bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards Low-NOx Operation in a Complex Burner: Optimization of an Annular Trapped Vortex Combustor
Authors: Xavier Pradip , Renou Bruno , Cabot Gilles , Boukhalfa Mourad A. , Cazalens Michel
Published: November 2013

This paper focuses on optimizing an innovative annular Lean Premixed staged burner, following the Trapped Vortex Combustor concept. The latter consists of a lean main flame stabilized by passing past a rich cavity pilot flame. Unfortunately, this configuration is highly sensitive to combustion instabilities and the flame is not well stabilized. This work consists of adjusting aerodynamic variables, chemical parameters and burner geometry to reach a “low-NOx” operation while reducing other pollutants and getting a stable flame. Results show that stability is reached when mass transfers between main and cavity zones are reduced. Then, the main bulk velocity is increased to reduce the cavity thermal expansion, due to the hot gas expansion. In addition, the cavity flow rate is reduced to prevent from penetrating and disturbing the main flow. Re-arranging injections in the cavity also avoid local unsteady equivalence ratios, which creates an unsteady heat release and combustion with pulses. Regarding NOx, a leaner main flame combined with a sufficiently rich cavity mixture creates local stoichiometric zones at the interface between the cavity and the main zone. The latter point is found to be a good anchoring mechanism. Compared with the original configuration, a stable point of operation is found: acoustic energy is reduced by an order of 100, NOx level is less than 0.4 g/kgfuel, CO is cut by 93% with no more Unburned Hydro-Carbons.
Investigations on Nusselt Number Enhancement in Ribbed Rectangular Turbine Blade Cooling Channels of Different Aspect Ratios and Rotation Numbers
Authors: Nouri Behnam , Lehmann Knut , Kühhorn Arnold
Published: November 2013

In the drive for higher cycle efficiencies in gas turbine engines, turbine blades are seeing an increasingly high heat load. This in turn demands improvements in the internal cooling system and a better understanding of both the level and distribution of the internal heat-transfer. A typical approach to enhance the internal cooling of the turbine blade is by casting angled ‘low blockage’ ribs on the walls of the cooling channels. The objective of the present paper is to determine the detailed Nusselt number distribution in rectangular internal channels with ribs. This knowledge can be used to guide the overall design e.g. to achieve high levels of heat-transfer where required. The effects of rotation as well as the interaction effects of the position and direction of ribs on opposite walls of the cooling channel have been investigated.

Numerical calculations have been carried out using the commercial CFD code Fluent to investigate the local Nusselt number enhancement factor in rectangular ducts of different aspect ratios (0.5, 1 and 2) which have 45° or 90° angled ribs located on two opposite walls. This has been studied for different Rotation number Ro (0–0.45) and with a Reynolds number >30000.

The first series of studies has been carried out with the same experimental setup as by Han [1]. The geometry was slightly changed to avoid the effect of high heat transfer at the entry.

This study identifies important vortical structures, which are dependent on the direction and the position of the ribs. This has a profound effect on the distribution of heat-transfer within the passage. It is shown that the two smooth walls of the duct have different average Nusselt number ratio Nu/NuFD enhancement depending on the rib angle.

In addition, based on numerical investigations, simple correlations have been developed for the rotational influence of the internal Nusselt number distribution. A major finding is that the effect of rotation is dominant for low aspect ratio channels and the local enhancement due to the rib position and angle is more dominant for high aspect ratio channels.
A Novel Method for Improvement of Aerodynamic Performance of Highly Loaded LP Turbine Airfoils for Aeroengines
Authors: Funazaki K. , Okamura K. , Ebina Y. , Sato Y. , Kosugi T. , Takahashi A. , Mamada A.
Published: November 2013

This paper proposes a novel method to improve aerodynamic performance of highly loaded Low-Pressure (LP) turbine airfoils for aeroengines over a relatively wide range of Reynolds number. This new method employs two types of approaches; one is the equipment of two-dimensional contouring with small step on the suction surface of the airfoil and the other approach is a re-shaping of the airfoil near the trailing edge. A linear cascade test facility is employed to investigate the aerodynamic performance of the newly proposed airfoils by use of a miniature Pitot probe. Suction surface boundary layers as well as airfoil wakes are also measured using a hot wire probe. In the experiment, various flow conditions, Reynolds number, wake-passing Strouhal number, are examined. Numerical simulations are carried out to have a better understanding of the flow field around the airfoil. URANS and LES are employed for this purpose. It is found that the proposed method has a capability to reduce the profile loss to some extent.
Experimental Investigation on the Heat Transfer of a Leading Edge Cooling System: Effects of Jet-to-Jet Spacing and Showerhead Extraction
Authors: Facchini Bruno , Maiuolo Francesco , Tarchi Lorenzo , Ohlendorf Nils
Published: November 2013

An experimental survey of a leading edge cooling scheme was performed to measure the Nusselt number distribution on a large scale test facility simulating the leading edge cavity of a pressure turbine blade. Test section is composed by two adjacent cavities, a rectangular supply channel and the leading edge cavity. The cooling flow impinges on the concave leading edge internal walls, by means of an impingement array located between the two cavities, and it is extracted through shower-head and film cooling holes. The impingement geometry is composed of a double array of circular holes. The aim of the present study is to point out the effects on the heat transfer coefficient of the radial jet pitch (y/d = 3 to 5) and the tangential jet pitch (x/d = 3 to 5). Moreover the influence of the shower-head extraction on the heat transfer distribution is investigated. Measurements were performed by means of a transient technique using narrow band Thermo-chromic Liquid Crystals (TLC). Jet Reynolds number was varied in order to cover the typical engine conditions of these cooling systems (Rej = 15000–45000). Results are reported in terms of detailed 2D maps, radial and tangential averaged Nusselt numbers.
Thermodynamic Optimization of Recuperated S-CO2 Brayton Cycles for Solar Tower Applications
Authors: Mohagheghi Mahmood , Kapat Jayanta
Published: November 2013

Supercritical carbon dioxide (S-CO2) Brayton cycle represents significant advantages in solar tower application. Various configurations of S-CO2 Brayton cycle employing recuperation, recompression, intercooling and reheating have been investigated. The thermodynamic performance of each cycle configuration is optimized by using Genetic Algorithm in which the maximum cycle efficiency is defined as the objective function. The optimization process is comprehensive, i.e., the decision variables such as temperature and pressure of turbines, compressors, re-heaters, inter-coolers, and the pinch point temperature difference are optimized simultaneously. The recompression inlet temperature and mass flow fraction are also optimized along with other decision variables where that is the case. The main limiting factors in the optimization process are maximum cycle temperature, minimum heat rejection temperature, and pinch point temperature difference. The maximum cycle pressure is also a limiting factor in all studied cases except the simple recuperated cycle. The optimized cycle efficiency can vary from 55.77% to 62.02% where the highest value is obtained for the recompression recuperated cycle with reheating and intercooling. The optimization is based on thermodynamic analysis only, even though decision making for practical systems should be based on thermo-economic optimization.
Noise Test of Revised Notched Nozzle Using a Jet Engine
Authors: Ishii Tatsuya , Tanaka Nozomi , Oishi Tsutomu , Ishii Yutaka
Published: November 2013

This paper describes engine noise tests conducted in an outdoor environment using a revised notched nozzle. A notch is a small dent formed at the nozzle edge that penetrates into the primary jet. The notched nozzle is expected to improve the acoustic performance with less deterioration in aerodynamic performance relative to that of a conventional nozzle. The slight penetration of the notch causes small disturbances immediately after the nozzle, driving the subsequent mixing process in the shear layer. This mixing process helps suppress both large-scale vortices in the far downstream region and excessive shear stress near the nozzle.

The authors have researched and developed various notched nozzles. Previous engine tests using a 6-notched nozzle showed that the notch itself caused additional noise by increasing the sound pressure level at higher frequencies. To counter this problem, a revised 18-notched nozzle was developed through computational and experimental studies. The authors’ previous paper [Ishii, et al.; ASME Paper GT2012-69507, 2012] showed that this nozzle increased the noise reduction toward the side direction of the nozzle under hot-jet conditions. However, there remain some unsolved issues. One issue is the scale of the nozzle. Another issue is the test conditions, such as the different effective cross-sectional areas.

In this light, a larger-scale nozzle with a diameter five times larger than that in the hot-jet model was prepared so as to adjust the nozzle aerodynamic performance. Noise tests of this nozzle were carried out using a turbojet engine together with far-field and phased array microphones, and the revised notched nozzle was found to show improved noise reduction performance compared to the previous design.
Experimental Analysis of V- to M-Shape Transition of Premixed CH4/H2/Air Swirling Flames
Authors: Guiberti T. F. , Zimmer L. , Durox D. , Schuller T.
Published: November 2013

Lean premixed swirling flames stabilized at the sudden expansion of a combustion chamber generally take a V or a M shape, depending on the burner geometry and flow conditions. It is not rare to observe transitions between these shapes as operating conditions of the combustor are modified, but the governing mechanisms of these transitions are not well understood. An experimental study is conducted to analyze the transition from an initially V-shaped flame to a M-shaped flame for swirling flames fed by CH4/H2/air mixtures anchored on a central bluff body when flow conditions and geometrical elements of the combustor are modified. Two situations are identified depending whether strong flame wall interactions take place at the quartz tube confining the flame. When the V-flame front is impinging and quenched at the combustion chamber wall, the transition to a M-shape is triggered by a flashback mechanism along the wall followed by the propagation of the flame tip along the outer shear-layer of the swirling jet in the direction of the external rim of the burner. This mechanism is controlled by the mixture Lewis number, a Karlovitz number based on the velocity gradient at the combustor wall, the swirl imparted to the flow and the cross section area ratio between the injection unit and combustion chamber defining a confinement ratio. Experiments conducted at a given mixture Lewis number indicate that the onset of flashback is determined by decreasing the Karlovitz number under a critical value. It is shown that this critical value decreases when the Lewis number increases, but it also depends on the confinement ratio and swirl number. In the absence of direct interaction between the V-flame tip and the chamber wall, the situation differs and this flashback mechanism along the combustion chamber wall ceases. Attempts are made in this case to identify the governing parameters triggering the V- to M-shape transition for small confinement ratios.
Statistical Methods for a Stochastic Analysis of the Secondary Air System of a Jet Engine Low Pressure Turbine
Authors: Antinori Giulia , Muller Yannick , Duddeck Fabian , Fischersworring-Bunk Andreas
Published: November 2013

In this paper several stochastic methods are evaluated with respect to their applicability for the analysis of fluid networks. The methods are applied for the analysis of a 1D flow model of the Secondary Air System (SAS) of a three stages low pressure turbine (LPT) of a jet engine.

The stochastic analysis is comprised of a sensitivity analysis followed by an uncertainty analysis. The sensitivity analysis is performed to gain a better understanding of the SAS physics and robustness, to identify the important variables and to reduce the number of parameters involved in the simulations for the uncertainty analysis. The uncertainty analysis, using probability distributions derived from the manufacturing process, allows to determine the effect of the input uncertainties on responses such as pressures, fluid temperatures and mass flow rates.

A review of the most common and relevant sampling methods is performed. A comparison of the respective computational cost and of the sample points distribution is proposed with the aim of finding the most suited method. The study shows that some of the sampling methods can not be recommended since they produce spurious correlations between independent input variables.

With regards to the sensitivity analysis, many literature sources state that the Pearson correlation method is only valid for linear models when assessing the importance of input variables. As the SAS is highly non-linear, non-parametric variance based methods are introduced here to make up for the limitations of the correlation method. Following the results of the study, it is recommended to combine the sampling method with a non-parametric variance based method. Thus, the main effects as well as all the interactions among variables are captured.
Heat-Flux Measurements for a Realistic Cooling Hole Pattern With Multiple Flow Conditions
Authors: Nickol Jeremy B. , Mathison Randall M. , Dunn Michael G.
Published: November 2013

Predicting cooling flow migration and its impact on surface heat flux for a turbine operating at design-corrected conditions is a challenging task. While recent data sets have provided a baseline for comparison, they have also raised many questions about comparison methods and the proper implementation of boundary conditions. Simplified experiments are helpful for bridging the gap between the experimental and computational worlds to develop the best procedures for generating predictions and correctly comparing them to experiments. To this end, a flat-plate configuration has been developed that replicates the cooling hole pattern of the pressure side of a high-pressure turbine blade.

The heat transfer for this configuration is investigated for a range of flow properties of current interest to the industry using a medium-duration blowdown facility. Heat-flux measurements are obtained using double-sided Kapton heat-flux gauges arrayed in two rows in the axial direction along the centerline of the hole pattern. Gauges are located upstream of the holes, in between rows of holes, and extending far downstream of the last row of holes. New parameters are proposed for analyzing the data including a corrected Stanton number and the length-corrected heat flux reduction parameter. These parameters are used for exploring the influence of Reynolds number and blowing ratio on local heat transfer. In addition, the temperatures of the main flow and the test section walls were varied to determine the effect of cooling on the local adiabatic wall temperature and to enable comparisons using the adiabatic cooling effectiveness.
A CFD Evaluation of Multiple RANS Turbulence Models for Prediction of Boundary Layer Flows on a Turbine Vane
Authors: Dyson Thomas E. , Bogard David G. , Bradshaw Sean D.
Published: November 2013

There is a growing trend toward the use of conjugate CFD for use in prediction of turbine cooling performance. While many studies have evaluated the performance of RANS simulations relative to experimental measurements of the momentum boundary layer, no studies have evaluated their performance in prediction of the accompanying thermal boundary layer. This is largely due to the fact that, until recently, no appropriate experimental data existed to validate these models. This study compares several popular RANS models — including the realizable k-ε and k-ω SST models — with a four equation k-ω model (“Transition SST”) and experimental measurements at selected positions on the pressure and suction sides of a model C3X vane. Comparisons were made using mean velocity and temperature in the boundary layer without film cooling under conditions of high and low mainstream turbulence. The best performing model was evaluated using modification of the turbulent Prandtl number to attempt to better match the data for the high turbulence case. Overall, the models did not perform well for the low turbulence case; they greatly over-predicted the thermal boundary layer thickness. For the high turbulence case, their performance was better. The Transition SST model performed the best with an average thermal boundary layer thickness within 15% of the experimentally measured values. Prandtl number variation proved to be an inadequate means of improving the thermal boundary layer predictions.
Adiabatic and Overall Effectiveness for a Fully Cooled Turbine Vane
Authors: Dyson Thomas E. , McClintic John W. , Bogard David G. , Bradshaw Sean D.
Published: November 2013

Adiabatic and overall effectiveness data were measured for a fully cooled, scaled up turbine vane model in a low speed linear cascade with a chord-exit Reynolds number of 700,000. The overall effectiveness is a measure of the external surface temperature relative to the mainstream temperature and the inlet coolant temperature, and consequently is a direct measure of how effectively the surface is cooled. This can be determined experimentally when the experimental model is constructed so that the Biot number of the model and the ratio of the external to internal heat transfer coefficient are chosen so that the model has a similar thermal behavior to that of an actual engine component. The model used in this study had a cooling design that consisted of 149 total coolant holes in 13 rows, including a showerhead containing five rows of holes. The model also incorporated an internal impingement cooling configuration. An identical model was also constructed out of low conductivity foam to measure adiabatic effectiveness. This is the first study to use a large scale, matched Biot number model to measure engine representative overall effectiveness for a vane employing full coverage film cooling. The focus of this research was to determine the relative contributions of the external and internal cooling, and to serve as a baseline for validation of computational simulations. Additionally, a simplified model using measurements of overall effectiveness with internal cooling alone was used to predict overall effectiveness downstream of the showerhead.
Endwall Heat Transfer Measurements of an Outlet Guide Vane at On and Off Design Conditions
Authors: Wang Lei , Sundén Bengt , Chernoray Valery , Abrahamsson Hans
Published: November 2013

The endwall heat transfer characteristics of forced flow past outlet guide vanes (OGVs) in a linear cascade have been investigated by using a liquid crystal thermography (LCT) method. The Reynolds number is kept at 250,000 and both on- and off-design conditions are tested. For the on-design condition where the incidence angle of OGVs is 30°, no obvious flow separation phenomenon was observed; on the contrary, for the off-design conditions where the incidence angle of OGVs is 0° and −31°, respectively, remarkable flow separation was noticed. The results indicate that the incidence angle of OGVs has a significant effect on the endwall heat transfer. In general, the endwall heat transfer coefficients for the off-design conditions are higher than the corresponding on-design condition. In addition, a preliminary CFD analysis was performed and presented. Basically, the results are consistent with the experiments but further investigations are needed in the future work.
Highest-Efficient Film Cooling by Improved NEKOMIMI Film Cooling Holes: Part 2 — Hot Gas Flow Conditions
Authors: Kusterer Karsten , Tekin Nurettin , Kasiri Azadeh , Bohn Dieter , Sugimoto Takao , Tanaka Ryozo , Kazari Masahide
Published: November 2013

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result to an increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. It is common knowledge today that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also mentioned as kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-counter-rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRV. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The original configuration was found to be difficult for fabrication by advanced machining processes. Thus, the improvement of this configuration has been reached by a set of geometry parameters, which lead to configurations easier to be manufactured but preserving the principle of the NEKOMIMI technology. Within a numerical parametric study several advanced configurations have been obtained and investigated under hot gas flow conditions. By systematic variation of the parameters a further optimization with respect to highest film cooling effectiveness has been performed. The best configuration outperforms the basic configuration by more than 20% regarding the overall averaged adiabatic film cooling effectiveness.
Impact of Defects and Damage in Aircraft Engines on the Exhaust Jet
Authors: Adamczuk Rafael R. , Buske Clemens , Roehle Ingo , Hennecke Christoph , Dinkelacker Friedrich , Seume Joerg R.
Published: November 2013

The inspection of aero engines is a complex and time-consuming process, often requiring the disassembling of the engine or boroscopic examinations. The development of a method to locate and characterize defects and damage at an early stage, without disassembling the engine would accelerate the inspection process. For that purpose, the spatial density distribution pattern of the exhaust jet of aircraft engines may be measured with the Background Oriented Schlieren method (BOS). The hypothesis is that defects in the hot gas path have a noticeable impact on the density pattern of the exhaust jet. To establish the connection between defects and measurable patterns, in the present paper numerical simulations of an aero engine are performed including three potential defects. Non-uniformities resulting from a burner malfunction, the increase of the radial gap between blade tip and casing as well as burned trailing edges are propagated with only small degree of dispersion through the turbine and reach the engine exit. The paper shows that each considered defect results in a different exhaust density pattern.
Techno-Economic Comparison of CO2 Capture Technologies Employed With Natural Gas Derived GTCC
Authors: Atsonios Kostantinos , Koumanakos Antonios , Panopoulos Kyriakos D. , Doukelis Aggelos , Kakaras Emmanuel
Published: November 2013

Carbon Capture and Storage can either concern the removal of carbon as CO2 in flue gases (post-combustion option) or before its combustion in a Gas Turbine (pre-combustion option). Among the numerous CO2 capture technologies, amine scrubbing (MEA and MDEA), physical absorption (Selexol™ and Rectisol™) and H2 separator membrane reactors are investigated and compared in this study. In the pre-combustion options, the final fuel combusted in the GT is a rich-H2 fuel. Process simulations in ASPEN Plus™ showed that the case of H2 separation with Pd-based membranes has the greatest performance as far as the net efficiency of the energy system is concerned. The economic assessment reveals that the technology is promising in terms of cost of CO2 avoided, provided that the current high membrane costs are reduced.
Unsteady Simulations of a Counter-Rotating Aspirated Compressor
Authors: Knapke Robert D. , Turner Mark G.
Published: November 2013

An unsteady analysis of the MIT counter-rotating aspirated compressor (CRAC) has been conducted using the Numeca FINE™/Turbo 3D viscous turbulent solver with the Non-Linear Harmonic (NLH) method. All three blade rows plus the aspiration slot and plenum were included in the computational domain. Both adiabatic and isothermal solid wall boundary conditions were applied and simulations with and without aspiration were completed. Comparison of the aspirated case with data is good. When compared to the adiabatic boundary condition, the isothermal boundary condition solutions showed improvements in predicting stage performance, most notably at the endwalls. The aspiration has a significant impact on the flow field and provides a 4.2% increase in efficiency over the non-aspirated case. Although the slot and plenum had been designed to aspirate 1% of the inlet mass flow, the experiment and simulations show that it chokes at about 0.5%. Details of the aspiration flow path choking mechanism, which was previously not well understood, are presented.
Unsteady Flow Features and Vibration Stresses of an Actual Size Steam Turbine Last Stage in Various Low Load Conditions
Authors: Shibukawa Naoki , Iwasaki Yoshifumi , Watanabe Mitsunori
Published: November 2013

Experimental investigations with a six stage real scale low pressure steam turbine operated at a very low load conditions are presented in this paper. Although the tested 35 inch last stage blades are circumferentially coupled at both tip and mid span with an intention to reduce the vibration stress, still its increase was observed at extremely low load condition.

The pressure fluctuations were measured by several silicon diaphragm sensors which were mounted on both inner and outer casings of the stator inlet, exit and blade exit position. The measurement of the vibration stress was performed by strain gauges on several blades.

The power spectra of unsteady pressures were precisely investigated considering both their location and steam flow condition. And the results implied that huge reverse flow and re-circulation started in the same location as a blade-to-blade CFD predicted. In terms of the correlation between vibration stress and the flow feature, the pressure fluctuation around the blade tip produces dominant effects on the vibration stress.

The unsteady pressure frequency were also investigated and compared with those of the blade resonance and rotational speed. Basic trends observed in the results are similar to what other researchers reported, and on top of that, the continuous trends of pressure fluctuation and blade vibration stress were systematically investigated. Even the wall pressure, not the pressure on blade surface, showed the effective fluctuations which excited the several nodes of natural frequencies of the last stage blade.

A series of FFT of fluid force by a full annulus quasi-steady CFD simulation seems to predict dominant mode of the excitation which account for the behavior of vibration stresses. The mechanism of the rapid stress increase was examined by considering CFD results and measured unsteady pressure data together.

As the test facility takes a responsibility as an independent power producer, the tests were conducted in real plant operations which include multi stage effects, inlet distortions, Reynolds Number effect and so on. The obtained data and the particular indicator of vibration stress increase can be used as a part of design tool validation with neither aerodynamic nor mechanical corrections.
Flow and Heat Transfer Characteristics in Latticework Cooling Channels With Dimple Vortex Generators
Authors: Rao Yu , Zhang Xiang , Zang Shusheng
Published: November 2013

A comparative numerical study has been conducted on the flow and heat transfer characteristics in the latticework cooling structure with three different subchannel configurations: rectangular subchannels, U shaped subchannels and U shaped subchannels with dimple vortex generators. Experiments have been conducted using the latticework structure with U shaped subchannels with dimples. The comparisons between the experimental and numerical data have shown that the numerical computation model can reasonably well predict the heat transfer and pressure loss in the latticework cooling channels. The computation results showed that the latticework cooling structure has significantly enhanced heat transfer performance, and remarkably increased heat transfer area. Over the Reynolds number range of 7,696–36,985, depending on the geometry of the subchannels the average Nusselt number of the latticework channel is about 1.9–2.3 times that of a smooth channel, but the friction factor is about 6.4–11.1 times that of a smooth channel. The U shaped subchannels with dimples provide the greatest heat transfer enhancement and the most uniform heat transfer both axially and laterally, whose average Nusselt number is about 16.0% higher than the other two subchannels. Compared to the U subchannel, the dimples in the U subchannels work as vortex generators and provide additional heat transfer enhancement, whereas distinctively increase the pressure loss. Compared to the latticework cooling with U subchannels, the latticework cooling with rectangular subchannels shows similar average heat transfer the latticework cooling with rectangular subchannels shows similar average heat transfer and pressure loss performance.
Aero-Thermal Optimization and Experimental Verification for the Discrete Film Cooling of a Turbine Airfoil
Authors: El Ayoubi Carole , Hassan Othman , Ghaly Wahid , Hassan Ibrahim
Published: November 2013

The optimization aims to maximize the film cooling performance while minimizing the corresponding aerodynamic penalty. The film cooling performance is assessed using the adiabatic film cooling effectiveness, while the aerodynamic penalty is measured with a mass-averaged total pressure loss coefficient. Two design variables are selected; the coolant to mainstream temperature ratio and total pressure ratio. Two staggered rows of discrete cylindrical film cooling holes on the suction surface of a turbine vane are considered. The effect of varying the coolant flow parameters on the adiabatic film cooling effectiveness and the aerodynamic loss is analyzed using the optimization method and three-dimensional Reynolds-averaged Navier-Stokes (RANS) simulations. The CFD predictions of the adiabatic film cooling effectiveness and aerodynamic performance are assessed and validated against corresponding experimental measurements. The optimal solutions are reproduced in the experimental facility and the Pareto front is substantiated with experimental data. A non-dominated sorting genetic algorithm (NSGA-II) is coupled with an artificial neural network (ANN) to perform a multiple objective optimization of the film coolant flow parameters on the suction surface of a high pressure gas turbine vane. The numerical predictions are employed to construct the artificial neural network that produces low-fidelity predictions of the objectives during the optimization. The Pareto front of optimal solutions is generated by the optimization methodology.
Effect of Endwall Film Cooling Upstream of an Airfoil/Endwall Junction to Suppress the Formation of Horseshoe Vortex in a Symmetric Airfoil
Authors: Takeishi Kenichiro , Oda Yutaka , Seguchi Junichi , Kozono Shintaro
Published: November 2013

The effects of film cooling air injection at an endwall on the endwall film cooling and the formation of a horseshoe vortex were investigated experimentally and numerically in the leading edge region of a symmetric vane. The film cooling jet was applied upstream of the airfoil/endwall junction to give counter-momentum to the horseshoe vortex, and the temperature fields and flow fields were investigated using laser-induced fluorescence (LIF) and particle image velocimetry (PIV), respectively, in comparison with a large eddy simulation (LES). A comparison of the film cooling effectiveness values found using LES showed good agreement with those found in wind tunnel tests with pressure-sensitive paint (PSP). It was found that an insufficient injection of film coolant could not suppress the formation of the horseshoe vortex, but reinforced its growth. In addition, the effect of the film coolant injection on the endwall heat transfer was examined. The results suggested that film coolant injection upstream of the leading edge has the potential to simultaneously cool the endwall and suppress the formation of the horseshoe vortex.
Numerical Investigation of the Effects of Dilution Hole Geometry on the Exit Temperature Profile and Emissions of an Aero-Engine LPP Combustor
Authors: Shang Mingtao , Lu Shuqiang , Mao Ronghai
Published: November 2013

Lean premixed pre-vaporized (LPP) combustion is a dominant low emission combustion technology. In a center-staged LPP combustor, diffusion combustion in pilot stage and premixed combustion in main stage are combined to fulfill combustion performances and emission requirements under various operating conditions. Different from traditional combustor, since more air flows into flame tube through the dome, the airflow used for adjusting outlet temperature is very limited. Three-dimensional numerical simulations are carried out in the present investigation to analyze the influence of dilution holes on combustor outlet temperature distribution and NOx emissions. Five cases of dilution holes are simulated and analyzed. Realizable k-ε model, partially premixed combustion model and discrete phase model are employed in present work. The simulation results show that there are high temperature regions between two adjacent domes under take off mode. Cases with dilution holes in position C achieve better OTDF. The more airflow issued from these dilution holes, the lower OTDF obtained. At the same time, the radial height of outlet circumferentially averaged temperature will be increased. Under idle mode, dilution holes in position D and E are both very useful to decrease OTDF, thus it would be beneficial to increase the size of dilution holes D and E to issue more dilution air while decreasing the size of hole C. Nevertheless this modification will deteriorate OTDF under take off mode. However, under take off and idle modes, most high temperature regions appears in upper side of outlet. Hence, increasing the percentage of dilution air flowing into the upper side of flame tube will decrease the RTDF and reduce the radial height of outlet maximum circumferentially averaged temperature. It is also found that the dilution air has little effect on NOx emission in all five cases, because the dilution holes are axially located in the downstream of the primary combustion area where most of NOx is produced.
CFD Investigation of Vane Nozzle and Impeller Design for HPT Blade Cooling Air Delivery System
Authors: Tian Shuqing , Zhang Qin , Liu Hui
Published: November 2013

In the design of a HPT blade cooling air delivery system, sufficient supply pressure and lower relative total temperature are required to guarantee HPT blades working properly in the high temperature environment. The pre-swirl vane nozzles and the radial impellers are used in the delivery system with lower radial location of pre-swirl nozzle to achieve the requirements.

In this paper, CFD analysis is utilized for designing the vane nozzles and the radial impellers. Two HPT blade cooling air delivery systems were explored. The baseline is a system without impellers, and the alternative is a system with impellers. The results show that the impeller contributes to the delivery system by pumping effectiveness thus decreasing the extracted air pressure. The parity of swirl ratio between the flow and the broach slots is a main factor that decreases the system pressure loss, which can be improved by the radial impellers. The well-designed contoured radial-impeller vane with 30° front angle and 20° trailing angle is recommended in the blade cooling air delivery system design because of its good aerodynamic performance and closely radial outflow. The cascade vane nozzle with more than 70° angle turn is recommended in the pre-swirl nozzle design. It has a good aerodynamic performance with discharge coefficient greater than 0.99 and deviation angle less than 1.3°.

The well-designed radial impeller pays big contributions to the blade cooling air delivery system with 11.4% increase of the thermal effectiveness and 10.2% decrease of the pressure loss versus the system without impellers.
Evaluation of Axial Compressor Characteristics Under Overspray Condition
Authors: Myoren Chihiro , Takahashi Yasuo , Yagi Manabu , Shibata Takanori , Kishibe Tadaharu
Published: November 2013

An axial compressor was developed for an industrial gas turbine equipped with a water atomization cooling (WAC) system, which is a kind of inlet fogging technique with overspray. The compressor performance was evaluated using a 40MW-class test facility for the advanced humid air turbine system. A prediction method to estimate the effect of WAC was developed for the design of the compressor. The method was based on a streamline curvature (SLC) method implementing a droplet evaporation model. Four test runs with WAC have been conducted since February 2012. The maximum water mass flow rate was 1.2% of the inlet mass flow rate at the 4th test run, while the design value was 2.0%. The results showed that the WAC decreased the inlet and outlet temperatures compared with the DRY (no fogging) case. These decreases changed the matching point of the gas turbine, and increased the mass flow rate and the pressure ratio by 1.8% and 1.1%, respectively. Since prediction results agreed with the results of the test run qualitatively, the compressor performance improvement by WAC was confirmed both experimentally and analytically. The test run with the design water mass flow rate is going to be conducted in the near future.
Application of a Fast Loosely Coupled Fluid/Solid Heat Transfer Method to the Transient Analysis of Low-Pressure-Turbine Disk Cavities
Authors: Altuna Arnau , Chaquet Jose M. , Corral Roque , Gisbert Fernando , Pastor Guillermo
Published: November 2013

A transient aero-thermal analysis of the disk cavities of an aero-engine LPT (Low Pressure Turbine) is presented. The full simulation includes a 2D thermal model of the solid parts combined with an axisymmetric flow model of six separate cavities interconnected through inlet and outlet boundaries. Computing elapsed time is significantly reduced by using a cluster of GPUs (Graphics Processing Units) making this approach compatible with turbine design time-frames. The problem of flow reversal that takes place in some of the cavity boundaries along the transient flight cycle is addressed in detail. The fully coupled numerical solution is validated against engine data and compared as well against an uncoupled simulation. It is shown that the coupled solution outperforms the uncoupled one in terms of accuracy, since it removes some hypotheses inherent to the uncoupled approach. It is believed that this is the first time that GPUs have been used to solve a fully coupled fluid/solid thermal problem of industrial interest for the gas turbine community.
Design of a Non-Reacting Combustor Simulator With Swirl and Temperature Distortion With Experimental Validation
Authors: Hall Benjamin F. , Chana Kam S. , Povey Thomas
Published: November 2013

Nonuniform combustor outlet flows have been demonstrated to have significant impact on the first and second stage turbine aerothermal performance. Rich-burn combustors, which generally have pronounced temperature profiles and weak swirl profiles, primarily affect the heat load in the vane but both the heat load and aerodynamics of the rotor. Lean burn combustors, in contrast, generally have a strong swirl profile which has an additional significant impact on the vane aerodynamics which should be accounted for in the design process. There has been a move towards lean burn combustor designs to reduce NOx emissions. There is also increasing interest in fully integrated design processes which consider the impact of the combustor flow on the design of the HP vane and rotor aerodynamics and cooling. There are a number of current large research projects in scaled (low temperature and pressure) turbine facilities which aim to provided validation data and physical understanding to support this design philosophy. There is a small body of literature devoted to rich burn combustor simulator design but no open literature on the topic of lean burn simulator design. The particular problem is that in non-reacting, highly swirling and diffusing flows, vortex instability in the form of a precessing vortex core or vortex breakdown is unlikely to be well matched to the reacting case. In reacting combustors the flow is stabilised by heat release, but in low temperature simulators other methods for stabilising the flow must be employed. Unsteady Reynolds-averaged Navier-Stokes and Large eddy simulation have shown promise in modelling swirling flows with unstable features. These design issues form the subject of this paper.
Cyclic Hot Corrosion of Thermal Barrier Coatings and Overlay Coatings
Authors: Eriksson Robert , Brodin Håkan , Johansson Sten , Östergren Lars , Li Xin-Hai
Published: November 2013

The influence, and interdependence, of water vapor and Na2SO4–50 mol% NaCl on the oxidation of a NiCoCrAlY coating and a thermal barrier coating (TBC) were studied at 750 °C. Water vapor was found to have a negligible effect on oxide composition, but influenced the oxide morphology on the NiCoCrAlY coating. Na2SO4–50 mol% NaCl deposits on the coatings influenced oxide composition, most notably by the promotion of a Y rich phase. The effect of Na2SO4–50 mol% NaCl deposits was also evident for the TBC coated specimen, where the formed metal/ceramic interface oxide was affected by salt reaching the interface by penetration of the zirconia TBC.
Combustion System Update SGT5-4000F: Design, Testing and Validation
Authors: Kock Boris F. , Prade Bernd , Witzel Benjamin , Streb Holger , Koenig Mike H.
Published: November 2013

The first Siemens AG SGT5-4000F engine with hybrid burner ring combustor (HBR) was introduced in 1996. Since then, frequent evolutionary design improvements of the combustion system were introduced to fulfill the continuously changing market requirements. The improvements particularly focused on increased thermodynamic performance, reduced emissions, and increasing operational flexibility in terms of load gradients, fuel flexibility, and turndown capability.

According to the Siemens product development process, every design evolution had to pass several validation steps to ensure high reliability and best performance. The single steps included cold flow and mixing tests at atmospheric pressure, high-pressure combustion tests in full-scale sector combustion test rigs, and full engine tests at the Berlin test facility (BTF).

After successful validation, the design improvements were gradually released for commercial operation. In a first step, cooling air reduction features have been implemented in 2005, followed by the introduction of a premixed pilot as second step in 2006. Both together resulted in a significant reduction of the NOx emissions of the system. In a third step, an aerodynamic burner modification was introduced in 2007, which improved the thermo-acoustic stability of the system towards higher turbine inlet temperatures and adapted to fuel preheating to allow for increased cycle efficiency. All three features together have been released as package in 2010 and to date accumulated more than 50,000 operating hours (fleet leader 24,000).

This paper reports upon the steps towards this latest design status of the SGT5-4000F and presents results from typical focus areas of lean premixed combustion systems in gas turbines including aero-dynamical optimization, fuel/air mixing improvements and cooling air management in the combustor.
Similarity Based Modeling for Turbine Exit Temperature Spread Monitoring on Gas Turbines
Authors: Palmé Thomas , Liard Francois , Therkorn Dirk
Published: November 2013

Failures in the gas path of a Gas Turbine will cause a deviation in the measured performance parameters. One of the most important parameters is the Turbine Exit Temperature (TET) and refers to the hot gas temperature at the exhaust of a Gas Turbine (GT). However, TET is not uniform at the turbine outlet and the temperature is therefore sometimes measured at several axial and radial positions. The TET has what can be considered a natural variation, an effect of operation in different ambient and operational conditions which influences the internal flow field. It can be informative on the health status of the GT by monitoring the TET variation during operation, as a number of failures or abnormal operation conditions will affect the TET distribution. A regular way of monitoring the TET is to use the average value from different sensor readings, or compare the highest deviating sensor to the average value of all sensors. However in order to detect anomalies as early as possible deviations from the healthy profile should be detected more finely across the section. In this paper, a data-driven similarity based algorithm called Auto Associative Kernel Regression is applied to the issue of monitoring the TET spread variation on an industrial gas turbine. A case study is supplied to show the practical usefulness of the algorithm to a field failure.
Thrust Vectoring Design Project at Six Universities: Part II — Impact on Student Learning and Lessons Learned
Authors: Rumpfkeil Markus P. , Turner Mark G. , VanKuren James T. , Roberts Rory , Bons Jeffrey , Smith Tim , Ausserer Joseph K.
Published: November 2013

Undergraduate students of six universities participated in a design and build outreach program sponsored by the US Air Force during the 2011–2012 academic year. The goal was to design and build a thrust vectoring system for a small jet engine (about 20 pounds of thrust). Student and professor exit surveys were taken with almost all participants contributing to these surveys. Based on the survey results and the professors’ insights, learning outcomes and student impact are assessed. In addition, any other lessons learned during this extensive project-based learning activity are described.