bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Local Cyclic Life Prediction for Gas Turbine Components With Sharply Notched Geometries
Authors: Mu¨cke Roland , Kiewel Holger
Published: March 2009

The safe and efficient operation of modern heavy duty gas turbines requires a reliable prediction of fatigue behaviour of turbine components. Fatigue damage is located in areas where cyclic stress and strain amplitudes are highest. Thus, geometrical notches associated with stress/strain concentrations and stress/strain gradients appear to be the most important sites for fatigue crack initiation. The paper addresses a non-local concept for fatigue life prediction of notched components. In contrary to various local approaches in the field, the proposed method explicitly accounts for stress and strain gradients associated with notches, cooling holes, fillets and other design features with stress raising effect. As a result, empirical analytical expressions for considering either strain or stress gradients on cyclic life prediction are obtained. The method has been developed from cyclic test data on smooth and notched specimens made of a ferritic 1.5CrNiMo rotor steel. The obtained analytical formulations have then been applied to test data on the Nickel base superalloy MAR-M247 CC showing a good agreement between prediction and measurement. Moreover, the proposed non-local lifing concept has been validated by component tests on turbine blade firtrees. The predicted cycles to failure correlates well to the experimental results showing the applicability of the proposed method to complex engineering designs.
Unsteady Entropy Measurements in a High-Speed Radial Compressor
Authors: Mansour M. , Chokani N. , Kalfas A. I. , Abhari R. S.
Published: March 2009

The time-dependent relative entropy field at the impeller exit of a centrifugal compressor is measured. This study is part of a broader effort to develop comprehensive measurement techniques that can be applied in the harsh environment of turbomachines. A miniature unsteady entropy probe (diameter 1.8mm) is designed and constructed in the present study. The unsteady entropy probe has two components: a one-sensor fast response aerodynamic probe and a pair of thin-film gauges. The time-dependent total pressure and total temperature are measured from the fast response aerodynamic probe and pair of thin-film gauges, respectively. The time-dependent relative entropy derived from these two measurements has a bandwidth of 40kHz and uncertainty of ±2J/kg. The measurements show that at the near design operating condition, the impeller exit flowfield is highly three-dimensional. Adjacent to the shroud there are high levels of relative entropy and at the mid-span there are low & moderate levels. Independent measurements made with a two-sensor aerodynamic probe show that the high velocity of the flow relative to the casing is responsible for the high relative entropy levels at the shroud. On the otherhand, at the mid-span, a loss free, jet flow region and a channel wake flow of moderate mixing characterize the flowfield. At both the shroud and mid-span, there are strong circumferential variations in the relative entropy. These circumferential variations are much reduced when the centrifugal compressor is operated near the onset of stall. In this condition the impeller exit flowfield is less highly skewed; however, the time-averaged relative entropy is higher than at the near design operating condition. The relative entropy measurements with the unsteady entropy probe are thus complementary to other measurements, and more clearly document the losses in the centrifugal compressor.
Manufacturing Process Improvement to Increase the Productivity of Gas Turbine Blade and Vane
Authors: Takahashi Kooji , Asano Hiroshi , Kojima Yota
Published: March 2009

In general, gas turbine combustors, turbine blades and vanes, called hot section parts, are considered consumables that require repair or replacement at periodic overhaul/inspections. The number of blades and vanes used for each power plant is ranges from several tens up to several hundreds. In order to assure timely supply for the demand by existing and/or new plants, it is extremely important to establish a manufacturing system for mass production. Additionally, there are continuing design changes resulting from both feed-back from actual operating units and new product development. Although these design changes generally add higher performance and added value to customer, the promotion of shortening the manufacturing lead time is a key of vital importance. To address this issue, MHI Takasago introduced one piece flow production lines into the row 1 blade and vane production section. This innovative change resulted in reduced distance between operations in the shops, reduction of stagnant items and improvement in the overall quality of the final product. Furthermore, the implementation of quality confirmation (in-process inspection) for the machined parts prevents defective parts from moving further in the manufacturing process and the continuous defection. As a result, a significant reduction in the defect rate has been accomplished. This trial has achieved an average reduction of total lead time of 20% for blades and 25% for vanes, compared with conventional lot production. Recently further improvements in production efficiency have been realized by improvement of tool and machining conditions, the equalization of machining time for each operation and eliminating unnecessary operations in standard works.
Real-Time Modelling of the Thermoacoustic Dynamics of a Gas Turbine Using a Gaussian Process
Authors: Schneider Ernst , Staudacher Stephan , Schuermans Bruno , Ye Haiwen , Meeuwissen Thiemo
Published: March 2009

Premixed gas turbine combustors operated at very lean conditions are prone to thermoacoustic instabilities. Thermoacoustic instabilities have negative effects on the operability of the combustion chamber. The prevention of thermoacoustic instabilities is a major design goal of the gas turbine combustor system as well as its control system. An appropriate real-time model helps the design of effective control algorithms for the prevention of thermoacoustic instabilities. This paper presents a black-box real-time modelling approach for thermoacoustic instabilities simulation using a Gaussian-Process. A Gaussian Process is a stochastic process that can approximate arbitrary functions, similar to Neural Networks, but with the advantage that it can be implemented and tuned in a more straightforward manner since a theoretical framework exists for the optimization of the hyperparameters influencing the process. The Gaussian Process can be trained in a fast and straight-forward manner. The trained Gaussian Process has been proven to be very efficient numerically, which enables it to be used in a real-time simulation environment. The real-time gas turbine model is to be used in the development of control algorithms that allow for low-NOx and robust operation of the gas turbine in conjunction with low acoustic pulsation levels. Verification on a gas turbine demonstrated the high accuracy of this modeling approach for a wide range of operating conditions. Moreover, it was shown that a Gaussian Process trained with data of one engine correctly reproduced acoustic pulsation behaviour of another engine.
Developments and Experiences With Pulsation Measurements for Heavy-Duty Gas Turbines
Authors: Zinn Hanspeter , Habermann Michael
Published: March 2009

The dynamical combustion processes (pulsations) of heavy-duty gas turbines must be supervised by suitable instrumentation for optimal operation of the engine regarding emissions and component life. But the hostile environment of the combustor makes it difficult to perform the measurements. There are two possible approaches to measure the combustor pulsations. Either a high temperature sensor is placed as close as possible to the combustion chamber to measure the acoustics directly (Cavity Type Probe), or the acoustic signal is led to the outside of the engine by means of a reflection free waveguide, where a dynamic pressure sensor picks up the passing signal (Long Line Probe). Both approaches were developed and investigated in detail. This paper describes the past and current efforts in refining the probe designs for use in the harsh operational environment while maintaining sensor accuracy, measurement range and lifetime as a rugged probe. Theoretical and laboratory investigations were undertaken to increase the useable frequency range of the Cavity Type Probe up to 8kHz under engine operation conditions. This was made possible with a smaller high temperature transducer, which is the result of a cooperative development project with a sensor manufacturer. Experiences with both probe concepts on Alstom’s GT26 Test Power Plant in Birr and on field engines provided clear confirmation that the Cavity Type Probe design with an advanced sensor now fulfils all initially defined requirements of acoustic combustion measurements on heavy-duty gas turbines. On the contrary, the waveguide design principle has fundamental limitations in the direct measurement of the combustion acoustics at gas turbine operating conditions.
An Investigation on Laminar Flame Speed as Part of Needed Combustion Characteristics of Biomass-Based Syngas Fuels
Authors: Braun-Unkhoff Marina , Kick Thomas , Frank Peter , Aigner Manfred
Published: March 2009

The present work reports on laminar flame speed measurements with biogenic gas mixtures over a wide range of parameters, such as preheat temperatures, pressure, equivalence ratio, and gas compositions. The biogenic gas mixtures were derived from gasification of ethanol and of corn silage as representatives for alternative fuels containing hydrogen and methane as major components (after CO2-sequestration), light hydrocarbons to some extent, and diluents such as nitrogen and carbon monoxide. In the present work, premixed flames were stabilized in a high pressure burner system at pressures up to 6 bars at preheat temperatures between 323 and 453 K and for equivalence ratios of φ = 0.5–1.6. In addition, a gas mixture of methane and hydrogen burning in air was investigated at atmospheric pressure. Furthermore, different detailed reaction mechanisms were used to predict the measured data. The trends and main features were captured by predictions applying different reaction mechanisms.
Effect of Fuel Dilution on the Structure and Pollutant Emission of Syngas Diffusion Flames
Authors: Hui Xin , Zhang Zhedian , Mu Kejin , Wang Yue , Xiao Yunhan
Published: March 2009

Combustion with diluted syngas is important for integrated gasification combined cycle (IGCC) system that attains high efficiency and low pollutant emissions. In syngas diffusion flames, peak flame temperature is higher than that in nature gas flames, so NOx emission is more significant. To achieve low NOx emission, fuel dilution is an effective way. In the present study, Flame structure and emission characteristics were experimentally and numerically studied in various fuel diluted syngas diffusion flames, and H2O, N2 and CO2 were employed as diluents respectively. The purpose of this paper is to better understand the behavior and mechanism of fuel diluted combustion and to provide fundamental data base for the development of syngas combustion techniques. Experiments were conducted by using jet diffusion flames in a model combustor. Flame size, exhaust temperature and emission concentration were measured. It was found that by introducing diluents into fuel stream, the stoichiometric surface was brought inward, namely the flame envelope shrunk due to a relatively low fuel concentration. The exhaust temperature was decreased. The results also indicated that with diluted fuel stream, there was an increase of CO emission and an apparent decrease of NO emission. For the same exhaust temperature, H2O had the most significant influence on NO emission among the three diluents, while CO2 affected CO emission most by inhibiting its oxidation thermally and chemically. Numerical simulations were performed in counterflow diffusion flames by applying Chemkin software. To reveal the mechanisms of various diluents in flames, the detailed chemistry of H2-CO-N2 system was employed. It was found that the concentration of OH radical is important for both NO and CO emissions. The OH concentration is affected not only by the type of diluents but also by the flame temperature, therefore it is determined by the coupling and competition of diluents’ chemical and thermal effects.
Redesign of a Transonic Compressor Rotor by Means of a Three-Dimensional Inverse Design Method: A Parametric Study
Authors: Bonaiuti Duccio , Pitigala Abeetha , Zangeneh Mehrdad , Li Yansheng
Published: March 2009

In the present paper, the redesign of a transonic rotor was performed by means of a three-dimensional viscous inverse design method. The inverse approach used in this work is one where the pressure loading, blade thickness distribution and stacking axis are specified and the camber surface is calculated accordingly. The design of transonic and supersonic axial compressors strongly relies on the ability to control the shock strength, location and structure. The use of an inverse design method allows one to act directly on aerodynamic parameters, like the blade loading, and provides an efficient tool to control the shock wave and its interaction with the boundary and secondary flows and with the tip clearance vortex. In the present study, the parametric investigation of the blade loading distribution was carried out. Few design parameters, with immediate physical meaning, were required to control the three-dimensional blade loading, and their impact on the design and off-design performance of the rotor was assessed by means of CFD calculations. Further investigations were then performed in order to study the impact on the rotor performance of the geometrical parameters (meridional channel and thickness distribution), which must be imposed in the design with the inverse method. As a result, it was possible to develop guidelines for the aerodynamic design of transonic rotors that can be exploited for similar design applications.
Instability Analysis for Thermal Barrier Coating by Fracture Mechanical Modelings
Authors: Kumar Amar N. , Nayak Amiya , Patnaik Alok R. , Wu Xijia , Patnaik Prakash C.
Published: March 2009

Two simplistic models based on fracture mechanics considerations are used to advance the understanding of instability conditions in TBC systems. First model assumes isostrain behavior at and prior to the onset of crack initiation and is based on elastic energy balance approach. The other model is used for layer buckling and crack propagation behavior. The analysis for crack initiation suggests that the crack tip driving force, KI can reach a high value that is comparable to the fracture resistance of the coating material at and near the TBC/TGO interface even for a small nominal applied stress. The stresses required for the crack driving force (KI or GI) exceeding the fracture resistance of TBC materials are found to be in the range of 0.05 to 0.5 GPa. This appears to be an order of magnitude lower than the reported tangential tensile stress values of 1 to 2 GPa, but matches closely with the simulated transverse stress. High crack driving force resulting from low stress and small size defects (around 2 microns) facilitates early crack initiation in TBC system.
Cost-Effective Intelligent Engine Health Monitoring for Naval Gas Turbines
Authors: Hurdle Tim
Published: March 2009

The Marine Olympus and Tyne are long serving marine gas turbine engines, which entered service in the early 70’s and whose design heritage goes as far back as the 1950’s. The engines, still in active service with twenty three navies, continue to provide propulsion power for aircraft carriers, frigates and destroyers in every ocean around the globe. Rolls-Royce has developed a “Total Care” (TC) contract with one of its major naval customers to replace the traditional “as incurred” support arrangement. Under Total Care, Rolls-Royce for a fixed price will provide engines, their spares and technical support for a 12 year period. A fundamental element of the “Total Care” strategy was to install Data Acquisition and Intelligent Engine Health Monitor/Hazard alert systems. This paper will describe the technical requirement and business justification for the introduction of an Engine Health Monitor at a seemingly late stage in the engine product life cycle. The paper will also show how the customer and other stakeholders were satisfied that such an investment was both cost effective and achievable. Topics covered include the unique approach required for legacy products, system supplier and cost issues, sensor selection, prototyping, campaigning the equipment into the fleet and how to effectively manage large quantities of data. The paper will show how the use of intelligent hazard detection processes and diagnostic systems extract maximum value through asset longevity and protection for the benefit of both the service provider and customer.
A First-Principles Based Methodology for Design of Axial Compressor Configurations
Authors: Iyengar Vishwas , Sankar Lakshmi N. , Denney Russ
Published: March 2009

A multi-objective technique for designing single stage compressors is described. The blade geometry is defined as a function of known parametric equations, and the coefficient multipliers are viewed as design variables. A design of experiment approach is used to reduce the large combinations of design variables into a smaller subset. A response surface method is used to approximate the performance (total pressure rise, and adiabatic efficiency) as a function of design variables, and an optimum configuration is determined. This method has been applied to a rotor-stator combination similar to NASA Stage 35 with encouraging results.
Integration of On-Line and Off-Line Diagnostic Algorithms for Aircraft Engine Health Management
Authors: Kobayashi Takahisa , Simon Donald L.
Published: March 2009

This paper investigates the integration of on-line and off-line diagnostic algorithms for aircraft gas turbine engines. The on-line diagnostic algorithm is designed for in-flight fault detection. It continuously monitors engine outputs for anomalous signatures induced by faults. The off-line diagnostic algorithm is designed to track engine health degradation over the lifetime of an engine. It estimates engine health degradation periodically over the course of the engine’s life. The estimate generated by the off-line algorithm is used to “update” the on-line algorithm. Through this integration, the on-line algorithm becomes aware of engine health degradation, and its effectiveness to detect faults can be maintained while the engine continues to degrade. The benefit of this integration is investigated in a simulation environment using a nonlinear engine model.
Estimating Deterioration Level of Aircraft Engines
Authors: Qiu Hai , Eklund Neil , Yan Weizhong , Bonissone Piero , Xue Feng , Goebel Kai
Published: March 2009

This paper describes an approach to estimate the deterioration level of aircraft engines using engine monitoring data and a physics-based engine model. The estimation process is carried out by a neural network, which is trained by data generated using a physical-based engine model complemented with an empirically derived engine deterioration model. The deterioration model allows manipulation of several engine health parameters, such as module efficiency and flow capacity, to simulate engine deterioration. Simulated sensor outputs are used to build independent transfer functions relating the sensor values to a deterioration level. A calibration model corrects the sensor readings to a reference condition so that the effect of variation of operating condition is minimized. The proposed approach can be used to assess engine deterioration level in real time. The proposed deterioration estimation approach is validated using real-world engine data.
Gaseous and Particle Emissions in the Exhaust of a T700 Helicopter Engine
Authors: Li-Jones Xu , Penko Paul F. , Williams Sherry , Moses Cliff
Published: March 2009

Emissions were measured for four fuels and six combinations of fuels and additives in the exhaust of a T700-GE-700 helicopter engine. The test matrix consisted of three engine power settings: idle, continuous, and maximum continuous. The four fuels were JP-5, F-76, and two synthesized fuels from the Fischer-Troph process, one containing zero sulfur and zero aromatics (synthetic A), and a second containing zero sulfur and 14 vol% aromatics (synthetic B). The JP-5 was also tested with a solvent that increased the aromatic content, and seeded with copper to simulate contamination from shipboard fuel-distribution systems. The JP-5 and F-76 were also tested with an additive commonly used to increase thermal stability. Carbon-monoxide (CO) emission-indices (EIs) for the JP-5 ranged from 53.4 g/kg at idle to 2.3 g/kg at maximum power. The EI of total hydrocarbons (THCs) ranged from 3.9 g/kg to 0.13 g/kg over the same power settings. The effect of the various fuels and additives on the emissions of CO and THCs was negligible (at the 95% confidence level), except at maximum power where CO from the F-76 was about 25% higher, and from the first synthetic, about 16% lower than the JP-5. At all power settings, the CO for JP-5 with the thermal-stabilizer additive were consistently lower by about 12%. Particulate matter was measured and displayed nearly log-normal distributions with a single-mode for all fuels tested. In all cases, count median-diameters (CMDs) ranged from about 20 to 60 nm, and increased with power setting. Mass emissions also increased with power setting. On a number basis, emissions ranged from 1.6 × 1013 to 1.7 × 1015 particles/kg, and increased with power setting for most of the fuels and fuel-additive combinations. The CMD and mass emissions for the JP-5 ranged from 30 to 50 nm and 0.06 to 0.49 g/kg from idle to maximum power. The F-76 produced the largest CMDs and highest particle mass at all conditions, with a CMD of 60 nm and mass emissions of 0.77g/kg occurring at maximum power. Synthetic A fuel produced the smallest particle CMDs and lowest particle mass at all power settings. The thermal-stability additive and variations in aromatic content, and copper particles, did not significantly affect the particle emissions. Particle mass measured with a filter-gravimetric method correlated well with the particle volume calculated from the measured number size-distributions, where the correlation yielded a particle density of 1000 kg/m3.
TBC Characterization Using Magnetic and Electric Field Sensors
Authors: Sheiretov Yanko , Evans Leslie , Schlicker Darrell , Zilberstein Vladimir , Goldfine Neil , Sikorski Ruth
Published: March 2009

Recent advances in magnetic and electric field sensors have enabled accurate measurements of bond coat and top coat material properties and thicknesses. This paper reviews current methods of using electric and magnetic field sensors for coating assessment in separate measurements and in a hybrid magnetic-electric sensor construct. Magnetic field (inductive) sensors can be used to characterize gas turbine components by providing critical information about the thickness and condition of the metallic bond coat and thickness of the top coat. Electric field (capacitive) sensors can be used to characterize ceramic top coats by providing information about the thickness, condition, and surface roughness of the top coat. Using multivariate inverse methods and precomputed model-derived databases, multiple unknown coating properties are estimated simultaneously and independently. The capability to independently estimate four unknowns with one sensor and as many as six unknowns with both sensors together enables practical application of this technology for manufacturing quality and in-service condition assessment. Together, these two sensors can provide an effective method of nondestructively characterizing both metallic and ceramic coatings on turbine components.
Comparative Investigation of Three Highly Loaded LP Turbine Airfoils: Part II — Measured Profile and Secondary Losses at Off-Design Incidence
Authors: Zoric T. , Popovic I. , Sjolander S. A. , Praisner T. , Grover E.
Published: March 2009

The first part of the paper compared the midspan aerodynamics and the secondary flows for a family of three low-pressure turbine (LPT) airfoils at design conditions. However, since a typical engine spends much of its time operating at off-design conditions, good tolerance of LPT airfoils to off-design operation is desired. The sensitivity of the midspan flow to Reynolds number was examined for the three airfoils in a paper presented at the 2006 ASME-IGTI Turbo-Expo. The present paper examines the performance of the airfoils for three values of incidence: −5, 0, and +5 degrees relative to design. Both the profile and secondary losses are considered. Detailed loading distributions measured at midspan are used to explain the behaviour of the profile flow and the resulting change in losses as the incidence was varied. The secondary flow behaviour is determined as at the design incidence from detailed flowfield measurements made downstream of the trailing edge using a seven-hole pressure probe. The results show that in terms of profile losses the baseline airfoil (which has a Zweifel coefficient Z = 1.08) and the front-loaded one with Z = 1.37 have comparable losses over the range of incidences examined. However, the aft-loaded airfoil with Z = 1.37 had noticeably higher profile losses than the other two. On the other hand, the front-loaded one has higher secondary losses than its aft-loaded counterpart at all conditions examined. This obviously poses a dilemma for the designer in terms of the choice of loading distribution. It was also noted that the distribution of loading seems to affect the secondary losses more than the loading level (Zweifel coefficient). An interaction of the secondary flows with the suction side separation bubble might be responsible in part for this finding.
Combustion Instabilities and Damping Effectiveness Evaluation on Test Rigs and Gas Turbine Engines
Authors: Oumejjoud Khalid , Stuttaford Peter J.
Published: March 2009

Power generation companies have turned to gas turbines as a means to meet the stringent emission requirements set by regulation. The boundary between low emissions and an unstable combustor are narrower than ever. Hence, combustion instabilities have become a major design challenge as combustors are developed to run as lean as possible in order to achieve stringent emissions targets. These combustion instabilities can limit the operational envelope of the machine and are often responsible for damage to the gas turbine. Thus, preventing or controlling such conditions is the main focus of the design community. In order to lower the risk associated with combustion instabilities issues, a proper understanding of the design and acoustics of the combustion system has to be acquired early in the development stage. A damping strategy should be developed to mitigate risk in the event of unacceptably high dynamics. Combustion rig testing is crucial to a new combustor development program. Matching the acoustic environment of the combustion rig and the engine provide valuable insight into future potential combustion dynamics problems in the engine and provides valuable data to assist troubleshooting such issues on the engine. This work illustrates the ability of rig testing to be a valuable design and optimization tool in addressing combustion dynamics. Rig test data was used to successfully optimize subsequent engine combustion dynamics. The effectiveness of a damping system is also illustrated on the combustion test rig.
Unsteady Turbine Blade and Tip Heat Transfer Due to Wake Passing
Authors: Ameri Ali A. , Rigby David L. , Steinthorsson Erlendur , Heidmann James , Fabian John C.
Published: March 2009

The geometry and the flow conditions of the first stage turbine blade of GE’s E3 engine have been used to obtain the unsteady three-dimensional blade and tip heat transfer. The isothermal wall boundary condition was used. The effect of the upstream wake of the first stage vane was of interest and was simulated by provision of a “gust” type boundary condition upstream of the blades. A one blade periodic domain was used. The consequence of this choice was explored in a preliminary study which showed little difference in the time mean heat transfer between a 1:1 and 2:3 vane/blade domains. The full three-dimensional computations are of the blade having a clearance gap of 2% the span. Comparison between the time averaged unsteady and steady heat transfer is provided. It is shown that there is a significant difference between the steady and time mean of unsteady blade heat transfer in localized regions. The differences on the suction side of the blade in the near hub and near tip regions were found to be rather significant. Steady analysis underestimated the blade heat transfer by as much as 20% as compared to the time average obtained from the unsteady analysis. As for the blade tip, the steady analysis and the unsteady analysis gave results to within two percent.
Design of Turbocharger Variable Nozzle
Authors: Zhang Jizhong , Zhuge Weilin , Hu Lifeng , Li Shuqi
Published: March 2009

Design of variable nozzle vane is the key for variable nozzle turbocharger (VNT) design. A VNT was constructed by assembling a variable nozzle into a conventional turbocharger with vaneless nozzle. The design methods and processes of the variable nozzle were presented in detail, which include thermodynamic design, structural and mechanical design, and CFD analysis. The CFD analysis showed that the aerodynamic performance of the variable nozzle was well accepted in different open positions. The engine-matching test showed that, the performance of the engine improved significantly with the VNT compared to the prototype turbocharger. The engine fuel consumption was reduced by 8.1g/Kw·h and the maximum torque increased by 250 N·m.
Fatigue Life Prediction for Large-Diameter Elastically-Constrained Ball Bearings
Authors: Sawicki Jerzy T. , Johansson Samuel A. , Rumbarger John H. , Sharpless Ronald B.
Published: March 2009

The application of large-diameter bearing rings and the thereof inherited low stiffness make them susceptible to local distortions caused by their surrounding structures, which are often under heavy loads. The standard accepted design criteria for these bearings are based on the estimation of the internal load distribution of the bearing, under the assumption of rigid circular and flat supporting structures, that keep the bearing inner and outer races in circular, flat, i.e., not deformed shapes. However, in the presence of structural distortions, the element load distribution can be severely altered and cannot be predicted via the standard design criteria. Therefore, the application of large-diameter ball and roller bearing rings as the critical components in rotating machines becomes more of a design task than making a catalog selection. The analytical and finite element approach for fatigue life prediction of such a bearing-application is presented. The undertaken approach and the results are illustrated based on the analysis and fatigue life simulation of the CT (Computed Tomography) -scanner’s main rotor bearing. It has been demonstrated that flexibility of the rings can significantly reduce the fatigue life of the ball bearing.
Performance Characteristics of a Turbo Expander Applied to the Expansion Process at a HFC134a Air-Conditioner
Authors: Cho Soo-Yong , Cho Chong-Hyun , Kim Chaesil
Published: March 2009

An experimental study is conducted on a small turbo expander which can be applied to the expansion process in place of an expansion valve in a regenerator or air-conditioner to recover energy from the throttling process. The operating gas is HFC134a and the maximum cooling capacity of the air-conditioner used in this experiment is 32.7kW. Four different axial-type rotors in the turbo expander are tested to find not only the performance difference on the rotor with/without the shroud but also the performance characteristics of the turbo expander when the partial admission rate is increased by changing the annular passage area of the rotor. Two rotors among four are shrouded on the tip of rotor; the first has a mean diameter of 71.85mm and the second 70.46mm. The remaining two rotors are tested after removing the shroud. These axial-type rotors operate in the supersonic flow generated at the supersonic nozzle, and the partial admission rate is 1.70% or 2.37% depending on the rotor size. In the experiment, pressure and temperature are measured at ten different locations in the experimental apparatus. In addition to these measurements, output power at the turbo expander is measured through a generator installed on a rotor shaft with the rotational speed. Performance data of the turbo expander are obtained at many part load operations by adjusting the output power of the generator. Experimental results show that the optimal velocity ratio decreases when the pressure ratio is decreased, and peak efficiencies, which are obtained at locally maximized efficiency depending on the operating condition, vary linearly against the subcooling temperature or the pressure ratio. A maximum 15.8% total-to-static efficiency is obtained when the pressure ratio and the partial admission ratio are 2.66 and 1.70%, respectively. When the partial admission rate is increased by reducing the annular passage area of the rotor without changing the nozzle area, the performance difference is negligible. Comparing with the total-to-static efficiencies obtained at a rotor with/without the shroud, the efficiencies obtained with the shroud are improved by nearly 3.7% for all operating conditions.
A Novel Method for Component Map Identification of a Gas Turbine Using Intelligent Method and Engine Performance Deck Data
Authors: Kong Changduk , Kho Seonghee , Ki Jayoung , Jun Yongmin
Published: March 2009

In this study a component map generation method which can identify component characteristics conversely from limited performance deck data provided by engine supplier was newly proposed using a hybrid method with the genetic algorithms and the system identification method. Generally component performance characteristics of compressor and turbine can be expressed as the third order equation with the related function of the engine rotational speed versus the pressure ratio, the mass flow function and the isentropic efficiency. According to the newly proposed scheme, firstly the scaling is performed at each engine rotational speed with some limited performance data which are provided by engine manufacturer, and then the component characteristic equations are obtained using system identification method. Then the initially obtained component characteristics are modified by considering engine component behavior for various operational conditions such as flight Mach number, altitude and atmospheric temperature using genetic algorithms. In the modification, the component characteristics obtained by system identification are used as initial data to reduce the calculation time. And finally component maps are generated by integrating the component characteristic equations taken at each engine rotational speed. In order to verify the proposed method, steady-state performance analysis using the newly generated component maps were performed, and the analysis results were compared with the performance deck data and the analysis results using the traditional scaling method. In this investigation, it was found that the newly proposed map generation method (1% errors) is more effective than the traditional scaling method (10% errors) in overall operational region.
An Experimental Investigation on the Unsteady Excitation Effect of Casing Treatment on a Low Speed Axial Compressor
Authors: Jiang Huabing , Lu Yajun , Yuan Wei , Li Qiushi
Published: March 2009

The performances of compressor should be remarkably improved if the interaction between the flow within treatment slots and the separated flow field around the rotor blades could be properly organized. An experiment was performed on a single stage low speed axial compressor to investigate the unsteady excitation effect of three arc curve skewed slot casing treatments which differ only in the number of treatment slots under uniform and distorted inlet flow conditions. The separated flow field around the rotor blade was investigated with a dynamic pressure probe to obtain the information on unsteady vortex shedding, and the frequency spectrum of the dynamic information was analyzed and utilized to guide the design of the casing treatment in confirming the number of slots. The performances of the compressor were measured for smooth casing and arc curve skewed slot casing treatments under uniform and distorted inlet flow conditions respectively. The stable operating range of the compressor can be improved with all these arc curve skewed slot casing treatments compared to smooth casing. However, only the casing treatment representing the same frequency as that of separated flow around the rotor blades could achieve prominent improvement in stability and total pressure rise coefficient of the compressor without efficiency penalty, where the unsteady separated flow around the rotor blades could couple with that injected from the treatment slots. Consequently, the flow structure was remarkably improved and the time-averaged aerodynamic performances especially the stability of the compressor were significantly enhanced. The number of treatment slots would effectively influence the unsteady interaction, and hence influence the effectiveness of the casing treatment. The frequency of unsteady interaction should be tuned close to the vortex shedding frequency or within the range of lock-in frequency to couple with the separated flow field around the rotor blades, which might be utilized to guide the design of casing treatment in confirming the number of treatment slots.
Investigation Into the Effect of Uncertainty in Thermal Properties on Turbomachinery Disc Heat Transfer Using Both a Monte Carlo Simulation Technique and a Taylor Series Uncertainty Propagation Method
Authors: Cooke Adam , Childs Peter , Long Christopher
Published: March 2009

The effect of uncertainties in the thermal properties of components and surrounding fluids is often ignored in the field of experimental turbomachinery heat transfer. The work reported here uses two different methods of uncertainty analysis to help quantify these effects: 1) a stochastic Monte Carlo simulation and 2) a Taylor series uncertainty propagation. These two methods were used on a steady state free disc test case having a turbulent flow regime. The disc modelled was made from IMI 318 titanium and had an inner and outer radius of 0.115 m and 0.22 m respectively, representative of engine and test rig geometry. The disc thickness was 0.016 m. Convective boundary conditions were derived from the relevant equation for local Nusselt number. The applied boundary conditions resulted in local heat transfer coefficients in the range of approximately 120 W/m2 K to 170 W/m2 K. Uncertainties for these heat transfer coefficients were a near identical match between the two different uncertainty methods and were found to be ± 0.66%. Calculated heat flux values fell within the range of approximately 1500 W/m2 and 5200 W/m2. The Monte Carlo uncertainty method returned uncertainty values varying from ± 1.17% to ± 0.47% from the inner and outer radii respectively. An extended Taylor series of uncertainty propagation returned uncertainties varying from ± 1.82% to ± 0.96%, from the inner and outer radius respectively and increased and decreased a number of times in between. These differences are due to assumptions and simplifications which need to be made when using the Taylor series method and shows that a Monte Carlo simulation analysis offers a better way of quantifying the uncertainties associated with disc to air heat transfer as it is more realistic. Studying the magnitudes of uncertainty allows the analyst to understand the impact that uncertainties in thermal properties can have on calculated values of disc to air heat fluxes and heat transfer coefficients.
Application of Non-Axisymmetric Endwall Contouring to Conventional and High-Lift Turbine Airfoils
Authors: Praisner T. J. , Allen-Bradley E. , Grover E. A. , Knezevici D. C. , Sjolander S. A.
Published: March 2009

Here we report on the application of non-axisymmetric endwall contouring to mitigate the endwall losses of one conventional- and two high-lift low-pressure turbine airfoil designs. The design methodology presented combines a gradient-based optimization algorithm with a three-dimensional CFD flow solver to systematically vary a free-form parameterization of the endwall. The ability of the CFD solver employed in this work to predict endwall loss modifications resulting from non-axisymmetric contouring is demonstrated with previously published data. Based on the validated trend accuracy of the solver for predicting the effects of endwall contouring, the magnitude of predicted viscous losses forms the objective function for the endwall design methodology. This system has subsequently been employed to optimize contours for the conventional-lift Pack B and high-lift Pack D-F and Pack D-A low-pressure turbine airfoil designs. Comparisons between the predicted and measured loss benefits associated with the contouring for Pack D-F design are shown to be in reasonable agreement. Additionally, the predictions and data demonstrate that the Pack D-F endwall contour is effective at reducing losses primarily associated with the passage vortex. However, some deficiencies in predictive capabilities demonstrate here highlight the need for a better understanding of the physics of endwall loss-generation and improved predictive capabilities. More detailed analysis of the contouring results for the Pack B design is presented in a companion paper (Knesevici et al. [1]).
Time Resolved Investigations of an Axial Compressor With Casing Treatment: Part 2 — Simulation
Authors: Emmrich R. , Kunte R. , Ho¨nen H. , Niehuis R.
Published: March 2009

A casing treatment with axial and radial skewed slots ending in a plenum chamber has numerically been investigated at a highly subsonic axial compressor stage. The aim was to understand the physical phenomena of this treatment family that are responsible for the stabilization of the blade passage flow and the drop in efficiency mostly observed. Unsteady 3D Reynolds-averaged simulations were performed with the commercial CFD Code TASCflow 2.12. The closure problem was faced with a standard k-ε high Reynolds turbulence model and a logarithmic wall function. Two configurations with solid casing and casing treatment were investigated at the operating points with maximum efficiency and on the stability line. The experimentally gained performance results of this configuration show an extension of the operating range of approximately 50% based on the operating range at nominal speed, while the efficiency for design conditions falls by 1.4%. Apart from this, measurements at part load conditions show operating points without any loss in efficiency. The numerical simulations predict this efficiency drop as well. The detailed analysis is performed for the solid casing and casing treatment configuration at the operating point on the stability line. Influences of the incidence flow, the tip clearance vortex and the blade suction side separation were investigated. Special interest is directed towards the interaction of the casing treatment with the blade passage flow field and a detailed analysis of the flow inside the casing treatment, the effect of the plenum chamber and the interaction with the treatment slot flow is performed.
Reduced Rough-Surface Parameterization for Use With the Discrete-Element Model
Authors: McClain Stephen T. , Brown Jason M.
Published: March 2009

The discrete-element model for flows over rough surfaces was recently modified to predict drag and heat transfer for flow over randomly-rough surfaces. However, the current form of the discrete-element model requires a blockage fraction and a roughness-element diameter distribution as a function of height to predict the drag and heat transfer of flow over a randomly-rough surface. The requirement for a roughness element-diameter distribution at each height from the reference elevation has hindered the usefulness of the discrete-element model and inhibited its incorporation into a computational fluid dynamics (CFD) solver. To incorporate the discrete-element model into a CFD solver and to enable the discrete-element model to become a more useful engineering tool, the randomly-rough surface characterization must be simplified. Methods for determining characteristic diameters for drag and heat transfer using complete three-dimensional surface measurements are presented. Drag and heat transfer predictions made using the model simplifications are compared to predictions made using the complete surface characterization and to experimental measurements for two randomly-rough surfaces. Methods to use statistical surface information, as opposed to the complete three-dimensional surface measurements, to evaluate the characteristic dimensions of the roughness are also explored.
Flow Structure and Turbulence in the Tip Region of a Turbomachine Rotor Blade
Authors: Soranna Francesco , Chow Yi-Chih , Uzol Oguz , Katz Joseph
Published: March 2009

The flow structure and turbulence in the tip region of a rotor blade operating downstream of a row of Inlet Guide Vanes (IGVs) are investigated experimentally in a refractive index matched facility that provides unobstructed view of the entire flow field. Stereo-PIV measurements are performed in closely spaced radial planes near the blade tip in a region extending from (slightly upstream of) the blade trailing edge to about 40% of the chord downstream of it. The data enable calculations of all the components of the phase-averaged velocity and vorticity vectors, as well as the strain rate, Reynolds stress, and turbulent diffusion tensors. Each rotor blade is confined between two tip-leakage vortices, a right hand vortex (RHV), generated by the subject blade and propagating along its right hand side, and a left hand vortex (LHV), generated by the previous blade in the same row and propagating along the left hand side of the subject blade. In addition, a trailing edge vortex (TEV) lays underneath the LHV and is subject to intense shearing/deformation by the LHV. RHV-induced radial gradients of radial phase-averaged velocity cause negative turbulence production, P, along the RHV-axis, and formation of a region of low P in the gap between the RHV and the blade suction surface. Trends of turbulent kinetic energy k and P within the RHV do not agree due to the effects of advection by the phase-averaged flow. To the left of the blade, shearing of the TEV by the LHV enhances turbulence production in the region between the two vortices and the rotor wake. Trends of turbulent kinetic energy and its production rate are in good agreement and peaks of k and P occur at the same location. As the TEV migrates away from the LHV, shearing effects become weaker and the dominant contributors to production are terms containing vortex-induced radial gradients of axial and radial velocities. Turbulent diffusion is a minor contributor to the evolution of turbulent kinetic energy in the tip region. It is also shown that the tip-leakage flow/vortex deteriorates the rotor blade performance, causing a ∼66% increase in shaft power input (per unit mass flow-rate) in the tip region in comparison with midspan.