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 Application of Active Flow Control on Airfoils at Ultralow Reynolds Numbers written by Carlos San Gabriel Romero and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In a previous research Active Flow Control techniques, such as sweeping jets, applied in an ultra-low Reynolds regime (Re=1000) were found effective to reattach an already separated flow achieving lift enhancements but also inducing a large skin-friction drag increase due to the high velocities near the airfoil surface. In this study, firstly the current actuator configurations have been analyzed with the objective of determining the most important factors involved in the increase of the viscous drag. Then, several hypothesis have been done with the aim of reducing this drag penalty while keeping the lift enhancement. The decision taken in this sense has been to apply geometrical modifications to the the actuators using two control parameters, the jet width and the jet angle in which the fluid is injected. Moreover these modifications have been applied to three different actuation types; blowing, suction and synthetic jets. The simulations have been carried in a 2D NACA0012 airfoil in which a remeshing has been done in order to apply the commented modifications. The obtained results show variations depending on in which actuation type are applied. The jet angle modification has obtained interesting results for the blowing jet, since an angle that maximizes the lift coefficient has been found. The jet width has also obtained an optimum value for a specific momentum coefficient, that moreover is suitable for the three actuations. In conclusion, it has been proved that that besides the momentum coefficient and the jet location the geometrical parameters of the actuator have also a considerable impact on the overall efficiency of the actuation.

Download or read book Active Flow Control Concepts for Rotor Airfoils Using Synthetic Jets written by Karthikeyan Duraisamy and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Active Control of Separation on a Low Reynolds Number Airfoil Using Synthetic Jet Actuation written by Mark Feero and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 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 Active Flow Control Over a Naca 0015 Airfoil by Synthetic Jet Actuators written by Pooya Kabiri and published by . This book was released on 2012 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Flow Control of a NACA 0015 Airfoil Using a Chordwise Array of Synthetic Jets written by Kevin Bales and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Active Flow Control of a Two dimensional NACA 0036 Airfoil with Synthetic Jet Excitations written by Jacob Wilson and published by . This book was released on 2005 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: An active flow control experiment was conducted on a 2-ft chord NACA 0036 airfoil at 10 degrees angle of attack in the Cal Poly 3' x 4' wind tunnel.

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 Cambered Jet flapped Airfoil Theory with Tables and Computer Programs for Application written by Henry W. Woolard and published by . This book was released on 1977 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: A quadrature method is derived for calculating the incompressible-flow aerodynamics of arbitrarily cambered jet-flapped airfoils. The anticipated application of the methodology is to high-speed subsonic flows (combat maneuvering aircraft) via the use of compressible-flow similarity transformations. The method yields the aerodynamic properties in terms of integrals having integrands which consist of the product of the camber-line ordinate and an influence function which is a parametric function of the jet-momentum coefficient. In general, the integrals involved must be evaluated by numerical methods. Tables of the necessary influence functions are given in the report.

Download or read book High Fidelity Numerical Modeling and Analysis of Low Reynolds Number Airfoils and Synthetic Jets written by Paul Ziade and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The shear layer development over a NACA 0025 airfoil at a low Reynolds number was investigated experimentally and with large-eddy simulation. Two angles-of-attack (AOA) were considered: 5deg and 12deg. Experiments and numerics confirm two flow regimes. The first regime (AOA=5deg) exhibits boundary layer reattachment with formation of a laminar separation bubble. The second regime consists of boundary layer separation without reattachment. The stability equations exhibit significant sensitivity to base flow variations, making experimental-numerical comparisons challenging. Linear stability analysis suggests that the first regime is characterized by high frequency instabilities with low spatial growth, whereas the second regime experiences low frequency instabilities with more rapid growth. Spectral analysis confirms the dominance of a central frequency, and the importance of nonlinear interactions with harmonics during transition. The sensitivity of the Orr-Sommerfeld equation due to base flow deviations was investigated with a Monte Carlo-type perturbation strategy and a Chebyshev collocation method. A separated boundary layer with a nominal shape factor of H=5.9 was perturbed for both velocity and wall-normal position deviations. Wide bands of eigenvalue spectra were obtained due to both perturbations. The standard deviation of the peak growth rate and frequency was found to be independent of Reynolds number. To broaden the results, six boundary layers were investigated with shape factors H=5.9-22. Perturbations resulting in a standard deviation of 1 % of the nominal shape factor were applied. Sensitivities of the peak growth rate and frequency are more pronounced at lower shape factors. The effect of synthetic jet cavity shape was investigated numerically and experimentally. In the examination of three cavities it was found that the cavity with the sharpest nozzle-to-cavity transition transmits the most momentum at the exit. The sharp transition within the cavity results in a stronger vortex, higher self-induced inward velocity, and more room for flow to exit the cavity during expulsion. It is shown that the shape of the internal cavity plays an important role in the flow behaviour at the nozzle exit. From a computational perspective, the flow field within the cavity must be computed to obtain accurate exit conditions for the synthetic jet.

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 Aerodynamic Flow Control Using Synthetic Jet Technology written by Michael Amitay and published by . This book was released on 1998 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Active Flow Control written by Rudibert King and published by Springer Science & Business Media. This book was released on 2007-08-29 with total page 441 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains contributions presented at the Active Flow Control 2006 conference, held September 2006, at the Technische Universität Berlin, Germany. It contains a well balanced combination of theoretical and experimental state-of-the-art results of Active Flow Control. Coverage combines new developments in actuator technology, sensing, robust and optimal open- and closed-loop control and model reduction for control.

Download or read book Flow Control Simulation with Synthetic and Pulsed Jet Actuator written by Sol Keun Jee and published by . This book was released on 2010 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two active flow control methods are investigated numerically to understand the mechanism by which they control aerodynamics in the presence of severe flow separation on an airfoil. In particular, synthetic jets are applied to separated flows generated by additional surface feature (the actuators) near the trailing edge to obtain Coanda-like effects, and an impulse jet is used to control a stalled flow over an airfoil. A moving-grid scheme is developed, verified and validated to support simulations of external flow over moving bodies. Turbulent flow is modeled using detached eddy simulation (DES) turbulence models in the CFD code CDP (34) developed by Lopez (54). Synthetic jet actuation enhances turbulent mixing in flow separation regions, reduces the size of the separation, deflects stream lines closer to the surface and changes pressure distributions on the surface, all of which lead to bi-directional changes in the aerodynamic lift and moment. The external flow responds to actuation within about one convective time, which is significantly faster than for conventional control surfaces. Simulation of pitching airfoils shows that high-frequency synthetic jet affects the flow independently of the baseline frequencies associated with vortex shedding and airfoil dynamics. These unique features of synthetic jets are studied on a dynamically maneuvering airfoil with a closed-loop control system, which represents the response of the airfoil in wind-tunnel experiments and examines the controller for a rapidly maneuvering free-flight airfoil. An impulse jet, which is applied upstream of a nominal flow separation point, generates vortices that convect downstream, interact with the separating shear layer, dismantle the layer and allow following vortices to propagate along the surface in the separation region. These following vortices delay the separation point reattaching the boundary layer, which returns slowly to its initial stall condition, as observed in wind-tunnel experiments. A simple model of the impulse jet actuator used herein is found to be sufficient to represent the global effects of the jet on the stalled flow because it correctly represents the momentum injected into the flow.

Download or read book Numerical Investigation of Flow Control Over an Airfoil written by Eray AKÇAYÖZ and published by LAP Lambert Academic Publishing. This book was released on 2010-05 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt: The synthetic jet is applied over an airfoil to control the flow separation. Response Surface Methodology is employed for the optimization of synthetic jet parameters at various angles of attack. The synthetic jet parameters; the jet velocity, the jet location, the jet angle and the jet frequency are optimized to maximize the lift to drag ratio. The jet power coefficient is kept constant in the optimization. The lift to drag ratio increased significantly especially at post stall angles of attack.