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# Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042010
This paper describes results from an experimental study on influences of liquid fuel properties on lean blowout limits in an aero-type combustor. In particular, this work aimed to elucidate the roles of fuel chemical and physical properties on blowout. Fuel chemical properties stem from the fuel chemical structure, thus governing chemical kinetic behaviors of oxidation characteristics (ignition or extinction time scales) and others (fuel thermal stability, or sooting tendencies). Fuel physical properties affect the spray characteristics (atomization and evaporation rates). Eighteen different fuels, with a wide range of physical and chemical fuel properties, were tested. Several of these fuels were custom blends, developed to break inter-correlations between various physical and chemical properties. Fuel physical and chemical property effects were further separated by measuring blowout boundaries at three air inlet temperatures between 300 and 550 K, enabling variation in vaporization rates. The condition at 300 K corresponds to a temperature that is less than the flash point for most of the studied fuels and, therefore, forming a flammable mixture was challenging in this regime. The opposite scenario occurred at 550 K, where fuel droplets evaporate quickly, and the temperature actually exceeds the autoignition temperatures of some of the fuels. At 300 K, the data suggest that blowout is controlled by fuel physical properties, as a correlation is found between the blowout boundaries and the fuel vaporization temperature. At 450 and 550 K, the blowout boundaries correlated well with the derived cetane number, related to the fuel oxidation rate.
TOPICS: Combustion chambers, Fuels, Aircraft, Temperature, Chemical properties, oxidation, Thermal stability, Flash point, Evaporation, Sprays, Ignition, Drops
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041962
In this paper, an artificial neural network is introduced in order to detect the occurrence of misfire in an internal combustion (IC) engine by analyzing the crankshaft angular velocity. This study presents three reliable misfire detection procedures. In the first two methods, the fault features are extracted using both time domain and frequency domain techniques, and a multi-layer perceptron (MLP) serves as the pattern recognition tool for detecting the misfiring cylinder. In the third method, a one-dimensional (1-D) convolutional neural network (CNN) that combines feature extraction capability and pattern recognition is adopted for misfire detection. The experimental data are obtained by setting a six in-line diesel engine with different cylinder misfiring to works under representative operating conditions. Finally, all three diagnostic methods achieved satisfactory results, and the 1-D CNN achieved the best performance. The current study provides a novel way to detect misfiring in IC engines. Keywords: misfire detection, internal combustion engine, artificial neural network (ANN), multi-layer perceptron (MLP), convolutional neural network (CNN)
TOPICS: Artificial neural networks, Cylinders, Multilayer perceptron, Pattern recognition, Internal combustion engines, Combustion, Engines, Diesel engines, Feature extraction
Technical Brief
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041963
Critical slowing down (CSD) is a phenomenon that is common to many complicated dynamical systems as they approach critical transitions/bifurcations. We demonstrate that pressure signals measured during the onset of thermoacoustic instabilities in a gas turbine engine test exhibit evidence of CSD well before the oscillation amplitude increases. CSD was detected through both the variance and the lag-1 auto-regressive coefficient in a rolling window of the pressure signal. Increasing trends in both metrics were quantified using Kendall's $\tau$, and the robustness and statistical significance of the observed increases were confirmed. Changes in the CSD metrics could be detected several seconds prior to changes in the oscillation amplitude. Hence, real-time calculation of these metrics holds promise as early warning signals of impending thermoacoustic instabilities.
TOPICS: Oscillations, Signals, Pressure, Dynamic systems, Gas turbines, Bifurcation, Robustness
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041932
Diesel engines are of great challenges due to stringent emission and fuel economy requirements. Compared with the conventional turbocharger system, regenerative assisted system provides additional degree of freedoms for turbocharger speed control. Hence, it significantly improves control capability for exhaust-gas-recirculation (EGR) and boost pressure. This paper focuses on modeling and control of a diesel engine air-path system equipped with an EGR subsystem and a variable geometry turbocharger (VGT) coupled with a regenerative hydraulic assisted turbocharger (RHAT). The challenges lie in the inherent coupling among EGR, turbocharger performance, and high nonlinearity of the engine air-path system. A control-oriented nonlinear RHAT system model is developed; and a linear quadratic (LQ) control design approach is proposed in this paper to regulate the EGR mass flow rate and boost pressure simultaneously and the resulting closed-loop system performance can be tuned by properly selecting the LQ control weighting matrices. The gain-scheduling LQ controllers for both VGT-EGR and VGT-EGR-RHAT systems are compared with the in-house baseline controller (dual PID controllers), against the nonlinear plant. The simulation results show that the designed multi-input and multi-output LQ gain-scheduling controller is able to manage the performance trade-offs between EGR mass flow and boost pressure tracking. With the additional assisted and regenerative power available on the turbocharger shaft for the RHAT system, engine transient boost pressure performance can be significantly improved without compromising the EGR tracking performance, compared with the baseline control.
TOPICS: Turbochargers, Diesel engines, Control modeling, Exhaust gas recirculation, Pressure, Control equipment, Engines, Flow (Dynamics), Gain scheduling, Design, Closed loop systems, Transients (Dynamics), Corporate average fuel economy, Fuel efficiency, Emissions, Geometry, Simulation results, Tradeoffs
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041933
Impingement cooling is commonly employed in gas turbines to control the turbine tip clearance. During the design phase, Computational Fluid Dynamics is an effective way of evaluating such systems but for most Turbine Case Cooling (TCC) systems resolving the small scale and large number of cooling holes is impractical at the preliminary design phase. This paper presents an alternative approach for predicting aerodynamic performance of TCC systems using a "smart" porous media to replace regions of cooling holes. Numerically (CFD) defined correlations have been developed, which account for geometry and local flow field, to define the porous media loss coefficient. These are coded as a user defined function allowing the loss to vary, within the calculation, as a function of the predicted flow and hence produce a spatial variation of mass flow matching that of the cooling holes. The methodology has been tested on various geometrical configurations representative of current TCC systems and compared to full cooling hole models. The method was shown to achieve good overall agreement whilst significantly reducing both the mesh count and the computational time to a practical level.
TOPICS: Cooling systems, Porous materials, Air flow, Modeling, Turbines, Cooling, Flow (Dynamics), Computational fluid dynamics, Design, Gas turbines, Impingement cooling, Clearances (Engineering), Geometry
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041920
Successful implementation of sCO2 power cycles requires high compressor efficiency at the design-point and over a wide operating range in order to maximize cycle power output and maintain stable operation over many transient and part-load conditions. This requirement is particularly true for air-cooled cycles where compressor inlet density is a strong function of inlet temperature that exhibits daily and seasonal variations as well as transient events. To meet these requirements, a novel centrifugal compressor stage design was developed that incorporates multiple range extension features, including a passive recirculating casing treatment and semi-open impeller design. This design was fabricated via direct metal laser sintering and tested in an open-loop test rig in order to validate simulation results and the effectiveness of the casing treatment configuration. Comparison of predicted performance in air and CO2 conditions resulted in a reduced diffuser width for the air test in order to match design velocities and demonstrate the casing treatment. Test results in air show that the casing treatment performance generally matched CFD predictions, demonstrating an operating range of 69% and efficiency above predictions across the entire map. The casing treatment configuration demonstrated performance improvements over a solid wall configuration at low flows, resulting in an effective 14% increase in operating range with a 0.5-point efficiency penalty. The test results are also compared to a traditional fully shrouded impeller with the same flow coefficient and similar head coefficient, showing a 42% range improvement over traditional designs.
TOPICS: Compressors, Supercritical carbon dioxide, Thermodynamic power cycles, Design, Cycles, Flow (Dynamics), Impellers, Transients (Dynamics), Diffusers, Computational fluid dynamics, Temperature, Metals, Lasers, Simulation results, Carbon dioxide, Sintering, Stress, Density
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041921
Supercritical CO2 power cycles incorporate a unique combination of high fluid pressure, temperature, and density as well as limited component availability (e.g., high-temperature trip valves) that can result in operational challenges, particularly during off-design and transient operation. These conditions and various failure scenarios must be considered and addressed during the facility, component, and control system design phase in order to ensure machinery health and safety during operation. This paper discusses significant findings and resulting design/control requirements from a detailed failure modes and effects analysis that was performed for the 1 MWe-scale supercritical CO2 test loop at Southwest Research Institute, providing insight into design and control requirements for future test facilities and applications. The test loop incorporates a centrifugal pump, axial turboexpander, gas-fired primary heat exchanger, and micro-channel recuperator for testing in a simple recuperated cycle configuration at pressures and temperatures up to 255 bara and 715°C, respectively. The analysis considered off-design operation as well as high-impact failures of turbomachinery and loop components that may require fast shutdowns and blowdowns. The balance between fast shutdowns/blowdowns and the need to manage thermal stresses in the turbomachinery resulted in staged shutdown sequences and impacted the design/control strategies for major loop components and ancillary systems including the fill, vent, and seal supply systems.
TOPICS: Transients (Dynamics), High temperature, Design, Temperature, Failure, Supercritical carbon dioxide, Turbomachinery, Vents, Microchannels, Thermodynamic power cycles, Health and safety, Test facilities, Density, Fluid pressure, Machinery, Control systems, Thermal stresses, Failure mechanisms, Heat exchangers, Testing, Valves, Centrifugal pumps, Cycles
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041922
A series of experiments were performed on a vertical EV burner with a constant coflow air of 873 L /min to generate turbulent lean premixed flow in order to study the impact of the addition of Acetylene/Argon mixture to the liquefied petroleum gas (LPG) on the temperature field and flame structure. The fluidics mechanism was inserted at a fixed position inside the entry section of the EV burner assembly. The flow rates of fuel (LPG/ C2H2/ Ar) and air were measured using calibrated rotameters. The different volume ratios of the fuel constituents were admitted via three solenoid valves and monitored using a labview program. The axial temperature profiles at different operating conditions were measured using (type S) thermocouple. Flame images were obtained-before and after fluidics insertion- using a high resolution digital camera.The experimental program aims at identifying and analyzing the changes in flame characteristics resulting from the insertion of fluidics while considering different proportions of the fuel constituents) (including pure LPG , as a reference case). The results obtained indicate the following: it was noticed that in most cases of pure LPG only , and other mixtures the images shows increase in the length of the flame and decrease of its luminosity as a result of higher degrees of swirl due to the fluidics insertion while the temperature profiles of the different flames were changed. It was indicated that NOx trend was decreased by 52% while the combustion efficiency was improved by 2.5%.
TOPICS: Turbulence, Flames, Fuels, Temperature profiles, Flow (Dynamics), Temperature, Combustion, Petroleum, Solenoids, Manufacturing, Resolution (Optics), Valves, Thermocouples, Nitrogen oxides
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041870
In the design of gas turbine combustors, efforts are engineered towards reducing the combustion pollutant emission levels. The pollutant emissions can be reduced by premixing the fuel and the air prior to ignition. However, the main challenges encountered with premixing are flame flashback and blowout, thus, the preference of diffusion flames. In this study, flame behavior, flow patterns, and thermochemical fields of backward-inclined diffusion jet flames in crossflow at low jet-to-crossflow momentum flux ratio of smaller than 0.04 were studied in a wind tunnel. The backward-inclination angle was varied within 0° to 50°. The flames presented three characteristic modes: crossflow dominated flame (low backward inclination angle) denoted by a large down-washed recirculation flame, transitional flame (mediate backward inclination angle) identified by a recirculation flame and a tail flame, and jet dominated flame (high backward inclination angle) characterized by a blue flame base, a yellow tail flame, and the absence of a recirculation flame. Short flames are detected in the regime of the crossflow dominated flames-an indication of improved fuel-air mixing. The findings suggest that for low exhaust emissions which are vigorously pursued in the aviation and thermal power plant industries, especially during low-load operations, the jet dominated flames are the preferable flames as they generate low unburned hydrocarbon, carbon monoxide, and nitric oxide emissions compared to the other flames.
TOPICS: Momentum, Diffusion (Physics), Flames, Emissions, Pollution, Fuels, Stress, Combustion chambers, Carbon, Design, Gas turbines, Exhaust systems, Combustion, Flow (Dynamics), Diffusion flames, Preferences, Ignition, Thermal power stations, Wind tunnels, Aviation
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041871
Dual fuel engines can achieve high efficiencies and low emissions but also can encounter high cylinder-to-cylinder variations on multi-cylinder engines. In order to avoid these variations, they require a more complex method for combustion phasing control such as model-based control. Since the combustion process in these engines is complex, typical models of the system are complex as well and there is a need for simpler, computationally efficient, control-oriented models of the dual fuel combustion process. In this paper, a mean-value combustion phasing model is designed and calibrated and two control strategies are proposed. Combustion phasing is predicted using a knock integral model, burn duration model and a Wiebe function and this model is used in both an adaptive closed loop controller and an open loop controller. These two control methodologies are tested and compared in simulations. Both control strategies are able to reach steady state in 5 cycles after a transient and have steady state errors in CA50 that are less than ±0.1 crank angle degree (CAD) with the adaptive control strategy and less than ±1.5 CAD with the model-based feedforward control method.
TOPICS: Fuels, Combustion, Diesel engines, Control modeling, Cylinders, Engines, Control equipment, Computer-aided design, Steady state, Emissions, Errors, Feedforward control, Engineering simulation, Cycles, Adaptive control, Simulation, Transients (Dynamics)
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041273
In this paper, a novel start-up procedure of an existing combined cycle power station is presented, and it uses a feedback loop between the steam turbine, the boiler and the gas turbine start-up controls. This feedback loop ensures that the steam turbine can be started up with a significant reduction in stresses. To devise and assess this start-up methodology, a flexible and accurate dynamic model was implemented in the SimulinkTM environment. It contains more than 100 component blocks (heat exchangers, valves, meters and sensors, turbines, controls, etc.), and the mathematical component sub-models are based on physical models and experimental correlations. This makes the model generally applicable to other power plant installations. The model was validated against process data related to the three start-up types (cold start, warm start, hot start). On this basis, the optimization model is implemented with feedback loops that control for example the exit temperature of the gas turbine based on the actual steam turbine housing temperature, resulting in a smoother heating up of the steam turbine. The optimization model was used to define the optimal inlet guide vanes position and gas turbine power output curves for the three types of start-up. These curves were used during real power station start-ups, leading to, for cold and warm starts, reductions in the start-up time of respectively 32.5% and 31.8%, and reductions in the fuel consumption of respectively 47.0% and 32.4%.
TOPICS: Optimization, Power stations, Gas turbines, Steam turbines, Feedback, Temperature, Sensors, Stress, Boilers, Turbines, Valves, Combined cycle power stations, Heat exchangers, Heating, Dynamic models, Fuel consumption, Inlet guide vanes
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041872
Room-temperature fatigue tests were conducted on Ti 834 with prior creep strains accumulated under constant load at 550oC and 600oC, respectively. Microstructural and fractographic examinations on specimens with prior creep strain > 3% revealed the failure process consisting of multiple surface crack nucleation and internal void generation by creep, followed by fatigue crack propagation in coalescence with the internally distributed damage, leading to the final fracture. The amount of prior creep damage increased with creep strain. The fatigue life of Ti 834 was significantly reduced by prior creep straining. The behavior is rationalized with the integrated creep-fatigue theory.
TOPICS: Creep, High cycle fatigue, Damage, Fatigue, Temperature, Stress, Nucleation (Physics), Fracture (Materials), Fracture (Process), Failure, Fatigue cracks, Fatigue life, Fatigue testing, Fractography, Surface cracks
Technical Brief
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039461
Matching of a two-stage turbocharging system is important for high efficiency engines because the turbocharger is the most effective method of exhaust heat recovery. In this study, we propose a method to match a two-stage turbocharging system for high efficiency over the entire range of operational conditions. Air flow is an important parameter because it influences combustion efficiency and heat load performance. First, the thermodynamic parameters of the engine and the turbocharging system are calculated in eight steps for selecting and matching the turbochargers. Then, by designing the intercooler intensity, distribution of pressure ratio, and compressor operational efficiency, it is ensured that the turbochargers not only meet the air flow requirements but also operate with high efficiency. The concept of minimum total drive power of the compressors is introduced at a certain boost pressure. It is found that the distribution of pressure ratio of the high- and low-pressure turbocharger should be regulated according to the engine speed by varying the rack position of the variable geometry turbocharger (VGT) to obtain the minimum total drive work. It is verified that two-stage turbochargers have high efficiency over the entire range of operational conditions by experimental research. Compared with the original engine torque, low-speed torque is improved by more than 10%, and the engine low fuel consumption area is broadened.
TOPICS: Engines, Turbochargers, Pressure, Torque, Compressors, Air flow, Heat recovery, Stress, Design, Exhaust systems, Geometry, Fuel consumption, Heat, Combustion
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041755
This research evaluated the operational conditions for a diesel engine with high compression ratio (CR) converted to spark ignition (SI), under stable combustion conditions close to the knocking threshold. The main fuel used in the engine was biogas, which was blended with natural gas, propane and hydrogen to improve combustion properties and using two equivalence ratios. The engine limit to test the maximum output power was using the knocking threshold, just below the knocking threshold the output power and generating efficiency are the highest possible for each blend. Leaner mixtures increased the engine knocking tendency because the required increase in the % throttle reduced the pressure drop at the inlet stroke and increased the mixture pressure at the end of the compression stroke, which finally reduced the ignition delay time of the end gas and increased the knocking tendency of the engine for all the blends. Therefore, the output power should be decreased to operate the engine below to the knocking threshold. Purified biogas achieved the highest output power and generating efficiency compared with the other blends and the original diesel operation, this blend was operated with five equivalence ratios. This alternative fuel blend exhibits an optimal balance between knocking resistance, low heating value, flame speed and energy density.
TOPICS: Biogas, Natural gas, Hydrogen, Spark-ignition engine, Engines, Compression, Combustion, Fuels, Density, Pressure, Diesel, Diesel engines, Flames, Heating, Ignition delay, Ignition, Pressure drop
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041756
Reactor coolant pump is one of the most important equipment of the coolant loop in a pressurized water reactor system. Its safety re-lies on the characteristics of the rotordynamic system. For a canned motor reactor coolant pump, the liquid coolant fills up the clearance between the metal shields of the rotor and stator inside the canned motor, forming a long clearance flow. The fluid induced forces of the clearance flow in canned motor reactor coolant pump and their effects on the rotordynamic characteristics of the pump are numeri-cally and experimentally analyzed in this work. A transient computational fluid dynamics (CFD) method has been used to investigate the fluid induced force of the clearance. A vertical experiment rig has also been established for the purpose of measuring the fluid in-duced forces. Fluid induced forces of clearance flow with various whirl frequencies and various boundary conditions are obtained through the CFD method and the experiment. Results show that clearance flow brings large mass coefficient into the rotordynamic system and the direct stiffness coefficient is negative under the normal operating condition. The rotordynamic stability of canned motor reactor coolant pump does not deteriorate despite the existence of significant cross-coupled stiffness coefficient from the fluid induced forces of the clearance flow.
TOPICS: Flow (Dynamics), Fluids, Engines, Motors, Clearances (Engineering), Pumps, Nuclear reactor coolants, Computational fluid dynamics, Stiffness, Coolants, Transients (Dynamics), Metals, Safety, Whirls, Pressurized water reactors, Stators, Rotors, Boundary-value problems, Stability
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041726
A new model approach is presented in this work for including convective wall heat losses in the Direct Quadrature Method of Moments (DQMoM) approach, which is used here to solve the transport equation of the one-point, one-time joint thermochemical probability density function (PDF). This is of particular interest in the context of designing industrial combustors, where wall heat losses play a crucial role. In the present work, the novel method is derived for the first time and validated against experimental data for the thermal entrance region of a pipe. The impact of varying model-specific boundary conditions is analysed. It is then used to simulate the turbulent reacting flow of a confined methane jet flame. The simulations are carried out using the DLR in-house Computational Fluid Dynamics (CFD) code THETA. It is found that the DQMoM approach presented here agrees well with the experimental data and ratifies the use of the new convective wall heat losses model.
TOPICS: Turbulence, Simulation, Engineering simulation, Heat losses, Chemically reactive flow, Computational fluid dynamics, Design, Pipes, Boundary-value problems, Combustion chambers, Density, Flow (Dynamics), Entrance region, Flames, Methane, Method of moments, Probability
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041654
This paper introduces a test facility specifically designed to measure the axial stiffness and damping coefficients of an oillubricated thrust collar (TC). The geometry, load, and speeds of the test facility are representative of a production integrally geared compressor (IGC). Separate electric motors spin the shafts according to an assumed gear ratio, a pneumatic air piston loader provides a non-contacting, static thrust force, a remotelycontrolled impact hammer delivers a perturbation force, and eddy-current motion probes record the resulting vibration. The paper uses a one degree of freedom (1DOF) axial motion model that neglects the static and dynamic stiffness of the bull wheel and presents estimates of the TC oil-film dynamic coefficients for pinion spin speeds between 5 and 10 krpm, and static loads between 200 and 400 N, using time-domain (log-dec and damped period) and static load-deflection techniques. The measurements show that the TC oil-film develops appreciable stiffness (tens of MN/m), and the 1DOF model used here is inadequate for higher loads. Axial runout on the interfacing surfaces of the test facility TC and bull wheel complicates parameter identification, but time-domain averaging effectively attenuates the runout while preserving the transient vibration that results from the impact hammer. Measurements of the TC oil-film stiffness, damping and virtual mass coefficients are useful to machinery OEMs or end-users seeking to predict or diagnose subsynchronous vibration in their machine that might be TC related.
TOPICS: Compressors, Thrust, Stress, Stiffness, Test facilities, Vibration, Particle spin, Hammers, Spin (Aerodynamics), Rotation, Machinery, Wheels, Damping, Gears, Eddies (Fluid dynamics), Electric motors, Transients (Dynamics), Degrees of freedom, Eddy currents (Electricity), Deflection, Geometry, Pistons, Probes
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041649
The National Jet Fuel Combustion Program (NJFCP) is an initiative being led by the Office of Environment & Energy at the FAA, to streamline the ASTM certification process for alternative aviation fuels. To achieve this objective, the program has identified specific applied research tasks in several areas. The National Research Council of Canada (NRC) is contributing to the NJFCP in the areas of sprays and atomization and high altitude engine performance. This paper describes work pertaining to atomization tests using a reference injection system which involves characterization of the nozzle, comparison of sprays and atomization quality of various conventional and alternative fuels, and the use of the experimental data to validate spray correlations. The paper also briefly explores the viability of a new spray diagnostic system that has potential to reduce test time in characterizing sprays. Measurements were made from ambient up to 10 bar pressures in NRC's High Pressure Spray Facility using optical diagnostics including laser diffraction, phase Doppler anemometry (PDA), LIF/Mie Imaging and laser sheet imaging to assess differences in the atomization characteristics of the test fuels. A total of nine test fluids including six NJFCP fuels and three calibration fluids were used. The experimental data was then used to validate semi-empirical models, developed through years of experience by engine OEMs and modified under the NJFCP, for predicting droplet size and distribution. The work offers effective tools for developing advanced fuel injectors, and generating data that can be used to significantly enhance multi-dimensional combustor simulations.
TOPICS: Fuels, Sprays, Aviation, Imaging, Fluids, Lasers, Engines, Simulation, Jet fuels, Drops, High pressure (Physics), Combustion chambers, Engineering simulation, Nozzles, Diffraction, Combustion, ASTM International, Calibration, Fuel injectors
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041651
Wind turbine industry has a special need for accurate post stall airfoil data. While literature often covers incidence ranges [-10deg;+25deg] smaller machines experience a range of up to 90 deg for horizontal axis and up to 360 deg for vertical axis wind turbines (VAWTs). The post stall data of airfoils is crucial to improve the prediction of the start-up behavior as well as the performance at low tip speed ratios. The present paper analyzes and discusses the performance of the symmetrical NACA 0021 airfoil at three Reynolds numbers (Re = 100k, 140k, and 180k) through 180 deg incidence. The typical problem of blockage within a wind tunnel was avoided using an open test section. The experiments were conducted in terms of surface pressure distribution over the airfoil for a tripped and a baseline configuration. The pressure was used to gain lift, pressure drag, moment data. Further investigations with positive and negative pitching revealed a second hysteresis loop in the deep post stall region resulting in a difference of 0.2 in moment coefficient and 0.5 in lift.
TOPICS: Reynolds number, Experimental analysis, Wind turbines, Airfoils, Vertical axis wind turbines, Pressure, Machinery, Symmetry (Physics), Form drag, Wind tunnels
research-article
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041519
After almost 20 years of absence from research agendas, interest in the vertical axis wind turbine (VAWT) technology is presently increasing again, after the research stalled in the mid 90's in favour of horizontal axis turbines (HAWTs). However, due to the lack of research in past years, there are a significantly lower number of design and certification tools available, many of which are underdeveloped if compared to the corresponding tools for HAWTs. To partially fulfil this gap, a structural FEA model, based on the Open Source multiphysics library PROJECT::CHRONO, was recently integrated with the Lifting Line Free Vortex Wake method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34m rotor. In this work some details about the newly implemented nonlinear structural model and its coupling to the aerodynamic solver are first given. Then, in a continuous effort to assess its accuracy, the code capabilities were here tested on a small scale, fast-spinning (up to 450 rpm) VAWT. After the code validation, an aero-elastically coupled simulation of a rotor self-start has been performed to demonstrate the capabilities of the newly developed model to predict the highly nonlinear transient aerodynamic and structural rotor response.
TOPICS: Simulation, Vertical axis wind turbines, Rotors, Horizontal axis wind turbines, Spinning (Textile), Turbines, Vortices, Wind turbines, Spin (Aerodynamics), Transients (Dynamics), Wakes, Design, Finite element analysis

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