bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Investigation of the Effect of Purge Flow on Film Cooling Effectiveness on a Rotating Turbine With Non-Axisymmetric Endwall Contouring
Authors: Rezasoltani M. , Schobeiri M. T. , Han J. C. 
Published: November 2013

The impact of the purge flow injection on aerodynamics and film cooling effectiveness of a three-stage high pressure turbine with non-axisymmetric endwall contouring has been experimentally investigated. As a continuation of the previously published work involving stator-rotor gap purge cooling, this study investigates film cooling effectiveness on the first stage rotor contoured platform due to a coolant gas injection. Film cooling effectiveness measurements are performed on the rotor blade platform using a pressure sensitive paint (PSP) technique. The present study examines, in particular, the film cooling effectiveness due to injection of coolant from the rotor cavity through the circumferential gap between the first stator followed by the first rotor. Efficiency and performance experiments were conducted with and without cooling injection to show (a) the impact of endwall contouring on the turbine efficiency and (b) the impact of film cooling injection in association with the endwall contouring.
The experimental investigation is carried out in a three-stage turbine facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL) at Texas A&M University. Its rotor includes non-axisymmetric endwall contouring on the first and second rotor row [1]. The turbine has two independent cooling loops. Film cooling effectiveness measurements are performed for three coolant-to-mainstream mass flow ratios of 0.5%, 1.0% and 1.5%. Film cooling data is also obtained for three rotational speeds, 3000 rpm (reference condition), 2550 rpm and 2400 rpm and compared with non-contoured endwall data.
Avoiding Compressor Surge During Emergency Shut-Down Hybrid Turbine Systems
Authors: Pezzini Paolo , Tucker David , Traverso Alberto 
Published: November 2013

A new emergency shutdown procedure for a direct-fired fuel cell turbine hybrid power system was evaluated using a hardware-based simulation of an integrated gasifier/fuel cell/turbine hybrid cycle (IGFC), implemented through the Hybrid Performance (Hyper) project at the National Energy Technology Laboratory, U.S. Department of Energy (NETL). The Hyper facility is designed to explore dynamic operation of hybrid systems and quantitatively characterize such transient behavior. It is possible to model, test and evaluate the effects of different parameters on the design and operation of a gasifier/fuel cell/gas turbine hybrid system and provide means of quantifying risk mitigation strategies.
An open-loop system analysis regarding the dynamic effect of bleed air, cold air by-pass and load bank is presented in order to evaluate the combination of these three main actuators during emergency shut-down. In the previous Hybrid control system architecture, catastrophic compressor failures were observed when the fuel and load bank were cut-off during emergency shut-down strategy. Improvements were achieved using a non-linear fuel valve ramp down when load bank was not operating. Experiments in load bank operation show compressor surge and stall after emergency shut-down activation. The difficulties in finding an optimal compressor and cathode mass flow for mitigation of surge and stall using these actuators are illustrated.
Comparison of the Accuracy of Time-Domain Measurement Methods for Combustor Damping
Authors: Wagner Michael , Jörg Christoph , Sattelmayer Thomas 
Published: November 2013

Combustors of modern gas turbines for power generation and mechanical drive are predominantly operated in premixed mode, which is sensitive to coupling between flame dynamics and combustor acoustics. In practice, combustor flames tend to drive instabilities at certain eigenfrequencies of the systems, according to the classical Rayleigh criterion. In order to guarantee combustor stability in the entire operation range of the engine it has to be avoided under all circumstances that the flame excites the system beyond its damping potential. One option to accomplish this is to provide sufficient damping capabilities of the combustor system so that the decay of acoustic energy inside the system always exceeds the excitation provided by the flame. Experimental methods for the determination of combustor damping rates therefore may become a valuable tool for combustor design in the future. In the past, methods with different accuracy, complexity and capabilities have been developed to gain experimental access to decay rates of the acoustic energy inside combustor systems.
In this study we compare accuracy and capabilities of three different time-domain methods that allow the determination of pressure decay rates from experimental dynamic pressure traces: A simple exponential fit to the measured dynamic pressure, a method based on the decay of acoustic energy and a newly developed statistical method are examined. In the first step, the methods are tested using artificially generated test signals. The simple signals decaying exponentially with the known rate α are of pure sinusoidal shape and have discrete frequencies. As practical dynamic pressure traces are in general corrupted with noise, in the second step of the analysis a certain amount of random noise is added to the test signal. The last step of the analysis involves realistic pressure signals obtained from a simple duct with throughflow. The results obtained from the different methods are compared with each other and differences regarding performance, accuracy, robustness as well as computational costs are presented.
Aerodynamic Design Optimization of Nacelle and Intake
Authors: Albert Moritz , Bestle Dieter 
Published: November 2013

Design of nacelle and intake for an aero engine is highly complex and always a compromise between contradicting design goals. The intake has to provide air for the engine with minimal pressure loss at all flight conditions like take-off, cruise, approach, or crosswind. Further the airflow has to be evenly distributed to allow satisfying operation of the fan, and the nacelle should produce as less drag as possible. Taking this into account, the ideal lip shape alternates between thin to minimize drag during cruise and thick contour to cover the requirements at off-design conditions.
To efficiently deal with these contradicting geometric design demands, a multi-objective optimization problem in 2D is defined. The major aim is to simultaneously minimize inner peak Mach number at off-design and outer peak Mach number at cruise conditions, i.e., two different flight conditions are taken into account which are evaluated in parallel. Three different parametric models are introduced to describe design changes, a first model, using superellipses and polynomials, a second one based on Class-Shape-Transformation, and a B-spline approach. To check the robustness of the design process, design of experiments for all three parameterization approaches have been performed. Based on these results proper design bounds are derived to ensure reliable CAD model generation, meshing and CFD analysis.
Optimization results from a multi-objective genetic algorithm demonstrate feasibility of the proposed approach. Compared to an existing design based on human experience, the designs found are better with respect to both objectives.
Numerical Study of Incidence Angles and Gap Heights in Turbine Cascades and Rotors on Tip Clearance Losses
Authors: Buske Clemens , Ullrich Wolfram C. , Roehle Ingo 
Published: November 2013

The design and optimization of turbines demands the use of fast low-fidelity tools. To obtain adequate results, loss correlations simplifying the complex turbine throughflow are implemented. Accounting for modern turbine designs and flow conditions, revisions of profile and secondary loss correlations were primarily focused upon, while improvements of the tip clearance loss correlations are difficult to achieve. Realistic engine-like conditions concerning variations of the tip clearance, blade loading and solidity are time- and cost-intensive to investigate.
This paper is focused on an extensive numerical study, intending to support experiments on tip clearance loss correlations. The losses of a high pressure axial turbine rotor are analyzed for different tip clearance gap heights and incidence angles at cruise condition. The results are contrasted with a cascade having comparable tip profile and gap heights. The cascade’s flow is comparable to the rotor, but with respect to experimental restrictions concerning inlet and outlet conditions.
Steady 3D calculations in the stationary and rotating frame were performed applying DLR’s turbomachinery CFD code TRACE using Menter’s SST k – ω turbulence model. The tip clearance loss coefficients were extracted from the flow field by post-processing data of an outlet plane and as massflow averaged global values. The findings are discussed referencing previous publications about the leakage flow system and tip clearance loss. Finally, a comparison to results from tip clearance loss correlations of Ainley-Mathieson and Dunham-Came is presented.
Cross Flow Effects on Endwall Heat Transfer in Film-Cooled Turbine Nozzle Guide Vanes
Authors: Reviol Rebecca , Franze Roman , Böhle Martin , Takeishi Kenichiro , Wiedermann Alexander 
Published: November 2013

Film cooling effects on endwalls in the stagnation point region are of special interest since the heat transfer is influenced drastically by secondary flows. Additionally, a complex vortex structure exists along the stagnation streamline which influences heat transfer on the endwall. The flow phenomenon is described and discussed in the open literature but it is still difficult to predict the heat transfer on the endwall and the turbine profile by CFD methods with sufficient accuracy.
In this paper it is examined how the flow field in the stagnation region should be simulated using CFD. The effect of meshes with various grid resolutions and turbulence models as k-ε-, k-ω-SST- and DES-turbulence models have been investigated. The CFD-data are compared with the experimental results obtained by Naphthalene Sublimation Method, Pressure Sensitive Paint, Laser Induced Fluorescence and Particle Image Velocimetry. Three cases, namely film cooling on a flat plate, the endwall flow near a symmetrical airfoil and the symmetrical airfoil with endwall film cooling, are examined in detail.
How to Upgrade Gas Turbines to Meet Customer Requirements and Be Fast to Market
Authors: Irmisch Stefan , Bauer Andreas , Ferber Jörgen , Kappis Wolfgang , Soumine Anton 
Published: November 2013

This paper summarizes the techniques and methods available today to allow for significant improvements of existing and previously upgraded Gas Turbine fleets, while keeping time to market and investment to the absolute minimum. This allows for flexibility to react to market changes and to extend the utilization of the customer’s assets. The successful application of these techniques is described using the example of the latest service upgrade of Alstom’s GT13E2 heavy duty gas turbine also showing first validation results.
In contrast to previous improvements, mostly focusing on an increase in power-output, this upgrade development followed a different strategy: As customers are demanding a reduction in Cost of Electricity, the focus this time was on increasing CC-efficiency and elongating service interval lengths. The design challenge has been to come up with an upgrade package, which limits the additional power-output while maximizing efficiency and lifetime at the same time. Limiting the additional power output is crucial to be retrofit-able into existing plants with a minimum in investment costs, as some plant components like Generators and Transformers, especially for previously upgraded units, may already be close to their capacity limits.
The paper describes in detail how the upgrade scope and design concept has been derived based on customer input. Among other measures, it is demonstrated how the consequent application of 3D design methods, the utilization of state-of the art airfoil profiling and clearance optimization in combination with an optimized thermodynamic cycle have been used to maximize the component and GT efficiencies. Furthermore it is shown how development time and risks have been minimized by a consequent application of a combined concurrent design & manufacturing approach and rapid prototyping methods for early design validation. Finally, short- and mid-term validation results after the first implementation and testing in spring 2012 are presented, confirming that the design targets have been met.
Investigation of the Turbulent Flame Speed for Natural Gas and Natural Gas/Hydrogen Mixtures at High Turbulence Levels and Volumetric Heat Release Rates
Authors: Zajadatz Martin , Zarzalis Nikolaos , Leuckel Wolfgang 
Published: November 2013

In gas turbine combustion application, there is a strong tendency towards high volumetric heat release rates without compromising ignition stability and the requirement of low emission concentrations of NOx, CO and unburned hydrocarbons. In order to meet these demands for industrial gas turbines the lean premixed combustion concept has been developed.
In the scope of this paper fundamental experimental work, which has been carried out in order to analyze the important topic of turbulence/chemistry interaction on a semi-technical scale, will be reported. The turbulent intensity and length scales have been varied by a generic burner system, which consists of four geometrically scaled burners. At atmospheric pressure conditions more than 700 Bunsen type flames in a Reynolds number range from 21000 to 128000 have been investigated. Gas/air mixture preheating has been included in the tests as a typical boundary condition for combustion in gas turbines. The natural gas was blended with 25 vol. % and 50 vol. % hydrogen in order to alter the kinetics of the fuel gas.
The influence of the aforementioned parameters on the turbulent flame speed were assessed and compared with existing correlations for the turbulent flame speed. Special emphasis has been taken on the influence of gas/air mixture preheating and kinetics.
Helicopter Mission Analysis for a Regenerated Turboshaft
Authors: Fakhre Ali , Pachidis Vassilios , Goulos Ioannis , Tashfeen Mahmood , Pilidis Pericles 
Published: November 2013

The aim of the study presented in this paper, is to compare helicopters employing simple cycle turboshaft engines, with helicopters employing novel regenerated turboshafts. Two existing helicopter configurations, a Twin Engine Light and a Twin Engine Medium are compared against regenerated configurations. The reference installed engines of both helicopters are notionally optimized by incorporating a heat exchanger, which enables heat transfer between the exhaust gas and the compressor delivery air to the combustion chamber. This process leads to a lower fuel input requirement as well as higher overall thermal efficiency compared to the reference simple cycle engine.
The benefits arising from the adoption of the heat exchanger for both configurations are firstly presented by conducting part-load performance analysis for each optimized engine against its reference simple cycle engine. The obtained results suggest substantial reduction in specific fuel consumption for a major part of the operating power range with respect to both helicopter configurations. The results also demonstrate that the heat exchanger effectiveness is a critical parameter in achieving further reductions in specific fuel consumption.
The study is further extended to investigate mission fuel burn saving limits for both helicopter configurations under the simulated part-load performance conditions by conducting a heat exchanger tradeoff study. The weight estimation correlation for the heat exchanger is adopted from the previously reported studies of similar fashion and is simulated accordingly for both helicopter configurations. A multi-disciplinary simulation tool with an integrated range of capabilities applicable to helicopter performance evaluation and mission analysis is adopted to simulate various types of missions, targeting wide range of helicopter operations. The results of the mission analysis suggest that the regenerated counterpart configurations are capable of achieving significant reductions in mission fuel burn. However, the level of gain from mission fuel burn savings is dependent on the selected helicopter mission profile, the recuperator design effectiveness as well as the overall evaluation criteria. The results also conclude that while the amount of benefit is dependent on various parameters, there is always an optimum “saving” region for each mission that justifies the need for regeneration.
Capacitive Film Thickness Measurements in a Ventless Aero-Engine Bearing Chamber: Influence of Operating Conditions and Offtake Design
Authors: Kurz Wolfram , Dullenkopf Klaus , Bauer Hans-Jörg 
Published: November 2013

The paper presents results from film thickness measurements in a bearing chamber test rig. The measurements were performed at different operating conditions and with two offtake designs. A discussion of the measurement technique using in-situ calibrated capacitive sensors shows good accuracy and repeatability.
The film thickness results are first compared to measurements with the same chamber in a vented configuration. The analysis of the measurements at various operating conditions shows a strong influence of the shaft speed, the chamber pressure, and the offtake design. In contrast to that, flow rate and scavenge ratio have only minor influence. Furthermore, the momentum flux of the core air flow is proposed as a suitable parameter with which the influence of shaft speed and pressure can be correlated to the film thickness distribution.
Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method
Authors: Martin Scott , Jemcov Aleksandar , de Ruijter Björn 
Published: November 2013

Here the premixed Conditional Moment Closure (CMC) method is used to model the recent PIV and Raman turbulent, enclosed reacting methane jet data from DLR Stuttgart [1]. The experimental data has a rectangular test section at atmospheric pressure and temperature with a single inlet jet. A jet velocity of 90 m/s is used with an adiabatic flame temperature of 2,064 K. Contours of major species, temperature and velocities along with velocity rms values are provided.
The conditional moment closure model has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes [2]. The simplified CMC model used here falls into the class of table lookup turbulent combustion models where the chemical kinetics are solved offline over a range of conditions and stored in a table that is accessed by the CFD code. Most table lookup models are based on the laminar 1-D flamelet equations, which assume the small scale turbulence does not affect the reaction rates, only the large scale turbulence has an effect on the reaction rates. The CMC model is derived from first principles to account for the effects of small scale turbulence on the reaction rates, as well as the effects of the large scale mixing, making it more versatile than other models. This is accomplished by conditioning the scalars with the reaction progress variable. By conditioning the scalars and accounting for the small scale mixing, the effects of turbulent fluctuations of the temperature on the reaction rates are more accurately modeled.
The scalar dissipation is used to account for the effects of the small scale mixing on the reaction rates. The original premixed CMC model used a constant value of scalar dissipation, here the scalar dissipation is conditioned by the reaction progress variable. The steady RANS 3-D version of the open source CFD code OpenFOAM is used. Velocity, temperature and species are compared to the experimental data. Once validated, this CFD turbulent combustion model will have great utility for designing lean premixed gas turbine combustors.
Effect of Film Cooling Arrangement on Impingement Heat Transfer on Turbine Blade Leading Edge
Authors: Yang Li , Kan Rui , Ren Jing , Jiang Hongde 
Published: November 2013

Impingement cooling plays an important role in gas turbine blade leading edge where proper heat transfer distribution is needed for extremely high and nonuniform thermal load.
A 2/3 cylinder leading edge model with 3 arrays of film cooling holes was investigated with 8 film cooling arrangements. The impingement parameters and the jet Reynolds number were kept the same for the 8 configurations. The transient liquid crystal (TLC) measurement was applied on heat transfer coefficient on the leading edge. A 3D numerical method with the SST k-ω model was verified by experimental data, which shows a heat transfer error less than 15%.
The film suction creates both local heat transfer enhancement and limit effect to wall jets. The hole position of film cooling holes significantly affects the shape of high heat transfer area and cooling of the intermediate area. The array angle of film cooling holes affects the spread of heat transfer laterally. The Nu in stagnation zone decreases with the increase of array angle of film cooling holes. Smaller pitch of film cooling holes helps decrease the size of fountaining flow and heat transfer valley. The Nu in stagnation zone increases with the decrease of pitch of film cooling holes.
The hole position of x0/P = 0.125 is recommended for the best cooling performance in the intermediate area. The configurations with θ = 13 or P/pf = 3 work best in this study.
Forced and Self-Excited Instabilities From Lean Premixed, Liquid-Fuelled Aeroengine Injectors at High Pressures and Temperatures
Authors: Hochgreb Simone , Dennis David , Ayranci Isil , Bainbridge William , Cant Stewart 
Published: November 2013

Measurements of unsteady pressure and chemiluminescence during flow forced operation of aeroengine lean direct injection fuel spray nozzles were made, with a goal to determine the response of the flame, subject to a range of air fuel ratios, fuel flow splits between pilot and mains injectors, and cooling flows. A rotating shutter installed at the downstream choked nozzle provided the excitation for forcing the mass flow rate between 100 to 600 Hz, at normalized intensities of 0.1 to 0.7 relative to the mean velocity at the injector. The experiments were performed at inlet conditions of 800 K and 5.7 bar.
Self-excitation created by the coupling between the flame and the combustor cavity was observed, in the form of a broad peak around 275 Hz. Numerical studies indicate that the peak is associated with an entropy spot (a region of non-uniform temperature) travelling from the flame to the choked nozzle, followed by the ensuing expansion wave towards the injector and amplification of the excitation. Investigation of previous studies suggests that similar phenomena may have been present in other studies at high pressure. The main impact of the self-excitation is the significant amplification of the velocity fluctuations from 0.1 of the mean velocity away from the self-excitation frequency to around 0.7 at the peak. The flame response, represented by the ratio of the fractional fluctuations in OH* chemiluminescence to the fractional velocity fluctuations at the injector, can be determined under conditions where the self-excitation heat release contributes only a small portion of the forced heat release, based on the measured background. The flame response shows a significant dependence on both air fuel ratio and fuel splits, with a decreasing gain towards higher frequency.
The results show that it is possible to generate high amplitude fluctuations on the flow using this method, and demonstrate the role of entropy spots during normal operation in lean direct injection systems. Finally, the results suggest that there is an interaction between the forcing frequency and the self-excitation, which may behave in a non-linear manner, and which deserves further investigation.