bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conversion of Liquid to Gaseous Fuel for Prevaporised Premixed Combustion in Gas Turbines
Authors: Wang Y. , Reh L. , Pennell D. , Winkler D. , Döbbeling K. 
Published: December 2014

Stationary gas turbines for power generation are increasingly being equipped with low emission burners. By applying lean premixed combustion techniques for gaseous fuels both NOx and CO emissions can be reduced to extremely low levels (NOx emissions <25vppm, CO emissions <10vppm). Likewise, if analogous premix techniques can be applied to liquid fuels (diesel oil, Oil No.2, etc.) in gas-fired burners, similar low level emissions when burning oils are possible. For gas turbines which operate with liquid fuel or in dual fuel operation, VPL (Vaporised Premixed Lean)-combustion is essential for obtaining minimal NOx-emissions. An option is to vaporise the liquid fuel in a separate fuel vaporiser and subsequently supply the fuel vapour to the natural gas fuel injection system; this has not been investigated for gas turbine combustion in the past.
This paper presents experimental results of atmospheric and high-pressure combustion tests using research premix burners running on vaporised liquid fuel. The following processes were investigated:
• evaporation and partial decomposition of the liquid fuel (Oil No.2);
• utilisation of low pressure exhaust gases to externally heat the high pressure fuel vaporiser;
• operation of ABB premix-burners (EV burners) with vaporised Oil No.2;
• combustion characteristics at pressures up to 25bar.
Atmospheric VPL-combustion tests using Oil No.2 in ABB EV-burners under simulated gas turbine conditions have successfully produced emissions of NOx below 20vppm and of CO below 10vppm (corrected to 15% O2). 5vppm of these NOx values result from fuel bound nitrogen. Little dependence of these emissions on combustion pressure bas been observed. The techniques employed also ensured combustion with a stable non luminous (blue) flame during transition from gaseous to vaporised fuel. Additionally, no soot accumulation was detectable during combustion.
Computation of Two-Phase Flows in Low-NOx Combustor Premix Ducts Utilizing Fuel Film Evaporation
Authors: Rosskamp Heiko , Willmann Michael , Wittig Sigmar 
Published: December 2014

For aircraft gas turbines as well as for industrial gas turbines current and future developments aim at the implementation of lean premixed-prevaporized (LPP) combustor techniques. For the development and optimization of these combustors powerful CFD-codes are required. A new code developed at the Institut für Thermische Strömungsmaschinen (ITS), University of Karlsruhe, provides detailed information on the gas flow as well as on the propagation and evaporation characteristics of liquid wall films inside combustors. The flow characteristics of the gas phase are predicted using a Finite-Volume 3D-Navier-Stokes code with k-ε turbulence modeling. To calculate the evaporation characteristics of a propagating wall film, a two-dimensional wall film model based on the boundary layer equations is proposed.
The present paper comprises a comparison between calculations and experiments for the verification of the code and a detailed study on the evaporation characteristics of fuel films. The results obtained allow judgement to be made on the risk of coke formation on the prefilming surface and suggest that in some operating points a LPP combustor can be operated utilizing solely film evaporation. In addition, the computer code developed also accounts for many familiar types of shear driven film flows such as internal prefilming air blast atomizer flows for example.
Rotordynamic Impact of Swirl Brakes on Labyrinth Seals With Smooth or Honeycomb Stators
Authors: Kwanka K. 
Published: December 2014

The flow through labyrinth seals of turbomachinery generates forces which can cause self-excited vibrations of the rotor above the stability limit. The stability limit is reached at a specific rotating speed or power. The continuous growth in of power density and rotating speed necessitates an exact prediction of the stability limit of turbomachinery.
Usually the seal forces are described with dynamic coefficients. A new, easy-to-handle identification procedure uses the stability behavior of a flexible rotor to determine the dynamic coefficients. Systematic measurements with a great number of labyrinth seal geometries lead to reasonable results and demonstrate the accuracy and sensitivity of the procedure. A comparison of the various methods used to minimize the excitation indicates which seal is more stable and will thus improve the dynamic behavior of the rotor.
A Numerical Study of Flutter in a Transonic Fan
Authors: Isomura Kousuke , Giles Michael B. 
Published: December 2014

The bending mode flutter of a modern transonic fan has been studied using a quasi-3D viscous unsteady CFD code. The type of flutter in this research is that of a highly loaded blade with a tip relative Mach number just above unity, commonly referred to as transonic stall flutter. This type of flutter is often encountered in modern wide chord fans without a part span shroud.
The CFD simulation uses an upwinding scheme with Roe’s 3rd-order flux differencing, and Johnson and King’s turbulence model with the later modification due to Johnson and Coakley. A dynamic transition point model is developed using the en method and Schubauer and Klebanoff’s experimental data.
The calculations of the flow in this fan reveal that the source of the flutter of IHI transonic fan is an oscillation of the passage shock, rather than a stall. As the blade loading increases, the passage shock moves forward. Just before the passage shock unstarts, the stability of the passage shock decreases, and a small blade vibration causes the shock to oscillate with a large amplitude between unstarted and started positions. The dominant component of the blade excitation force is due to the foot of the oscillating passage shock on the blade pressure surface.
Theory and Methodology of Optimally Measuring Vibratory Strains in Closely Spaced Modes
Authors: Yang M.-T. , Griffin J. H. 
Published: December 2014

Stress ratios are traditionally used to infer maximum stresses in blades from strain measurements. This method may not be applicable to all the modes of modern low aspect ratio (LAR) blades since LAR blades often have high frequency “tip” modes which are so closely spaced that slight changes in structural properties can cause significant mode shape changes.
In this paper, it is first shown that the actual tip modes of a LAR blade can be well approximated as linear combinations of the “nominal” modes. The stress field of the blade can then be estimated by calculating the modal content from multiple strain measurements. However, since placement and gage inaccuracies can introduce significant errors in the calculation, it is necessary to find the optimal gage placement which minimizes the error in estimated stresses. An error estimate using “norms” and an efficient optimization method are developed for this purpose.
The Effect of Turbulence on the Heat Transfer in Closed Gas-Filled Rotating Annuli
Authors: Bohn Dieter , Gier Jochen 
Published: December 2014

Higher turbine inlet temperatures are a common measure for increasing the thermal efficiency of modern gas turbines. This development not only leads to the need for more efficient turbine blade cooling but also to the requirement of a more profound knowledge of the mechanically and thermally stressed parts of the rotor. For determining thermal stresses from the temperature distribution in the rotor of a gas turbine, one has to encounter the convective transfer in rotor cavities. In the special case of an entirely closed gas-filled rotating annulus the convective flow is governed by a strong natural convection.
Owen and other researchers have found, that the presence of turbulence and its inclusion in the modeling of the flow causes significant differences in the flow development in rotating annuli with throughflow like e.g. different vortex structures. However, in closed rotating annuli there is still a lack of knowledge concerning the influence of turbulence. Based on previous work, in this paper the influence of turbulenceon the flow structure and on the heat transfer is investigated.
The flow is investigated numerically with a three-dimensional Navier-Stokes solver, based on a pressure correction scheme. To account for the turbulence, a low-Reynolds-number k-ε-model is employed. The results are compared with experiments performed at the Institute of Steam and Gas Turbines. The computations demonstrate that turbulence has a considerable influence on the overall heat transfer as well as on the local heat transfer distribution. Three-dimensional effects are discussed by comparing the three-dimensional calculation with a two-dimensional calculation of the same configuration and are found to have some impact.
Characterization of Oscillations During Premix Gas Turbine Combustion
Authors: Richards George A. , Janus Michael C. 
Published: December 2014

The use of premix combustion in stationary gas turbines can produce very low levels of NOx emissions. This benefit is widely recognized, but turbine developers routinely encounter problems with combustion oscillations during the testing of new pre mix combustors. Because of the associated pressure fluctuations, combustion oscillations must be eliminated in a final combustor design. Eliminating these oscillations is often time-consuming and costly because there is no single approach to solve an oscillation problem.
Previous investigations of combustion stability have focused on rocket applications, industrial furnaces, and some aeroengine gas turbines. Comparatively little published data is available for premised combustion at conditions typical of an industrial gas turbine.
In this paper, we report experimental observations of oscillations produced by a fuel nozzle typical of industrial gas turbines. Tests are conducted in a specially designed combustor, capable of providing the acoustic feedback needed to study oscillations. Tests results are presented for pressures up to 10 atmospheres, and with inlet air temperatures to 588 K (600 F) burning natural gas fuel.
Based on theoretical considerations, it is expected that oscillations can be characterized by a nozzle reference velocity, with operating pressure playing a smaller role. This expectation is compared to observed data, showing both the benefits and limitations of characterizing the combustor oscillating behavior in terms of a reference velocity rather than other engine operating parameters. This approach to characterizing oscillations is then used to evaluate how geometric changes to the fuel nozzle will affect the boundary between stable and oscillating combustion.
Comparative Rotating Stall and Surge Characteristic of a Centrifugal Compressor With Three Different Types of Diffusers
Authors: Engeda Abraham 
Published: December 2014

The diffuser system of a centrifugal compressor comes basically in two general categories either as vaneless or vaned diffuser. Vaned diffusers can further be subdivided into two depending on channel geometry as straight channel or curved channel, or depending on solidity. Three different diffuser types: a vaneless, conventional vaned and a low solidity vaned were tested in the present study. All diffusers were tested downstream of the same impeller. All the diffusers had the same diffuser exit radius to impeller tip radius ratio.
The influence of each type of diffuser on the performance and stall characteristics of the inducer and impeller as a whole was studied. In addition, diffuser stall characteristics of each type diffuser were also studied. The type of diffuser had no significant effect on inducer and impeller stall. The inducer was more stable with the conventional vaned diffuser configuration. Rotating Stall was detected with the vaneless diffuser configuration at the onset of surge. Four stall cells rotated in the same direction as the impeller at 122 Hz.
Numerous works have been documented on rotating stall and surge for centrifugal compressors. Prediction of the inception of rotating stall and surge for a specific geometry and operation is not yet fully possible. Therefore, experimental results and correlations are still of great importance.
A Steam-Augmented Gas Turbine With Reheat Combustor for Surface Ships
Authors: Urbach Herman B. , Knauss Donald T. , Garman Richard W. , Gupta Ashwani K. , Sexton Michael R. 
Published: December 2014

The steam-augmented gas turbine (SAGT) differs from commercial steam-injected gas turbines where steam flow may be considerably less than 15% of air flow. SAGT combustors may operate near stoichiometric combustion conditions with steam flow as high as 50% of air flow, thus achieving specific powers exceeding 555 hp-sec/lb.
A previous simulation study of the steam-augmented gas turbine, which did not include compressor and turbine maps, examined the applicability of the concept in the Navy’s DDG-51-class ship environment. In this re-examination, component maps were employed to establish credible off-design engine performance, and to confirm estimates of overall ship fuel requirements based solely on anticipated component efficiencies. Also, the present simulation employs a heat-exchanger sub-program fully integrated into the main software program. The re-examination has led to several revisions and refinements of previous conclusions, which are discussed in the text.
The SAGT engine concept described herein, dispenses with intercoolers, but adds a low-pressure reheat combustor. The low-pressure combustor flame temperature exceeds 2700° F, which analyses show to be stable. Exhaust gas temperatures are not permitted to fall below 450° F, and the heat recovery steam generator is designed to hold feedwater temperatures close to 300° F to avoid the gas-side acid dewpoint.
At the most efficient operating points, the efficiency of this new reheat SAGT engine exceeds 44.5% with a 2200° F turbine inlet temperature, at an ambient 100°-F temperature. Moreover, it exhibits a 23% reduction in overall system volume. Simulation data show that the maximum efficiency of the SAGT engine peaks at engine powers required for cruising speeds, in contrast to the efficiency of the LM2500, which peaks at full-throttle. Since Navy ships operate near cruise conditions for the majority of their mission time, a SAGT plant uses 29% less fuel than the baseline LM2500 plant. Moreover, employing conservative cost estimates, the SAGT plant is quite competitive on a first-acquisition cost basis with gas turbines currently in the fleet.
Bidirectional Brush Seals
Authors: Hendricks Robert C. , Wilson Jack , Wu Tom , Flower Ralph 
Published: December 2014

Presented is a study of the use of a set of I.D./O.D. bidirectional brush seals to reduce the leakage losses in a wave rotor. Relative to the baseline configuration, data indicate the use of brush seals enhanced wave rotor efficiency from 36 to 45 percent at low leakages (small rotor endwall gap spacings) and from 15 to 33 percent at high leakages (larger endwall gap spacings). These brush seals are capable of sealing positive or negative pressure drops with respect to the axial direction.
Surface tribology for these tests suggested little evidence of grooving although the bristles did wear-in and the rotor surface appeared polished.
Multicriteria Optimization of Time Control Laws of Short Take-Off and Vertical Landing Aircraft Power Plant
Authors: Egorov I. N. , Kretinin G. V. , Leshchenko I. A. 
Published: December 2014

A multicriteria optimization methodology has been discussed to determine time control laws of advanced aircraft gas turbine engines of complex structure. The resulting optimum control laws ensure top improvement of several defined power plant effectiveness criteria in the system of aircraft at transient work modes. The power plant work quality increase effect is attained due to its work process adaptation for numerous requirements from the side of the aircraft.
The proposed methodology effectiveness has been shown by the example of optimizing problem solving to determine time control laws of variable elements of short take-off and vertical landing aircraft power plant.
Numerical Prediction of the Dynamic Behaviour of Premixed Flames Using Systematically Reduced Multi-Step Reaction Mechanisms
Authors: Bohn Dieter , Li Yuhong , Matouschek Gero , Krüger Uwe 
Published: December 2014

Environmental compatibility requires low emission burners for both gas turbine power plants and jet engines. In the past, significant progress has been made in the development of low NOx and CO burners by introducing lean premixed techniques. Unfortunately these burners often have a more pronounced tendency than conventional burner designs to produce combustion driven oscillations. The oscillations may be excited to such an extent that strong pulsation may occur, and this is associated with a risk of engine failure.
In order to describe the acoustical behaviour of the complete burner system, it is crucial to determine the unit function response of the flame itself. Using a new method which was presented in 1996 by Bohn et al. [1] the dynamic flame behaviour can be predicted by means of a full Navier-Stokes-simulation of the complex combustion process for both the steady-state and transient case.
The authors have successfully used this method to obtain the frequency response of turbulent diffusion flames which are mainly controlled by the mixing process. Chemical kinetics become dominant for premixed flames. Therefore, the combustion process of a premixed methane-air mixture is modelled using a systematically reduced 6-step reaction mechanism which takes account of a set of 25 elementary reactions. This reduced mechanism was implemented in the 3D-Navier-Stokes solver in order to perform a combined flow and combustion computation.
The dynamic combustion process of a laminar premixed methane flame in a matrix burner configuration has been investigated. At first, the steady-state combustion process was simulated using the code described above. The results are compared with experimental data. Very good agreement over a wide range of equivalence ratios has been found for quantities such as laminar burning velocity or adiabatic flame temperature. The steady state results are then used as an operating point from which the transient flame behaviour after a sudden jump in the mass flow at the burner inlet has been obtained. Finally, these data lead to the unit function response which can be transferred into frequency space by a Laplace transformation.
The frequency response of the premixed methane flame obtained by a Navier-Stokes simulation has been compared with both experimental as well as analytical solutions. It must be stressed that a pure delay time element which is often used as an analytical formulation is not suitable to describe the dynamic flame behaviour in detail. The frequency response shows the characteristics of a higher order delay time element with several important details.
Parametric studies on the influence of equivalence ratio and the flow pattern of the internal burner fluid flow which are of interest for gas turbine applications, show the importance of the detailed knowledge of the dynamic flame behaviour for the stability analysis of a gas turbine combustor.
A Detailed Analysis of Film Cooling Physics: Part III — Streamwise Injection With Shaped Holes
Authors: Hyams Daniel G. , Leylek James H. 
Published: December 2014

The physics of the film cooling process for shaped, streamwise-injected, inclined jets is studied for blowing ratio (M = 1.25, 1.88), density ratio (DR = 1.6), and length-to-diameter ratio (L/D = 4) parameters typical of gas turbine operations. A previously documented computational methodology is applied for the study of five distinct film cooling configurations: (1) cylindrical film hole (reference case); (2) forward-diffused film hole; (3) laterally-diffused film hole; (4) inlet shaped film hole, and (5) cusp-shaped film hole. The effects of various film hole geometries on both flow and thermal field characteristics is isolated, and the dominant mechanisms responsible for differences in these characteristics are documented. Special consideration is given to explaining crucial flow mechanisms from a vorticity point of view. It is found that vorticity analysis of the flow exiting the film hole can aid substantially in explaining the flow behavior downstream of the film hole. Results indicate that changes in the film hole shape can significantly alter the distribution of the exit-plane variables, therefore strongly affecting the downstream behavior of the film.
Computational solutions of the steady, Reynolds-averaged Navier-Stokes equations are obtained using an unstructured/adaptive, fully implicit, pressure-correction solver. Turbulence closure is obtained via the high Reynolds number k-ε model with generalized wall functions. Detailed field results as well as surface phenomena involving adiabatic film effectiveness (η) and heat transfer coefficient (h) are presented. When possible, computational results are validated against corresponding experimental cases from data found in the open literature. Detailed comparisons are made between surface and field results of the film hole shapes investigated in this work; design criteria for optimizing downstream heat transfer characteristics are then suggested.
Thermodynamic Analysis of Closed Loop Cooled Cycles
Authors: Watson Darren T. , Ritchey Ian 
Published: December 2014

Closed loop steam cooling schemes have been proposed by a number of manufacturers for advanced Combined Cycle Gas Turbine (CCGT) power plant (see for example Corman (1996) and Briesch et al. (1994)) asserting that thermal efficiencies in excess of 60% (LHV) are achievable combined with significant improvements of ∼15% in specific power (see Corman (1995)). In understanding the efficiency advantage however, the relative performance of each cooling system (subject to the same practical constraints and technology levels) is a better indicator then the absolute value.
Assessment of the performance of such novel schemes generally involves a detailed numerical analysis of an integrated cycle which may often prevent validation of the results or obscure an understanding of the physical basis for the claimed improvements. Here, to overcome this, a group of simplified expressions are defined for the variation of each cycles efficiency due to cooling which show where the differences come from. These expressions are based simply on a calculation of the marginal increase in heat rejected, to the environment from the cycle, due to an increase in the level of cooling. After these relationships are validated using detailed heat balance calculations they are used to compare the main cooling options, namely open loop air, closed loop air and closed loop steam when subject to the same practical constraints and assumptions. Based on these results it is proposed that the relative advantage of closed loop cooling may not be as significant as previously thought. Furthermore, it is shown that the closed loop cooling efficiency gain is heavily dependent on the performance and reliability of substantial Thermal Barrier Coatings (TBCs).
Finally, although the majority of recent interest in closed loop cooling schemes has focused upon CCGT plant, there are other systems where the benefits of closed loop steam cooling appear to be greater, in particular cycles involving steam injected gas turbines. Such a cycle is analysed here with a number of advanced cooling options.