- Professor Catedrático/Full Professor. -Head ClusterDEM research Lab http://clusterdem.ubi.pt -Line Coordinator for Energy and Fluids at Center for Mechanical and Aerospace Sciences and Technology (Research Center of Portuguese National Foundation for Science and Technology)-Vice-Rector of University of Beira Interior (Research Address: Portugal
This paper presents a numerical performance evaluation of the electrostatic rotary bell sprayer (... more This paper presents a numerical performance evaluation of the electrostatic rotary bell sprayer (ERBS) with a particular focus on droplet charge, electric field, and ambient conditions through the implementation of a high-voltage control-ring field pattern effect into the fully turbulent airflow and by including the atomized droplets discrete phase. The simulation shows that the inclusion of droplet charging and electric field coupling, with different parametric values, significantly impacts the atomized droplet distribution over the spray plume and the deposition rate. This analysis was conducted using a three-dimensional (3D) Eulerian–Lagrangian model to describe the two-phase spraying flow by extending the base OpenFOAM package. The procedure includes an unsteady compressible Navier–Stokes solver combined with a large Eddy simulation approach to model turbulence effects on the air flowfield. This is coupled to the spray dynamics by including droplet trajectory tracking, wall film dynamics, and electric field charge. The approach is further extended to include the evaporation phenomenon and the transport of its products. Compared to a conventional ERBS, herein, we provide an in-depth analysis of the fluid dynamic characteristics around the ERBS with a control-ring field pattern for vorticity, velocity, and electrical fields. The results indicate that the control-ring operation improves the performance and transfer efficiency of the ERBS, and it also helps to harmonize the direction of the charged paint droplets. For the first time, finding a balance between the effect of the inside bell cup surface and control-ring voltage and charged droplet has been conducted.
Modeling Coandã effect has been a fundamental issue in fluid dynamic research in the XX century. ... more Modeling Coandã effect has been a fundamental issue in fluid dynamic research in the XX century. It has lost some interest because of the improvement in CFD, even if it could be still important in the area of the preliminary design of aerodynamic devices that benefits of fluid deflection by convex surfaces. An effective model of Coandã effect has not been defined, and fundamental questions are still open. The influence of convective heat exchange on Coandã adhesion of a fluid stream on a convex surface in the presence of a temperature gradient between the fluid and the convex surface is a problem, which affects many practical cases, but it is still marginally approached by scientific literature. This paper aims to start an effective research direction on the effects of convective heat exchange on Coandã effect. It approaches the problem with a set of CFD simulations. It analyses the previous hypotheses, which are based on Prandtl number and evidences the need of a more effective mod...
Two fundamental questions are still open about the complex relation between fluid dynamics and th... more Two fundamental questions are still open about the complex relation between fluid dynamics and thermodynamics. Is it possible (and convenient) to describe fluid dynamic in terms of second law based thermodynamic equations? Is it possible to solve and manage fluid dynamics problems by mean of second law of thermodynamics? This chapter analyses the problem of the relationships between the laws of fluid dynamics and thermodynamics in both first and second law of thermodynamics in the light of constructal law. In particular, taking into account constructal law and the diffusive formulation of Bejan number, it defines a preliminary step through an extensive thermodynamic vision of fluid dynamic phenomena.
This paper presents a new design methodology of cross flow ventilated heat sinks. An accurate des... more This paper presents a new design methodology of cross flow ventilated heat sinks. An accurate design of both finned and circular pin system with inline configuration has been produced. The model is based on the well tested experimental lumped parameter analysis of cross-flow heat exchangers by Gnielinski. The presented method is intended to support the design of heat sinks with well defined performances of cross flow ventilated heat sinks. An evaluation of the physical properties of the sink is performed and different cases are calculated. They allow comparing the performance in terms of both geometrical parameters of the exchanger and air speed. An effective model of the equations is produced and on this basis a multi-objective optimization is performed.
This paper investigates by an energetic approach possible new configurations of aircrafts, which ... more This paper investigates by an energetic approach possible new configurations of aircrafts, which can rival in low speed operations against helicopters. It starts from an effective energy balance of helicopters during fundamental operations: takeoff, horizontal flight, hovering, and landing. The energy state of a helicopter can be written as: E = ½ mV 2 + mgh + ½ I ω 2 (1) where m is mass of helicopter, I is total rotor inertia, ω is rotor rotational speed. By taking the partial derivative with respect to time of equation 1, the power is expressed as dE/dt = ΔP = mV dV/dt + mg dh/dt (2) By optimizing the energy balance of the helicopter a new aircraft configuration has been obtained that allow a very high lift even at very low speed, but drastically reducing the energy consumption during horizontal flight. The total power required is obtained by rotor power and overall efficiency factor (η) and HP req total = η HP req rotor By equations (1) and (2) it has been produced a preliminary ...
Environmental and economic issues related to the aeronautic transport, with particular reference ... more Environmental and economic issues related to the aeronautic transport, with particular reference to the high-speed one are opening new perspectives to pulsejets and derived pulse detonation engines. Their importance relates to high thrust to weight ratio and low cost of manufacturing with very low energy efficiency. This papers presents a preliminary evaluation in the direction of a new family of pulsejets which can be coupled with both an air compression system which is currently in pre-patenting study and a more efficient and enduring valve systems with respect to today ones. This new pulsejet has bee specifically studied to reach three objectives: a better thermodynamic efficiency, a substantial reduction of vibrations by a multi-chamber cooled architecture, a much longer operative life by more affordable valves. Another objective of this research connects directly to the possibility of feeding the pulsejet with hydrogen. This paper after a preliminary analysis of the pulsejet ta...
The advantages associated to Vertical Short-Take-Off and Landing (V/STOL) have been demonstrated ... more The advantages associated to Vertical Short-Take-Off and Landing (V/STOL) have been demonstrated since the early days of aviation, with the initial technolology being based on airships and later on helicopters and planes. Its operational advantages are enormous, being it in the field of military, humanitarian and rescue operations, or even in general aviation. Helicopters have limits in their maximum horizontal speed and classic V/STOL airplanes have problems associated with their large weight, due to the implementation of moving elements, when based on tilting rotors or turbojet vector mechanical oriented nozzles. A new alternative is proposed within the European Union Project ACHEON (Aerial Coanda High Efficiency Orienting-jet Nozzle). The project introduces a novel scheme to orient the jet that is free of moving elements. This is based on a Coanda effect nozzle supported in two fluid streams, also incorporating boundary layer plasma actuators to achieve larger deflection angles. ...
Cycloidal rotors have revealed a noticeable potential to be further enhanced when running at diff... more Cycloidal rotors have revealed a noticeable potential to be further enhanced when running at different operating conditions. The present work demonstrates the active control methodology in order to achieve improved performances in cycloidal rotors operating in forward-flight and lift-up phases. The proposed optimization analysis comprises computational fluid dynamics (CFD) simulations for the numerical database and an artificial neural network (ANN) to propose optimum operating states in each of the mentioned flying phases instead of the hover state under ground effects. CFD predictions were conducted for various operating conditions of pitching oscillations and rotating speeds at each forward or lift-up speed. By training the ANN algorithm using the database attained from CFD simulations, the optimization process was further surveyed for each corresponding flying mode. The targeting concept is to operate with an active mode of employing pitching angles rather than using constant oscillations at all rotation speeds. The ANN approach effectively proposed an optimized pitching schedule for both forward and lift-up phases after analyzing a wide range of parameters in order to reach an optimum aerodynamic efficiency. Because the blade and flow properties are all considered at each specific point on the continuous azimuth of the circular (360°) trajectory, the mutual collaboration of CFD and ANN analysis showed to be advantageous for enhanced operations
This study analyzes the effect of DBD plasma actuators on the unsteady flow of a cycloidal rotor ... more This study analyzes the effect of DBD plasma actuators on the unsteady flow of a cycloidal rotor with six blades of NACA 0016 type using computational fluid dynamics (CFD). The flow field modeling is performed through a sliding mesh technique that was used with k-ω SST turbulence model. The plasma body force generated by a dielectric barrier discharge DBD actuator is modeled with the phenomenological Shyy's model. The impact of plasma actuators on the flow is studied using two actuators located on the upper and bottom surfaces of the airfoil in each of the cyclorotor blades. Three cases are studied: actuation off; actuation over the upper surface of the blades; actuation over the bottom surface of the blades. The vorticity field and the evolution of the lift, thrust and power consumption are analyzed for when a control law is designed that combines both actuations based on the two last cases. The results show that the use of the proposed control law for plasma actuation improves the cyclorotor lift peak value per blade in 11% and the overall thrust by 1.5%. It is also demonstrated that the plasma actuator mitigates the virtual camber on the cyclorotor, this effect is named counter-virtual camber. We show that DBD actuators produce a reduction on the recirculation bubble at the blades suction surface. This effect is important to reduce the thickness of the blades, bringing improvements in terms of mitigating unsteady periodic mass acceleration in cyclorotors.
A novel design of the dielectric barrier discharge (DBD) actuator/sensor is proposed for mapping ... more A novel design of the dielectric barrier discharge (DBD) actuator/sensor is proposed for mapping the location of icing on a surface. The new design uses segmentation of the embedded electrode of the DBD actuator. Segmented DBD actuator/sensor devices were fabricated and experimentally tested in terms of mechanical, thermal and sensing abilities. The sensing capability of the new actuator was analyzed experimentally. Stationary and dynamic icing tests were conducted and the electrical characteristics of the DBD were measured. A parametric study on the effect of the electrode dimensions on the degree of sensitivity of the device was performed. Experimental results show that by using a segmented configuration it is possible to sense the onset of ice formation and also to detect its location. Furthermore, it is possible to detect the initiation of the melting process and measure the time for the water/ice to be completely expelled from the surface. It is also shown that the segmented actuator has better deicing performance in comparison to the conventional actuators. It is also shown that the thermal and active flow control abilities are not compromised by the segmented configuration and thus this device may perform deicing, ice formation and location detection and active flow control.
Canadian Society for Mechanical Engineering International Congress (2020), 2020
Aircraft with the capabilities of hovering and Vertical Takeoff and Landing (VTOL) are increasing... more Aircraft with the capabilities of hovering and Vertical Takeoff and Landing (VTOL) are increasing for various applications. Carrying payloads, controlling cameras and surveillance, critical missions like firefighters, payload carrying from non-terrain regions like forests with high demanding of maneuverability and such environmental circumstances are of examples for the mentioned aircraft types. Although helicopters are typically the most famous crafts of these types, other designs are already available as alternatives, whereas each specific design can be selected according to the expectations. Cycloidal rotor (cyclorotor) has recently been potentially proposed for propulsion system in VTOL aircraft. Higher maneuverability, less noise pollution and more stable flights are some advantageous of the stated systems compared with those of screw propellers employed in helicopters. The present work illustrates a novel conceptual design of a VTOL propulsion system consisting two cycloidal rotors combined with pair-wings which is submitted as an international patent. The downwash jet releasing from the front cyclorotor is partially being processed through the pair-wings towards the rear rotor. The wings are capable of being adjusted for enhanced flow control. Being capable of VTOL from both ground and marine surfaces is the other significant characteristic of the proposed propulsion system. Plasma actuators are employed on pair-wing in order to further enhance the efficiency as an advanced flow control technique. Both numerical and experimental results are presented to further clarify this novel propulsion mechanism.
Violent respiratory diseases, i.e., coronavirus (COVID-19), spread through saliva in coughs and s... more Violent respiratory diseases, i.e., coronavirus (COVID-19), spread through saliva in coughs and sneezes or are even exhaled in the form of microbial pathogen micro-droplets. Therefore, in this work, a comprehensive fully coupled Eulerian-Lagrangian method has been applied for infection control, thus leading to a deeper understanding of the saliva-disease-carrier droplet transmission mechanisms and also of their trajectory tracking by using the OpenFOAM package. This model determines the droplet-air interactions, the breakup process, and turbulent dispersion forces on each micro-droplet that is expelled within the respiratory tract in a correct way. By examining a broad range of initial velocities, size distributions, injection angles of saliva micro-droplets, and mouth opening areas, we predict the maximum opening area that can be driven by micro-droplets. One important contribution of this work is to present a correlation for the length and width of the overall direct maximum reach of the micro-droplets, driven by a wide range of mild coughs to intense sneezes. Our results indicate that the movement of the expelled droplets is mainly influenced by their size, angle, velocity, and environmental factors. During a virus crisis, like COVID-19, this paper can be used to determine the "social distance" between individuals to avoid contamination, by inhaling or touching their bodies, due to these saliva-disease-carrier droplets in sneezing, at various social distance positions such as face-to-face, meeting standing, and near equipment. The safe distance must be increased to around 4 m during a sneeze. By wearing a face mask and by bending the head during a sneeze as a protective action, we can reduce the contamination area to one-third and three-quarters, respectively. Furthermore, the dispersion of the film of the expelled saliva micro-droplets and the spatial relationship between the subjects, which affects the airflow inside the room, are also analyzed in detail. Published under license by AIP Publishing. https://doi.
Plasma actuators are electronic devices commonly used for active flow control. These devices have... more Plasma actuators are electronic devices commonly used for active flow control. These devices have been shown to be effective in a wide variety of fluids engineering applications. In order to increase the efficiency of these devices, the combination of micro exposed electrodes with stair-shaped dielectric layers is proposed. The flow induced by micro and macro stair-shaped plasma actuators is experimentally evaluated and its mechanical efficiency is estimated. Furthermore, durability tests are performed in order to show that stair-shaped dielectric layers also allow to increase the device lifetime. It is shown that by combining micro exposed electrodes with stair-shaped dielectric layers it is possible to achieve mechanical efficiencies 8 times greater than in a conventional macro actuator. In addition, degradation tests demonstrate that stair-shaped dielectric layers degrade slower and lead to an increased lifetime.
Aircraft being capable of Vertical Takeoff and Landing (VTOL) and hover are increasingly emerging... more Aircraft being capable of Vertical Takeoff and Landing (VTOL) and hover are increasingly emerging in various critical and routine applications. Rescue missions in roads and environmental disasters, observance and monitoring-based carriers, surveillance and payload carriage in environments that require high maneuverability and controllability are just a few examples in which this type of aircraft is essential. Helicopters are the most typical aircraft in this kind, but concerning the thrusting mechanism, several alternatives are yet in hand. The tendency to equip aircraft with cycloidal rotors (shortly say, cy-clorotors) as means of Vertical TakeOff and Landing thrusters has increased in recent years. These devices present several advantages such as considerably lower noise production and more stable hover and vertical displacements in comparison with conventional screw propellers as used in helicopters. In the present work a novel concept of propulsion system combining two cy-cloidal rotors with a pair-wing system is presented. A double wing assembly is designed to place in between the two cycloro-tors on each side of the aircraft. The bottom wing is intended to divide the flow in two separate portions through the downwash region of the front cycloidal rotor. To improve the efficiency of this propulsion system, the implementation of plasma actuators in the pair-wing system will be experimentally studied. The concept behind this novel propulsion system is explained and numerical and experimental results, that support its operation concept, are presented.
International Journal of Heat and Fluid Flow , 2019
Here we implemented a 3D comprehensive Eulerian-Lagrangian model in order to investigate the elec... more Here we implemented a 3D comprehensive Eulerian-Lagrangian model in order to investigate the electrostatic spray transfer processes in the high-speed rotary bell sprayer. This efficient algorithm contains spray dynamics, airflow, paint droplets tracking and an electrostatic effect to simulate atomization. The algorithm is implemented using the OpenFOAM package. A solver for the particle trajectory was used to illustrate the process of spray transport and also the interaction of the airflow and the particle that is solved by momentum coupling. Creating an initial condition of the particle approach has been proposed that is matched with practical applications. The fluid-dynamics is simulated by solving the unsteady 3D compressible Navier-Stokes equations. Unsteady flow is computed by using a Large eddy simulation (LES) turbulence approach, while the motion of the particles is simulated by tracking the droplet size distribution approach. The model correctly predicts that the bell cup spin forces the paint particles to fall off from the bell surface towards the high-velocity airflow. The present work illustrates a tentative benchmark and contains a systematic analysis of the recirculation zone length, the toroidal vortex, the overspray phenomena and the flowfield characteristics like mean velocity, pressure, turbulent kinetic energy and velocity fluctuation. The results indicate as dominant operating parameter the air-paint flow rate with voltage level deeply affecting the spray shape. A more uniform distribution of the coating is obtained by growing this high-velocity shaping airflow, although the values of the transfer efficiency (TE) are reduced. The distribution of the particle size is very sensitive to changes in the rotational speed. Experimental results obtained in this study put forward a clear link between the shaping air flow rate and the rotation frequency on the aerodynamics and also provide valuable insights to design modern ERBS. The paint spray distribution obtained in the present work is validated against coating experimental results with suitable accuracy.
This work presents a study on the operational characteristics of a cyclorotor-thruster able to be... more This work presents a study on the operational characteristics of a cyclorotor-thruster able to be applied in an aircraft, particularly in take-off and landing phases. Firstly, the behavior of cyclorotor principles in ascending and descending phases while in close distance to the ground was numerically studied. In addition, a second study phase was also conducted by Artificial Neural Network (ANN) to train the obtained database of results obtained numerically to further interpret the operating conditions in ground effect. CFD results predict that the optimum operational status of cyclorotor in close-ground altitudes is 30 ºpitching oscillation and 200 rpm for rotating speed. The results are indicating that the vertical distance of the aircraft highly influences their efficiency and functionality in producing thrust. A wide range of parameters is assessed using ANN analysis in several flying altitudes from the ground take-off level up to a reasonable height in which still the ground effects are noticeable. These results strongly indicate that an active control of both pitching oscillation and rotation speed is essential in operating at the optimum desired state.
This paper presents a numerical performance evaluation of the electrostatic rotary bell sprayer (... more This paper presents a numerical performance evaluation of the electrostatic rotary bell sprayer (ERBS) with a particular focus on droplet charge, electric field, and ambient conditions through the implementation of a high-voltage control-ring field pattern effect into the fully turbulent airflow and by including the atomized droplets discrete phase. The simulation shows that the inclusion of droplet charging and electric field coupling, with different parametric values, significantly impacts the atomized droplet distribution over the spray plume and the deposition rate. This analysis was conducted using a three-dimensional (3D) Eulerian–Lagrangian model to describe the two-phase spraying flow by extending the base OpenFOAM package. The procedure includes an unsteady compressible Navier–Stokes solver combined with a large Eddy simulation approach to model turbulence effects on the air flowfield. This is coupled to the spray dynamics by including droplet trajectory tracking, wall film dynamics, and electric field charge. The approach is further extended to include the evaporation phenomenon and the transport of its products. Compared to a conventional ERBS, herein, we provide an in-depth analysis of the fluid dynamic characteristics around the ERBS with a control-ring field pattern for vorticity, velocity, and electrical fields. The results indicate that the control-ring operation improves the performance and transfer efficiency of the ERBS, and it also helps to harmonize the direction of the charged paint droplets. For the first time, finding a balance between the effect of the inside bell cup surface and control-ring voltage and charged droplet has been conducted.
Modeling Coandã effect has been a fundamental issue in fluid dynamic research in the XX century. ... more Modeling Coandã effect has been a fundamental issue in fluid dynamic research in the XX century. It has lost some interest because of the improvement in CFD, even if it could be still important in the area of the preliminary design of aerodynamic devices that benefits of fluid deflection by convex surfaces. An effective model of Coandã effect has not been defined, and fundamental questions are still open. The influence of convective heat exchange on Coandã adhesion of a fluid stream on a convex surface in the presence of a temperature gradient between the fluid and the convex surface is a problem, which affects many practical cases, but it is still marginally approached by scientific literature. This paper aims to start an effective research direction on the effects of convective heat exchange on Coandã effect. It approaches the problem with a set of CFD simulations. It analyses the previous hypotheses, which are based on Prandtl number and evidences the need of a more effective mod...
Two fundamental questions are still open about the complex relation between fluid dynamics and th... more Two fundamental questions are still open about the complex relation between fluid dynamics and thermodynamics. Is it possible (and convenient) to describe fluid dynamic in terms of second law based thermodynamic equations? Is it possible to solve and manage fluid dynamics problems by mean of second law of thermodynamics? This chapter analyses the problem of the relationships between the laws of fluid dynamics and thermodynamics in both first and second law of thermodynamics in the light of constructal law. In particular, taking into account constructal law and the diffusive formulation of Bejan number, it defines a preliminary step through an extensive thermodynamic vision of fluid dynamic phenomena.
This paper presents a new design methodology of cross flow ventilated heat sinks. An accurate des... more This paper presents a new design methodology of cross flow ventilated heat sinks. An accurate design of both finned and circular pin system with inline configuration has been produced. The model is based on the well tested experimental lumped parameter analysis of cross-flow heat exchangers by Gnielinski. The presented method is intended to support the design of heat sinks with well defined performances of cross flow ventilated heat sinks. An evaluation of the physical properties of the sink is performed and different cases are calculated. They allow comparing the performance in terms of both geometrical parameters of the exchanger and air speed. An effective model of the equations is produced and on this basis a multi-objective optimization is performed.
This paper investigates by an energetic approach possible new configurations of aircrafts, which ... more This paper investigates by an energetic approach possible new configurations of aircrafts, which can rival in low speed operations against helicopters. It starts from an effective energy balance of helicopters during fundamental operations: takeoff, horizontal flight, hovering, and landing. The energy state of a helicopter can be written as: E = ½ mV 2 + mgh + ½ I ω 2 (1) where m is mass of helicopter, I is total rotor inertia, ω is rotor rotational speed. By taking the partial derivative with respect to time of equation 1, the power is expressed as dE/dt = ΔP = mV dV/dt + mg dh/dt (2) By optimizing the energy balance of the helicopter a new aircraft configuration has been obtained that allow a very high lift even at very low speed, but drastically reducing the energy consumption during horizontal flight. The total power required is obtained by rotor power and overall efficiency factor (η) and HP req total = η HP req rotor By equations (1) and (2) it has been produced a preliminary ...
Environmental and economic issues related to the aeronautic transport, with particular reference ... more Environmental and economic issues related to the aeronautic transport, with particular reference to the high-speed one are opening new perspectives to pulsejets and derived pulse detonation engines. Their importance relates to high thrust to weight ratio and low cost of manufacturing with very low energy efficiency. This papers presents a preliminary evaluation in the direction of a new family of pulsejets which can be coupled with both an air compression system which is currently in pre-patenting study and a more efficient and enduring valve systems with respect to today ones. This new pulsejet has bee specifically studied to reach three objectives: a better thermodynamic efficiency, a substantial reduction of vibrations by a multi-chamber cooled architecture, a much longer operative life by more affordable valves. Another objective of this research connects directly to the possibility of feeding the pulsejet with hydrogen. This paper after a preliminary analysis of the pulsejet ta...
The advantages associated to Vertical Short-Take-Off and Landing (V/STOL) have been demonstrated ... more The advantages associated to Vertical Short-Take-Off and Landing (V/STOL) have been demonstrated since the early days of aviation, with the initial technolology being based on airships and later on helicopters and planes. Its operational advantages are enormous, being it in the field of military, humanitarian and rescue operations, or even in general aviation. Helicopters have limits in their maximum horizontal speed and classic V/STOL airplanes have problems associated with their large weight, due to the implementation of moving elements, when based on tilting rotors or turbojet vector mechanical oriented nozzles. A new alternative is proposed within the European Union Project ACHEON (Aerial Coanda High Efficiency Orienting-jet Nozzle). The project introduces a novel scheme to orient the jet that is free of moving elements. This is based on a Coanda effect nozzle supported in two fluid streams, also incorporating boundary layer plasma actuators to achieve larger deflection angles. ...
Cycloidal rotors have revealed a noticeable potential to be further enhanced when running at diff... more Cycloidal rotors have revealed a noticeable potential to be further enhanced when running at different operating conditions. The present work demonstrates the active control methodology in order to achieve improved performances in cycloidal rotors operating in forward-flight and lift-up phases. The proposed optimization analysis comprises computational fluid dynamics (CFD) simulations for the numerical database and an artificial neural network (ANN) to propose optimum operating states in each of the mentioned flying phases instead of the hover state under ground effects. CFD predictions were conducted for various operating conditions of pitching oscillations and rotating speeds at each forward or lift-up speed. By training the ANN algorithm using the database attained from CFD simulations, the optimization process was further surveyed for each corresponding flying mode. The targeting concept is to operate with an active mode of employing pitching angles rather than using constant oscillations at all rotation speeds. The ANN approach effectively proposed an optimized pitching schedule for both forward and lift-up phases after analyzing a wide range of parameters in order to reach an optimum aerodynamic efficiency. Because the blade and flow properties are all considered at each specific point on the continuous azimuth of the circular (360°) trajectory, the mutual collaboration of CFD and ANN analysis showed to be advantageous for enhanced operations
This study analyzes the effect of DBD plasma actuators on the unsteady flow of a cycloidal rotor ... more This study analyzes the effect of DBD plasma actuators on the unsteady flow of a cycloidal rotor with six blades of NACA 0016 type using computational fluid dynamics (CFD). The flow field modeling is performed through a sliding mesh technique that was used with k-ω SST turbulence model. The plasma body force generated by a dielectric barrier discharge DBD actuator is modeled with the phenomenological Shyy's model. The impact of plasma actuators on the flow is studied using two actuators located on the upper and bottom surfaces of the airfoil in each of the cyclorotor blades. Three cases are studied: actuation off; actuation over the upper surface of the blades; actuation over the bottom surface of the blades. The vorticity field and the evolution of the lift, thrust and power consumption are analyzed for when a control law is designed that combines both actuations based on the two last cases. The results show that the use of the proposed control law for plasma actuation improves the cyclorotor lift peak value per blade in 11% and the overall thrust by 1.5%. It is also demonstrated that the plasma actuator mitigates the virtual camber on the cyclorotor, this effect is named counter-virtual camber. We show that DBD actuators produce a reduction on the recirculation bubble at the blades suction surface. This effect is important to reduce the thickness of the blades, bringing improvements in terms of mitigating unsteady periodic mass acceleration in cyclorotors.
A novel design of the dielectric barrier discharge (DBD) actuator/sensor is proposed for mapping ... more A novel design of the dielectric barrier discharge (DBD) actuator/sensor is proposed for mapping the location of icing on a surface. The new design uses segmentation of the embedded electrode of the DBD actuator. Segmented DBD actuator/sensor devices were fabricated and experimentally tested in terms of mechanical, thermal and sensing abilities. The sensing capability of the new actuator was analyzed experimentally. Stationary and dynamic icing tests were conducted and the electrical characteristics of the DBD were measured. A parametric study on the effect of the electrode dimensions on the degree of sensitivity of the device was performed. Experimental results show that by using a segmented configuration it is possible to sense the onset of ice formation and also to detect its location. Furthermore, it is possible to detect the initiation of the melting process and measure the time for the water/ice to be completely expelled from the surface. It is also shown that the segmented actuator has better deicing performance in comparison to the conventional actuators. It is also shown that the thermal and active flow control abilities are not compromised by the segmented configuration and thus this device may perform deicing, ice formation and location detection and active flow control.
Canadian Society for Mechanical Engineering International Congress (2020), 2020
Aircraft with the capabilities of hovering and Vertical Takeoff and Landing (VTOL) are increasing... more Aircraft with the capabilities of hovering and Vertical Takeoff and Landing (VTOL) are increasing for various applications. Carrying payloads, controlling cameras and surveillance, critical missions like firefighters, payload carrying from non-terrain regions like forests with high demanding of maneuverability and such environmental circumstances are of examples for the mentioned aircraft types. Although helicopters are typically the most famous crafts of these types, other designs are already available as alternatives, whereas each specific design can be selected according to the expectations. Cycloidal rotor (cyclorotor) has recently been potentially proposed for propulsion system in VTOL aircraft. Higher maneuverability, less noise pollution and more stable flights are some advantageous of the stated systems compared with those of screw propellers employed in helicopters. The present work illustrates a novel conceptual design of a VTOL propulsion system consisting two cycloidal rotors combined with pair-wings which is submitted as an international patent. The downwash jet releasing from the front cyclorotor is partially being processed through the pair-wings towards the rear rotor. The wings are capable of being adjusted for enhanced flow control. Being capable of VTOL from both ground and marine surfaces is the other significant characteristic of the proposed propulsion system. Plasma actuators are employed on pair-wing in order to further enhance the efficiency as an advanced flow control technique. Both numerical and experimental results are presented to further clarify this novel propulsion mechanism.
Violent respiratory diseases, i.e., coronavirus (COVID-19), spread through saliva in coughs and s... more Violent respiratory diseases, i.e., coronavirus (COVID-19), spread through saliva in coughs and sneezes or are even exhaled in the form of microbial pathogen micro-droplets. Therefore, in this work, a comprehensive fully coupled Eulerian-Lagrangian method has been applied for infection control, thus leading to a deeper understanding of the saliva-disease-carrier droplet transmission mechanisms and also of their trajectory tracking by using the OpenFOAM package. This model determines the droplet-air interactions, the breakup process, and turbulent dispersion forces on each micro-droplet that is expelled within the respiratory tract in a correct way. By examining a broad range of initial velocities, size distributions, injection angles of saliva micro-droplets, and mouth opening areas, we predict the maximum opening area that can be driven by micro-droplets. One important contribution of this work is to present a correlation for the length and width of the overall direct maximum reach of the micro-droplets, driven by a wide range of mild coughs to intense sneezes. Our results indicate that the movement of the expelled droplets is mainly influenced by their size, angle, velocity, and environmental factors. During a virus crisis, like COVID-19, this paper can be used to determine the "social distance" between individuals to avoid contamination, by inhaling or touching their bodies, due to these saliva-disease-carrier droplets in sneezing, at various social distance positions such as face-to-face, meeting standing, and near equipment. The safe distance must be increased to around 4 m during a sneeze. By wearing a face mask and by bending the head during a sneeze as a protective action, we can reduce the contamination area to one-third and three-quarters, respectively. Furthermore, the dispersion of the film of the expelled saliva micro-droplets and the spatial relationship between the subjects, which affects the airflow inside the room, are also analyzed in detail. Published under license by AIP Publishing. https://doi.
Plasma actuators are electronic devices commonly used for active flow control. These devices have... more Plasma actuators are electronic devices commonly used for active flow control. These devices have been shown to be effective in a wide variety of fluids engineering applications. In order to increase the efficiency of these devices, the combination of micro exposed electrodes with stair-shaped dielectric layers is proposed. The flow induced by micro and macro stair-shaped plasma actuators is experimentally evaluated and its mechanical efficiency is estimated. Furthermore, durability tests are performed in order to show that stair-shaped dielectric layers also allow to increase the device lifetime. It is shown that by combining micro exposed electrodes with stair-shaped dielectric layers it is possible to achieve mechanical efficiencies 8 times greater than in a conventional macro actuator. In addition, degradation tests demonstrate that stair-shaped dielectric layers degrade slower and lead to an increased lifetime.
Aircraft being capable of Vertical Takeoff and Landing (VTOL) and hover are increasingly emerging... more Aircraft being capable of Vertical Takeoff and Landing (VTOL) and hover are increasingly emerging in various critical and routine applications. Rescue missions in roads and environmental disasters, observance and monitoring-based carriers, surveillance and payload carriage in environments that require high maneuverability and controllability are just a few examples in which this type of aircraft is essential. Helicopters are the most typical aircraft in this kind, but concerning the thrusting mechanism, several alternatives are yet in hand. The tendency to equip aircraft with cycloidal rotors (shortly say, cy-clorotors) as means of Vertical TakeOff and Landing thrusters has increased in recent years. These devices present several advantages such as considerably lower noise production and more stable hover and vertical displacements in comparison with conventional screw propellers as used in helicopters. In the present work a novel concept of propulsion system combining two cy-cloidal rotors with a pair-wing system is presented. A double wing assembly is designed to place in between the two cycloro-tors on each side of the aircraft. The bottom wing is intended to divide the flow in two separate portions through the downwash region of the front cycloidal rotor. To improve the efficiency of this propulsion system, the implementation of plasma actuators in the pair-wing system will be experimentally studied. The concept behind this novel propulsion system is explained and numerical and experimental results, that support its operation concept, are presented.
International Journal of Heat and Fluid Flow , 2019
Here we implemented a 3D comprehensive Eulerian-Lagrangian model in order to investigate the elec... more Here we implemented a 3D comprehensive Eulerian-Lagrangian model in order to investigate the electrostatic spray transfer processes in the high-speed rotary bell sprayer. This efficient algorithm contains spray dynamics, airflow, paint droplets tracking and an electrostatic effect to simulate atomization. The algorithm is implemented using the OpenFOAM package. A solver for the particle trajectory was used to illustrate the process of spray transport and also the interaction of the airflow and the particle that is solved by momentum coupling. Creating an initial condition of the particle approach has been proposed that is matched with practical applications. The fluid-dynamics is simulated by solving the unsteady 3D compressible Navier-Stokes equations. Unsteady flow is computed by using a Large eddy simulation (LES) turbulence approach, while the motion of the particles is simulated by tracking the droplet size distribution approach. The model correctly predicts that the bell cup spin forces the paint particles to fall off from the bell surface towards the high-velocity airflow. The present work illustrates a tentative benchmark and contains a systematic analysis of the recirculation zone length, the toroidal vortex, the overspray phenomena and the flowfield characteristics like mean velocity, pressure, turbulent kinetic energy and velocity fluctuation. The results indicate as dominant operating parameter the air-paint flow rate with voltage level deeply affecting the spray shape. A more uniform distribution of the coating is obtained by growing this high-velocity shaping airflow, although the values of the transfer efficiency (TE) are reduced. The distribution of the particle size is very sensitive to changes in the rotational speed. Experimental results obtained in this study put forward a clear link between the shaping air flow rate and the rotation frequency on the aerodynamics and also provide valuable insights to design modern ERBS. The paint spray distribution obtained in the present work is validated against coating experimental results with suitable accuracy.
This work presents a study on the operational characteristics of a cyclorotor-thruster able to be... more This work presents a study on the operational characteristics of a cyclorotor-thruster able to be applied in an aircraft, particularly in take-off and landing phases. Firstly, the behavior of cyclorotor principles in ascending and descending phases while in close distance to the ground was numerically studied. In addition, a second study phase was also conducted by Artificial Neural Network (ANN) to train the obtained database of results obtained numerically to further interpret the operating conditions in ground effect. CFD results predict that the optimum operational status of cyclorotor in close-ground altitudes is 30 ºpitching oscillation and 200 rpm for rotating speed. The results are indicating that the vertical distance of the aircraft highly influences their efficiency and functionality in producing thrust. A wide range of parameters is assessed using ANN analysis in several flying altitudes from the ground take-off level up to a reasonable height in which still the ground effects are noticeable. These results strongly indicate that an active control of both pitching oscillation and rotation speed is essential in operating at the optimum desired state.
Nesta obra apresentam-se as matérias relevantes para um curso avançado de turbomáquinas, incluind... more Nesta obra apresentam-se as matérias relevantes para um curso avançado de turbomáquinas, incluindo aspetos importantes para o projeto e a análise do seu funcionamento. A informação é exposta de forma sistematizada e analiticamente rigorosa, sendo profusamente ilustrada, facilitando assim a assimilação dos aspetos mais complexos. Utiliza-se uma abordagem pedagógica atual que permite tornar o conhecimento mais acessível a estudantes do ensino universitário e politécnico, assim como aos profissionais da engenharia na sua atividade diária, nas empresas, para autoformação, atualização e consulta. O livro compreende sete capítulos. Inclui uma visão histórica, apresenta capítulos inteiros dedicados aos ventiladores, bombas, compressores, turbinas a gás centrífugas e axiais, e ainda às turbinas hidráulicas e análise dimensional. O último capítulo trata do projeto computacional avançado de turbomáquinas. Em cada capítulo são apresentados exemplos de exercícios resolvidos.
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Papers by Jose Pascoa
charge, electric field, and ambient conditions through the implementation of a high-voltage control-ring field pattern effect into the fully turbulent airflow and by including the atomized droplets discrete phase. The simulation shows that the inclusion of droplet charging and electric
field coupling, with different parametric values, significantly impacts the atomized droplet distribution over the spray plume and the deposition rate. This analysis was conducted using a three-dimensional (3D) Eulerian–Lagrangian model to describe the two-phase spraying flow
by extending the base OpenFOAM package. The procedure includes an unsteady compressible Navier–Stokes solver combined with a large
Eddy simulation approach to model turbulence effects on the air flowfield. This is coupled to the spray dynamics by including droplet trajectory tracking, wall film dynamics, and electric field charge. The approach is further extended to include the evaporation phenomenon and
the transport of its products. Compared to a conventional ERBS, herein, we provide an in-depth analysis of the fluid dynamic characteristics
around the ERBS with a control-ring field pattern for vorticity, velocity, and electrical fields. The results indicate that the control-ring operation improves the performance and transfer efficiency of the ERBS, and it also helps to harmonize the direction of the charged paint droplets.
For the first time, finding a balance between the effect of the inside bell cup surface and control-ring voltage and charged droplet has been
conducted.
The present work demonstrates the active control methodology in order to achieve improved performances in cycloidal rotors operating
in forward-flight and lift-up phases. The proposed optimization analysis comprises computational fluid dynamics (CFD) simulations for
the numerical database and an artificial neural network (ANN) to propose optimum operating states in each of the mentioned flying phases
instead of the hover state under ground effects. CFD predictions were conducted for various operating conditions of pitching oscillations
and rotating speeds at each forward or lift-up speed. By training the ANN algorithm using the database attained from CFD simulations, the
optimization process was further surveyed for each corresponding flying mode. The targeting concept is to operate with an active mode of
employing pitching angles rather than using constant oscillations at all rotation speeds. The ANN approach effectively proposed an optimized
pitching schedule for both forward and lift-up phases after analyzing a wide range of parameters in order to reach an optimum aerodynamic
efficiency. Because the blade and flow properties are all considered at each specific point on the continuous azimuth of the circular (360°)
trajectory, the mutual collaboration of CFD and ANN analysis showed to be advantageous for enhanced operations
the optimum operational status of cyclorotor in close-ground altitudes is 30 ºpitching oscillation and 200 rpm for rotating speed. The results are indicating that the vertical distance of the aircraft highly influences their efficiency and functionality in producing thrust. A wide range of parameters is assessed using ANN analysis in several flying altitudes from the ground take-off level up to a reasonable height in which still the ground effects are noticeable. These results strongly indicate that an active control of both pitching oscillation and rotation speed is essential in operating at the optimum desired state.
charge, electric field, and ambient conditions through the implementation of a high-voltage control-ring field pattern effect into the fully turbulent airflow and by including the atomized droplets discrete phase. The simulation shows that the inclusion of droplet charging and electric
field coupling, with different parametric values, significantly impacts the atomized droplet distribution over the spray plume and the deposition rate. This analysis was conducted using a three-dimensional (3D) Eulerian–Lagrangian model to describe the two-phase spraying flow
by extending the base OpenFOAM package. The procedure includes an unsteady compressible Navier–Stokes solver combined with a large
Eddy simulation approach to model turbulence effects on the air flowfield. This is coupled to the spray dynamics by including droplet trajectory tracking, wall film dynamics, and electric field charge. The approach is further extended to include the evaporation phenomenon and
the transport of its products. Compared to a conventional ERBS, herein, we provide an in-depth analysis of the fluid dynamic characteristics
around the ERBS with a control-ring field pattern for vorticity, velocity, and electrical fields. The results indicate that the control-ring operation improves the performance and transfer efficiency of the ERBS, and it also helps to harmonize the direction of the charged paint droplets.
For the first time, finding a balance between the effect of the inside bell cup surface and control-ring voltage and charged droplet has been
conducted.
The present work demonstrates the active control methodology in order to achieve improved performances in cycloidal rotors operating
in forward-flight and lift-up phases. The proposed optimization analysis comprises computational fluid dynamics (CFD) simulations for
the numerical database and an artificial neural network (ANN) to propose optimum operating states in each of the mentioned flying phases
instead of the hover state under ground effects. CFD predictions were conducted for various operating conditions of pitching oscillations
and rotating speeds at each forward or lift-up speed. By training the ANN algorithm using the database attained from CFD simulations, the
optimization process was further surveyed for each corresponding flying mode. The targeting concept is to operate with an active mode of
employing pitching angles rather than using constant oscillations at all rotation speeds. The ANN approach effectively proposed an optimized
pitching schedule for both forward and lift-up phases after analyzing a wide range of parameters in order to reach an optimum aerodynamic
efficiency. Because the blade and flow properties are all considered at each specific point on the continuous azimuth of the circular (360°)
trajectory, the mutual collaboration of CFD and ANN analysis showed to be advantageous for enhanced operations
the optimum operational status of cyclorotor in close-ground altitudes is 30 ºpitching oscillation and 200 rpm for rotating speed. The results are indicating that the vertical distance of the aircraft highly influences their efficiency and functionality in producing thrust. A wide range of parameters is assessed using ANN analysis in several flying altitudes from the ground take-off level up to a reasonable height in which still the ground effects are noticeable. These results strongly indicate that an active control of both pitching oscillation and rotation speed is essential in operating at the optimum desired state.
O livro compreende sete capítulos. Inclui uma visão histórica, apresenta capítulos inteiros dedicados aos ventiladores, bombas, compressores, turbinas a gás centrífugas e axiais, e ainda às turbinas hidráulicas e análise dimensional. O último capítulo trata do projeto computacional avançado de turbomáquinas. Em cada capítulo são apresentados exemplos de exercícios resolvidos.