heat transfer in ITD’s and to obtain high quality experimental data for the improvement of the CFD-based design tools. This paper consists of two parts. The first one, this one, presents and discusses the results of the experimental study. In the second part, a comparison between the experimental results and a numerical analysis is presented. The duct studied was a state-of-the-art “aggressive” design with nine thick non-turning structural struts. It was tested in a large-scale low-speed experimental facility with a single-stage HPT. In this paper measurements of the steady convective heat transfer coefficient (HTC) distribution on both endwalls and on the strut for the duct design inlet conditions are presented. The heat transfer measurement technique used is based on infrared-thermography. Part of the results of the flow measurements is also included.
Numerical Study of Internal Flow Fields in Steam Turbine Stages With Balance Holes
Authors: Luo Chang , Song Liming , Li Jun , Feng Zhenping , Cao Shouhong , Wu Zhihua , Wu Qilin
Published: January 2011

A new calculation model is proposed to simulate flows in the steam turbine stages with balance holes in this paper. The model describes the flows in a 2.5 stage turbine with focus on the second stage and the corresponding seals, balance holes and disk cavities. The aerodynamic performance of the turbine stages is predicted by using a three-dimensional Reynold-Averaged Navier-Stokes (RANS) solver. The Spalart-Allmaras one equation turbulence model is adopted, and the RANS solver is run in steady mode using the mixing plane approach. In order to analyze the impact of leakage flow on main flow, the aerodynamic performance of the ideal flow path turbine stages (without balance holes and seals) is also calculated. The numerical results show that the total-total efficiency of the turbine stages with balance holes is 1.81% lower than that of ideal flow path turbine stages. The flow characteristics in the seals, disk cavities and balance holes and their influence on the mainstream are described. Finally, the influence of the balance hole diameter and radius crossing the balance hole axis on the turbine stage performance is studied. The variations of the torque, axial thrust and relative efficiency with the diameter and radius are presented respectively.
Validated F-T Fuel Surrogate Model for Simulation of Jet-Engine Combustion
Authors: Naik Chitralkumar V. , Puduppakkam Karthik V. , Modak Abhijit , Wang Cheng , Meeks Ellen
Published: January 2011

Validated surrogate models have been developed for two Fisher-Tropsch (F-T) fuels. The models started with a systematic approach to determine an appropriate surrogate fuel composition specifically tailored for the two alternative jet-fuel samples. A detailed chemical kinetic mechanism has been assembled for these model surrogates starting from literature sources, and then improved to ensure self-consistency of the kinetics and thermodynamic data. This mechanism has been tested against fundamental laboratory data on auto-ignition times, laminar flame-speeds, extinction strain rates, and NOx emissions. Literature data used to validate the mechanism include both the individual surrogate-fuel components and actual F-T fuel samples where available. As part of the validation, simulations were performed for a wide variety of experimental configurations, as well as a wide range of temperatures and equivalence ratios for fuel/air mixtures. Comparison of predicted surrogate-fuel behavior against data on real F-T fuel behavior also show the effectiveness of the surrogate-matching approach and the accuracy of the detailed-kinetics mechanisms. The resulting validated mechanism has been also reduced through application of automated mechanism reduction techniques to provide progressively smaller mechanisms, with different degrees of accuracy, that are reasonable for use in CFD simulations employing detailed kinetics.
Axial Transonic Rotor and Stage Behavior Near the Stability Limit
Authors: Gannon Anthony J. , Hobson Garth V. , Davis William L.
Published: January 2011

Transient casing pressure data from a transonic rotor and rotor-stator stage measured using high-speed pressure probes embedded in the casewall over the rotor tips is analyzed. Using long data sets sampled at a high frequency, low-frequency (less than once-per-revolution) non-axisymmetric flow phenomena were detected while operating at steady-state conditions near stall. Both the rotor and stage cases are investigated and the difference in behavior of a rotor with and without a stator blade row is investigated. Data for both cases over the speed range 70–100% of design and from choke to near the stability limit (stall or surge) is presented. The root mean square power of the low-frequency signal as well as its fraction of the total pressure signal is presented. It was thought that the behavior of these signals as stall was approached could lead to some method of detecting the proximity of stall. For the rotor-only configuration the strength of these non-axisymmetric phenomena increased as stall was approached for all speed-lines. However for the stage configuration, more representative of an operational machine, these were of a lower magnitude and did not exhibit a clearly increasing trend as stall was approached. This would seem to indicate that the stator suppressed these signals somewhat. It is also shown that these non-axisymmetric phenomena led to a significant variation of the mean relative inlet flow angle into the rotor blade. During stable operation near to stall at 100% speed for the rotor-only case a 1.9° variation of this angle was measured. This compared with a 5.6° variation over the entire speed line. Further it was observed that while the rotor and stage cases had different stability limits their peak relative inlet flow angles near stall were similar for both along most speed-lines.
Study on Aerodynamic Redesign of a High Pressure Ratio Centrifugal Compressor
Authors: Zhang Chaolei , Deng Qinghua , Feng Zhenping
Published: January 2011

This paper describes the aerodynamic redesign and optimization of a typical single stage centrifugal compressor, in which the total pressure ratio was improved from the original 4.0 to final 5.0 with the restrictions of keeping the impeller tip diameter, the design rotational speed and the design mass flow rate unchanged. Firstly the backsweep angle and the outlet blade height of the impeller were adjusted and the vaned diffuser was redesigned. Then a sensitivity analysis of the aerodynamic performance correlated to the primary redesign centrifugal compressor stage with respect to the chosen redesign variables was conducted, according to the parameterized results of the impeller and the vaned diffuser. Secondly the impeller and the vaned diffuser were optimized respectively under the stage environment at the design operation condition to improve the stage isentropic efficiency by using a global optimization method which coupled Evolutionary Algorithm (EA) and Artificial Neural Network (ANN), provided by the commercial software NUMECA DESIGN-3D. Subsequently the detailed performance maps of the centrifugal compressor stage corresponding to the primary redesign configuration and the optimum configuration were presented by Computational Fluid Dynamics (CFD) simulation. Finally the flow fields correlated to the centrifugal compressor configurations before and after optimization at the design operation condition were also compared and analyzed in detail. As a result the design target was achieved after the primary redesign, as a 2.7% gain in stage efficiency and a 3.6% increase in stage pressure ratio were obtained when compared with the primary redesign configuration after optimization. Moreover, the aerodynamic performance of the optimum configuration at the off-design operation conditions was also improved.
Supersonic Jet Noise Reduction Using Fluidics, Mechanical Chevrons and Fluidically Enhanced Chevrons
Authors: Munday David , Heeb Nick , Gutmark Ephraim , Liu Junhui , Kailasanath K.
Published: January 2011

This paper presents observations and simulations of the impact of several technologies on modifying the flow field and acoustic emissions from supersonic jets from nozzles typical of those used on military aircraft. The flowfield is measured experimentally by shadowgraph and particle image velocimetry (PIV). The acoustics are characterized by near and far-field microphone measurements. The flow and near-field pressures are simulated by monotonically integrated large-eddy simulation (MILES). Use of unstructured grids allows accurate modeling of the nozzle geometry. The nozzle geometries used in this research are representative of practical engine nozzles. The emphasis of the work is on “off-design” or non-ideally expanded flow conditions. The technologies applied to these nozzles include chevrons, fluidic injection and fluidically enhanced chevrons. The fluidic injection geometry and fluidic enhancement geometry follow the approach found successful for subsonic jets by Alkislar, Krothapalli & Butler [1] employing jets pitched 60° into the flow, impinging on the shear layer just past the tips of the chevrons, or in the same axial position when injection is without chevrons.
Influence of Rotor Blade Fillets on Aerodynamic Performance of Turbine Stage
Authors: Shi Yan , Li Jun , Feng Zhenping
Published: January 2011

In this paper, steady and unsteady flow simulations were performed to investigate the influence of rotor fillet on the performance of turbine stage, based on 3D compressible Navier-Stokes equations closed with the Spalart-Allmaras turbulence model. The profile of Aachen turbine was employed and the fillet modeled by two shape parameters was placed at the junctions between the rotor blade and the endwalls (at both tip and hub). Based on the comparisons of the efficiency and the flow rate of turbine stage among the cases with different fillet shapes, the roles of two shape parameters were evaluated. To understand the mechanism of the rotor fillet influence on the flow field, the aerodynamic load, secondary flow and loss were analyzed and compared between the cases with and without the rotor fillet. It is found that the fillet is capable of restraining the flow separation near the leading edge of the rotor blade while inducing the displacement of the flow from the endwalls towards the mid-span, which enhances the loss generated by the interaction between the secondary flow and the main stream. Consequently, associated with the distribution of the loss at the outlet of the turbine stage, the best clocking position near the endwalls for the downstream blade moves about 10%∼20% of rotor pitch in the direction of rotor rotation. Therefore, the shape of the fillet in the rotor blade should be especially controlled in the process of the rotor design and manufacture, even though it is a minor part in the turbomachine.
Comparison of Film Effectiveness and Cooling Uniformity of Conical and Cylindrical-Shaped Film Hole With Coolant-Exit Temperature Correction
Authors: Nguyen Cuong Q. , Johnson Perry L. , Bernier Bryan C. , Ho Son H. , Kapat Jayanta S.
Published: January 2011

Data from conical-shaped film cooling holes is extremely sparse in open literature, especially the cooling uniformity characteristic, an important criterion for evaluating any film cooling design. The authors will compare the performance of conical-shaped holes to cylindrical-shaped holes. Cylindrical-shaped holes are often considered a baseline in terms of film cooling effectiveness and cooling uniformity coefficient. The authors will study two coupons with conical-shaped holes, which have 3° and 6° diffusion angles, named CON3 and CON6 respectively. A conjugate heat transfer computational fluid dynamics model and an experimental wind tunnel will be used to study these coupons. The three configurations: cylindrical baseline, CON3, and CON6, have a single row of holes with an inlet metering diameter of 3mm, length-to-nominal diameter of 4.3, and an injection angle of 30°. In this study, the authors will also take into account the heat transfer into the coolant flow from the coolant channel. In other words, coolant temperature at the exit of the coolant hole will be different than that measured at the inlet, and the conjugate heat transfer model will be used to correct for this difference. For the numerical model, the realizable k-ε turbulent model will be applied with a second order of discretization and enhanced wall treatment to provide the highest accuracy available. Grid independent studies for both cylindrical-shaped film cooling holes and conical-shaped holes will be performed and the results will be compared to data in open literature as well as in-house experimental data. Results show that conical-shaped holes considerably outperform cylindrical-shaped holes in film cooling effectiveness at all blowing ratios. In terms of cooling uniformity, conical-shaped holes perform better than cylindrical-shaped holes for low and mid-range blowing ratios, but not at higher levels.
Impulse Testing and Blade Load Simulation Tools to Estimate Cyclic Stress Life in Blades and Impellers
Authors: Simmons Harold R. , Allison Timothy C.
Published: January 2011

A pragmatic approach for estimating cyclic stresses in rotating airfoils based on impulse testing with strain gauge sensors and application of simplified aerodynamic excitations is presented. The method has been successfully applied to determine the root causes of blade and impeller failures in gas turbines, steam turbines, and industrial compressors. The method provides guidance for quickly determining the natural frequency most responsible for a failure by analyzing experimental stress data at blade resonances, incorporating the Campbell diagram to evaluate frequency margins, and applying the Goodman diagram to evaluate endurance stress margins. The effects of mis-tuned blade responses can be included and operating lifetimes can be evaluated by use of the Palmgren-Miner analysis. Example cases of significant failure analyses for an axial flow gas turbine compressor and a driven industrial compressor are used to illustrate how the method is used.
Hybrid LES/RANS Study of Turbulent Flow in a Linear Compressor Cascade With Moving Casing
Authors: Borello Domenico , Delibra Giovanni , Hanjalic´ Kemal , Rispoli Franco
Published: January 2011

In this work a robust hybrid LES/RANS model has been applied to the prediction of secondary flows in a linear compressor cascade with moving casing simulating the relative motion between blade and the casing. The hybrid LES/RANS model uses the well established Ζ-f URANS model of Hanjalic´ et al. (2004) in the near wall region coupled with dynamic Smagorinsky LES. The switch between the two zones is based on a couple of parameters defining the boundary of interface region: the first one is a grid-detection parameter expressed as a function of the ratio between the turbulent and LES characteristic length scales while the switching to pure LES is obtained when the subgrid scale viscosity is greater than eddy viscosity (Delibra et al., 2010). We present hybrid LES/RANS results of a 3D linear compressor cascade with a tip leakage equal to 1.65% of chord. We compare two cascade configurations: with stationary casing and with moving casing. The second simulation allows to scrutinize the exclusive influence of the relative motion between casing and blades on the tip leakage vortex and the turbulent structures developing in the wake. The quality of the results and their agreement with experiments are encouraging in terms of prediction of the main flow characteristics and identification of turbulence structures.
Unsteady Acoustic Forcing on an Impeller Due to Coupled Blade Row Interactions
Authors: Richards Simon K. , Ramakrishnan Kishore , Shieh Chingwei M. , Moyroud Franc¸ois , Picavet Alain , Ballarini Valeria , Michelassi Vittorio
Published: January 2011

This article contains an investigation of the unsteady acoustic forcing on a centrifugal impeller due to coupled blade row interactions. Selected results from an aeromechanical test campaign on a GE Oil and Gas centrifugal compressor stage with a vaneless diffuser are presented. The most commonly encountered sources of impeller excitation due to upstream wake interaction were identified and observed in the testing campaign. A 30/rev excitation corresponding to the sum of upstream and downstream vane counts caused significant trailing edge vibratory stress amplitudes. Due to the large spacing between the impeller and the return channel vanes, this 30/rev excitation was suspected to be caused by an aero-acoustic excitation rather than a potential disturbance. The origin of this aero-acoustic excitation was deduced from an acoustic analysis of the unsteady compressor flow derived from CFD. The analysis revealed a complex excitation mechanism caused by impeller interaction with the upstream vane row wakes and subsequent acoustic wave reflection from the downstream return channel vanes. The findings show it is important to account for aero-acoustic forcing in the aeromechanical design of low pressure ratio centrifugal compressor stages.
Bayesian Approach for Fatigue Life Prediction From Field Data
Authors: Kim Nam H. , Pattabhiraman Sriram , Houck Lonnie A.
Published: January 2011

Due to uncertainty in design, manufacturing and operating processes, the initial prediction of a machine’s useful life is often quite different from that of the actual machine. In this paper, we utilize the Bayesian technique to incorporate the field data with the initial predictions in order to improve the prediction. The field data is interpreted in terms of the probability of having defective hardware, and then the likelihood function is generated from the binomial distribution. Since the predictions incorporate field experience, as time progresses and more data becomes available the probabilistic predictions are continuously updated. This results in a continuous increase of confidence and accuracy of the prediction. The resulting distributions can then be used directly in risk analysis, maintenance scheduling, and financial forecasting by both manufacturers and operators of heavy-duty gas turbines. This presents a quantification of the real time risk for direct comparison with the volatility of the power market.
Dynamic Simulation and Control Strategy for Three-Shaft Marine Electric Propulsion Gas Turbine
Authors: Wei Chenyu , Zang Shusheng
Published: January 2011

Three-shaft gas turbine was applied to marine electric propulsion system. The dynamic performance and control strategy of the three-shaft marine electric propulsion gas turbine arrested investigator’s attention, because they are very different from that of single-shaft gas turbine due to the complicated rotor structure. In this study, a model of nonlinear differential equation set is built to calculate the dynamic performance of three-shaft gas turbine and a simulation model of three-shaft marine electric propulsion gas turbine is constructed using the platform of MATLAB/SIMULINK. An adaptive software is developed for three-shaft gas turbine simulation. The new matching problems and changing rules among parameters are investigated in the case of load rejection of marine electric propulsion system. Multi-closed loop control system, instead of traditional control system, is introduced in order to improve the system quality and safety.
CMC Combustor Liner Demonstration in a Small Helicopter Engine
Authors: Bhatia Tania , Jarmon David , Shi Jun , Kearney Scott , Kojovic Aleksandar , Hu John , Prociw Alexander
Published: January 2011

UTRC and P&W Canada partnered to demonstrate an advanced combustor configuration that was enabled by high temperature CMC materials, in a PW200 series combustor. The PW200 series have reverse-flow combustors and the program presented significant challenges in design and fabrication. The advanced CMC configuration was successfully tested in a PW206 combustor rig. At full power, a 40–50% reduction in pattern factor relative to the bill-of-material metal combustor was measured. The combustor exit plane temperatures were generally better mixed due to the combined effects of (1) eliminating the cold film layers near the combustor walls and (2) the increase in fuel injector count enabled by the increase in dilution air. The CMC combustor was also successfully tested in an engine configuration. Post test gas path surfaces of the EBC coated CMC combustor components were in good condition.
Dynamic Buckling of Coiled Tubing During a Completion/Workover Application
Authors: Bhalla Kenneth , Gong Lixin
Published: January 2011

The purpose of this paper is to present how hand-calculations and a general finite element analysis program can be utilized to determine under what conditions coiled tubing (CT) could buckle helically in a vertical well. This is especially useful when determining loads on the tubing in a completion or work-over application. Two situations are considered as described below. • A Quasi-Static case when either: –Weight is slacked off from the surface. or –A bottom force that may be generated by reservoir pressure for instance. • A Dynamic case, which occurs when: –Weight is slacked off too quickly and the tubing impinges upon an object causing an impulse to be generated into the tubing. This paper presents the theory for the hand calculations and shows how the hand calculations may be utilized for a field example. In addition, the same field example is considered in the general finite element analysis program and the limitations of the hand calculations are discussed as well as the capability of the dynamic finite element model simulation. Hand calculations restrict us to the quasi-static scenario and only allow an assessment of the deformation of the coiled tubing deformation in the linear-elastic range. In contrast, the general purpose finite element analysis software allows for large deformation, and non-linear material behavior. In addition, the general purpose finite element analysis software allows for tubing evaluation locally after lockup of the tubing occurs. Generally hand calculations or quasi-static simulators have been used to assess the deformation of tubing during an impact event; these have proven to be inadequate because they cannot capture the transient event and do not model the inertial forces correctly. The general purpose finite element code provides better estimates of the deformation and stress state of the tubing. When assessing the dynamic behavior of tubing, it would be prudent to utilize the capability of general purpose finite element software to obtain realistic and an accurate assessment of the deformation and stress state of the tubing.
Pipe-in-Pipe Walking: Understanding the Mechanism, Evaluating and Mitigating the Phenomenon
Authors: Chen Q. , Chia H. K.
Published: January 2011

This paper addresses the walking phenomenon of pipe-in-pipe system, which can cause the cumulative axial displacement, leading to the potential failures of tie-ins or risers. The main mechanism that drives the pipe-in-pipe walking is the nonlinear spacer-pipe friction (between the inner pipe and outer pipe) and pipe-soil friction, together with thermal transients along the pipe-in-pipe system during start-up and shutdown. Sensitivity studies are also performed by investigating the effect of variation in spacer-pipe friction coefficient, pipe-soil friction coefficient, transient temperature profile and internal pressure through detailed finite element simulation with Abaqus. The paper also presents some methods to mitigate the pipe-in-pipe walking and some advantages of selecting pipe-in-pipe system in deepwater development.
Analysis of Flow Induced Acoustic Waves in a Vibrating Offshore Pipeline
Authors: Osheku Charles A. , Olunloyo Vincent O. S. , Akano Theddeus T.
Published: January 2011

Flow induced acoustic wave characteristics in a vibrating subsea pipeline is investigated. For this problem, acoustic wave equations are formulated and matched for the various vibrating segments. The pipeline system is idealized as a network of fluid conveyance elastic beams resting on a moving seabed via recent advances in subsea pipeline vibrations. By employing operational methods, closed forms results as influenced by internal fluid variables and subsea soil geotechnical properties, are computed for design applications. It is further shown that the vibration of any pipeline system is modulated by transverse, longitudinal and vibro-acoustic natural frequencies.
A Parametric Study on the External Mechanics of Ship/Iceberg Collision
Authors: Liu Zhenhui , Amdahl Jo̸rgen , Lo̸set Sveinung
Published: January 2011

Generally, in the accidental limits design domain, the ship/iceberg impacts are divided into external mechanics and internal mechanics. The external mechanics deals with the momentum and energy balance while the internal mechanics is dealing with local structure failure. The present paper focuses on the former one. Due to large contact force, it is reasonable to neglect all other forces here. The ship/iceberg impact might usually happen as an eccentric impact, because the collision is likely to take place in the foreship area. Experience has shown that in such cases, the ship and iceberg motion, like roll, pitch and yaw ect., all should be considered. Based on this, a full 6 DOF closed form theory of the external mechanics of ship/iceberg collision is derived based on Strong (2004) and T.Pedersen and Zhang’s work (1998). And the theory is applied to study the ship/iceberg collision. One challenge here is to obtain the geometrical features of the iceberg, like the COG (center of gravity), mass and also the gyration radius. Due to the large possibilities of the iceberg shape and size, a simplified iceberg geometry shape is proposed to be representative of real shapes. The parametric study here focuses on the geometry shape of the ship hull in the bow area in the form of waterline angle and frame angle. What’s more, the vertical collision position and the friction factor are also investigated. Discussions and conclusions based on the results will be presented.
Vibration and Stability Behaviour of Sandwiched Viscoelastic Pipes Conveying a Non-Newtonian Fluid
Authors: Olunloyo Vincent O. S. , Osheku Charles A. , Kuye Sidikat I.
Published: January 2011

Internal fluid flow parameters in conjunction with elastomechanical properties of conveyance systems have significantly modulated flow induced vibrations in pipeline and riser systems. Recent advances on the mechanics of sandwich elastic systems as effective vibration and noise reduction mechanisms have simulated the possibility of replacing traditional steel pipes with sandwich pipes in deepwater environment. The dynamic behaviour and stability of sandwich elastic pipes conveying a non-Newtonian fluid are investigated in this paper. For this problem, a set of generalised non-linear equations governing the vibration of sandwich pipes held together in pressurised environment and conveying a non-Newtonian fluid is presented. By linearizing the governing partial differential equation matching the problem physics, under slight perturbation of the internal fluid velocity and other flow variables closed form analytical results for the system dual natural frequencies and stability under external excitation are computed for field designs and applications. Results show that for a given length of pipe, beyond the critical velocity, instability increases with the velocity of conveyance.