Use Of Synthetic Jets Research Articles

Expressive, Scalable, Mid-Air Haptics with Synthetic Jets

Non-contact, mid-air haptic devices have been utilized for a wide variety of experiences, including those in extended reality, public displays, medical, and automotive domains. In this work, we explore the use of synthetic jets as a promising and under-explored mid-air haptic feedback method. We show how synthetic jets can scale from compact, low-powered devices, all the way to large, long-range, and steerable devices. We built seven functional prototypes targeting different application domains, in order to illustrate the broad applicability of our approach. These example devices are capable of rendering complex haptic effects, varying in both time and space. We quantify the physical performance of our designs using spatial pressure and wind flow measurements, and validate their compelling effect on users with stimuli recognition and qualitative studies.

Experimental Investigations on Flow Control of the Rotor via the Synthetic Jets in Forward Flight

To study the effects of synthetic jet control on the aerodynamic performance of a rotor in forward flight, we conducted a series of experiments with varying rotor rotation speeds and free stream velocities. In the test, we used a six-component balance and a PIV system and designed a blade with a particular structure that covered the frame. The experimental results revealed that the synthetic jet could effectively delay flow separation over the blade and enhance the aerodynamic efficiency of the rotor. Moreover, we investigated how different jet parameters influenced the flow control effects of synthetic jets on the rotor’s aerodynamic characteristics. We drew some valuable conclusions from our analysis. In forward flight, the jet located closer to the leading edge of the blade had a stronger impact on improving the aerodynamic performance of the rotor. The jet with a 90° jet angle increased the rotor normal force by 225%, which was the maximum possible increase, while the jet with a 30° inclined angle had the best control effects on preventing flow separation in the retreating blade. Our study provides valuable insights into the use of synthetic jets for rotor flow control and suggests possible applications for improving rotorcraft performance and stability.

Effect of blade aspect ratio on the performance tradeoff between figure of merit and bending-torsion dynamics of wind turbines with synthetic jets

In this experimental study, two three-bladed rotors with a blade aspect ratio of 7.79 and 9.74 representing a 25% increase were tested. Each blade contains an S809 airfoil with zero pre-built twist and 20 high-performance synthetic jet actuators distributed along the span. The rotor was tested at four rotor speeds, Ω of 250, 500, 750, and 1,000 revolutions per minute (RPM) and three collective blade pitch angles, θc of 2, 5, and 8 degrees. Rotor thrust was measured using a high-capacity load cell, and blade bending and torsion was measured at four equally spaced radial locations on the blade defined by r/R= 0.24, 0.48, 0.72, and 0.96 using four onboard inertial measurement units. The spanwise flow over the suction surface of the blade was measured using laser Doppler velocimetry (LDV) techniques. The local Reynolds number produced with the test rotor speeds at the measurement locations ranges from 8.31 × 104≤Re∞≤ 9.49 × 105. It was found that rotor aerodynamic efficiency as quantified by the figure of merit is directly linked to blade aspect ratio and the magnitude of spanwise flow over the blade. The rotor with a higher blade aspect ratio produces less overall spanwise flow and is more aerodynamically efficient, however the blade also generates larger mean and fluctuating bending and torsion displacements, which are undesirable for aeroelastic stability. The use of synthetic jets on the blade mitigates the root mean square of the bending and pitch displacements above Ω= 250 RPM and θc= 2°. It was found that at Ω= 1,000 RPM, the blade structures undergo a second mode bending response indicating a condition of structural instability due to higher aerodynamic loading. At this rotor speed, flow control on the outboard of the blade reduces unsteady bending as quantified by arms up to a maximum of 36.5%, and unsteady torsion, θrms up to 22.9% compared to the baseline for the rotor with an aspect ratio of 9.74.

Synthetic jets as a flow control device for performance enhancement of vertical axis hydrokinetic turbines: A 3D computational study

In the present work, a vertical axis turbine with straight blades was analyzed through a numerical simulation in three dimensions, the performance of the turbine was studied while synthetic jets were used as an active flow control method. To carry out the simulations, the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations were solved on Star CCM+, through the k-ω SST turbulence model. The dynamics of the turbine movement were described using the Overset Mesh technique, capturing the transient characteristics of the flow field. Hydrodynamic coefficients and vorticity fields were obtained to describe the flow behaviour, and the results were compared with two-dimensional simulations of the same system. Turbine performance with tangential synthetic jets located on the intrados and extrados of the airfoil shows an increase in the torque and power output of the turbine. Moreover, using simple estimates, synthetic jets used less power than the increment in power generated at the turbine shaft, showing that efficiency of the turbine increases with the use of synthetic jets. However, the increment in the turbine performance is not as high as in previous two-dimensional studies reported in the literature.

Use of synthetic jet to a fully-active flapping foil for power extraction enhancement

The power extraction performance of a fully-active flapping foil with synthetic jet is numerically investigated in this work. An elliptic airfoil with ratio of 8, which is placed in a two-dimensional laminar flow, is adopted to extract power from the flow. The foil implements the imposed translational and rotational motions synchronously. A pair of synthetic jets with the same frequency and strength is integrated into the upper and lower surfaces of flapping foil. As a result, the flow field around the foil could be affected by the synthetic jets greatly. At the Reynolds number of 1000 and the pitching axis location of half chord, the effects of the jet strength, the inclined angle between the jet direction and the chord line, as well as the phase angle between the synthetic jets and the flapping motion on the power extraction performance are systematically investigated. Compared with the traditional flapping foil, it is demonstrated that the enhancement of power extraction efficiency can be achieved with the help of synthetic jets. Based on the numerical analysis, it is indicated that the jet flow on the foil surfaces alters the vortex-shedding process and modifies the pressure distribution on the foil surface. As a result, the overall power extraction of the flapping foil can be benefitted.

Use of the RANS/ILES Method to Study the Efficiency of Synthetic Jet Application for Flow Control in an S-Shaped Intake Integrated with an Airframe

The flow in the subsonic S-shaped air intake with a D-shaped inlet and circular outlet cross sections is calculated with the combined high-resolution RANS/ILES method. A flat plate, on which the air intake is mounted, is used as an airframe simulator. The boundary layer is specified at the beginning of the plate, and its profile is close to the profile of the turbulent boundary layer. The calculations were performed on a structured grid containing 7 × 106 cells; good agreement with the experiment data is obtained. The causes of large flow nonuniformities at the outlet of air intake are revealed; the efficiency of the use of synthetic jets to improve its characteristics is studied. The influence of the regime parameters of synthetic jets and the location of slots for their egress on the air-intake flow is analyzed.

Heat transfer coefficients during the impingement cooling with the use of synthetic jet

The paper presents experimental studies on heat transfer phenomena which occurs during the impingement cooling with the use of synthetic jet. The synthetic jet was created by a special actuator consisting in a plexiglass cavity and a loudspeaker. An air was a working fluid. The effect of synthetic jet actuator geometry and supply parameters on heat transfer enhancement has been investigated. The experiment was performed with the use of classical thermal balance method. Heat transfer coefficients at a stagnation point have been obtained. Measurements were carried out in the range of excitation frequency f = 5 ÷ 600 Hz and of root mean square voltage E = 1, 2, 3, 4, 6 V. Changes of actuator geometry included: orifice diameters d = 9, 15, 24 mm, orifice thickness t = 3, 5, 20 mm and cavity depth H = 20, 40, 60 mm. On the basis of measurements results the correlations for the stagnation point Nusselt number of an axisymmetric impinging synthetic jet characterized by large Reynolds numbers have been obtained. Nusselt number has been determined in the function on scaling parameters: Reynolds number, jet-to-surface spacing x/d and the dimensionless stroke length L0. Reynolds numbers were ranging from 3600 to 22950, x/d = 1 ÷ 20 and L0 = 0.84 ÷ 170.5. The scaling parameters have significantly extended the range of research so far. The obtained Nusselt number correlations provide heat transfer calculations at large Reynolds numbers and are expected to have practical applications.

Study of the Possibilities of Gasdynamic Air Flow Control in the Spatial Air Intake of a Light Supersonic Business-Class Aircraft by the RANS/ILES Method

The effect of the boundary-layer bleed system on the flow and characteristics of the spatial air intake of a supersonic business-class aircraft integrated with an airframe simulator was studied by the combined high-resolution Reynolds Averaged Navier–Stokes Implicit Large Eddy Simulation method (RANS/ILES ). Two variants of geometry with and without the boundary-layer bleed system were considered. The effect of gasdynamic flow control with the use of synthetic jets was studied for both air intake variants. The effect produced by the boundary-layer bleed system and the regime parameters of synthetic jets on the flow in the air intake and its characteristics, the level of turbulent fluctuations, and the surge boundary was studied. The level of velocity and pressure fluctuations was established to be lower at the outlet of the air intake without the boundary-layer bleed system. The application of synthetic jets made it possible to reduce the total pressure losses and level of turbulent fluctuations in the channel of the air intake and at its outlet, thus increasing the range of its stable operation.

Wind tunnel quantification of dynamic stall on an S817 airfoil and its control using synthetic jet actuators

AbstractWind tunnel experiments were performed to quantify the aerodynamic characteristics of the S817 airfoil in dynamic stall conditions, and the subsequent application of active flow control to modify the manner by which dynamic stall incepts. Both quasi‐2D and cantilevered finite span configurations were tested. Surface pressure, six‐component force‐torque sensor, and stereoscopic particle image velocimetry (SPIV) were used to quantify the baseline flow and the benefits of actuating synthetic jets (installed at x/c = 0.35, angled 45° into the flow, and at a momentum coefficient Cμ = 0.012). The airfoil was pitched at reduced frequencies of kf = 0.025 and 0.05 and at shallow and deep stall. Vortex induced lift from dynamic stall was observed and was eliminated by the use of synthetic jets for nearly all conditions; pitching moment deviation was also observed to be significant, and was eliminated at shallow stall and significantly reduced during deep dynamic stall when the synthetic jets were actuated. Moreover, the activation of synthetic jets resulted in significant reduction in the hysteresis (area within the pitching up and pitching down load history) of the lift and pitching moment through all experimental conditions, as much as 41% and 85%, respectively. SPIV flow fields in shallow dynamic stall demonstrated that actuation of synthetic jets confined the separated region to the trailing edge, in both the instantaneous and time averaged sense. To further reduce the lift and pitching moment hysteresis at high angles of attack, a pulse modulation technique was used and showed a marked increase in synthetic jet performance compared with the continuously actuated case and achieved this result with approximately 65% less power consumption.

Enhancement of aerodynamic performance of a heaving airfoil using synthetic-jet based active flow control

In this study, we explore the use of synthetic jet (SJ) in manipulating the vortices around a rigid heaving airfoil, so as to enhance its aerodynamic performance. The airfoil heaves at two fixed pitching angles, with the Strouhal number, reduced frequency and Reynolds number chosen as St = 0.3, k = 0.25 and Re = 100, respectively, all falling in the ranges for natural flyers. As such, the vortex force plays a dominant role in determining the airfoil’s aerodynamic performance. A pair of in-phase SJs is implemented on the airfoil’s upper and lower surfaces, operating with the same strength but in opposite directions. Such a fluid-structure interaction problem is numerically solved using a lattice Boltzmann method based numerical framework. It is found that, as the airfoil heaves with zero pitching angle, its lift and drag can be improved concurrently when the SJ phase angle relative to the heave motion varies between and . But this concurrent improvement does not occur as the airfoil heaves with pitching angle. Detailed inspection of the vortex evolution and fluid stress over the airfoil surface reveals that, if at good timing, the suction and blowing strokes of the SJ pair can effectively delay or promote the shedding of leading edge vortices, and mitigate or even eliminate the generation of trailing edge vortices, so as to enhance the airfoil’s aerodynamic performance. Based on these understandings, an intermittent operation of the SJ pair is then proposed to realize concurrent lift and drag improvement for the heaving airfoil with pitching angle.

Acoustic aspects of synthetic jet generated by acoustic actuator

Thermal overstressing as a result of miniaturization is the foremost challenge for the next generation electronic devices. Shrinking size of electronic devices makes this problem even worse. Conventional cooling module which uses fan and a heat sink seems to be inadequate for cooling of electronic devices due to space constraints and higher circuit densities. Synthetic jet is a novel flow technique which synthesizes stagnant air to form a jet and is potentially useful for cooling applications. It results from periodic oscillations of a diaphragm in a cavity such that there is no net mass addition to the system. It is being recently researched as an effective alternative to fan but the existing rules on noise emissions constitute an impediment to the practical use of synthetic jet. Besides several nonauditory health effects, prolonged exposure to high levels of noise can cause noise-induced hearing loss. To adopt ameliorative solutions and for adherence to legislative regulations, it is essential to assess the noise exposure. Present study is embarked on to investigate the effect of excitation frequency and voltage on sound pressure level of synthetic jet for orifices of different diameter and thickness. This jet acoustic research is performed in an imperative and controlled acoustic environment, i.e. acoustic test chamber. Spectrum analysis clearly indicates impedance mismatch between audio amplifier and electric transducer used to generate the jet flow. Over the past few years extensive experimental and analytical results have led to good understanding of synthetic jet but study on impedance mismatch has always been elusive. The results on synthetic jet heat transfer, flow, and acoustic characteristics cannot be faithfully reproduced due to such hurdle. In order to vanquish or conquest over it, matching the impedance between source and the load is inevitable. The conclusion of this paper unveils the necessity of impedance matching for high fidelity measurements of synthetic jet.

Numerical simulations of active flow control with synthetic jets in a Darrieus turbine

This study presents two-dimensional numerical simulations of the flow around a cross-flow vertical-axis water turbine (straight-bladed Darrieus type) using active flow control by means of synthetic jets. The performance of the turbine is quantitatively analyzed from the hydrodynamic coefficients (torque coefficient, power coefficient, tangential force coefficient, normal force coefficient, lift coefficient and drag coefficient) and qualitatively by the flow behavior (vorticity field). Numerical simulations of the turbine were carried out using a time-accurate Reynolds-averaged Navier-Stokes (RANS) in ANSYS FLUENT with the shear stress transport k−ω turbulence model. A transient rotor-stator model with a sliding mesh technique was used to capture the changes in the flow field at each time step. Numerical results show that the use of synthetic jets over the extrados and intrados of the airfoil increases the net torque and power output of the turbine. Besides, this increment in the net power generated by the turbine is higher than the power consumed by the synthetic jets. Therefore, it is demonstrated that the global efficiency of the turbine increases by means of this active flow control technique. Several flow phenomena such as vortex shedding and their interference with the blades were also studied and analyzed.

Heat transfer and fluid flow characteristics of impinging jet using combined device with triangular tabs and synthetic jets

The fluid flow and heat transfer characteristics of an impinging jet with a combined active–passive device were investigated. The combined device consisted of triangular tabs and a synthetic jet array that provided periodic disturbance to the jet’s shear layer. The Reynolds number based on the nozzle diameter (D) was 3.9×104, and the nozzle-to-wall spacing (L/D) was 2. Four triangular tabs were attached to the nozzle outlet. The synthetic jets were issued at an angle of 30° against the primary jet. Under the triangular tab operation, the longitudinal vortices were generated and the transverse vortex of the primary jet collapsed. Moreover, the velocity of the primary jet increased because of contracted flow. Under the synthetic jet operation, the development of the transverse vortex was promoted due to the increased instability of the shear layer. The jet’s periodic disturbances strengthened because of the use of synthetic jets. The combined device operation led to increased velocity magnitude and periodic disturbance of the primary jet; thus, the peak RMS value of the velocity fluctuation was enhanced and the peak local Nusselt number near the stagnation point increased by 35% compared with cases where the device was not used. Additionally, the area-averaged Nusselt number was 10% larger than that obtained without the device. The heat transfer was governed by the jet’s velocity, RMS, and periodic velocity fluctuation. These results indicate that the fluid flow and heat transfer characteristics of an impinging jet could be controlled by optimizing the actuation conditions of the combined active–passive device.

Synthetic jet actuation for load control

The reduction of wind turbine blade loads is an important issue in the reduction of the costs of energy production. Reduction of the loads of a non-cyclic nature requires so-called smart rotor control, which involves the application of distributed actuators and sensors to provide fast and local changes in aerodynamic performance. This paper investigates the use of synthetic jets for smart rotor control. Synthetic jets are formed by ingesting low-momentum fluid from the boundary layer along the blade into a cavity and subsequently ejecting this fluid with a higher momentum. We focus on the observed flow phenomena and the ability to use these to obtain the desired changes of the aerodynamic properties of a blade section. To this end, numerical simulations and wind tunnel experiments of synthetic jet actuation on a non-rotating NACA0018 airfoil have been performed. The synthetic jets are long spanwise slits, located close to the trailing edge and directed perpendicularly to the surface of the airfoil. Due to limitations of the present experimental setup in terms of performance of the synthetic jets, the main focus is on the numerical flow simulations. The present results show that high-frequency synthetic jet actuation close to the trailing edge can induce changes in the effective angle of attack up to approximately 2.9°.

Experimental Investigation of the Use of Synthetic Jets for Mixing in Vessels

Mixing is an important process in various industries. Different designs have been suggested in order to reduce the local shear rates in mechanically stirred mixing vessels, also known as continuously stirred tank reactors, in order to account for the mixing requirements for sensitive materials such as biological materials and biofluids where the high shear rate may damage the sensitive materials. This paper reports on the development of a continuously stirred tank reactor that can be used to achieve a variety of mixing assignments. This mixing is achieved using synthetic jets. The mixing performance was assessed using flow visualization techniques. The effects of fluid viscosity on mixing time were investigated. The results are very encouraging and are suggestive that the use of synthetic jets in mixing is a viable alternative to the conventional methods of mixing in vessels.

Efficiency enhancement in transonic compressor rotor blades using synthetic jets: A numerical investigation

Several passive and active techniques were studied and developed by compressor designers with the aim of improving the aerodynamic behavior of compressor blades by reducing, or even eliminating, flow separation. Fluidic-based methods, in particular, have been investigated for a long time, including both steady and unsteady suction, blowing and oscillating jets. Recently, synthetic jets (zero mass flux) have been proposed as a promising solution to reduce low-momentum fluid regions inside turbomachines. Synthetic jets, with the characteristics of zero net mass flux and non-zero momentum flux, do not require a complex system of pumps and pipes. They could be very efficient because at the suction part of the cycle the low-momentum fluid is sucked into the device, whereas in the blowing part a high-momentum jet accelerates it. To the authors’ knowledge, the use of synthetic jets has never been experimented in transonic compressor rotors, where this technique could be helpful (i) to reduce the thickness and instability of blade suction side boundary layer after the interaction with the shock, and (ii) to delay the arising of the low-momentum region which can take place from the shock-tip clearance vortex interaction at low flow operating conditions, a flow feature which is considered harmful to rotor stability. Therefore, synthetic jets could be helpful to improve both efficiency and stall margin in transonic compressor rotors. In this paper, an accurate and validated CFD model is used to simulate the aerodynamic behavior of a transonic compressor rotor with and without synthetic jets. Four technical solutions were evaluated, different for jet position and velocity, and one was investigated in detail.

Interaction of Synthetic Jet Propulsion with Airfoil Aerodynamics at Low Reynolds Numbers

The use of synthetic jets for propulsion of fixed-wing Micro Air Vehicles (MAVs) is investigated experimentally in the low Reynolds number range. Interaction of a synthetic jet located at the trailing-edge of the wing with wing aerodynamics is studied with flow visualization and velocity measurements at low Reynolds numbers. The effects of excitation frequency, momentum coefficient, angle of attack, and Reynolds number were studied in detail. The separated region in the wake becomes smaller as the momentum coefficient is increased gradually. Once the momentum coefficient reaches a critical value, there is zero net drag. There is also reattachment of the separated shear layer near the trailing-edge, with expected enhancement in lift. Above the critical value of the momentum coefficient, the jet produces net thrust. Even at relatively higher incidences, zero net drag can be obtained and the reattachment of the shear layer to the upper wing surface is possible. The reattachment of the separated shear layer becomes easier with increasing Reynolds number. The favorable effect of increasing Reynolds number is most apparent at low Reynolds numbers. There is a strong effect of pulsing frequency and the results suggest an optimum range of Strouhal number St = 2 to 5. Also, preliminary experiments for a generic airfoil with internal actuator were carried out. Although the drag of this design is somewhat larger, zero net drag can be achieved when the synthetic jet is activated.