Abstract-
This talk will describe studies on the actively controlled gas jet injected
transversely into crossflow, also known as the transverse jet. The transverse
jet has widespread technological applications, ranging from dilution and fuel
jet injection in gas turbine engines to thrust vector control systems for high
speed aerospace vehicles. In our experimental studies, the dynamics of the jet
actuation system are measured, characterized, and modeled, allowing a dynamic
compensator or feedforward controller to be developed which permits the jet to
be forced in a more precisely prescribed manner. Use of the controller allows
for straightforward comparisons to be made among different conditions for jet
excitation. Clear identification can be made of specific excitation frequencies
and characteristic temporal pulse widths which optimize transverse jet
penetration and spread through the formation of distinct, deeply-penetrating
vortex structures. Exploration of these optimal forcing conditions has led to
a fundamental examination of the transverse jet's nearfield shear layer
instabilities. Unusual features of these instabilities, whereby transition
from convective to absolute instability can occur under specific conditions,
indicate the potential for future directions in the application of jet control.
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