Josep Bergada - Academia.edu (original) (raw)
Papers by Josep Bergada
Computers & mathematics with applications, Sep 1, 2023
Iniciativa Digital Politècnica. Oficina de Publicacions Acadèmiques Digitals de la UPC eBooks, Apr 1, 2021
En este libro, se introducen una serie de problemas que requieren una resolución numérica. En la ... more En este libro, se introducen una serie de problemas que requieren una resolución numérica. En la resolución de problemas de mecánica de fluidos, es muy usual que la solución venga dada en forma de una o varias ecuaciones diferenciales. En consecuencia, todos los problemas que aquí se presentan incluyen un programa que permite resolver el problema de forma genérica y extensiva. Esta obra se ha diseñado para que el lector no solo pueda aprender los conceptos esenciales de la mecánica de fluidos, sino que además aprenda a diseñar programas que le permitan resolver problemas que, por su dificultad, deban ser resueltos numéricamente. Considerando el nivel de los problemas que se introducen aquí, se recomienda al lector que se familiarice con los conceptos básicos de mecánica de fluidos antes de consultar este libro. Los autores desean que la información que se presenta en estas páginas resulte de utilidad para ampliar conocimientos tanto de mecánica de fluidos como de programación.
The aim of the paper is to simulate numerically the Fluid-Structure Interaction for flow through ... more The aim of the paper is to simulate numerically the Fluid-Structure Interaction for flow through valves of a hermetic compressor using immersed boundary method. The paper is primarily concerned with the mathematical structure and implementation of the Immersed Boundary Method which includes both the Immersed Boundary form of the equations of motion and also the Immersed Boundary numerical Scheme. The flow pattern of the fluid in the compressor is intimately connected with the performance of the valves, and this paper presents a solution of the Navier-Stokes equations in 2D of a Newtonian fluid under laminar regime, in the presence of moving immersed boundaries, being the fluid treated as isothermal. The immersed boundary method has evolved into a generally useful method for problems of Fluid-structure interaction. In this approach, the mathematical formulation employs a mixture of Eulerian and Lagrangian variables, the fluid is represented in a Eulerian coordinate frame and the structures or the interacting surfaces are considered in a Lagrangian coordinate frame. The two types of variables are linked by interaction equations that involve a smoothed approximation to the Dirac delta function, constructed according to the principles established in [1], which plays a prominent role. In the numerical scheme motivated by the Immersed Boundary formulation, the Eulerian variables are defined on a fixed Cartesian frame, and the Lagrangian variables are defined on a curvilinear mesh that moves freely through the fixed Cartesian mesh without being constrained to adapt to it in any way at all. Eulerian/Lagrangian identities govern the transfer of data from one mesh to another. A structured non-uniform staggered grid based two dimensional finite volume model is used to solve the equations of the fluid flow in laminar regime and a second-order Adams Bashforth-Crank Nicholson scheme is used for temporal discretization and preconditioned Bi-conjugate gradient stabilized method is used to solve the derived system of equations. The numerical results presented show the average volumetric flow and the respective temporal valve displacements for different Laminar Reynolds numbers.
Journal of Applied Mechanical Engineering, Sep 7, 2016
El presente libro es fruto de la experiencia adquirida durante toda una carrera universitaria. Mu... more El presente libro es fruto de la experiencia adquirida durante toda una carrera universitaria. Muchos de los problemas que en él se exponen fueron, en su momento, problemas de examen de la asignatura Mecánica de Fluidos. Por una parte, esta obra está diseñada para presentar, de manera sencilla, diversos temas básicos de la mecánica de fluidos que todo estudiante de la asignatura debe conocer. Asimismo, pretende ser un libro de repaso para quienes, habiendo estudiado Ingeniería y trabajando en la industria, necesiten fijar determinados conceptos sobre la materia. Finalmente, esta obra también quiere servir de apoyo a todas las escuelas de los países de habla hispana que imparten las diversas ingenierías, y ser un instrumento útil de repaso de la temática presentada.
Applied Sciences
The Boundary Layer (BL) dynamic performance greatly affects the forces acting on any Bluff body [... more The Boundary Layer (BL) dynamic performance greatly affects the forces acting on any Bluff body [...]
Applied Sciences
The suspensions used in heavy vehicles often consist of several oil and two gas chambers. In orde... more The suspensions used in heavy vehicles often consist of several oil and two gas chambers. In order to perform an analytical study of the mass flow transferred between two gas chambers separated by a nozzle, and when considering the gas as compressible and real, it is usually needed to determine the discharge coefficient of the nozzle. The nozzle configuration analyzed in the present study consists of a T shape, and it is used to separate two nitrogen chambers employed in heavy vehicle suspensions. In the present study, under compressible dynamic real flow conditions and at operating pressures, discharge coefficients were determined based on experimental data. A test rig was constructed for this purpose, and air was used as working fluid. The study clarifies that discharge coefficients for the T shape nozzle studied not only depend on the pressure gradient between chambers but also on the flow direction. Computational Fluid Dynamic (CFD) simulations, using air as working fluid and wh...
This paper analyzes the pressure distribution, leakage, force, and torque between the barrel and ... more This paper analyzes the pressure distribution, leakage, force, and torque between the barrel and the port plate of an axial piston pump. A detailed set of new equations is developed, which takes into account important parameters such as tilt, clearance and rotational speed, and timing groove. The pressure distribution is derived for different operating conditions, together with a complementary numerical analysis of the original differential equations, specifically written for this application and used to validate the theoretical solutions. An excellent agreement between the two approaches is shown, allowing an explicit analytical insight into barrel/port plate operating characteristics, including consideration of cavitation. The overall mean force and torques over the barrel are evaluated and show that the torque over the XX axis is much smaller than the torque over the YY axis, as deduced from other nonexplicit simulation approaches. A detailed dynamic analysis is then studied, and it is shown that the torque fluctuation over the YY axis is typically 8% of the torque total magnitude. Of particular novelty is the prediction of a double peak in each torque fluctuation resulting from the more exact modeling of the piston/port plate/timing groove pressure distribution characteristic during motion. A comparison between the temporal torque fluctuation pattern and another work shows a good qualitative agreement. Experimental and analytical results for the present study demonstrate that barrel dynamics do contain a component primarily directed by the torque dynamics.
The book presents some basic Fluid Mechanics concepts and has a large amount of solved problems. ... more The book presents some basic Fluid Mechanics concepts and has a large amount of solved problems. Chapters related to fundamental equations, fluid under dominant viscosity and compressible flow are particularly interesting. Total number of pages 709.
As fluidic actuators have the advantage of lacking moving parts, their use in real applications b... more As fluidic actuators have the advantage of lacking moving parts, their use in real applications brings high reliability. This is why, once having overcome their drawbacks, which means being able to provide the appropriate momentum and frequency, they could extensively be used in a wide range of applications. The present paper will present a CFD evaluation of the flow inside a fluidic oscillator. Initially a standard fluidic actuator will be simulated and the results compared with existing experimental data. In a second step, several geometric parameters will be modified; the actuator performance under these new conditions is reported. The paper aims to be an aid for future innovative oscillator designs.
Proceedings of the JFPS International Symposium on Fluid Power, 2002
This paper overviews a direct method to evaluate the pressure distribution and the leakage across... more This paper overviews a direct method to evaluate the pressure distribution and the leakage across the clearance gap between a piston and cylinder block and similarly for the clearance between the associated slipper and swash plate. The method, based on the well-known Couette-Poiseulle and Reynolds equations for laminar flow, takes into account the reality of many piston/slipper designs. The new set of equations are used to consider the nature of the leakage flow for a piston with five grooves, and for a slipper with one groove, and within a 9co = Pump angular velocity (rad/s)
Textile Research Journal, 2007
ABSTRACT Traditional spinning systems are reaching profitability limits due to high production co... more ABSTRACT Traditional spinning systems are reaching profitability limits due to high production costs and low productivity. Pneumatic spinning is seen as a developing system; its productivity is much higher than that achieved by conventional systems. This paper evaluates one of the main factors that prevents an increase of productivity in pneumatic spinning. This is the air currents generated at the drafting cylinder entrance, which interact with the incoming fibers, diverting them from their expected path. Using laser anemometry, the airflow velocity distribution around drafting cylinders has been measured and it has been found that vorticity is created at the cylinder entrance. Extensive CFD simulation on the airflow drag by the cylinders has given a clear inight into the vortex created, producing valuable information on how cylinder design affects the vorticity created. It has been found experimentally that the use of a drafting cylinder with holes in it produced good results, reducing the air currents and allowing a sharp increase in yarn quality, as well as an increase in productivity. A study of vortex kinematics has been undertaken, bringing a better understanding of vortex creation, development, and breakdown.
International Journal of Mechanical Sciences, 2013
ABSTRACT In the design of high pressure piston pumps/motors, some manufacturers use pistons which... more ABSTRACT In the design of high pressure piston pumps/motors, some manufacturers use pistons which have grooves being cut along the piston length, while others do not use grooves at all. The present paper clarifies the effect of grooves cut along the pistons surface via studding the effect of the number of grooves and their location over the piston surface. Piston force, torque, leakage, areas where cavitation might appear and piston stability, will be, in the present paper and for a set of piston/grooves configurations, carefully evaluated. A finite volume based Reynolds equation model has been formulated for the piston-cylinder clearance which considers the piston eccentricity and the relative tangential movement between piston and barrel. Different grooves configurations have been evaluated in search of finding minimum leakage, minimum appearance of cavitation and maximum restoring torque. Design instructions to optimize the piston behavior are also given, therefore the information and methodology presented in the present paper, is expected to be used as a designing tool for future machines. The piston/cylinder leakage is considered as laminar under all working conditions. The Fluid used is hydraulic oil ISO 32. (c) 2012 Elsevier Ltd. All rights reserved.
Sensors
Fluidic oscillators are often used to modify the forces fluid generates on any given bluff body; ... more Fluidic oscillators are often used to modify the forces fluid generates on any given bluff body; they can also be used as flow, pressure or acoustic sensors, with each application requiring a particular oscillator configuration. Regarding the fluidic oscillators’ main performance, a problem which is not yet clarified is the understanding of the feedback channel effect on the oscillator outlet mass flow frequency and amplitude, especially under compressible flow conditions. In order to bring light to this point, a set of three-dimensional Direct Numerical Simulations under compressible flow conditions are introduced in the present paper; four different feedback channel lengths and two inlet Reynolds numbers Re = 12,410 and Re = 18,617 are considered. From the results obtained, it is observed that as the inlet velocity increases, the fluidic oscillator outlet mass flow frequency and amplitude increase. An increase of the feedback channel length decreases the outlet mass flow oscillati...
The aim of the present study is to simulate and analyze the interaction of two dimensional flow p... more The aim of the present study is to simulate and analyze the interaction of two dimensional flow past a square cylinder in a laminar regime with an upstream mixing layer developed by an axis symmetrical horizontal splitter plate. The mixing layer is generated upstream of the square cylinder by mixing two uniform streams of fluid with different velocities above and below the splitter plate. A range of upstream domain lengths, distances between the splitter plate and the square cylinder, and upstream velocity ratios between the two streams of fluid are analyzed. Unconfined flow over a square cylinder placed in uniform upstream flow is initially analyzed as it plays a crucial role in understanding the properties of the wake. The results are compared with the existing literature to validate the code developed and they are found to be in very good agreement. It is observed from the present study that at smaller velocity ratios, the vortices shed into the wake consist of both clockwise and anticlockwise moment vortices. As velocity ratio is increased only clockwise moment vortices are shed downstream and anticlockwise vortices are shed as Kelvin-Helmholtz instabilities. In all simulations undertaken the same phenomena is observed independent of the upstream Reynolds number, indicating that velocity ratio is a primary parameter influencing the flow. Different instability modes were observed and they were highly dependent on the upstream velocity ratio.
Applied Sciences
The number of applications where fluidic oscillators are expected to be used in the future, is ra... more The number of applications where fluidic oscillators are expected to be used in the future, is raising sharply, then their ability of interacting with the boundary layer to modify forces on bluff bodies, enhancing heat transfer or decreasing noise generation, are just few of the applications where fluidic oscillators can be used. For each application a particular pulsating frequency and amplitude are required to minimize/maximize the variable under study, force, Nusselt number, etc. For a given range of Reynolds numbers, fluidic oscillators present a linear relationship between the output frequency and the incoming fluid flow, yet it appears the modification of the internal fluidic oscillator geometry may affect this relation. In the present paper and for a given fluidic oscillator, several performance parameters will be numerically evaluated as a function of different internal modifications via using 3D-CFD simulations. The paper is also evaluating the relation between the momentum...
Energies
One of the main advantages of fluidic oscillators is that they do not have moving parts, which br... more One of the main advantages of fluidic oscillators is that they do not have moving parts, which brings high reliability whenever being used in real applications. To use these devices in real applications, it is necessary to evaluate their performance, since each application requires a particular injected fluid momentum and frequency. In this paper, the performance of a given fluidic oscillator is evaluated at different Reynolds numbers via a 3D-computational fluid dynamics (CFD) analysis. The net momentum applied to the incoming jet is compared with the dynamic maximum stagnation pressure in the mixing chamber, to the dynamic output mass flow, to the dynamic feedback channels mass flow, to the pressure acting to both feedback channels outlets, and to the mixing chamber inlet jet oscillation angle. A perfect correlation between these parameters is obtained, therefore indicating the oscillation is triggered by the pressure momentum term applied to the jet at the feedback channels outle...
Journal of Fluids Engineering
The present paper introduces a novel transient experimental method employed to determine the disc... more The present paper introduces a novel transient experimental method employed to determine the discharge coefficient of constant section nozzles of small diameters of 1–3 mm and with a length/diameter ratio of around one. Flow is considered to be real and compressible; the discharge process was analyzed at relatively high pressures, the fluid used was N2. Based on the experimental data, a generalized expression characterizing the discharge coefficient for nozzles of different diameters, lengths, and fluid conditions was developed. In order to check the precision of the analytical equation presented, experimental upstream reservoir pressure decay was compared with the temporal pressure decay obtained using the new analytical equation. Good correlation was achieved for pressure differentials up to 7.6 MPa. Despite the fact that the procedure established can be extended to other gases and nozzle configurations, so far the equation presented to estimate the discharge coefficient, can only...
Computers & mathematics with applications, Sep 1, 2023
Iniciativa Digital Politècnica. Oficina de Publicacions Acadèmiques Digitals de la UPC eBooks, Apr 1, 2021
En este libro, se introducen una serie de problemas que requieren una resolución numérica. En la ... more En este libro, se introducen una serie de problemas que requieren una resolución numérica. En la resolución de problemas de mecánica de fluidos, es muy usual que la solución venga dada en forma de una o varias ecuaciones diferenciales. En consecuencia, todos los problemas que aquí se presentan incluyen un programa que permite resolver el problema de forma genérica y extensiva. Esta obra se ha diseñado para que el lector no solo pueda aprender los conceptos esenciales de la mecánica de fluidos, sino que además aprenda a diseñar programas que le permitan resolver problemas que, por su dificultad, deban ser resueltos numéricamente. Considerando el nivel de los problemas que se introducen aquí, se recomienda al lector que se familiarice con los conceptos básicos de mecánica de fluidos antes de consultar este libro. Los autores desean que la información que se presenta en estas páginas resulte de utilidad para ampliar conocimientos tanto de mecánica de fluidos como de programación.
The aim of the paper is to simulate numerically the Fluid-Structure Interaction for flow through ... more The aim of the paper is to simulate numerically the Fluid-Structure Interaction for flow through valves of a hermetic compressor using immersed boundary method. The paper is primarily concerned with the mathematical structure and implementation of the Immersed Boundary Method which includes both the Immersed Boundary form of the equations of motion and also the Immersed Boundary numerical Scheme. The flow pattern of the fluid in the compressor is intimately connected with the performance of the valves, and this paper presents a solution of the Navier-Stokes equations in 2D of a Newtonian fluid under laminar regime, in the presence of moving immersed boundaries, being the fluid treated as isothermal. The immersed boundary method has evolved into a generally useful method for problems of Fluid-structure interaction. In this approach, the mathematical formulation employs a mixture of Eulerian and Lagrangian variables, the fluid is represented in a Eulerian coordinate frame and the structures or the interacting surfaces are considered in a Lagrangian coordinate frame. The two types of variables are linked by interaction equations that involve a smoothed approximation to the Dirac delta function, constructed according to the principles established in [1], which plays a prominent role. In the numerical scheme motivated by the Immersed Boundary formulation, the Eulerian variables are defined on a fixed Cartesian frame, and the Lagrangian variables are defined on a curvilinear mesh that moves freely through the fixed Cartesian mesh without being constrained to adapt to it in any way at all. Eulerian/Lagrangian identities govern the transfer of data from one mesh to another. A structured non-uniform staggered grid based two dimensional finite volume model is used to solve the equations of the fluid flow in laminar regime and a second-order Adams Bashforth-Crank Nicholson scheme is used for temporal discretization and preconditioned Bi-conjugate gradient stabilized method is used to solve the derived system of equations. The numerical results presented show the average volumetric flow and the respective temporal valve displacements for different Laminar Reynolds numbers.
Journal of Applied Mechanical Engineering, Sep 7, 2016
El presente libro es fruto de la experiencia adquirida durante toda una carrera universitaria. Mu... more El presente libro es fruto de la experiencia adquirida durante toda una carrera universitaria. Muchos de los problemas que en él se exponen fueron, en su momento, problemas de examen de la asignatura Mecánica de Fluidos. Por una parte, esta obra está diseñada para presentar, de manera sencilla, diversos temas básicos de la mecánica de fluidos que todo estudiante de la asignatura debe conocer. Asimismo, pretende ser un libro de repaso para quienes, habiendo estudiado Ingeniería y trabajando en la industria, necesiten fijar determinados conceptos sobre la materia. Finalmente, esta obra también quiere servir de apoyo a todas las escuelas de los países de habla hispana que imparten las diversas ingenierías, y ser un instrumento útil de repaso de la temática presentada.
Applied Sciences
The Boundary Layer (BL) dynamic performance greatly affects the forces acting on any Bluff body [... more The Boundary Layer (BL) dynamic performance greatly affects the forces acting on any Bluff body [...]
Applied Sciences
The suspensions used in heavy vehicles often consist of several oil and two gas chambers. In orde... more The suspensions used in heavy vehicles often consist of several oil and two gas chambers. In order to perform an analytical study of the mass flow transferred between two gas chambers separated by a nozzle, and when considering the gas as compressible and real, it is usually needed to determine the discharge coefficient of the nozzle. The nozzle configuration analyzed in the present study consists of a T shape, and it is used to separate two nitrogen chambers employed in heavy vehicle suspensions. In the present study, under compressible dynamic real flow conditions and at operating pressures, discharge coefficients were determined based on experimental data. A test rig was constructed for this purpose, and air was used as working fluid. The study clarifies that discharge coefficients for the T shape nozzle studied not only depend on the pressure gradient between chambers but also on the flow direction. Computational Fluid Dynamic (CFD) simulations, using air as working fluid and wh...
This paper analyzes the pressure distribution, leakage, force, and torque between the barrel and ... more This paper analyzes the pressure distribution, leakage, force, and torque between the barrel and the port plate of an axial piston pump. A detailed set of new equations is developed, which takes into account important parameters such as tilt, clearance and rotational speed, and timing groove. The pressure distribution is derived for different operating conditions, together with a complementary numerical analysis of the original differential equations, specifically written for this application and used to validate the theoretical solutions. An excellent agreement between the two approaches is shown, allowing an explicit analytical insight into barrel/port plate operating characteristics, including consideration of cavitation. The overall mean force and torques over the barrel are evaluated and show that the torque over the XX axis is much smaller than the torque over the YY axis, as deduced from other nonexplicit simulation approaches. A detailed dynamic analysis is then studied, and it is shown that the torque fluctuation over the YY axis is typically 8% of the torque total magnitude. Of particular novelty is the prediction of a double peak in each torque fluctuation resulting from the more exact modeling of the piston/port plate/timing groove pressure distribution characteristic during motion. A comparison between the temporal torque fluctuation pattern and another work shows a good qualitative agreement. Experimental and analytical results for the present study demonstrate that barrel dynamics do contain a component primarily directed by the torque dynamics.
The book presents some basic Fluid Mechanics concepts and has a large amount of solved problems. ... more The book presents some basic Fluid Mechanics concepts and has a large amount of solved problems. Chapters related to fundamental equations, fluid under dominant viscosity and compressible flow are particularly interesting. Total number of pages 709.
As fluidic actuators have the advantage of lacking moving parts, their use in real applications b... more As fluidic actuators have the advantage of lacking moving parts, their use in real applications brings high reliability. This is why, once having overcome their drawbacks, which means being able to provide the appropriate momentum and frequency, they could extensively be used in a wide range of applications. The present paper will present a CFD evaluation of the flow inside a fluidic oscillator. Initially a standard fluidic actuator will be simulated and the results compared with existing experimental data. In a second step, several geometric parameters will be modified; the actuator performance under these new conditions is reported. The paper aims to be an aid for future innovative oscillator designs.
Proceedings of the JFPS International Symposium on Fluid Power, 2002
This paper overviews a direct method to evaluate the pressure distribution and the leakage across... more This paper overviews a direct method to evaluate the pressure distribution and the leakage across the clearance gap between a piston and cylinder block and similarly for the clearance between the associated slipper and swash plate. The method, based on the well-known Couette-Poiseulle and Reynolds equations for laminar flow, takes into account the reality of many piston/slipper designs. The new set of equations are used to consider the nature of the leakage flow for a piston with five grooves, and for a slipper with one groove, and within a 9co = Pump angular velocity (rad/s)
Textile Research Journal, 2007
ABSTRACT Traditional spinning systems are reaching profitability limits due to high production co... more ABSTRACT Traditional spinning systems are reaching profitability limits due to high production costs and low productivity. Pneumatic spinning is seen as a developing system; its productivity is much higher than that achieved by conventional systems. This paper evaluates one of the main factors that prevents an increase of productivity in pneumatic spinning. This is the air currents generated at the drafting cylinder entrance, which interact with the incoming fibers, diverting them from their expected path. Using laser anemometry, the airflow velocity distribution around drafting cylinders has been measured and it has been found that vorticity is created at the cylinder entrance. Extensive CFD simulation on the airflow drag by the cylinders has given a clear inight into the vortex created, producing valuable information on how cylinder design affects the vorticity created. It has been found experimentally that the use of a drafting cylinder with holes in it produced good results, reducing the air currents and allowing a sharp increase in yarn quality, as well as an increase in productivity. A study of vortex kinematics has been undertaken, bringing a better understanding of vortex creation, development, and breakdown.
International Journal of Mechanical Sciences, 2013
ABSTRACT In the design of high pressure piston pumps/motors, some manufacturers use pistons which... more ABSTRACT In the design of high pressure piston pumps/motors, some manufacturers use pistons which have grooves being cut along the piston length, while others do not use grooves at all. The present paper clarifies the effect of grooves cut along the pistons surface via studding the effect of the number of grooves and their location over the piston surface. Piston force, torque, leakage, areas where cavitation might appear and piston stability, will be, in the present paper and for a set of piston/grooves configurations, carefully evaluated. A finite volume based Reynolds equation model has been formulated for the piston-cylinder clearance which considers the piston eccentricity and the relative tangential movement between piston and barrel. Different grooves configurations have been evaluated in search of finding minimum leakage, minimum appearance of cavitation and maximum restoring torque. Design instructions to optimize the piston behavior are also given, therefore the information and methodology presented in the present paper, is expected to be used as a designing tool for future machines. The piston/cylinder leakage is considered as laminar under all working conditions. The Fluid used is hydraulic oil ISO 32. (c) 2012 Elsevier Ltd. All rights reserved.
Sensors
Fluidic oscillators are often used to modify the forces fluid generates on any given bluff body; ... more Fluidic oscillators are often used to modify the forces fluid generates on any given bluff body; they can also be used as flow, pressure or acoustic sensors, with each application requiring a particular oscillator configuration. Regarding the fluidic oscillators’ main performance, a problem which is not yet clarified is the understanding of the feedback channel effect on the oscillator outlet mass flow frequency and amplitude, especially under compressible flow conditions. In order to bring light to this point, a set of three-dimensional Direct Numerical Simulations under compressible flow conditions are introduced in the present paper; four different feedback channel lengths and two inlet Reynolds numbers Re = 12,410 and Re = 18,617 are considered. From the results obtained, it is observed that as the inlet velocity increases, the fluidic oscillator outlet mass flow frequency and amplitude increase. An increase of the feedback channel length decreases the outlet mass flow oscillati...
The aim of the present study is to simulate and analyze the interaction of two dimensional flow p... more The aim of the present study is to simulate and analyze the interaction of two dimensional flow past a square cylinder in a laminar regime with an upstream mixing layer developed by an axis symmetrical horizontal splitter plate. The mixing layer is generated upstream of the square cylinder by mixing two uniform streams of fluid with different velocities above and below the splitter plate. A range of upstream domain lengths, distances between the splitter plate and the square cylinder, and upstream velocity ratios between the two streams of fluid are analyzed. Unconfined flow over a square cylinder placed in uniform upstream flow is initially analyzed as it plays a crucial role in understanding the properties of the wake. The results are compared with the existing literature to validate the code developed and they are found to be in very good agreement. It is observed from the present study that at smaller velocity ratios, the vortices shed into the wake consist of both clockwise and anticlockwise moment vortices. As velocity ratio is increased only clockwise moment vortices are shed downstream and anticlockwise vortices are shed as Kelvin-Helmholtz instabilities. In all simulations undertaken the same phenomena is observed independent of the upstream Reynolds number, indicating that velocity ratio is a primary parameter influencing the flow. Different instability modes were observed and they were highly dependent on the upstream velocity ratio.
Applied Sciences
The number of applications where fluidic oscillators are expected to be used in the future, is ra... more The number of applications where fluidic oscillators are expected to be used in the future, is raising sharply, then their ability of interacting with the boundary layer to modify forces on bluff bodies, enhancing heat transfer or decreasing noise generation, are just few of the applications where fluidic oscillators can be used. For each application a particular pulsating frequency and amplitude are required to minimize/maximize the variable under study, force, Nusselt number, etc. For a given range of Reynolds numbers, fluidic oscillators present a linear relationship between the output frequency and the incoming fluid flow, yet it appears the modification of the internal fluidic oscillator geometry may affect this relation. In the present paper and for a given fluidic oscillator, several performance parameters will be numerically evaluated as a function of different internal modifications via using 3D-CFD simulations. The paper is also evaluating the relation between the momentum...
Energies
One of the main advantages of fluidic oscillators is that they do not have moving parts, which br... more One of the main advantages of fluidic oscillators is that they do not have moving parts, which brings high reliability whenever being used in real applications. To use these devices in real applications, it is necessary to evaluate their performance, since each application requires a particular injected fluid momentum and frequency. In this paper, the performance of a given fluidic oscillator is evaluated at different Reynolds numbers via a 3D-computational fluid dynamics (CFD) analysis. The net momentum applied to the incoming jet is compared with the dynamic maximum stagnation pressure in the mixing chamber, to the dynamic output mass flow, to the dynamic feedback channels mass flow, to the pressure acting to both feedback channels outlets, and to the mixing chamber inlet jet oscillation angle. A perfect correlation between these parameters is obtained, therefore indicating the oscillation is triggered by the pressure momentum term applied to the jet at the feedback channels outle...
Journal of Fluids Engineering
The present paper introduces a novel transient experimental method employed to determine the disc... more The present paper introduces a novel transient experimental method employed to determine the discharge coefficient of constant section nozzles of small diameters of 1–3 mm and with a length/diameter ratio of around one. Flow is considered to be real and compressible; the discharge process was analyzed at relatively high pressures, the fluid used was N2. Based on the experimental data, a generalized expression characterizing the discharge coefficient for nozzles of different diameters, lengths, and fluid conditions was developed. In order to check the precision of the analytical equation presented, experimental upstream reservoir pressure decay was compared with the temporal pressure decay obtained using the new analytical equation. Good correlation was achieved for pressure differentials up to 7.6 MPa. Despite the fact that the procedure established can be extended to other gases and nozzle configurations, so far the equation presented to estimate the discharge coefficient, can only...