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Sensors and Actuators A 138 (2007) 213–220

Experimental investigation of a fluidic actuatorgenerating hybrid-synthetic jets

V. Tesar ∗, Z. Travnıcek, J. Kordık, Z. RandaInstitute of Thermomechanics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

Received 20 September 2006; received in revised form 11 January 2007; accepted 24 April 2007Available online 27 April 2007

bstract

Hybrid-synthetic jets are similar to the usual zero-time-mean-flow synthetic jets, differing from them by superposition of a steady outflow fromhe nozzle. This makes the hybrid-synthetic jets suitable for applications like impingement cooling, where the usual synthetic jets fail because ofhe re-ingestion of the heated fluid. The discussed actuator generating these jets operates without any moving parts. In contrast to the better known

ectifier type actuators developed recently e.g. by Travnıcek, Fedorchenko, and others, it is based on the idea of a fluidic alternator. Experiments withn alternatior-type actuator model, operating with air, concentrated on the oscillation frequency and its dependence on parameters like feedbackoop length. In spite of similarity to the analogous actuator described in Tesar et al. in 2006 the present results are very different.

2007 Elsevier B.V. All rights reserved.

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eywords: Hybrid-synthetic jets; Synthetic jets; Fluidics; Fluidic feedback; Os

. Introduction

Hybrid-synthetic jets are an interesting case of pulsatile jetows. Recently they became of importance from both theoreticaloint of view [1] and because of the number of applications theyade possible. They share with the usual, zero-mass-flow-rate

ynthetic jets [2] the character of a flow synthesized from a trainf vortices (as long as criteria, such as those of Holman et al.3] are met) but differ in the superimposed steady outflow fromhe nozzle. This makes them suitable for impingement cool-ng or similar convective transfer tasks [4], where absence oforking fluid replacement in the usual synthetic jets precludessing their otherwise excellent heat and/or mass transfer capa-ility for an extended period of time. The list of applications ofhe hybrid-synthetic jets includes a control of flows past liftingurfaces [5], thermal processing of food by hot air jets (someesults presented in [6]), and maneuvering of small autonomousnderwater vehicles [7]. Also, impinging hybrid-synthetic jets

ecently found an interesting use in the anti-terrorist war. In theersion with an annular nozzle they are employed in screeningersons by contact-less collecting of samples of illicit substances

∗ Corresponding author. Tel.: +420 2 660 52270.E-mail address: tesar@it.cas.cz (V. Tesar).

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924-4247/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.sna.2007.04.064

on frequency; Fluidic oscillator

rom their clothing [8]. In contrast to the steady air jets used forhis purpose so far, they ruffle the textiles to release the sampledubstances by prevent diluting the sample by the added air fromhe nozzle.

. Fluidic actuators of the alternator type

There are two, principally antipodal approaches to design-ng an actuator for generation of the hybrid-synthetic jets. Theetter known way, followed by Travnıcek, Fedorchenko and oth-rs, e.g. [1,7,9,14,17], uses the fluidic rectification[11,16]—aonversion of an alternating fluid flow into the one-directionalow. A generator of alternating flow with a reciprocating pis-

on or diaphragm is used together with what may be describeds an imperfect rectifier—the ‘imperfection’ (not meant in anyerogatory sense) producing the alternating component of theozzle flow. A useful quantitative measure of the rectificationerfection, according to [1], is the volumetric efficiency ε, theatio of the output fluid volume to the total displaced volumeuring the operation cycle. With perfect rectification, all theisplaced fluid leaves the nozzle to form a non-returning jet,

eading to ε = 1. On the other hand, the usual synthetic jets gen-rators without any rectifier element have rectification efficiency= 0. The hybrid-jet actuator designs assume places on the scaleetween these two extreme values.

214 V. Tesar et al. / Sensors and Actuators A 138 (2007) 213–220

Fig. 1. The basic principle of fluidic alternators. The core is a bridge circuit ofthe same topology as in a full-wave rectifier. Flow paths in the first half of theohb

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perating cycle are shown in 1 above, while 2 below shows them in the secondalf-cycle. In contrast to the automatic operation of a rectifier, the alternatorridge has to be controlled by an input control signal X.

The present author has been developing another actuatoresign for the same purpose. It was recently described, e.g. in5,6,10]. Seemingly this design does not share anything withhe earlier rectification principle. Indeed, the underlying idea ishe very opposite to that of the fluidic rectifier. It is the ideaf a fluidic alternator—a device performing the complementaryask: converting a supplied steady flow into an alternating flow.here are no moving parts at all, the alternating flow is producedy a self-excited fluidic oscillator. The perfect alternator oper-tion, as schematically represented in Fig. 1, is again actuallyndesirable for the present task. The produced flow would con-ist of completely symmetric positive and negative half-cyclesnd the generated jet would be the standard synthetic jet. What iseeded is an ‘imperfect’ alternator. The absence of moving com-onents brings a number of operational as well as manufacturingdvantages.

Perhaps surprisingly, the underlying topology of the alterna-or type actuators [12,13,15,16] as represented in Fig. 1 is alsoquivalent to the Gratz bridge [16] of the full-wave fluidic rec-ifiers. The main difference is in the devices in the alternatorridge controlled by an input signal, in contrast to the automaticperation of the passive devices of the rectifier bridge, which isictated by the motion of the reciprocating piston. The choicef the fluidic devices that form the alternator is limited by theequirement of their controllability. Of the available possibil-ties, the vortex amplifiers with controllable turning down of

he flow are usually too slow. They do not meeting the usual fre-uency requirements of the synthetic jets. This leaves as the mostuitable choice the jet-type devices, usually the diverter-type flu-dic amplifiers. They may be easily provided with a feedback

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ectangular waveshapes. Suction from atmosphere in one nozzle is added to theutflow from the other nozzle. Also shown is the expression for the volumetricfficiency ε for this character of the flows.

oop turning them into the self-excited oscillators. The oscilla-ion frequency is adjustable by the feedback loop tube length.he amplifiers are mostly bistable, employing the Coanda effectf the alternative attachment of the jet to one of two oppo-itely located walls. With the jets switched between the twoutlets, these actuators are quite naturally of the two-phase orouble-acting kind—counterparts to the double-acting rectifierctuators described in [7,9,17]. Fig. 2 presents the two idealime dependences of the velocities in the two exit nozzles of thelternator-type actuator. The operation at a low frequency rel-tive to the fast switching process in the amplifier is assumed,o that the waveshapes are practically rectangular. The nega-ive velocity wn in one exit nozzle – the minus sign indicatinguction from the atmosphere – is equal to the surplus veloc-ty in the other nozzle by which the exit flow is faster thanwice the time mean exit velocity wn. For the rectangular depen-ences, also shown in Fig. 2 is the formula for evaluation of theolumetric efficiency ε. The ‘perfect’, leak-less alternator oper-tion means ε = 1 while ε = 0 represents the case of the usualynthetic jet. The name of the quantity ε, taken over from ear-ier usage in a different context, may be not well fitting. It is,owever, a useful characterization parameter for the discussedctuators, placing a particular design on the scale from ε = 0o 1.

The basic configurations of the actuator designs of this typeescribed so far in literature – all of them operating with air – isresented in the following Fig. 3. The illustration aims at sug-esting the essential topological affinity with the Gratz bridgeonfiguration in Fig. 1. The correspondence is not easily dis-ernible, because the two arms of the bridge and three of itsertices – those corresponding to the vertices T, U, V in Fig. 1here do not actually exist as material components. There are

lso no conduits transfering the generated alternating flows. Allhis is left to fluid flows in the atmosphere. Because of the com-

onality of the two downstream arms, and the absence of anyow controlling devices there, the arm connecting T with U can-ot transfer to the second nozzle the low pressure available inhe inlet of the driving pump. Fortunately, in the jet-type diverter

mplifiers there is an effect which can secure the desirable returnow in the second nozzle. It is the jet-pumping effect of the jet

eaving the main nozzle of the amplifier (cf. Fig. 7). It is actu-lly this jet-pumping effect, acting in the control nozzles of the

V. Tesar et al. / Sensors and Actua

Fig. 3. The alternator actuator with the unvented diverter amplifier. The twobbr

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snirlohtdtascbmlTcis seen in the bottom part of Fig. 6. The following Fig. 7 showsa detail view of the core part, providing an impression of thesurface quality and shape perfection obtainable with the usedlaser cutting manufacturing method. The height of the assem-

ridge arms leading to terminal T are actually absent – as in fact is most of theridge, the dominant part in the schematic representation in Fig. 1 – because theole of the vertices T, U, V is taken over by the atmosphere.

mplifier (with higher intensity on the ON side towards whichhis jet is attached by the Coanda effect), which also drives theeedback signal in the feedback loop.

. Experimental investigation

The device described in the present paper is a recently builtcaled-up model of an actuator of the alternator type. The essen-ial parameter of these devices is the oscillation frequency andnvestigation of this parameter was the main subject of this study.he frequency f [Hz] is determined by the feedback mechanismnd is dependent mainly on two parameters: on the length ofhe feedback loop and on the flow rate supplied to the supplyerminal S. The latter dependence is there due to the general ten-ency of no-moving-part aerodynamic oscillations to maintainconstant value of the Strouhal number, Sh:

h = fb

w(1)

here the standard characteristic length dimension in fluidic jet-ype devices is the main nozzle width b [m] and the characteristicelocity w [m/s] is the bulk (spatial average) velocity in the mainozzle exit. With the latter proportional to the supplied air flowate, this tendency results in the frequency rise as the flow rates increased.

The known feedback loop length and measured oscillationrequency (and hence the time spent by the switching signal toravel the loop length) make possible evaluation of the effectiveignal transfer velocity in the loop. This was already describedn [10] in investigations of an actuator quite similar to the presentne. The experimental data for the earlier model revealed twoperating regimes. There was the expected constant or nearlyonstant Sh regime at low Reynolds numbers Re < 3000, which

s a value which may perhaps suggest laminar character of theow. The propagation velocity in the loop was there from 5 to0 times higher than the velocity in the main nozzle. At highere values the propagation velocity was also high but constant,

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tors A 138 (2007) 213–220 215

ndependent of the supplied flow rate. The experimental datan [10] suggested that the signal travels in the feedback loopssentially as an acoustic wave. Its propagation velocity wasbviously equal to the speed of sound in a tube with heat transfernto the isothermal boundary layer.

Surprisingly, despite similarity of the present actuator geom-try – which may indeed superficially seem to be almost identicalthe signal transfer mechanism was now found different. The

ropagation velocity in this device is essentially equal to theain nozzle exit velocity, much smaller than described in [10]

nd a mere fraction of the speed of sound. This experimentalnding is of paramount value for designers of actuators intended

o generate the interesting, important, and advantageous newype of synthetic jets.

.1. The laboratory model

Like the device in [10], the actuator generated two hybrid-ynthetic jets mutually phase shifted by 180◦ (suction into oneozzle simultaneous with outflow through the other one) accord-ng to Fig. 2. While the earlier models were designed to meet theequirements of an application in control of flow past an airplaneifting surfaces [5], the present model was built to drive a pairf annular nozzles generating annular impinging jets in surfaceeating application [6]. As in Fig. 3 and in the earlier models,he essential part of the actuator is an unvented planar bistableiverter fluidic amplifier, converted into a self-excited oscilla-or by providing it with a feedback loop. The geometry of themplifier is specified in Fig. 4 showing the main outer dimen-ions and Fig. 5 indicating the dimensions of the most importantore part. All the dimensions are given in multiples of the widthof the main nozzle—the nozzle connected to the supply ter-inal S. The model, with its main nozzle width b = 2 mm, was

arger than the intended final operational microfluidic version.he amplifier consists of a stack of three plates with identicalavities, made by laser cutting. A photograph of one of the plates

ig. 4. Geometry of the amplifier cavity, laser cut in three plates stacked onop of each other and closed on top and bottom by cover plates. Dimensions in

ultiples of the main nozzle width b = 2 mm.

216 V. Tesar et al. / Sensors and Actuators A 138 (2007) 213–220

Fs

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Fig. 7. Photograph of model components. The laser-cut cavity of the amplifierin one of the identical three stacked plates is shown in the bottom part of thepicture. The top part shows the bottom cover plate and the two annular exitn

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ig. 5. Geometry of the critical, core part of the amplifier immediately down-tream from the main nozzle, the exit width of which is b = 2 mm.

led stack of three plates was equal to 7.5b (aspect ratio, λ = 7.5).he exits of the amplifier were connected to the annular noz-les seen in the top part of Fig. 6. Performance of diverter typescillators is influenced by blockage of the amplifier exits byhe connected load. In the present case, however, this load wasather small—the annular exit area of each nozzle was 2.446-imes the area of the amplifier main nozzle. The nozzles werentended to generate an annular impinging hybrid-synthetic jet.uch annular jets and the effects they cause on the impingementall are known to be very sensitive to even small deviations in

he exit slot width. To ensure equal width of the annular slot ofhe nozzle, the nozzle design incorporated a number of features

aintaining the concentricity of nozzle components, at the costf the air flowpath inside the nozzles being rather complex. Thisn some operating regimes resulted in increased turbulence in thessuing jets.

An important part of the oscillator is the mutual connec-ion of the two control nozzles, terminals X1 and X2 in Fig. 4,orming the feedback loop. This converts the amplifier into theelf-excited oscillator. The connection was made by a circular

ig. 6. Photograph of the most important part of the device: the core part of themplifier (cf. Fig. 5).

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ozzles generating the annular hybrid-synthetic jet.

ross-section tube of internal diameter equal to 4b. The tubeength was varied during the experimental investigations fromhe minimum 250b up to 2000b. This length together with their flow rate determine the oscillation frequency, which could bedjusted in the range from 2 to 45 Hz. The lower value was sim-ly due to the limited available length of the tubing; experienceith similar oscillators [10] indicates that frequency lower at

east by a decimal order of magnitude is attainable with very longubes. Less successful were attempts at decreasing the frequencyy reducing the air flow rate. The bistability of the used amplifier,ecessary for a well-defined switching leading to the rectangularave-shape of the produced flow pulses, depends on the Coanda

ttachment effect. This is really effective only in turbulent flows.o wonder the regular oscillation cease to exist at and below

ransitional Reynolds numbers. In the present case, the lowesteynolds number value at which it was possible to keep regularscillation was Re = 1 171. Below that, some switching pulsesere missing and the signal to noise ratio decreased below thealues at which the device can be useful. On the other hand, alsoncreasing the frequency by using a very short feedback tube

engths and high flow rates has led to problems. The regular rect-ngular wave shapes detected at the annular nozzle exits by hotire anemometer then give way to irregularities having turbulent

haracter.

Actuators A 138 (2007) 213–220 217

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Fig. 9. A typical example of the dependence of Strouhal number, Sh on the mainnai

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V. Tesar et al. / Sensors and

.2. Frequency measurements

The device was operated with air. The processed signal wasbtained from a hot wire probe placed downstream from thexit of one of the annular nozzles. The signal was used with-ut linearization and the other usual signal processing steps.cross most of the operating range, the oscillation frequency

ould be measured simply by a counter. This became unreli-ble at small flow rates, where the turbulent fluctuations becameommensurable with the low-intensity signal. It also ceased toe reliable at the other end of the range, with short feedbackoops. There the switching time becomes comparable with thescillation period, which distorted the otherwise nearly rect-ngular wave-shapes. In both cases the data exhibited whatas (but in some instances merely seemed to be) an excessive

catter. Because of the essential importance of the frequencys the parameter of the actuator, the experiments especiallyt low Reynolds numbers were repeated by the first author’sollaborators, using a more sophisticated processing of theata. The same unprocessed signal of the hot wire probe wasampled periodically for a long time and stored in a digitalorm and then processed by a discrete Fourier transforma-ion. The resultant spectrum was then smoothed by applying a

oving averaging—using ensembles of 100 data points sym-etrically located on both sides of a particular investigated

requency.An example of application of this procedure is presented

n Fig. 8. It was obtained with cold (annular exit temperature3.5 ◦C) air flow with mean velocity of the flow in the amplifierain nozzle 57.5 m/s. Of course, in the 2.446-times larger

nnular exit area the velocities were lower, despite the increasey the air sucked in through the other nozzle. The hot-wireensor data were sampled at a sampling frequency fs = 1 kHz,

hich means that the resultant spectrum contains useful datanly up to the Nyquist frequency fs/2 = 500 Hz. Acquiring all31 072 samples at this sampling frequency took more thanmin. The first impression from Fig. 8 may be of a rather

ig. 8. A typical example of frequency spectrum obtained by processing the sig-al from the hot wire sensor placed in front of one of the two annular exit nozzlesFig. 6). If the signal were linearized, the plotted voltage would correspond tobsolute velocity magnitude (the hot wire probe does not discriminate the flowirection). The run shown here involved 131 072 data samples. The value ofnterest extracted from the smoothed spectrum is the frequency f = 24.727 Hz inhe dominant (>1 V) peak.

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ozzle Reynolds number, Re for a particular loop length. Heating the suppliedir leads to changes in the oscillation frequency, but the results are practicallyndistinguishable in the dimensionless Re–Sh plotting.

trong noise, but it should be noted that the co-ordinatesre logarithmic so that the data at the first peak, where theesultant oscillation frequency was evaluated, are more than twoecimal orders of magnitude above the noise. Presence of theower higher-frequency peaks demonstrates the non-harmonic,ractically rectangular waveshapes.

Because of the planned use of the generated impinging jetsn heat transfer applications, a considerable concern was causedy the noticeable change of the oscillation frequency when theupplied air into the oscillator was heated by an upstream heater.ortunately, plotting the results obtained at different exit temper-tures in dimensionless co-ordinates, evaluated by consideringhe changed air properties, has shown that the frequency changes merely a consequence of the change in air specific volume andiscosity. In the example of measurements at four different exitemperatures for a particular feedback loop length in Fig. 9, thetrouhal number, Sh according to Eq. (1) is plotted as a functionf Reynolds number, Re:

e = wb

ν(2)

valuated from the usual conditions in the main nozzle of themplifier, the nozzle width b [m] as the characteristic length, theain nozzle exit velocity w [m/s], and (kinematic) viscosity ν

m2/s]. The differences between the resultant dependences arensignificant, smaller than a characteristic measure of the datacatter.

.3. Propagation velocity

The results in the example Fig. 9 show that the Strouhalumber, Sh according to Eq. (1) fails to be an invariant of thenvestigated phenomenon. The reasons for it are twofold. First, inig. 9 there is an apparent systematic growth of Sh with increas-

ng Re. This dependence is weak and was not found for all the

eedback loop lengths. More importantly, the Sh values evalu-ted from the nozzle width as the characteristic length were nothe same with different feedback loop tube lengths l. Indeed,n the similar experiments described in [10] the dependence of

218 V. Tesar et al. / Sensors and Actuators A 138 (2007) 213–220

Fig. 10. Plotted as a function of the main nozzle Reynolds number, Re is herethe modified Strouhal number, equivalent to relative effective velocity of signalpat

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ropagation wpropag. The values near to 1.0 show that the switching signal prop-gates in the feedback loop at a velocity roughly equal to the exit velocity w inhe main nozzle.

he measured oscillation frequency f on the length l was foundo be practically an inverse proportionality f ∼ 1/l. As a stepowards finding an invariant, it was decided in [10] to introducemodified Strouhal number by multiplying Sh evaluated fromq. (1) by the relative length l/b. It is essentially this quantityhich is used in Fig. 10 for plotting all the data from the present

xperiments. The modification in Fig. 10 actually involves mul-iplication by a constant 2.0. This has no effect on the characterf the dependence, but brings an interesting interpretation. Asong as the jet switching in the amplifier is a fast process, thescillation period�t = 1/f is practically almost equal to two prop-

gation times of the switching signal in the feedback loop. Thushe quantity actually plotted on the vertical co-ordinate may benterpreted as an estimate of the relative value of the propagationelocity wpropag.

ig. 11. Modified Strouhal number dependence on Re obtained with the morerecise frequency evaluations revealed systematic dependences in what initiallyeemed to be just a scatter. At low Reynolds numbers and with short loop lengths,he data may be fitted with straight lines, the slopes of which increase with l fromnitially negative values through zero to positive.

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ig. 12. The growth of the slope of the fitted straight lines in Fig. 11 with thencreasing loop length l.

Plotted in Fig. 10 are results of two independent separatexperimental investigations. In contrast to the earlier results in10], the propagation velocities are here much lower, practicallyqual to the bulk velocity w of the air flow in the main nozzle ofhe amplifier. This was found already in earlier measurementssing the counter, but was considered suspicious—the more sohat it exhibited what seemed to be a large scatter. There waso observable tendency: measurements al lower relative feed-ack loop lengths l/b suggested an increase of wpropag/w withncreasing l/b, but the data for the large lengths l/b = 2000 did

ot agree with this trend.

In an attempt to eliminated the doubts, the measurementsere repeated using the above described spectrum analysis.his cleared all doubts about the measured values of the fre-

ig. 13. Dependence of the Strouhal number, Sh on the loop length l at threemall constant Reynolds numbers revealed another distinguishable systematicependence when the improved frequency spectrum measurements reduced thecatter.

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uency. The general character of the dependences, with valuesf wpropag/w near to 1.0, remained. The data also refused to settleo a single value eliminating the “scatter”. The more exact newerata actually show that what seemed to be a scatter is demonstra-ion of a systematic dependence. This is presented for the newata in Figs. 11 and 12 for short loop lengths. The decrease ofhe effective value of the ratio wpropag/w with decreasing loopengths l/b is not surprising in itself. It might be, in principle,xplained by the growing influence of the jet switching time inhe amplifier.

Unfortunately, the other way of viewing the results, theependences at a constant Reynolds number as plotted in Fig. 13,o not support this simple explanation.

. Conclusions

The paper presents recent experimental results obtained withhe new model of the jet-type actuator for generation of theybrid-synthetic jets. The measurements were of improved accu-acy, based on evaluating the complete frequency spectrum.urprisingly, despite of the similarity with the earlier model [10],

he present results are different. The propagation velocity in theeedback loop, evaluated from known loop length and measuredscillation frequency, is found in the new model to be practicallyqual to the bulk velocity w of the air flow in the main (supply)ozzle of the amplifier. Since the latter is in principle the causef the pressure difference across the feedback tube which driveshe feedback flow, the comparable magnitudes seem to be rea-onable. However, it is strange that this was not found with thearlier model in [10]. Present experimental findings are doubt-ess of importance the designers of actuators generating thisnteresting and important new type of synthetic jets, but theyeave much to be explained by additional future investigations.

cknowledgments

Authors are grateful for the financial support they receivedrom the Research and Development Project 1M06031 of

SMT CR, as well as the GACR research grant no.01/07/1499.

eferences

[1] Z. Travnıcek, T. Vıt, V. Tesar, Hybrid synthetic jets as the nonzero-mass-flux synthetic jets, Phys. Fluids 18 (2006).

[2] B.L. Smith, A. Glezer, The formation and evolution of synthetic jets, Phys.Fluids 10 (1998).

[3] R. Holman, Y. Utturkar, R. Mittal, B.L. Smith, L. Cattafesta, Formationcriterion for synthetic jets, AIAA J. 43 (10) (2005) 2110.

[4] V. Tesar, Z. Travnıcek, Pulsating and synthetic impinging jets, J. Visual-ization, ISSN 1343-8875, 8 (3) (2005) 201.

[5] V. Tesar, Fluidics applied to flow control by synthetic jets, in: Proceed-ings of the Conference “Topical Problems of Fluid Mechanics 2006”, p.171, ISBN 80-85918-98-6, Institute of Thermomechanics AS CR, February

2006.

[6] V. Tesar, Conditions on the Wall under a Pair of Phase-Shifted, Imping-ing Hybrid-Synthetic Annular Jets, Paper ISFV12-86.1, Proceedings of the12th International Symposium on Flow Visualization, Gottingen, Septem-ber 2006.

St(vfl

tors A 138 (2007) 213–220 219

[7] Ch.-Ch. Chen et al., Visualization of New Synthetic Jet Actuator for Under-water Vehicles, Paper IFVS12-86.4, Proceedings of the 12th InternationalSymposium on Flow Visualization, Gottingen, September 2006.

[8] V. Tesar, Z. Travnıcek, Apparatus for Collection of Samples from the Sur-face of Examined Objects—in Czech, Patent Application No. PV 2006-214,Czech Republic, filed March 30, 2006.

[9] Z. Travnıcek, A.I. Fedorchenko, A.-B. Wang, Enhancement of synthetic jetsby means of an integrated valve-less pump. Part I. Design of the actuator,Sensors Actuators A: Phys. 120 (2005) 232.

10] V. Tesar, C.-H. Hung, W.B. Zimmerman, No-moving-part hybrid-syntheticjet actuator, Sensors Actuators A: Phys. 125 (2006) 15.

11] S. Lee, K.J. Kim, Designs of IPMC actuator-driven valve-less micropumpand its flow rate estimation at low Reynolds numbers, Smart Mater. Struct.15 (2006) 1103.

12] Tesar V., Fluidic pump driven by alternating air flow, Proceedings ofPNEU-HIDRO’81, IVth Colloquium on Pneumatics and Hydraulics, Gyor,Hungary, September 1981.

13] S. Saito et al. Development of a fluidic pump driven by a bistable element,in: Proceedings of FLUCOME ’88, Sheffield, 1988.

14] Z. Travnıcek, V. Tesar, J. Kordık, Double-acting hybrid synthetic jets withtrigonally and Hexagonally arranged niozzles, in: Proceedings of Flucome2007, Tallahassee, Florida, 2007.

15] V. Tesar, Fluidic Jet-Type Rectifier: Experimental Study of Generated Out-put Pressure, Fluidics Quarterly, vol. 14, Ann Arbor, USA, December1982.

16] V. Tesar, Rectifier circuits for microfluidics, in: Proceedings of ‘Develop-ments in Machinery Design and Control’, Bysgoszcz-Bierzglowo, Poland,September, 2006.

17] Z. Travnıcek, V. Tesar, A.-B. Wang, Enhancement of synthetic jets bymeans of an integrated valve-less pump. Part II. Numerical and experimen-tal studies, Sensors Actuators A (Phys.) 125 (2005) 50.

iographies

rof. Ing. Vaclav Tesar, CSc received his degree in mechanical engineeringn 1963 from Faculty of Mechanical Engineering, Czech Technical Univer-ity (CVUT), Prague, Czech Republic. From 1963 to 1999 he was employedt the Department of Fluid Mechanics and Thermodynamics at CVUT as anssistant, later Docent, and finally Full Professor. He received CSc degree (an

quivalent of PhD) from CVUT Prague in 1972. From 1994 to 1998 he was theead of the Department of Fluid Mechanics and Thermodynamics, Faculty ofechanical Engineering CVUT Prague. In 1985, he was Visiting Professor ateio University, Yokohama, Japan. In 1992 he stayed as Visiting Professor atorthern Illinois University, DeKalb, USA. Between 1999 and 2005 was Profes-

or at the Department of Chemical and Process Engineering, Process Fluidicsroup, the University of Sheffield, UK. Since 2006 is employed at the Insti-

ute of Thermomechanics of the Academy of Sciences of the Czech Republicn Prague. His research interests cover shear flows, in particular jets and wallets and the application of these flows in the no-moving-part fluidics. He isamed as the inventor on 196 Czech Patents, mainly on various fluidic devices.ecently became involved in the new field of microfluidics. He is an authorf 4 textbooks and more than 300 papers in various journals and conferenceroceedings.

ng. Zdenek Travnıcek, CSc received his degree in Mechanical Engineer-ng from the Czech Technical University (CVUT) in Prague in 1985. From985 to 1995 he was employed at the former National Research Institute forachine Design (SVUSS) in Prague-Bechovice. He received his PhD degree

rom CVUT in Prague in 1994. In 1996, he joined the Institute of Thermo-echanics, Academy of Sciences of the Czech Republic. Since 2004, he is

he Head of the Heat/Mass Transfer Laboratory. The most significant staysbroad: Institute of Engineering Thermophysics of the Ukrainian Academy of

ciences (ITTF, Department of Prof. J.P. Dyban), Kiev, Ukraine (1990); Insti-

ute of Applied Mechanics, National Taiwan University, Taipei, Taiwan R.O.C.1998–1999 and 2002–2003); Heat Transfer Laboratory, Johns Hopkins Uni-ersity, Baltimore, USA (2000/2001). His research interests cover experimentaluid mechanics and heat/mass transfer, passive/active thermal flow control (pri-

2 Actua

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20 V. Tesar et al. / Sensors and

arily of jets and wakes), convective heat/mass transfer enhancement, andmpinging jets. He is the author or co-author of 25 journal papers, 62 papers inarious conference proceedings, 38 research reports, and one Patent Certificatef Taiwan, R.O.C.

ozef Kordık is just about to finish his studies and receive his degree in Mechan-cal Engineering from the Czech Technical University (CVUT) in Prague. From006 has been employed on part-time basis at the Institute of Thermomechanics,cademy of Sciences of the Czech Republic. He is already a co-author of four

ontributions to scientific conference proceedings. His interest (and subject of

aoTia

tors A 138 (2007) 213–220

is recent Diploma Thesis) is experimental investigation of unsteady flows andomputer processing of complex experimental data sets.

denek Randa received his degree in Mechanical Engineering from the Czechechnical University (CVUT) in Prague in 1993. From 1993 to 2005 he was an

ssistant lecturer at the Department of Fluid Dynamics and Power Engineeringf Czech Technical University in Prague. In 2005, he joined the Institute ofhermomechanics, Academy of Sciences of the Czech Republic. His research

nterests cover experimental fluid mechanics (impinging jet flows), hot wirenemometry, flow visualization, Particle Image Velocimetry.