bluuebunny/crossref_metadata_2025 huggingface dataset:
A Computational Investigation of Hot Gas Ingress Through the Rim Seal of a Counter-Rotating Turbine Cavity With Annulus
Authors: Liu Dongdong , Luo Xiang , Tao Zhi
Published: August 2015

The hot gas ingestion through rim seals of counter-rotating turbine disks with annulus flow is investigated by numerical simulation in this paper. Three models were calculated in this paper, counter-rotating turbine cavity with annulus and radial sealing inlet, the same geometric configuration but in rotor-stator system and the counter-rotating turbine cavity without annulus. The axial Reynolds number of annulus was set at 5.99×105 and rotating Reynolds number was set at 2.35×105, the non-dimensional sealing flow rate was changed from 279 to 1116. The results of simulation indicated that counter-rotating cavity with radial inlet was found to have a much higher sealing efficiency than the stator-rotor cavity at the equivalent condition. The flow path of ingestion gas was considered to be the cause for this. For the difference of flow structure of cavities, the annulus air is ingested the middle of cavity for counter-rotating cavity rather than flowed towards the static wall for rotor-stator cavity. Therefore, the sealing efficiency for counter-rotating cavity is high in both of the walls but low inside the cavity. In addition, preswirl of sealing air was found to affect the sealing efficiency by changing the flow inside cavity and making the early mixing of sealing air and ingestion gas.
Heterogeneous Optimization Strategies for Carved and Squealer-Like Turbine Blade Tips
Authors: De Maesschalck C. , Lavagnoli S. , Paniagua G. , Verstraete T. , Olive R. , Picot P.
Published: August 2015

Superior rotor tip geometries possess the potential to simultaneously mitigate aerodynamic losses and severe thermal loads onto the rotor overtip region. However, classical design strategies are usually constrained to a specific type of geometry, narrowing the spread of shape topologies considered during the design phase. The current paper presents two novel multi-objective optimization methodologies that enable the exploration of a broad range of distinct tip configurations for unshrouded rotor blades.

The first methodology is a shape optimization process that creates a fully carved blade tip shape defined through a Bezier surface controlled by 40 parameters. Combined with a differential evolution optimization strategy, this approach is applied to a rotor blade for two tip gap sizes: 0.85% (tight) and 1.38% (design) of the blade span. The second methodology is based on a topology optimization process that targets the creation of arbitrary tip shapes comprising one or multiple rims with a fixed height. The tip section of the blade has been divided into more than 200 separate zones, where each zone can be either part of an upstanding rim or part of the cavity floor. This methodology was tested with a level-set approach in combination with a differential evolution optimizer, and coupled to an optimization routine based on genetic algorithms.

The current study was carried out on a modern high-pressure turbine operating at engine-like Reynolds and high subsonic outlet Mach numbers. A fully hexahedral unstructured mesh was used to discretize the fluid domain. The aerothermal performance of each tip profile was evaluated accurately through RANS simulations adopting the SST turbulence model. Multi-objective optimizations were set for both design strategies that target higher aerodynamic rotor efficiencies and simultaneous minimization of the heat load.

This paper illustrates a wide variety of profiles obtained throughout the optimization and compares the performance of the different strategies. The research shows the potential of such novel methodologies to reach new unexplored types of blade tip designs with enhanced aerothermal performances.
Multi-Coordination of Actuators in Advanced Power Systems
Authors: Pezzini Paolo , Bryden Kenneth M. , Tucker David , Banta Larry
Published: August 2015

Multi-coordination of actuators for a highly integrated, tightly coupled advanced power system was evaluated using the Hybrid Performance (Hyper) project facility at the U.S. Department of Energy’s National Energy Technology Laboratory (NETL). A two-by-two scenario in a fuel cell, turbine hybrid power system was utilized as a representative problem in terms of system component coupling during transients and setpoint changes. In this system, the gas turbine electric load is used to control the turbine speed, and the cold air bypass valve regulated fuel cell cathode mass flow.

Perturbations in the turbine speed caused by variations in the waste heat from the fuel cell affect the cathode airflow, and the cold-air bypass control action required for constant cathode airflow strongly affects the turbine speed. Previous implementation of two single-input, single-output (SISO) controllers failed to provide acceptable disturbance rejection and setpoint tracking under these highly coupled conditions. A multiple-input, multiple-output (MIMO) controller based on the classic internal model control (IMC) concept was implemented and experimentally tested for the first time using the Hyper project facility.

The state-space design of the MIMO configuration, the control law integration into the digital control platform, and the experimental comparison with the SISO case are presented.
Design, Characterization, and Verification of a Closed Loop Wind Tunnel With Linear Cascade and Upstream Wake Generator
Authors: Gonzalez Carlos R. , Bidan Guillaume F. , Bitting Jason W. , Foreman Christopher M. , Junca-Laplace Jean-Philippe , Wood Kevin D. , Nikitopoulos Dimitris E.
Published: August 2015

A new cascade wind tunnel has been designed and constructed at the LSU Wind Tunnel Laboratory. The objective was to develop a versatile test facility, suitable for a wide range of experimental studies and measurements on turbine airfoils, especially with regards to film-cooling incorporating realistic unsteady effects due to passing wakes. The test section consists of a four passage linear cascade composed of three full blades and two shaped wall blades. The 2D blade shape profile of the cascade is a high-lift, low-pressure turbine L1A profile provided by the US Air Force Research Laboratories (AFRL), with a 152-mm axial chord. The Reynolds number based on the axial chord length at the nominal freestream velocity of 50 ms−1 is 500,000. A conveyor-based system was designed and fabricated to simulate the passing wakes of the upstream vanes (or blades) on the test blades (or vanes) depending on which airfoil types are put on the stationary frame and the moving frame of the conveyor. The original implementation uses blade profiles on the stationary frame and thick plate wake generators on the translating frame. Results are presented from hot-wire surveys conducted to characterize and qualify the velocity and turbulence intensity distributions and associated spectral characteristics at the cascade test section inlet, in the wake of the vanes and in the wake of the test blade. A blade instrumented with 123 pressure taps was used to acquire static pressure profiles of the cascade central blade, which were compared to the ones from the nominal airfoil design as well as to those obtained from a CFD simulation of the cascade flow. Incoming velocity and temperature profiles were found to be uniform to within a few percentage points, and the pressure coefficient distribution was found to be in good agreement with design values. The passage periodicity of the conveyor-belt-driven, flat-plates was verified and their wake was characterized. These results verified that the cascade wind tunnel operates according to design, thus proving to be a reliable test-bed for film cooling studies with and without unsteady wake effects. The design also incorporates an in-house-designed, miniature periscopic and adjustable laser sheet generating system integrated within the “dummy” blades to enable Particle Image Velocimetry measurements in the intra-blade domain.
The Effect of Aspect Ratio on Compressor Performance
Authors: To Ho-On , Miller Robert J.
Published: August 2015

This paper considers the effect of aspect ratio on compressor performance. It is shown that the aspect ratio at which max efficiency occurs is relatively low, typically between 1 and 1.5. At these aspect ratios, decomposition of the flow field into freestream and endwall flows becomes difficult. In this paper, a unique approach is taken; McKenzie’s ‘linear repeating stage’ concept is used and a novel way of defining freestream flow is proposed. Through these simplifications and methods, physically accurate decomposition of the flow field for aspect ratios as low as ∼0.7 can be achieved.

This ability to accurately decompose the flow field leads to two key findings. Firstly, the commonly accepted relationship of endwall loss coefficient varying inversely with aspect ratio is inaccurate. Instead, a new term, which the authors refer to as ‘effective aspect ratio’, should replace aspect ratio. It is shown that not doing so can result in efficiency errors of ∼0.6% at low aspect ratios. Secondly, there exists a low aspect ratio limit below which the two endwall flows interact causing a large separation to occur along the span. From these findings, a low order model is developed to model the effect of varying aspect ratio on performance.

The last section of this paper uses this low order model as well as a simple analytical model to show that to a first order, the optimum aspect ratio is just a function of the loss generated by the endwalls at zero clearance and the rate of increase in profile loss due to blade thickness. This means that once the endwall configuration has been selected i.e. cantilever or shroud, the blade thickness sets the optimum aspect ratio.
Fuel Efficiency Optimization for a Divided Exhaust Period Regulated Two-Stage Downsized SI Engine
Authors: Hu Bo , Akehurst Sam , Brace Chris , Lu Pengfei , Copeland Colin D. , Turner J. W. G.
Published: August 2015

In our previous paper, a new gas exchange concept termed Divided Exhaust Period Regulated 2-stage (DEP R2S) system has been proposed. In this system, two exhaust valves in each cylinder are separately functioned with one valve feeding the exhaust mass flow into the high pressure (HP) manifold whilst the other valve evacuating the remaining mass flow directly into the low pressure (LP) manifold. By adjusting the timing of the exhaust valves, the target boost can be controllable whilst improving the engine’s pumping work and scavenging is attainable which results in better fuel efficiency from the gas exchange perspective.

This paper will continue this study by adding an appropriate knock model to examine the benefits this concept could bring to the combustion phasing. The results at full load showed that under knock limited spark advance (KLSA) and fully optimized exhaust valve timing condition, the DEP R2S system benefited from lower pumping loss and better scavenging due to the reduced backpressure and improved pulsation interference despite suffering from reduced expansion ratio and expansion work. The combustion phasing was advanced across the engine speed which is mainly attributed to the reduced residual and the reduced requirement of gross IMEP. The net BSFC was observed to improve by up to 3% depending on the engine operating points. At part load, the DEP R2S system could be used as a mechanism to extend the ‘duration’ of the exhaust valve. This will reduce the recompression effect of the exhaust residuals during the beginning and the end of the exhaust stroke compared to the original R2S model with late exhaust valve opening and early exhaust valve opening. In addition, increased internal EGR due to the increased overlap between the LP and the intake valve is also beneficial for the improved PMEP as the throttle can be further opened to reduce the corresponding throttling loss. The average net BSFC improvement is expected to be approximately 6–7%.
A Throttle Loss Recovery Concept Using an Expander for a 2.0 Litre Turbocharged Gasoline Engine
Authors: Lu P. , Hu B. , Brace C.
Published: August 2015

In the internal combustion engine, a large amount of energy is rejected in the form of exhaust heat without being converted into brake work.

Additionally, in gasoline engines, throttle losses are also a considerable disadvantage limiting the capability to achieve higher thermal efficiency. Under part load conditions, both the power demand and engine speed are much lower than the maximum achievable. The throttle is partially closed to restrict inlet air mass flow to regulate the brake power production. To overcome the friction and turbulence losses at the small throttle opening, negative pressure is produced in the manifold at the cost of engine power.

This paper explores the effectiveness of an expander installed in the inlet duct of the engine to lessen, even eliminate, the throttle losses by allowing power to be reclaimed from the pressure drop across the expander, which will otherwise be wastefully dissipated across the throttle. In this way the pumping losses are reduced.

The engine system was modelled in GT-Power which is a 1-dimensional engine simulation code. The limits in decreasing in pressure drop through the throttle and the power generation from the expander were explored. Together with a turbo machine recovering energy from the exhaust flow, this system was able to enhance the fuel economy by about 5% when operating at 1.75 bar BMEP from 500–3000rpm compared with a conventional turbocharged engine. The influence of the expander machinery on the combustion and the turbocharger performance was also discussed. To achieve the highest performance level, careful optimization of the expander size and control strategy and proper matching with engine system are critical.
Undergraduate Project in Compressor Rig Design, Fabrication and Testing for Complete Engineering Training
Authors: Vo Huu Duc , Trépanier Jean-Yves
Published: August 2015

An ambitious project in propulsion was introduced as part of the final-year integrator project offerings of the mechanical and aerospace engineering programs at École Polytechnique de Montréal in 2011–2012. It has been running successfully for the past three academic years. The project consists in the design, fabrication and placement into service of a functional instrumented multi-stage compressor test rig, including the compressor, for research in compressor aerodynamics. A team of 15–17 senior-year undergraduate engineering students are given set of design and performance specifications and measurement requirements, an electric motor and drive, a data acquisition system and some measurement probes. They must complete the project in two semesters with a budget on the order of Can$15,000. The compressor is made from rapid prototyping to keep production cost and time reasonable. However, its required rotation speed of 7200 rpm stretches the limits of the plastic material and presents the same structural challenges as industrial compressors running at higher speeds.

The students are split into sub-teams according to the required disciplines, namely compressor aerodynamics, general aerodynamics, structures, dynamics, mechanical design and integration, instrumentation and project management. For the initial phase, which covers the first two months, the students receive short seminars from experts in academia and industry in each discipline and use the knowledge from fundamental engineering courses to analytically model the different components to come up with a preliminary design. In the second phase, covering months three through six, the students are trained at commercial simulation tools and use them for detailed analysis to refine and finalize the design. In each of the first two phases, the students present their work in design reviews with a jury made up of engineers from industry and supervising professors. During the final phase, the compressor is built and tested with data acquisition and motor control programs written by the students. Finally, the students present their results with comparison of measured performance with numerical and analytical predictions from the first two phases and hand over their compressor rig with design and test reports as well as a user manual and an assembly/maintenance manual.

This complete project allows the students to put into practice virtually all the courses of their undergraduate engineering curriculum while giving them an extensive taste of the rich and intellectually challenging environment of gas turbine and turbomachinery engineering.
Effects of Vortex-Vortex Interaction in a Compressor Cascade With Vortex Generators
Authors: Zheng Tan , Qiang Xiaoqing , Teng Jinfang
Published: August 2015

This paper presents a numerical investigation to explore the effects of vortex generators on a high speed compressor cascade. Secondary flow effects like the corner separation vortex have an influence on the performance of a compressor cascade such as leading to increased losses. In order to control the corner separation vortex and reduce losses, an extensive study of vortex generators applied to a compressor cascade is conducted. A preliminary study by steady 3D RANS simulations is performed using the Spalart-Allmaras turbulence model. The aerodynamic performance as well as the behavior of the corner separation vortex is investigated in the compressor cascade without vortex generators. Then, a vortex generator is added to the cascade, which is numerically simulated. Various configurations are considered, which are decided by the height and installation angle of the vortex generator. Comparison of the performance attained by these configurations results in an optimum scheme that has minimum losses. Furthermore, unsteady 3D DES simulations are performed with the optimum configuration. This method that predicts the flow field more precisely could help verify the accuracy of the RANS results. Finally, by analyzing all the resulting aerodynamic performance and numerical flow phenomena, the mechanism of vortex-vortex interaction is presented and discussed, which could be a criterion to reduce the corner separation flow and enhance the performance of axial compressors.
Combination Effects of Upstream-Ramp and Swirling Coolant Flow on Film Cooling Characteristics
Authors: Yang Wenshuo , Pu Jian , Wang Jianhua
Published: August 2015

This paper presents an experimental investigation on the performances of a new film cooling structure design, in which a ramp is placed upstream of cylindrical film hole and a cylindrical cavity with two diagonal impingement holes is set at the inlet of the film hole to generate a swirling coolant flow entering the film hole. The experiments are carried out by two undisturbed measurement techniques, Planar Laser Induced Fluorescence (PLIF) and Time-Resolved Particle Image Velocimetry (TRPIV) in a water tunnel. The effects of the upstream-ramp angle, blowing ratio (BR) and coolant impingement angle on the film cooling performances of a flat plate are studied at three ramp angles (0°, 15° and 25°), two coolant swirling directions (clockwise and counter-clockwise), two impingement angles (15° and 30°), and three BRs (0.6, 1.0, and 1.4). The experimental results show that at high BRs, the combination structures of the upstream-ramp with the swirling coolant flow generated by the impingement angles can significantly improve film cooling performances; the best combination is at 30° impingement angle and 25° ramp angle. The reason can be explained by the fact that the swirling flow is significantly pressed onto wall through the upstream-ramp. Using the analogous analysis of heat and mass transfer, the adiabatic film effectiveness averaged over a cross section is obtained, and the analysis indicates that at high BRs, the combined effect of the a ramp with a large angle of 25° with 30° impingement angle can increase the film effectiveness up to 30% in comparison with the case without ramp at the exit of the film hole. The images captured by PLIF exhibit an interesting phenomenon, i.e. the swirling coolant in different directions can influence the counter vortex pair (CVP) in rotating layer, and the coolant swirling direction in clockwise enhances the right mixing of the CVP with coolant ejection, whereas the coolant swirling direction in counter-clockwise enhances the left mixing of the CVP with coolant ejection.
Overall Cooling Effectiveness Characteristic and Influence Mechanism on an Endwall With Film Cooling and Impingement
Authors: Li Mingfei , Li Xueying , Ren Jing , Jiang Hongde
Published: August 2015

The cooling system is required to ensure gas turbine can work at high temperature, which has exceeded the material limitation. An endwall cooling test rig was built up to conduct the endwall cooling research. A detailed work was done for analyzing characteristics of endwall heat transfer and discussing the multi-parameter influence mechanism of overall cooling effectiveness. The main flow side heat transfer coefficient, adiabatic film cooling effectiveness and overall cooling effectiveness were measured in the experiments. The effects of coolant mass flowrate ratio (MFR) were considered through the measurement. In order to analyze how each of the parameters works on overall cooling effectiveness, a one-dimensional correlation was developed. The results showed that obvious enhancement could be found in cooling effectiveness by increasing coolant MFR, and the film jet can be easily attached to the surface after the acceleration of the main flow in the nozzle channel. Comparing with film cooling effectiveness, overall cooling effectiveness distribution is more uniform, which is due to the influence of internal cooling. The verified one-dimensional analysis method showed that the improvement in film cooling would be most efficient to heighten overall cooling effectiveness. The improvement in film cooling would be more efficient when film cooling effectiveness is in high level than in low level. However, the enhancement of internal heat transfer is more efficient when internal heat transfer coefficient is low.
Turbine Blade Life Prediction Using Fluid-Thermal-Structural Interaction Modelling
Authors: Ubulom I. A. , Shankar K. , Neely A. J.
Published: August 2015

The stringent structural requirements posed on aircraft engines, especially the high pressure turbine blades, result from the diversity of the extreme operational conditions they are subjected to. The accurate life assessment of the blades under these conditions therefore demands accurate analytical tools and techniques, and also an elaborate understanding of the operational conditions. Given the drive to reduce cost related to experimental testing, numerical approaches are often adopted to aid in the initial design stages. With recent advancement in numerical modelling, the simultaneous integration of the various numerical codes of fluid flow and structural analysis (otherwise known as fluid-structure interaction) is projected to provide reliable input into fatigue life prediction programs. This study adopts the numerical method of fluid-structure interaction to investigate the fatigue properties of the Aachen turbine test case. A load-time history obtained for the high stress monitor position is superimposed on that from a quasi-static FE solution, and used as input into a fatigue estimation tool. The low cycle fatigue (LCF) is estimated using the Basquin-Coffin-Manson correlation with corrections for mean stress and multi-axial fatigue effects. An FFT analysis of the fluctuating aerodynamic loads show signals with significant high frequency content. There is noticeable increased energy signal at the rotor inlet as compared to stator inlet. The stator inlet signals, however, are characterized by multiple resonances of frequency with lower energy content. By avoiding the resonances, the fatigue analysis predicts a safe design with a safety factor level of 3 for the rotor.
Experimental Investigation of Coolant-to-Mainstream Scaling Parameters With Cylindrical and Shaped Film Cooling Holes
Authors: Anderson Joshua B. , Boyd Emily J. , Bogard David G.
Published: August 2015

The performance of film cooling designs is typically quantified by the adiabatic effectiveness, with results presented in terms of non-dimensional parameters such as the blowing ratio, momentum flux ratio, or velocity ratio of the coolant to the overflowing mainstream gas. In order to appropriately model experimental film cooling designs, the correct coolant flow parameter should be selected. In this work, a single row of axial round holes and shaped holes were placed in a flat plate and tested within a recirculating wind tunnel at low speeds and temperatures. Mainstream turbulence intensity and boundary layer thickness were set similar to expected engine conditions. The density ratio of the coolant was varied from 1.2 to 1.6 in order to independently vary the parameters listed above, which were tested at six different conditions for each density ratio. High-resolution IR thermography was used to measure adiabatic effectiveness downstream of the single row of cooling holes. The results indicate that adiabatic effectiveness performance of cylindrical and shaped holes are scaled most effectively using velocity ratio, providing much more accurate results then when the blowing ratio is used.
Forced Coefficients for a Short Length, Open-Ends Squeeze Film Damper With End Grooves: Experiments and Predictions
Authors: San Andrés Luis , Jeung Sung-Hwa , Bradley Gary
Published: August 2015

Squeeze Film Dampers (SFDs) are effective to ameliorate shaft vibration amplitudes and to suppress instabilities in rotor-bearing systems. Compact aero jet engines implement ultra-short length SFDs (L/D ≤ 0.2) to satisfy stringent weight and space demands with low parts count. This paper describes a test campaign to identify the dynamic forced response of an open ends SFD (L=25.4 mm, D=125.7 mm), single film land and oil fed through three holes (120° apart), operating with similar conditions as in an aircraft engine. Two journals make for two SFD films with clearances cA=0.129 mm and cB=0.254 mm (small and large). The total oil wetted length equals Ltot=36.8 mm that includes deep end grooves, width and depth = 2.5 × 3.8 mm, for installation of end seals. In the current experiments, the end seals are not in place. A hydraulic static loader pulls the bearing cartridge (BC) to a preset static eccentricity (eS) and two electromagnetic shakers excite the BC with single frequency loads to create circular orbits, centered and off-centered, over a prescribed frequency range ω=10–100Hz. The whirl amplitudes range from r=0.05cA–0.6cA and r=0.15cB–0.75cB while the static eccentricity increases to eS=0.5cA and eS=0.75cB, respectively. Comparisons of force coefficients between the two identical dampers with differing clearances show that the small clearance damper (cA) provides ∼4 times more damping and ∼1.8 times the inertia coefficients than the damper with large clearance (cB). The test results demonstrate damping scales with ∼1/c3 and inertia with ∼1/c, as theory also shows. Analysis of the measured film land pressures evidence that the deep end grooves contribute to the generation of dynamic pressures enhancing the dynamic forced response of the test SFDs. A thin film flow model with an effective groove depth delivers predictions that closely match the test damping and inertia coefficients. Other predictions, based on the short length bearing model, use an effective length Leff ∼1.17L to deliver damping coefficients 15% larger than the experimental results; however, inertia coefficients are ½ of the identified magnitudes. The experiments and analysis complement earlier experimental work conducted with centrally grooved SFDs.
Secondary Deviation and Unsteady Blockage in an LP Turbine due to Off-Design Operation
Authors: Lipfert Martin , Marx Martin , Habermann Jan , Rose Martin G. , Staudacher Stephan , Guendogdu Yavuz , Freygang Udo
Published: August 2015

A two-stage low pressure turbine is tested at the aerodynamic design point and a strong off-design point representing flight idle conditions. The tests are performed on an altitude test facility at engine representative conditions. Time-resolved measurements are performed with dual-film probes up- and downstream of the second NGV row. The aim is to study the flow field for secondary deviation and the generation of losses in the NGV row. The experimental results are compared with multistage URANS predictions. The simulations match the measured data and allow for detailed analysis of the time-resolved flow field. With off-design operation a strong increase in cross-flow is observed due to radial migration. Wake fluid from the first stage tends to migrate towards the hub section and changes the blockage unsteadily in the NGV row. At off-design operation a distinction between a two-dimensional primary flow to the secondary flow areas is no longer possible.
A Comparative Study on the Options in Combining Solid Oxide Fuel Cell With Gas Turbine
Authors: Yi Ji Hye , Choi Ju Hwan , Kim Tong Seop
Published: August 2015

Various options in combining a solid oxide fuel cell (SOFC) with a gas turbine (GT) were compared in this study. The combination of an SOFC with either a simple gas turbine or a gas/steam turbine combined cycle was investigated. For each combined system, the effect of using a recuperative heat exchanger was examined. The design parameters of a state-of-the-art gas turbine for central power stations were used. The GT modeling included modulation of turbine coolant flow depending on turbine working conditions. An SOFC temperature of 900°C was used. Given a currently available reference voltage, pressure-dependent SOFC cell voltage was used. The analysis was divided into two parts. In the first part, the turbine inlet temperature of the reference gas turbine was given and the influence of pressure ratio was analyzed. In the second part, the influence of varying turbine inlet temperature was analyzed to search for optimal design conditions. The results showed that the SOFC/GTCC systems would provide considerably higher efficiencies than the SOFC/GT systems. The optimal pressure ratio in terms of system efficiency is over 30 for non-recuperated systems but is around 10 for recuperated systems. Reducing the extra fuel to the gas turbine combustor improves system efficiency, especially in the SOFC/GT systems. With zero extra fuel, efficiencies of all of the four systems exceed 70%, the highest of which is obtained by the recuperated SOFC/GTCC layout.
Direct Numerical Simulations of a High Pressure Turbine Vane
Authors: Wheeler Andrew P. S. , Sandberg Richard D. , Sandham Neil D. , Pichler Richard , Michelassi Vittorio , Laskowski Greg
Published: August 2015

In this paper we establish a benchmark data set of a generic high-pressure turbine vane generated by direct numerical simulation (DNS) to resolve fully the flow. The test conditions for this case are a Reynolds number of 0.57 million and an exit Mach number of 0.9, which is representative of a modern transonic high-pressure turbine vane. In this study we first compare the simulation results with previously published experimental data. We then investigate how turbulence affects the surface flow physics and heat transfer. An analysis of the development of loss through the vane passage is also performed. The results indicate that free-stream turbulence tends to induce streaks within the near wall flow, which augment the surface heat transfer. Turbulent breakdown is observed over the late suction surface, and this occurs via the growth of two-dimensional Kelvin-Helmholtz spanwise roll-ups, which then develop into lambda vortices creating large local peaks in the surface heat transfer. Turbulent dissipation is found to significantly increase losses within the trailing-edge region of the vane.
Thermal Incineration of VOCs in a Jet-Stabilized Micro Gas Turbine Combustor
Authors: Schwärzle A. , Monz T. O. , Aigner M.
Published: August 2015

Using gas turbines for waste gas treatment is a promising technology compared to other thermal oxidizing systems in terms of total efficiency, due to the combined heat and power production. In this work, experiments have been carried out where an air stream containing volatile organic compounds (VOCs) is fed to a micro gas turbine combustor which is co-fired using natural gas. All experiments were conducted at atmospheric pressure. For lower preheat temperatures, the equivalence ratio of the pilot stage was step-wise increased at constant global air to fuel ratios to further extend the operation limit. The VOC destruction efficiency of the burner is analyzed for various oxygenated VOCs and concentrations with a maximum lower heating value of the VOC containing air stream of 0.25 MJ/Nm3. The stability range of the burner is presented for various equivalence ratios with a global volumetric heat release up to 33 MW/m3 and air preheat temperatures up to 650 °C. The flame is analyzed in terms of shape, length and lift-off height, using the OH* chemiluminescence signal detected by an ICCD-camera. At same air numbers, changes on the flame are insignificant to the different VOCs in most cases. Regarding the emissions of NOx, the VOC containing air is beneficial at all air numbers, while a decrease in CO is only observed for lower air numbers. A minimum of CO emissions for both preheat temperatures is obtained at an adiabatic flame temperature of 1671 K.
Advanced Water Droplet Erosion Protection for Modern Low Pressure Steam Turbine Steel Blades
Authors: Schuerhoff Joerg , Ghicov Andrei , Sattler Karsten
Published: August 2015

Blades for low pressure steam turbines operate in flows of saturated steam containing water droplets. The water droplets can impact rotating last stage blades mainly on the leading edge suction sides with relative velocities up to several hundred meters per second. Especially on large blades the high impact energy of the droplets can lead to a material loss particularly at the inlet edges close to the blade tips. This effect is well known as “water droplet erosion”.

The steam turbine manufacturer use several techniques, like welding or brazing of inlays made of erosion resistant materials to reduce the material loss. Selective, local hardening of the blade leading edges is the preferred solution for new apparatus Siemens steam turbines. A high protection effect combined with high process stability can be ensured with this Siemens hardening technique. Furthermore the heat input and therewith the geometrical change potential is relatively low. The process is flexible and can be adapted to different blade sizes and the required size of the hardened zones. Siemens collected many years of positive operational experience with this protection measure.

State of the art turbine blades often have to be developed with precipitation hardening steels and/or a shroud design to fulfill the high operational requirements. A controlled hardening of the inlet edges of such steam turbine blades is difficult if not impossible with conventional methods like flame hardening. The Siemens steam turbine factory in Muelheim, Germany installed a fully automated laser treatment facility equipped with two co-operating robots and two 6 kW high power diode laser to enable the in-house hardening of such blades. Several blade designs from power generation and industrial turbines were successfully laser treated within the first year in operation.

This paper describes generally the setup of the laser treatment facility and the application for low pressure steam turbine blades made of precipitation hardening steels and blades with shroud design, including the post laser heat treatments.
Blue Combustion: Stoichiometric Hydrogen-Oxygen Combustion Under Humidified Conditions
Authors: Schimek Sebastian , Stathopoulos Panagiotis , Tanneberger Tom , Paschereit Christian Oliver
Published: August 2015

The use of renewable energy sources raises the demand of fast and flexible storage techniques and fast power availability to ensure electrical grid stability. A promising storage approach is the production of hydrogen and oxygen by electrolysis. The possibility of using a completely closed cycle of water, hydrogen and oxygen promises an attractive approach for high efficiency, zero emission energy storage. Since electrolysis can be carried out under high pressure, the compressor part of the gas turbine would be unnecessary, which is beneficial in terms of efficiency. Furthermore, high turbine pressure ratios, compared to typical gas turbine applications, can be reached easily.

However, the combustion of hydrogen and oxygen in gas turbines is a challenging task. Hydrogen and oxygen mixtures are extremely reactive and result in very high flame temperatures. In the present study the feasibility of steam-diluted combustion of hydrogen and oxygen at stoichiometric conditions is shown. A suitable combustor is developed and experimentally validated. The degree of humidity is varied systematically for stoichiometric hydrogen oxygen combustion. Flame shapes, temperature estimations and operating limits are compared and discussed.
Space-Time Gradient Method for Unsteady Bladerow Interaction: Part I — Basic Methodology and Verification
Authors: Yi J. , He L.
Published: August 2015

For advanced turbomachinery development, there is increasing interest to carry out unsteady analyses for flows through multiple bladerows during a design stage. Even with the huge increase in computer processing power currently available, direct unsteady calculations in a whole annulus domain are still very time consuming. Efficient alternative methods with truncations in time and/or in space have been developed for unsteady turbomachinery flows in the past 20 years or so, but they all are associated with related limitations.

The present development is motivated to maintain as many modelling fidelities of direct unsteady solution methods as possible while still have a significant speed-up. To this end, a new steady-solution-like unsteady time-domain methodology has been developed for bladerow interactions.

No circumferential domain truncation is required so that a direct periodic (repeating) condition can be applied. For each mesh cell, the temporal gradient term as required to balance the discretized unsteady flow equation is obtained by specially sequenced spatial variations of corresponding cells in multiple-passages. Consequently the rotor-stator interface treatment becomes completely compatible to that of a direct unsteady solution. Thus a fully conservative interface is easily achieved, in contrast to existing truncated models where interface treatments tend to be complicated and non-conservative. The simultaneous solution procedure with the space-time gradient (STG) link enables an unsteady flow solution to converge at a rate comparable to that of a steady solution.

The background, motivation/justification, basic methodology and some preliminary verifications are described in this paper as Part I. Further validations and applications with extension to more complex configurations and flow conditions will be presented in Part II.
Power Augmentation Technologies: Part I — Literature Review
Authors: Ancona M. A. , Bianchi M. , Melino F. , Peretto A.
Published: August 2015

There exists a widespread interest in the application of gas turbine Power Augmentation Technologies (PATs) in both electric power generation and mechanical drive markets. This interest is attributable to liberalization in the power generation sector, increased electric rates during peak demand period and need for a proper selection of the gas turbine in a given application.

In the Part I of this study, a comprehensive literature review of the current technologies — investigating analytical, experimental, and practical aspects — is provided. Moreover, a schematic comparison, useful for the PATs selection, will be presented and discussed.
Investigation on Fluidic Throat Control of Fixed Geometric Nozzle and Coupling Performance With Aero-Engine
Authors: Wang Z. X. , Shi J. W. , Zhou L. , Zhang X. B. , Sun X. L. , Zan H.
Published: August 2015

Fluidic throat control is one key technology of fixed geometry thrust vectoring nozzle. Based on CFD numerical simulation, the flow characteristics of fluidic throat control by high pressure secondary flow injected into throat of nozzle, and performance of nozzle were investigated. The coupling method of nozzle with fluidic throat control and aero-engine was proposed. Firstly, the approximate model of nozzle with fluidic throat control was established by combining the design of experiment and response surface methodology. Then the aero-engine simulation model with air extraction was established. And by mass flow balance and pressure balance relationship, the approximate model of fluidic throat control nozzle and aero-engine simulation model with air extraction were combined into coupling model. Simulation results show that, due to the high pressure secondary flow injected into nozzle throat, there exist obvious high and low speed layers near nozzle throat, and the secondary injection made the nozzle flow over expand. Through the check of validation of approximate model, it shows good precision and can be used for the coupling model. For coupling performance, under different air extraction ratios from fan, the operating point on compressor map did not move obviously, the change of throat area affects the fan operating points greatly, and made it move to the surge boundary. And in the simulation, at the air extraction ratio of 12%, the throat control ratio of 17.8% was achieved.
The Impact of Low-Speed Fan Design on Noise: An Exploratory Study
Authors: Moreau Antoine , Guérin Sébastien
Published: August 2015

The steady evolution since the 1950’s towards higher bypass ratio engines has enhanced the acoustic role of the fan compared to the jet. This paper addresses the following question: does a further decrease in fan pressure ratio and rotor tip speed provide a significant reduction of fan broadband and tonal noise?

The paper presents two conceptual parametric studies conducted with a fast analytical aerodynamic and acoustic prediction tool. The tool includes an aerodynamic fan design model which provides the quantities necessary to assess the trade-off between efficiency and noise at given thrust conditions. The fan acoustic model has a theoretical formulation for broadband and tonal noise sources which is not based on empirical correlations; it is applied on conventional and contra-rotating fan concepts.

The first study proposes a variation of the design fan pressure ratio and evaluates for each concept its impact on noise at three acoustic off-design points. The results obtained, which are in line with a past NASA study, indicate that the optimum pressure ratio in terms of fan noise is well below the fuel-burn optimum. Significant noise reductions of the broadband and tonal interaction components can be achieved with fans operating in a fully subsonic domain. Alternatively, designing at higher speed and pressure ratio near the fuel-burn optimum may invite to consider the contra-rotating fan as a candidate: it performs there very well in terms of buzz-saw and broadband noise compared to the conventional fan.

The second study addresses the variation of design rotor tip speed at constant fan pressure ratio. Although reduced tip speed may suppress buzz-saw noise, the increased loading related to it implies large blade solidities and wakes which causes a significant increase in broadband noise. Thus, there is an optimum loading that will depend on the severity of fan inflow distortion and on the onset of buzz-saw noise. Here again these conclusions confirm some experimental work performed by NASA on two different fans, and by Rolls-Royce on a third one.
Experimental Investigations on Effects of Unsteady Wakes on the Secondary Flows in the Linear T106 Turbine Cascade
Authors: Kirik Ilker , Niehuis Reinhard
Published: August 2015

The present work extends previous investigations on the secondary flows around a steady base flow to detailed time-averaged and time-resolved flow field measurements up- and downstream of a low pressure turbine (LPT) cascade. Unsteady inflow was generated by a moving bar system.

The inlet conditions were determined using single hot wire anemometry and a pitot probe. Further detailed measurements of the three-dimensional flow field were carried out downstream of the cascade with triple hot wire anemometry, a conventional five hole pressure probe, and a dynamic pressure probe equipped with a single Kulite sensor. All measurements have been performed with and without moving bars. Cases with different Strouhal numbers and flow coefficients have been considered by varying the pitch of the moving bars between 40 mm and 80 mm and circumferential speed between 10m/s and 20m/s in order to investigate the influence of unsteady inflow in particular on the secondary flow field near the endwalls.

It turned out that the effects of the incoming wakes are evident in the time-accurate data in terms of their interaction with secondary flow vortices. On a time-averaged basis, however, the influence of the incoming wakes on the secondary flow field turned out to be small for the small inlet boundary layer.
Power Augmentation Technologies: Part II — Thermo-Economic Analysis
Authors: Ancona M. A. , Bianchi M. , Melino F. , Peretto A.
Published: August 2015

There exists a widespread interest in the application of gas turbine Power Augmentation Technologies (PATs) in both electric power generation and mechanical drive markets. This interest is attributable to liberalization in the power generation sector, increased electric rates during peak demand period and need for a proper selection of the gas turbine in a given application.

In the Part II of this study, an analytical evaluation of the ambient temperature effect on gas turbines performance is presented. Further, the achievable power boost due to the installation of the most adopted PAT strategies is deeply investigated. Considering a whole year of operation for a large number of worldwide locations, also the behavior change — due to the use of the PATs — on both the energy production and the economic aspect will be analyzed and discussed.
Numerical Assessment of Using Sherman-Morrison, Neumann Expansion Techniques for Stochastic Analysis of Mistuned Bladed Disc System
Authors: Yuan Jie , Scarpa Fabrizio , Allegri Giuliano , Patsias Sophoclis , Rajasekaran Ramesh
Published: August 2015

The paper presents an assessment about using two classical reduced-order techniques, the Sherman-Morrison-Woodbury (SMW) formula and the Neumann expansion method, to enhance the computational efficiency of the stochastic analysis in mistuned bladed disc systems. The frequency responses of the blades are evaluated for different mistuning patterns via stiffness perturbations. A standard matrix factorization method is used as baseline to benchmark the results obtained from the SMW formula and Neumann expansion methods. The modified SMW algorithm can effectively update the inversion of an uncertainty matrix without the need of separated inversions, however with a limited increase of the computational efficiency. Neumann expansion techniques are shown to significantly decrease the required CPU time, while maintaining a low relative error. The convergence of the Neumann expansion however is not guaranteed when the excitation frequency approaches resonance when the mistuned system has either a low damping or high mistuning level. A scalar-modified Neumann expansion is therefore introduced to improve convergence in the neighbourhood of the resonance frequency.