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Hamid Johari
Mechanical Engineering Department
Worcester Polytechnic Institute
Effects of Unsteadiness on Turbulent Shear
Flows
Abstract
Various research efforts in the past two decades have established that
imposed unsteadiness may have a tremendous effect on the structure, mixing,
and combustion of turbulent shear flows. In this talk, three different flow
fields that are affected by unsteadiness will be briefly explored. The first
two concern the pulsing of jets used for combustion and separation control,
respectively. The characteristics of fully modulated fuel jets, where the
flow is completely shut-off during the pulsing cycle, vary from that
associated with individual burning puffs to a steady jet flame. The key
parameters in this problem are the aspect ratio of the injected fuel slug
and the duty-cycle of the pulse train. The second flow field of interest is
that of surface mounted vortex generator jets used for separation control,
specifically in low-pressure turbine applications. Pulsing of vortex
generator jets alters the flow structure and allows deeper penetration of
the jet into the boundary layer, thus resulting in significantly improved
performance of such jets. The last case is that of a parachute canopy during
terminal descent. Here, the effects of unsteadiness are a result of the
fluid-structure interaction between the vortical flow in the near wake and
the flexible canopy fabric. The movement of canopy skirt modifies the
vortical structure in the near wake and the shedding frequency.
Biosketch
Hamid Johari is a Professor of Mechanical Engineering and a member of the
Aerospace Engineering Program at Worcester Polytechnic Institute. He earned
his B.S. in Engineering and Applied Science from the California Institute of
Technology in 1983, and his M.S. and Ph.D. in Aeronautics from the
University of Washington in 1985 and 1989, respectively. His primary field
of research is experimental fluid mechanics, with emphasis on turbulent
mixing, unsteady and vortex-dominated flows, and non-intrusive diagnostics.
His research projects have been funded by ARO, NASA, NSF, Sea Grant and
industrial partners. Professor Johari is a Fellow of ASME, an Associate
Fellow of AIAA, and a member of APS. He currently serves as an Associate
Editor for the ASME Journal of Fluids Engineering. His teaching interests
are in the areas of thermal-fluid sciences, propulsion and turbulence. He
received the Ralph R. Teetor Educational Award from SAE in 1999.
Tuesday, June 8, 2004
Bourns Hall, Room A265
10:10 a.m.-11:00 a.m.
(Refreshments will be served at 10:00 a.m.) |
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