Download or read book Numerical Study of Active Flow Control Using Synthetic Jets written by Jeremy Dennis Roth and published by . This book was released on 2003 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active Flow Control (AFC) using synthetic jets (SJ's) is numerically simulated for several simple aerodynamic shapes at high Reynolds numbers using the Computational Fluid Dynamics (CFD) computer program, CFL3D. AFC is the manipulation of a flow field around a given body in a fluid. AFC is used to improve the resulting flow characteristics bodies produce in regimes of flow separation which result from large pressure gradients. In the AFC device (SJ's) used in this study fluid is periodically displaced from a cavity with an orifice. A SJ relies on the entertainment of the local ambient fluid mass external to the device. Therefore, with the use of SJ's a significant decrease in complexity and weight is possible as compared to other more traditional AFC devices involving mass transfer. The objective of this study is to illustrate how AFC in the form of SJ's can be utilized to enhance the aerodynamic performance of simple aerodynamic shapes such as a circular cylinder, airfoil, and three-dimensional wing in flow conditions which result in boundary layer separation. A flat plate with zero pressure gradient is also analyzed in order to determine the effect of SJ's in the absence of boundary layer separation. In order to provide a fundamental understanding of the enhanced aerodynamic performance an additional investigation of classical boundary layer parameters is performed. Computational results are then presented for the bodies of interest with no AFC and validated with experimental results where available. Secondly, results for the numerical investigations with AFC are presented. The results of this study demonstrate that SJ's enhance the aerodynamic characteristics of the configurations and provide more favorable conditions in those regimes of the flow that are normally highly separated. The present study also revealed that a three-dimensional flow is quite similar in character to two-dimensional flows in the presence of SJ's. Overall, this study illustrates SJ's are effective in boundary layer control, and can be used to improve the aerodynamics of aerospace vehicles.
Download or read book Numerical Study on Active Flow Control Using Synthetic Jet Actuators Over a NACA 4421 Airfoil written by Xavier Guerrero Pich and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This study is focused on evaluating the effects of using a Zero Net Mass Flux (ZNMF) actuator on a NACA 4421 airfoil for active flow control. First part of the study presents the fundamentals of boundary layer and a study of the available devices which are more used for flow control, focusing on the ZNMF. The steps for creating the mesh to perform numerical simulations of the airfoil are explained, and the results of the CFD simulations are compared with experimental data as a vaseline balidation. In the secord part, the ZNMF is studied in order to set the parameters of the actuator and to simulate its effect on CFD, and moreover the numerical simulations of the airfoil with the ZNMF set up are performed and the results are evaluated. The evaluation will show the most optimum parameters for the actuator, as well as the effects that the ZNMF has on the airfoil's behaviour.
Download or read book Flow Control Techniques and Applications written by Jinjun Wang and published by Cambridge University Press. This book was released on 2019 with total page 293 pages. Available in PDF, EPUB and Kindle. Book excerpt: Master the theory, applications and control mechanisms of flow control techniques.
Download or read book Active Flow Control of Subsonic Flow in an Adverse Pressure Gradient Using Synthetic Jets and Passive Micro Flow Control Devices written by Michael E. Denn and published by . This book was released on 2013 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several recent studies have shown the advantages of active and/or passive flow control devices for boundary layer flow modification. Many current and future proposed air vehicles have very short or offset diffusers in order to save vehicle weight and create more optimal vehicle/engine integration. Such short coupled diffusers generally result in boundary layer separation and loss of pressure recovery which reduces engine performance and in some cases may cause engine stall. Deployment of flow control devices can alleviate this problem to a large extent; however, almost all active flow control devices have some energy penalty associated with their inclusion. One potential low penalty approach for enhancing the diffuser performance is to combine the passive flow control elements such as micro-ramps with active flow control devices such as synthetic jets to achieve higher control authority. The goal of this dissertation is twofold. The first objective is to assess the ability of CFD with URANS turbulence models to accurately capture the effects of the synthetic jets and micro-ramps on boundary layer flow. This is accomplished by performing numerical simulations replicating several experimental test cases conducted at Georgia Institute of Technology under the NASA funded Inlet Flow Control and Prediction Technologies Program, and comparing the simulation results with experimental data. The second objective is to run an expanded CFD matrix of numerical simulations by varying various geometric and other flow control parameters of micro-ramps and synthetic jets to determine how passive and active control devices interact with each other in increasing and/or decreasing the control authority and determine their influence on modification of boundary layer flow. The boundary layer shape factor is used as a figure of merit for determining the boundary layer flow quality/modification and its tendency towards separation. It is found by a large number of numerical experiments and the analysis of simulation data that a flow control device's influence on boundary layer quality is a function of three factors: (1) the strength of the longitudinal vortex emanating from the flow control device or devices, (2) the height of the vortex core above the surface and, when a synthetic jet is present, (3) the momentum added to the boundary layer flow.
Download or read book Synthetic Jets written by Kamran Mohseni and published by CRC Press. This book was released on 2014-09-17 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: Compiles Information from a Multitude of SourcesSynthetic jets have been used in numerous applications, and are part of an emergent field. Accumulating information from hundreds of journal articles and conference papers, Synthetic Jets: Fundamentals and Applications brings together in one book the fundamentals and applications of fluidic actuators.
Download or read book Numerical Simulation of Synthetic Jets written by Alejandra Lorenzo Mora and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Synthetic jet actuators (SJA) or zero-net mass flux (ZNMF) actuators are devices consisting of a cavity with a small orifice or slot, inside of which is a moving oscillator. Thecavity is connected to the external medium by means of a neck. The oscillator drivercan be a diaphragm, whose periodic movement makes the fluid leave and enter the cav-ity. When the flow exits from the neck a train of vortices is formed, to be able to obtainthe jet, these vortices cannot be swallowed back into the cavity when the membrane is moving down. To ensure that this is not happening the parameter jet formation criteria(JFC) is defined. The JFC only depends on geometrical parameters as the longitudeand the amplitude of the membrane, when the movement of the membrane is periodic.When the jet is successfully formed, it is able to transfer kinetic energy and momentumto the fluid without a mass addition. Several potential applications of this technologyexist, e.g, active flow control (AFC), cooling and fuel mixing.The present work solves a SJA impinged into a hot wall. The case at low Reynolds(Re= 50) is considered to be laminar and incompressible. Four different neck longitudes are compared to see which is the importance of the neck length. The strategy to solve these cases is running three meshes with different densities. The simulationwith the less dense mesh can run more cycles spending less computational time, theresults of this mesh are the inputs of the denser mesh. The case is configured usingmoving mesh techniques for the actuator membrane. In this situation, the decouplingof velocity and frequency is no longer possible and other strategies need to be applied.Velocity and temperature are found to reach a steady state after about 50 actuatorcycles, however, the Nusselt number features a low frequency that makes the whole case longer to converge. It is estimated that a number of around 200 actuator cyclesare needed for the Nusselt number to reach the steady state. This fact complicates theflow, despite the fact that the Reynolds number is low. The effect of changing the necklength has a direct effect on the velocity but has little influence on the temperature orthe Nusselt number.
Download or read book Numerical Studies of the Application of Active Flow Control to Subsonic and Transonic Airfoil Flows Using a Synthetic Jet Actuator written by Jose L. Vadillo and published by . This book was released on 2005 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Active Flow Control on Cambered Airfoils at Ultralow Reynolds Using Synthetic Jets written by Pau Valdepeñas Pujol and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Active flow control methods have been widely studied for more than a decade in order to improve the airfoil's efficiency. This study is focused on fluidic actuation (the addition or subtraction of momentum to/from the boundary layer by blowing and/or sucking fluid). A synthetic jet is a very particular type of fluidic actuation that involves periodic blowing and suction with zero-net-mass-flow over a the full period. Its success as an active flow control device has been extensively reported by several authors. As it can be seen synthetic jet technology provides good results on boundary layer reattachment and therefore, an improvement on the airfoil's efficiency. What is more, is a generic system that can be widespread on multiple types of airfoils such as unmanned aerial vehicles and conventional airplanes airfoils. The effectiveness of control in mitigating boundary separation depends on a number of parameters related both to the flow itself and the control input such as: frequency and amplitude of the excitation, the excitation shape, exit diameter and cavity shape. Since the synthetic jet system has several degrees of freedom and the flux is unpredictable, multiple simulations have to be done in order to assess the best configuration to achieve the maximum airfoil's efficiency. The well-known excitation of the synthetic jet is the zero-net-mass-flow that combines both expulsion and suction periodically. In this study, we also evaluate other types of excitations that imply more or less energy into the system that is characterized with the momentum coefficient. The goal is to assess thoroughly this existent trade-off between the aerodynamics performance and the momentum coefficient. And finally, extract deep conclusions and assess the best synthetic jet configuration where the aerodynamics performances are improved with a low momentum coefficient.. To extract suitably conclusions we pass through a thorough and intricate process that starts with the adapted and generic discretized surface for the synthetic jet that we use to solve the Navier-Stokes equations, then the appropriate conversions to simulate with spectral element framework Nektar++ and finally the detailed extraction of results. Moreover, we adopt to this study a practical approach with an unmanned aerial vehicle (UAV Skywalker x6) airfoil's photogrammetry that we use to simulate.
Download or read book Time Accurate Simulations of Synthetic Jet Based Flow Control for An Axisymmetric Spinning Body written by and published by . This book was released on 2004 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes a computational study undertaken to consider the aerodynamic effect of synthetic jets as a means of providing the control authority needed to maneuver a projectile at a low subsonic speed. A time-accurate Navier-Stokes computational technique has been used to obtain numerical solutions for the unsteady jet-interaction flow field for a spinning projectile at a subsonic speed, Mach 0.24, and angle of attack, 0 degree. Numerical solutions have been obtained by Reynolds-averaged Navier-Stokes (RANS) and hybrid RANS-large-eddy simulation turbulence models. Unsteady numerical results show the effect of the jet on the flow field and the aerodynamic coefficients, particularly the lift force. These numerical results are being used to assess if synthetic jets can be used to provide the control authority needed for maneuvering munitions to hit the targets with precision.
Download or read book Study of the Boundary Layer Flow Control Using Synthetic Jets by Means of Spectro consistent Discretizations written by David Duran Perez and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This report presents a study of the interaction of AFC (specifically, synthetic jets) with the laminar boundary layer of a NACA 0012 airfoil. First of all, in order to understand the phenomenology of Navier-Stokes equations, a spectro-consistent Computational Fluid Dynamics (CFD) code has been developed from scratch. By using a spectro-consistent discretization, the fundamental symmetry properties of the underlying differential operators are preserved. This code also helps to understand how the energy is transported from big to small scales. After solving a paradigmatic problem (TGV) using the aforementioned code, a mature CFD code (Alya) is used to simulate the flow around the NACA 0012 airfoil. Alya software also uses a spectro-consistent code but in Finite Element Method (FEM). Once the reference cases are solved for different angles of attack, a boundary condition representing an idealized synthetic jet is implemented. A systematic parametrization of the synthetic jet has been performed in order to assess the level of flow control in the boundary layer. Results demonstrate that, by selecting a correct combination of actuator frequency and momentum coefficient, the lift coefficient increases while the drag coefficient decreases producing a better lift-to-drag ratio. This aerodynamic improvement implies that a better circulation control is achieved, less noise is produced and less fuel consumption is required. It is also worth noting that, for high angles of attack, it is necessary to perform 3D flow simulations in order to capture the entire physics of the problem.
Download or read book Study written by Carlos Martínez Segarra and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A synthetic jet is formed by the oscillating movement of a membrane located inside a cavity. Such movement allows ambient fluid to be dragged inside and outside, hence producing a jet that is able to transfer both linear momentum and kinetic energy into the system without any external mass flux. It offers multiple interesting applications, the most relevant being active flow control and thermal control of electronic devices. This work focuses on the study of a discharge of a slotted synthetic jet actuator into an opened external medium. Numerical simulations using Large Eddy Simulations have been performed to analyze the jet behavior and vortex dynamics. Three mesh densities and two different cases based on the SJA governing parameters have been evaluated during the analysis. This study reveals that the advected vortex pair reaches a higher altitude before becoming the jet as the jet formation criteria becomes greater. This causes a bigger gradient on turbulent kinetic energy at higher altitudes which is closely related to the distance from the actuator orifice in which the vortex pair starts coalescing into the jet. Vortex penetration also increases with the jet formation criteria as such parameter is directly related to the actuator membrane deflection. A bigger jet formation criteria allows the membrane to deflect more, hence more fluid is dragged downstream resulting in the increase of the linear momentum contribution to the system. Such phenomenon straightaway affects the jet half-width which also increases with the jet formation criteria. This study also reveals that both cases share the same potential core which suggests that the ingestion and expulsion dynamics of a synthetic jet are independent of the jet formation criteria.
Download or read book Computational Study of a NACA4415 Airfoil Using Synthetic Jet Control written by Omar Dario Lopez Mejia and published by . This book was released on 2009 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt: Synthetic jet actuators for flow control applications have been an active topic of experimental research since the 90's. Numerical simulations have become an important complement of that experimental work, providing detailed information of the dynamics of the controlled flow. This study is part of the AVOCET (Adaptive VOrticity Control Enabled flighT) project and is intended to provide computational support for the design and evaluation of closed-loop flow control with synthetic jet actuators for small scale Unmanned Aerial Vehicles (UAVs). The main objective is to analyze active flow control of a NACA4415 airfoil with tangential synthetic jets via computational modeling. A hybrid Reynolds-Averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) turbulent model (called Delayed Detached-Eddy Simulation-DDES) was implemented in CDP, a kinetic energy conserving Computational Fluid Dynamics (CFD) code. CDP is a parallel unstructured grid incompressible flow solver, developed at the Center for Integrated Turbulence Simulations (CITS) at Stanford University. Two models of synthetic jet actuators have been developed and validated. The first is a detailed model in which the flow in and out of the actuator cavity is modeled. A second less costly model (RSSJ) was also developed in which the Reynolds stress produced by the actuator is modeled, based on information from the detailed model. Several static validation test cases at different angle of attack with modified NACA 4415 and Dragon Eye airfoils were performed. Numerical results show the effects of the actuators on the vortical structure of the flow, as well as on the aerodynamic properties. The main effect of the actuation on the time averaged vorticity field is a bending of the separation shear layer from the actuator toward the airfoil surface, resulting in changes in the aerodynamic properties. Full actuation of the suction side actuator reduces the pitching moment and increases the lift force, while the pressure side actuator increases the pitching moment and reduces the lift force. These observations are in agreement with experimental results. The effectiveness of the actuator is measured by the change in the aerodynamic properties of the airfoil in particular the lift ([Delta]C[subscript t]) and moment ([Delta]C[subscript m]) coefficients. Computational results for the actuator effectiveness show very good agreement with the experimental values (over the range of -2° to 10°). While the actuation modifies the global pressure distribution, the most pronounced effects are near the trailing edge in which a spike in the pressure coefficient (C[subscript p]) is observed. The local reduction of C[subscript p], for both the suction side and pressure side actuators, at x/c = 0.96 (the position of the actuators) is about 0.9 with respect to the unactuated case. This local reduction of the pressure is associated with the trapped vorticity and flow acceleration close to the trailing edge. The RSSJ model is designed to capture the synthetic jet time averaged behavior so that the high actuation frequencies are eliminated. This allows the time step to be increased by a factor of 5. This ad hoc model is also tested in dynamic simulations, in which its capacity to capture the detail model average performance was demonstrated. Finally, the RSSJ model was extended to a different airfoil profile (Dragon Eye) with good results.
Download or read book The Isolated Synthetic Jet in Crossflow written by Norman W. Schaeffler and published by BiblioGov. This book was released on 2013-08 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: An overview of the data acquisition, reduction, and uncertainty of experimental measurements made of the flowfield created by the interaction of an isolated synthetic jet and a turbulent boundary layer is presented. The experimental measurements were undertaken to serve as the second of three computational fluid dynamics validation databases for Active Flow Control. The validation databases were presented at the NASA Langley Research Center Workshop on CFD Validation of Synthetic Jets and Turbulent Separation Control in March, 2004. Detailed measurements were made to document the boundary conditions for the flow and also for the phase-averaged flowfield itself. Three component Laser-Doppler Velocimetry, 2-D Particle Image Velocimetry, and Stereo Particle Image Velocimetry were utilized to document the phase-averaged velocity field and the turbulent stresses.
Download or read book Flow and Heat Transfer of Impinging Synthetic Jets written by Arnau Miró Jané and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Synthetic jets are produced by the oscillatory movement of a membrane inside a cavity, causing fluid to enter and leave through a small orifice. This results in a net jet that is able to transfer kinetic energy and momentum to a fluid medium without the need of an external fluid source. This is why synthetic jets are interesting and will have key roles in a wide range of relevant applications such as active flow control, thermal cooling or fuel mixing. From the phenomenological point of view, synthetic jets are formed by elaborate flow patterns given their non-linear nature and, under certain conditions, unstable complex flows can be observed. The present dissertation is focused on the investigation of the fluid flow and thermal performance of synthetic jets. Two different synthetic jet actuator geometries (i.e., slotted and circular) are studied. The jets in both configurations are confined by two parallel isothermal plates with an imposed temperature difference, and impinge into a heated plate located at a certain distance from the actuator orifice. The unsteady three-dimensional Navier-Stokes equations are solved for a range of Reynolds numbers using time-accurate numerical simulations. Moreover, a detailed model of the actuator that uses Arbitrary Lagrangian-Eulerian (ALE) formulation to account for the movement of the actuator membrane is developed. This model, based on the governing numbers of the flow, is used to conduct the numerical analyses. The flows obtained in both configurations are noticeably different and three-dimensional for almost all the Reynolds numbers considered. The jet in the slotted configuration is formed by a pair of vortices that undergo turbulent transition and eventually coalesce into the jet. The external flow is dominated by two major recirculation structures that find their counterparts inside the actuator cavity. A new vortical structure, observed in confined slotted jets, appears as an interaction of the synthetic jet flow with the bottom wall and results in a change on the jet's heat transfer mechanisms. On the other hand, the jet in the circular configuration presents three different flow regions that have been identified according to the literature: the main vortex ring, the trailing jet and the potential core. In this case, the external flow is dominated by the main vortex ring and the trailing jet, thus presenting a different morphology and heat transfer behavior than the slotted configuration. A detailed analysis of the vortex trajectories has shown that the advected vortices on the circular configuration reach the impingement before their slotted counterparts. Distributions of turbulent kinetic energy at the expulsion and vortex swirl and shear strength have revealed that the flow on the circular jet is mostly concentrated near the jet centerline, while it is more spread for the slotted configuration. For these reasons, at the same jet ejection velocity and actuator geometry, synthetic jet formation on the circular configuration can occur at higher frequencies than on the slotted configuration. The analysis of the synthetic jet outlet temperature has shown that assuming a uniform profile is reasonable if the Reynolds number is high enough. Moreover, the outlet jet temperature is significantly higher than the cold plate temperature. The two configurations present different impinging behaviors due to the differences on the flow. Heat transfer analysis on the hot wall has revealed that the circular configuration reaches a higher heat transfer peak than the slotted configuration, however, heat transfer decays faster in the circular configuration when moving away from the jet centerline. Eventually, correlations for the heat transfer at the hot wall and the outlet temperature with the Reynolds number are proposed. They can be useful to include the cavity effects when using simplified models that do not account for actuator cavity.
Download or read book Large eddy Simulation and Active Flow Control of Low reynolds Number Flow Through a Low pressure Turbine Cascade written by Shirdish Poondru and published by . This book was released on 2008 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: Separation control of the LPT flow was implemented using synthetic normal jets, synthetic vortex-generator jets, and pulsed vortex-generator jets (VGJs) at Re ~ 10,000, for four blowing ratios ranging from 0.5 to 4.7, where the blowing ratio is defined as the ratio of the jet-exit velocity magnitude to the local free-stream velocity. All the jets were implemented by specifying an analytical boundary condition at the jet exit surface. The effectiveness of the jets was assessed in terms of the integrated wake loss coefficient values, and the modified Zweifel coefficient values. The Zweifel coefficient represents the component of the integrated blade Cp distribution contributing to the direction of rotation. Among the three types of control jets implemented, the synthetic normal jets were found to be more effective than the synthetic or pulsed VGJs. For pulsed VGJs, the effective blowing ratio was found to be 2.0 in the present study, compared to the value of 0.4 documented in the literature for control at a Re = 25,000, indicating a strong dependence of the effective blowing ratio on Re. The study also examined the flow control mechanisms of the synthetic normal jets and vortex-generator jets. It was found that the mechanism for effectiveness of synthetic jets was a combination of instability-triggered transition and free-stream momentum entrainment. Finally, the synthetic jets and synthetic VGJs were found to be more effective when the jets were located just upstream of the natural separation point.
Download or read book Active Control of Flow Separation Over an Airfoil written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-09-25 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: Designing an aircraft without conventional control surfaces is of interest to aerospace community. In this direction, smart actuator devices such as synthetic jets have been proposed to provide aircraft maneuverability instead of control surfaces. In this article, a numerical study is performed to investigate the effects of unsteady suction and blowing on airfoils. The unsteady suction and blowing is introduced at the leading edge of the airfoil in the form of tangential jet. Numerical solutions are obtained using Reynolds-Averaged viscous compressible Navier-Stokes equations. Unsteady suction and blowing is investigated as a means of separation control to obtain lift on airfoils. The effect of blowing coefficients on lift and drag is investigated. The numerical simulations are compared with experiments from the Tel-Aviv University (TAU). These results indicate that unsteady suction and blowing can be used as a means of separation control to generate lift on airfoils. Ravindran, S. S. Langley Research Center NASA/TM-1999-209838, NAS 1.15:209838, L-17932
Download or read book Time Accurate Aerodynamic Modeling of Synthetic Jets for Flow Control written by and published by . This book was released on 2003 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper describes a computational study undertaken to determine the aerodynamic effect of tiny unsteady synthetic jets as a means to provide the control authority needed to maneuver a spinning projectile at low subsonic speeds. Advanced Navier-Stokes computational techniques have been developed and used to obtain numerical solutions for the unsteady jet-interaction flow field at subsonic speeds and small angles of attack. Unsteady numerical results show the effect of the jet on the flow field and on the aerodynamic coefficients. The unsteady jet is shown to substantially alter the flow field both near the jet and the base region of the projectile that in turn affects the forces and moments even at zero degree angle of attack. The results have shown the potential of computational fluid dynamics to provide insight into the jet interaction flow fields and provided guidance as to the locations and sizes of the jets to generate the maximum control authority to maneuver a projectile to hit its target with precision.
