bluuebunny/crossref_metadata_2025 huggingface dataset:
The GT140 P-Machine is Extensively Tested for Commercial Application
Authors: Nilsson Jan C. , Anderson Jim , Thörnblad Per
Published: December 2014

In order to attain large utility PFBC plant size a fourfold scale-up of the existing 80–100 MW design was undertaken. This has resulted in the design and manufacture of a new gas turbine, the GT140P, which is an integral part of the 400 MWe PFBC plant. The first GT140P has been subjected to rigorous testing prior to installation in Japan, further verifying the PFBC concept.
Turbulent Spot Characteristics in Boundary Layers Subjected to Streamwise Pressure Gradient
Authors: Johnson Mark W.
Published: December 2014

The development of linear perturbations within laminar boundary layers subjected to a full range of adverse and favourable pressure gradients has been predicted numerically. Comparison of the predictions with published flow visualisation results enabled identification of the perturbation regions associated with the turbulent spot, trailing vortex streaks and oblique waves along the spot flanks. The effect of streamwise pressure gradient on spot characteristics (spot leading and trailing edge velocity, calming region trailing edge velocity and spot spreading half angle) was determined and was found to be consistent with published experimental data. The new data extends the range to severe adverse pressure gradient (separation) and to stronger favourable gradients. Correlations for the spot characteristics are provided.
A 3D Automatic Optimization Strategy for Design of Centrifugal Compressor Impeller Blades
Authors: Yiu K. F. C. , Zangeneh M.
Published: December 2014

In deriving automatic numerical optimization algorithms for aerodynamic applications, the design parameters are usually chosen to be the unknown airfoil/blade profiles. However, there are certain advantages in using the pressure/velocity distribution as the design variable in some applications; the designed distribution can then be used in a 3D inverse design method to generate the actual profile shape. Here, this approach will be addressed. Two methods are used to parametrize the circulation distribution for compressor blades. Dawes’s code is used to predict the viscous effect. An automatic optimization algorithm is developed to minimize the loss with respect to the design parameters.
Cooling Air Flow in a Multi Disc Industrial Gas Turbine Rotor
Authors: Brillert D. , Reichert A. W. , Simon H.
Published: December 2014

The objective of this paper is to investigate the secondary air system in a multidisc rotor. The investigation was performed using Navier-Stokes calculations, network modeling and measurements taking into account new test data from Siemens’ Model V84.3A gas turbine prototype.

The objective of the investigation was to better the understanding of flow patterns and to generate a simple model for describing mean flow values.

The flow patterns predicted on the basis of Navier-Stokes calculations are described and the losses associated with fluid flow through rotating cavities of multidisc rotors are evaluated. High losses are generated in the radial flow through the corotating discs, and this investigation therefore concentrates on this flow. The investigated mass flowrates are relatively high when compared with the mass flow naturally transported on rotating discs (Cw > 105). One part of the mass flow is forced to flow along the boundary layers. The other part is transported outside of the boundary layers like a free potentially inviscid flow.

On the basis of the investigation of the Navier Stokes-calculations, a simple analytical model of the radial flow through the corotating discs is developed. Good agreement was found to exist between the experimental data and the results of the simple model.
The U.S. Department of Energy’s Advanced Turbine Systems Program
Authors: Layne Abbie W. , Hoffman Patricia A.
Published: December 2014

Advanced Turbine Systems (ATS) technology can capture the majority of the new electric power generation market well into the next century. U.S. Department of Energy (DOE) programs supporting the development of ATS technology will enable gas turbine manufacturers to provide ATS systems to the commercial marketplace by the year 2000.

We present a progress report on the DOE ATS Program. We discuss the technical challenges facing and the advanced critical technology requirements and system configurations needed to meet the goals of the Program. Progress has been made in the areas of materials, heat transfer, aerodynamics, and combustion. Applied research conducted by university, industry, and Government organizations has resulted in advanced designs and power cycle configurations for ATS that operate on natural gas, coal, and biomass fuels. We present details on ATS Program research, development, and technology validation and readiness activities. We conclude by discussing the future direction of the Program and its relationship to other Government programs.
An Open Approach to Condition Monitoring, Diagnosis and Decision Support Systems
Authors: Shahroudi K. Eftekhari
Published: December 2014

In increasing the availability and reducing the maintenance costs of gasturbines in critical applications, there has been an increasing trend towards Condition Monitoring, Diagnostic and Decision Support systems (CMD&D). The idea is to reduce the number of routine preventative maintenance procedures, in favor of techniques that continuously monitor the health and diagnose faults as they develop. Early isolation of the root cause of problems, allows the operators to better plan the corrective maintenance actions, taking into account the gasturbine and the other units with which it collaborates.

Clearly, this requires expertise in many fields such as Data Acquisition, Trending, Aerothermodynamic Performance, Vibration, Emissions, Fault Isolation, etc. In addition, it is increasingly becoming expensive to have experts available at all locations, so the solution obviously lies in (Semi-)autonomous systems. Their task would be to monitor the health and diagnose symptoms of machinery, perhaps in collaboration with junior experts locally and senior experts at a remote center.

This report outlines some of the results of a short but broad technical exploration in the questions of why none of the existing packages have achieved widespread acceptance, and how a turbine control manufacturer can play a significant role. A conceptual solution is presented which can meet the challenging functionality, data abstraction, automation and communication requirements by integration of expertise and modules from different groups. However, details on how to turn the concept into a product have been puposely ommitted in order to safeguard proprietory activity.
A Parametric Study of CHAT Cycle Performance: Thermodynamic and Design Features
Authors: Facchini B. , Ferrara G. , Masi G.
Published: December 2014

The CHAT (Cascade Humid Air Turbine) cycle introduction has recently been proposed for a more simple and profitable application of the humid air turbine. The very interesting performance announced for this plant has been evaluated in this paper, particular attention is devoted to the multi-stage evaporation process and its thermodynamic limits.

A detailed thermodynamic analysis of the most important cycle parameters, like various pressure levels, fire temperatures and blade coolant bleeding can permit the evaluation of better plant performances. The results show a substantial agreement with other published data and they confirm the good efficiency and high specific power of the CHAT cycle.

Considering the proposed compressor and turbine for the CHAT plant an off design simulation of the plant is also realized to estimate the real behaviour of turbomachinery components.

Moreover this study is based on ESMS code already developed by the authors and the new components model (thermodynamic, design and off-design simulation) introduced for this work are presented.
Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall
Authors: Kang M. B. , Kohli A. , Thole K. A.
Published: December 2014

The leading edge region of a first stage stator vane experiences high heat transfer rates especially near the end wall making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for the stagnation plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at the higher Reynolds number due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand the mean velocity, turbulent kinetic energy and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point which moves closer to the stator vane at the lower Reynolds number.
Film Cooling Effectiveness and Mass/Heat Transfer Coefficient Downstream of One Row of Discrete Holes
Authors: Goldstein R. J. , Jin P. , Olson R. L.
Published: December 2014

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35° inclination angle with 3d hole spacing and relatively small hole length to diameter ratio (L/d = 6.3). Both film cooling effectiveness and mass/heat transfer coefficient are determined for blowing rates from 0.5 to 2.0 with density ratio of 1.0. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficient obtained following injection of naphthalene-vapor-saturated air with that of pure air injection. This technique enables one to obtain detailed local information on film cooling performance. The laterally-averaged and local film cooling effectiveness agree with previous experiments. The difference between mass/heat transfer coefficients and previous heat transfer results indicates that conduction error may play an important role in the earlier heat transfer measurements.
Vaporization Cooling for Gas Turbines, the Return-Flow Cascade
Authors: Kerrebrock Jack L. , Stickler David B.
Published: December 2014

A new paradigm for gas turbine design is treated, in which major elements of the hot section flow path are cooled by vaporization of a suitable two-phase coolant. This enables the blades to be maintained at nearly uniform temperature without detailed knowledge of the heat flux to the blades, and makes operation feasible at higher combustion temperatures using a wider range of materials than is possible in conventional gas turbines with air cooling. The new enabling technology for such cooling is the Return-Flow Cascade, which extends to the rotating blades the heat flux capability and self-regulation usually associated with heat-pipe technology. In this paper the potential characteristics of gas turbines that use vaporization cooling are outlined briefly, but the principal emphasis is on the concept of the Return-Flow Cascade. The concept is described and its characteristics are outlined. Experimental results are presented that confirm its conceptual validity and demonstrate its capability for blade cooling at heat fluxes representative of those required for high pressure ratio high temperature gas turbines.
The Development of a Computer Code for the Estimation of Combustor Exhaust Temperature Using Simple Gas Analysis Measurements
Authors: Bideau Richard J.
Published: December 2014

Advances in gas turbine technology have led to levels of turbine inlet temperature that preclude the use of thermocouple and simple gas analysis techniques for gas temperature determination. Simple gas analysis schemes rely on the measurement of a very limited range of species in the gas sample, typically CO2, CO and hydrocarbons (UHC). A method of estimating the other important species is required. Simple gas analysis schemes that rely only on elemental mass balance equations to determine the concentration of species are inadequate where high temperature results in significant dissociation.

A method has been developed to enable temperature determination at levels that render simple schemes inaccurate. The procedure is based on the measurement of CO2, CO, UHC and oxides of nitrogen in the exhaust gas. Other species concentrations are calculated using an assumption of partial thermodynamic equilibrium. This allows the calculation of many important combustion parameters. The method has been implemented as a computer code, with an object orientated design approach using the C++ language.

The paper details the theory behind the approach and its implementation. The expected errors for practical applications are discussed and quantified. The method is illustrated by an exhaust temperature pattern factor investigation of an annular combustor. Temperatures determined by thermocouples are compared with those calculated from gas samples.
Dual-Laser Probe Measurement of Blade-Tip Clearance
Authors: Dhadwal Harbans S. , Kurkov Anatole P.
Published: December 2014

This paper describes two dual-laser probe integrated fiber optic systems for measuring blade tip clearance in rotating turbomachinery. The probes are nearly flush with the casing inner lining resulting in minimal flow disturbance. The two probes are closely spaced in a circumferential plane and are slanted at an angle relative to each other so that the blade tip traverse time of the space between the two laser beams varies with the tip radius allowing determination of the tip clearance at the rotor operating conditions. The tip clearance can be obtained for all the blades in a rotor with a single system, provided there are no synchronous vibrations present at a particular operating condition. These probes were installed in two holders; one provided an included angle between the probes of 20 degrees, and the other provided an included angle of 40 degrees. The two configurations were calibrated in a vacuum spin rig facility that is capable of reproducing realistic blade tip speeds.
Improved Model for the Design and Analysis of Centrifugal Compressor Volutes
Authors: Van den Braembussche R. A. , Ayder E. , Hagelstein D. , Rautenberg M. , Keiper R.
Published: December 2014

This paper describes a new model for the analysis of the flow in volutes of centrifugal compressors. It explicitly takes into account the vortical structure of the now that has been observed during detailed 3D flow measurements. It makes use of an impeller and diffuser response model to predict the non-uniformity of the volute inlet flow due, to the circumferential variation of the pressure at the volute inlet, and is therefore applicable also at off-design operation of the volute.

Predicted total pressure loss and static pressure rise coefficients at design and off-design operation have been compared with experimental data for different volute geometries but only one test case is presented here. Good agreement in terms of losses and pressure rise is observed at most operating points and confirms the validity of the impeller and diffuser response model.
Endwall Blockage in Axial Compressors
Authors: Khalid S. Arif , Khalsa Amrit S. , Waitz Ian A. , Tan Choon S. , Greitzer Edward M. , Cumpsty Nicholas A. , Adamczyk John J. , Marble Frank E.
Published: December 2014

This paper presents a new methodology for quantifying compressor endwall blockage and an approach, using this quantification, for defining the links between design parameters, flow conditions, and the growth of blockage due to tip clearance flow. Numerical simulations, measurements in a low speed compressor, and measurements in a wind tunnel designed to simulate a compressor clearance flow are used to assess the approach. The analysis thus developed allows predictions of endwall blockage associated with variations in tip clearance, blade stagger angle, inlet boundary layer thickness, loading level, loading profile, solidity and clearance jet total pressure. The estimates provided by this simplified method capture the trends in blockage with changes in design parameters to within 10%. More importantly, however, the method provides physical insight into, and thus guidance for control of, the flow features and phenomena responsible for compressor endwall blockage generation.
Physics of Hot Crossflow Ingestion in Film Cooling
Authors: McGrath E. Lee , Leylek James H.
Published: December 2014

Computational fluid dynamics (CFD) is used to isolate the flow physics responsible for hot crossflow ingestion, a phenomenon that can cause failure of a film cooled gas turbine component. In the gas turbine industry, new compound-angle shaped hole (CASH) geometries are currently being developed to decrease the heat transfer coefficient and increase the adiabatic effectiveness on film cooled surfaces. These new CASH geometries can have unexpected flow patterns that result in hot crossflow ingestion at the film hole. This investigation examines a 15° forward-diffused cylindrical film hole injected streamwise at 35° with a compound angle of 60° (FDIFF60) and with a length-to-diameter ratio (L/D) of 4.0. Qualitative and quantitative aspects of computed results agreed well with measurements, thus lending credibility to predictions. The FDIFF60 configuration is a good representative of a typical CASH geometry, and produces flow mechanisms that are characteristic of CASH film cooling. FDIFF60 has been shown to have impressive downstream film cooling performance, while simultaneously having undesirable ingestion at the film hole. In addition to identifying the physical mechanisms driving ingestion, this paper documents the effects on ingestion of the blowing ratio, the density ratio, and the film hole Reynolds number over realistic gas turbine ranges of 0.5 to 1.88, 1.6 to 2.0, and 17,350 to 70,000, respectively. The results of this study show that hot crossflow ingestion is caused by a combination of coolant blockage at the film hole exit plane and of crossflow boundary layer vorticity that has been re-oriented streamwise by the presence of jetting coolant: Ingestion results when this re-oriented vorticity passes over the blocked region of the film hole. The density ratio and the film hole Reynolds number do not have a significant effect on ingestion over the ranges studied, but the blowing ratio has a surprising non-linear effect. Another important result of this study is that the blockage of coolant hampers convection and allows diffusion to transfer heat into the film hole even when ingestion is not present. This produces both an undesirable temperature gradient and high temperature level on the film hole wall itself. Lessons learned about the physics of ingestion are generalized to arbitrary CASH configurations. The systematic computational methodology currently used has been previously documented and has become a standard for ensuring accurate results. The methodology includes exact modeling of flow physics, proper modeling of the geometry including the crossflow, plenum, and film hole regions, a high quality mesh for grid independent results, second order discretization, and the two-equation k-ε turbulence model with generalized wall functions. The steady, Reynolds-averaged Navier-Stokes equations are solved using a fully-elliptical and fully-implicit pressure-correction solver with multi-block unstructured and adaptive grid capability and with multi-grid convergence acceleration.
Optimization of Design of High Pressure Compact and Light-Weight Liquid Heat Exchangers
Authors: Avran P. , Soudarev A. , Soudarev B. , Soudarev V.
Published: December 2014

Results of an experimental study with a support of DRET (France) of two designs of liquid heat exchangers made of multi-channel aluminium tubes are presented with the objective to develop a fuel-oil recuperator, compact and light (less than 3 Kg). It was demonstrated that the application of a combined approach to heat exchange enhancements using three-dimensional turbulators as semi-spherical craters and bulges on channel walls of internal paths allows to increase the specific heat output of the heat exchanger from 10.5 to 13.3 kW/kg.
Design of Tubular Humidifiers for Evaporative Gas Turbine Cycles
Authors: Dalili Farnosh , Westermark Mats
Published: December 2014

In the evaporative gas turbine (EvGT) cycle, also referred to as the humid air turbine (HAT) cycle, the compressed air is humidified with water to increase the mass flow through the expander, resulting in high power output and high exhaust heat recovery potential. This paper presents a design methodology for tubular humidifiers, in which pressurized air is led inside of smooth metallic tubes and is brought into contact with a falling water film. The heat required for humidification is mainly taken from exhaust gas from the gas turbine on the shell side and also by recirculating water through the intercooler and the aftercooler.

The most important parameters for designing tubular humidifiers are: heat transfer coefficient on the flue gas side; and mass transfer coefficient for water vapor on the air side. Important design aspects include: proper wetting of the tubes; how to avoid flooding of the tubes; entrainment of water droplets into the air stream; and boiling in the water film.

All calculations in this paper are based on an evaporative gas turbine cycle applied for combined heat and power generation with a partial-flow humidification circuit, where a fraction of the compressed air is humidified while a major part is by-passed directly to the recuperator. It is concluded that the required heat exchanging surface can be reduced if humidification is carried out for only a fraction of the air (20–30 percent). Finned tubes are recommended to enhance the heat transfer per unit tube length.
Calculation of Convective Heat Transfer in Square-Sectioned Gas Turbine Blade Cooling Channels
Authors: Saidi Arash , Sundén Bengt
Published: December 2014

Internal cooling channels are commonly used to reduce the thermal loads on the gas turbine blades to improve overall efficiency. In this study a numerical investigation has been carried out to provide a validated and consistent method to deal with the prediction of the fluid flow and the heat transfer of such channels with square cross sections. The rotation modified Navier-Stokes and energy equations together with a low-Re number version of the k-ε turbulence model are solved with appropriate boundary conditions. The solution procedure is based on a numerical method using a collocated grid, and the pressure-velocity coupling is handled by the SIMPLEC algorithm. The computations are performed with the assumption of fully developed periodic conditions.

The calculations are carried out for smooth ducts with and without rotation and effects of rotation on the heat transfer are described. Similar numerical calculations have carried out for channels with rib-roughened walls. The obtained results are compared with available experimental data and empirical correlations for the heat transfer rate and the friction factor. Some details of the flow and heat transfer fields are also presented.
Turbine Disc-Rim Cooling Design Criteria for Modern Two Stage High Pressure Turbine Aero-Engines
Authors: Mirzamoghadam Alexander V.
Published: December 2014

Modern aero-engines with two stage high pressure turbines (HPT) are attractive because they offer higher turbine polytropic efficiencies compared to the single stage. When considering the complexity associated with the secondary cooling airflow system, however, the two stage turbine is more vulnerable to excess air performance losses and requires more effort to optimize. This paper addresses the established design criteria with an emphasis on cooling air supply to the second stage turbine blades. The available cooling air is compressor delivery air fed to the front face of the rim via the first turbine stage, and lower pressure air from an earlier compressor stage is fed internally to the rear cavity. A comparison is made of the effectiveness of disc-rim cooling achieved with alternate forward and rear air feed systems to the rotor blades based on aerothermal analytical methods. Both front and rear cover-plate as well as disc feed holes are considered, and the applicable heat transfer correlation along with cavity boundary layer/mixing temperature assumptions are described. The 2-D axisymmetric finite element transient thermal model, for each design case, has been run with a square speed cycle and in this study, the aerothermal behavior at steady state maximum take-off condition is compared. Results indicate that low pressure compressor air in a cover-plate is thermally more effective than feed holes on the front or rear side of the disc, if pre-swirled compressor exit air from the first stage seals the second stage disc-rim. This is also valid if cavity boundary layer air from an earlier compressor stage sealing the rim (on either side) reaches a temperature as high as the area-weighted-mean (AWM) rim temperature due to contamination by hot gas ingestion. Although the front system offers a better overall cooling effectiveness, in comparing the front and rear feed hole concepts using cooling air from a compressor mid-stage, the rear feed hole is more effective in reducing the AWM temperature in the rotor bucket-groove, as well as the maximum rim temperatures of the second stage disc.
Numerical Investigation of the Influence of Specific Vortex Generation on the Mixing Process of Film Cooling Jets
Authors: Vogel Dirk T.
Published: December 2014

Vortices generated and designed in internal cooling systems of film cooled turbine blades have a significant influence on the aerodynamic mixing process of the coolant and the main flow. Of course the resulting distribution of the film cooling effectiveness is strongly influenced by the behaviour of the coolant mixing. The vortices are generated by a special design of the cooling channel and film cooling holes and by the comparable flow phenomena coming along with the problem of jets in crossflow.

The multi-block Navier-Stokes solver TRACES with special features for the simulation of complex and turbulent mixing phenomena is applied to solve the flow field and the heat fluxes and temperature distribution in the turbine blade structure simultaneously. The code is validated for the simulation of film cooling and heat transfer and was also compared to other codes taking part in the AGARD Working group 26 (Dunham, 1996 [4]) working on the test cases “NASA-Rotor-37” and DLR-Turbine guide vane “VT1B”.

As a result of extensive parameter studies (Vogel, 1996 [18]) a vortex mixing model will be established which describes the existing vortices and their effect on the film cooling mixing process in detail. It was found that vortex generation inside the internal cooling channel with an opposite direction of rotation compared with the main kidney shaped jet vortex system can reduce the amount of coolant air significantly without reducing the film cooling effectiveness. All numerical investigations presented in this paper were carried out using a model geometry. No experimental results were available for this geometry. The validation of the code concerning film cooling mixing was presented in [15], [16], [17] and [18] (Vogel, 1994–1996). The geometries applied in those validations were quite similar to those used in this paper. Nevertheless for credibility some comparisons between experimental and numerical data are presented.
Subgrid Two-Phase Mixing and Combustion Modeling for Large-Eddy Simulations
Authors: Menon Suresh , Pannala Sreekanth
Published: December 2014

A subgrid scalar mixing and combustion model originally developed for gas phase combustion has been extended to include the liquid phase. This approach includes a more fundamental treatment of the effects of the final stages of droplet vaporization, molecular diffusion, chemical reactions and small scale turbulent mixing than other LES closure techniques. As a result, Reynolds, Schmidt and Damkohler number effects are explicitly included. This model has been implemented within an Eulerian-Lagrangian two phase large-eddy simulation (LES) formulation. In this approach, the liquid droplets are tracked using the Lagrangian approach up to a pre-specified cut-off size. The evaporation of the Lagrangian droplets and the evaporation and mixing of the droplets smaller than the cutoff size is modeled within the subgrid using an Eulerian two-phase model. The issues related to the implementation of this subgrid model within the LES are discussed in this paper along with some preliminary results that demonstrate its capabilities.
Modified Humid Air Turbine Cycle for Biomass Gasification
Authors: Cavani Adrin
Published: December 2014

Performance and design data are presented for energy conversion of biomass in modified HAT cycles in a combined heat and power plant. The computations are performed by the heat balance software GateCycle and based on a gas turbine LM 2500 from General Electric. The processing of biomass includes drying of wet biomass fuel, gasification at atmospheric pressure, gas cooling and wet gas cleaning of the product gas and gas compression to pressure requirement of the gas turbine combustion system.

A further problem in biomass fuelled power systems and humidified gas turbine (HAT cycle) is to accomplish stable combustion in a gas turbine combustor with humidified air along with product gas having low heating value. To avoid the problem, the air humidification is performed only on a fraction of the compressed air stream, which makes it possible to use dry air (unhumidified air) for the combustion in the primary zone and humidified air for diluting and cooling. It is shown that part-airflow humidification gives similar or slightly improved performance (specific power and cycle efficiency) and also reduces the need of area for heat exchanging and recuperating.
Applying the Relationship Between the Amount of CO2 and O2 in Flue Gases to Reduce the NOx Emission Measurement Uncertainty
Authors: van Oost M. L. E.
Published: December 2014

A method has been found to reduce the high measurement uncertainty of NOx emissions of gas turbines.

Calculation of the measurement uncertainty of NOx emission measurements shows that the high uncertainty is not only due to the uncertainty of the NOx emission measurement itself but is also due to the correction to 15 % O2 in the flue gases.

A second, independent method to determine the percentage oxygen in the flue gases is introduced in addition to the direct sampling method. This second method provides additional information resulting in a significant reduction of the measurement uncertainty.

The solution found has the advantage that the additionally required measurement equipment is kept to a minimum.

Experience with the new method in field tests are excellent.
A Prediction Model for Separated-Flow Transition
Authors: Hatman Anca , Wang Ting
Published: December 2014

The present study formulates an improved approach for analyzing separated-flow transition that differentiates between the transition process in boundary layers which are laminar at separation and those which are already transitional at separation.

The paper introduces new parameters that are necessary in classifying separated-flow transition modes and in accounting for the concomitant evolution of transition in separated shear layer and the average effect of periodic separation bubble build-up and vortex shedding. At least three separated-flow transition modes are positively distinguished: (a) transitional separation, with the transition starting upstream of the separation point and developing mostly as natural transition, (b) laminar separation - short bubble mode, with the onset of transition induced downstream of the separation point by inflexional instability and with a quick transition completion, and (c) laminar separation - long bubble mode, with the onset of transition also induced downstream of the separation point by inflexional instability, and with the transition completion delayed. Passing from one mode to another takes place continuously through a succession of intermediate stages.

The location of maximum bubble elevation has been proved to be the controlling parameter for the separated flow behavior. It was found that, downstream of the separation point, the experimental data expressed in terms of distance Reynolds number Rex can be correlated better than momentum or displacement thickness Reynolds number data. For each mode of separated-flow transition, the onset of transition, the transition length, and separated flow general characteristic are determined. This prediction model is developed mainly on low free-stream turbulence flat plate data and limited airfoil data. Extension to airfoils and high turbulence environment requires additional study.
External Heat Transfer Predictions in a Highly-Loaded Transonic Linear Turbine Guide Vane Cascade Using an Upwind Biased Navier-Stokes Solver
Authors: Gehrer Arno , Jericha Herbert
Published: December 2014

External heat transfer predictions are performed for two-dimensional turbine blade cascades. The Reynolds-averaged Navier-Stokes equations with algebraic (Arnone and Pacciani, 1996), one-equation (Spalart and Allmaras, 1994) and two-equation (low-Re k-ε, Biswas and Fukuyama, 1994) turbulence closures are solved with a fully-implicit time-marching finite volume method.

Comparisons with measurements (Arts et al., 1990, 1994) for a highly-loaded transonic turbine nozzle guide vane cascade show good agreement in some cases, but also reveal problems with transition prediction and turbulence modeling.

Special attention has been focused on the low-Re k-ε model concerning the influence of the inlet boundary condition for the ε-equation and problems in the stagnation point region.
The Role of Tip Leakage Vortex Breakdown in Compressor Rotor Aerodynamics
Authors: Furukawa Masato , Inoue Masahiro , Saiki Kazuhisa , Yamada Kazutoyo
Published: December 2014

The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier-Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubble-like recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending to the upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow resulting from the contraction of the bubble-like structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at near-stall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise and pitchwise directions. The growth of the breakdown causes the blockage and the loss to increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.
Numerical and Experimental Investigation of the Wake Flow Downstream of a Linear Turbine Cascade
Authors: Sanz Wolfgang , Gehrer Arno , Woisetschläger Jakob , Forstner Martin , Artner Wolfgang , Jericha Herbert
Published: December 2014

In turbomachinery the wake flow together with the inherent unsteadiness caused by interaction between stator and rotor has a significant impact on efficiency and performance. The prediction of the wake flow depends largely on the turbulence modeling. Therefore in this study the evolution of a viscous wake downstream of a linear turbine cascade is experimentally and computationally investigated. In a transonic cascade test stand Laser Doppler Velocimeter (LDV) measurements of velocity and turbulent kinetic energy are done in several axial planes downstream of the blade trailing edge. Two different turbulence models are then incorporated into a two-dimensional Navier-Stokes solver to calculate the turbulent wake flow and the results are compared with the experimental data to test the quality of the turbulence models. The large discrepancies between measurement and Calculation are assumed to be caused by the periodic vortex shedding from the blunt trailing edge which is not taken into account by the turbulence models. But further research is needed to resolve this issue.
High-Speed Flow in an Annular Cascade With Tip Clearance: Numerical Investigation
Authors: Politis E. S. , Giannakoglou K. C. , Papailiou K. D.
Published: December 2014

The high-speed flow in an annular cascade with two tip clearance sizes is numerically modeled using a Navier-Stokes solver and the high-Reynolds-number k-ε turbulence model. The numerical predictions should be regarded as complementary to the experimental work conducted in the NTUA annular cascade facility, designed for studying tip-clearance effects in compressor cascades. In the numerically simulated experiment, the stationary blades are mounted on the casing and the tip clearance is formed between them and the spinning hub. The purpose of the present paper is to scrutinize flow trends identified during the measurements and elucidate the flow patterns in the blade passage for rotating and stationary hub.
A Theory for Predicting the Turbulent-Spot Production Rate
Authors: Mayle R. E.
Published: December 2014

A theory is presented for predicting the production rate of turbulent spots. The theory, based on that by Mayle-Schulz for bypass transition, leads to a new correlation for the spot production rate in boundary layer flows with a zero pressure gradient. The correlation, which agrees reasonably well with data, clearly shows the effects of both free-stream turbulence level and length scale. In addition, the theory provides an estimate for the lowest level of free-stream turbulence causing bypass transition.
Sub-Scale Demonstration of the Active Feedback Control of Gas-Turbine Combustion Instabilities
Authors: Sattinger Stanley S. , Neumeier Yedidia , Nabi Aharon , Zinn Ben T. , Amos David J. , Darling Douglas D.
Published: December 2014

Described are sub-scale tests that successfully demonstrate active feedback control as a means of suppressing damaging combustion oscillations in natural-gas-fueled, lean-premix combustors. The control approach is to damp the oscillations by suitably modulating an auxiliary flow of fuel injected near the flame. The control system incorporates state observer software that can ascertain the frequency, amplitude, and phase of the dominant modes of combustion oscillation, and a sub-scale fuel flow modulator that responds to frequencies well above 1 kHz.

The demonstration was conducted on a test combustor that could sustain acoustically coupled combustion instabilities at preheat and pressurization conditions approaching those of gas-turbine engine operation. With the control system inactive, two separate instabilities occurred with combined amplitudes of pressure oscillations exceeding 70 kPa (10 psi). The active control system produced four-fold overall reduction in these amplitudes. With the exception of an explainable control response limitation at one frequency, this reduction represented a major milestone in the implementation of active control.
Combustion System Damping Augmentation With Helmholtz Resonators
Authors: Gysling D. L. , Copeland G. S. , McCormick D. C. , Proscia W. M.
Published: December 2014

This paper describes an analytical and experimental investigation to enhance combustion system operability using side branch resonators. First, a simplified model of the combustion system dynamics is developed in which the large amplitude pressure oscillations encountered at the operability limit are viewed as limit cycle oscillations of an initially linear instability. Under this assumption, increasing the damping of the small amplitude combustion system dynamics will increase combustor operability. The model is then modified to include side branch resonators. The parameters describing the side branch resonators and their coupling to the combustion system are identified, and their influence on system stability is examined. The parameters of the side branch resonator are optimized to maximize damping augmentation and frequency robustness.

Secondly, the model parameters for the combustor and side branch resonator dynamics are identified from experimental data. The analytical model predicts the observed trends in combustor operability as a function of the resonator parameters and is shown to be a useful guide in developing resonators to improve the operability of combustion systems.
One-Dimensional Model to Quantify NOx Reduction in Gas Turbines Using EGR
Authors: Botros K. K. , de Boer M. J. , Kibrya G.
Published: December 2014

A one dimensional model based on fundamental principles of gas turbine thermodynamics and combustion processes was constructed to quantify the principle of exhaust gas recirculation (EGR) for NOx reduction. The model utilizes the commercial process simulation software ASPEN PLUS®. Employing a set of 8 reactions including the Zeldovich mechanism, the model predicted thermal NOx formation as function of amount of recirculation and the degree of recirculate cooling. Results show that addition of sufficient quantities of uncooled recirculate to the inlet air (i.e. EGR>∼4%) could significantly decrease NOx emissions but at a cost of lower thermal efficiency and specific work. Cooling the recirculate also reduced NOx at lower quantities of recirculation. This has also the benefit of decreasing losses in the thermal efficiency and in the specific work output. Comparison of a ‘rubber’ and ‘non-rubber’ gas turbine confirmed that residence time is one important factor in NOx formation.
Near Term Gas Turbine Program to Enable the Use of “Renewable” Fuels
Authors: Moritz Robert R.
Published: December 2014

To be suitable for gas turbine use, renewable energy resources are typically processed to produce a cleaned gaseous fuel which tends to be of low energy density relative to natural gas. Depending on the process and source, the derived fuel gas may also contain a large fraction of Hydrogen. Such gases may require enrichment to permit stable combustion and also carry some hazard of flashback due to the Hydrogen content. Previous experience also suggests that even small traces of ash which could be carried through the gas cleaning have the potential to cause airfoil fouling.

Allison Engine Company produces engines for electric power generation in the range up to 7 MW and expects to offer derivatives up to 12 MW by the year 2000. Two series of engines are involved, offering different virtues and challenges in renewable fuels use. It is planned to extend the range of renewable fuels utilized by all these engines by carrying out a rig and engine demonstration program. A major goal is to operate a gas turbine using the product gas from a high quality biomass gasifier.
Preliminary Assessment of Advanced Gas Turbines for CVX
Authors: Bannister Ronald L. , Horazak Dennis A.
Published: December 2014

To support the propulsion and electrical requirements of an all-electric CVX, the use of heavy-duty power generation gas turbines could be considered as a viable alternative to conventional steam propulsion. A 300 MWe total plant baseload capacity is needed for an all-electric ship requiring 200 MWe for propulsion and a peak electric catapult power requirement of 200 MWe.

Applications of advanced marine gas turbines to provide electric power to an all-electric CVX have a major advantage in that the gas turbines do not have to be located in the same area as the electric propulsion motors. The possibility of locating the turbine-generators topside to minimize the ship impacts associated with long runs of large intake and exhaust ducts was briefly studied and is discussed herein.
Wavelet Analysis of Transitional Flow Data Under High Free-Stream Turbulence Conditions
Authors: Volino Ralph J.
Published: December 2014

Transitional flow data from boundary layers subject to strong acceleration (K as high as 9×10−6) and high free-stream turbulence (∼8%) were analyzed using wavelet transforms. Wavelet analysis provides the energy content of a signal on both a frequency and instantaneous time basis. It differs from traditional Fourier spectral analysis, which can only provide the spectral energy on a time averaged basis. Instantaneous velocity data from intermittent, transitional boundary layers were segregated into turbulent and non-turbulent zones through conditional sampling. Wavelet analysis was used to determine the frequency content of the velocity fluctuations and turbulent shear stress in the two zones separately. The streamwise velocity fluctuations in the turbulent and non-turbulent zones appeared similar. This was attributed to the effect of the free-stream turbulence, which had the same effects on both zones. The wall-normal fluctuations and turbulent shear stress were of significantly higher magnitude and frequency in the turbulent zone. These results suggest that turbulence models should be based on transport quantities rather than turbulent kinetic energy. The regions just upstream and just downstream of turbulent zones were also analyzed, to check for possible important frequencies leading to the initiation of turbulence or characteristic of the “calm” zone trailing a turbulent spot. No distinct behavior was observed in either of these zones. Uncertainty values associated with the wavelet spectra are high due to the short data records available. Results are shown to be valid in spite of these uncertainties, however longer data records should be acquired in future studies.
An Exergy Analysis of Novel Power Generation Systems
Authors: Neto Alcides Codeceira , Pilidis Pericles
Published: December 2014

The present paper describes the application of the exergy method to several power cycles of current interest in the Brazilian power scene. The ability of the exergy method to highlight component irreversibilities is of particular interest in this investigation.

In this paper the exergy analysis for a simple gas turbine cycle, a combined gas/steam cycle, a combined gas/steam/freon cycle and a chemically recuperated gas turbine have been performed.

As a yardstick for comparison a standard gas turbine engine with and without a steam bottoming cycle has been employed. The fuel considered is natural gas. The analysis of this system has been carried out using the exergy method.

For the simple gas turbine cycle a biomass fuel has been employed as an alternative. The attraction of this fuel is its low impact on the environment and its plentiful supply in many regions in Brazil.