I am researcher at Institute of Mathematical Statistics and Applied Mathematics of the Romanian Academy of Science, PhD in Aerodynamics and Fluid Mechanics.
In the last decades, the wind energy became more attractive to Romania. Hence many resources are ... more In the last decades, the wind energy became more attractive to Romania. Hence many resources are being allocated to develop energetic systems based on wind energy. In this work, using CFD (ANSYS Fluent), we investigate the possibility of harvesting wind energy with a controlled pitch-plunge wing system. For large amplitude of the periodic motions we develop a computational methodology, which uses the moving grid option offered by the ANSYS Fluent code, to evaluate the amount of energy extracted from the wind.
Landing phase is the most important phase of the flight of an airplane because the safety of pass... more Landing phase is the most important phase of the flight of an airplane because the safety of passengers and the aircraft largely depends by the accuracy of maneuver. In this paper we will analyze in detail the aircraft dynamics and control at each phase of landing, which is presented, with the specific speed values of the model. This paper is devoted to a detailed analysis of the landing maneuver, focusing on the possible elevator control laws during the free flight from the obstacle to the ground touchdown. It sought to determine some elevator control laws so that the vertical velocity and the slope of the plane at the contact with the ground is as small and to be within the flight safety. This assessment was made for two landing scenarios: Short Landing and Long Landing , putting into evidence the advantages or disadvantages of each of the two techniques. Analysis of the entire landing maneuvers, defined by the phases of: free flight from the obstacle, two points ground roll, three points ground roll and final braking to stop, allowed the evaluation of the physical Landing Distance and the operational Landing Distance , LDA ( Landing Distance Available ). The final results, characterizing the physical and operational distances obtained from this study, are reasonable and realistic and are in good correlation with those for the other actual planes, from the same category, with the aircraft model analyzed in the paper. This confirms that the aerodynamic data and the dynamic models used in this paper structured and developed by the requirements of regulation 23 CS, are the best suited to analyze the landing maneuvers.
The correlation between wind tunnel experimental results and free stream flight results is diffic... more The correlation between wind tunnel experimental results and free stream flight results is difficult even for incompressible flows and 2D configurations. This correlation becomes more difficult to be found if the geometrical configuration contains high lift devices such as Kruger and flaps due to the significant amount of separations. Futhermore, the wall of subsonic wind tunnel cause massive wave pressure reflections especially for high blockage, which affects dramatically the aerodynamic coefficients of experimented models. Unfortunately, very few papers and books deal with this delicate subject even if the appearence of subsonic wind tunnel dates over 100 years ago. For this reason, the present paper dela with this complex subject in order to bring some new light in this complex field. This paper is based on an impressive number of RANS simulations for plain airfoils and 2D high lift configurations for wind tunnel and free stream conditions in order to find some useful correlations for INCAS subsonic wind tunnel.
The purpose of this paper is to evaluate the aerodynamic characteristics of a wing-disc, for a ci... more The purpose of this paper is to evaluate the aerodynamic characteristics of a wing-disc, for a civil application in the fire-fighting system. The aerodynamic analysis is performed using a CFD code, named ANSYS Fluent, in the flow speed range up to 25 m/s, at lower and higher angle of attack. The simulation is three-dimensional, using URANS completed by a SST turbulence model. The results are used to examine the flow around the disc with increasing angle of attack and the structure of the wake.
ICNAAM 2010: International Conference of Numerical Analysis and Applied Mathematics 2010, 2010
Most aerodynamic design tools for horizontal-axial wind turbines are based on the blade-element m... more Most aerodynamic design tools for horizontal-axial wind turbines are based on the blade-element momentum theory (BEM). Due to the nature of this theory, the design tools need 2-D steady sectional lift and drag curves as an input. In practice, flow over a wind turbine rotor blade is neither two-dimensional nor steady, and is affected by rotation. Pioneering experiments have identified a consequence: at inboard rotor blade sections stall is delayed. This so-called Himmelskamp effect [1] gives a larger lift than predicted and, as a result, a higher power and loading than expected. Consequently, an aerodynamic model is needed to explain and predict sectional lift and drag under rotating conditions.
In this paper, using Computational Fluid Dynamics (CFD), we investigate a passive flow control sy... more In this paper, using Computational Fluid Dynamics (CFD), we investigate a passive flow control system using a thin channel, a channel that connects two different pressure points on a convex surface. The tendency to redistribute the pressure on the surface will maintain the jet attached to the convex surface, thus enhancing the Coandã effect. Numerical results on two-dimensional and three-dimensional configurations show that the jet can be kept attached to the surface for a longer distance and deflected, in our simulations, with approx. 8° towards the direction of the jet in the configuration without channel.
NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2011: International Conference on Numerical Analysis and Applied Mathematics, 2011
A based method for modeling the aerodynamics of horizontal axis wind turbine has been developed. ... more A based method for modeling the aerodynamics of horizontal axis wind turbine has been developed. Circulation control is implemented by tangentially blowing a small high-velocity jet over a highly curved surface, such as a rounded trailing edge. This causes the boundary layer and the jet sheet to remain attached along the curved surface due to the Coanda effect and causing the jet to turn without separation. This analysis has been validated for the experimental data of a rotor tested at NASA Ames Research Center. Comparisons have been done against measurements for surface pressure distribution, force coefficients normal and tangential to the chord line, torque and root bending moments. This approach for enhancing the circulation around the airfoil sections (and hence L/D and power production) has been examined and found to produce useful increases in power at low wind speeds.
PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2014 (ICNAAM-2014), 2015
This paper aims to achieve a practical study about the quality of the aerodynamic results provide... more This paper aims to achieve a practical study about the quality of the aerodynamic results provided by CFD simulation compared with the high level confidence of the experimental results. Numerical simulation were developed at low Reynolds Number, specific for a high lift airfoil. Some ideas and strategies have been issued for choosing a suitable turbulence model or a suitable low Reynolds airfoil for UAV’s or a wind turbine blade.
11TH INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2013: ICNAAM 2013, 2013
In the last years the wind turbine with vertical axis (VAWT) began to be more attractive due bene... more In the last years the wind turbine with vertical axis (VAWT) began to be more attractive due benefits in exploitation, the power range covering usually the domain 2 kW-20 kW. But, VAWTs suffer from many complicated aerodynamically problems, of which dynamic stall is an inherent phenomenon when they are operating at low values of tip speed ratio (TSR < 4), and this has a significant impact on vibration, noise, and power output of the VAWTs. For this reason, in the present work we perform a computational investigation of a two-dimensional dynamic stall phenomenon around a NACA0012 airfoil in oscillating motion at relative low Reynolds number (∼105). The unsteady flow is investigated numerically using RANS approach with two turbulence models (k-ω SST and transition SST). The same analysis was performed to evaluate three flow control methods: two passive and one active.
NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2011: International Conference on Numerical Analysis and Applied Mathematics, 2011
ABSTRACT The trailing edge region of a single element wing fitted with Gurney flap has been studi... more ABSTRACT The trailing edge region of a single element wing fitted with Gurney flap has been studied. The complex flow separation phenomena on airfoils with Gurney flap at low Reynolds numbers have some specific features as the separation on set and reattachment locations and the streamline pattern. A detailed study shows the influence of the flap on the efficiency of the centrifugal compressor.
Traditionally, the wind turbine performance is defined in terms of power extraction performance (... more Traditionally, the wind turbine performance is defined in terms of power extraction performance (expressed non-dimensionally as power coefficient, CP, with its maximum value \( C_{{P_{B} }} = 16/27 \)) while the turbine ability to start is normally ignored. Nevertheless, if a turbine cannot accelerate through start-up, its power extraction performance is severely limited, especially at low wind speeds. The criterion of starting behavior at relatively low Reynolds numbers, appropriate for the urban application, therefore offers another expectation to improve the overall performance concerning the period that the turbine needs to start might be achieved which might lead to a significant increase in energy turn-out. The work will focus upon vertical-axis machines of Darrieus type using an H-rotor in which the blades are straight and parallel to their axis of rotation. For the small such turbines, i.e. in low Reynolds number flows, some researchers have stated that the Darrieus-type turbine is inherently not self-starting. The concept of a vertical-axis counter-rotating rotor is used to overcome the starting drawback of small Vertical Axis Wind Turbines (hereafter VAWT). For this purpose, we attempt to simulate the flow around a Counter-Rotating VAWT (CR-VAWT) with Large Eddy Simulation (LES) and both starting behavior and power performance is outlined by comparing with an equivalent conventional turbine.
In the last decades, the wind energy became more attractive to Romania. Hence many resources are ... more In the last decades, the wind energy became more attractive to Romania. Hence many resources are being allocated to develop energetic systems based on wind energy. In this work, using CFD (ANSYS Fluent), we investigate the possibility of harvesting wind energy with a controlled pitch-plunge wing system. For large amplitude of the periodic motions we develop a computational methodology, which uses the moving grid option offered by the ANSYS Fluent code, to evaluate the amount of energy extracted from the wind.
Landing phase is the most important phase of the flight of an airplane because the safety of pass... more Landing phase is the most important phase of the flight of an airplane because the safety of passengers and the aircraft largely depends by the accuracy of maneuver. In this paper we will analyze in detail the aircraft dynamics and control at each phase of landing, which is presented, with the specific speed values of the model. This paper is devoted to a detailed analysis of the landing maneuver, focusing on the possible elevator control laws during the free flight from the obstacle to the ground touchdown. It sought to determine some elevator control laws so that the vertical velocity and the slope of the plane at the contact with the ground is as small and to be within the flight safety. This assessment was made for two landing scenarios: Short Landing and Long Landing , putting into evidence the advantages or disadvantages of each of the two techniques. Analysis of the entire landing maneuvers, defined by the phases of: free flight from the obstacle, two points ground roll, three points ground roll and final braking to stop, allowed the evaluation of the physical Landing Distance and the operational Landing Distance , LDA ( Landing Distance Available ). The final results, characterizing the physical and operational distances obtained from this study, are reasonable and realistic and are in good correlation with those for the other actual planes, from the same category, with the aircraft model analyzed in the paper. This confirms that the aerodynamic data and the dynamic models used in this paper structured and developed by the requirements of regulation 23 CS, are the best suited to analyze the landing maneuvers.
The correlation between wind tunnel experimental results and free stream flight results is diffic... more The correlation between wind tunnel experimental results and free stream flight results is difficult even for incompressible flows and 2D configurations. This correlation becomes more difficult to be found if the geometrical configuration contains high lift devices such as Kruger and flaps due to the significant amount of separations. Futhermore, the wall of subsonic wind tunnel cause massive wave pressure reflections especially for high blockage, which affects dramatically the aerodynamic coefficients of experimented models. Unfortunately, very few papers and books deal with this delicate subject even if the appearence of subsonic wind tunnel dates over 100 years ago. For this reason, the present paper dela with this complex subject in order to bring some new light in this complex field. This paper is based on an impressive number of RANS simulations for plain airfoils and 2D high lift configurations for wind tunnel and free stream conditions in order to find some useful correlations for INCAS subsonic wind tunnel.
The purpose of this paper is to evaluate the aerodynamic characteristics of a wing-disc, for a ci... more The purpose of this paper is to evaluate the aerodynamic characteristics of a wing-disc, for a civil application in the fire-fighting system. The aerodynamic analysis is performed using a CFD code, named ANSYS Fluent, in the flow speed range up to 25 m/s, at lower and higher angle of attack. The simulation is three-dimensional, using URANS completed by a SST turbulence model. The results are used to examine the flow around the disc with increasing angle of attack and the structure of the wake.
ICNAAM 2010: International Conference of Numerical Analysis and Applied Mathematics 2010, 2010
Most aerodynamic design tools for horizontal-axial wind turbines are based on the blade-element m... more Most aerodynamic design tools for horizontal-axial wind turbines are based on the blade-element momentum theory (BEM). Due to the nature of this theory, the design tools need 2-D steady sectional lift and drag curves as an input. In practice, flow over a wind turbine rotor blade is neither two-dimensional nor steady, and is affected by rotation. Pioneering experiments have identified a consequence: at inboard rotor blade sections stall is delayed. This so-called Himmelskamp effect [1] gives a larger lift than predicted and, as a result, a higher power and loading than expected. Consequently, an aerodynamic model is needed to explain and predict sectional lift and drag under rotating conditions.
In this paper, using Computational Fluid Dynamics (CFD), we investigate a passive flow control sy... more In this paper, using Computational Fluid Dynamics (CFD), we investigate a passive flow control system using a thin channel, a channel that connects two different pressure points on a convex surface. The tendency to redistribute the pressure on the surface will maintain the jet attached to the convex surface, thus enhancing the Coandã effect. Numerical results on two-dimensional and three-dimensional configurations show that the jet can be kept attached to the surface for a longer distance and deflected, in our simulations, with approx. 8° towards the direction of the jet in the configuration without channel.
NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2011: International Conference on Numerical Analysis and Applied Mathematics, 2011
A based method for modeling the aerodynamics of horizontal axis wind turbine has been developed. ... more A based method for modeling the aerodynamics of horizontal axis wind turbine has been developed. Circulation control is implemented by tangentially blowing a small high-velocity jet over a highly curved surface, such as a rounded trailing edge. This causes the boundary layer and the jet sheet to remain attached along the curved surface due to the Coanda effect and causing the jet to turn without separation. This analysis has been validated for the experimental data of a rotor tested at NASA Ames Research Center. Comparisons have been done against measurements for surface pressure distribution, force coefficients normal and tangential to the chord line, torque and root bending moments. This approach for enhancing the circulation around the airfoil sections (and hence L/D and power production) has been examined and found to produce useful increases in power at low wind speeds.
PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2014 (ICNAAM-2014), 2015
This paper aims to achieve a practical study about the quality of the aerodynamic results provide... more This paper aims to achieve a practical study about the quality of the aerodynamic results provided by CFD simulation compared with the high level confidence of the experimental results. Numerical simulation were developed at low Reynolds Number, specific for a high lift airfoil. Some ideas and strategies have been issued for choosing a suitable turbulence model or a suitable low Reynolds airfoil for UAV’s or a wind turbine blade.
11TH INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS 2013: ICNAAM 2013, 2013
In the last years the wind turbine with vertical axis (VAWT) began to be more attractive due bene... more In the last years the wind turbine with vertical axis (VAWT) began to be more attractive due benefits in exploitation, the power range covering usually the domain 2 kW-20 kW. But, VAWTs suffer from many complicated aerodynamically problems, of which dynamic stall is an inherent phenomenon when they are operating at low values of tip speed ratio (TSR < 4), and this has a significant impact on vibration, noise, and power output of the VAWTs. For this reason, in the present work we perform a computational investigation of a two-dimensional dynamic stall phenomenon around a NACA0012 airfoil in oscillating motion at relative low Reynolds number (∼105). The unsteady flow is investigated numerically using RANS approach with two turbulence models (k-ω SST and transition SST). The same analysis was performed to evaluate three flow control methods: two passive and one active.
NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2011: International Conference on Numerical Analysis and Applied Mathematics, 2011
ABSTRACT The trailing edge region of a single element wing fitted with Gurney flap has been studi... more ABSTRACT The trailing edge region of a single element wing fitted with Gurney flap has been studied. The complex flow separation phenomena on airfoils with Gurney flap at low Reynolds numbers have some specific features as the separation on set and reattachment locations and the streamline pattern. A detailed study shows the influence of the flap on the efficiency of the centrifugal compressor.
Traditionally, the wind turbine performance is defined in terms of power extraction performance (... more Traditionally, the wind turbine performance is defined in terms of power extraction performance (expressed non-dimensionally as power coefficient, CP, with its maximum value \( C_{{P_{B} }} = 16/27 \)) while the turbine ability to start is normally ignored. Nevertheless, if a turbine cannot accelerate through start-up, its power extraction performance is severely limited, especially at low wind speeds. The criterion of starting behavior at relatively low Reynolds numbers, appropriate for the urban application, therefore offers another expectation to improve the overall performance concerning the period that the turbine needs to start might be achieved which might lead to a significant increase in energy turn-out. The work will focus upon vertical-axis machines of Darrieus type using an H-rotor in which the blades are straight and parallel to their axis of rotation. For the small such turbines, i.e. in low Reynolds number flows, some researchers have stated that the Darrieus-type turbine is inherently not self-starting. The concept of a vertical-axis counter-rotating rotor is used to overcome the starting drawback of small Vertical Axis Wind Turbines (hereafter VAWT). For this purpose, we attempt to simulate the flow around a Counter-Rotating VAWT (CR-VAWT) with Large Eddy Simulation (LES) and both starting behavior and power performance is outlined by comparing with an equivalent conventional turbine.
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