Accepted Manuscripts

Harald H.-W. Funke, Nils Beckmann, Jan Keinz and Sylvester Abanteriba
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038882
The Dry-Low-NOx (DLN) Micromix combustion technology has been developed as low emission combustion principle for industrial gas turbines fueled with hydrogen or syngas. The combustion process is based on the phenomenon of jet-in-crossflow-mixing. Fuel is injected perpendicular into the air-cross-flow and burned in a multitude of miniaturized, diffusion-like flames. The miniaturization of the flames leads to a significant reduction of NOx emissions due to the short residence time of reactants in the flame. In the Micromix research approach, CFD analyses are validated towards experimental results. The combination of numerical and experimental methods allows an efficient design and optimization of DLN Micromix combustors concerning combustion stability and low NOx emissions. The paper presents a comparison of several numerical combustion models for hydrogen and hydrogen-rich syngas. They differ in the complexity of the underlying reaction mechanism and the associated computational effort. The performance of a hybrid Eddy-Break-up model with a one-step global reaction is compared to a complex chemistry model and a Flamelet Generated Manifolds model, both using detailed reaction schemes for hydrogen or syngas combustion. Validation of numerical results is based on exhaust gas compositions available from experimental investigation on DLN Micromix combustors. The conducted evaluation confirms that the applied detailed combustion mechanisms are able to predict the general physics of the DLN-Micromix combustion process accurately. The Flamelet Generated Manifolds method proved to be generally suitable to reduce the computational effort while maintaining the accuracy of detailed chemistry.
TOPICS: Combustion, Hydrogen, Nitrogen oxides, Syngas, Flames, Emissions, Combustion chambers, Flamelet generated manifold, Chemistry, Exhaust systems, Computational fluid dynamics, Design, Experimental methods, Optimization, Turbines, Combustion technologies, Fuels, Eddies (Fluid dynamics), Industrial gases, Physics, Stability, Flow (Dynamics), Diffusion (Physics)
Xin Deng, Brian Weaver, Cori Watson, Michael Branagan, Houston G. Wood and Roger Fittro
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038857
Oil-lubricated bearings are widely used in high speed rotating machines such as those used in the aerospace and automotive industries that often require this type of lubrication. However, environmental issues and risk-adverse operations have made water lubricated bearings increasingly popular. Due to different viscosity properties between oil and water, the low viscosity of water increases Reynolds numbers drastically and therefore makes water-lubricated bearings prone to turbulence effects. The turbulence model is affected by eddy-viscosity, while eddy-viscosity depends on wall shear stress. Eddy-viscosity together with flow viscosity form the effective viscosity, which is the coefficient of the shear stress in the film. The turbulence model and Reynolds equation are bound together to solve when hydrodynamic analysis is performed, therefore improving the accuracy of the turbulence model is also vital to improving a bearing model's ability to predict film pressure values, which will determine the velocity and velocity gradients in the film. The velocity gradients in the film are the other term determining the shear stress. In this paper, three approaches applying Reichardt's formula were used to model eddy-viscosity in the fluid film. These methods are for determining where one wall's effects begin and the other wall's effects end. Trying to find a suitable model to capture the wall's effects, with aim to improve the accuracy of the turbulence model. The results of this study could aid in improving future designs and models of both oil and water lubricated bearings.
TOPICS: Eddies (Fluid dynamics), Viscosity, Modeling, Fluid films, Thrust bearings, Water, Turbulence, Bearings, Shear stress, Risk, Reynolds number, Aerospace industry, Pressure, Flow (Dynamics), Lubrication, Machinery
Michal Siorek, Stephen A. Guillot, Song Xue and Wing Ng
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038856
This paper describes studies completed using a quarter-scaled rig to assess the impact of turbine exit swirl angle and strut stagger on a turbine exhaust system consisting of an integral diffuser-collector. Advanced testing methods were applied to ascertain exhaust performance for a range of inlet conditions aerodynamically matched to flow exiting an industrial gas turbine. Flow visualization techniques along with complementary Computational Fluid Dynamics (CFD) predictions were used to study flow behavior along the diffuser endwalls. Complimentary CFD analysis was also completed with the aim to ascertain the performance prediction capability of modern day analytical tools for design phase and off-design analysis. The K-Epsilon model adequately captured the relevant flow features within both the diffuser and collector, and the model accurately predicted the recovery at design conditions. At off-design conditions, the recovery predictions were found to be pessimistic. The integral diffuser-collector exhaust accommodated a significant amount of inlet swirl without a degradation in performance, so long as the inlet flow direction did not significantly deviate from the strut stagger angle. Strut incidence at the hub was directly correlated with reduction in overall performance, whereas the diffuser-collector performance was not significantly impacted by strut incidence at the shroud.
TOPICS: Diffusers, Struts (Engineering), Gas turbines, Exhaust systems, Design, Flow (Dynamics), Computational fluid dynamics, Turbines, Testing, Industrial gases, Flow visualization
Youyao Fu, Bing Xiao, Chengwei Zhang, Jun Liu and Jiangxiong Fang
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038836
Diesel-natural gas dual fuel engine has gained increasing interesting in recent years because of its excellent power and economy. However, the reliability of the dual fuel engine does not meet the requirements of practical application. The piston maximun temperature(PMT) of the dual fuel engine easily exceeds the security border. In view of this, this paper proposes a method based on the lasso regression to estimate the PMT of the dual fuelengine, so as to real-timely monitor the health state of the dual fuel engine. Specifically, PMTs under some working conditions were off-line acquired by the finite element analysis with ANSYS. A model is presented to describe the relationship between the PMT and some indirect engine variables, including NOx emission, excess air coefficient, engine speed and inlet pressure, and the model parameters are optimized using the lasso regression algorithm, which can be easily implemented by the electronic control unit(ECU). Finally, the model is employed to real-timely estimate the PMT of the dual fuel engine. Experiments reveal that the proposed model produces satisfying predictions with deviations less than11
TOPICS: Temperature, Fuels, Engines, Diesel, Pistons, Nitrogen oxides, Emissions, Security, Reliability, Algorithms, Economics , Finite element analysis, Pressure
Chana Goldberg, Devaiah Nalianda, Panagiotis Laskaridis and Pericles Pilidis
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038837
Conventional propulsion systems are typically represented as uninstalled system to suit the simple separation between airframe and engine in a podded configuration. However, boundary layer ingesting systems are inherently integrated, and require a different perspective for performance analysis. Simulations of boundary layer ingesting propulsions systems must represent the change in inlet flow characteristics which result from different local flow conditions. In addition, a suitable accounting system is required to split the airframe forces from the propulsion system forces. The research assesses the performance of a conceptual vehicle which applies a boundary layer ingesting propulsion system - NASA's N3-X blended wing body aircraft - as a case study. The performance of the aircraft's distributed propulsor array is assessed using a performance method which accounts for installation terms resulting from the boundary layer ingesting nature of the system. A `thrust split' option is considered which splits the source of thrust between the aircraft's main turbojet engines and the distributed propulsor array. An optimum thrust split for a specific fuel consumption at design point is found to occur for a thrust split value of 94.1%. In comparison, the optimum thrust split with respect to fuel consumption for the design 7500 nmi mission is found to be 93.6%, leading to a 1.5% fuel saving for the configuration considered.
TOPICS: Flow (Dynamics), Boundary layers, Thrust, Propulsion systems, Design, Fuel consumption, Engines, Accounting, Engineering simulation, Vehicles, Aircraft, Wings, Turbojets, Simulation, Separation (Technology), Fuels
Hilal Bahlawan, Mirko Morini, Michele Pinelli, Pier Ruggero Spina and Mauro Venturini
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038838
This paper documents the set-up and validation of nonlinear autoregressive exogenous (NARX) models of a heavy-duty single-shaft gas turbine. The data used for model training are time series datasets of several different maneuvers taken experimentally on a gas turbine General Electric PG 9351FA during the start-up procedure and refer to cold, warm and hot start-up. The trained NARX models are used to predict other experimental datasets and comparisons are made among the outputs of the models and the corresponding measured data. Therefore, this paper addresses the challenge of setting up robust and reliable NARX models, by means of a sound selection of training datasets and a sensitivity analysis on the number of neurons. Moreover, a new performance function for the training process is defined to weigh more the most rapid transients. The final aim of this paper is the set-up of a powerful, easy-to-build and very accurate simulation tool which can be used for both control logic tuning and gas turbine diagnostics, characterized by good generalization capability.
TOPICS: Gas turbines, Sensitivity analysis, Time series, Simulation, Transients (Dynamics)
Jian Liu and Honghu Ji
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038813
Investigations on infrared radiation suppression of axisymmetric vectoring exhaust nozzle are meaningful, due to the requests for maneuverability and infrared stealth capability of aircrafts. In this paper, the synthetic suppression scheme of film cooling and low-emissivity coating was adopted on the center body and divergent flaps of the nozzles at 0°, 10°, and 20° vectoring angles. The infrared signatures of both the baseline axisymmetric vectoring exhaust nozzles and the nozzles with infrared suppression were measured. Comparing the infrared signatures of the nozzles with and without infrared suppression measures, the infrared suppression effectiveness of the film cooling and low-emissivity coating was obtained. The investigation results indicate that the infrared signatures of axisymmetric vectoring exhaust nozzle decrease with the increase of vectoring angle. The film cooling enables a remarkable decrease of the infrared signatures of axisymmetric vectoring exhaust nozzles. The synthetic suppression of film cooling and low-emissivity coating enables a further decrease of infrared signatures. For the case studied in this paper, the integrated radiation intensities of the nozzles with film cooling and low-emissivity coating at 0°, 10°, and 20° vectoring angles are decreased by 52.3%, 57.9%, and 37.2% at 0° measurement angle, respectively.
TOPICS: Coating processes, Coatings, Emissivity, Nozzles, Exhaust systems, Film cooling, Infrared radiation, Aircraft, Radiation (Physics)
Vinícius Tavares Silva, Cleverson Bringhenti, Jesuino T. Tomita and Anderson Frasson Fontes
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038814
This paper describes a methodology used for propeller performance estimation which was implemented in an in-house modular program for gas turbine performance prediction. A model based on subsonic generic propeller maps and corrected for compressibility effects, under high subsonic speeds, was proposed and implemented. Considering this methodology, it is possible to simulate conventional turboprop architectures and counter-rotating open rotor (CROR) engines in both steady-state and transient operating conditions. Two simulation scenarios are available: variable pitch angle propeller with constant speed; or variable speed propeller with constant pitch angle. The simulations results were compared with test bench data and two gas turbine performance commercial software were used to fulfill the model validation for conventional turboprop configurations. Furthermore, a direct drive CROR engine was simulated using a variable inlet guide vanes (VIGV) control strategy during transient operation. The model has shown to be able to provide several information about propeller-based engine performance using few input data and a comprehensive understanding on steady-state and transient performance behavior was achieved in the obtained results.
TOPICS: Engines, Transients (Dynamics), Rotors, Propellers, Steady state, Gas turbines, Simulation, Architecture, Computer software, Model validation, Inlet guide vanes, Compressibility
Shining Chan, Huoxing Liu, Fei Xing and Hang Song
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038815
This paper adapted and extended the preliminary two-step wave rotor design method with another step of experimental validation, so that it became a self-validating wave rotor design method with three steps. Firstly, the analytic design based on unsteady pressure wave models was elucidated and adapted to a design function. It was quick and convenient for a first prediction of the wave rotor. Secondly, the CFD simulation was adapted so that it helped to adjust the first prediction. It provided detailed information of the wave rotor inner flow. Thirdly, an experimental method was proposed to complement the validation of the wave rotor design. This experimental method realized tracing the pressure waves and the flows in the wave rotor with measurement on pressure and temperature distributions. The critical point of the experiment is that the essential flow characteristics in the rotor were reflected by the measurements in the static ports. In all, the three steps compensated for each other in a global design procedure, and formed an applicable design method for generic cases.
TOPICS: Waves, Design methodology, Rotors, Design, Pressure, Flow (Dynamics), Simulation, Gates (Closures), Temperature distribution, Computational fluid dynamics
Tashfeen Mahmood, Anthony J B Jackson, Vishal Sethi, Bidur Khanal and Fakhre Ali
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038816
During the second half of the 90's, NASA performed experimental investigations on six novel Thrust Reverser designs; Core Mounted Target Type Thrust Reverser (CMTTTR) design is one of them. To assess the CMTTTR efficiency and performance, NASA conducted several wind tunnel tests at Sea Level Static conditions. The results from these experiments are used in this paper series to validate the CFD results. This paper is part one of the three-part series; Part 1 and 2 discusses the CMTTTR in stowed and deployed configurations, all analysis in the first two papers are performed at SLS conditions. Part3 discusses the CMTTTR in the forward flight condition. The key objectives of this paper are: first, to perform the 3D CFD analysis of the reverser in stowed configuration; all analyses are performed at SLS condition. The second objective is to validate the acquired CFD results against the experimental data provided by NASA[1]. The third objective is to verify the fan and overall engine net thrust values acquired from the aforementioned CFD analyses against those derived based on 1-D engine performance simulations. The fourth and final objective is to examine and discuss the overall flow physics associated with the CMTTTR under stowed configuration. To support the successful implementation of the overall investigation, full-scale 3DCAD models are created, representing a fully integrated GE90 engine, B777 wing, and pylon configuration. Overall a good agreement is found between the CFD and test results; the difference between the two was less than 5%.
TOPICS: Thrust reversers, Computational fluid dynamics, Engines, NASA, Thrust, Simulation, Physics, Flow (Dynamics), Design, Engineering simulation, Wind tunnels, Wings, Flight, Seas
Tashfeen Mahmood, Anthony J B Jackson, Vishal Sethi, Bidur Khanal and Fakhre Ali
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038817
CMTTTR design was proposed by NASA in the second half of the 90's. NASA carried out several experiments at static conditions, and their acquired results suggested that the performance characteristics of the CMTTTR design falls short to comply with the mandatory TR performance criteria, and were therefore regarded as an infeasible design. However, the authors of this paper believe that the results presented by NASA for CMTTTR design require further exploration to facilitate the complete understanding of its true performance potential. This Part2 paper is a continuation from Part1and presents a comprehensive three-dimensional (CFD) analyses of the CMTTTR in deployed configuration; the analyses at forward flight conditions will be covered in Part 3. The key objectives of this paper are: first, to validate the acquired CFD results with the experimental data provided by NASA: this is achieved by measuring the static pressure values on various surfaces of the deployed CMTTTR model. The second objective is to estimate the performance characteristics of the CMTTTR design and corroborate the results with experimental data. The third objective is to estimate the Pressure Thrust (i.e. axial thrust generated due to the pressure difference across various reverser surfaces) and discuss its significance for formulating the performance of any thrust reverser design. The fourth objective is to investigate the influence of kicker plate installation on overall TR performance. The fifth and final objective is to examine and discuss the overall flow physics associated with the thrust reverser under deployed configuration.
TOPICS: Thrust reversers, Computational fluid dynamics, Design, NASA, Pressure, Thrust, Performance characterization, Physics, Flow (Dynamics), Flight
Yunus Emre Ayranci and Ozgen Akalin
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038818
Measurement of film thickness between piston ring and cylinder bore has been a challenge for decades; laser induced fluorescence method (LIF) was used by several groups and promising results are obtained for the investigation of lubricant film transport. In this study, blue light generated by a laser source is transmitted to a beam splitter by means of a fiber optic cable and combined with another fiber optic line, then transmitted to the piston ring and cylinder bore conjunction. The light causes the fluorescence dye present in the lubricant to emit light in a longer wavelength, i.e. green. Reflected light is recollected; blue wavelength components are filtered out using a narrow band pass optical filter, and only components in the florescence wavelength is transmitted to a photomultiplier tube. The photomultiplier produces a voltage proportional instantaneous lubricant film thickness. Then, the photomultiplier signal is calibrated for lubricant film thickness using a laser textured cylinder bore with known geometries. Additional marks were etched on the liner for calibration. The LIF system is adapted to a piston ring and cylinder bore friction test system simulating engine conditions. Static piston ring and reciprocating liner configuration of the bench test system allows the collection of continuous lubricant film thickness data as a function of crank angle position. The developed system has potential to evaluate new designs, materials and surface properties in a controlled and repeatable environment.
TOPICS: Lubricants, Cylinders, Film thickness, Piston rings, Wavelength, Lasers, Fibers, Fluorescence, Friction, Cables, Engines, Surface properties, Calibration, Filters, Signals
Saket Verma and Lalit M Das
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038798
In-cylinder pressure based combustion descriptors have been widely used for engine combustion control and spark advance scheduling. Although these combustion descriptors have been extensively studied for gasoline fuelled SI engines, adequate literature is not available on use of alternative fuels in SI engines. In an attempt to partially address this gap, present work focuses on spark advance modelling of hydrogen-fuelled SI engines based on combustion descriptors. In this study, two such combustion descriptors, namely, position of the pressure peak (PPP) and 50% mass fraction burned (MFB) have been used to evaluate the efficiency of the combustion. With a view to achieve this objective, numerical simulation of engine processes was carried out in computational fluid dynamics (CFD) software ANSYS FLUENT and simulation data were subsequently validated with the experimental results. In view of typical combustion characteristics of hydrogen fuel, spark advance plays a very crucial role in the system development. Based on these numerical simulation results, it was observed that the empirical rules used for combustion descriptors (PPP and 50% MFB) for the best spark advance in conventional gasoline fuelled engines do not hold good for hydrogen engines. This work suggests revised empirical rules as: PPP is 8-9 degrees ATDC and position of 50% MFB is 0-1 degrees ATDC for the MBT conditions. This range may vary slightly with engine design but remains almost constant for a particular engine configuration. Furthermore, using these empirical rules spark advance timings for the engine are presented for its working range.
TOPICS: Combustion, Modeling, Hydrogen, Spark-ignition engine, Engines, Computational fluid dynamics, Gasoline, Pressure, Computer simulation, Fuels, Computer software, Cylinders, Engine design, Hydrogen fuels, Simulation
Sun Xiaolin, Wang Zhanxue, Zhou Li, Shi Jingwei and Cheng Wen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038793
Serpentine nozzles have been used in stealth fighters to increase their survivability. For real turbofan aero-engines, the existence of the double ducts (bypass and core flow), the tail cone, the struts, the lobed mixers and the swirl flows from the engine turbine, could lead to complex flow features of serpentine nozzle. The aim of this paper is to ascertain the effect of different inlet configurations on the flow characteristics of a double serpentine convergent nozzle. The detailed flow features of the double serpentine convergent nozzle including/excluding the tail cone and the struts are investigated. The effects of inlet swirl angles and strut setting angles on the flow field and performance of the serpentine nozzle are also computed. Results show that the vortices, which inherently exist at the corners, are not affected by the existence of the bypass, the tail cone and the struts. The existence of the tail cone and the struts leads to differences in the high-vorticity regions of the core flow. The static temperature contours are dependent on the distributions of the x-streamwise vorticity around the core flow. The high static temperature region is decreased with the increase of the inlet swirl angle and the setting angle of the struts. The performance loss of the serpentine nozzle is mostly caused by its inherent losses such as the friction loss and the shock loss. The performance of the serpentine nozzle is decreased as the inlet swirl angle and the setting angle of the struts increase.
TOPICS: Nozzles, Flow (Dynamics), Vorticity, Temperature, Engines, Shock (Mechanics), Struts (Engineering), Corners (Structural elements), Turbines, Vortices, Ducts, Turbofans, Aircraft engines, Friction
Rebecca Zarin Pass, Sankaran Ramakrishnan and Chris Edwards
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038794
We systematically determine the maximally efficient manner of using water and air in a single-cycle steady-flow combustion gas-turbine power plant. In doing so, we identify the upper limit to exergy efficiency for dry and wet gas-turbine engines through architectures that employ regenerative work, heat, and matter transfers using imperfect practical devices. For existing device technology, the derived optimal architectures can theoretically achieve exergy efficiencies above 65% without employing a bottoming cycle. This surpasses known efficiencies for both wet and combined cycles. We also show that when optimally used, non-reactive matter transfers, like water, provide an alternative, but not superior, thermal regeneration strategy to direct heat regeneration.
TOPICS: Engines, Gas turbines, Architecture, Cycles, Water, Exergy, Heat, Matter, Flow (Dynamics), Combustion, Power stations, Combined cycles
Enrico Munari, Gianluca Delia, Mirko Morini, Emiliano Mucchi, Michele Pinelli and Pier Ruggero Spina
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038765
Nowadays, the operative range limit of compressors is still a key aspect of the research into turbomachinery. In particular, the study of the mass flow rate lower limit represents a significant factor in order to predict and avoid the inception of critical working conditions and instabilities such as stall and surge. The identification of the typical precursors of these two phenomena can imply many advantages, in both stationary and aeronautic applications, such as avoiding the loss of production (in industry) and efficiency of systems, and reducing the maintenance and repairing cost. Many approaches can be adopted to achieve this target, but one of the most fascinating is the vibro-acoustic analysis of the compressor response during operation. At the Engineering Department of the University of Ferrara, a test bench, dedicated to the study of the performance of an aeronautic turboshaft engine multistage compressor, has been equipped with a high frequency data acquisition system. A set of triaxle accelerometers and microphones, suitable for capturing broad-band vibration and acoustic phenomena, were installed in strategic positions along the compressor and the test rig. A great amount of vibro-acoustic data were firstly processed through an innovative data analysis technique, and then correlated to the thermodynamic data recorded. Subsequently, the precursor signals of stall and surge were detected and identified demonstrating the reliability of the methodology used for studying compressor instabilities. The experimental data offer a valid alternative way of analyzing and detecting unstable compressor behavior characteristics by means of non-intrusive measurements.
TOPICS: Acoustics, Compressors, Surges, Maintenance, Flow (Dynamics), Engines, Accelerometers, Reliability, Vibration, Microphones, Signals, Turbomachinery, System efficiency, Data acquisition systems
Aditya Saurabh, Hassan Imran, Holger Nawroth, Christian Oliver Paschereit and Lipika Kabiraj
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038766
Fractal analysis is undertaken to characterize flame surface fluctuations on an unconfined turbulent premixed flame and the resulting far-field acoustics fluctuations. Results indicate that combustion noise is monofractal and is characterized by an anti-correlated structure with a Hurst exponent less than 0.5. The anti-correlated nature was identified in the pressure fluctuations as well as flame surface fluctuations for small time scales. Additionally, results suggest that flame surface fluctuations are multifractal for large time scales. The calculated Hurst exponent increases noticeably with the equivalence ratio and decreases slightly with Reynolds number for the investigated operating conditions. Variation in the Hurst exponent for combustion noise data is compared with a case study of synthetic fluctuations comprised of linear combinations of white and $1/f^2$ noise. These results provide a more detailed characterization of the temporal structure of flame surface fluctuations and resulting noise emission from turbulent premixed flames than is presently known.
TOPICS: Combustion, Noise (Sound), Fractals, Fluctuations (Physics), Flames, Turbulence, Acoustics, Reynolds number, Pressure, Emissions
Manuel Hildebrandt, Corina Schwitzke and Hans-Jörg Bauer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038767
Because of the superior sealing characteristics compared to labyrinth seals, brush seals found an increased spread in turbomachinery in recent years. Their outstanding sealing performance results mainly from their flexibility. Thus, a very small gap between the rotor and bristle package can be obtained without running the risk of severe detrimental deterioration in case of rubbing. Thanks to the flexible structure of the brush seal the contact forces during a rubbing event are reduced, however the frictional heat input can still be considerable. The geometry of the seal has a decisive influence on the resulting contact forces and consequently the heat input. The complex interactions between the geometric parameters of the seal and the heat input and leakage characteristics are not yet fully understood. This paper presents the investigation of the influence of the geometric parameters of a brush seal on the heat input into the rotor and the leakage behaviour. Two seals with different packing densities were tested under relevant engine conditions. The transient temperature rise during the rub event was recorded with 24 thermocouples in close proximity to the rub contact embedded in the rotor structure. By comparing the temperature curves with the results of a thermal finite element analysis of the rotor the heat input into the rotor was calculated iteratively. It could be shown that the packing density has a decisive influence on the overall operating behavior of a brush seal. Furthermore, results for the heat flux distribution between seal and rotor are shown.
TOPICS: Heat, Leakage, Rotors, Packing (Shipments), Sealing (Process), Packings (Cushioning), Temperature, Engines, Heat flux, Risk, Density, Transients (Dynamics), Finite element analysis, Flexible structures, Geometry, Thermocouples, Turbomachinery
Chiara Gastaldi, Teresa Berruti and Muzio M. Gola
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038773
The purpose of this paper is to propose an effective strategy for the design of turbine blades with underplatform dampers. The strategy involves damper "pre-optimization", already proposed by the authors, to exclude, before the blades-coupled nonlinear calculation, all those damper configurations leading to low damping performance. This paper continues this effort by applying pre-optimization to determine a damper configuration which will not jam, roll or detach under any in-plane platform kinematics (i.e. blade bending modes). Once the candidate damper configuration has been found, the damper equilibrium equations are solved by using both the multi-harmonic balance (MHB) method and the direct time integration (DTI) to the purpose of finding the correct number of Fourier terms to represent displacements and contact forces. It is shown that, contrarily to non-preoptimized dampers which may display an erratic behavior, one harmonic term together with the static term ensure accurate results. These findings are confirmed by a state-of-the-art code for the calculation of the nonlinear forced response of a damper coupled to two blades. Experimental FRFs of the test case with a nominal damper are available for comparison. The comparison of different damper configurations offers a "high level" validation of the pre-optimization procedure and highlights the strong influence of the blades mode of vibration on the damper effectiveness. It is shown that the pre-optimized damper is not only the most effective, but also the one that leads to a faster and more flexible calculation.
TOPICS: Dampers, Optimization, Blades, Vibration, Damping, Design, Kinematics, Turbine blades, Equilibrium (Physics)
Martin White, Christos N. Markides and A.I. Sayma
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038754
In this paper the effect of working fluid replacement within an organic Rankine cycle turbine is investigated by evaluating the performance of two supersonic stators operating with different working fluids. After designing the two stators, intended for operation with R245fa and Toluene working fluids with stator exit Mach numbers of 1.4 and 1.7 respectively, the performance of each stator is evaluated using ANSYS CFX. It is then hypothesised that the stator design points can be scaled to alternative working fluids by conserving the Prandtl-Meyer function and the polytropic index within the nozzle. A scaling method is developed and further CFD simulations for the scaled operating points verify that the Mach number distributions within the stator, and the non-dimensional velocity triangles at the stator exit, remain unchanged. This confirms that the method developed can predict stator performance following a change in the working fluid. Finally, a study investigating the effect of working fluid replacement on the thermodynamic cycle is completed. The results show that the same turbine could be used in different systems with power outputs varying between 17 and 112 kW, suggesting the potential of matching the same turbine to multiple heat sources by tailoring the working fluid selected.
TOPICS: Fluids, Turbines, Organic Rankine cycle, Stators, Mach number, Design, Engineering simulation, Nozzles, Heat, Simulation, Thermodynamic cycles, Computational fluid dynamics

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