bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural Evolution of GdZ and DySZ Based EB-PVD TBC Systems After Thermal Cycling at High Temperature
Authors: Munawar Ahmed Umar , Schulz Uwe
Published: November 2013

Lower thermal conductivity and high temperature stability are the two properties which are highly desired from ceramic top coat materials in TBC systems. Gadolinium Zirconate, Gd2Zr2O7, (GdZ) and Dyprosia Stabilized Zirconia (DySZ) are two of the candidate materials with such properties and consequently the TBC system would be able to work at higher turbine inlet temperature (TIT) or the lifetime can be increased. In the present study, life time measurements are done for single and double layered Electron Beam Physical Vapor Deposition (EB-PVD) GdZ and DySZ samples by thermal-cycling tests. The double layered TBCs consisted of a thin 7YSZ layer and, on top, the new candidate material. Both single and double layered samples of GdZ and DySZ have shown similar or better lifetimes than the standard 7YSZ samples. However, single layered TBCs showed better lifetime results than the respective double layers. In this study, changes in the microstructure, diffusion of elements and sintering of the TBC materials with aging are observed.
Experimental Investigation of the Effects of Nozzle Length on the Performance of Low Mach Number Air-Air Ejector With Entraining Diffuser
Authors: Namet-Allah A. , Birk A. M.
Published: November 2013

The core flow separation in air-air ejectors is significantly affected by the length of the exhaust nozzle. This length was changed by moving the annulus’ center body end 4, 7, and 12 cm upstream and 1 cm downstream of the nozzle inlet. The velocity profiles at the nozzle exit were measured at different mass flow rates and at 10, 20 and 30 degree swirl angles. These measurements were also conducted at two annulus’ center body end positions with elliptical and square shapes, 12 and 7 cm upstream of the nozzle inlet, using two nozzle exit diameters. At 4, 7, and 12 cm upstream and 1 cm downstream of the nozzle inlet, the ejector performance was also measured at ambient temperature and at different flow swirl angles. It was found that the square shape of the annulus’ center body decreased the size of the core flow separation behind the annulus center body compared with the elliptical shape by improving the flatness of the flow velocity at the nozzle exit under different mass flow rates, swirl angles, positions of the annulus’ center body, and nozzle exit diameters. It was seen that moving the end of the annular center body upstream has considerable effects on the size and nature of the core separation behind the annulus’ center body and consequently on the ejector performance.

At a zero swirl angle, the ejector pumping ratio slightly increased, decreased, and then increased again by moving the annulus’ center body from 12 cm to 7 cm upstream, from 7 cm to 4 cm upstream, and from 4 cm upstream to 1 cm downstream of the nozzle inlet respectively. These changes in the annulus’ center body position caused the back pressure coefficient to decrease, increase, and then increase again. The same trend in pumping ratio and back pressure was observed for both 10 and 20 degree flow swirl angle conditions when the annulus’ center body was moved as described.
The Development of a Hot Section Eddy Current Sensor for Turbine Tip Clearance Measurement
Authors: Chana K. S. , Cardwell M. T. , Sullivan J. S.
Published: November 2013

Gas turbine efficiency can be improved with tighter turbine tip clearances. An approach being developed by engine manufacturers deploys active tip clearance monitoring where the turbine casing diameter is actively controlled in-service either mechanically or thermally. Typically current engines operate at about 1% clearance of blade span. With active control this could potentially be reduced significantly.

Ideally active tip clearance control requires closed loop feedback measurements to maintain very small clearances without the risk of blade tip contact with the casing liner. Therefore reliable and robust sensors systems are required that can operate at the elevated temperatures found in modern gas turbines. Currently there are limited sensor systems available that can operate at these temperatures and survive typical sensor life requirements of many thousands of hours.

This study details development of a high temperature eddy current sensor system for hot section applications. The investigation encompasses development and validation of an integrated sensor design to provide tip clearance measurements. The sensor is designed to withstand temperatures of order 1500 to 1600K. Test facilities used to validate the system include a RB168 Mk 101 Spey engine and a Rolls-Royce VIPER engine. The turbine casings of both engines were modified to fit sensors directly above the rotor. The accuracy of the system was validated in a high speed rotor test facility with engine representative blading. Accuracy of the eddy current sensor was compared and validated against a dynamic laser micrometer system.
Experimental Investigation of Effect of Tip Coolant Ejection on Internal Flow Characteristics Within a Realistic Blade Coolant Channel
Authors: Pu Jian , Ke Zhaoqing , Wang Jianhua , Wang Lei , You Hongde
Published: November 2013

This paper presents an experimental investigation on the characteristics of the fluid flow within an entire coolant channel of a low pressure (LP) turbine blade. The serpentine channel, which keeps realistic blade geometry, consists of three passes connected by a 180° sharp bend and a semi-round bend, 2 tip exits and 25 trailing edge exits. The mean velocity fields within several typical cross sections were captured using a particle image velocimetry (PIV) system. Pressure and flow rate at each exit were determined through the measurements of local static pressure and volume flow rate. To optimize the design of LP turbine blade coolant channels, the effect of tip ejection ratio (ER) from 180° sharp bend on the flow characteristics in the coolant channel were experimentally investigated at a series of inlet Reynolds numbers from 25,000 to 50,000. A complex flow pattern, which is different from the previous investigations conducted by a simplified square or rectangular two-pass U-channel, is exhibited from the PIV results. This experimental investigation indicated that: a) in the main flow direction, the regions of separation bubble and flow impingement increase in size with a decrease of the ER; b) the shape, intensity and position of the secondary vortices are changed by the ER; c) the mass flow ratio of each exit to inlet is not sensitive to the inlet Reynolds number; d) the increase of the ER reduces the mass flow ratio through each trailing edge exit to the extent of about 23–28% of the ER = 0 reference under the condition that the tip exit located at 180° bend is full open; e) the pressure drop through the entire coolant channel decreases with an increase in the ER and inlet Reynolds number, and a reduction about 35–40% of the non-dimensional pressure drop is observed at different inlet Reynolds numbers, under the condition that the tip exit located at 180° bend is full open.
Influence of Coolant Density on Turbine Platform Film-Cooling With Stator-Rotor Purge Flow and Compound-Angle Holes
Authors: Liu Kevin , Yang Shang-Feng , Han Je-Chin
Published: November 2013

A detailed parametric study of film-cooling effectiveness was carried out on a turbine blade platform. The platform was cooled by purge flow from a simulated stator-rotor seal combined with discrete hole film-cooling. The cylindrical holes and laidback fan-shaped holes were accessed in terms of film-cooling effectiveness. This paper focuses on the effect of coolant-to-mainstream density ratio on platform film-cooling (DR = 1 to 2). Other fundamental parameters were also examined in this study — a fixed purge flow of 0.5%, three discrete-hole film-cooling blowing ratios between 1.0 and 2.0, and two freestream turbulence intensities of 4.2% and 10.5%. Experiments were done in a five-blade linear cascade with inlet and exit Mach number of 0.27 and 0.44, respectively. Reynolds number of the mainstream flow was 750,000 and wad based on the exit velocity and chord length of the blade. The measurement technique adopted was conduction-free pressure sensitive paint (PSP) technique. Results indicated that with the same density ratio, shaped holes present higher film-cooling effectiveness and wider film coverage than the cylindrical holes, particularly at higher blowing ratios. The optimum blowing ratio of 1.5 exists for the cylindrical holes, whereas the effectiveness for the shaped holes increases with increase of blowing ratio. Results also show that the platform film-cooling effectiveness increases with density ratio but decreases with turbulence intensity.
Aerodynamic and Acoustic Optimization of Axial Fans for Locomotive Cooling Systems
Authors: Bamberger Konrad , Carolus Thomas , Mauch Uwe , Knirsch Sebastian
Published: November 2013

The aerodynamic and acoustic performance of a locomotive cooling module is optimized by a new design strategy for the fan unit. The fan selection or development of the cooling modules is usually based on the specific design point but without consideration of installation effects.

The new approach considers the fan development in a more integrated manner. A simplified 1:4 model of the cooling system is constructed and used for system analysis, numerical flow simulations, and experimental validation. The subsequent fan and guide vane optimization is based on numerical simulations embedded in an optimization algorithm taking installation effects into account. The noise emitted by the fan is addressed by a smoothed inflow velocity profile, a new blade sweep strategy, the reduction of secondary flows, and the reduction of fan size and rotational speed.

The optimized fan unit is then integrated into the non-simplified full-scale system. Experiments reveal an energy saving of 20% and an overall sound power level reduction of 6 dB with even higher reduction of the tone at blade passing frequency.

All results are discussed with respect to transferability to other cooling modules. It is found that a set of general design recommendations originates from this work, whereas the optimization loops would need to be repeated for other cooling module types.
Identification of Surrogate Control Variables for a Robust Active Flow Controller of an Experimental High Speed Stator Cascade
Authors: Steinberg S. J. , King R. , Tiedemann C. , Peitsch D.
Published: November 2013

Active flow control is a powerful option to ensure secure operation and enhancement of the performance of axial compressors. To achieve these goals for aerodynamically highly loaded compressor blade profiles even under disturbed conditions, the magnitude of the actuation needs to be adjusted by a closed-loop controller. To this end, sensors must be placed at some meaningful positions at the surface of the blades giving information about the flow situation inside the passages. The sensor information can then lead to surrogate control variables to close the loop. Often, good sensor positions are unknown initially and therefore chosen naively or experience-driven. To obtain more informative surrogate control variables, a different approach is chosen here. Starting with a highly instrumented blade inside a linear stator cascade, featuring 16 pressure gauges in an area which is suspected to lead to high information content with respect to detrimental flow separations at the sidewalls, a Principal Component Analysis is done. The principal components provide valuable information about where and how intensively the flow is influenced by the actuation. This is validated by comparison with the results of oil flow visualizations and wake measurements. The goal is to find a linear combination of as few sensors as possible to provide a meaningful input for the closed-loop controller. As experiments are conducted up to Ma = 0.8, the signal-to-noise ratio becomes a critical issue. For this reason, specifically weighted data are introduced here. A linear combination of sensor data is obtained, describing the main effects of the actuation with an almost linear mapping. For the given set of sensors, that linear combination achieves a maximum signal-to-noise ratio, which makes it well suited as a control variable. The practical usefulness of the control variable within a robust ℋ∞-flow controller is verified in experiments in a high speed stator cascade.
Stiffness and Leakage Characterization of Ceramic-Metallic Rope Seals
Authors: Sarawate Neelesh
Published: November 2013

Ceramic-metallic rope seals are suitable for use in high-temperature and low-cycle displacement applications. This paper discusses performance aspects that need to be considered during seal selection such as the maximum load generated at assembly and during operation, seal resiliency and leakage performance for a given application. Extensive load-displacement and leakage tests are conducted on several candidate seals. Selected rope seals are of hybrid seal type consisting of ceramic fiber core along with an outer sheath of fine metallic wires. Test parameters include rope manufacturers, rope diameters, and combination of core/sheath materials. Testing is performed on as-received ropes as well as ropes that are heat-treated at temperatures over 1000°F. The load-displacement behavior is non-linear, hysteretic and varies with the number of loading cycles. The force generated by the rope at a given displacement decreases with increasing number of loading cycles for a given displacement. The ropes do not recover to their original size after the first cycle of compression, and the residual height decreases with increasing cycles. The seal behavior tends to saturate after about 5 loading cycles. The rope selection for a particular application needs to consider the saturating residual deflection and maximum force generated. Leakage testing was also performed for rope seals placed in a rectangular race-track type geometry. The seals demonstrate good leakage resistance under desired pressure conditions. The ropes with smaller diameters show the best leakage performance, but exhibit low spring-back.
Rotating Stall Inception Inside the Low Pressure Compressor of a Twin-Spool Turbofan Engine
Authors: Stößel Marcel , Bindl Stefan , Niehuis Reinhard
Published: November 2013

In order to preserve fossil resources aviation industry faces major challenges to reduce engine fuel consumption. Therefore efforts are concentrated to increase efficiency of any engine component. Investigations at the Institute of Jet Propulsion at the University of Federal Armed Forces in Munich focus on the compressor module. Especially the compression system of a gas turbine is designed to operate at very high aerodynamic loads. This makes it one of the most critical components during transient engine operation or inlet flow distortion. Rotating stall and surge have to be avoided in any situation during engine operation. For this reason a detailed knowledge of the flow phenomena of the compressor in normal conditions as well as near the stability limit is essential. Often those research activities are carried out at compressor rigs but not in by utilizing real turbo engines.

As a research test vehicle at the Institute of Jet Propulsion the Larzac 04 C5 twin-spool turbofan engine is operated at the engine test facility. The gas turbine is equipped with additional instrumentation and control systems exceeding those of conventional engine monitoring systems by far. Especially a set of high frequency pressure transducers has been installed above the tip of the first stage of the low pressure compressor in order to investigate tip flow phenomena. Besides the information on the flow phenomena in the tip region of the compressor blades these signals can also be used to detect the upcoming of rotating stall precursors. A special algorithm which was developed at the institute is able to estimate the stall and to trigger an active countermeasure. This was demonstrated successfully for a wide range of operating points.

Stall inception in different speed ranges is crucial to be detected reliably. More than all high spool speeds challenge an active stabilization system. With the stall typically rising in time periods of less than three rotor revolutions, the requirements regarding high speed data processing are enormous. Since computer technology now provides systems, which are capable to handle such a task and still are compact and robust enough to be used in the rough environment of engine test beds, the challenge remains to set up fitting actuator systems. The test vehicle at the Institute of Jet Propulsion is therefore equipped with fast acting valves, which feed an injector casing mounted closely upstream of the low-pressure compressor. Test series have been performed, which proof the stabilizing capabilities of the entire system. Even at high spool speeds the stall was sufficiently suppressed and a stable operation of the engine was guaranteed.
Assessment of Life Cycle Emissions of Bio-SPKs for Jet Engines
Authors: Lokesh Kadambari , Prakash Atma , Sethi Vishal , Goodger Eric , Pilidis Pericles
Published: November 2013

Bio-Synthetic Paraffinic Kerosene (Bio-SPK) is one of the most anticipated renewable energy to conventional Jet kerosene (CJK). Bio-SPK is plant lipid which is thermo-chemically converted to kerosene like compositions to serve as “Drop-in” biojet fuel. The environmental impact of Bio-SPK is to be understood to determine its potential as a carbon neutral / negative fuel. Assessment of Life Cycle Emissions of Bio-SPKs (ALCEmB) aims to deliver a quantitative, life cycle centered emissions (LCE) model, reporting the process related-carbon footprint of Bio-SPKs. This study also encompasses the key emission-suppressing feature associated with biofuels, termed as “Biomass Credit”. The Bio-SPKs chosen for this analysis and ranked based on their “Well-to-Wake” emissions are Camelina SPK, Microalgae SPK and Jatropha SPK. The Greenhouse gases (GHGs) emitted at each stage of their life cycles have been represented in the form of CO2 equivalents and the LCE of each of the Bio-SPKs were weighed against that of a reference fuel, the CJK. Camelina SPK among the three Bio-SPKs analyzed, was determined to have a relatively lower carbon footprint with a <70% carbon reduction relative to CJK followed by Jatropha SPK and Microalgae SPK respectively. In general, Bio-SPKs were able to reduce their overall LCE by 60–70%, at baseline scenario, relative to its fossil derived counterpart.
The Effect of Airfoil Clocking on Efficiency and Noise of Low Pressure Turbines
Authors: Vázquez Raúl , Torre Diego , Serrano Adolfo
Published: November 2013

The effect of airfoil clocking (stator-stator interaction) on efficiency and noise of low pressure turbines (LPT) was investigated experimentally in a multistage turbine high-speed rig. The rig consisted of three stages of a state-of-the-art LPT. The stages were characterized by a very high wall-slope angle, reverse cut-off design, very high lift and very high aspect ratio airfoils.

The rig had identical blade count for the second and third stators. The circumferential position of the second stator was individually adjusted with respect to the third stator. Eight different circumferential clocking locations over one pitch were back-to-back tested.

The rig was heavily instrumented with miniature five hole probes, hot wires, hot films, total pressure and temperature rakes, pressure tappings on the airfoil surface, two array of Kulites in a rotatory module, etc. Every clocking location was tested with the same instrumentation and at the same operating conditions with the intention of determining the impact of the clocking on the overall efficiency and noise.

Due to the large amount of data, the results of this test will be reported in several papers. The present paper contains the impact on the overall efficiency, radial traverses, static pressure fields on the airfoils and averaged sound pressure levels in the duct.

The comparison of the results suggests that the efficiency is weakly affected by clocking; however the effect on noise is noticeable for some acoustic tones at certain operating conditions.
Large-Eddy Simulation and Conjugate Heat Transfer Around a Low-Mach Turbine Blade
Authors: Duchaine Florent , Maheu Nicolas , Moureau Vincent , Balarac Guillaume , Moreau Stéphane
Published: November 2013

Determination of heat loads is a key issue in the design of gas turbines. In order to optimize the cooling, an exact knowledge of the heat flux and temperature distributions on the airfoils surface is necessary. Heat transfer is influenced by various factors, like pressure distribution, wakes, surface curvature, secondary flow effects, surface roughness, free stream turbulence and separation. All these phenomenon are challenges for numerical simulations. Among numerical methods, Large Eddy Simulations (LES) offers new design paths to diminish development costs of turbines through important reductions of the number of experimental tests. In this study, LES is coupled with a thermal solver in order to investigate the flow field and heat transfer around a highly loaded low pressure water-cooled turbine vane at moderate Reynolds number (150 000). The meshing strategy (hybrid grid with layers of prisms at the wall and tetrahedra elsewhere) combined with a high fidelity LES solver gives accurate predictions of the wall heat transfer coefficient for isothermal computations. Mesh convergence underlines the known result that wall-resolved LES requires discretisations for which y+ is of the order of one. The analysis of the flow field gives a comprehensive view of the main flow features responsible of heat transfer, mainly the separation bubble on the suction side that triggers transition to a turbulent boundary layer and the massive separation region on the pressure side. Conjugate heat transfer computation gives access to the temperature distribution in the blade, which is in good agreement with experimental measurements. Finally, given the uncertainty on the coolant water temperature provided by experimentalist, uncertainty quantification allows apprehending the effect of this parameter on the temperature distribution.
Experimental Investigation of the Flashback Limits and Flame Propagation Mechanisms for Premixed Hydrogen-Air Flames in Non-Swirling and Swirling Flow
Authors: Baumgartner Georg , Sattelmayer Thomas
Published: November 2013

In modern industrial gas turbines swirling flow is widely used for stabilizing flames at the transition from the burner to the combustor. In premixed combustion systems using highly reactive fuels, flashback due to combustion induced vortex breakdown (CIVB) has been observed frequently when swirl was present. This paper focuses on the effect of low swirl intensities on the flashback propensity and the predominant flashback mechanisms in a hydrogen-air tube burner. An existing test rig with a vertical quartz tube and a generic swirl generator has been used. At the tube exit the flame was stabilized in the free atmosphere. The turbulent flashback limits were measured for hydrogen-air mixtures at atmospheric conditions over a broad range of equivalence ratios for both non-swirling and swirling flow. The upstream flame propagation during flashback was observed through the OH*-chemiluminescence captured by two synchronized intensified high-speed cameras in a 90° arrangement, both looking at the flame from the side. In addition to that, a high-speed particle image velocimetry (PIV) system was used to insert a horizontal laser sheet into the vertical tube in order to investigate the propagation path of the leading flame tip through a time series of Mie-scattering images from the bottom. As expected, it turned out that the flame always flashes back along the wall boundary layer for non-swirling flow. For swirling flow it could be shown that again only boundary layer flashback takes place for equivalence ratios lower than ϕ≈0.75. In this rather lean region, the resistance against flashback is improved compared to non-swirling flow due to higher wall velocity gradients. For higher equivalence ratios, flashback is initiated through CIVB. That is, the flame enters the tube on the burner centerline until its tail gets in touch with the burner walls. Subsequently, there is a shift in flashback mechanism and the flame propagates further upstream along the wall boundary layer. For the given setup and these near-stoichiometric mixture compositions, this resulted in a significantly increased flashback propensity when compared with non-swirling flames. The present studies showed that imposing low swirl upon the burner flow can improve the resistance against boundary layer flashback for low and moderate equivalence ratios, whereas the change to the CIVB mechanism deteriorates the performance for high equivalence ratios.
Maximizing Contacting Filament Seal Performance Retention
Authors: Jahn Ingo H. J.
Published: November 2013

The initial superior performance of contacting filament seals compared to traditional seals such as labyrinth seals has been well reported in the literature. A challenge that remains for these seals is ensuring that this performance advantage is retained throughout their operating life, especially if there is uncertainty in the operating cycle. In the current paper, a seal model based on generic seal characteristics is used to explore the relationships between these characteristics, the seal performance, and the seal performance retention. Using this approach seal characteristics are identified that result in a seal that performs well and maintains performance for a given operating cycle. In addition it is demonstrated that the performance and performance retention is maintained even if the seal operating conditions are altered significantly, implying that these seals are more robust also.
Aerodynamics of Linearly Arranged Rad-Rad Swirlers, Effect of Number of Swirlers and Alignment
Authors: Kao Yi-Huan , Tambe Samir B. , Jeng San-Mou
Published: November 2013

A series of experiments have been conducted to study the aerodynamic characteristics of a confined swirling flow generated by multiple rad-rad swirlers arranged linearly. The rad-rad swirlers used in this study are identical, and consist of an inner, primary swirler generating counter-clockwise rotation and an outer, secondary swirler generating clockwise rotation. A two-component Laser Doppler Velocimetry (LDV) system was employed to measure the velocity in the flow field. Initial measurements were conducted on unconfined and confined flow generated by a single swirler to serve as the baseline reference for the multi-swirler arrangements. Tests were conducted for 3 and 5 swirlers arranged in a line, with a spacing of 2D between the swirler centers, where D is the swirler exit diameter. An additional 5 swirler configuration was tested, where the exit plane of the center swirler was shifted 3.2 mm (1/8 inch) in the streamwise direction.

The flow field generated by the multi-swirler arrangement is very complex, due to the interaction between the swirling jets of adjacent swirlers. The number of swirlers is seen to have a clear impact on the entire flow structure, as well as each recirculation zone. For the 3 swirler arrangement, a weak CTRZ is observed for the center swirler, whereas strong CTRZs are observed for the two outer swirlers. For the 5 swirler arrangement, the CTRZ pattern for the 3 inner swirlers is the same strong-weak-strong as seen for the 3 swirler arrangements, with weak CTRZs observed for the two outer swirlers. Higher interaction between swirlers is observed for the 5 swirler arrangement, as compared to the case with 3 swirlers. Since the swirlers are identical, the region between swirlers features merging of two opposing swirling jets, producing high turbulence intensity in the near field region.

For the case with the offset center swirler, the swirling jet from this swirler did not merge with its neighbors in the near field region. This resulted in strong CTRZ for the center swirler, accompanied by weaker CTRZs at its immediate neighbors, which is reverse of the CTRZ strength pattern observed for the initial 5 swirler arrangement.
Overall Thermal Performance of a Rectangular Channel With an Array of Elongated Pedestals
Authors: Huang S. , Yan Y. Y. , Maltson J. D. , Utriainen E.
Published: November 2013

Experiments have been conducted to investigate the overall thermal performance of a rectangular channel implemented with an elongated pedestal array. The staggered pedestals were elongated in the spanwise direction in order that the jet flow from between the pedestals impinges at the centre of the pedestals in the downstream row. The average heat transfer coefficient of the pedestal and the local heat transfer coefficient distribution of the bottom channel wall were investigated for different geometrical arrangements. The pressure drop across the pedestal bank was measured. The transient liquid crystal method was used to obtain the local heat transfer coefficient distribution on the bottom channel wall and the lumped capacitance method was used to measure the average heat transfer coefficient of the pedestals in the last two rows of the bank. Five pressure taps were arranged on the centerline of each gap between two pedestal rows to measure the pressure drop. The heat transfer coefficients were measured over the Reynolds number range from 10,000 to 30,000. The minimum flow area to the channel cross-section flow area ratio ranged from 0.149 to 0.333. The effects of pedestal geometry and array distribution were investigated in detail showing the relationship between the pedestal array geometry, heat transfer enhancement and pressure drop. Conclusions were drawn on the effects of geometry and flow conditions on overall thermal performance of the respective channels.
Experimental and Computational Studies of an Ultra-Compact Combustor
Authors: Blunck David , Shouse Dale , Neuroth Craig , Battelle Ryan , Lynch Amy , Sekar Balu , Zelina Joseph , Erdmann Timothy , Burrus David , Howard Rebecca , Briones Alejandro , Richardson Daniel , Caswell Andrew
Published: November 2013

Reducing the weight and decreasing pressure losses of aviation gas turbine engines improves the thrust-to-weight ratio and improves efficiency. In ultra-compact combustors (UCCs), engine length is reduced and pressure losses are decreased by merging a combustor with adjacent components using a systems engineering approach. High-pressure turbine inlet vanes can be placed in a combustor to form a UCC. Eliminating the compressor outlet guide vanes (OGVs) and maintaining swirl through the diffuser can result in further reduction in engine length and weight. Cycle analysis indicates that a 2.4% improvement in engine weight and a 0.8% increase in thrust-specific fuel consumption are possible when a UCC is used. Experiments and analysis were performed in an effort to understand key physical and chemical processes within a trapped-vortex UCC. Experiments were performed using a combustor operating at pressures in the range of 520–1030 kPa (75–150 psi) and inlet temperature of 480–620 K (865–1120 °R). The primary reaction zone is in a single trapped-vortex cavity where the equivalence ratio was varied from 0.7 to 1.8. Combustion efficiencies and NOx emissions were measured and exit temperature profiles obtained, for various air loadings, cavity equivalence ratios, and configurations with and without turbine inlet vanes. A combined diffuser-flameholder (CDF) was used in configurations without vanes to study the interaction of cavity and core flows. Higher combustion efficiency was achieved when the forward-to-aft momentum ratios of the air jets in the cavity were near unity or higher. Discrete jets of air immediately above the cavity result in the highest combustion efficiency. The air jets reinforce the vortex structure within the cavity, as confirmed through coherent structure velocimetry of high-speed images. A more uniform temperature profile was observed at the combustor exit when a CDF is used instead of vanes. This is the result of increased mass transport along the face of the flame holder. Emission indices of NOx were between 3.5 and 6.5 g/kgfuel for all test conditions. Ultra-compact combustors (with a single cavity) can be run with higher air loadings than those employed in previous testing with a trapped-vortex combustor (two cavities) with similar combustion efficiencies being maintained. The results of this study suggest that the length of combustors and adjacent components can be reduced by employing a systems level approach.
Effects of the Last Stage Rotor Tip Leakage Flow on the Aerodynamic Performance of the Exhaust Hood for Steam Turbines
Authors: Li Jun , Li Zhigang , Feng Zhenping
Published: November 2013

The static pressure recovery coefficient of the exhaust hood has significant impact on the aerodynamic performance of the low pressure cylinder for steam turbines. Numerical investigations on the aerodynamic performance of the exhaust hood and full last stage with consideration of the rotor tip leakage were presented in this paper. Three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions and k–ε turbulent model were utilized to analyze the static pressure recovery performance of the exhaust hood using the commercial CFD software ANSYS-CFX. Effect of the last stage rotor tip leakage flow on the aerodynamic performance of the downstream exhaust hood was conducted by comparison of the computational domains for the exhaust hood and full last stage with and without tip clearance. The numerical results show that the last stage rotor tip leakage jet can suppress the flow separation near the diffuser wall of the exhaust hood and improve its static pressure recovery performance. The detailed flow fields of the exhaust hood with and without consideration of the rotor tip leakage flow were also illustrated and corresponding flow mechanism was discussed.
Influence of Tip Shape on Reynolds Number Sensitivity for a Seven Hole Pressure Probe
Authors: Crawford James , Birk A. M.
Published: November 2013

The effects of tip shape on the Reynolds number sensitivity of a seven hole pressure probe are studied over a range of flows associated with practical use of turbomachinery. It is shown that at low flow angles, the response of a conical or hemispherical tipped probe is independent of Reynolds number above Re = 3000, and at high flow angles, Re = 6000. Despite there not being a discernable difference in the average error in flow properties at different Reynolds numbers between the two tip shapes, it is shown that the hemispherical tip is preferred because the pressure distributions around the tip are more consistent.
Assessment of a Gas Turbine NOx Reduction Potential Based on a Spatiotemporal Unmixedness Parameter
Authors: Dederichs Stefan , Habisreuther Peter , Zarzalis Nikolaos , Beck Christian , Krebs Werner , Prade Bernd
Published: November 2013

The paper presents a one-dimensional approach to assess the reduction potential of NOx emissions for lean premixed gas turbine combustion systems. NOx emissions from these systems are known to be mainly caused by high temperatures; not only from an averaged perspective but especially related to poor mixing quality of fuel and air.

The method separates the NOx chemistry in the flame front zone and the post flame zone (slow reaction). A one-dimensional treatment enables the use of detailed chemistry. A look up table parameterized by reaction progress and equivalence ratio is used to improve the computational efficiency.

The influence of mixing quality is taken into account by a probability density function of the fuel element based equivalence ratio, which itself translates into a temperature distribution. Hence, the NOx source terms are a function of reaction progress and equivalence ratio. The reaction progress is considered by means of the two-zone approach. Based on unsteady CFD data, the evolution of the probability density function with residence time has been analyzed.

Two types of definitions of an unmixedness quantity are considered. One definition accounts for spatial as well as temporal fluctuations and the other is based on the mean spatial distribution. They are determined at the location of the flame front.

The paper presents a comparison of the modeled results with experimental data. A validation and application have shown very good quantitative and qualitative agreement with the measurements. The comparison of the unmixedness definitions has proven the necessity of unsteady simulations. A general emissions - unmixedness correlation can be derived for a given combustion system.
Study of a Rich/Lean Staged Combustion Concept for Hydrogen at Gas Turbine Relevant Conditions
Authors: Bolaños Felipe , Winkler Dieter , Piringer Felipe , Griffin Timothy , Bombach Rolf , Mantzaras John
Published: November 2013

The combustion of hydrogen-rich fuels (> 80 % vol. H2), relevant for gas turbine cycles with “pre-combustion” carbon capture, creates great challenges in the application of standard lean premix combustion technology. The significant higher flame speed and drastically reduced auto-ignition delay time of hydrogen compared to those of natural gas, which is normally burned in gas turbines, increase the risk of higher NOX emissions and material damage due to flashback. Combustion concepts for gas turbines operating on hydrogen fuel need to be adapted to assure safe and low-emission combustion.

A rich/lean (R/L) combustion concept with integrated heat transfer that addresses the challenges of hydrogen combustion has been investigated. A sub-scale, staged burner with full optical access has been designed and tested at gas turbine relevant conditions (flame temperature of 1750 K, preheat temperature of 400 °C and a pressure of 8 bar).

Results of the burner tests have confirmed the capability of the rich/lean staged concept to reduce the NOx emissions for undiluted hydrogen fuel. The NOx emissions were reduced from 165 ppm measured without staging (fuel pre-conversion) to 23 ppm for an R/L design having a fuel-rich hydrogen pre-conversion of 50 % at a constant power of 8.7 kW.

In the realized R/L concept the products of the first rich stage, which is ignited by a Pt/Pd catalyst (under a laminar flow, Re ≈ 1900) are combusted in a diffusion-flame-like lean stage (turbulent flow Re ≈ 18500) without any flashback risk. The optical accessibility of the reactor has allowed insight into the combustion processes of both stages. Applying OH-LIF and OH*-chemiluminescence optical techniques, it was shown that mainly homogeneous reactions at rich conditions take place in the first stage, questioning the importance of a catalyst in the system, and opening a wide range of optimization possibilities.

The promising results obtained in this study suggest that such a rich/lean staged burner with integrated heat transfer could help to develop a new generation of gas turbine burners for safe and clean combustion of H2-rich fuels.
Effect of Hole Exit Shaping on Film Cooling Performance for Tripod Hole Injection Over a Flat Surface
Authors: LeBlanc Christopher N. , Ramesh Sridharan , Ekkad Srinath V. , Alvin Mary Anne
Published: November 2013

The effect of hole exit shaping on both heat transfer coefficient and film cooling effectiveness of tripod injection holes is examined experimentally on a flat plate. Previously, it has been clearly proven that tripod hole configurations provide at least 50–60% more cooling effectiveness while using 50% less coolant than standard cylindrical and shaped hole exit geometries. Temperature data is collected using infrared thermography at different operating conditions to determine the benefit of shaping the hole exits for an already proven tripod hole configuration. The test rig consists of a rectangular test section with a main stream flow at 7.9 m/s and coolant flow injected through the bottom surface through the film cooling injection holes. A unique transient IR technique has been used to determine both the adiabatic film effectiveness and heat transfer coefficient from a single test. Two different exit shaping have been considered, one with a 5° flare and layback and one with a 10° flare and layback. Results show that exit shaping improves the performance of these tripod holes compared to the cylindrical hole exits. The 10° flare and layback exit performs slightly better than the 5° flare and layback exit.
Tripod Hole Geometry Performance for a Vane Suction Surface Near Throat Location
Authors: Ramesh Sridharan , LeBlanc Chris , Ekkad Srinath V. , Alvin Mary Anne
Published: November 2013

Film cooling performance depends strongly on the hole exit geometry, blowing ratio, and hole location. The goal of this study is to evaluate film cooling geometries that can provide better protection over the suction surface of the airfoil beyond the throat region. This study compares the performance of standard cylindrical; fan-shaped (10° flare/laidback); tripod hole geometry (15° breakout angle); and tripod holes with shaped exits (5° flare on 15° tripod). Film cooling holes are located just upstream of the throat region on the suction side of an airfoil. The airfoil is a scaled up first stage vane from GE E3 engine and is mounted on a low speed linear cascade wind tunnel. A range of blowing ratios from 0.5 to 2.0 was covered for a cylindrical hole, while ensuring all other hole geometries run under similar mass flow rate conditions. Steady state IR (Infra-Red) technique was employed to measure adiabatic film cooling effectiveness. Results show that the tripod holes with and without shaped exits provide much higher film effectiveness than cylindrical and slightly higher effectiveness than shaped exit holes using 50% lesser cooling air while operating at the same blowing ratios. Effectiveness values up to 0.2–0.25 are seen 40-hole diameters downstream for the tripod hole configurations thus providing cooling in the important trailing edge portion of the airfoil.
Heat Transfer Characteristics of Jet Array Impingement at Low Streamwise Spacing
Authors: Claretti Roberto , Hossain Jahed , Verma S. B. , Kapat J. S. , Downs James P. , Goebel Gloria E.
Published: November 2013

The present work studies the effect of low streamwise jet-to-jet spacing and uneven spanwise jet-to-jet spacing on target wall heat transfer coefficient in impingement cooling systems. Temperature sensitive paint alongside constant flux heaters were used to gather heat transfer data on the target wall. Two different geometries have been tested with varying jet-to-jet spanwise distance. The streamwise jet spacing was set to 3 jet diameters, the spanwise jet spacing was set to 3, 8 and 13 jet diameters while the jet-to-target spacing was set to 3 jet diameters. The tests were run at three average jet Reynolds numbers of 10,000, 13,000 and 16,000. Results show little effect of crossflow on the target wall heat transfer. Nusselt number profiles are compared to the Florschuetz prediction, the area averaged Nusselt number matches closely; however, the Florschuetz correlation shows a decreasing trend in Nusselt number as a function of streamwise distance while the data shows a Nusselt number profile that remains relatively constant as a function of streamwise distance, x. To better understand the flow physics behind this trend, a CFD run was set up using the ν2-f turbulence model for all cases. Computational and experimental results display a strong similarity of their heat transfer trends. The crossflow is seen to not be able to reattach behind each jet due to their proximity to one another.
Numerical Investigation of Impingement Heat Transfer on a Flat and Square Pin-Fin Roughened Plates
Authors: Wan Chaoyi , Rao Yu , Zhang Xiang
Published: November 2013

A numerical investigation of the heat transfer characteristics within an array of impingement jets on a flat and square pin-fin roughened plate with spent air in one direction has been conducted. Four types of optimized pin-fin configurations and the flat plate have been investigated in the Reynolds number range of 15000–35000. All the computation results have been validated well with the data of published literature. The effects of variation of jet Reynolds number and different configurations on the distribution of the average and local Nusselt number and the related pressure loss have been obtained. The highest total heat transfer rate increased up to 162% with barely any extra pressure loss compared with that of the flat plate. Pressure distributions and streamlines have also been captured to explain the heat transfer characteristic.
Numerical Simulation of an Eight-Stage Axial Subsonic Compressor With Wet Compression
Authors: Luo Mingcong , Zheng Qun , Sun Lanxin , Deng Qingfeng , Yang Junjie
Published: November 2013

In this paper, wet compression effects on an eight-stage axial subsonic compressor is simulated by steady numerical methods. Special attention is paid to the compressor design operating condition and rotating stall boundary to contrast and analyze the changes such as the compressor performance and the flow field characteristics under dry and wet conditions. The motions of water droplets are also simulated and analyzed. The results indicate that wet compression could weaken or eliminate the flow separation, improve the flow capacity, efficiency and pressure ratio of this compressor and make the compressor operating near the rotating stall boundary enter into the normal working condition.
Spatially Resolved Heat Transfer Coefficient in a Rib-Roughened Channel Under Coriolis Effects
Authors: Mayo Ignacio , Arts Tony , Clinckemaillie Julien , Lahalle Aude
Published: November 2013

Heat transfer in a magnified rotating ribbed channel is studied by means of liquid crystal thermometry. The test section consists of four Plexiglas walls, forming a rectangular cross section, mounted on a large rotating disk together with the complete necessary measurement chain. The investigated wall is equipped with ribs perpendicular to the main flow direction, it is heated in such a way to achieve a uniform heat flux boundary condition. Facing the need of two-dimensional experimental heat transfer data, tets were carried out in order to quantify the convective heat transfer distribution on the wall between two consecutive ribs under rotating conditions. Different Rotation numbers (0, 0.06, 0.11 and 0.17) were tested at a Reynolds number of 15,000. For the selected heat flux and rotation rates, and based on previous aerodynamic and thermal investigations presented in open literature, no effect of buoyancy is expected, while the Coriolis forces play an important role in the determination of heat transfer. The rotating cases were performed in both senses of rotation in order to allow the studied wall to act as both a trailing and a leading side. At the highest Rotation number, the results confirm that heat transfer is enhanced up to 17% along the trailing side compared with the non-rotating case. This is due to the secondary flows and shear layer instability instigated by the Coriolis forces. On the other hand, heat transfer on the leading side is reduced up to 19% at the highest rotation number; this is caused by the stabilization of the shear layer and the contribution of the secondary flows.