bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of an overset grid method for the performance analysis of flapping airfoils
Authors: Lemmi G. , Giaccherini S. , Marconcini M. , Pinelli L. 
Published: December 2022

Abstract
With the growing importance of renewable energy, the interest in energy-harvesting technologies based on flow-induced vibrations of airfoils has been rekindled in the past few years. Compared to conventional turbines, these devices are centrifugal stress-free and hence they are structurally more robust. They are also environmentally friendly due to the relatively low speeds, thus reducing the impact on flying animals. In order to numerically investigate these types of devices, mesh motion techniques must be used so that the computational grid can adapt to the time-varying shape of the domain and boundaries, thus preserving its robustness and quality. During the last years, many different dynamic mesh approaches have been developed to better predict the behaviour of a flow interacting with solid moving bodies. The aim of the present work is to apply and validate the overset grid method offered by the OpenFOAM software. In this type of mesh, one or more grid blocks are allowed to overlap with other sets of cells to solve the fluid domain with moving bodies, thus showing many potential advantages compared to the other existing dynamic mesh approaches. In the first part of this work, a numerical investigation of the flow over a stationary SD 7003 airfoil at low Reynolds number has been performed using an unsteady RANS approach. The computed results have then been compared to experimental and high-fidelity computational data available from the literature in order to validate the presented model in terms of numerical domain configuration, mesh refinement, and turbulence modelling. Subsequently, unsteady RANS simulations have been performed on the SD 7003 and NACA 0012 airfoils for two different amplitudes of flapping motion, i.e., 30° and 45°. Finally, the results obtained with the OpenFOAM overset grid solver have been compared with the numerical and experimental benchmarks presented by Kurtulus, showing an excellent agreement with both computed and measured data.
Experimental and numerical investigation of a micro-ORC system for heat recovery from data centers
Authors: Ancona M A , Bianchi M , Branchini L , Pascale A De , Melino F , Ottaviano S , Peretto A , Poletto C 
Published: December 2022

Abstract
In the effort to enhance the recovery of waste energy, data centers are drawing attention because of the huge amount of heat discharged from the computer racks. Organic Rankine cycle (ORC) power systems are a viable solution to exploit servers’ waste heat, as it is available at very low temperatures. The purpose of this study is to assess the feasibility of integrating a micro-ORC system into data centers cooling systems and its potential energy saving. An experimental analysis is carried out on a kW-scale ORC test bench, with R134a as working fluid. Heat is supplied at temperatures and flow rates in the range respectively 40-55 °C and 1.8-5 m3/h, consistently with typical values observed in data centers application, showing the second law efficiency varying between 5% and 13%. Furthermore, a steady-state model of the micro-ORC has been recalibrated and validated against experimental data; the built-in volume ratio of the reciprocating piston expander has been optimized to improve the filling performance of the machine. A parametric analysis, varying the boundary conditions within their range of interest for this application, and the working fluid (R1234yf and R1234ze(E)), shows that a maximum second law efficiency of 30% is achievable with R1234ze(E).
Exergo-economic and exergo-environmental analysis of a binary geothermal power plant with solar boosting
Authors: Giusti E. , Ciappi L. , Ungar P. , Zuffi C. , Fiaschi D. , Manfrida G. , Talluri L. 
Published: December 2022

Abstract
The exploitation of renewable energies is a solution to the energy, economic and environmental issues related to the massive use of fossil resources. Thus, investing in renewable technologies is essential to achieve the carbon-neutral scenario within 2050. In this framework, geothermal energy may have a key role. In particular, power plants with a closed binary cycle are suitable for harnessing geothermal resources with low and medium enthalpy levels. They are prone to be integrated with other renewable devices to increase the global power output.
Geothermal fluid can be drawn constantly from underground throughout the day and seasons. Conversely, the availability and intensity of solar energy depend on weather conditions and the time of year. In Italy, geothermal energy is currently harvested for continuous electricity generation, while solar energy is mainly used for photovoltaic generation. For small-to-medium size plants, rated between 5 and 20 MWe, the geothermal and thermodynamic solar hybridization may lead to relevant benefits for the economic competitiveness regarding separate photovoltaic or thermodynamic solar systems.
This article aims to investigate the economic and environmental aspects of geothermal power plants with a closed binary cycle coupled with a topper cycle fed by linear parabolic solar collectors. The system operation in both design and off-design conditions was analysed, and exergo-economic and exergo-environmental simulations were conducted. The application site was selected near Torre Alfina (Italy). It has a water-dominant reservoir with a pressure of 44 bar, a temperature of 140 °C, and content of non-condensable gases (NCGs) approximately equal to 2% by weight. At the design point, the net power is 8.4 MW and the first and second principle efficiencies are 9.31% and 18.45%, respectively. The exergo-economic and exergo-environmental analyses indicate that the components with the highest economic and environmental impact are the condenser, the field of solar collectors, the evaporator, and the low-pressure turbine. The levelized cost of electricity (LCOE) is equal to 14.19 c€/kWh.
Re-designing district heating networks through innovative CO2 solutions
Authors: Ungar P , Milli L , Manfrida G , Fiaschi D , Talluri L 
Published: December 2022

Abstract
One of the main problems of current district heating networks is the significant heat losses that occur due to the high temperature of the heat distribution fluid (usually, water in the Italian climate conditions). Moreover, in ORC- or steam-turbine-based cogeneration power plants, the heat distribution fluid is heated directly by the condenser of the ORC cycle resulting in low efficiency of the power production section of the system. Considerable power is also employed for pumping the district heating flow rate through a long distribution ring. In this work, the effect of replacing water with low-temperature CO2 as a working fluid in a district heating network is analyzed. Specifically, a real district heating installation (the Biogenera-Calenzano network) providing at design conditions 850 kW of electricity and 1.7 MW (average) of heat is assessed using an experimental data set, simulating the equivalent working conditions with CO2 distributed through the network.
The proposed innovative solution continues to receive the heat from the condenser of an ORC cycle, but the temperature of the working fluid is significantly lower providing a relevant increase in the power production because of the reduction of the condenser temperature (determining an increase of the expansion ratio of the turbine). The increased power production of the turbine exceeds the power needed by local heat pumps which should be installed near the utilities of the district heating network to provide flexible heat on demand.
How to extrapolate 3D aerodynamic coefficients from HAWT CFD simulations: an inverse BEM approach
Authors: Mauro Stefano , Lanzafame Rosario , Messina Michele , Brusca Sebastian 
Published: December 2022

Abstract
In the present work the authors developed a methodology based on an inverse BEM method, to easily extrapolate 3D aerodynamic coefficients from HAWT CFD 3D simulation results. Specifically, since the BEM method was based on the solution of a discrete number of blade radial sections, the CFD model was implemented in Ansys Fluent in such a way to split the surface of one of the blades in a certain number of sections already at the CAD level. Therefore, the normal and tangential aerodynamic forces were calculated for each radial section and subsequently provided directly within the modified BEM code developed in Matlab. Thus, the BEM code iterated for the axial and tangential induction factors and calculated the lift and drag coefficients, the related local angle of attack, the torque, the power and the power coefficient for each specific operating condition simulated. The methodology proposed here was validated using the NREL Phase VI rotor geometry for which a very good agreement between numerical and experimental data was found. Furthermore, this allowed for an insight into the 3D effects over the blade since it was possible to compare the experimental 2D and the 3D lift and drag coefficients section by section.
Sustainable opportunities to recover power plants’ waste heat: a benchmark of techno-economically optimized heat pumps
Authors: Grisolia T , Vannoni A , Sorce A , Calabria M 
Published: December 2022

Abstract
Current climate targets, adopted worldwide, pursue the decarbonization of all energy sectors. In power generation, the spread of RES has caused the shift of the Combined Cycle Gas Turbine (CCGT) power plants’ traditional role from providing constant baseload power to flexible operations providing services and backup capacity to the grid, as a consequence, the revenues opportunities on the traditional electricity markets (e.g., day-ahead, and intra-day markets) are no longer certain. At the same time is urgent to address a significant carbon intensity reduction in the heating sector, which is responsible for a large part of the current greenhouse gas emissions. Exploiting the low-exergy waste heat of CCGT’s water-cooled condenser as a thermal source for vapor compression heat pumps can meet two targets. On one hand, the revenues from heat production enhance the viability of the CCGT power plant, often essential for the security of the electrical supply. On the other hand, the heat delivered to the user represents a low-carbon alternative to traditional gas-fired boilers or even to air-sourced heat pumps characterized by lower efficiency. This work assesses the recovery of thermal energy from the sea cooling water at the bottoming cycle condenser of Tirreno Power 794 MWel CCGT in Vado Ligure through a high-temperature heat pump using R600 as a working fluid. Cooling water represents a privileged heat source and the integration into the power plant’s site allows running the HP at a lower cost than the electricity retail price. The case study takes into account the new Vado Ligure sports hall, to size the HP and explore the economic and environmental performances. The proposed layout is compared with the main solutions available: air source heat pump, gas, and electric boilers. The results show that on a lifespan of 20 years such integration of a heat pump with a CCGT could lead to consistent economical savings and emissions cuts.
Influence of the trigger time window on the detection of gas turbine trip
Authors: Losi E , Venturini M , Manservigi L , Bechini G 
Published: December 2022

Abstract
Gas turbine (GT) trip is one of the most disrupting events that affect GT operation, since its occurrence causes a reduction of equipment remaining useful life as well as revenue loss because of business interruption. Thus, early detection of incipient symptoms of GT trip is crucial to ensure efficient operation and lower operation and maintenance costs. This paper applies a data-driven methodology that employs a Long Short-Term Memory (LSTM) neural network and a clustering technique to identify the time point at which trip symptoms are triggered. The same methodology also partitions trips into homogeneous clusters according to their most likely trigger position. The methodology is applied to two real-world case studies composed of a collection of trips, of which the causes are different, taken from various fleets of industrial GTs. Data collected from twenty sensors during three days of operation before trip occurrence are analyzed. For each trigger scenario, this paper investigates different lengths of the training and testing time window (namely “trigger time window”), by considering up to 24, 18, 12 or 6 hours before and after the considered trigger position. The results demonstrate that longer time windows allow an improvement of the predictive capability.
Wells turbine efficiency improvements: experimental application of a speed control strategy
Authors: Licheri Fabio , Ghisu Tiziano , Cambuli Francesco , Puddu Pierpaolo 
Published: December 2022

AbstractSystems based on the OWC principle allow to convert the sea-wave energy into electrical energy. The potential energy contained in the wave motion is first converted into the pneumatic energy of a bi-directional airflow, generated by the oscillatory displacement of a column of water inside a chamber. Then, an air turbine, such as the Wells turbine, placed at the top of the chamber, converts the pneumatic energy into mechanical energy at its shaft, which can be coupled to an electric motor to produce energy. The turbine’s performance is strongly affected by the non-stationary behavior of the airflow, which continuously changes its intensity. Control solutions based on the variation of the turbine rotational speed can overcome this limitation.This work aims to study a speed-controlled Wells turbine with an experimental approach, making use of a turbine coupled to an Oscillating Water Column (OWC) simulator. A control law for the rotational speed has been defined and applied to the turbine in order to move the turbine’s operating conditions as close as possible to its maximum efficiency point, for the majority of the piston period.The experimental results prove the effectiveness of the proposed control strategy for moving the operating conditions and for obtaining operating conditions close to the best efficiency point for the majority of the wave period.
Analysis of satellite-derived data for the study of fouling in aircraft engines
Authors: Zanini Nicola , Suman Alessio , Friso Riccardo , Pinelli Michele 
Published: December 2022

Abstract
Atmospheric particulate is one of the main causes of performance degradation in gas turbine engines, especially in the aeronautical field where filter barriers are absent. The ingested particles can stick to the blade surfaces of the engine, varying their shape and roughness. As a consequence, engine performance degradation takes place. The type and the amount of the particles ingested depend on the flight zones and altitude. During their missions, aircrafts follow a prescribed path defined in terms of altitude, longitude, and latitude. During its route, the aircraft engine encounters different environments characterized by different temperature, pressure, and air composition. Regarding the latter issue, the knowledge of this characteristic can be key information when these statistics are needed for obtaining data useful for engine degradation assessment or prediction. Many satellites, such as the environmental satellite CALIPSO, are employed to study the terrestrial aerosol and clouds profile by using a LIDAR (Laser Detection and Ranging). This technology is commonly used to determine the distance between a light emitter and an object and it is based on the light refraction phenomenon. Backscatter coefficients profiles data, which characterize the distribution of particles and aerosols in the atmosphere, are available in the open literature from the findings of CALIPSO. In this work, a new methodology to estimate the aerosol type and concentration encountered by an aircraft during a mission is proposed. To test the feasibility of this method, two aircraft missions for different length scales (medium and long haul) are analyzed and an estimate of the particulate encountered by the engines is provided. The mission analysis has been conducted by discretizing the altitude profile, longitude, and latitude coordinates of each flight and then cross-referencing them with the particulate concentration obtained from CALIPSO data.
A Study on Accounting for Drift Velocities on Liquid Jets Injected in Cross Flow
Authors: Sahranavardfard Nasrin , Pandal Adrian , Rahantamialisoa Faniry Nadia Zazaravaka , Battistoni Michele 
Published: December 2022

AbstractThe efficiency and combustion performance of propulsion systems, like internal combustion (IC) engines and gas turbines, is known to be related to the performance of the fuel and air mixing process. Operating conditions and fuels are rapidly changing, therefore new CFD models which accurately accounts for all physical aspects, still maintaining a simple framework, are extremely important. In this work we consider the drift velocity contribution, which often is overlooked or neglected, defined as the velocity of the dispersed phase relative to the mixture volumetric mean velocity in a single fluid formulation, a key variable in two-phase mixture model. Water test cases are here considered for the study. The present work investigates the structure and the droplet velocity field of a plain liquid jet injected into a high-pressure air crossflow. Because of the large scale separation between the small features of the interface and the overall jet we use the diffuse-interface treatment in a single-fluid Eulerian framework. A Σ- Y family model is implemented in the OpenFOAM framework which includes liquid diffusion due to drift-flux velocities and a new formulation of the spray atomization. The main objective is to explore the droplet velocity distribution and the jet structure with and without considering the drift flux correction and compare the related results with the experimental data.
Towards a low-noise axial fan for automotive applications
Authors: Casari Nicola , Oliani Stefano , Pinelli Michele , Piovan Mattia , Paola Elisa de , Stoica Luana G. , Marco Alessandro Di , Mollica Enrico 
Published: December 2022

Abstract
The demand for quieter vehicles is pushing manufacturers of components for the automotive industry to seek for solutions to reduce the overall noise emissions. The cooling fan makes no exception: the aerodynamic interaction of the blades with the incoming flow generates turbulence and pressure fluctuations which ultimately translate into noise generation. A variety of expedients have been introduced to limit the produced noise, but no univocal solution has been found.
In modern research, Computational Fluid Dynamics (CFD) has been successfully applied to blades and fans for both the flow and acoustic field derivation. By including the acoustic field, researchers have been able to predict the effect of changes in the blade geometry on the overall sound emission. This work reports a conjugate numerical-experimental study of a reference profile in different flow conditions, in order to validate the CFD acoustic prediction and to lay the basis for improved candidates able to lower the fan-generated noise.
Robust Proportional-Derivative Control on SO(3) for Quadrotor under Inertia Perturbation
Authors: Setiawan N , Hidayatullah I R , Pratama G N P 
Published: December 2022

Abstract
The presence of inertia perturbation should not be ignored, it may harm the stability of quadrotor. There are many causes, one of them is due to the payload attached to the quadrotor. Here, the inertia perturbation comes from the payload that subject to the laying position and the mass. Although unknown, the mass and position of payload are limited to certain value. In this paper, we provide the robust Proportional-Derivative (PD) control of a quadrotor while considering the inertia perturbation. The control law is designed by generating torques in SO(3) group which will regulate the angles and the angular velocity to reach the equilibrium points. In the same time, the inertia perturbation is countered by a proposed compensator. The effectiveness of the control law is clarified by using numerical simulation. The results show that the control law prevails in stabilizing the quadrotor in both nominal condition and the condition under inertia perturbation. It is verified that the proposed control law can stabilize the quadrotor despite being under inertia perturbation.
A Vision and GPS Based System for Autonomous Precision Vertical Landing of UAV Quadcopter
Authors: Priambodo A S , Arifin F , Nasuha A , Muslikhin  , Winursito A 
Published: December 2022

Abstract
This research aims to develop an algorithm for the precision vertical landing process on a quadcopter using GPS sensors and computer vision. This research consists of 2 main parts: GPS-based control used by the quadcopter to return to the home area and computer vision-based control in the form of ArUco marker detection, which is used by the quadcopter in order to land precisely. Detection of the ArUco marker that is used goes through 2 stages: the application of threshold and ratio and the process of calculating the black and white area, which can then be searched for four corners of the marker. The algorithm designed works well on the Webots simulation program with mid-computer specifications. The ArUco marker detection process is fast and reliable, so it does not overload the processor unit so that the simulation process can run well. From 30 tests with different initial positions, the average error of the landing position of the quadcopter at coordinate X is 0.02 meters, and coordinates Y is 0.03 meters. All test results show that the quadcopter can land inside the landing pad area without any parts coming out.
Design of automatic water level control system using fuzzy logic
Authors: Khairudin M. , Hakim M. L. , Rahmawan O. A. , Alfiati W. N. , Widowati A , Prasetyo E. 
Published: December 2022

ABSTRACT
With less rainwater that is absorbed into the ground, and the obstruction of water flow causes flooding. The floodgates on river dams are still using manual systems by utilizing human operators, in this case sometimes mistakes occur in decision making. The solution to this problem is to create an automatic sluice system, so that when the condition of the water discharge at the intake is excessive or insufficient, the sluice can open and close pursuant to the required automation of water flow. Measurement of water discharge using a water flow sensor, the results of the sensor readings will be forwarded to the actuator as a door actuator. In this study, the design of the floodgate control system on the dam was carried out through the fuzzy logic technique. The water level and flow sensor data are processed by fuzzy logic technique to control the opening of the floodgates and the condition of the weir. The benefit of this system is easy to monitor and control the floodgates on the weir, with proper control and supervision it will make the water flow evenly distributed, as well as provide early warning information to anticipate when river water overflows and has the potential to flood.