Aerodynamic Flow Control Using Synthetic
Jet Actuators
by
Ari Glezer, Ph.D.
Professor, Woodruff School of Mechanical Engineering
Georgia Institute of Technology
Atlanta, GA 30332
Wednesday, April 21, 1999
1:25 - 2:15 p.m.
Room 102 ME
Broadcast on UNITE Channel B
Coffee will be available in 152 ME following the seminar
A novel approach to manipulation and control
of shear flows using surface fluidic actuators based on synthetic
jet technology will be discussed. Synthetic jets are zero-mass-flux
in nature and are synthesized from the working fluid in the flow
system in which they are embedded. Although there is no net mass
injection, the jets enable momentum transfer into the flow system
to be controlled. Thus the interaction of a synthetic jet with
an embedding flow near the flow surface from results in formation
of closed recirculating regions and in an apparent modification
of the surface shape. These attributes enable synthetic-jet control
systems to effect significant global modification of embedding
flows on scales that are one to two orders of magnitude larger
than the characteristic length scale of the jets. While conventional
excitation methods have been limited to frequency bands tailored
to the linear receptivity mechanisms of a given flow, fluidic
actuation facilitates exploitation of nonlinear mechanisms for
amplification of disturbances in a very broad frequency band.
Several applications of fluidic technology based on synthetic
jets will be presented, including jet mixing and thrust management,
and modification of aerodynamic surfaces.
The interaction of the jets with a cross flow
results in an apparent modification of the surface shape and is
exploited for dynamic control of flow reattachment and separation
over a thick airfoil. Without control, the airfoil stalls at a
= 50. With control, fully attached flow can be achieved up to
a = 150 and partial reattachment and recovery of lift can be achieved
up to the maximum angle tested, a = 250. Both the location and
the strength of the control input affect the extent of the reattached
flow. Dramatic increases in lift and decreases in pressure drag
are observed as a result of the reattached flow, and the present
work has indicated that control can be achieved up to the maximum
Reynolds number tested (Rec = 800,000). The response of the flow
to time-modulated control input is measured in the cross stream
plane of the airfoil wake using phase-locked two-component hot-wire
anemometry at a = 150 (Rec =310,000), for which the uncontrolled
flow is separated and the dimensionless (natural) shedding frequency
is F+ = 0.7. Control is effected using jet formation frequencies
that are either well above (F+ = 10) or of the same order (F+
= 0.9) as the natural shedding frequency. For both frequencies,
the collapse of the separated flow region is associated with a
strong momentary reduction in lift that is marked by the formation
and shedding of a vortex having vorticity of the same sense as
on the top (suction) surface. The subsequent recovery is accompanied
by the shedding of a stronger, opposite sign vortex ultimately
leading to a substantial increase in the mean lift (and a corresponding
reduction in pressure drag) which is approximately the same for
both actuation frequencies. However, while at F+=10 the shedding
of organized vortical structures subsides following the initial
transient, actuation at F+ = 0.9 leads to a time-periodic shedding
of a train of vortices (at the actuation frequency) that correspond
to (peak to peak) lift coefficient fluctuations of up to 50% of
the mean.
Ari Glezer is a Professor of Fluid Mechanics
in the George W. Woodruff School of Mechanical Engineering at
Georgia Institute of Technology where he moved in 1992 from the
Aerospace and Mechanical Engineering Department at the University
of Arizona. Professor Glezer received his B.S. degree in Aeronautics
from Tel Aviv University in 1974 and his M.S. and Ph.D. degrees
in Aeronautics (Fluid Mechanics) from the California Institute
of Technology in 1975 and 1981, respectively. Professor Glezer's
research interests are in the area of flow manipulation and control
including aerodynamic performance, mixing processes, fluidic-driven
heat transfer with emphasis on electronic cooling, thrust vectoring
and jet noise, and the development of novel fluidic actuators.
Informal Faculty Luncheon: Wednesday, April 21,
1999, 11:45 am, Room 404, Campus Club. Prof. Glezer will be able
to attend.
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