bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model-Based Unified Framework for Detection and Mitigation of Cyclic Torque Imbalance in a Gasoline Engine
Authors: Anjum Raheel , Yar Ahmed , Murtaza Ghulam , Ahmed Qadeer , Bhatti A. I. 
Published: January 2021

Abstract
Torque produced by the internal combustion (IC) engine is desired to be of similar value for consecutive combustion cycles; nevertheless, difference occurs in the cyclic torque due to uncertainties in its generation. Variations between output work of successive combustion cycles are considered as the main cause of imbalance in the cyclic torque. Such variations are displayed in engine output torque and affect the engine performance. In this paper, a novel model-based unified framework is proposed for the detection and mitigation of cyclic torque imbalance in a gasoline engine by employing the first principle-based engine model (FPEM). Engine speed dynamics in the model are transformed to develop the direct relationship between engine speed dynamics and fuel input. Fault in fuel injection subsystem is induced to generate imbalance in the cyclic torque. FPEM-based uniform second-order sliding mode (USOSM) observer is applied for estimation of the unknown input, i.e., net piston force (fn) from engine speed dynamics to detect imbalance in the cyclic torque. Estimated net piston force (f⁁n) is utilized to design the control law for certainty equivalence super twisting algorithm (CESTA) based fault tolerant control (FTC) technique to mitigate the torque imbalance. The results of numerical simulation demonstrated that the desired objective is achieved by the proposed unified framework.
Effects of Surface Irregularities and Coatings on Thermal Emittance of Selected Metals Between 373 and 1073 K
Authors: Tanda Giovanni , Misale Mario 
Published: January 2021

Abstract
In many areas of engineering, radiation heat transfer plays an important role and it is of great importance the knowledge of the thermal radiative properties of the surfaces involved. Radiation properties of solid materials are highly dependent on surface characteristics, e.g., surface roughness, surface damage, oxide layers, and deposited thin films, and cannot be assumed as those of pure materials, typically referred to optically smooth surfaces (OS). An experimental investigation of the thermal emittance of some metals (nickel, titanium, silver, and stainless steel) is presented. Experiments were conducted by using a radiometric apparatus able to measure the total normal emittance under different temperature and pressure conditions. The aim of this paper was to identify the separate roles of surface microgeometry alterations (surface roughness), surface damage, and surface coatings (i.e., presence of either thin films deposited onto a smooth surface or oxide layers formed on both smooth and rough surfaces) by undertaking carefully selected sets of experiments covering a relatively large temperature range.
Flexible-Joint Humanoid Balancing Augmentation via Full-State Feedback Variable Impedance Control
Authors: Spyrakos-Papastavridis Emmanouil , Dai Jian S. 
Published: January 2021

Abstract
This paper attempts to address the quandary of flexible-joint humanoid balancing performance augmentation, via the introduction of the Full-State Feedback Variable Impedance Control (FSFVIC), and Model-Free Compliant Floating-base VIC (MCFVIC) schemes. In comparison to rigid-joint humanoid robots, efficient balancing control of compliant bipeds, powered by Series Elastic Actuators (or harmonic drives), requires the design of more sophisticated controllers encapsulating both the motor and underactuated link dynamics. It has been demonstrated that Variable Impedance Control (VIC) can improve robotic interaction performance, albeit by introducing energy-injecting elements that may jeopardize closed-loop stability. To this end, the novel FSFVIC and MCFVIC schemes are proposed, which amalgamate both collocated and non-collocated feedback gains, with power-shaping signals that are capable of preserving the system's stability/passivity during VIC. The FSFVIC and MCFVIC stably modulate the system's collocated state gains to augment balancing performance, in addition to the non-collocated state gains that dictate the position control accuracy. Utilization of arbitrarily low-impedance gains is permitted by both the FSFVIC and MCFVIC schemes propounded herein. An array of experiments involving the COmpliant huMANoid reveals that significant balancing performance amelioration is achievable through online modulation of the full-state feedback gains (VIC), as compared to utilization of invariant impedance control.
Influence of Tip Clearance on the Hydrodynamic Damping Characteristics of a Hydrofoil
Authors: Zeng Yongshun , Yao Zhifeng , Zhang Shijie , Wang Fujun , Xiao Ruofu 
Published: January 2021

AbstractTip clearance in hydraulic machines may complicate the fluid–structure interaction (FSI) effects. In this investigation, a mode-based approach (modal work) is evaluated and employed to quantitatively predict the added mass, added stiffness, and hydrodynamic damping ratio, in relation to the first-order bending mode of a vibrating hydrofoil. The investigated relative tip clearance ranges from 0.067% to 2% of the span length. The predicted vortex shedding frequency, natural frequency, and hydrodynamic damping ratio of the hydrofoil are in good agreement with the previously published experimental results, with relative deviations within 9.92%, 6.97%, and 11.23%, respectively. Simulation results show that the added mass, added stiffness, and hydrodynamic damping ratio increase inversely as the tip clearance increases. In particular, as the relative tip clearance increases from 0.067% to 2%, the added mass in still water, the added stiffness, and hydrodynamic damping ratio at a velocity of 10 m/s decrease by 18.66%, 9.36%, and 27.99%, respectively. As the tip clearance increases, the inversely increased pressure difference between the upper and lower surfaces of the vibrating hydrofoil is the main reason for the inversely increased hydrodynamic damping ratio. This is due to the energy leakages via the tip clearance region increase as the tip clearance increases, which may cause less fluid force to resist the vibration of the hydrofoil, resulting in less negative modal work done by the fluid load on the hydrofoil.
The Effects of Specific Heat and Viscosity on Film Cooling Behavior
Authors: Wiese Connor J. , Rutledge James L. 
Published: January 2021

Abstract
For many years, there has been interest in evaluating the effect of density differences between the coolant and the freestream in terms of the cooling effectiveness. Numerous experiments have been conducted with different cooling gases or different temperature gases to evaluate the effect of the density ratio. With little agreement on the best way to scale the density ratio effect, it has become commonplace for some researchers to insist upon matching the density ratio for the experimental work. Unfortunately, the density is not the only property that differs between the various coolant gases used in experiments, and it is certainly not the only property difference between the coolant and the freestream in actual engines. In the present work, we isolate some of these effects through film-cooling experiments with carefully selected and conditioned coolant gases at near-identical densities but exhibiting other property differences. Most significantly, coolant specific heat varied, but subtle viscosity and thermal conductivity effects were present. Through measurements of the adiabatic effectiveness from a film-cooling hole on a leading-edge model, we are able to show that the specific heat effect is just as important as the density effect, providing more evidence that effects in prior research attributed to density differences are actually a combination of density and other property differences.
Active Flow Control Utilizing an Adaptive Blade Geometry and an Extremum Seeking Algorithm at Periodically Transient Boundary Conditions
Authors: Werder Tobias , Liebich Robert , Neuhäuser Karl , Behnsen Clara , King Rudibert 
Published: January 2021

Abstract
As a consequence of constant volume combustion in gas turbines, pressure waves propagating upstream the main flow into the compressor system are generated leading to incidence variations. Numerical and experimental investigations of stator vanes have shown that active flow control (AFC) by means of adaptive blade geometries is beneficial when such periodic incidence variations occur. A significant risk reduction in a compressor facing disturbances can thereby be achieved concerning stall or choke. Experimental investigations on such an AFC method with simultaneous application of a closed-loop control are missing in order to demonstrate its potential. This work investigates a linear compressor cascade that is equipped with a 3D-manufactured piezo-adaptive blade structure. The utilized actuators are piezoelectric macro-fiber-composites. A throttling device is positioned downstream the trailing edge plane to emulate an unsteady combustion process. Periodic transient throttling events with a frequency of up to 20 Hz cause incidence changes to the blade’s leading edge. Consequently, pressure fluctuations on the blade’s surface occur, having a significant impact on the pressure recovery downstream of the stator cascade. Experimental results of harmonically actuating the piezo-adaptive blade with the corresponding disturbance frequency show that the impact of disturbances can be reduced to approximately 50%. However, this is only effective if the phase shift of the harmonic actuation is adjusted correctly. Using an inadequate phase shift reverses the positive effects, causing the aforementioned stall, choke, or significant losses. In order to find the optimum phase shift, even under varying, possibly unpredictable operating conditions, an extremum seeking controller is presented. This gradient-based approach is minimizing the pressure variance over time by carefully adjusting the phase shift of the harmonic actuation of the AFC system.
Effects of Mach Number and Secondary Flows on Ultra-Low Aspect Ratio Radial Outflow Turbine Cascade Aerodynamics
Authors: Grönman Aki , Tiainen Jonna , Uusitalo Antti 
Published: January 2021

Abstract
Radial outflow turbines are an alternative for axial turbines for example in heat recovery applications. They are, however, also often characterized by ultra-low aspect ratios. In these designs, the secondary losses dominate the overall loss share, and under a certain aspect ratio, the secondary structures from the hub and shroud begin to interact. This interaction causes a decrease in aerodynamic performance. Previous studies have suggested that the general flow phenomena between radial outflow and axial turbines could share several similarities due to observed trends in performance prediction. The blade outlet Mach number is known to affect the spanwise positions of the secondary vortices in axial turbine blading and therefore, its effect is also tested here for an ultra-low aspect ratio radial outflow turbine cascade. In addition, there are currently no cascade level experimental data publicly available, and the suitability of axial turbine loss correlations under these conditions remains an open question. From this background, the current study presents an experimental, numerical, and loss correlation analysis of the effects of an isentropic Mach number in a radial outflow turbine cascade. An experimental campaign is used to validate the numerical model both quantitatively and qualitatively. In addition, the validity of the axial turbine loss correlation is extended to ultra-low aspect ratios by introducing a new variable called penetration length. The main findings are: 1. The flow phenomena do not differ significantly from what has been observed with axial turbines, 2. The effect of penetration length calculation method on the loss breakdown is relatively low, and 3. With ultra-low aspect ratio radial outflow turbines, the loss breakdown is markedly changed when the extended Benner’s approach is employed.
Large Eddy Simulation of a Transonic Linear Cascade With Synthetic Inlet Turbulence
Authors: Bertolini Ettore , Pieringer Paul , Sanz Wolfgang 
Published: January 2021

Abstract
The aim of this work is to predict the boundary layer transition and the heat transfer on a highly loaded transonic turbine cascade using Large Eddy Simulations (LESs) with prescribed inlet synthetic turbulence. The numerical simulations were performed for the flow in a linear turbine cascade tested at the von Karman Institute for Fluid Dynamic (MUR test case). For the numerical case, two operating conditions with two different levels of free-stream turbulence intensity are evaluated. For the lower turbulence level case (Tu = 0.8%, MUR132) a laminar inflow is used for the LES simulations whereas for the higher one (Tu = 6%, MUR237) the inlet turbulence is prescribed by using the Synthetic Eddy Method (SEM) of Jarrin. The first part of this work deals with the LES setup. The standard Smagorinsky model was used as closure model. A value of the Smagorinsky constant CS = 0.05 was chosen whereas the turbulent viscosity was reduced in the region closest to the wall by changing the definition of the Smagorinsky length scale. To handle the strong fluctuations in the flow field the cell fluxes are computed using the WENO-P scheme. In the second part, precursor RANS and LES simulations are used to set the optimal values of the SEM parameters and to guarantee the correct level of turbulence at the blade leading edge. The turbulence decay of the synthetic turbulence is compared with the one of the RANS κ–ωSST model. Finally, a comparison between experimental and numerical results is done and the ability of LES to predict the boundary layer transition and the heat transfer on the blade surface is evaluated for the two different inflow conditions.
Robust Aerodynamic Design of Nacelles for Future Civil Aero-Engines
Authors: Schreiner B. Deneys J. , Tejero Fernando , MacManus David G. , Sheaf Christopher 
Published: January 2021

Abstract
As the growth of aviation continues it is necessary to minimise the impact on the environment, through reducing NOx emissions, fuel-burn and noise. In order to achieve these goals, the next generation of Ultra-High Bypass Ratio engines are expected to increase propulsive efficiency through operating at reduced specific thrust. Consequently, there is an expected increase in fan diameter and the associated potential penalties of nacelle drag and weight. In order to ensure that these penalties do not negate the benefits obtained from the new engine cycles, it is envisaged that future civil aero-engines will be mounted in compact nacelles. While nacelle design has traditionally been tackled by multi-objective optimisation at different flight conditions within the cruise segment, it is anticipated that compact configurations will present larger sensitivity to off-design conditions. Therefore, a design method that considers the different operating conditions that are met within the full flight envelope is required for the new nacelle design challenge.
The method is employed to carry out multi-point multi-objective optimisation of axisymmetric aero-lines at different transonic and subsonic operating conditions. It considers mid-cruise conditions, end-of-cruise conditions, the sensitivity to changes in flight Mach number, windmilling conditions with a cruise engine-out case and an engine-out diversion scenario. Optimisation routines were conducted for a conventional nacelle and a future aero-engine architecture, upon which the aerodynamic trade-offs between the different flight conditions are discussed. Subsequently, the tool has been employed to identify the viable nacelle design space for future compact civil aero-engines for a range of nacelle lengths.
Combustion System Upgrades for High Operation Flexibility and Low Emission: Design, Testing and Validation of the SGT5-4000F
Authors: Blaette Lutz , Boettcher Andreas , Streb Holger 
Published: January 2021

Abstract
The first Siemens AG SGT5-4000F was introduced in 1996. Since then, the combustion system was improved in several evolutionary steps in order to enhance the engine performance and emission requirements. Especially emissions requirements will become more challenging in the future as the typical limits will likely drop from 25ppm NOx to 15ppm or even single digit. In addition to clean power solutions, the market simultaneously demands increased operational flexibility in terms of load gradients, fuel flexibility (special fuels, hydrogen addition) and turndown capability.
The SGT5-4000F fleet consists of more than 350 units in operation with ∼20Mio accumulated operating hours. Retrofit ability to the fleet is therefore an important aspect of the combustion system development.
The paper reports upon the development of the latest improvements of the combustion system of SGT5-4000F engines, which have been achieved by application of the latest numerical design tools, advanced statistical machine learning techniques and utilization of additive manufacturing. Results from testing and validation of the modifications at the Siemens Clean Energy Center (CEC) for stand-alone combustion tests and Berlin Test Facility (BTF) for full scale engine tests will be presented.
The system improvement includes aero-dynamic, fuel / air mixing and combustor cooling air management optimizations, which are the typical focus areas for lean premixed combustion systems in gas turbines.
Sensitivity of Multi-Stage Compressor Performance Assessment to Measurement Rake Positions
Authors: Chilla M. , Pullan G. , Thorne G. 
Published: January 2021

Abstract
For an accurate performance assessment of a multi-stage compressor, the circumferentially non-uniform flow at the compressor exit needs to be understood and sampled in a way that minimizes uncertainties. To quantify the effect of the measurement rake positions in the exit duct on compressor performance a combined computational and experimental approach is used on a modern 4-stage compressor. The computational analysis is based on unsteady calculations of a 180-degree sector of the test compressor and experimental verification is provided by comparing to area-traverse data downstream of the outlet guide vanes.
It is shown that the exit measurement rakes are subject to circumferential flow variations caused primarily by the combined effect of the potential field of the struts housed within the exit duct and the wakes originating from the outlet guide vanes. A circumferential camber pattern, applied to the outlet guide vanes, designed to shield the upstream compressor blade rows against the potential field of the exit struts, is found to reduce the amplitude of the circumferential variation in stagnation pressure and shift its circumferential phase. Recognizing that a smaller numerical model, consisting only of the last rotor, the outlet guide vanes and the exit struts, is sufficient to capture the relevant flow mechanisms, the circumferential variations in stagnation pressure and temperature at the rake position are quantified as a function of the exit capacity. The stagnation pressure and temperature uncertainty within a +/-2 deg circumferential range around the nominal rake position is found to be up to 2.25 times larger than the change of the nominal values over an 87.1–106.0% variation of the exit capacity.
Three options to position the rakes to reduce the uncertainty in compressor efficiency are presented — moving the rake downstream as well as leaning and verniering the rakes over the outlet guide vane pitch. Moving the rake from the leading edge to the trailing edge plane of the exit struts reduced the efficiency uncertainty by 2.6%, while leaning and verniering the rakes reduced the efficiency uncertainty by 0.2% and 0.7% respectively. The knowledge gained from the large-scale, detailed CFD predictions can used to support future measurement campaigns.
Competitive Bidding by Surrogate Modeling of Steam Parameter Influence on the Attainable Start Numbers of Turbine Casings
Authors: Seiler Marcel , Züch Vitali , Dumstorff Peter , Almstedt Henning 
Published: January 2021

Abstract
The continued expansion of fluctuating energy sources such as wind turbines and solar systems will increase the demand for more flexible operation modes of power plants. Especially steam turbines with all their components will have to sustain a higher amount of start-stop cycles in order to compensate for variations in wind and solar radiation. Besides the rotor, inner casings are an example for main steam turbine components which are strongly loaded by thermal cycles at each start and shut down procedure. A precise prediction of the attainable number of start-stop cycles enables a more flexible operation within the guaranteed lifetime. However, this would require time-consuming FE calculations for each power plant due to their specific steam parameters.
In this paper, a physics based surrogate model is discussed for a fast prediction of permissible start-stop cycles at plant specific steam parameters. The correlation between the physical properties from the surrogate model (wall temperature difference and the resulting stresses) and the attainable number of start-stop cycles from the FE model is determined. A validation with a different inner casing design within a usual wall temperature range confirms the high accuracy level of the surrogate model compared to uncertainties like material scatter or casting tolerances. With the provided approach typically a higher number of starts can be efficiently calculated in the bidding phase compared to assuming only one conservative value for each turbine type or size. Furthermore, the steam parameters can be optimized for increasing the number of starts to the required value without additional and time-consuming FE calculations.
Modeling of Natural Gas Composition Effect on Low NOx Burners Operation in Heavy Duty Gas Turbine
Authors: Romano S. , Meloni R. , Riccio G. , Nassini P. C. , Andreini A. 
Published: January 2021

Abstract
This paper addresses the impact of natural gas composition on both the operability and emissions of lean premixed gas turbine combustion system. This is an issue of growing interest due to the challenge for gas turbine manufacturers in developing fuel-flexible combustors capable of operating with variable fuel gases while producing very low emissions at the same time. Natural gas contains primarily methane (CH4) but also notable quantities of higher order hydrocarbons such as ethane (C2H6) can also be present. A deep understanding of natural gas combustion is important to obtain the highest combustion efficiency with minimal environmental impact.
For this purpose, Large Eddy Simulations of an annular combustor sector equipped with a partially-premixed burner are carried out for two different natural gas compositions with and without including the effect of flame strain rate and heat loss resulting in a more adequate description of flame shape, thermal field and extinction phenomena.
Promising results, in terms of NOx, compared against available experimental data, are obtained including these effects on the flame brush modelling, enhancing the fuel-dependency under non adiabatic condition.