bluuebunny/crossref_metadata_2025 huggingface dataset:
Spray and Emission Characteristics Near Lean Blow Out in a Counter-Swirl Stabilized Gas Turbine Combustor
Authors: Colby Jonathan A. , Menon Suresh , Jagoda Jechiel
Published: September 2008

An experimental study of a single, swirl cup burner is carried out to improve understanding of the lean reacting flow field near idle conditions for an annular spray combustor. The counter-swirler is mounted horizontally in a trapezoidal cross-section combustor with quartz plate walls. Liquid fuel, Jet-A, is initially atomized using a simplex nozzle, and then a designed re-atomization occurs from the swirler hardware. Measurements of non-reacting and reacting gas phase velocities enable the direct comparison of critical flow features at various power settings. Droplet diameter and exhaust composition measurements confirm that the initial droplet size is a key factor in emission levels. Smaller droplets in the spray periphery tend to evaporate and burn premixed, while larger droplets in the spray core convect downstream and burn with a sheath-type, non-premixed flame. The presence of small fuel droplets in the spray may ensure more complete combustion and improve combustor stability at lean, low power settings.
Components Map Generation of Gas Turbine Engine Using Genetic Algorithms and Engine Performance Deck Data
Authors: Kong Changduk , Ki Jayoung , Lee Changho
Published: September 2008

In order to estimate the gas turbine engine performance precisely, the component maps containing their own performance characteristics should be needed. Because the components map is an engine manufacturer’s propriety obtained from many experimental tests with high cost, they are not provided to the customer generally. Some scaling methods for gas turbine component maps using experimental data or data partially given by engine manufacturers had been proposed in previous study. Among them the map generation method using experimental data and genetic algorithms (Kong et al., 2004) had showed a possibility composing the component maps from some random test data. However not only this method needs more experimental data to obtain the more realistic component maps but also it requires some more calculation time to treat the additional random test data by component map generation program. Moreover some unnecessary test data may introduce to generate inaccuracy in component maps. And the map generation method called as the system identification method using partially given data from engine manufacturer (Kong et al., 2003) can improve the traditional scaling methods by multiplying the scaling factors at design point to off-design point data of the original performance maps, but some reference map data at off-design points should be needed. In this study a component map generation method which may identify component map conversely from some calculation results of a performance deck provided by engine manufacturer using the Genetic Algorithms was newly proposed to overcome the previous difficulties. As a demonstration example for this study, the PW206C turbo shaft engine for the tilt rotor type Smart UAV (Unmanned Aerial Vehicle) which has been developed by KARI (Korea Aerospace Research Institute) was used. In order to verify the proposed method, steady-state performance analysis results using the newly generated component maps were compared with them performed by EEPP (Estimated Engine Performance Program) deck provided by engine manufacturer. And also the performance results using the identified maps were compared with them using the traditional scaling method. In this investigation, it was found that the newly proposed map generation method would be more effective than the traditional scaling method and the methods explained at the above.
Multi-Functional Energy System (MES) With Multi Fossil Fuels and Multi Products
Authors: Jin Hongguang , Han Wei , Gao Lin
Published: September 2008

A new kind of multi functional energy system (MES) with multi fossil fuels and multi products is proposed in this paper. This new system consumes coal and natural gas as fuel simultaneously, and co-generates methanol and power. Coal and natural gas are utilized synthetically based on the method of dual-fuel reforming, which integrates the methane/steam reforming and the combustion of coal. During the dual-fuel reforming the coal is indirectly transformed into clean syngas only by being burnt without pure oxygen. The new system combines the process of chemical and power generation, along with integration of thermal energy and material. In this manner, the energy including both chemical energy of fuel and thermal energy can be used more effectively from the view point of the operation of the whole system. As a result, the total exergy efficiency of this new system was about 60–66%. Compared with the conventional systems, the new system provides an energy savings of about 8–14%. The results obtained here indicate that this new system may provide a new way to utilize coal and natural gas more efficiently and economically.
Low Fuel-NOx Combustion of Synthetic LCV Gas
Authors: Adouane Belkacem , Witteveen Guus , de Jong Wiebren , van Buijtenen Jos P.
Published: September 2008

Fuel NOx is one of the main issues related to the combustion of biomass derived Low Calorific Value (LCV) Gas. The high NOx emissions accompanying the combustion of that fuel in gas turbines or gas engines are compromising the CO2 neutral character of biomass and are a barrier towards the introduction of this green energy source in the market. The reduction of NOx emissions has been one of the main preoccupations of researchers in the LCV gas combustion field. Although, much has been achieved for thermal NOx which is caused mainly by the conversion of the nitrogen of the air in high temperature regions, less work has been devoted to the reduction of fuel NOx, which has as a main source the fuel bound nitrogen FBN, namely ammonia in case of biomass. Reducing the conversion of the FBN to NOx has been the main issue in recent research work. However, fuel NOx could be reduced significantly applying methods; like washing the gas in a scrubber prior its entrance to the combustor, and SNCR or SCR methods applied at the exhaust. But those solutions stay very expensive in terms of polluted waste water and catalyst cost. In this paper, the approach is to reduce the conversion of FBN to NOx inside a newly designed combustor. The idea is to optimize the combustion process ending up with the lowest possible conversion of FBN to NOx. The LCV gas used in the experiments described in this paper is made by mixing CO, CO2, H2, natural gas and N2 with proportions comparable to those of the real LCV gas. This gas is then doped with NH3 to simulate the FBN. In this paper the conversion ratio of FBN to NOx versus the FBN concentration is presented. Furthermore, the system is investigated in terms of the effect of CH4 concentration on the conversion of FBN to NOx. And measurements along the combustor axis were performed with a traversing probe where temperature and important emissions along the axis were measured. In all the experiments described in the paper, The LCV gas has an HHV (High Calorific Value) ranging from 4 to 7Mj/nm3. The newly designed combustor contains an embedded inner cylinder. In these experiments presented are without that embedded cylinder. The purpose of the current experiments is to be compared to the later experiments with the insert in order to define clearly the effect of the inner cylinder. Furthermore, this arrangement, i.e. without the insert, gave us the opportunity to traverse the combustor by a probe and to measure temperature and species profiles, which is of a great importance in defining the key parameter controlling the conversion of NH3 to NOx.
Novel Ceramic Abradable Coatings With Enhanced Performance
Authors: Sporer Dieter R. , Taeck Ulrike , Dorfman Mitchell R. , Nicoll Andrew R. , Giannozzi Massimo , Giovannetti Iacopo
Published: September 2008

Abradable coatings are employed in modern gas turbine engines to minimize clearance and reduce over-tip leakage by allowing blade tips to cut into the coating. While such clearance control coatings have been used in the compressor modules of jet engines and stationary gas turbines for many years, their use in the High Pressure (HP) section of turbine modules is relatively new. Because of the high temperatures encountered there, ceramic materials must be used to provide a durable seal. In this paper the performance of two novel ceramic abradable seal coatings is reviewed and compared to a baseline system. Emphasis is placed on the resistance to thermal shock and erosion. The abradability of coatings by hard tipped blades is reviewed using a wear map consisting of five distinctly different rub test conditions. Among the coatings considered, an APS sprayed dysprosia stabilized zirconia ceramic abradable offers a potentially superior combination of thermal shock resistance, abradability and erosion resistance for high temperature turbine seal applications.
Heat Transfer in an Airfoil Trailing Edge Configuration With Shaped Pedestals Mounted Internal Cooling Channel and Pressure Side Cutback
Authors: Chen Shuping P. , Li Peiwen W. , Chyu Minking K. , Cunha Frank J. , Abdel-Messeh William
Published: September 2008

Described in this paper is an experimental study of heat transfer over a trailing edge configuration preceded with an internal cooling channel of pedestal array. The pedestal array consists of both circular pedestals and oblong shaped blocks. Downstream to the pedestal array, the trailing edge features pressure side cutback partitioned by the oblong shaped blocks. The local heat transfer coefficient over the entire wetted surface in the internal cooling chamber has been determined by using a “hybrid” measurement technique based on transient liquid crystal imaging. The hybrid technique employs the transient conduction model in a semi-infinite solid for resolving the heat transfer coefficient on the endwall surface uncovered by the pedestals. The heat transfer coefficient over a pedestal can be resolved by the lumped capacitance method with an assumption of low Biot number. The overall heat transfer for both the pedestals and endwalls combined shows a significant enhancement compared to the case with thermally developed smooth channel. Near the downstream most section of the suction side, the land, due to pressure side cutback, is exposed to the stream mixed with hot gas and discharged coolant. Both the adiabatic effectiveness and heat transfer coefficient on the land section are characterized by using the transient liquid crystal technique.
The Influence of Heat Transfer Effects on Turbine Performance Characteristics
Authors: Stamatis A. G. , Mathioudakis K.
Published: September 2008

A method allowing the evaluation of the effects related to heat transfer to the turbine blades on its performance characteristics is presented. The effects investigated are the change of passage dimensions, resulting from heat transfer and the change in flow field, exhibited mainly as a different boundary layer development. Change of hot gas temperature combined with cooling air temperature and possibly flow rate, result in a change of the temperature of the blade material, leading to dimension changes, because of the thermal expansion (dilatation). The changes in dimensions have a direct effect on turbine performance. An immediate consequence is a modification of the mass flow characteristic, due to a change of the throat area. Heat transfer also influences the properties of the gas flowing through the passage and in particular the characteristics of the boundary layers developing on the nozzle vanes and hub, tip endwals. Change of the thickness of this layer results in a change of blockage through the passage, a fact that influences directly the turbine flow function. The influence of both effects on turbine performance is studied. The study is performance oriented, aiming to the derivation of simplified models, which can be introduced in engine cycle decks.
A PIV Study of a Plasma Discharge Flow-Control Actuator on a Flat Plate in an Aggressive Pressure Induced Separation
Authors: Boxx I. G. , Newcamp J. M. , Franke M. E. , Woods N. M. , Rivir R. B.
Published: September 2008

An experimental study was performed to examine the effect of a dielectric barrier discharge plasma flow control actuator. The actuator was applied to a flat plate boundary layer in a pressure distribution approximating that of the suction side of an aft-loaded low-pressure turbine blade. Particle image velocimetry was used to obtain two-dimensional velocity field data on four boundary layers with velocity profiles that included fully attached laminar, turbulent, nominally separated and high-separated. Values of Rec ranged from 4500 to 75,000. For the separated boundary-layers the actuator was located downstream of the separation point. Four E-fields were characterized for each case. The actuator was able to induce boundary layer reattachment even when located downstream of the initial separation point. The length scale over which this re-attachment occurs was strongly dependent upon the applied E-field. The actuators also caused significant reduction in the overall boundary layer thickness as a result of the modification of the near-wall static pressure distribution.
Computational Study of a Midpassage Gap and Upstream Slot on Vane Endwall Film-Cooling
Authors: Hada Satoshi , Thole Karen A.
Published: September 2008

Currently, turbines are being designed to operate with increasing inlet temperatures to improve the engine’s performance. To reduce NOx combustion, combustors are being designed to provide flat pattern factors. For these reasons, the endwall of the first stage vane is under severe heat transfer conditions. Film-cooling is one of the most effective cooling methods for the endwall of the vane. This paper presents results from a computational study of a film-cooled endwall. The endwall design considers both an upstream slot and a mid-passage slot, whereby the slot considered is both aligned and misaligned with respect to the endwall. Results indicate reasonable agreement between computational predictions and experimental measurements of adiabatic effectiveness levels along the vane endwall. The results of this study show the mid-passage slot has a large effect on the endwall film coverage. In addition, the relative height of the upstream slot to the downstream endwall is important to consider for improving the cooling benefit from the leakage flow between the combustor and turbine.
Connection of Thermal and Emissions- Performance of GT-Plants
Authors: von Rappard Axel W. , Andersen Helmer
Published: September 2008

The new issue of the PTC22 performance test code explains the evaluation of power and heat rate, as well the determination of the exhaust gas mass flow and its composition. The verification of emission requirements is normally tested independently from the thermal performance test and the actual EPA methods refer normally to an extensive determination of the exhaust gas flow, by measuring the velocity profile in the stack or the exhaust gas system of the gas turbine. This paper explains an easier way of determining the exhaust gas volume- or mass flow that is used as reference for all emission data. Additionally it shows that the emission measurement can easily be used as a verification of the exhaust gas mass flow determined in the thermal performance test. The basis for both tests is, however, an accurate fuel flow measurement. Since this measurement is also used for the heat rate or thermal efficiency determination it can certainly be used for the verification of the emissions performance. An uncertainty analysis has been added as well. The authors try to explain the procedure in a way the performance engineers on site can understand.
Investigation of Gas Turbine Parameters on Repowering of Existing Steam Power Plants as Fully Fired Combined Cycle
Authors: Sarabchi K. , Nayyeri V.
Published: September 2008

Most of investment in power generation industry tends to combined gas and steam turbine power plants due to thermodynamic and economic reason. Beside this tendency repowering of existing power plants is an attractive option for upgrading and life extension of existing power plants. In fact repowering is usage of combined cycle advantages for increasing power output and efficiency in steam power plants. Several approaches are proposed for repowering regards to condition of existing power plants such as life period and condition of parts of that and most important off all boiler condition. One of this approaches which provide opportunity of existing boiler reusing is converting existing power plant to fully fired combined cycle by installing a gas turbine and integration of that with existing steam units boiler. The aim of this paper is investigation of condition and how to integration of gas turbine and boiler. Also by exerting the condition and limitation in integration, the effect of gas turbine parameters to power output and efficiency of after repowering have been investigated. Finally the best condition of gas turbine parameters with high power and efficiency will be introduced.
Flame-Out Detection for Gas Turbine Engines Based Upon Thermocouple Signal Analysis
Authors: Gardiner D. P. , Pucher G. , Allan W. D. , LaViolette M.
Published: September 2008

This paper describes an experimental study to examine the potential of using Exhaust Gas Temperature (EGT) thermocouples for prompt flame-out detection in gas turbine engines. The approach taken involved accelerating the response of a shielded, slow response thermocouple using electronic processing of the signal. Thus, the abrupt drop in temperature characteristic of a flame-out could be detected within a much shorter time period than would be possible through a conventional thermocouple temperature measurement method. This was intended to provide a robust alternative to existing optical flame-out sensors which have fast response but can be susceptible to false flame-out indications due to window sooting. A production EGT thermocouple with online electronic processing was compared with a production optical flame sensor from a GE F-404 and a laboratory photodiode sensing system. The devices were tested in a full scale GE J-85 combustion chamber sector rig with optical access. The results showed that the thermocouple flame sensor had a response time to flame-outs of less than 100 ms. This was much faster than a conventional thermocouple, but still an order of magnitude longer than the optical flame sensor. However, whereas the optical flame sensor could yield ambiguous results about the presence of flame under some conditions, the thermocouple flame sensor provided a clear indication of flame-out events for all the conditions that were tested.
Prediction of Time Until Failure for a Micro Turbine With Unspecified Faults
Authors: Davison Craig R. , Birk A. M.
Published: September 2008

The potential extensive use of micro turbines in distributed power generation will produce a requirement for maintenance scheduling. The wide variety of operating environments and loads will demand that simple hour counters be overly conservative. Additionally, more advanced techniques, such as producing databases of the engine history or metallography, would have expenditures that far outweigh the benefit for such low cost engines. The technique presented in this paper predicts the remaining life of the engine based on operating data since the last overhaul. The technique is independent of the component degrading and uses specific fuel consumption as the determinant of failure, but does not require the measurement of fuel flow or power. The prime advantages of this technique are the requirement for few additional sensors beyond those needed for engine control, and the ability to predict the time until failure without knowledge of the fault occurring or input from the engine user. The system utilizes an algorithm to determine the form of the trend the path to failure is taking and applies exponential smoothing, which is then extrapolated forward to the failure conditions. Since the prediction is based on the operating data since the last overhaul, it initially performs very poorly, but as the engine approaches failure it improves. Depending on the form of the trend, good predictions begin between 30% and 70% through the life of the engine. The system was tested with a computer model of a micro turbojet engine with five different faults ranging from blockage of inlet filters to turbine degradation. Both single and combined faults were tested with similar success. The engine model, including healthy baseline and degraded operation, was validated with an experimental program.
An Assessment Methodology for Data-Driven and Model-Based Techniques for Engine Health Monitoring
Authors: Butler Steven W. , Pattipati Krishna R. , Volponi Allan , Hull Jon , Rajamani Ravi , Siegel Jason
Published: September 2008

In this paper, we will discuss the performance, evaluation, and optimization of pattern recognition techniques for applications in system diagnostics. One reason for measuring performance of a diagnostic technique is to clearly quantify it. Another is to compare its performance with that of competing designs. We discuss traditional dichotomous performance measures as well as extensions of these methods to handle multiple classes. We describe a MATLAB toolbox that we have designed to aid developers in rapid testing and optimization. The tool allows the user to select test features, design tests, determine optimal decision thresholds and improve diagnostic performance. The toolbox is demonstrated using modeled engine data. For illustrative purposes, the performances of Partial Least Squares, Principle Component Analysis, Support Vector Machine, and Probabilistic Neural Network data-driven classifiers are compared to that of a model-based classifier developed for a particular engine using modeled data.
Studies on Wake-Induced Bypass Transition of Flat-Plate Boundary Layers Under Pressure Gradients and Free-Stream Turbulence
Authors: Funazaki Ken-Ichi , Koyabu Eitaro
Published: September 2008

This study investigates wake-induced bypass transition of a flat-plate boundary layer that experiences favorable and adverse pressure gradients. The effect of free-stream turbulence is also examined. This paper mainly focuses on how the pressure gradients affect the transitional behavior of the wake-disturbed boundary layer with and without the influence of free-stream turbulence. A wall-contouring of the test duct generates the flow acceleration and deceleration on the flat plate, emulating aft-loading or front-loading pressure distributions of actual turbine blades. A spoked-wheel type wake generator is used to produce wakes moving over the boundary layer. Detailed boundary layer measurements are performed by use of a hot-wire anemometer. In addition to velocity fluctuations, which clearly indicate transition process, intermittency factors are obtained and compared with the results given by a transition model. Noticeable differences in transitional behavior are observed between the cases with and without the enhanced free-stream turbulence. It is also confirmed that the wake width as well as the direction of the bar movement are influential factors to the bypass transition.
System Study on Partial Gasification Combined Cycle With CO2 Recovery
Authors: Xu Yujie , Jin Hongguang , Lin Rumou , Han Wei
Published: September 2008

A partial gasification combined cycle with CO2 recovery is proposed in this paper. Partial gasification adopts cascade conversion of the composition of coal. Active composition of coal is simply gasified, while inactive composition, that is char, is burnt in a boiler. Oxy-fuel combustion of syngas produces only CO2 and H2O, so the CO2 can be separated through cooling the working fluid. This decreases the amount of energy consumed to separate CO2 compared with conventional methods. The novel system integrates the above two key technologies, by injecting steam from a steam turbine into the combustion chamber of a gas turbine, to combine the Rankine cycle with the Brayton cycle. The thermal efficiency of this system will be higher based on the cascade utilization of energy level. Compared to the conventional IGCC, the compressor of the gas turbine, HRSG and gasifier are substituted for a pump, reheater and partial gasifier, so the system is simplified obviously. Furthermore, the novel system is investigated by means of EUD (Energy-Utilization Diagram) methodology and provides a simple analysis of their economic and environmental performance. As a result, the thermal efficiency of this system may be expected to be 46%, with recovery of 50% of CO2, which is 3–5% higher than that of an IGCC system. At the same time, the total investment cost of the new system is about 21.5% lower than that of an IGCC. The promising results obtained here with higher thermal efficiency, lower cost and less environmental impact provide an attractive option for clean coal utilization technology.
The Optimum Parameters of a HTGR Helium Turbine Cycle and Numerical Analyses of Helium Turbine Cascades
Authors: Zhou Jiahui , Zheng Qun , Li Yijin
Published: September 2008

Modular high temperature gas-cooled reactor (HTGR) coupled with helium turbine is considered as one of the leading candidates for future nuclear power plants. This paper analyzes the thermodynamic process of the precooled, intercooled and regenerated HTGR gas turbine cycle, presents the effects of various parameters on the efficiency, and derives an optimum pressure ratio. In addition, the turbine cascades performances of different working fluids, say helium and air, are numerically simulated with CFD software. Comparisons between the two cascades are made in this paper.
Time-Resolved Heat Transfer Measurements on the Tip Wall of a Ribbed Channel Using a Novel Heat Flux Sensor: Part II — Heat Transfer Results
Authors: Jenkins Sean , von Wolfersdorf Jens , Weigand Bernhard , Roediger Tim , Knauss Helmut , Kraemer Ewald
Published: September 2008

Measurements using a novel heat flux sensor were performed in an internal ribbed channel representing the internal cooling passages of a gas turbine blade. These measurements allowed for the characterization of heat transfer turbulence levels and unsteadiness not previously available for internal cooling channels. In the study of heat transfer, often the fluctuations can be equally as important as the mean values for understanding the heat loads in a system. In this study comparisons are made between the time-averaged values obtained using this sensor and detailed surface measurements using the transient thermal liquid crystal technique. The time-averaged heat flux sensor and transient TLC results showed very good agreement, validating both methods. Time-resolved measurements were also corroborated with hot film measurements at the wall at the location of the sensor to better clarify the influence of unsteadiness in the velocity field at the wall on fluctuations in the heat flux. These measurements resulted in turbulence intensities of the velocity and heat flux of about 20%. The velocity and heat flux integral length scales were about 60% and 35% of the channel width respectively, resulting in a turbulent Prandtl number of about 1.7 at the wall.
Multi-Objective Optimization and Performance Analysis of BCHP Systems Using Genetic Algorithms
Authors: Huang Jintao , Yue Chen , Feng Zhenping
Published: September 2008

The performance assessment criteria of the BCHP (Building Cooling Heating and Power) system include thermodynamic parameters (primary energy rate, exergy efficiency) and economic parameters (economic exergy rate, payback periods) and environmental factors (emission). These criteria are affected by many factors such as the performance of power equipment, unit initial cost, energy demand, primary and second energy price, annual interest rate, operation hours. The scheme with minimum primary energy rate may also have high equipment cost which leads to longer payback periods, so that it is impossible to find a solution that simultaneously satisfies all of them. A genetic algorithm is then chosen to carry out the search for the optimal solution in this paper. The set of optimal solutions lead to the minimum values of the primary energy rate at fixed payback periods, or to the lowest payback periods at fixed primary energy rate. The optimization results are obtained under various load conditions (yearly average energy demand, changeable thermal-power rate, cooling-power rate and typical monthly load demand). The optimal unit capacity choice and operational strategy are discussed which is very important in design and operation process.
On the Importance of Adaptive Control in Extraction/Condensing Turbines
Authors: Lampart Piotr , Puzyrewski Romuald
Published: September 2008

Adaptive control in low-pressure (LP) steam turbines is applicable to the conditions of steam extraction, leading to significant gains in flow efficiency and turbine power. This paper summarizes the importance of adaptive control, making a set of computations based on the model of adaptive stage with adjustable nozzle blades that can adapt the geometry of the blading system to the changing flow conditions. An increase of turbine efficiency and power coming from adaptive control is estimated for a group of two exit stages of an extraction/condensing turbine of power 60 MW. The calculations are made with the help of a computer code FlowER — a 3D solver of turbomachinery flows based on Reynolds-averaged Navier-Stokes (RANS) equations for perfect gas.
Improved Performance and Reduced Emission From Coal and Gas Fuelled GT-SOFC and GT-MCFC Plants: Some Studies
Authors: Ghosh S. , De S. , Saha S.
Published: September 2008

This paper presents conceptual models of some novel GT-SOFC and GT-MCFC plants for power and cogeneration operating on gasified coal or natural gas. Simulated performance of the modeled plants in terms of energy efficiency, emission reduction, fuel energy savings (for cogeneration) with respect to separate reference plants for power generation and utility heat production is presented and analyzed. Influences of variations in some design and operating parameters on the plant performance are also reported in the paper. A study with a coal gasification combined cycle plant using SOFC upstream of GT suggests that such plants have the potential of delivering power at an overall efficiency level exceeding 50%. A similar plant delivering both power and utility heat can potentially save about 30% of fuel with respect to separate plants for power and heat. For a conceptualized natural gas fuelled GT-MCFC CHP plant, an electrical efficiency of more than 40% and fuel energy saving exceeding, 30% are achievable. Using a CO2 separator placed at fuel cell exhaust, CO2 can be trapped in a closed cycle. CO2 emission reduction as high as 60% is achievable for such plants.
Increasing Adiabatic Film-Cooling Effectiveness by Using an Upstream Ramp
Authors: Na S. , Shih T. I.-P.
Published: September 2008

A new design concept is presented to increase the adiabatic effectiveness of film cooling jets without unduly increasing surface heat transfer and pressure loss. Instead of shaping the film-cooling hole at its downstream end as is done for shaped holes, this study proposes a geometry modification upstream of the film-cooling hole to modify the approaching boundary-layer flow and its interaction with the film-cooling jet. Computations, based on the ensemble-averaged Navier-Stokes equations closed by the realizable k-ε turbulence model, were used to examine the usefulness of making the surface just upstream of the film-cooling hole into a ramp with backward-facing step. The effects of the following parameters were investigated: angle of the ramp (8.5°, 10°, 14°), distance between the backward-facing step of the ramp and the film-cooling hole (0.5D, D), and blowing ratio (0.36, 0.49, 0.56, 0.98). Results obtained show that an upstream ramp with a backward-facing step can greatly increase film-cooling adiabatic effectiveness. The laterally averaged adiabatic effectiveness with ramp can be two or more times higher than without the ramp. Also, the ramp increases the surface area that each film-cooling jet protects. However, using the ramp does increase drag. The increase in surface heat transfer was found to be minimal.
Improvement of Heat Transfer Performance of Turbulence Promoter Ribs
Authors: Horiuchi Yasuhiro , Kizuka Nobuaki , Marushima Shinya
Published: September 2008

Numerical and experimental approaches were taken to improve the heat transfer performance of V-shaped staggered (VSG) ribs. At first, a numerical method using Large Eddy Simulations (LES) was employed to determine the effect of VSG rib-induced flow on the local heat transfer coefficient distributions. The results revealed that the secondary flows generated by the rib configuration carry cold coolant air from the passage core region to the rib-roughened wall, thus enhancing heat transfer. Conversely, behind each rib there is a recirculation zone that does not contribute to enhanced heat transfer. Based on said results, six types of the advanced V-shaped staggered (AVSG) rib configurations were proposed. The test apparatus employing a comparative method was used to measure the total heat transfer coefficient and pressure loss coefficient of the VSG and AVSG ribs. It was concluded that thermal performance of the most effective type was 25% higher than that of VSG.
A Stochastic Model for a Compressor Stability Measure
Authors: Dhingra Manuj , Neumeier Yedidia , Prasad J. V. R. , Breeze-Stringfellow Andrew , Shin Hyoun-Woo , Szucs Peter N.
Published: September 2008

A stability measure rooted in the unsteady characteristics of the flow field over the compressor rotor has been previously developed. The present work explores the relationship between the stochastic properties of this measure, called the correlation measure, and the compressor stability boundary. A stochastic model has been developed to gauge the impact of the correlation measure’s stochastic nature on its applicability to compressor stability management. The genesis of this model is in the fundamental properties of a specific stochastic process, one that is created by the threshold-crossings of a random process. The model validation utilizes data obtained on three different axial compressor facilities. These include a single stage low speed axial compressor, a four stage low speed research compressor and an advanced technology demonstrator high speed compressor. This paper presents details of the model development and validation, as well as, closed loop experimental results to demonstrate correlation measure’s usefulness in compressor stability management.
Response Time Optimisation of the Rankine Compression Gas Turbine (RCG)
Authors: Ouwerkerk H. , de Lange H. C.
Published: September 2008

The Rankine Compression Gas turbine (RCG) is a new type of combined cycle that delivers all power on one free power turbine. With its free power turbine the intended fields of application of the RCG are mechanical drives and ship propulsion. For the RCG to become successful in these fields of application a short response time from part-load to full-load is vital. Experiments with an experimental set-up at the Technische Universiteit Eindhoven showed that the response time would benefit from after-spray and supplementary firing. Therefore, these items were implemented in an overdrive controller that was designed to accelerate the RCG cycle more quickly. Simulations showed that the overdrive controller dramatically reduces the response time of the modeled RCG-cycle in a transient from 50% part-load to full-load from 20 minutes down to about 2 minutes. This is an impressive improvement of the response time and is believed to make the RCG suitable for mechanical drives and ship propulsion.
Interactions Between Propagating Wakes and Flow Instabilities in the Presence of a Laminar Separation Bubble
Authors: Gostelow J. P. , Thomas R. L.
Published: September 2008

Laminar separation was investigated experimentally on a flat plate under a strongly diffusing self-similar pressure distribution. This gave a long and thin laminar separation bubble. Boundary layer velocity traverses were performed at numerous longitudinal stations. Using a single hot wire a combination of individual traces, phase averaging and time averaging was used. To supplement this, an array of microphones was installed to give instantaneous contours of pressure perturbation and to investigate the time dependent flow features. Microphone data were consistent with the strong amplification, under the adverse pressure gradient, of instabilities predicted far upstream of the separation point. Driven at the Tollmien-Schlichting (T-S) frequency, these instabilities grew into turbulent spots developing in the shear layer of the separation bubble. Reattachment of the bubble was caused by transition of the separated shear layer. The waves were strongest in the later stages of transition. Once the coherence was lost, in a turbulent layer, the amplitude became diminished. Wake disturbances were injected into the flow and traced through the flow field. The wake interaction resulted in turbulent patches which penetrated to the wall. Following the patches was the calmed region, detectable as a region of reduced wave activity in the transition region following each turbulent strip. For a short time at the end of the calmed region the viscous instability waves continued to propagate for a considerable distance downstream, in concert with the calmed region, in an otherwise turbulent zone.
Passive Shroud Cooling Concepts for HP Turbines: CFD Based Design Approach
Authors: Janke E. , Haselbach F. , Whitney C. , Kanjirakkad V. , Thomas R. , Hodson H.
Published: September 2008

One option to improve the cycle efficiency of current state-of-the-art aero engines is to increase the turbine inlet temperature. Since this temperature is above the melting temperature for the alloys utilised in the turbine component already today, efficient cooling methods must be developed that consider both aerodynamic and aerothermal aspects of cooling. Here, the goal is to extract as little as possible secondary air from the main hot gas cycle for cooling and to use this coolant then aerodynamically and aerothermally as efficient as possible. The paper to be presented documents a CFD based design approach that lead to a new passive shroud cooling concept and the definition of its operational parameters. By using a simple one dimensional method [10] for predicting the aerodynamic losses resulting from such a cooling configuration in connection with 3d Navier-Stokes solvers (RANS) for predicting film cooling effectiveness contours on the rotor shroud surfaces, the new cooling configuration was developed. The concept was then tested and confirmed experimentally as documented in more detail in Part 2 of this paper. It is noted that only 70% of the coolant mass flow required for the current configuration was used for the new concept whereas the aerodynamic efficiency measured remained nearly constant. Improving upon existing passive shroud cooling systems where the coolant is injected directly into the labyrinth of the shroud, the new approach comprises cooling holes that inject the coolant upstream of the labyrinth and through the stator platform into the main passage flow. Here, it is important that the bulk of the coolant is placed below the dividing streamlines between main passage flow and labyrinth flow. Thereby, it can be achieved that the major part of the coolant indeed reaches the thermally loaded target surfaces on the shroud bottom at various axial gaps due to different operating points of the turbine. Besides the improved film-cooling effectiveness measured, the second important aspect of the new concept is the achievement of as small as possible additional aerodynamic losses due to coolant ejection into a high speed flow region. It will be shown that both goals can be achieved by the new concept. Furthermore, CFD results on film-cooling performance and aerodynamic losses will be shown and compared with experimental data.
Effects of Thermal Barrier Coatings on Approaches to Turbine Blade Cooling
Authors: Boyle R. J.
Published: September 2008

Reliance on Thermal Barrier Coatings (TBC) to reduce the amount of air used for turbine vane cooling is beneficial both from the standpoint of reduced NOx production, and as a means of improving cycle efficiency through improved component efficiency. It is shown that reducing vane cooling from 10% to 5% of mainstream air can lead to NOx reductions of nearly 25% while maintaining the same rotor, inlet temperature. An analysis is given which shows that, when a TBC is relied upon in the vane thermal design process, significantly less coolant is required using internal cooling alone compared to film cooling. This is especially true for small turbines where internal cooling without film cooling permits the surface boundary layer to remain laminar over a significant fraction of the vane surface.
Nacelle Design for Mixed Turbofan Engines
Authors: Tomita Jesui´no Takachi , Bringhenti Cleverson , Barbosa Joa˜o Roberto , de Jesus Antonio Batista
Published: September 2008

Nacelles are responsible for good engine performance and considerable percentage of total aircraft drag, thus fuel consumption. Energy conservation and cost of fuel, among others, require good nacelle design. CFD calculations of the flow around it are a major design tool to predict shock waves, internal boundary layer in the nacelle forebody, high velocity zones and wake. Commercially available software may be used to calculate and visualize the flow at the most critical parts of the nacelle, allowing design modifications aiming at optimizations. This paper overviews the literature on nacelles, the methodologies involved in the design. A case study is presented for a long duct nacelle design, using an axis-symmetric model. Performance characteristics at important operating conditions are also presented.
Droplet Trajectories and Collection on Fan Rotor at Off-Design Conditions
Authors: Das Kaushik , Hamed Awatef A. , Basu Debashis
Published: September 2008

A numerical investigation is conducted to study water droplet collection on a high bypass turbofan engine booster rotor under different rotational speeds. An Eulerian-Lagrangian approach is used in formulating the flow and droplet governing equations in the rotating reference frame. A one-way interaction model is used to model the effects of momentum and energy exchange effects with the flow on the droplets as they travel through the rotor. Results are presented for the computed flow field, droplet trajectories, water collection efficiency and droplet exit mass and temperature profiles at 60%, 70%, 80%, 90%, and 100% design rotational speeds. The highest collection is predicted near the tip at the pressure surfaces leading edge. It then drops considerably at 40%–60% of the booster rotor blade chord and remains low over the aft portion of the pressure side. In general, the rotor blade collection efficiency is strongly influenced by rotor speed and increases as the rotational speed decreases.
Enhancement of Impingement Cooling in a High Cross Flow Channel Using Shaped Impingement Cooling Holes
Authors: Chambers Andrew C. , Gillespie David R. H. , Ireland Peter T. , Mitchell Mark
Published: September 2008

Impingement systems are common place in many turbine cooling applications. Generally these systems consist of a target plate that is cooled by the impingement of multiple orthogonal jets. While it is possible to achieve high target surface heat transfer with this configuration, the associated pressure drop is generally high and the cooling efficiency low. Furthermore, especially in large impingement arrays, the build-up of cross flow from upstream jets can be significant and result in deflection of downstream impingement jets reducing the resultant heat transfer coefficient distribution. This paper presents a computational and experimental investigation into the use of shaped elliptical or elongated circular impingement holes designed to improve the penetration of the impinging jet across the coolant passage. This is of particular interest where there is significant cross flow. Literature review and computational investigations are used to determine the optimum aspect ratio of the impingement jet. The improved heat transfer performance of the modified design is then tested in an experimental rig with varying degrees of cross flow at engine representative conditions. In all cases a 16% increase in the Nusselt number on the impingement target surface in the downstream half of the cooling passage was achieved. Under the first 4 impingement holes Nusselt number enhancement of enhancement of 28–77% was achieved provided no additional cross flow was present in the passage. When appropriately aligned, a significant reduction in the stress concentration factor caused by the addition of a hole can be achieved using this design.
Internal Cooling Near Trailing Edge of a Gas Turbine Airfoil With Cooling Airflow Through Blockages With Holes
Authors: Lau S. C. , Cervantes J. , Han J. C. , Rudolph R. J.
Published: September 2008

Naphthalene sublimation experiments were conducted to study heat transfer for flow through blockages with holes in an internal cooling passage near the trailing edge of a gas turbine airfoil. The cooling passage was modeled as two rectangular channels whose heights decreased along the main flow direction. The air made a right-angled turn before passing through two blockages with staggered holes in each channel, and left the channel through an exit that was partially blocked by periodic lands with rounded leading edges. There were ten holes along each blockage and all of the holes had rounded edges. Local heat (mass) transfer was measured, and overall heat (mass) transfer results were obtained, on the exposed surfaces of one of the walls downstream of the two blockages, for Reynolds numbers (based on the hydraulic diameter of the channel at the upstream surface of the first blockage) between 5,000 and 36,000. The results showed that the blockages with the larger hole-to-channel cross-sectional area ratio in one of the two test sections enhanced the heat (mass) transfer downstream of the blockages more than the blockages with the smaller open area ratio in the second test section. For the geometric configurations and flow conditions studied, the average heat (mass) transfer was higher downstream of the second blockage than downstream of the first blockage. The configurations of the inlet channel and the exit slots considered in this study did not significantly affect the local heat (mass) transfer distributions or the average heat (mass) transfer downstream of the blockages.