bluuebunny/crossref_metadata_2025 huggingface dataset:
Reliable FE Modeling of Chord-Wise Blade Modes in Compressor Design Process
Authors: Fedorov Ilya , Szwedowicz Jaroslaw , Kappis Wolfgang , Putchkov Igor
Published: January 2011

To meet the highest compressor efficiency and resonance free operation, the design process of a modern compressor blade requires several iterations between the aerodynamic and mechanical integrity disciplines. The 1D beam theories, usually used in the concept design process, do not consider the local flexibility of a flat, tapered and twisted geometry of an axial compressor airfoil. Therefore, chord-wise bending resonances of the compressor blade, excited by flow field upstream and downstream, cannot be predicated in a reliable manner. In the paper, firstly the sensitivity of compressor blade vibrations is analysed in terms of airfoil design parameters, rotor coupling effects, and mistuning phenomena. Owing to high bending stiffness of a welded shaft, a numerical CWB tool is developed mainly for reliable predictions of chord-wise bending resonances of the compressor blade in the design process. Finally, the tool reliability is demonstrated by a good agreement of the numerical and experimental resonance frequencies, which have been measured with the tip-timing system at the front stage of the axial compressor in the field. Regarding the measured compressor bladed disc, the numerical sensitive study is carried out to determine an impact of contact uncertainties in the blade root on the computed resonance frequencies. The paper shows how physical uncertainties of the root contact and airfoil mistuning are involved in practical manner into the design process of compressor blades. In the design process, the presented CWB tool allows for fast and reliable mitigation of chord-wise bending resonances, which requires the collective solution between the aerodynamics and mechanical integrity disciplines, as it is illustrated in this paper.
Experimental Analysis of Altitude Relight Under Realistic Conditions Using Laser and High-Speed Video Techniques
Authors: Mosbach T. , Sadanandan R. , Meier W. , Eggels R.
Published: January 2011

The altitude relight performance of a lean fuel injector and combustor was investigated at the altitude relight test rig at the Rolls-Royce Strategic Research Centre (SRC) in Derby. The studies were performed for different mass flow rates of air and kerosene, a combustor temperature and pressure of 278 K and 0.5 bar, respectively. Good optical access to the combustion chamber enabled the application of optical and laser measuring techniques. High-speed video imaging in the UV and visible wavelength range at a frame rate of 3.5 kHz was used to visualize the temporal development of the flame kernel. The observed differences between the UV and visible flame emissions demonstrate the different origins of the luminosity, i.e. OH* chemiluminescence and soot radiation. Further, laser-induced fluorescence of kerosene and OH radicals was applied at a frame rate of 5 Hz to visualize the fuel distribution and regions of hot and reacting mixtures. For two exemplary flames with different mass flow rates and fuel-to-air ratios, the steady burning flames after successful ignition are characterized in this paper by the distributions of kerosene, OH*, OH and soot luminosity. An example of the flame kernel development for a successful ignition is given by an image sequence from a high-speed video recording of the chemiluminescence. The importance of the upstream movement of the flame kernel as a condition preceding successful flame stabilization is identified.
Numerical Benchmark of Turbulence Modeling in Gas Turbine Rotor-Stator System
Authors: Da Soghe Riccardo , Innocenti Luca , Andreini Antonio , Poncet Se´bastien
Published: January 2011

Accurate design of the secondary air system is one of the main tasks for reliability and performance of gas turbine engines. The selection of a suitable turbulence model for the study of rotor-stator cavity flows, which remains an open issue in the literature, is here addressed for several operating conditions. A numerical benchmark of turbulence models is indeed proposed in the case of rotor-stator disk flows with and without superimposed throughflow. The predictions obtained by the means of several two equation turbulence models available within the CFD solver Ansys CFX 12.0 are compared with those previously evaluated by Poncet et al. (1; 2) through the Reynolds Stress Model (RSM) of Elena and Schiestel (3; 4) implemented in a proprietary finite volume code. The standard k-ε and k-ω SST models including high and low Reynolds approaches, have been used for all calculations presented here. Furthermore, some tests were performed using the innovative k-ω SST-CC and k-ω SST-RM models that take into account the curvature effects via the Spalart-Shur correction term (5) and the reattachement modification proposed by Menter (6) respectively. The numerical calculations have been compared to extensive velocity and pressure measurements performed on the test rig of the IRPHE’s laboratory in Marseilles (1; 2). Several configurations, covering a large range of real engine operating conditions, were considered. The influence of the typical non dimensional flow parameters (Reynolds number and flowrate coefficient) on the flow structure is studied in detail. In the case of an enclosed cavity, the flow exhibits a Batchelor-like structure with two turbulent boundary layers separated by a laminar rotating core. When an inward axial throughflow is superimposed, the flow remains of Batchelor type with a core rotating faster than the disk because of conservation of the angular momentum. In this case, turbulence intensities are mainly confined close to the stator. Turbulence models based on a low Reynolds approach provide better overall results for the mean and turbulent fields especially within the very thin boundary layers. The standard k-ω SST model offers the best trade-off between accuracy and computational cost for the parameters considered here. In the case of an outward throughflow, the k-ω SST in conjunction with a low Reynolds approach and RSM models provide similar results and predict quite well the transition from the Batchelor to the Stewartson structures.
A Study on Engine Health Monitoring in the Frequency Domain
Authors: Borguet S. , Henriksson M. , McKelvey T. , Le´onard O.
Published: January 2011

Most of the techniques developed to date for module performance analysis rely on steady-state measurements from a single operating point to evaluate the level of deterioration of an engine. One of the major difficulties associated with this estimation problem comes from its underdetermined nature. It results from the fact that the number of health parameters exceeds the number of available sensors. Among the panel of remedies to this issue, a few authors have investigated the potential of using data collected during a transient operation of the engine. A major outcome of these studies is an improvement in the assessed health condition. The present contribution proposes a framework that formalises this observation for a given class of input signals. The analysis is performed in the frequency domain, following the lines of system identification theory. More specifically, the mean-squared estimation error is shown to drastically decrease when using transient input signals. The study is conducted with an engine model representative of a commercial turbofan.
Numerical Validation of Heat Transfer Augmentation Factor in Serpentine Passages With Ribbed Walls
Authors: Ramakumar B. V. N. , Kollati Vighneswara R. , Liu Jong S. , Crites Daniel C. , Goswami Shraman , Kulkarni Vaman
Published: January 2011

The objectives of this study are to validate and calibrate a commercially available CFD code, ANSYS CFX, for aerodynamic and heat transfer predictions in serpentine passages with ribbed walls and to understand the relationship between complex flow fields and heat transfer behavior. The validation was accomplished with the test results of Al-Hadhrami and Han [1] who tested a two-pass, radially outward – 180° bend – radially inward, square serpentine passage with two opposite rib roughened walls. Two configurations of ribs, two Reynolds numbers, two rotational numbers, and two channel orientations were considered for this study. An augmentation factor was used to compare the CFD heat transfer predictions with the experimental results. This augmentation factor is defined as the ratio of the local Nusselt number to that of a fully developed, smooth, circular pipe flow at the same Reynolds number. For the cases studied the CFD predictions were found to match the experimental results within the experimental uncertainty band of 20% except on the leading side of the highest rotational number case where the CFD under predicted the heat transfer augmentation. Streamlines and flow field results obtained at different locations are presented for better understanding of the heat transfer behavior.
Vapor Phase Deposition Using a Plasma Spray Process
Authors: von Niessen Konstantin , Gindrat Malko
Published: January 2011

Plasma spray - physical vapor deposition (PS-PVD) is a low pressure plasma spray technology recently developed by Sulzer Metco AG (Switzerland) to deposit coatings out of the vapor phase. PS-PVD is developed on the basis of the well established low pressure plasma spraying (LPPS) technology. In comparison to conventional vacuum plasma spraying (VPS) and low pressure plasma spraying (LPPS), these new process use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional physical vapor deposition (PVD) technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and electron beam - physical vapor deposition (EB-PVD) coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Due to the forced gas stream of the plasma jet, complex shaped parts like multi-airfoil turbine vanes can be coated with columnar thermal barrier coatings using PS-PVD. Even shadowed areas and areas which are not in the line of sight to the coating source can be coated homogeneously. This paper reports on the progress made by Sulzer Metco to develop a thermal spray process to produce coatings out of the vapor phase. Columnar thermal barrier coatings made of Yttria stabilized Zircona (YSZ) are optimized to serve in a turbine engine. This includes coating properties like strain tolerance and erosion resistance but also the coverage of multiple air foils.
A Unified Nonlinear Adaptive Approach for Detection and Isolation of Engine Faults
Authors: Tang Liang , Zhang Xiaodong , DeCastro Jonathan A. , Farfan-Ramos Luis , Simon Donald L.
Published: January 2011

A challenging problem in aircraft engine health management (EHM) system development is to detect and isolate faults in system components (i.e., compressor, turbine), actuators, and sensors. Existing nonlinear EHM methods often deal with component faults, actuator faults, and sensor faults separately, which may potentially lead to incorrect diagnostic decisions and unnecessary maintenance. Therefore, it would be ideal to address sensor faults, actuator faults, and component faults under one unified framework. This paper presents a systematic and unified nonlinear adaptive framework for detecting and isolating sensor faults, actuator faults, and component faults for aircraft engines. The fault detection and isolation (FDI) architecture consists of a parallel bank of nonlinear adaptive estimators. Adaptive thresholds are appropriately designed such that, in the presence of a particular fault, all components of the residual generated by the adaptive estimator corresponding to the actual fault type remain below their thresholds. If the faults are sufficiently different, then at least one component of the residual generated by each remaining adaptive estimator should exceed its threshold. Therefore, based on the specific response of the residuals, sensor faults, actuator faults, and component faults can be isolated. The effectiveness of the approach was evaluated using the NASA C-MAPSS turbofan engine model, and simulation results are presented.
Oxidation Behavior of Sputter Deposited Nanocrystalline and Conventional Plasma Sprayed MCrAl(Y) Coatings
Authors: Cheruvu N. Sastry , Wei Ronghua , Gandy David W.
Published: January 2011

The MCrAl-type coatings with, or without, yttrium are widely used for oxidation and/or hot corrosion protection of hot section components of gas turbine engines. Recently, there has been great interest in developing nano or microcrystalline coatings since these coatings offer excellent oxidation and corrosion resistance compared to the conventional coatings. Cyclic oxidation and microstructral degradadation behavior of sputter deposited nanocrystalline Ni-20Cr-10Al coating has been investigated at 1010°C. The coating was deposited on Haynes 230 samples using a magnetron sputtering technique. This technique produced a coating with a grain size of ∼9 nm. The cyclic oxidation results showed that the sputter deposited Ni-20Cr-10Al coating exhibited better oxidation resistance in terms of weight loss kinetics compared to the conventional plasma-sprayed NiCoCrAlY and PWA 286 coatings. The Al content in the nanocrystalline coating was consumed in a relatively short time due to inward and outward diffusion of Al. The accelerated consumption of Al was presumably due to enhanced grain boundary diffusion resulting from the ultra-fine grain structure in the coating. Variation of oxide-scale spallation resistance during thermal cycling, internal oxidation of the coatings, and the rate of Al consumption due to inward and outward diffusion of Al between the nanocrystalline and plasma sprayed coatings is presented.
Investigation for the Effects of Circumferential Grooves on the Unsteadiness of Tip Clearance Flow to Enhance Compressor Flow Instability
Authors: Zhao Shengfeng , Lu Xingen , Zhu Junqiang , Zhang Hongwu
Published: January 2011

The use of slots and grooves in the shroud over the tips of compressor blades, known as casing treatment, is a powerful method to control tip leakage flow through the clearance gap and enhance the flow stability in compressors. This paper presents a contribution to the understanding of the physical mechanism by which circumferential groove casing treatment manipulates the tip clearance flow’s unsteadiness. A series of computational studies were carried out to understand the physical mechanism responsible for improvement in stall margin of a high subsonic axial-flow compressor rotor due to the circumferential groove casing treatment from an unsteady viewpoint. Detailed analyses of the flow visualization at the tip have exposed the different tip flow topologies between the cases with circumferential groove and with untreated smooth wall. It was found that the primary stall margin enhancement afforded by the circumferential groove casing treatment is a result of the unsteady tip clearance flow manipulation. Breaking balance of incoming/tip clearance flow axial momentum by inducing the radial movement and tangential movement and delay the occurrence of tip clearance’s unsteadiness are the physical mechanisms responsible for extending the compressor stall margin.
Multi-Objective Optimization Design Method for Tandem Compressor Cascade at Design and Off Design Conditions
Authors: Ju Yaping , Zhang Chuhua
Published: January 2011

Recently, there has been a renewed interest in the research of tandem compressor cascades due to the high stage pressure ratio and low control cost. Firstly, the computational fluid dynamics (CFD) method is employed to examine the particular aerodynamic performance of the tandem cascade. Then we propose an automatic multi-objective optimization design method of the tandem cascade for the superior aerodynamic performance under the multiple operation conditions. Particular efforts have been devoted to the gap geometry optimization in terms of the front and aft airfoil relative position, camber turning ratio as well as chord ratio. The multi-objective optimization algorithm comprises a refined multi-objective genetic algorithm (MOGA) and a developed artificial neural network (ANN) model which is used to fast approximate the aerodynamic performance of the tandem cascade. The results show that the tandem cascade outperforms the single cascade in terms of producing higher pressure ratio and lower losses while the operation range is rather narrow. The optimized all-better-than (ABT) tandem cascade has its design point performance significantly improved while the operation range slightly widened. We also find that a slight axial proximity and separation of the tandem airfoils are beneficial to widening the positive and negative operation range, respectively. This research is useful to the tandem compressor cascade design in minimizing the stage number of the engine compressors.
Coupled Aero-Thermo-Mechanical Simulation for a Turbine Disc Through a Full Transient Cycle
Authors: Sun Zixiang , Chew John W. , Hills Nicholas J. , Lewis Leo , Mabilat Christophe
Published: January 2011

Use of computational fluid dynamics (CFD) to model the complex, 3D disc cavity flow and heat transfer in conjunction with an industrial finite element analysis (FEA) of turbine disc thermo-mechanical response during a full transient cycle is demonstrated. The FEA and CFD solutions were coupled using a previously proposed efficient coupling procedure. This iterates between FEA and CFD calculations at each time step of the transient solution to ensure consistency of temperature and heat flux on the appropriate component surfaces. The FEA model is a 2D representation of high pressure (HP) and intermediate pressure (IP) turbine discs with surrounding structures. The front IP disc cavity flow is calculated using 45° sector CFD models with up to 2.8 million mesh cells. Three CFD models were initially defined for idle, maximum take-off (MTO) and cruise conditions, and these are updated by the automatic coupling procedure through the 13000 seconds full transient cycle from standstill, to idle, maximum take-off, and cruise conditions. The obtained disc temperatures and displacements are compared with an earlier standalone FEA model which used established methods for convective heat transfer modelling. It was demonstrated that the coupling could be completed using a computer cluster with 60 cores, within about two weeks. This turn around time is considered fast enough to meet design phase requirements and in validation it also compares favorably to that required to hand-match an FEA model to engine test data, which is typically several months.
Predicting the Profile Loss of High-Lift Low Pressure Turbines
Authors: Coull John D. , Hodson Howard P.
Published: January 2011

The overall efficiency of Low Pressure (LP) turbines is largely determined by the two-dimensional profile loss, which is dominated by the contribution of the suction surface boundary layer. This boundary layer typically features a laminar separation bubble and is subjected to an inherently unsteady disturbance environment. The complexity of the flow behavior makes it difficult to numerically predict the profile loss. To address this problem, an empirical method is proposed for predicting the boundary layer integral parameters at the suction surface trailing edge, allowing the profile loss to be estimated. Extensive measurements have been conducted on a flat plate simulation of the suction surface boundary layer. The disturbance environment of real machines was modeled using a moving-bar wake generator and a turbulence grid. From this dataset, empirically based methods have been formulated using physical principles for the prediction of the momentum thickness and shape factor at the suction surface trailing edge. The predictions of these methods may be used to estimate the profile loss of a given cascade, which achieves reasonable agreement with the available data. By parameterizing the shape of the suction surface velocity distribution, the method is recast as a preliminary design tool. This may be used to guide the selection of the key design parameters (such as the blade loading and velocity distribution shape) and enables a reasonable estimation of the unsteady profile loss to be made at a very early stage of design. To illustrate the capabilities of the preliminary design tool, different styles of velocity distribution are evaluated for fixed blade loading and flow angles. The predictions suggest that relatively “flat-top” designs will have the lowest profile loss, but good performance can also be achieved with front-loaded “peaky” distributions. The latter designs are more likely to have acceptable incidence tolerance.
Alternative Approaches to Continuous Compliance Monitoring for Gas Turbines Under 40 CFR Part 60, Part 75, and Part 98 Regulations in the United States
Authors: Swanson Brian
Published: January 2011

Quantifying emissions and complying with environmental regulations are important issues for gas turbine plants. These objectives can often be met with either a CEMS (Continuous Emission Monitoring System) using gas analyzers or a software only PEMS (Predictive Emissions Monitoring System). PEMS interface directly with the turbine control system and represent a lower cost alternative to traditional CEMS. PEMS are a compliance monitoring alternative consisting of a model of the turbine operations and its emissions. PEMS can be used to track plant combustion efficiency. PEMS can allow for more efficient operation of the plant because the PEMS system tracks excess emissions and can be used to determine the causes of and reduce pollution. This paper reviews the use of PEMS at three different turbine facilities and highlights the costs and benefits of using a PEMS for documenting emissions of priority pollutants and Green House Gases (GHG), but also in terms of overall plant efficiency, operator awareness and involvement, improvements in process control, waste and emission minimization, and in focusing the available manpower resources on core plant operations as opposed to non-core analyzer-based compliance systems. The PEMS were used for compliance with 40 CFR Part 60 and in some cases also Part 75. In addition, the Part 60 PEMS were subjected to the new performance standard (PS-16) published earlier this year by U.S. EPA.
Experimental Study of Discharge Coefficients for Radial Orifices in High-Speed Rotating Shafts
Authors: Sousek Jan , Pfitzner Michael , Niehuis Reinhard
Published: January 2011

In modern multi shaft gas turbine engines the cooling air taken from the compressor passes through various stationary or rotating holes or orifices to the turbine stage. The discharge coefficient of rotating orifices may vary considerably depending on the operating point and the geometry of the orifice and its surroundings. The predictability of this behavior is crucial for safe and efficient operation and for the life specification and the reliability of the components. This paper reports on measurements of the characteristics of flow discharge through radial orifices in a rotating system, with cross-flow included and on parameters suitable for correlation of the test data. A test rig was designed to simulate shaft diameters, rotation speeds and pressure ratios typical for real gas turbine designs. The pressure ratio across the orifices varied from 1.05 to 1.5 and the Mach number of the flow approaching the holes was 0;0.1;0.15 and 0.2. Hole configurations with different L/d (length-to-diameter) ratio and with round and sharp edges were examined. Inserts representing the different hole types are used to achieve flexibility of the rig. The upstream and downstream static pressure and the pressure drop across the radial holes are measured by sub miniature pressure transducers rotating with the outer shaft. A correlation parameter optimal for presentation of the test data is derived and data are compared to literature.
Aerodynamics and Heat Transfer for a Cooled One and One-Half Stage High-Pressure Turbine: Part I—Vane Inlet Temperature Profile Generation and Migration
Authors: Mathison R. M. , Haldeman C. W. , Dunn M. G.
Published: January 2011

As controlled laboratory experiments using full-stage turbines are expanded to replicate more of the complicated flow features associated with real engines, it is important to understand the influence of the vane inlet temperature profile on the high-pressure vane and blade heat transfer as well as its interaction with film cooling. The temperature distribution of the incoming fluid governs not only the input conditions to the boundary layer but overall fluid migration. Both of these mechanisms have a strong influence on surface heat flux and therefore component life predictions. To better understand the role of the inlet temperature profile, an electrically heated combustor emulator capable of generating uniform, radial, or hot-streak temperature profiles at the high-pressure turbine vane inlet has been designed, constructed, and operated over a wide range of conditions. The device is shown to introduce a negligible pressure distortion while generating the inlet temperature conditions for a stage-and-a-half turbine operating at design-corrected conditions. For the measurements described here, the vane is fully cooled and the rotor purge flow is active but the blades are un-cooled. Detailed temperature measurements are obtained at rake locations upstream and downstream of the turbine stage as well as at the leading edge and platform of the blade in order to characterize the inlet temperature profile and its migration. The use of miniature butt-welded thermocouples at the leading edge and on the platform (protruding into the flow) on a rotating blade is a novel method of mapping temperature profile. These measurements show that the reduction in fluid temperature due to cooling is similar in magnitude for both a uniform and radial vane inlet temperature profile.
Conceptual Study of a Hybrid Turbofan Engine With Inter Turbine Burner
Authors: Tang Koon-ging , Rao Arvind G. , van Buijtenen J. P.
Published: January 2011

Most of the improvement in aviation during the last 7 decades has been mainly due to the advancement in the propulsion systems and technologies. The Advisory Council for Aeronautics Research in Europe (ACARE) has set ambitious objectives to be completed by 2020 and beyond; the major being reduction of CO2 emissions by more than 50%, for which significant improvement of the propulsion systems is required. However, it appears that a technological plateau has been reached with conventional engine architecture. The paper presents a novel hybrid engine architecture with inter turbine burner (ITB). The hybrid engine with two combustion chambers offers the possibility of operating on hydrocarbon fuels as well as liquid hydrogen, enabling the aimed reduction of CO2 emissions by 50% without encountering the storage problems related to pure hydrogen powered aircraft.
Experimental Investigation of a Generic, Fuel Flexible Reheat Combustor at Gas Turbine Relevant Operating Conditions
Authors: Fleck Julia M. , Griebel Peter , Steinberg Adam M. , Sto¨hr Michael , Aigner Manfred , Ciani Andrea
Published: January 2011

Fuel flexibility in stationary gas turbines (GT) is becoming increasingly important due to the use of a broader spectrum of primary energy sources, particularly H2-rich fuels derived from the gasification of coal or biomass. GTs also must be able to operate at extremely low emission levels, which is currently achieved with lean-premixed burner designs. To investigate the performance of highly reactive fuels in the reheat combustion concept, mainly with respect to autoignition and flashback limits, a generic reheat combustor with excellent optical access has been developed. The first objective of this work was to carefully characterize the mixing section in order to derive well-defined boundary conditions for the subsequent autoignition studies. Initial autoignition results at T > 1000 K and p = 15 bar are presented for natural gas (NG) and H2-rich fuels. No autoignition was detected for NG at the investigated operating conditions. For H2/NG/N2 blends with a constant volumetric N2 concentration of 20% and H2 concentrations higher than 76%, autoignition in the mixing section was detected.
Simulations of Flow Ingestion and Related Structures in a Turbine Disk Cavity
Authors: Julien Steve , Lefrancois Julie , Dumas Guy , Boutet-Blais Guillaume , Lapointe Simon , Caron Jean-Francois , Marini Remo
Published: January 2011

Preliminary results of unsteady numerical simulations of disk cavity flow in interaction with the main gaspath flow in an axial turbine are presented in this article. A large periodic sector including vanes, blades and disk cavity of approximately 74° has been used in order to allow for the formation of large scale flow structures within the cavity. Three purge flow rates have been tested, namely no purge, low purge and high purge flow rates. Energetic large scale flow structures are detected through flow visualizations for the two lowest purge flow rates. They are found to rotate at an angular velocity slightly less than the rotor speed. The presence of the large scale structures involves important pressure perturbations inside the cavity that may lead to deep mass flow ingress, whereas the unsteady vane-blade interaction seems to cause only shallow ingress. Increasing purge flow rate appears to have a stabilizing effect on the pressure fluctuations inside the cavity and to reduce the intensity of the large scale flow structures.
An Assessment of Non-Intrusive Probabilistic Methods for Turbomachinery Problems
Authors: Shankaran Sriram , Barr Brian , Mallina Ramakrishna , Avancha Ravikanth , Stein Alex
Published: January 2011

The ability to quantify the impact of uncertainty on performance is an important facet of engineering design. Computational Fluid Dynamics (CFD) studies during the design cycle typically utilize estimates of boundary conditions, geometry and model constants, all of which have uncertainty that could lead to variations in the estimated performance of the design. Traditionally, engineering environments have relied on Monte-Carlo (MC) simulations to obtain probabilistic estimates. But MC methods have poor convergence rate leading to prohibitive computational requirements when used in conjunction with medium to high fidelity computational tools. In this study, we will use an alternate probabilistic approach. We assume that the uncertainties in our computational system can be modeled as random variables with known/prescribed distributions, use CFD solvers to estimate the performance measures and then use a psuedo-spectral probabilistic collocation technique to determine regression/interpolation fits. The psuedo-spectral discrete expansion uses the orthogonal polynomials from the Askey-Wiener basis and finds the coefficients of the expansion [1]. We will restrict our attention to problems with one random variable and hence can without ambiguity choose the Gauss quadratures as the optimal choice to obtain statistical data (mean, variance, moments etc.) of the performance measures. The computational frame-work will be first validated against Monte-Carlo simulations to assess convergence of pdfs. It will then be used to assess the variability in compressor blade efficiency and turbine vane loss due to uncertainty in inflow conditions. The results will be used to answer the following questions. Do we need new probabilistic algorithms to quantify the impact of uncertainty? What is the optimal basis for standard performance metrics in turbomachinery? What are the computational and accuracy requirements of this probabilistic approach? Are there alternate (more efficient) techniques? We believe that the answers to the above questions will provide a quantitative basis to assess the usefulness of non-intrusive (and possibly intrusive) probabilistic methods to analyze variability in engineering designs.
Response Statistics and Reliability Analysis of a Mistuned and Frictionally Damped Bladed Disk Assembly Subjected to White Noise Excitation
Authors: Kumar Pankaj , Narayanan S.
Published: January 2011

In the design of gas turbine engines, the analysis of nonlinear vibrations of mistuned and frictionally damped blade-disk assembly subjected to random excitation is highly complex. The transitional probability density function (PDF) for the random response of nonlinear systems under white or coloured noise excitation (delta-correlated) is governed by both the forward Fokker-Planck (FP) and backward Kolmogorov equations. This paper presents important improvement and extensions to a computationally efficient higher order, finite difference (FD) technique for the solution of higher dimensional FP equation corresponding to a two degree of freedom nonlinear system representative of vibration of tip shrouded frictionally damped bladed disk assembly subjected to Gaussian white noise excitation. Effects of friction damping on the mean square response of a blade are investigated. The friction coefficient of the damper is assumed to be a function of the sliding velocity of the contact surface. The effects of stiffness and damping mistuning on the forced response of frictionally damped bladed disk are investigated. Numerical studies are presented for a pair of mistuned blades of cyclic assemblies. The response and reliability of a blade subjected to random excitation is also obtained. With time averaged probability density as an invariant measure, the probability of large excursion in case of damping mistuning is also presented. The results of the FD method are validated by comparing with Monte Carlo Simulation (MCS) results.
Environmental Influences on Engine Performance Degradation
Authors: Wensky Tobias , Winkler Lutz , Friedrichs Jens
Published: January 2011

Environmental influences have an increasing effect on the performance degradation and durability of modern aircraft engines. The study provides information on environmental effects using in-flight engine data and results of engine overhauls performed at MTU Maintenance. According to these investigations global regions are classified into erosive and anthropogenic polluted areas. Both types of regional effects significantly degrade performance and engine durability. The investigation, which is based upon the in-flight data taken from Engine Trend Monitoring (ETM), provides one approach for the estimatation of environmental effects on aircraft engine performance degradation. The results of the monitored engines provide detailed information on the environmental effects atlocal airports. The Exhaust Gas Temperature (EGT) that has been measured under flight conditions is compared with a calculated EGT of a calibrated fully thermodynamic gas path engine model (MOPS). Therefore, the EGT also serves as an indicator for performance degradation, increase of specific fuel consumption and the need for on-wing maintenance actions. Further information provided by the engine shop visit data at MTU Maintenance allows for an estimation of environmental influences on durability and overhaul costs. The on-wing time of maintained shop visit data is compared with a model for on-wing time calculation, whereas variations in durability were observed and analyzed under the aspects of environmental influences. Depending on the variations, corrections were made by defining the factors contributing to the classifications of environmental effects. These corrective factors provide information on reduced durability and increased operating costs. The result of the ETM performance degradation analysis shows significant variations in engine performance degradation as a result of specific regional operation. The analyses of maintenance data as well as performance degradation measured by ETM show remarkable environmental effects on engine durability and an increase in maintenance costs.
Numerical Simulation of a Gas Turbine Model Combustor Operated Near the Lean Extinction Limit
Authors: Rebosio Francesca , Widenhorn Axel , Noll Berthold , Aigner Manfred
Published: January 2011

This work focuses on the numerical simulation of a gas turbine model combustor operated near the lean extinction limit using a hybrid LES-RANS model. A broad experimental database for the testcase is available from previous works, allowing an accurate evaluation of the performance of the chosen combination of turbulence and combustion models. Both time-averaged variables and typical instantaneous distributions are presented. The averaged parameters enable a first characterization of the flame and show the typical structures for swirled flames. Additionally, the unsteady characteristic quantities reveal vortex shedding and a helical vortex structure, which are crucial for mixing of recirculated hot products. Comparison of radial profiles from the computed and experimental data exhibits very good agreement, even for the relative simple chemical kinetic reaction scheme adopted.
On the Effects of Syngas Clean-Up Temperature in IGCCs
Authors: Giuffrida Antonio , Romano Matteo C.
Published: January 2011

This paper deals with the thermodynamic analysis of an IGCC power plant with hot syngas clean-up, where sulfur, particulate matter and trace contaminants are removed without cooling the syngas down to near-ambient temperature. With particular attention to the simulation of the desulfurization unit, adopting a regenerative process using a ZnO-based sorbent, a range of clean-up temperatures was investigated in order to evaluate its effects on overall plant performance. The study reveals the attractive chance of achieving overall electric efficiencies around 50%. However, a limited sensitivity of IGCC efficiency on desulfurization temperature was also obtained, since no significant improvements were accomplished for temperatures over 400°C. In order to support and better understand the results, a second law analysis was also carried out for the assessed cases. In addition, the effects of syngas clean-up temperature on the design and operation of the main IGCC processes and components, which can be relevant, were discussed.
Evaluation of Operating Range and Performance of Supersonic Ejector Using Mean-Line Approach
Authors: Biba Yuri
Published: January 2011

A mean-line approach has been applied to evaluate characteristics of a two-stage supersonic ejector operating at a gas turbine-driven compression unit. One-dimensional concept of calculating flow parameters in the nozzle, mixing chamber, and supersonic diffuser of the ejector is based on isentropic relationships. In the current study, a set of empiric corrections is being used to account for losses. Ejector operating and performance maps are generated defining motive pressure range that satisfies a range of suction pressure values and the corresponding maximum suction flow rates.
Compressor Performance and Operability in Swirl Distortion
Authors: Sheoran Yogi , Bouldin Bruce , Krishnan P. Murali
Published: January 2011

Inlet swirl distortion has become a major area of concern in the gas turbine engine community. Gas turbine engines are increasingly installed with more complicated and tortuous inlet systems, like those found on embedded installations on Unmanned Aerial Vehicles (UAVs). These inlet systems can produce complex swirl patterns in addition to total pressure distortion. The effect of swirl distortion on engine or compressor performance and operability must be evaluated. The gas turbine community is developing methodologies to measure and characterize swirl distortion. There is a strong need to develop a database containing the impact of a range of swirl distortion patterns on a compressor performance and operability. A recent paper presented by the authors described a versatile swirl distortion generator system that produced a wide range of swirl distortion patterns of a prescribed strength, including bulk swirl, twin swirl and offset swirl. The design of these swirl generators greatly improved the understanding of the formation of swirl. The next step of this process is to understand the effect of swirl on compressor performance. A previously published paper by the authors used parallel compressor analysis to map out different speed lines that resulted from different types of swirl distortion. For the study described in this paper, a computational fluid dynamics (CFD) model is used to couple upstream swirl generator geometry to a single stage of an axial compressor in order to generate a family of compressor speed lines. The complex geometry of the analyzed swirl generators requires that the full 360° compressor be included in the CFD model. A full compressor can be modeled several ways in a CFD analysis, including sliding mesh and frozen rotor techniques. For a single operating condition, a study was conducted using both of these techniques to determine the best method given the large size of the CFD model and the number of data points that needed to be run to generate speed lines. This study compared the CFD results for the undistorted compressor at 100% speed to comparable test data. Results of this study indicated that the frozen rotor approach provided just as accurate results as the sliding mesh but with a greatly reduced cycle time. Once the CFD approach was calibrated, the same techniques were used to determine compressor performance and operability when a full range of swirl distortion patterns were generated by upstream swirl generators. The compressor speed line shift due to co-rotating and counter-rotating bulk swirl resulted in a predictable performance and operability shift. Of particular importance is the compressor performance and operability resulting from an exposure to a set of paired swirl distortions. The CFD generated speed lines follow similar trends to those produced by parallel compressor analysis.
Influence of Coolant Density on Turbine Blade Film-Cooling Using Pressure Sensitive Paint Technique
Authors: Narzary Diganta P. , Liu Kuo-Chun , Rallabandi Akhilesh P. , Han Je-Chin
Published: January 2011

Adiabatic film-cooling effectiveness is examined on a high pressure turbine blade by varying three critical engine parameters, viz., coolant blowing ratio, coolant-to-mainstream density ratio and freestream turbulence intensity. Three average coolant blowing ratios (BR = 1.2, 1.7, and 2.2 on the pressure side and BR = 1.1, 1.4, and 1.8 on the suction side), three average coolant density ratios (DR = 1.0, 1.5, and 2.5), and two average freestream turbulence intensities (Tu = 4.2% and 10.5%) are considered. Conduction-free Pressure Sensitive Paint (PSP) technique is adopted to measure film-cooling effectiveness. Three foreign gases— N2 for low density, CO2 for medium density, and a mixture of SF6 and Argon for high density are selected to study the effect of coolant density. The test blade features 2 rows of cylindrical film-cooling holes on the suction side (45° compound), 4 rows on the pressure side (45° compound) and 3 around the leading edge (30° radial). The inlet and the exit Mach numbers are 0.24 and 0.44, respectively. Reynolds number of the mainstream flow is 7.5E105 based on the exit velocity and blade chord length. Results suggest that the PSP is a powerful technique capable of producing clear and detailed film effectiveness contours with diverse foreign gases. Large improvement on the pressure side and moderate improvement on the suction side effectiveness is witnessed when blowing ratio is raised from 1.2 to 1.7 and 1.1 to 1.4, respectively. No major improvement is seen thereafter with the downstream half of the suction side showing drop in effectiveness. The effect of increasing coolant density is to increase effectiveness everywhere on the pressure surface and suction surface except for the small region on the suction side, xss/Cx<0.2. Higher freestream turbulence causes effectiveness to drop everywhere except in the region downstream of the suction side where significant improvement in effectiveness is seen.
Numerical Simulation of Clocking Effect on Wake Transportation and Interaction in a 1.5-Stage Axial Turbine
Authors: Li Wei , Ouyang Hua , Du Zhao-hui
Published: January 2011

To give insight into the clocking effect and its influence on the wake transportation and its interaction, the unsteady three-dimensional flow through a 1.5-stage axial low pressure turbine is simulated numerically using a density-correction based, Reynolds-Averaged Navier-Stokes equations commercial CFD code. The 2nd stator clocking is applied over ten equal tangential positions. The results show that the harmonic blade number ratio is an important factor affecting the clocking effect. The clocking effect has a very small influence on the turbine efficiency in this investigation. The efficiency difference between the maximum and minimum configuration is nearly 0.1%. The maximum efficiency can be achieved when the 1st stator wake enters the 2nd stator passage near blade suction surface and its adjacent wake passes through the 2nd stator passage close to blade pressure surface. The minimum efficiency appears if the 1st stator wake impinges upon the leading edge of the 2nd stator and its adjacent wake of the 1st stator passed through the mid-channel in the 2nd stator.
Increasing Operational Stability in Low NOx GT Combustor by a Pilot Flame
Authors: Levy Yeshayahou , Gany Alon , Goldman Yakov , Erenburg Vladimir , Sherbaum Valery , Ovcharenko Vitaly , Rosentsvit Leonid , Chudnovsky Boris , Herszage Amiel , Talanker Alexander
Published: January 2011

The need for NOx reduction in gas turbine (GT) stimulates research for new combustion methods. Lean combustion is a method in which combustion takes place under low equivalence ratio and relatively low combustion temperatures. As such, it has the potential to lower the effect of the relatively high activation energy nitrogen-oxygen reactions which are responsible for substantial NOx formation during combustion processes. Moreover, lowering temperature reduces the reaction rate of the hydrocarbon-oxygen reactions and deteriorates combustion stability. The objective of the present study is to reduce the lower equivalence ratio limit of the stable combustion operational boundary in lean GT combustors. A lean premixed gaseous combustor was equipped with a surrounding concentric pilot flame operating under rich conditions, thus generating a significant amount of reactive radicals. The main combustor’s mixture composition was varied from stoichiometric to lean mixtures. The pilot’s mixture composition varied by changing the air flow rate, within a limited reach mixtures range. The pilot gas flow rate was always lower than five percent of the total gas supply at the specific stage of the experiments. The experiments and simulation showed that despite the high temperatures obtained in the vicinity of the pilot ring, the radicals’ injection by the pilot combustion has the potential to lower the limit of the global equivalence ratio (and temperatures) while maintaining stable combustion. Therefore the amount of generated NOx is expected to be significantly reduced as compared to a similar combustor of identical inlet and exit temperatures. In order to study the relevant mechanisms responsible for combustion stabilization, CFD and CHEMKIN simulations were performed to reveal the detailed flow characteristics and their spatial distribution within the combustor. Based on the CFD results, the CHEMKIN model was developed. The CHEMKIN simulations for atmospheric pressure showed satisfactory agreement with experimental results. Further simulation confirmed the advantageous of the technique also at elevated pressures. It is therefore important to understand the relevant mechanisms responsible for combustion stabilization and their spatial distribution within the combustor. The present work discusses an experimental- CFD-CHEMKIN combined approach aimed at studying the influence of radicals generated in the pilot ring combustion on the processes taking place in the main combustor.