Flow Control Techniques and Applications

Flow Control Techniques and Applications
Author: Jinjun Wang
Publisher: Cambridge University Press
Total Pages: 293
Release: 2019
Genre: Science
ISBN: 1107161568

Master the theory, applications and control mechanisms of flow control techniques.

Experimental Study on the Use of Synthetic Jet Actuators for Lift Control

Experimental Study on the Use of Synthetic Jet Actuators for Lift Control
Author:
Publisher:
Total Pages: 94
Release: 2014
Genre: Dissertations, Academic
ISBN:

An experimental study on the use of synthetic jet actuators for lift control is conducted. The synthetic jet actuator is placed on the pressure side towards the trailing edge on a NACA 65(2)-415 airfoil representative of the cross section of an Inlet Guide Vane (IGV) in an industrial gas compressor. By redirecting or vectoring the shear layer at the trailing edge, the synthetic jet actuator increases lift and decreases drag on the airfoil without a mechanical device or flap. A compressor map that defines upper and lower bounds on operating velocities and airfoil dimensions, is compared with operating conditions of the low-speed wind tunnel at San Diego State University, to match gas compressor conditions in the wind tunnel. Realistic test conditions can range from Mach=0.12 to Mach= 0.27 and an airfoil chord from c=0.1 m to c=0.3 m. Based on the operating conditions, a final airfoil model is fabricated with a chord of c=0.1m. Several synthetic jet actuator designs are considered. A initial synthetic jet is designed to house a piezoelectric element with a material frequency of 1200 hz in a cavity with a volume of 4.47 cm33 a slot width of 0.25 mm, and a slot depth of 1.5 mm. With these dimensions, the Helmholtz frequency of the design is 1800Hz. Particle Image Velocimetry (PIV) experiments show that the design has a jet with a peak centerline jet velocity of 26 m/s at 750 Hz. A modified slant face synthetic jet is designed so that the cavity fits flush within the NACA airfoil surface. The slanted synthetic jet has a cavity volume of 4.67 cm3, a slot width of 0.25 mm, and a slot depth of 3.45 mm resulting in a Helmholtz frequency of 1170 hz for this design. PIV experiments show that the jet is redirected along the slant face according to the Coanda effect. A final synthetic jet actuator is directly integrated into the trailing edge of an airfoil with a cavity volume of 4.6 cm3, a slot width of 0.2 mm, and a slot depth of 1.6 mm. The Helmholtz frequency is 1450 Hz and matches closely with the piezoelectric element material frequency. The slot is designed so that actuator creates a jet normal to the airfoil surface. A wind tunnel model of the airfoil is 3D-printed with nine actuators integrated along the span of the airfoil. The synthetic jet slots cover 61% of the airfoil's span and the synthetic jet slots are located at a 13% chord upstream of the trailing edge. Tests are performed at multiple free stream velocities ranging from 17 m/s to 54 m/s which is the equivalent of an airfoil Reynolds number of Re=1:5_105 to Re=4:5_105. The integrated synthetic jet actuator increases lift. The increase is dependent on the freestream velocity, the actuation frequency, and angle of attack. For actuation at 1450 hz, and various freestream velocities, the synthetic jet actuator increases the lift by 2% at [lower case alpha]=7° to 7% at[lower case alpha] =15° . The synthetic jet increases L/D by 2% at[lower case alpha]=7° to 15% at [lower case alpha]=15° . Velocity contours obtained through PIV show that the synthetic jet turns the trailing edge shear layer similar to a Gurney flap, which increases lift. The synthetic jet reduces the wake velocity defect through injection of momentum, reducing the drag on the airfoil.

An Experimental Study of Synthetic Jet Actuators with Application in Airfoil LCO Control

An Experimental Study of Synthetic Jet Actuators with Application in Airfoil LCO Control
Author: Sanjay Krishnappa
Publisher:
Total Pages: 194
Release: 2016
Genre: Actuators
ISBN:

An experimental study on the development and implementation of Synthetic Jet Actuators (SJAs) is conducted for eliminating aeroelastic phenomenon such as Limit Cycle Oscillations (LCO). One of the biggest challenges involved in the design of UAVs operating in unsteady atmosphere conditions is the susceptibility of the airframe to aeroelastic instabilities, such as flutter or LCO. Suppression of such instabilities can be achieved through the implementation of Active Flow Control (AFC) techniques, however to this day, a limited amount of experimental studies exist. Thus, the focus of this work is to develop a new AFC method consisting of an actuator that is directly instrumented in the internal volume of the airfoil. Due to the complex geometry of airfoil/actuator integration, advanced manufacturing technique has been employed for rapid manufacturing of these complex parts. In addition, a newly designed experimental test facility is fabricated to study the effect of the developed actuator on aerodynamic performance. Parametric analysis are conducted to investigate the effect of actuator along the airfoil surface, Reynolds number, and angle of attack. Results of this study demonstrated the actuator effectiveness on overall aerodynamic performance and show consistent trends with high-order Computational Fluid Dynamics (CFD).

Synthetic Jets

Synthetic Jets
Author: Kamran Mohseni
Publisher: CRC Press
Total Pages: 378
Release: 2014-09-17
Genre: Science
ISBN: 1439868115

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.

Experimental Design and Analysis of Piezoelectric Synthetic Jets in Quiescent Air

Experimental Design and Analysis of Piezoelectric Synthetic Jets in Quiescent Air
Author: Poorna Popatrao Mane
Publisher:
Total Pages:
Release: 2005
Genre:
ISBN:

Flow control can lead to saving millions of dollars in fuel costs each year by making an aircraft more efficient. Synthetic jets, a device for active flow control, operate by introducing small amounts of energy locally to achieve non-local changes in the flow field with large performance gains. These devices consist of a cavity with an oscillating diaphragm that divides it, into active and passive sides. The active side has a small opening where a jet is formed, whereas and the passive side does not directly participate in the fluidic jet. Research has shown that the synthetic jet behavior is dependent on the diaphragm and the cavity design hence, the focus of this work. The performance of the synthetic jet is studied under various factors related to the diaphragm and the cavity geometry. Four diaphragms, manufactured from piezoelectric composites, were selected for this study, Bimorph, Thunder®, Lipca and RFD. The overall factors considered are the driving signals, voltage, frequency, cavity height, orifice size, and passive cavity pressure. Using the average maximum jet velocity as the response variable, these factors are individually studied for each actuator and statistical analysis tools were used to select the relevant factors in the response variable. For all diaphragms, the driving signal was found to be the most important factor, with the sawtooth signal producing significantly higher velocities than the sine signal. Cavity dimensions also proved to be relevant factors when considering the designing of a synthetic jet actuator. The cavities with the smaller orifice produced lower velocities than those with larger orifices and the cavities with smaller volumes followed the same trend. Although there exist a relationship between cavity height and orifice size, the orifice size appears as the dominant factor. Driving frequency of the diaphragm was the only common factor to all diaphragms studied that was not statistically significant having a small effect on jet velocity. However along with waveform, it had a combined effect on jet velocity for all actuators. With the sawtooth signal, the velocity remained constant after a particular low frequency, thus indicating that the synthetic jet cavity could be saturated and the flow choked. No such saturation point was reached with the sine signal, for the frequencies tested. Passive cavity pressure seemed to have a positive effect on the jet velocity up to a particular pressure characteristic of the diaphragm, beyond which the pressure had an adverse effect. For Thunder® and Lipca, the passive cavity pressure that produced a peak was measured at approximately 20 and 18kPa respectively independent of the waveform utilized. For a Bimorph and RFD, this effect was not observed. Linear models for all actuators with the factors found to be statistically significant were developed. These models should lead to further design improvements of synthetic jets.

Investigation of Synthetic Jets Heat Transfer and Flow Field

Investigation of Synthetic Jets Heat Transfer and Flow Field
Author: Carlo Salvatore Greco
Publisher: Youcanprint
Total Pages: 187
Release: 2015-04-30
Genre: Technology & Engineering
ISBN: 8891187844

Synthetic jets are devices able to “synthetize” a jet from the ambient in which they are embedded through a simple membrane oscillation inside a cavity with an orifice. Such features make them high reliable, silent and easy to be miniaturized. For these reasons, they are widely investigated as electronic cooling devices. The present research is focused on the design and analysis of a different type of synthetic jet device compared to its single classical configuration. Such a device his experimentally characterized through the study of its free and impinging flow field and the evaluation of its heat transfer performance.

Experimental Analysis of a Synthetic Jet Actuator Under Different Configurations

Experimental Analysis of a Synthetic Jet Actuator Under Different Configurations
Author: Juan Sebastian Marin Quintero
Publisher:
Total Pages:
Release: 2017
Genre:
ISBN:

Boundary layer separation has always been an interesting topic to develop and understand, where the synthetic jets present a big potential to reduce the drag coefficients and increase the efficiency in the vehicles. The behavior of the synthetic jets can be varied by changing different aspects in the cavity such as the diameter and length of the neck and also by changing the parameters of the actuator as the frequency and the amplitude. An experimental research is presented which describes the experiments specifications, the different variations in the cavity and in the actuators and also the results according to the configuration used.

Unsteady Aerodynamics of Airfoils and Characterization and Modeling of Axisymmetric Synthetic Jets

Unsteady Aerodynamics of Airfoils and Characterization and Modeling of Axisymmetric Synthetic Jets
Author: Xi Xia
Publisher:
Total Pages: 288
Release: 2018-11-29
Genre: Technology & Engineering
ISBN: 9780530000107

Abstract: This thesis has two main parts. The aerodynamic part is motivated by the interest in unveiling the flying secrets of natural fliers, e.g. birds and insects. The understandings will provide insights in the design and control of micro air vehicles (MAVs) for improved aerodynamic performance. The second part of the thesis focuses on the study of synthetic jets for aerodynamic flow control over MAVs. This is motivated by the promising effects of synthetic jets in enhancing mixing and controlling flow separation. The thesis starts with the unsteady aerodynamic modeling of a flat plate based on the Joukowski transformation and vortex method. The analytical solution includes both translational and rotational motions of the flat plate. The force calculation suggests that the lift generation caused by a stabilized leading edge vortex is a combined effect of the motions of both leading-edge and trailing-edge vortices. To extend this model to an arbitrarily-shaped airfoil, the wall boundary condition on the airfoil is enforced by introducing a bound vortex sheet at the location of the airfoil boundary. Furthermore, an analytical vortex-sheet formation condition is proposed to accurately evolve the wake vortices, and is based on the conservation laws of mass and momentum as well as Kelvin's circulation theorem. This condition resolves the paradox of the Giesing-Maskell model, which does not recover the steady-state Kutta condition. The thesis continues with an investigation of synthetic jets in a quiescent environment. An effective-eddy-viscosity concept is adopted to provide a unified modeling approach for the entrainment and mixing of any round jet, continuous or synthetic. The experimental study is focused on characterizing the spreading and decay features in the transitional region and far field of synthetic jets. The far-field momentum flux of a synthetic jet is modeled by calculating the hydrodynamic impulse of the vortical structure formed in the near field. Synthetic jets issuing into a crossflow are also studied and a self-similar model is developed for the trajectory and velocity of the midplane flow field. It is found that the crossflow velocity is enhanced in the near field due to the induced effect of the tilted vortex rings. This finding provides an auxiliary explanation for the mechanism of a synthetic jet in flow-separation control. Dissertation Discovery Company and University of Florida are dedicated to making scholarly works more discoverable and accessible throughout the world. This dissertation, "Unsteady Aerodynamics of Airfoils and Characterization and Modeling of Axisymmetric Synthetic Jets" by Xi Xia, was obtained from University of Florida and is being sold with permission from the author. A digital copy of this work may also be found in the university's institutional repository, IR@UF. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation.