Formation, evolution and scaling of plasma synthetic jets

2017 ◽  
Vol 837 ◽  
pp. 147-181 ◽  
Author(s):  
Haohua Zong ◽  
Marios Kotsonis
Keyword(s):  
Vortex Ring ◽  
Propagation Velocity ◽  
High Speed ◽  
Energy Deposition ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Actuation Frequency ◽  
Jet Velocity ◽  
Deposition Energy ◽  
Steady Jets

Plasma synthetic jet actuators (PSJAs), capable of producing high-velocity pulsed jets at high frequency, are well suited for high-Reynolds-number subsonic and supersonic flow control. The effects of energy deposition and actuation frequency on the formation and evolution characteristics of plasma synthetic jets (PSJs) are investigated in detail by high-speed phase-locked particle imaging velocimetry (PIV). Increasing jet intensity with energy deposition is mainly contributed by the increasing peak jet velocity ($U_{p}$), while decreasing jet intensity with actuation frequency is attributed to both the reduced cavity density (primary factor) and the shortened jet duration (secondary factor). The total energy efficiency of the considered PSJA ($O(0.01\,\%)$) reduces monotonically with increasing frequency, while the time-averaged thrust produced by the PSJA is positively proportional to both the deposition energy and the frequency. A simplified theoretical model is derived and reveals a scaling power law between the peak jet velocity and the non-dimensional deposition energy (exponent$1/3$). The propagation velocity of the vortex ring attached at the jet front shows a non-monotonic behaviour of initial sharp increase and subsequent mild decay. The peak values for both the propagation velocity and the circulation of the front vortex ring are reached approximately two exit diameters away from the exit. Finally, analysis of the time-averaged flow fields of the issuing PSJ indicates that the axial decay rate of the centreline velocity is proportional to the actuation frequency whereas it is invariant with the energy deposition. The jet spreading rate of the PSJ is found to be higher than steady jets but lower than piezoelectric synthetic jets. Similarly, the entrainment coefficients of the PSJ are found to be twice as high as the values for comparable steady jets.

scholarly journals The mechanism of vortex bifurcation vis-à-vis axial switching in rectangular synthetic jets

2020 ◽  
Author(s):  
Abhay Kumar ◽  
Arun K Saha ◽  
Pradipta K Panigrahi ◽  
Ashish Karn
Keyword(s):  
Vortex Ring ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Operational Parameters ◽  
Actuation Frequency ◽  
Flow Physics ◽  
Forward Stroke ◽  
Narrow Region ◽  
Switching Regime ◽  
Wide Range

The present study investigates the vortex dynamics of the rectangular shaped synthetic jet and reports the occurrence of vortex ring bifurcation along with other reported modes such as axial switching and the vortex suction. The novel finding of vortex ring bifurcation of rectangular synthetic jets has been observed without any other mode of excitation except the periodic axial actuation. The experiments on synthetic jets have been conducted at different actuation frequencies and both qualitative and quantitative characterization of the flow structures has been carried out using Laser Induced Fluorescence (LIF) and Laser Doppler Velocimetry, respectively. LIF flow visualization provides insights into the size of the vortex and the vortex evolution with respect to time, enabling us to propose the flow physics behind the axial switching and the vortex bifurcation processes for rectangular synthetic jets. The proposed flow physics is then quantitatively evidenced by the time-averaged velocity measurements. Vortex splitting or bifurcation is found to occur in the minor axis plane of orifice and the divergence angle depends on the actuation frequency and average velocity of fluid expelled through the orifice in the forward stroke of diaphragm. In the case of occurrence of axial switching, a maximum of three axial switching events are observed before vortex breakup. Finally, by systematically carrying out experiments across a wide range of operational parameters, a narrow region corresponding to the vortex bifurcation has been identified on a Reynolds Number-Strouhal Number map, along with other modes such as axial switching regime and the vortex suction regime. Based on our measurements, a mechanism of vortex bifurcation vis-à-vis axial switching has also been suggested.

Analytical and Experimental Investigation of Different Synthetic Jet Actuator Configurations

Aerospace ◽  
2004 ◽  
Author(s):  
Sandra Ugrina ◽  
Alison Flatau
Keyword(s):  
Resonant Frequency ◽  
Smart Materials ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Laser Vibrometer ◽  
Synthetic Jet Actuator ◽  
Exit Nozzle ◽  
Geometry Configuration ◽  
Jet Velocity ◽  
Constant Temperature Anemometer

The ultimate goal of this project is to actively control the flow over a micro air vehicle using smart materials. MAVs are a new type of aircraft operating at Reynolds numbers of about 50,000 that are one to two orders of magnitude lower than encountered in larger aircraft. The intention is to implement smart structures and couple them with fluids to improve the deteriorated aerodynamics of MAVs and help improve efficiency, stability and maneuverability of such vehicles. The actuators used in this work for artificially controlling the boundary layer are piezoelectrically driven synthetic jets. We theoretically investigated and predicted the behavior of the synthetic jet as we changed the geometry and material property parameters of the actuator. Analytical results were then compared to the results obtained from the experiments. It is crucial to be able to accurately design a strong unimorph to be implemented as an active component of a synthetic jet actuator and design the geometry configuration of the cavity that will best couple with the chosen membrane. A condenser microphone, a constant temperature anemometer (CTA) and a laser vibrometer were used to quantify actuator performance. It was observed that the size of the cavity and the size and shape of the exit nozzle were related and the performance of the actuator increased when the structure was tuned such that the resonant frequency of the diaphragm and that of the cavity were close to matching. A square unimorph made of PZT-5H and bonded to a 0.20- mm brass shim maximized jet velocity for the actuators studied. Optimum direction of change in the volume and the dimensions of the nozzle will strongly depend on the resonant frequency of the membrane in use. In this situation, increasing either the volume of the cavity or the thickness of the nozzle made the two frequencies move away from each other producing reduction in jet velocity. Increasing the area of the nozzle, made the structure behave more as needed and was taken as a key parameter for tuning the base geometry of the device.

Active Flow Control on a Highly Loaded Compressor Stator Cascade With Synthetic Jets

2016 ◽  
Author(s):  
Yong Qin ◽  
Ruoyu Wang ◽  
Yanping Song ◽  
Fu Chen ◽  
Huaping Liu
Keyword(s):  
Flow Separation ◽  
Coupling Effect ◽  
Active Flow Control ◽  
Pressure Rise ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Main Flow ◽  
Control Effect ◽  
Actuation Frequency ◽  
Highly Loaded

Numerical investigations on the control effects of synthetic jets are conducted upon a highly loaded compressor stator cascade. The influence of forcing parameters including actuation frequency, jet amplitude and slot location are analyzed in detail with the single-slit synthetic jet. Besides, a new slot arrangement is put forward for the purpose of effectively controlling flow separation. Simulation results validate the remarkable effectiveness of the single-slit synthetic jet on controlling flow separation. Owing to the coupling effect between the jet and the main flow, the actuation appears to be most efficient under the characteristic frequency of the main flow passing through the airfoil. Additionally, with the increase of jet momentum coefficient, the control effect is enhanced at first and then decreased, depending on the two aspects: the improvements of aerodynamic performance by momentum injection and the additional flow losses caused by the jet. Compared to other actuator configurations, the segment synthetic jet with three sections can more effectively deflect the end-wall cross flow and thus impede the development of corner vortex, which helps to restrain the accumulation of low momentum fluid towards the corner, emphasizing the importance of slot arrangement. Accordingly, under the optimum condition, the total pressure loss coefficient gains a 15.8% reductions and the static pressure rise coefficient is increased by 5.01%.

Examination of a Variable-Diameter Synthetic Jet

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Spencer O. Albright ◽  
Stephen A. Solovitz
Keyword(s):  
Particle Image Velocimetry ◽  
Vortex Ring ◽  
Mass Flux ◽  
Particle Image ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Variable Diameter ◽  
Constant Diameter ◽  
Image Velocimetry ◽  
Jet Actuators

Synthetic jet actuators are used to produce net axial momentum flow without net mass flux. Through strategic application, such devices can be used for flow control, propulsive thrust, and cooling. A novel application uses a variable-diameter orifice to constrict the exiting flow, and the motion can be synchronized with the pulse of the jet. This device is examined using phase-locked particle image velocimetry (PIV), permitting investigation of the flow fields and momentum flow. When compared to fixed-diameter synthetic jets, the variable-diameter actuator produces a larger vortex ring that lingers nearer the aperture. In addition, the experiments show increased momentum when the aperture is contracted in phase with the pulsing jet, with peak levels more than twice that of a constant-diameter jet.

Pressure Loading of Piezo Composite Unimorphs

2005 ◽  
Vol 888 ◽  
Author(s):  
Poorna Mane ◽  
Karla Mossi ◽  
Robert Bryant
Keyword(s):  
Active Flow Control ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Synthetic Jet Actuator ◽  
Active Pressure ◽  
Average Maximum ◽  
Non Local ◽  
Jet Velocity ◽  
Active Flow ◽  
Jet Velocities

ABSTRACTOver the past decade synthetic jets have emerged as a promising means of active flow control. They have the ability to introduce small amounts of energy locally to achieve non-local changes in the flow field. These devices have the potential of saving millions of dollars by increasing the efficiency and simplifying fluid related systems. A synthetic jet actuator consists of a cavity with an oscillating diaphragm. As the diaphragm oscillates, jets are formed through an orifice in the cavity. This paper focuses on piezoelectric synthetic jets formed using two types of active diaphragms, Thunder® and Lipca. Thunder® is composed of three layers; two metal layers, with a PZT-5A layer in between, bonded with a polyimide adhesive. Lipca is a Light WeIght Piezo Composite Actuator, formed of a number of carbon fiber prepreg layers and an active PZT-5A layer. As these diaphragms oscillate, pressure differences within the cavity as well as average maximum jet velocities are measured. These parameters are measured under load and no-load conditions by controlling pressure at the back of the actuator or the passive cavity. Results show that the average maximum jet velocities measured at the exit of the active cavity, follow a similar trend to the active pressures for both devices. Active pressure and jet velocity increase with passive pressure to a maximum, and then decrease. Active pressure and the jet velocity peaked at the same passive cavity pressure of 18kPa for both diaphragms indicating that the same level of pre-stresses is present in both actuators even though Lipca produces approximately 10% higher velocities than Thunder®.

scholarly journals Heat Transfer Behaviour and Flow Field Characterisation of Impinging Synthetic Jets for a Wide Range of Parameters

2010 ◽  
Author(s):  
Rayhaan Farrelly ◽  
Alan McGuinn ◽  
Tim Persoons ◽  
Darina Murray
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
High Speed ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Local Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Flow Measurements ◽  
Wide Range

Impinging synthetic jets are considered as a potential solution for convective cooling, in applications that match their main characteristics (high local heat transfer rates, zero net mass flux, scalability, active control). Nevertheless the understanding of heat transfer to synthetic jets falls short of that available for steady jets. To address this, this paper uses detailed flow field measurements to help identify the main heat transfer mechanisms in impinging synthetic jets. Local heat transfer measurements have been performed for an impinging round synthetic jet at a range of Reynolds numbers between 1000 and 3000, nozzle to plate spacings between 4D and 16D and stroke lengths (L0) between 2D and 32D. The heat transfer results show evidence of distinct regimes in terms of L0/D and L0/H ratios. Based on appropriate scaling, four heat transfer regimes are identified which justifies a detailed study of the flow field characteristics. High speed particle image velocimetry (PIV) has been employed to measure the time-resolved velocity flow fields of the synthetic jet to identify the flow structures at selected L0/H values corresponding to the identified heat transfer regimes. The flow measurements support the same regimes as identified from the heat transfer measurements and provide physical insight for the heat transfer behaviour.

Active flow control by means of endwall synthetic jet on a high-speed compressor stator cascade

2017 ◽  
Vol 232 (6) ◽  
pp. 641-659
Author(s):  
Yong Qin ◽  
Yanping Song ◽  
Fu Chen ◽  
Ruoyu Wang ◽  
Huaping Liu
Keyword(s):  
Flow Control ◽  
Pressure Loss ◽  
Total Pressure ◽  
High Speed ◽  
Pressure Rise ◽  
Synthetic Jet ◽  
Total Pressure Loss ◽  
Momentum Exchange ◽  
Actuation Frequency ◽  
Flow Mixing

The underlying physics of the endwall synthetic jet in improving the aerodynamic performance of a high-speed compressor stator cascade is investigated in this paper. The effects of both injected momentum and actuation frequency are discussed in detail. In the investigations, the injected momentum is controlled by either changing the maximum jet velocity or modifying the tube diameter. Numerical results demonstrate that the streamwise momentum addition and flow mixing enhancement are the key factors of the endwall synthetic jet in improving the cascade performance. The high momentum fluid injected into the flow field can reenergize the passage flow, and the generated streamwise jet vortex contributes to the strengthening of flow mixing. Consequently, the momentum exchange between the low momentum fluid region and the main flow is enhanced and boundary layer separation on the blade suction surface is delayed. The loss characteristic in the corner region is improved as well. The intensified flow mixing will also increase the total pressure loss in the near-endwall region, which as a result will worsen the cascade performance, and hence the total effect of the endwall synthetic jet depends on the sum of its impacts. Moreover, the injected momentum and the actuation frequency have strong influences on the flow control effect. With the momentum coefficient and the reduced frequency being Cµ = 0.131% and F+ = 1.0, the reduction in total pressure loss coefficient and the increment in pressure rise coefficient are 7.3% and 3.3%, respectively.

Evolution of elliptic synthetic jets at low Reynolds number

2019 ◽  
Vol 868 ◽  
pp. 66-96 ◽  
Author(s):  
Xu-Dong Shi ◽  
Li-Hao Feng ◽  
Jin-Jun Wang
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Vortex Ring ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Stereoscopic Particle Image Velocimetry ◽  
Entrainment Rate ◽  
Streamwise Vortices ◽  
Primary Vortex ◽  
Stroke Length

The influence of the nozzle aspect ratio ($AR=1$, 2 and 4), stroke length ($L_{0}=1.85$, 3.7 and 5.55) and Reynolds number ($Re=79$, 158, 316 and 632) on the behaviour of elliptic synthetic jets is studied experimentally. Laser-induced fluorescence and two-dimensional and stereoscopic particle image velocimetry are used to analyse the vortex dynamics and evolution mechanism. It is found that the fluid elements around the major axis of an elliptic vortex ring move downstream faster and tend to approach the centreline, while the fluid elements around the minor axis move downstream at a slower speed and away from the centreline, thereby resulting in the occurrence of the well-known axis-switching phenomenon for elliptic synthetic jets. During this process, a pair of arc-like vortices forms ahead of the primary vortex ring, and they are constituted by streamwise vortices in the leg part and spanwise vortices in the head part; two pairs of streamwise vortices form from the inside of the primary vortex ring and develop in the tails. The streamwise vortices are pushed away progressively from the centreline by the synthetic jet vortex rings that are formed during the subsequent periods. These additional vortical structures for non-circular synthetic jets show regular and periodic characteristics, which are quite different from the previous findings for non-circular jets. Their mutual interaction with the vortex ring causes significant changes in the topology of elliptic synthetic jets, which further results in the variation of the statistical characteristics. Increasing the aspect ratio, stroke length and Reynolds number will make the evolution of the synthetic jet become more unstable and complex. In addition, the entrainment rate of an elliptical synthetic jet is larger than that of a circular synthetic jet and it increases with the nozzle aspect ratio ($AR\leqslant 4$) and Reynolds number. It is indicated that the formation of streamwise vortices could enhance the entrainment rate. This finding provides substantial evidence for the potential application of elliptic synthetic jets for effective flow control.

Characterization and Thrust Optimization of Synthetic Jets

2006 ◽  
Author(s):  
Yury Loayza ◽  
Kamran Mohseni
Keyword(s):  
Velocity Field ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Voltage Response ◽  
Zero Mass ◽  
Formation Number ◽  
Temporal And Spatial ◽  
Jet Velocity ◽  
Velocity Changes ◽  
Hotwire Anemometry

A synthetic jet is a zero-mass pulsatile jet. A common approach in creating a synthetic jet is to use a cavity with an orifice on one side and an oscillating membrane on another side. In this study the dynamics of a piezoelectrically driven synthetic jet is investigated using a laser nano sensor to capture the temporal and spatial deflection of the membrane. The frequency and voltage response of the piezoelectric membrane for different cavity dimensions are presented, while the velocity field of the resulted jet is characterized by hotwire anemometry. Subsequently, the volume of the expelled jet for any given exit diameter is correlated to the resulting jet velocity. It is found that at a formation number around 3 the nature of the average jet velocity changes and the resulting jet velocity shows less sensitivity to the formation number.

scholarly journals Frequency Response of Synthetic Jets Emanating From an Array of Circular Orifices

2021 ◽  
Author(s):  
Nadim Arafa ◽  
Pierre Sullivan ◽  
Alis Ekmekci
Keyword(s):  
Frequency Response ◽  
Excitation Frequency ◽  
Acoustic Mode ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Mode Shapes ◽  
Long Span ◽  
Jet Actuators ◽  
The Mean ◽  
Jet Velocity

Abstract The effect of the excitation frequency of synthetic jet actuators on the mean jet velocity of synthetic jets issuing from an array of circular orifices is investigated experimentally. Herein, the focus is placed on an array of circular orifices, rather than a single orifice, as it brings the advantage of covering long-span airfoils. The array consists of 16 circular orifices, each having a diameter of 3.42 mm, distributed over a span of 300 mm. The jets are generated by the excitation of a single cavity via 16 piezoelectric elements. Localized velocity measurements at the exit of the orifices show that the mean jet velocity varies with the excitation frequency. Several distinct resonant peaks were observed in the frequency response. Acoustic simulations of the cavity showed that these peaks correspond to acoustic mode shapes of the cavity. Due to the high-aspect ratio of the cavity, several acoustic mode shapes exist in the excitation frequency range aside from the Helmholtz resonance frequency. Moreover, the mean jet velocity emanating from the array shows a variation from orifice to orifice, depending on the excited acoustic mode.

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