bluuebunny/crossref_metadata_2025 huggingface dataset:
The Impact of Realistic Inlet Swirl in a 1 ½ Stage Axial Turbine
Authors: Schmid Gregor , Krichbaum Alexander , Werschnik Holger , Schiffer Heinz-Peter
Published: September 2014

Further improvements of gas turbine design can be expected if realistic turbine inlet conditions are applied. These include discrete swirl cores and hot spots which exit from the combustion chamber. A large scale turbine rig is currently reconfigured at Technische Universität Darmstadt to analyse the effect of realistic swirl intensity on turbine flow and heat transfer. A comparison is to be made between swirling and axial inflow conditions. The swirl generator causes a recirculation zone inside the combustion chamber. As a result, the total pressure at turbine inlet is reduced at midspan and increased near the end walls. In addition, incidence angles of ±15° occur at hub and casing of the nozzle guide vane (NGV). This swirl and the shape of the pressure profile are typical for modern lean combustion concepts which are relevant to reduce emissions like NOX.

During the design of the test rig, computational flow simulations are carried out. Different swirl orientations and clocking positions are investigated in advance. Depending on these parameters, there is a potential of 0.5 % efficiency between the optimal and the worst configuration. Comparing swirling with axial inflow conditions, an efficiency deficit of more than 2 % has been found which is mainly due to the increased turbulence level for swirling flow. In addition, heat transfer through the NGV hub is increased by approximately 20%. This paper aims for understanding the generation of these aerodynamic and thermal losses to allow for their elimination in future engine designs. Therefore, the most complex case of a realistic swirl generator is successively simplified towards a case with axial inflow: Two-dimensional inflow conditions including discrete swirl and loss cores are compared to radial distributions of inflow variables and globally constant values. The influence of swirling inflow, total pressure profile and turbulence level are simulated separately in order to identify their individual impact on aerodynamic and thermal losses.
Non-Axisymmetric Endwall Contouring in a Compressor Cascade With Tip Gap
Authors: Varpe Mahesh K. , Pradeep A. M.
Published: September 2014

This paper describes the design of a non-axisymmetric hub contouring in a shroudless axial flow compressor cascade operating at near stall condition. Although, an optimum tip clearance reduces the total pressure loss, further minimization of the losses using hub contouring was achieved. The design methodology presented here combines an evolutionary principle with a three-dimensional CFD flow solver to generate different geometric profiles of the hub systematically. The total pressure loss coefficient was used as a single objective function to guide the search process for the optimum hub geometry. The resulting three dimensionally complex hub promises considerable benefits discussed in detail in this paper. A reduction of 15.2% and 16.23% in the total pressure loss and secondary kinetic energy, respectively, was achieved in the wake. The blade loading was observed to improve by about 4.53%. Other complementary benefits are also listed in the paper. The results confirm that non-axisymmetric contouring is an effective method for reducing the losses and thereby improving the performance of the cascade.
Laminar and Turbulent Flame Speeds for Natural Gas/Hydrogen Blends
Authors: Morones A. , Ravi S. , Plichta D. , Petersen E. L. , Donohoe N. , Heufer A. , Curran H. J. , Güthe F. , Wind T.
Published: September 2014

Hydrogen-based fuels have become a primary interest in the gas turbine market. To better predict the reactivity of mixtures containing different levels of hydrogen, laminar and turbulent flame speed experiments have been conducted. The laminar flame speed measurements were performed for various methane and natural gas surrogate blends with significant amounts of hydrogen at elevated pressures (up to 5 atm) and temperatures (up to 450 K) using a heated, high-pressure, cylindrical, constant-volume vessel. The hydrogen content ranged from 50% to 90% by volume. All measurements were compared to a chemical kinetic model, and good agreement within experimental measurement uncertainty was observed over most conditions. Turbulent combustion experiments were also performed for pure H2 and 50:50 H2:CH4 mixtures using a fan-stirred flame speed vessel. All tests were made with a fixed integral length scale of 27 mm and with a turbulent intensity level of 1.5 m/s at 1 atm initial pressure. Most of the turbulent flame speed results were in either the corrugated or thin reaction zones when plotted on a Borghi diagram, with Damköhler numbers up to 100 and turbulent Reynolds numbers between about 100 and 450. Flame speeds for a 50:50 blend of H2:CH4 for both laminar and turbulent cases were about a factor of 1.8 higher than for pure methane.
Rotor Lifecycle Management Program
Authors: Wrobel Michal , Richter Mark , Zimmermann Rene , Kiewel Holger , Ullrich Andreas
Published: September 2014

Minimizing the maintenance costs has become an ever growing topic in the power generation industry. Consequently, OEM’s constantly increase their efforts to exploit the full lifetime potential of capital intensive components, as for instance gas turbine rotors. More than ever, it is essential to have a closed loop from the design knowledge to solid facts about the actual condition of a gas turbine rotor in the field, in order to optimize the utilization and therefore to reduce total lifecycle costs.

During initial design an iterative component design process is applied, comprising of analytical calculations and component and engine tests, to design a reliable, robust and maintenance friendly component. Individual component risk profiles (i.e. failure probability and consequences) have to be taken into account during the design phase to cover uncertainties regarding the operating regime, operating conditions and environment, resulting in the minimum expected lifetime.

The lifetime of gas turbine components is limited and primarily depends on factors like the operating regime, dictating the mechanical and thermal loads, actual material properties, environmental conditions and the level of maintenance. Those parameters have a scatter and also interact with each other. As a consequence the progress of component degradation varies and the individual component lifetime isn’t known in detail at the time of the design.

The purpose of a Rotor Lifecycle Management Program is to detect individual component degradation early in the lifecycle, in order to exploit the maximum rotor lifetime while ensuring safe operation.

Periodic monitoring and condition assessment of the individual rotor is the first step, performed during standard type C inspections and comprising of visual inspection, dimensional and advanced non-destructive measurements. Typically the monitoring schedule is based on the operating regime and the operating history of the specific rotor.

The combination of the monitoring results with validated analytical design models, extensive material data and the overall gas turbine rotor fleet experience of the OEM, allows proper planning of lifetime extension measures, such as repair and reconditioning activities. Specific repair solutions for both on-site and shop applications have been developed.

A rotor lifecycle management program is a „living” program. The monitoring scope and schedule as well as the repair solutions portfolio are continuously optimized and adapted as a result of detailed analysis of operating data and inspection results of the whole global fleet.
CFD Analysis of the Aerodynamics and Aeroacoustics of the NASA SR2 Propeller
Authors: Tan Chun Hern , Voo Keng Soon , Siauw Wei Long , Alderton James , Boudjir Amel , Mendonça Fred
Published: September 2014

NASA’s SR2 8-bladed propeller rotating at 6487rpm [1, 2, 3, 4] Advance Ratio of 3.06 and Mach Number of 0.6 is used to assess the aerodynamic and noise performance prediction capabilities of a standard commercial CFD code.

The main purpose of this study is to benchmark the performance prediction against experimental data for Power Coefficient and near-field noise measurements. Comparisons are made between single rotating and multiple rotating regions across a sliding mesh interface. We also focus on the effectiveness of capturing the downstream convection of tip vortex structures, in the wake of the propeller, modeled with all 8 blades, with a view towards using the approach to understand the interaction of these wake features with aerodynamic surfaces.

Noise predictions are performed using the standard FfowcsWilliams-Hawkings impermeable surface method for rotating dipoles. This is compared with near-field noise predictions using direct noise simulation from the unsteady compressible CFD code and experimental data, in terms of the measured dB intensity at the blade passing frequency and harmonics.

Additional unsteady CFD simulation was conducted for a separate SR2 propeller with a calibrated blade angle. The preliminary results of the direct near-field noise computation of dB intensity at the blade passing frequency have shown improved agreement with wind tunnel data at aft angles to the propeller plane.

Practices are demonstrated which result in low dependency on the sliding mesh interface location. Tip vortex structures and downstream convection are well captured by judicious choice of mesh refinement in the wake of the propeller.
Experimental Investigation of Turbine Phantom Cooling on Endwall With Trailing Edge Discharge Flow
Authors: Zhang Yang , Yuan Xin
Published: September 2014

The film cooling ejection on High Pressure (Hp) turbine component surface is strongly affected by the complex flow structure in the nozzle guide vane or rotor blade passages. The action of secondary flow in the main passage could dominate the film cooling effectiveness distribution on the component surfaces. The film cooling ejections from endwall and airfoil trailing edge are mixed by the secondary flow. Considering a small part of the coolant ejection from trailing edge discharge flow will move from the airfoil trailing edge pressure side to endwall downstream and then cover some area, the interaction between the coolants injected from endwall and airfoil trailing edge is worth investigating. Though the temperature of coolant discharge flow from trailing edge increases after the mixing process in the internal cooling procedure, the ejections moving from airfoil to endwall still have the potential of second order cooling. This part of the coolant is called “Phantom cooling flow” in the paper. A typical scale-up model of Hp turbine NGV is used in the experiment to investigate the cooling performance of ejection from trailing edge. Instead of the airfoil trailing edge platform itself, the film cooling effectiveness is measured on the downstream part of the endwall. This paper is focused on the trailing edge discharge flow with compound angle effects and the coolant from discharge holes moving from trailing edge to endwall surface. The coolant flow is injected from the straight discharge holes with a compound angle of 15deg and 45deg respectively. The film cooling holes on the endwall are used simultaneously to investigate the combined effects. The blowing ratio and different configurations of compound angle holes are selected to be the changing parameters in the paper. The experiment is completed with the blowing ratio changing from M = 0.7 to M = 1.3 and the compound angle is introduced to the entire row of trailing edge discharge holes (full span), with inlet Reynolds numbers of Re = 3.5×105 and an inlet Mach number of Ma = 0.1.
Application of Riblets on Turbine Blade Endwall Secondary Flow Control
Authors: Miao X. , Zhang Q. , Jiang H. , Qi H.
Published: September 2014

Within the past ten years, significant improvements have been achieved in the laser manufacturing process. It is feasible now to obtain various small-scale surface features (such as dimples, riblets, grooves, etc.) with the current manufacturing readiness level of laser surface texturing techniques. In this paper, the aerodynamic impact of the employment of riblets on turbine endwall has been investigated through combined CFD and experimental studies in a low speed linear cascade environment. Detailed comparisons of the flow structures have been made for cases with and without riblets on the endwall. The results show that endwall riblets can effectively reduce the strength of the pressure side leg of the horseshoe vortex, lower the cross passage pressure gradient, and alleviate the lift up of the passage vortex. A test section with seven passages and eight blades was used to validate the CFD observations. Both numerical and experimental results indicate that, the addition of riblets can be an effective approach to reduce the endwall secondary flow, and there is a large space for further optimization.
Swirl Flame Response to Traveling Acoustic Waves
Authors: Saurabh Aditya , Steinert Richard , Moeck Jonas P. , Paschereit Christian O.
Published: September 2014

The advent of annular combustors introduced a new facet of flame-acoustic interaction: flame coupling with standing and spinning azimuthal acoustic waves. Such coupling involves an acoustic field that is essentially transverse to the flame. Recent experiments on single burner test rigs have provided significant insight into flame interaction with transverse standing waves. However, experiments that focus on the spinning/rotating nature of azimuthal instabilities are still lacking. In this report, we demonstrate a methodology for studying spinning azimuthal instabilities on a single burner test rig. This methodology is based on analyzing flame response to a traveling acoustic wave generated in the combustor. We generate traveling acoustic waves in our transverse acoustic forcing test-rig by converting one end of the transverse extensions to a non-reflecting end. This is achieved through the implementation of the technique of impedance tuning. In the paper, we have discussed this implementation, followed by discussions on the effects of a traveling acoustic wave on a swirl-stabilized flame. The discussion is in the form of a comparison of flame oscillations for traveling wave and standing wave transverse forcing cases. Results show that the effect of transverse pressure oscillations dominates the flame response to traveling acoustic waves.
Parametric Performance of a Class of Standard Discharge Scrolls for Industrial Centrifugal Compressors
Authors: Giachi Marco , Ramalingam Vidyasagar , Belardini Elisabetta , De Bellis Fabio , Reddy Chanukya
Published: September 2014

For many reasons, the discharge volute of a centrifugal compressor is becoming more and more critical for the performance of the machine. The most important are the need to reduce the size of the casing and to minimize the delivery time and cost of the compressor. A database of standard geometries represents a good engineering solution to both these requirements. In fact, it is possible, from a mechanical point of view, to design a class of similar volutes to fit different casings and stages. On the other hand, from the performance point of view, very little has been done to describe families of similar scrolls and how the performance of a baseline geometry can be adapted to take into account the differences which exist in the scrolls of the same family. A lot of data are available in literature but they refer to single specific geometries and to optimized individual designs. In this paper, a description of the analysis which has been done to investigate which may be the most convenient parameters to describe the volute performance is presented together with some experimental results which have been used to validate the analysis.
Comparison of Gas Turbines and Power-to-Gas Plants for Improved Wind Park Energy Dispatchability
Authors: Guandalini Giulio , Campanari Stefano , Romano Matteo C.
Published: September 2014

According to IEA projections for the year 2050, up to 50% of the energy demand in the next decades could be covered by non-programmable sources (e.g. wind and solar power), which can significantly affect power quality, grid stability and power generation planning. Moreover, in several countries a fast growth of installed power based on renewables could not be followed by a simultaneous growth of local grid capacities, leading to increase probability of load shedding events, reducing the productivity of renewable power plants.

In this perspective, an important role will be played by technologies which allow improving the dispatchability of non-programmable renewable power plants like wind parks.

While a classical approach to grid power modulation relies on gas turbines, an increasing attention is given nowadays to new technologies, not based on fossil fuels, specially focusing on the adoption of energy storage systems. Among these options, one of the most promising relies on the “power-to-gas” concept, which consists in producing hydrogen by water electrolysis and injecting it into the natural gas infrastructure, as currently considered by some research projects and demonstration-scale plants.

With respect to hydrogen storage technologies, this option limits the need of a local hydrogen storage reservoir, reducing the investment costs, improving the renewable fraction of gaseous fuels and allowing to oversize the renewable installed power with respect to the grid capacity.

In this work a preliminary investigation of the economic feasibility of this system is carried out, starting from the example of the forecasted scenario of wind power evolution in some EU countries. A statistical approach is applied in order to evaluate the error in energy production forecasts. As results, a preliminary sizing of the whole system is proposed, estimating the economic outlook, the possible annual energy and emission balances and the influence of the uncertainty in declared production from wind power plants.

A comparison with power modulation based on gas turbines is set up in order to evaluate which are the parameters that influence the economic viability of both solutions, evidencing the different operational criteria of the two systems and their impact on the dispatchability of energy.
Impact of Low-Rank Coal on Air-Blown IGCC Performance
Authors: Giuffrida Antonio
Published: September 2014

This paper presents simulation results of air-blown coal gasification-based combined cycles when using low-rank coals, by means of a previously realized thermodynamic model. In detail, besides considering a sub-bituminous coal, attention is also paid to a brown coal, pre-dried to reduce its high moisture content.

When gasifying a sub-bituminous as received coal the results highlight a slight reduction in IGCC LHV efficiency, with an absolute difference less than 1 percentage point if compared to the case with bituminous coal. This result is accomplished with an increase in net power output (almost 8 percentage points).

As concerns the brown coal, a pre-drying before gasification is considered because of its significant moisture content (65 wt%). In particular, three cases with different pre-drying levels are analyzed, with the highest residual moisture content limited to 30 wt%. Even considering an energy-saving technology as the fluidized bed dryer with integrated waste heat recovery, the specific demand for coal drying amounts to 2.1–2.3 percentage points referred to the (pre-dried) coal thermal input, seriously affecting both the final IGCC efficiency and its power output in comparison with the case of bituminous coal. Higher residual moisture in coal leads to lower IGCC efficiency, whereas the net power is always less than the one delivered by the plant with the sub-bituminous coal. However, comparing the cases with sub-bituminous coal and brown coal with the minimum moisture content (10 wt%), LHV and HHV efficiencies present opposite trends, since HHV efficiency for the case with brown coal is even better than with sub-bituminous coal.
Investigations on Stator Hub End Losses and its Control in an Axial Flow Compressor
Authors: George Kurian K. , Agnimitra Sunkara S. N. , George Jubin Tom , Joseph Melvin , Pradeep A. M. , Roy Bhaskar
Published: September 2014

In an axial flow compressor, the presence of separated flow near the hub-end of a stator would result in an overall loss in the performance. In the present paper, stator hub-stall is attempted to be eliminated for a high hub-tip ratio (0.8) axial flow compressor stage consisting of a highly loaded rotor and stator. Numerical and experimental studies on an untreated straight stator (straight-stacked, twisted) blade show a large vortex near its hub. The large vortex is attempted to be reduced by modifying the present blade by (i) providing an additional twist at the hub-end of the stator blade (ii) providing a hub-clearance (a cantilevered blade fixed from the casing). The straight (untreated) stator, hub-end-bend version and the hub-clearance version are studied for two different rotor-tip clearances. Detailed computational analysis of the variation of hub-clearance at a fixed rotor-tip clearance is also carried out. Throughout the study, experiments are carried out on the above discussed different stator (untreated & hub-treated) configurations, in combination with the same rotor, at a fixed rotor-tip clearance. The studies show that the flow conditions are improved near the hub of the highly loaded stator blade both by the hub-end-bend design and by the hub-clearance provided.
Design, Modeling and Experimentation of a Reversible HP-ORC Prototype
Authors: Dumont Olivier , Quoilin Sylvain , Lemort Vincent
Published: September 2014

This paper presents an innovative system comprising a heat pump connected to a solar roof and a geothermal heat exchanger. This heat pump is also able to invert its cycle and operate as an ORC. By using the whole rooftop (hereunder called “absorber”) as a heat source, a large amount of heat is generated throughout the year. This heat is used in priority to cover the building annual heating needs and the surplus heat generated during the summer is utilized to generate electricity in a so-called HP/ORC module. This paper will thus focus on these two main points: designing of the prototype and results from experimentation. This paper demonstrates the feasibility of such a prototype with encouraging performance in ORC and HP modes. Experimentally, a COP of 4.2 is reached in heat pump mode and a global efficiency of 5.6 is obtained in ORC mode. Possible means of improvement and perspectives are finally described.
Extensive Experimental Study of Circumferential Single Groove in an Axial Flow Compressor
Authors: Li Jichao , Lin Feng , Wang Sichen , Du Juan , Nie Chaoqun , Chen Jingyi
Published: September 2014

Circumferential single-groove casing treatment becomes an interesting topic in recent few years, because it is a good tool to explore the interaction between the groove and the flow in blade tip region. The stall margin improvement (SMI) as a function of the axial groove location has been found for some compressors, such a trend cannot be predicted by steady high-fidelity CFD simulations. Recent efforts show that to catch such a trend, multi-passage, unsteady flow simulations are needed as the stalling mechanism itself involves cross-passage flows and unsteady dynamics. This indicates a need to validate unsteady numerical simulation results. In this paper, an extensive experimental study of a total of fifteen single casing grooves in a low-speed axial compressor rotor is presented, the groove location varies from 0.4% to 98.3% of axial tip chord are tested. The unsteady pressure data both at casing and at the blade wake with different groove locations are measured and processed, including the movement of trajectory of tip leakage flow, the evolution of unsteadiness of tip leakage flow (UTLF), the unsteady spectrum signature during the stall process, and the outlet unsteady flow characteristic along the span. These data provide a case study for validation of the unsteady CFD results, and may be helpful for further interpretation on the stalling mechanism affected by circumferential casing grooves.
Approximation of the Porosity and Flow Resistance of Porous Ceramic and Their Influence on a Sound Absorption Model
Authors: Ries Hans-Christoph , Malangré Daniel , Eigenbrod Christian
Published: September 2014

Recently discussed sound absorption models for porous ceramic materials use porosity and flow resistance as variables. The prediction of the porosity and especially flow resistance of a porous ceramic is not trivial even though it was examined intensively. A particular issue is the use of porosity and flow resistance as variables without judging their likelihood, so that physically impossible combinations of porosity and flow resistance are calculated. To prevent this, a model is presented to predict the porosity and airflow resistance of a freeze cast ceramic with spherical pores provided by sacrificial templating. The model is validated by measurements of the flow resistance of ceramic samples with different porosity and pore–size distributions. An optimal sacrificial template diameter for the desired application is presented.
Feasibility Assessment for ORC Generation System Development Using Low Temperature Geothermal Water
Authors: Kho Seonghee , Ki Jayoung , Kang Myoungcheol
Published: September 2014

Since around 70°C of geothermal water exists in Seokmo-do of Republic of Korea, this study is to assess the feasibility of electricity generation by utilizing ORC system, and the pertinent economic impact.

It is generally believed that economic feasibility can be secured only when the source of geothermal water is above 100°C in order to generate electricity by operating ORC system.

However, there was an exceptional case that ORC system was commercialized by Pratt-Whitney for around 70 °C of geothermal water in the hot springs of Chena, Alaska.

The annual average temperature in the hot springs of Chena, Alaska is approximately 1°C whereas that of Seokmo-do is around 11°C, which makes 10°C of annual average temperature difference in operational environment between the two. Thus, the 2 phases of absorption refrigerating machine is considered for the ORC generation system.

With establishing ORC system in consideration of operational environment, the feasibility of the development of ORC system in Seokmo-do is assessed by performance analysis and economic feasibility.

As a result of the assessment, it is identified that the economic feasibility can be secured if the price of electricity is over $0.42/kWh same as that of photovoltaic generation as an incentive of the RPS program granted by the Korean government.
Comparison of a State of the Art and a High Stage Loading Rotor
Authors: Selic Thorsten , Lengani Davide , Schönleitner Florian , Marn Andreas , Broszat Dominik
Published: September 2014

This paper presents measurement results of a 1½ stage LPT test rig at Graz University of Technology incorporating two different rotor geometries: one with a regular blade loading and a second rotor with a highly loaded blade geometry. The test rig was designed in cooperation with MTU Aero Engines and represents the last 1.5 stages of a commercial aero engine. Considerable efforts were put on the adjustment of all relevant model parameters (Mach number, blade count ratio, airfoil aspect ratio, blade loading, etc.) to reproduce the full scale LPT situation. The rig diameter is approximately half of that of a commercial aero engine LPT. The number of blades and vanes for the two investigated stages as well as the pressure ratio and power output are identical, resulting in a decrease in rotational speed of the HSL rotor. Measurement data from a fast response pressure probe (FRAPP) is used to compare the flow fields of the two different stages.

The effect of the different stage designs can be seen when comparing the exit flow fields. The highly loaded stage shows a more pronounced tip leakage vortex compared to the datum stage. The highly loaded stage shows wider wakes with a lower total pressure deficit. The fluctuations of total pressure within the flow field are directly related to the upstream wake. If the measurement position is located within a stator wake, the fluctuations are significantly smaller than out of the wake.
Characterization of Advanced Combustor Cooling Concepts for Metallic Walls and Oxide Ceramic Matrix Composites in a Reacting Flow
Authors: Behrendt Thomas , Richter Tim , Söhngen Anna-Samira
Published: September 2014

Effusion or full-coverage cooling is a promising approach to cooling especially the walls of lean combustors where the cooling air consumption is to be reduced significantly. Due to typical velocity distributions and cooling air pressure drop in a combustor the effectiveness can be further increased by reducing the cooling air momentum. Double skin designs like impingement effusion cooling offer a significant improvement but at the drawback of a complex and expensive manufacturing process. In this contribution different advanced cooling concepts offering a similar reduction of the cooling air jet momentum in a single skin design for metal and ceramic walls are characterized under realistic conditions. Lateral trenches as well as effusion holes with 90° turns are used. Their total cooling effectiveness is compared to a plain single skin effusion cooling concept. A configuration with cooling air flowing parallel to the surface into lateral trenches revealed the highest and most uniform distribution of the cooling effectiveness. The metallic samples are manufactured using additive manufacturing offering additional degrees of freedom in the cooling design in comparison to conventional manufacturing techniques.
Thermodynamic Analysis of Innovative Micro Gas Turbine Cycles
Authors: Nikpey Homam , Mansouri Majoumerd Mohammad , Assadi Mohsen , Breuhaus Peter
Published: September 2014

The growing global energy demand has been faced with increasing concerns about climate change over recent decades. In order to cover the additional demand and to mitigate CO2 emissions, one option is to utilize renewable energies such as solar and wind power. These energy sources are, however, intermittent by nature. Therefore, it is inevitable that a quick balancing and back-up power should be available to maintain grid stability at a certain level.

Gas turbine (GT) technology could certainly be one alternative for back-up/balancing power and could be utilized to complement renewable energy in the energy market. However, the GT industry needs to consider innovative cycle configurations to attain higher system performance and lower emissions and to cope with renewable powers. In this regard, the humid air turbine (HAT) cycle and the exhaust gas recirculation (EGR) cycle are amongst the promising GT cycles.

In the current study a micro gas turbine (MGT), a Turbec T100, has been selected as the base case for further investigation. A thermodynamic model for the base case has been developed in IPSEpro software and validated using experimental data obtained from an existing test facility in Stavanger, Norway.

Based on this validated model, system performance calculations for other alternative cycles, i.e. EGR and HAT cycles, have been carried out. Results confirm that the performance improvement potential is significant for the HAT cycle with only minor modifications to the baseline MGT cycle. The EGR cycle, with a maximum attainable recirculation ratio of 50%, shows a slightly lower level of performance compared to the base case. However, its potential for future CO2 capture is greater compared to the base case and the HAT cycle. The overall cycle efficiencies for the base case, the HAT, and the EGR cycles at full load operation, i.e. 100kW power, are 31.1%, 32.8%, and 30.4%, respectively.
The Impact of Representative Aerodynamic Flow Fields on Liquid Fuel Atomisation in Modern Gas Turbine Fuel Injectors
Authors: Barker A. G. , Carrotte J. F.
Published: September 2014

In modern gas turbine engines swirl is typically imparted to the airflow as it enters the region of heat release to stabilize the flame. This swirling airstream is often highly turbulent and contains non-uniformities such as swirl vane wakes. However, it is within this environment that fuel atomization takes place. This paper is concerned with the potential effect of these airstream characteristics on the atomization process. Such a flow field is difficult to capture within simplified geometries and so measurements have been made within, and downstream of, injector representative geometries. This is experimentally challenging and required the application of a variety of techniques. The geometry considered is thought typical of an air-blast style injector, as may be used within current or future applications, whereby liquid fuel is introduced onto a pre-filming surface over which an airstream passes.

Data is presented which characterizes the atomizing airstream presented to the pre-filming region. This includes significant flow field non-uniformities and turbulence characteristics that are mainly associated with the swirling flow along with the vanes used to impart this swirl. The subsequent development of these aerodynamic features over the pre-filming surface is also captured with, for example, swirl vane wakes being evident through the injector passage and into the downstream flow field. It is argued these characteristics will be common to many injector designs. Measurements with and without fuel indicate the effect of the liquid film, on the non-dimensional aerodynamic flow field upstream of the pre-filming region, is minimal. However, the amount of airflow passing through the pre-filming passage is affected. In addition to characterization of the airstream, its impact on the liquid fuel film and its development along the pre-filming surface is visualized. Furthermore, PDA measurements downstream of the fuel injector (i.e. the injector ‘far-field) are presented and the observed spray characteristics spatially correlated with the upstream aerodynamic atomizing flow field. Hence for the first time a series of experimental techniques have been used to capture and correlate both near and far field atomization characteristics within an engine representative aerodynamic flow field.
The Oxy-Fuel, Supercritical CO2 Allam Cycle: New Cycle Developments to Produce Even Lower-Cost Electricity From Fossil Fuels Without Atmospheric Emissions
Authors: Allam R. J. , Fetvedt J. E. , Forrest B. A. , Freed D. A.
Published: September 2014

The Allam Cycle is a new, high-pressure, oxy-fuel, supercritical CO2 cycle that generates low-cost electricity from fossil fuels while producing near-zero air emissions; all CO2 generated by the system is produced as a high-pressure, pipeline-ready by-product for use in enhanced oil recovery, industrial processes, or sequestration.

The base cycle was developed by 8 Rivers Capital and is being commercialized by NET Power, LLC in partnership with Toshiba Corporation, Exelon Corporation, and CB&I. The four parties are currently developing a natural gas-fired power plant to demonstrate this system. Target net efficiencies for the natural gas and coal versions of this cycle, based on current process modeling, are 59% and 52% (LHV) respectively, both with full carbon capture and no other air emissions. Detailed designs indicate that NET Power plants, with full carbon capture, will produce lower-cost electricity than state-of-the-art fossil fuel plants without CCS.

8 Rivers Capital continues to develop on top of the Allam Cycle platform. Building upon the original single turbine design, 8 Rivers has developed a two-turbine design that combines the benefits of the original, high-pressure Allam Cycle with a low-pressure reheat cycle. This new design can enable Allam Cycle-based plants to greatly increase power output with only a moderate increases in capital cost, substantially lowering the overall plant $/kW cost. Such a configuration would enable Allam Cycle plants to produce even lower-cost electricity than the single turbine Allam Cycle design currently being commercialized by NET Power, CB&I, Toshiba and Exelon. This paper outlines the design considerations utilized for the base Allam Cycle development and then details this new cycle design and its potential benefits.
Microstructure Analysis of Broached Inconel-718 Gas Turbine Disc Fir-Trees
Authors: Rosenbaum A. , Chamanfar A. , Jahazi M. , Bonakdar A.
Published: September 2014

Broaching has long been used for machining of fir-trees in gas turbine discs. The fir-tree arrangement is employed for mechanical attachment of blades to disc. Surface and subsurface microstructure changes induced by broaching affect the fatigue resistance of the disc. Therefore, a reliable and quantitative microstructure mapping of the broached fir-trees is essential for the basic optimization of the broaching process. In this study, the microstructure of the surface and subsurface layers of fir-trees in an industrial gas turbine Inconel-718 disc has been analyzed using optical microscopy and scanning electron microscopy. The focus has been on the characterization of defects generated by broaching at the surface and subsurface layers of fir-trees. Also, characterization of the grain size, γ″, γ′, and δ particles from the broached surface to the parent material has been carried out. Characteristics of these microstructural features are key inputs for the development of material based FEM models predicting the fatigue life of the disc. From microstructure studies, the presence of defects such as plucking and distorted layer was observed. The characteristics of these defects (size and morphology) were compared with those of the design limits determined by gas turbine engine manufacturer. Furthermore, significant variation in the volume fraction of δ particles was observed in the area affected by broaching compared with the parent material. These observations are related to the thermomechanical history of the material during the broaching process. Finally, the impact of microstructure evolution on microhardness variation from the broached surface to the parent material is discussed.
A Robust Mixing Plane Method and its Application in 3D Inverse Design of Transonic Turbine Stages
Authors: Ray Saurya Ranjan , Zangeneh Mehrdad
Published: September 2014

A robust mixing plane method satisfying interface flux conservation, non-reflectivity and retaining interface flow variation; valid at all Mach numbers and applicable for any machine configuration is formulated and implemented in a vertex based finite volume solver for flow analysis and inverse design of turbomachinery stage configurations. The formulation is based on superposing perturbed flow variables in the form of 3D characteristics obtained along the flow direction on the exchanged mixed out average quantities at the stage interface. A condition is derived in the mixed-out averaging procedure to distinguish between the subsonic and supersonic flow conditions at the interface. Using preconditioning technique, the new functionality is demonstrated to be applicable for a wide range of interface conditions and over different machine configurations with small spatial gap across the blade rows. The method is shown to satisfy flux conservation across the interface without generating spurious oscillations in the flow field at the domain boundaries and validated against available commercial solvers.

Subsequently, a blade re-design approach in a multi-row configuration is conceptualised and demonstrated by the application of the 3D inverse design method on a single stage Low Pressure Turbine. Meridional load variation, stage reaction and blade stacking angle are considered as the design variables to explore the design space. Conducting design runs at a fixed mass flow boundary condition and similar overall loading condition; the optimised configuration is shown to satisfy redistributed meridional load, providing performance improvement while maintaining a similar level of flow rate and work extraction as the baseline configuration.
Effects of Endwall Boundary Layer Thickness and Blade Tip Geometry on Flow Through High Pressure Turbine Passages
Authors: Volino Ralph J.
Published: September 2014

Experiments were conducted in a linear high pressure turbine cascade with an adjustable tip gap at one endwall. The cascade included a wake generator with moving rods that simulated the effect of an upstream vane row. Cases were documented with no tip gap, a gap of 1.5% of axial chord, and a gap of 3.8% of chord. Cases with flat blade tips were considered with thick and thin endwall boundary layers. Cases with flat tips and squealer tips were documented with the thin endwall boundary layer. For all cases data were acquired both with and without upstream wakes. Documentation included total pressure loss fields in the endwall region and corresponding velocity fields acquired using particle image velocimetry (PIV). The PIV measurements showed the various vortices in the flow field and their response to unsteady wakes. The strength and position of the vortices were directly related to regions of high total pressure loss. Reducing the endwall boundary layer thickness tended to reduce losses, but also resulted in increased leakage flow, which increased losses, particularly in cases with a large tip gap. The squealer tip reduced losses compared to the flat tip cases.
Successfully Validated Combustion System Upgrade for the SGT5/6-8000H Gas Turbines: Technical Features and Test Results
Authors: Janus Bertram , Bigalk Joachim , Helmers Lennard , Witzel Benjamin , Ghermay Yohannes , Huth Michael , Johnson Cliff , Landry Kyle , Sunshine Robert
Published: September 2014

An upgrade of the lean premixed combustion system installed in the SGT5-8000H in Irsching/Germany was developed for the 50 Hz and 60 Hz versions of the SGTX-8000H gas turbines. It features lower CO and NOx emissions by improving combustion aerodynamics and reduction of the air consumption of the combustion system.

Furthermore an improved secondary air managing system increases the amount of air, which can be supplied in a controllable way to the turbine in part load operation and, thus, increases the combustor temperature. This is done in stepwise increasing the air mass flow to the turbine by feeding compressor exit air to different distinct turbine stages. All in all this system extends the turn down capability beyond the level achievable by the new combustion system alone.

The new combustion system and the secondary air managing system were installed in full scale and tested in the SGT6-8000H test facility of the Siemens Gas turbine plant in Berlin.

The results have subsequently successfully been validated in the first commercial application on a customer site.

This paper presents the technical features of the systems, the development program and the test results.
The Effects of Turbulence Length Scale on Turbulence and Transition Prediction in Turbomachinery Flows
Authors: Bode Christoph , Aufderheide Thorben , Kožulović Dragan , Friedrichs Jens
Published: September 2014

An approach for estimation of the turbulence length scale at the inflow boundary is proposed and presented. This estimation yields reasonable turbulence decay, supporting the transition model in accurately predicting the laminar-turbulent transition location and development. As an additional element of the approach, the sensitivity of the turbulence model to free-stream values is suppressed by limiting the eddy viscosity in non-viscous regions. Therefore the well known realizability constraint after Durbin [1] is modified. The method is implemented in DLR’s turbomachinery flow solver TRACE in the framework of the k–ω turbulence model by Wilcox [2] and the γ–Reθ transition model by Langtry and Menter [3]. The improved model is tested to the T106A turbine testcase and validated at the T161 turbine cascade under low speed conditions and T170 turbine cascade at high speed conditions.
A Grey-Box Identification Approach for Thermoacoustic Network Models
Authors: Jaensch S. , Emmert T. , Silva C. F. , Polifke W.
Published: September 2014

This work discusses from a system theoretic point of view the low order modeling and identification of the acoustic scattering behavior of a ducted flame.

In this context, one distinguishes between black-box and grey-box models. The former rely on time series data only and do not require any physical modeling of the system that is to be identified. The latter exploit prior knowledge of the system physics to some extent and in this sense are physically motivated.

For the case of a flame stabilized in a duct, a grey-box model is formulated that comprises an acoustic part as well as sub-models for the flame dynamics and the jump conditions for acoustic variables across the region of heat release. Each of the subsystems can be modeled with or without physical a priori knowledge, in combination they yield a model for the scattering behavior of the flame.

We demonstrate these concepts by analyzing a CFD model of a laminar conical premixed flame. The grey-box approach allows to optimize directly the scattering behavior of the identified model. Furthermore, we show that the method allows to estimate heat release rate fluctuations as well as the flame transfer function from acoustic measurements only.
Assessing the Potential of Gas-Recuperation in Reheated Gas Turbines Within Combined Gas-Steam Power Plants
Authors: Doligalski Adam , Sanchez de Leon Luis , Zachos Pavlos K. , Pachidis Vassilios
Published: September 2014

This paper presents a comparative analysis between two different gas turbine configurations for implementation within combined cycle power plants, aiming to downselect the most promising one in terms of thermal efficiency at design point. The analysed gas turbines both feature the same dual-pressure steam bottoming cycle, but differ in the gas turbine cycle itself: the first configuration comprises a single-shaft reheated gas turbine with variable position of the reheater (representative of the current approach of the industry to combined cycle power plants), whilst the second configuration comprises a dual-shaft reheated-recuperated engine with free power turbine. Comparison of the two competing gas turbine configurations is conducted by means of systematic exploration of the combined cycle design space. The analysis showed that the reheated-recuperated configuration delivers higher thermal efficiency than the more conventional reheated (non-recuperated) gas turbine and is identified, therefore, as a competitive option for future combined cycle power generation systems.
Stabilizing a 46 MW Multi-Stage Utility Steam Turbine Using Integral Squeeze Film Bearing Support Dampers
Authors: Ertas Bugra , Cerny Vaclav , Kim Jongsoo , Polreich Vaclav
Published: September 2014

A 46 MW 5,500 rpm multistage single casing utility steam turbine experienced strong subsynchronous rotordynamic vibration of the first rotor mode; preventing full load operation of the unit. The root cause of the vibration stemmed from steam whirl forces generated at secondary sealing locations in combination with flexible rotor-bearing system. Several attempts were made to eliminate the subsynchronous vibration by modifying bearing geometry and clearances, which came short of enabling full load operation.

The following paper presents experimental tests and analytical results focused on stabilizing a 46 MW 6,230kg utility steam turbine experiencing subsynchronous rotordynamic instability. The paper advances an integral squeeze film damper (ISFD) solution, which was implemented to resolve the subsynchronous vibration and allow full load and full speed operation of the machine. The present work addresses the bearing-damper analysis, rotordynamic analysis, and experimental validation through waterfall plots, and synchronous vibration data of the steam turbine rotor. Analytical and experimental results show that using ISFD improved the stability margin by a factor of 12 eliminating the subsynchronous instability and significantly reducing critical speed amplification factors. Additionally, by using ISFD the analysis showed significant reduction in interstage clearance closures during critical speed transitions in comparison to the hard mounted tilting pad bearing configuration.