Micromachined synthetic jet actuators and applications thereof

Details Micromachined synthetic jet actuators and applications thereof Micromachined synthetic jet actuators and applications thereof

1997-11-13

2002-10-01

Scherbel, David A. (Department: 3752)

Fluid sprinkling, spraying, and diffusing

Processes

Vibratory or magneto-strictive projecting

C239S102200

Reexamination Certificate

active

06457654

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to fluid control devices and, more particularly, to micromachined synthetic jet actuators for controlling fluid flows though creation of a synthetic jet stream to interact with the fluid flow.
BACKGROUND OF THE INVENTION
The ability to manipulate and control the evolution of shear flows has tremendous potential for influencing system performance in diverse technological applications, including: mixing and combustion processes, lift and drag of aerodynamic surfaces, and thrust management. That these flows are dominated by the dynamics of a hierarchy of vortical structures, evolving as a result of inherent hydrodynamic instabilities (e.g., Ho & Huerre, 1984), suggests control strategies based on manipulation of these instabilities by the introduction of small disturbances at the flow boundary. A given shear flow is typically extremely receptive to disturbances within a limited frequency band and, as a result, these disturbances are rapidly amplified and can lead to substantial modification of the base flow and the performance of the system in which it is employed.
There is no question that suitable actuators having fast dynamic response and relatively low power consumption are the foundation of any scheme for the manipulation and control of shear flows. Most frequently, actuators have had mechanically moving, parts which come in direct contact with the flow [e.g., vibrating ribbons (Schubauer & Skramstad
J. Aero Sci.
14 1947), movable flaps (Oster & Wygnanski, 1982), or electromagnetic elements (Betzig
AIAA,
1981)]. This class of direct-contact actuators also includes piezoelectric actuators, the effectiveness of which has been demonstrated in flat plate boundary layers (Wehrmann 1967, and Jacobson & Reynolds
Stan. U. TF
-64 1995), wakes (Wehrmann
Phys. Fl.
8 1965, 1967, and Berger
Phys. Fl. S
191 1967), and jets (Wiltse & Glezer 1993). Actuation can also be effected indirectly (and, in principle, remotely) either through pressure fluctuations [e.g., acoustic excitation (Crow & Champagne
JFM
48 1971)] or body forces [e.g., heating (Liepmann et al. 1982, Corke & Mangano
JFM
209 1989, Nygaard and Glezer 1991), or electromagnetically (Brown and Nosenchuck,
AIAA
1995)].
Flow control strategies that are accomplished without direct contact between the actuator and the embedding flow are extremely attractive because the actuators can be conformally and nonintrusively mounted on or below the flow boundary (and thus can be better protected than conventional mechanical actuators). However, unless these actuators can be placed near points of receptivity within the flow, their effectiveness degrades substantially with decreasing power input. This shortcoming can be overcome by using fluidic actuators where control is effected intrusively using flow injection (jets) or suction at the boundary. Although these actuators are inherently intrusive, they share most of the attributes of indirect actuators in that they can be placed within the flow boundary and require only an orifice to communicate with the external flow. Fluidic actuators that perform a variety of “analog” (e.g., proportional fluidic amplifier) and “digital” (e.g., flip-flop) throttling and control functions without moving mechanical parts by using control jets to affect a primary jet within an enclosed cavity have been studied since the late 1950's (Joyce,
HDL
-
SR
1983). Some of these concepts have also been used in open flow systems. Viets (
AIAA J.
13 1975) induced spontaneous oscillations in a free rectangular jet by exploiting the concept of a flip-flop actuator and more recently, Raman and Cornelius (
AIAA J.
33 1995) used two such jets to impose time harmonic oscillations in a larger jet by direct impingement.
More recently, a number of workers have recognized the potential for MEMS (micro electro mechanical systems) actuators in flow control applications for large scale systems and have exploited these devices in a variety of configurations. One of a number of examples of work in this area is that of Ho and his co-investigators (e.g., Liu, Tsao, Tai, and Ho, 1994) who have used MEMS versions of ‘flaps’ to effect flow control. These investigators have opted to modify the distribution of streamwise vorticity on a delta wing and thus the aerodynamic rolling moment about the longitudinal axis of the aircraft.
BACKGROUND TECHNOLOGY FOR SYNTHETIC JETS
It was discovered at least as early as 1950 that if one uses a chamber bounded on one end by an acoustic wave generating device and bounded on the other end by a rigid wall with a small orifice, that when acoustic waves are emitted at high enough frequency and amplitude from the generator, a jet of air that emanates from the orifice outward from the chamber can be produced. See, for example, Ingard and Labate,
Acoustic Circulation Effects and the Nonlinear Impedance of Orifices,
The Journal of the Acoustical Society of America, March, 1950. The jet is comprised of a train of vortical air puffs that are formed at the orifice at the generator's frequency.
The concern of scientists at that time was only with the relationship between the impedance of the orifice and the “circulation” (i.e., the vortical puffs, or vortex rings) created at the orifice. There was no suggestion to combine or operate the apparatus with another fluid stream in order to modify the flow of that stream (e.g., its direction). Furthermore, there was no suggestion that following the ejection of each vortical puff, a momentary air stream of “make up” air of equal mass is drawn back into the chamber and that, as a result, the jet is effectively synthesized from the air outside of the chamber and the net mass flux out of the chamber is zero. There was also no suggestion that such an apparatus could be used in such a way as to create a fluid flow within a bounded (or sealed) volume.
Such uses and combinations were not only not suggested at that time, but also have not been suggested by any of the ensuing work in the art. So, even though a crude synthetic jet was known to exist, applications to common problems associated with other fluid flows or with lack of fluid flow in bounded volumes were not even imagined, much less suggested. Evidence of this is the persistence of certain problems in various fields which have yet to be solved effectively.
Vectoring of a Fluid Flow
Until now, the direction of a fluid jet has chiefly been controlled by mechanical apparatus which protrude into a jet flow and deflect it in a desired direction. For example, aircraft engines often use mechanical protrusions disposed in jet exhaust in order to vector the fluid flow out of the exhaust nozzle. These mechanical protrusions used to vector flow usually require complex and powerful actuators to move them. Such machinery often exceeds space constraints and often has a prohibitively high weight. Furthermore, in cases like that of jet exhaust, the mechanism protruding into the flow must withstand very high temperatures. In addition, large power inputs are generally required in order to intrude into the flow and change its direction. For all these reasons, it would be more desirable to vector the flow with little or no direct intrusion into the flow. As a result, several less intrusive means have been developed.
Jet vectoring can be achieved without active actuation using the coanda effect, or the attachment of a jet to a curved (solid) surface which is an extension one of the nozzle walls (Newman, B. G. “The Deflexion of Plane Jets by Adjacent Boundaries-Coanda Effect,”
Boundary Layer and Flow Control
v. 1, 1961 edited by Lachmann, G. V. pp. 232-265.). However, for a given jet momentum, the effect is apparently limited by the characteristic radius of the curved surface. The effectiveness of a coanda surface can be enhanced using a counter current flow between an external coanda surface and a primary jet. Such a system has been used to effect thrust vectoring in low-speed and high-speed jets by Strykowski et al. (Strykow

Affiliated with

Also associated with

Rating

Micromachined synthetic jet actuators and applications thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Micromachined synthetic jet actuators and applications thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Micromachined synthetic jet actuators and applications thereof will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2955395