bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-Dimensional Flow and NOx Emissions in Deflagrative Internal Combustion Wave Rotor Configurations
Authors: Nalim Razi , Pekkan Kerem
Published: February 2009

A wave rotor is proposed for use as a constant volume combustor. A novel design feature is investigated as a remedy for hot gas leakage, premature ignition and pollutant emissions that are possible in this class of unsteady machines. The base geometry involves fuel injection partitions that allow stratification of fuel/oxidizer mixtures in the wave rotor channel radially, enabling pilot ignition of overall lean mixture for low NOx combustion. In this study, available turbulent combustion models are applied to simulate approximately constant volume combustion of propane and resulting transient compressible flow. Thermal NO production histories are predicted by simulations of the STAR-CD code. Passage inlet/outlet/wall boundary conditions are time-dependent, enabling the representation of a typical deflagrative internal combustor wave rotor cycle. Some practical design improvements are anticipated from the computational results. For a large number of derivative design configurations, fuel burn rate, two-dimensional flow and emission levels are evaluated. The sensitivity of channel combustion to initial turbulence levels is evaluated.
Modeling and Simulation of a Turbulent Premixed Methane/Air Flame Based on the G-Equation
Authors: Repp S. , Sadiki A. , Khiviousk E. , Janicka J.
Published: February 2009

Using a consistent coupling of the ILDM-method for the chemical kinetics with the G-equation approach for describing the flame front propagation, the kinetic effects in the post-flame region of turbulent premixed flames are investigated. Turbulent flow and mixing fields are described by means of first order moment closures, whilst a multidimensional presumed PDF approach is applied to capture the turbulence-chemistry interaction. Mean scalar quantities of both side of the premixed flame front are calculated based on reaction progress variables conditioned on the G-evolution equation. The model derived, very well applicable to premixed and partially premixed flames, is used to simulate a turbulent premixed methane/air flame. A fair agreement with experimental data for major concentration fields and minor species could be achieved. Apparently, the coupling to the G-equation does not provide more additional accuracy in a case where the consideration of piloting plays a non negligible role.
Performance Evaluation of Multi-Stage SOFC and Gas Turbine Combined Systems
Authors: Nishida Kousuke , Takagi Toshimi , Kinoshita Shinichi , Tsuji Tadashi
Published: February 2009

Solid oxide fuel cell (SOFC) and gas turbine hybrid power generation systems have gained more and more attention with regard to the development of the high performance distributed energy systems. The SOFC can be combined with a gas turbine because the SOFC operating temperature of about 1000°C matches the turbine inlet temperature. In this study, we proposed the multi-stage type SOFC/GT combined system and compared the system performance of it with that of other combined systems using the thermal efficiency and exergy evaluation. It is noted that the thermal efficiency of the 3-stage type SOFC/GT combined system can reach more than 70% (HHV) at low pressure ratio.
The Chronological Development of the Cheng Cycle Steam Injected Gas Turbine During the Past 25 Years
Authors: Cheng Dah Yu , Nelson Albert L. C.
Published: February 2009

The Cheng Cycle gas turbine has enjoyed its 25th anniversary since its conception. More than 100 sites around the world including the United States, Japan, Australia, Italy, Germany, and the Netherlands have used the Cheng Cycle. A chronology will be presented in this paper which will highlight the steps taken to develop the fully automated, load following power and cogeneration system. The Cheng cycle operates with a steam to air ratio trajectory that has its highest “peak efficiency” at the onset of a turbine’s operation. The peak efficiency point was coined as the Cheng point by Dr. Urbach [ref.1] of the US Navy’s David Taylor Research Center. Many thermodynamic and professional textbooks refer to the original Dual Fluid Cycle as the Cheng Cycle. Besides the high efficiency feature, the Cheng Cycle is mechanically simple and flexible in operation. It can put power on line faster than a combined cycle, and it has extremely clean emissions at low cost. The future performance of the Advanced Cheng Cycle will also be projected.
Cost Optimization of Water Recovery Systems for Steam Injected Gas Turbines
Authors: Blanco Gabriel , Ambs Lawrence L.
Published: February 2009

Steam injection in gas turbines has been used for many years to increase the power output as well as the efficiency of the system and, more recently, to reduce the formation of NOx during the combustion. The major drawback in steam-injected gas turbine technology is the need of large amounts of fresh water that is eventually lost into the atmosphere along with the exhaust gases. Nowadays, fresh water is not readily available in many places due to either local water shortages or environmental legislation that protects water sources from depletion and pollution. In order to deal with water constraints, water recovery systems (WRS) to recuperate the injected steam from the exhaust gases and return it to the steam injection system can be implemented. In this project, computer models for two different WRS configurations have been developed and tested. The computer models allow finding the optimum size, power requirements and capital costs of the heat exchangers involved in a particular WRS configuration. The models can also simulate the performance of WRS during a given period of time, calculating the energy consumed by fans and pumps in the process. This paper explains the details of the computer models and illustrates, as an example, the results obtained when both WRS configurations are applied to the GE LM2500 gas turbine. These results support the technical and economic feasibility of steam recovery for medium-size steam-injected gas turbines.
Comparative Analysis of Off-Design Performance Characteristics of Single and Two Shaft Industrial Gas Turbines
Authors: Kim J. H. , Kim T. S. , Sohn J. L. , Ro S. T.
Published: February 2009

Off-design steady performance and operating characteristics of single and two shaft gas turbines for electric power generation have been investigated comparatively. A set of balance equations has been derived based on validated component models. A simultaneous calculation scheme has been employed, which is flexible to various engine configurations. Part-load performance analyses of two commercial gas turbines have been carried out to compare operating characteristics between single and two shaft engines. The predicted performance characteristics of both engines coincide soundly with the manufacturer’s data and also correspond with the inherent characteristics of each configuration. The adoption of the VIGV modulation has been addressed in order to examine the possibility of leveling up the heat recovery capacity by maintaining a high turbine exhaust temperature (TET) when those gas turbines are used for combined cycle plants. Maintaining TET at its design value as far as the VIGV modulation allows has been simulated and it has been determined that the TET control is possible at up to 40% and 50% load in the single and two shaft engine, respectively. Combined cycle performances have also been investigated for two engine configurations in different operating modes. While the VIGV modulation produces a favorable influence over the combined cycle performance of the single shaft configuration, the two shaft engine does not appear to be effectively improved by the VIGV modulation since the degradation of gas turbine performance counteracts the advantage of the higher performance of the bottoming (steam turbine) cycle.
Complex Energy Systems Exploiting Solar Energy and Natural Gas Vaporization
Authors: Bisio Giacomo , Bosio Alessandro , Cartesegna Marco , Rubatto Giuseppe
Published: February 2009

The fossil fuel reserves are limited. In addition, usable energy supply has a considerable impact on the environment, even if some effects, which are usually alleged, are far from being fully established. Natural gas is often found in remote locations far from developed industrial nations. Where possible, the gas is transported by pipeline to the end user. However, where oceans separate the gas source and the user, or there are other difficulties, the only viable way to transport the gas is to convert it into liquid natural gas (LNG) and to convey it using insulated LNG tankers. This paper outlines the results of an examination of a complex system, employing solar energy, for the production of electrical energy and the vaporization and superheating of LNG. It is to be remarked that, differently from the usual combined systems, both the thermal source and the thermal sink are exergy sources.
Equipment of a Sister Ship of Aircraft Carrier “Charles De Gaulle” With 2 HTR Nuclear Reactor Instead of the Actual Two PWR: Preliminary Study — Main Results
Authors: Fribourg Charles
Published: February 2009

An explorative and preliminary study has been done by a small crew of students of the Ecole des Applications Militaires de l’Energie Atomique (Cherbourg FRANCE) under the directives and councils of TECHNICATOME and the CEA (Commissariat a` l’Energie Atomique). Main results: • The HTR reactor types are interesting for equipping military great ship like an air craft carrier, the general design as result of a preliminary study shows that mass and size of the propulsion system can be more favourable than with PWR reactors.
Assessment of Various Film Cooling Configurations Including Shaped and Compound Angle Holes Based on Large Scale Experiments
Authors: Dittmar J. , Schulz A. , Wittig S.
Published: February 2009

The demand of improved thermal efficiency and high power output of modern gas turbine engines leads to extremely high turbine inlet temperatures and pressure ratios. Sophisticated cooling schemes including film cooling are widely used to protect vanes and blades from failure and to achieve high component life-times. Besides standard cylindrical cooling hole geometry, shaped injection holes are used in modern film cooling applications in order to improve cooling performance and to reduce the necessary cooling air flow. However, complex hole shapes may lead to manufacturing constraints and high costs. This paper evaluates some film cooling injection geometry with different complexity. The comparison is based on measurements of the adiabatic film cooling effectiveness and the heat transfer coefficient downstream of the injection location. In total, 4 different film cooling hole configurations are investigated: A single row of fanshaped holes with and without a compound injection angle, a double row of cylindrical holes and a double row of discrete slots, both in staggered arrangement. All holes are inclined 45° with respect to the model’s surface. During the measurements, the influence of coolant blowing ratio is determined. Additionally, the influence of cooling air feeding direction into the fanshaped holes with the compound injection angle is investigated. An infrared thermography measurement system is used for highly resolved mappings of the model’s surface temperature. Accurate local temperature data is achieved by an In-Situ calibration procedure with the help of single thermocouples embedded in the test plate. A subsequent finite elements heat conduction analysis takes three-dimensional heat fluxes inside the test plate into account.
Film Cooling Effectiveness Due to Discrete Holes Within a Transverse Surface Slot
Authors: Bunker Ronald S.
Published: February 2009

The goal of many turbine airfoil film cooling schemes is the achievement of a tangentially injected 2D layer of protective film over the surface. In common nomenclature, this is referred to as 2D slot film cooling, which can achieve adiabatic effectiveness levels approaching unity at the injection location. Since continuous and uninterrupted slots are not structurally feasible in the high pressure turbine components, other approximate film cooling geometries have been sought. The present study examines two film cooling geometries which are formed by the combination of internal discrete film holes feeding continuous 2D surface slots. Experiments have been performed within a flat plate wind tunnel test section, which includes an accelerating freestream condition to model the surface of a turbine airfoil. As suggested by the experiments of Wang et al. [1], a normal 2D surface slot is located transverse to the mainstream flow direction. The slot is fed by a row of discrete coolant supply holes oriented in the spanwise direction with inclination angle of 30-degrees, pitch-to-diameter ratio of 3.57, and length-to-diameter ratio of 5.7. The slot depth-to-hole diameter ratio is S/D of 3. Two such slots were tested, one with axial width-to-hole diameter ratio of 1.13, and the other with ratio of 1.5. Tests were conducted for supply hole blowing ratios of 0.75 to 4, density ratios of 1.8, and a freestream approach turbulence intensity of 4.5%. The holes-within-slot film effectiveness data are compared with both axial and radial film data, ie. S/D equal to zero, obtained in the same test section. The holes-in-slot geometries demonstrate two important characteristics, (1) a relative insensitivity of the adiabatic film effectiveness to blowing rate, and (2) no observed film blow-off at high blowing rates. In addition, a novel film cooling arrangement is demonstrated in which the surface slot is very shallow, forming a narrow trench with S/D of only 0.43. It is shown that this novel surface geometry yields the best film effectiveness of all cases tested.
Influence of the Hub Endwall Cavity Flow on the Time-Averaged and Time-Resolved Aero-Thermodynamics of an Axial HP Turbine Stage
Authors: De´nos R. , Paniagua G.
Published: February 2009

This experimental research investigates the influence of the hub endwall cavity flow on the aerodynamics and heat transfer of a high-pressure transonic turbine stage tested under engine representative conditions. The measurements include the hub and tip endwall static pressure downstream of the vane, the static pressure and heat transfer on the rotor blade at 15% span and on the hub platform as well as the stage downstream total pressure and temperature. Both steady and unsteady aspects are addressed. The hub endwall cavity flow has a significant influence on both the time-averaged and time-resolved components of the measured quantities. The effects are shown to be mainly due to an increase of the pitchwise averaged static pressure at hub downstream of the vane when cavity flow ejection is activated.
Heat Transfer Coefficient and Film-Cooling Effectiveness on a Gas Turbine Blade Tip
Authors: Kwak Jae Su , Han Je-Chin
Published: February 2009

The detailed distributions of heat transfer coefficient and film cooling effectiveness on a gas turbine blade tip were measured using a hue detection based transient liquid crystal technique. Tests were performed on a five-bladed linear cascade with blow down facility. The blade was a 2-dimensional model of a first stage gas turbine rotor blade with a profile of the GE-E3 aircraft gas turbine engine rotor blade. The Reynolds number based on cascade exit velocity and axial chord length was 1.1 × 106 and the total turning angle of the blade was 97.7°. The overall pressure ratio was 1.32 and the inlet and exit Mach number were 0.25 and 0.59, respectively. The turbulence intensity level at the cascade inlet was 9.7%. The blade model was equipped with a single row of film cooling holes at both the tip portion along the camber line and near the tip region of the pressure-side. All measurements were made at the three different tip gap clearances of 1%, 1.5%, and 2.5% of blade span and the three blowing ratios of 0.5, 1.0, and 2.0. Results showed that, in general, heat transfer coefficient and film effectiveness increased with increasing tip gap clearance. As blowing ratio increased, heat transfer coefficient decreased, while film effectiveness increased. Results also showed that adding pressure-side coolant injection would further decrease blade tip heat transfer coefficient but increase film effectiveness.
Heat Transfer Enhancement in Square Ducts With V-Shaped Ribs of Various Angles
Authors: Jia Rongguang , Saidi Arash , Sunde´n Bengt
Published: February 2009

Experimental studies have revealed that both downstream and upstream pointing V-shaped ribs result in better heat transfer enhancement than transverse straight ribs of the same geometry. Secondary flows induced by the angled ribs are believed to be responsible for this higher heat transfer enhancement. Further investigations are needed to understand this. In the present study, the heat and fluid flow in V-shaped-ribbed ducts is numerically simulated by a multi-block 3D solver, which is based on solving the Navier-Stokes and energy equations in conjunction with a low-Reynolds number k-ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM), while turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Firstly, the simulation results of transverse straight ribs are validated against the experimental data, for both velocity and heat transfer coefficients. Then, the results of different rib angles (45° and 90°) and Reynolds number (15,000–30,000) are compared to determine the goodness of different rib orientations. Detailed velocity and thermal field results have been used to explain the effects of the inclined ribs and the mechanisms of heat transfer enhancement.
Unsteady and Calming Effects Investigation on a Very High Lift LP Turbine Blade: Part I — Experimental Analysis
Authors: Coton Thomas , Arts Tony , Lefebvre Michae¨l , Liamis Nicolas
Published: February 2009

An experimental and numerical study was performed about the influence of incoming wakes and the calming effect on a very high lift low pressure turbine rotor blade. The first part of the paper describes the experimental determination of the pressure loss coefficient and the heat transfer around the blade mounted in a high speed linear cascade. The cascade is exposed to incoming wakes generated by high speed rotating bars. Their aim is to act upon the transition/separation phenomena. The measurements were conducted at a constant exit Mach number equal to 0.8 and at three Reynolds number values, namely 190000, 350000 and 650000. The inlet turbulence level was fixed at 0.8%. An additional feature of this work is to identify the boundary layer status through heat transfer measurements. Compared to the traditionally used hot films, thin film heat flux gages provide fully quantitative data required for code validation. Numerical computations are presented in the second part of the paper.
Experimental Analysis of Dust Separation in the Internal Cooling Air System of Gas Turbines
Authors: Schneider O. , Dohmen H. J. , Reichert A. W.
Published: February 2009

For further improvements in efficiency and performance a better understanding of the internal cooling air system of gas turbines, which provides the turbine rotor blades with cooling air, is necessary. With the increase of cooling air passing through the internal air system, a greater amount of air borne particles are transported to the film cooling holes at the turbine blade surface. In spite of their small size, these holes are critical for blade cooling. Blockage of only a few holes could have harmful effects on the cooling film surrounding the blade. As a result, a reduced mean time between maintenance or even unexpected operation faults of the gas turbine during operation occurs. With a new test rig, the behaviour of particles in the internal cooling air system could be investigated at realistic flow conditions compared to a modern, real world gas turbine. It is possible to simulate different particle sizes and dust concentrations in the coolant air. A first comparison of design expectations and measurements, showing the behaviour of air borne particles in the internal cooling air system under realistic environmental conditions is given in the paper. Further the design tools for nearly a full internal air system flow path could be validated with this new test rig.
Through Life Management of Naval Gas Turbines for Extended Service Lives and Reduced Lifetime Costs
Authors: Bolwell Richard
Published: February 2009

Marine gas turbines have been used for many decades in a diverse range of commercial and naval marine vessels, almost exclusively for main propulsion duties in a number of different configurations. As well as providing an outline of the scope of operation, this paper aims to discuss the key Life Extension Program’s and Cost Reduction Strategies developed by the UK Ministry of Defence in support of the two international collaborative Memoranda of Understanding (MoU) for the marine Olympus, Tyne and Spey gas turbines. Where available, discussion is supported with evidence from emerging equipment maintenance policies, equipment modifications and data collected from components and engines returned from the fleet for repair or overhaul. In addition, and in terms of the economy of scale advantages that the arrangements offer, an assessment of accumulated savings and projected financial return is provided with an insight into the operational benefits and improved capability that the program’s realise.
Development of Operating Temperature Prediction Method Using Thermophysical Properties Change of TBC
Authors: Fujii Tomoharu , Takahashi Takeshi
Published: February 2009

Thermal barrier coatings (TBCs) have become an indispensable technology as the temperature of turbine inlet gas has increased. TBCs reduce the temperature of the base metal, but a reduction of internal pores by sintering occurs when using TBCs, and so the thermal barrier performance of TBCs is deteriorated. This in turn increases the temperature of the base metal and could shorten its lifespan. The authors have already clarified by laboratory acceleration tests that the deterioration of the thermal barrier performance of TBCs is caused by a decrease in the non-contact area that exists inside TBCs [1]. This non-contact area is a slit space that exists between thin layers and is formed when TBCs are coated. This paper examines the relations between the decrease of the non-contact area and the exposure conditions, by measuring the thermal conductivity and the porosity of TBCs exposed to the temperatures that exist in an actual gas turbine, and derives the correlation with exposure conditions. As a result, very high correlations were found between the thermal conductivity and exposure conditions of TBCs, and between the porosity and exposure conditions. A very high correlation was also found between the thermal conductivity and porosity of TBCs. In addition, techniques for predicting TBC operating temperature were examined by using these three correlations. The correlation of diameter and exposure conditions of the gamma prime phase, which exists in nickel base super alloys, is used as a general method for predicting the temperature of parts in hot gas paths [2]. This paper proposes two kinds of operating temperature prediction methods, which are similar to this general method. The first predicts the operating temperature from thermal conductivity measurements of TBCs before and after use, and the second predicts the operating temperature from thermal conductivity measurements of TBCs after use and porosity measurements before use. The TBC operating temperatures of a combustor that had been used for 12,000 hours with an actual E-class gas turbine were predicted by these two methods. The advantage of these methods is that the temperature of all parts with TBC can be predicted.
Diagnosis of Installation Problems of Turbomachinery
Authors: El-Shafei A.
Published: February 2009

Many turbomachines perform well in factory testing, but experience difficulties in the field, mainly due to installation problems. The problems encountered range from misalignment and frame distortion to structural resonance and skid leveling. In this paper, a structured vibration analysis procedure is developed to identify installation problems in rotating machinery. Spectral analysis is the main tool for vibration analysis of turbomachinery faults, however many problems appear at a single frequency. In this case phase analysis, time waveform, orbit and operating deflection shape (ODS) analysis become very important. The paper presents a novel methodology for the diagnosis of installation problems in turbomachinery and provides examples of cases with installation faults, and discusses methods of identification and solution.
Combustion Turbine F-Class Life Management of 1st Stage Turbine Blades
Authors: Wan Eric S. , Crimi Paul , Scheibel John , Viswanathan R.
Published: February 2009

Whenever the operations and maintenance economics so dominate the operation of a particular power producer, engineering insight is the plant’s vanguard in maintaining and managing costs. To provide a basis for operators to confront the spiraling parts replacement costs that are so closely tied to the durability of the hot section, EPRI has developed the Gas Turbine Life Management Platform (LMP), an effort which has been directly supported by F-Class turbine operators. Tested and verified on the advanced 7FA and 9FA class of turbine designs, the LMP provides unprecedented detail on temperatures and stresses throughout a selected hot section component. In turn, the platform relies on explicit details of stress and temperature to track the damage due to creep, coating oxidation and TMF (thermal mechanical fatigue). Supplied with operating data, it graphically represents the recent practices of either base load or peaking service. The platform supplies the engineering data needed by operators to make informed decisions regarding the disposition (continued use, repair, or scrap) of these most advanced and expensive parts. In this paper, the procedures of predicting temperature/life and how well these predictions correlated with field observations will be discussed in detail.
Flutter Analysis of a Transonic Fan
Authors: Srivastava R. , Bakhle M. A. , Keith T. G. , Stefko G. L.
Published: February 2009

This paper describes the calculation of flutter stability characteristics for a transonic forward swept fan configuration using a viscous aeroelastic analysis program. Unsteady Navier-Stokes equations are solved on a dynamically deforming, body fitted, grid to obtain the aeroelastic characteristics using the energy exchange method. The non-zero inter-blade phase angle is modeled using phase-lagged boundary conditions. Results obtained show good correlation with measurements. It is found that the location of shock and variation of shock strength strongly influenced stability. Also, outboard stations primarily contributed to stability characteristics. Results demonstrate that changes in blade shape impact the calculated aerodynamic damping, indicating importance of using accurate blade operating shape under centrifugal and steady aerodynamic loading for flutter prediction. It was found that the calculated aerodynamic damping was relatively insensitive to variation in natural frequency.
Friction Damping of Interlocked Vane Segments: Validation of Friction Model and Dynamic Response
Authors: Berruti T. , Filippi S. , Gola M. M. , Salvano S.
Published: February 2009

Aim of the present work is the validation against experimental results of the dynamic calculation of a vane segment with two friction contacts. The segment is in contact with two adjacent supports as in the experimental setup [1]. An empirical friction model derived from the experiments is introduced. The calculation has been performed for different interlocking values (different values of force normal to the contact surfaces). An analysis about the dependence of the parameters of the adopted empirical contact model on the hysteresis cycle shapes has been performed.
The Use of Sweep and Dihedral in Multistage Axial Flow Compressor Blading: Part I — University Research and Methods Development
Authors: Gallimore Simon J. , Bolger John J. , Cumpsty Nicholas A. , Taylor Mark J. , Wright Peter I. , Place James M. M.
Published: February 2009

This paper describes the introduction of 3D blade designs into the core compressors for the Rolls-Royce Trent engine with particular emphasis on the use of sweep and dihedral in the rotor designs. It follows the development of the basic ideas in a university research project, through multistage low-speed model testing, to the application to high pressure engine compressors. An essential element of the project was the use of multistage CFD and some of the development of the method to allow the designs to take place is also discussed. The first part of the paper concentrates on the university-based research and the methods development. The second part describes additional low-speed multistage design and testing and the high-speed engine compressor design and test.
Unshrouded Rotor Tip Clearance Effects in Expander Cycle Turbines
Authors: Helmers Lennard , Klingmann Jens
Published: February 2009

Steady flow in axial one-stage turbines is assessed numerically and experimentally. The simulations are performed on coarse meshes using a standard numerical approach (3D, steady state, kε-turbulence model, wall function at solid boundaries). In order to allow for conclusions drawn from these rapid numerical studies, the approach was compared with an explicit LDA (Laser Doppler anemometry) mapping of the velocity field downstream the rotor on a representative turbine stage. A two-component LDA system allowed for measurements of axial and tangential velocity components at varying depth (radius) in the flow channel, Measurements thus correspond to a full plane at constant axial position in the rotating frame of reference of the rotor. Comparison between LDA velocity mapping and CFD results shows good agreement. A series of subsequent simulations is thus used to judge the impact of varied blade/stage design parameters. Two turbine layouts are defined for identical operating conditions and shaft power. The flow in the unshrouded rotor blade row is analyzed for the influence of varying tip clearance size and the dependency on stage velocity triangles. – Known correlations for tip clearance losses (typically used in mean line predictions) are used, though the blade row geometry considered is beyond the limits the correlations are intended for. The absolute loss level found in CFD simulations differs significantly from what is expected when using loss correlations. Still the variation with tip gap size is predicted well by some of the investigated models. As dependency of tip clearance losses on stage velocity triangles is considered, none of the tested correlations gives results consistent with the numerical simulations. The use of standard correlations ‘beyond the limits’ is thus considered to introduce high uncertainty. Due to the good consistency between LDA and numerical results, the conclusions are considered to be valid for stage designs similar to the ones analyzed.
The Effects of Wake-Passing Unsteadiness Over a Highly-Loaded Compressor-Like Flat Plate
Authors: Ottavy Xavier , Vilmin Stephane , Opoka Maciek , Hodson Howard , Gallimore Simon
Published: February 2009

The present study is concerned with wake-induced unsteady effects in axial-compressor blade rows. The goal is to exploit these effects in order to design high-lift blades without increasing the profile loss, as has been achieved for low-pressure turbine blades. In the first part of this paper, the experimental means and the computational fluid dynamics tools are described. The rig features a flat plate that can be subjected to different velocity distributions representative of the suction side of a real compressor blade. Cylindrical bars mounted on a moving system simulate the incoming wakes from the upstream blade row in the compressor. Results are presented for steady flow and for unsteady compressor-like conditions. In all cases, the separation bubble of the steady flow is suppressed by the turbulence that is induced in the boundary layer by the wakes at approximately 10% of the suction side. Its reappearance is then delayed by a region of stable laminar-like flow and low loss, the so-called calming effect that follows the wake-induced patch. The paper describes these phenomena for an example of configuration. It is then shown that it should be possible to increase the lift by 35% while keeping the same level of loss as the initial conventional pressure distribution of the study.
Effect of Upstream Unsteady Flow Conditions on Rotor Tip Leakage Flow
Authors: Sirakov Borislav T. , Tan Choon S.
Published: February 2009

A study has been conducted, using unsteady three-dimensional Reynolds-averaged Navier-Stokes simulations to determine the impact on rotor performance of the interaction between the stator wakes and rotor tip clearance flow. The key effects of the interaction are: (1) a decrease in loss and blockage associated with tip clearance flow; (2) an increase in passage static pressure rise. Performance benefit is seen in the whole operability range of interest, from near design to high loading. The benefit is modest near design and increases with loading. Significant beneficial changes occur when the phenomenon of tip clearance flow double-leakage is present. Double-leakage occurs when the tip clearance flow passes through the tip gap of the neighboring blade. Double-leakage typically takes place at high loading but can be present at design condition, as well. A benefit due to unsteady interaction is also observed in the operability range of the rotor. A new generic causal mechanism is proposed to explain the observed changes in performance. It identifies the interaction between the tip clearance flow and the pressure pulses, induced on the rotor blade pressure surface by the upstream wakes, as the cause for the observed effects. The direct effect of the interaction is a decrease in the time-average double-leakage flow through the tip clearance gap so that the stream-wise defect of the exiting tip flow is lower with respect to the main flow. A lower defect leads to a decrease in loss and blockage generation and hence an enhanced performance compared to that in the steady situation. The performance benefits increase monotonically with loading and scale linearly with upstream wake velocity defect.
Experimental Investigation of Unsteady Rotor Tip Flows in a High Speed Compressor Throttled to Stall
Authors: Lin Feng , Chen Jingyi , Li Meilin
Published: February 2009

This paper is one of the efforts where the classical passive controls of compressor instability, such as casing treatment, high pressure bleeding, steady jet injection, and so on, are given a fresh look in the context of unsteady flow and system dynamics. Understanding the underlying mechanism that these passive control schemes use to improve the stability will help engineers design compressors that are robust to external disturbances. In this paper, the unsteady tip flows in a high speed, single-stage, and transonic axial compressor are experimentally investigated. The pressure signals obtained from the sensors located on the casing of the rotor are studied with a one-dimensional, continuous wavelet transform. Practical issues are discussed so that one can decode the information in the wave spectrograms correctly. The characteristics of wavelet transform of unsteady traveling signals are studied. Using this wavelet tool, it is found that disturbances in tip flows exist over a thousand rotor revolutions before the onset of stall. They are characterized by the interconnected frequency/scale components in wavelet spectrograms. The time instants of their appearances can also be identified. However, they do not directly lead to stall because the development of such disturbances is intermittent. The link that relates such tip flow disturbances to stall is missing, or more precisely, casing measurement alone is not sufficient for detecting the true cause of stall.
A Fundamental Model of Mistuning for a Single Family of Modes
Authors: Feiner D. M. , Griffin J. H.
Published: February 2009

A new reduced order model of mistuned bladed disk vibration is presented. This new approach is shown to accurately represent the response of real turbine geometries when only a single family of modes is excited. Yet its mathematical form is even simpler than that of a mass-spring model. Because it requires only minimal input data, this model is much easier to use than previous reduced order methods. Furthermore, its simplicity allows the fundamental parameters that control mistuning to be readily identified.
Influencing the Secondary Losses in Compressor Cascades by a Leading Edge Bulb Modification at the Endwall
Authors: Mu¨ller R. , Sauer H. , Vogeler K. , Hoeger M.
Published: February 2009

Recent investigations have shown a significant reduction of secondary losses in turbine cascades using a modification of the blade at the endwall, a so called bulb. This paper deals with the same objective but is focussed on experimental and numerical work in compressor cascades. The cascades are modified near the endwall with a similar bulb as the earlier turbine cascades. The investigations have been carried out on a modified profile hub section of the Dresden Low Speed Research Compressor (LSRC) rotor blade, a compressor profile with a nominal turning of 18 degree. A datum configuration and a bulb configuration were tested in the Dresden Low Speed Cascade Wind Tunnel. An intensified suction side branch of the horse shoe vortex by a bulb was expected counterrotating to the passage vortex with an influence on its propagation. The interaction of the passage vortex and the boundary layer on the blade suction side is influenced. The superposition of both is decreased and the losses developing by this effect are significantly lower. The cases show a reduction in losses of 0.5–1.5% as a function of the blade turning. This equals a reduction of the isolated secondary losses by 15–25% with respect to the reference profile. It supports the physical understanding of the role of the horse shoe vortex in the loss production due to the passage vortex in compressor cascades. Detailed results of total pressure measurements are presented for both cascades.
Robust Optimal Positioning of Strain Gauges on Blades
Authors: Mignolet Marc P. , Choi Byeong-Keun
Published: February 2009

This paper focuses on the formulation and validation of an automatic strategy for the selection of the locations and directions of strain gauges to capture at best the modal response of a blade in a series of modes. These locations and directions are selected to render the strain measurements as robust as possible with respect to random mispositioning of the gauges and gauge failures. The approach relies on the evaluation of the signal-to-noise ratios of the gauge measurements from finite element strain data and includes the effects of gauge size. A genetic algorithm is used to find the strain gauge locations-directions that lead to the largest possible value of the smallest modal strain signal-to-noise ratio, in the absence of gauge failure, or of its expected value when gauge failure is possible. A fan blade is used to exemplify the applicability of the proposed methodology and to demonstrate the effects of the essential parameters of the problem, i.e. the mispositioning level, the probability of gauge failure, and the number of gauges.
Progress in SiC/SiC Ceramic Composite Development for Gas Turbine Hot-Section Components Under NASA EPM and UEET Programs
Authors: DiCarlo James A. , Yun Hee Mann , Morscher Gregory N. , Bhatt Ramakrishna T.
Published: February 2009

The successful application of ceramic matrix composites as hot-section components in advanced gas turbine engines will require the development of constituent materials and processes that can provide the material systems with the key thermostructural properties required for long-term component service. Much initial progress in identifying these materials and processes was made under the former NASA Enabling Propulsion Materials Program using stoichiometric Sylramic™ silicon-carbide (SiC) fibers, 2D-woven fiber architectures, chemically vapor-infiltrated (CVI) BN fiber coatings (interphases), and SiC-based matrices containing CVI SiC interphase over-coatings, slurry-infiltrated SiC particulate, and melt-infiltrated (MI) silicon. The objective of this paper is to discuss the property benefits of this SiC/SiC composite system for high-temperature engine components and to elaborate on further progress in SiC/SiC development made under the new NASA Ultra Efficient Engine Technology Program. This progress stems from the recent development of advanced constituent materials and manufacturing processes, including specific treatments at NASA that improve the creep, rupture, and environmental resistance of the Sylramic fiber as well as the thermal conductivity and creep resistance of the CVI SiC over-coatings. Also discussed are recent observations concerning the detrimental effects of inadvertent carbon in the fiber-BN interfacial region and the beneficial effects of certain 2D-architectures for thin-walled SiC/SiC panels.
Influence of Inlet Guide Vane Control on Combined Cycle Power Plant Transients
Authors: Domachovski Zygfryd , Dzida Merek
Published: February 2009

The gas turbine efficiency drops quickly at part load as it is very dependant on turbine firing temperature. Therefore in combined cycle power plants the inlet guide vane is adjusted to maintain the high combustion chamber exhaust temperature. Simulations on influence of the inlet guide vane position control on combined cycle power plant transients have been carried out.
Measurement and Analysis of Ingestion Through a Turbine Rim Seal
Authors: Gentilhomme O. , Hills N. J. , Turner A. B. , Chew J. W.
Published: February 2009

Experimental measurements from a new single stage turbine are presented. The turbine has 26 vanes and 59 rotating blades with a design point stage expansion ratio of 2.5 and vane exit Mach number of 0.96. A variable sealing flow is supplied to the disc cavity upstream of the rotor and then enters the annulus through a simple axial clearance seal situated on the hub between the stator and rotor. Measurements at the annulus hub wall just downstream of the vanes show the degree of circumferential pressure variation. Further pressure measurements in the disc cavity indicate the strength of the swirling flow in the cavity, and show the effects of mainstream gas ingestion at low sealing flows. Ingestion is further quantified through seeding of the sealing air with nitrous oxide or carbon dioxide and measurement of gas concentrations in the cavity. Interpretation of the measurements is aided by steady and unsteady computational fluid dynamics solutions, and comparison with an elementary model of ingestion.
Component Tests With a Model V84.3A Gas Turbine in the Siemens Test Facility in Berlin
Authors: Lechner Christof , Mertens Bernward , Warnack Dieter , Weltersbach Dirk , Ho¨nen Herwart
Published: February 2009

In its Gas Turbine Development and Manufacturing Center in Berlin Siemens runs a test bed for gas turbine prototypes. Since the end of 1998, the new model V84.3A gas turbine has been undergoing tests at this facility. One focus of last year’s tests was on flow field measurements with pneumatic probes in the exit flow duct of the turbine at various load levels to characterize the flow in the diffuser and provide a data base. Another item was the further investigation of the compressor surge margin and the validation of a newly-developed on-line surge prediction system.
Versatile Heat Source for Nuclear Gas Turbine and Hydrogen Production Facility
Authors: McDonald Colin F.
Published: February 2009

Recent media articles about nuclear power renaissance are encouraging, but this controversial topic is far from being embraced by major industrial powers. The fact is, that within the next two to three decades or so most of the first generation US nuclear power plants, currently producing about 20 percent of the nation’s electrical power, will be near the end of their design lives. In addition to providing needed power, a major argument put forward for the introduction of next generation smaller and safer nuclear plants relates to the growing concern about greenhouse gas emission and global warming. However, overcoming public and institutional resistance to nuclear power remains a formidable endeavor, and in reality the introduction of new plants in sufficient numbers to significantly impact the market will not be realized for several decades. Clearly vision is needed to define the requirements for new nuclear plants that will meet the needs of consumers by say the middle of the 21st century. Market forces will mandate changes in the energy supply sector, and to be in concert with environmental concerns new nuclear plants must have operational flexibility. In addition to economical electrical power, energy needs in the future could include hydrogen production in slgnificant quantity (for fuel cells in the transportation and power sectors) and fresh water by desalination for urban, industrial and agricultural users. The High Temperature Reactor (HTR) has the capability to meet these projected needs. With an established technology base, and successful plant operation in Germany, the helium cooled pebble bed reactor (PBR) must be regarded as a leading second generation nuclear plant. Operational versatility by virtue of its high temperature capability is assured, and high availability can be realized with its on-line refueling approach. While the multipurpose HTR may be several decades away from playing a significant rote in the commercial market place, this paper emphasizes the need for technical planning today to establish a nuclear heat source adaptable to both a high efficiency helium timed cycle gas turbine and large scale hydrogen production facilities, thus extending the role of nuclear power beyond just the supply of electrical power.
Numerical Simulation of Film Cooling on the Tip of a Gas Turbine Blade
Authors: Acharya Sumanta , Yang Huitao , Ekkad Srinath V. , Prakash Chander , Bunker Ron
Published: February 2009

Numerical simulations of flow and heat transfer are presented for a GE-E3 turbine blade with a film-cooled tip. Results are presented for both a flat tip and a squealer tip. Straight-through coolant holes are considered, and the calculation domain includes the flow development in the coolant delivery tubes. Results are presented with three different tip gaps representing 1%, 1.5% and 2.5% of blade span, a blowing ratio (ratio of coolant-jet-exit velocity to average passage flow velocity) of 1, and an inlet turbulence intensity of 6.1%. On a flat tip, film coolant injection is shown to lower the local pressure ratio and alters the nature of the leakage vortex. High film cooling effectiveness and low heat transfer coefficients are obtained along the coolant trajectory; these values increase slightly with increasing tip clearances. For a squealer tip, the flow inside the squealer cavity exhibits streamwise directed flow, which alters the trajectory of the coolant jets and reduces their effectiveness.
An Investigation on Turbine Tip and Shroud Heat Transfer
Authors: Chana Kam S. , Jones Terry V.
Published: February 2009

Detailed experimental investigations have been performed to measure the heat transfer and static pressure distributions on the rotor tip and rotor casing of a gas turbine stage with a shroud-less rotor blade. The turbine stage was a modern high pressure Rolls-Royce aero-engine design with stage pressure ratio of 3.2 and nozzle guide vane (ngv) Reynolds number of 2.54E6. Measurements have been taken with and without inlet temperature distortion to the stage. The measurements were taken in the QinetiQ Isentropic Light Piston Facility and aerodynamic and heat transfer measurements are presented from the rotor tip and casing region. A simple two-dimensional model is presented to estimate the heat transfer rate to the rotor tip and casing region as a function of Reynolds number along the gap.