Michael
P. Hallberg
Research Interests
-jet stability, global modes, absolute instability, open-loop control, computational fluid dynamics, cosmology
Publications
"Open-loop control of fully nonlinear self-excited oscillations." In Physics of Fluids.
"Suppression of global modes in low-density axisymmetric jets using coflow." In Physics of Fluids.
"On the universality of global modes in low-density axisymmetric jets." In Journal of Fluid Mech.
"Stability and control of very low density axisymmetric jets." AIAA-2006-3704 from the 3rd AIAA Flow Control Conference.
Research
I am currently a Ph.D. candidate in mechanical engineering at the University of Minnesota.
I work in the Shear Flow Control Lab under the direction of Prof. P.J. Strykowski.
I was funded under a grant from the National Science Foundation with the goal of recreating certain critical elements of a plasma jet using room temperature gasses. Plasma jets are created by sending a gas through a nozzle in the presence of a high-energy spark that heats the gas to very high temperatures (>10000K). Plasma jets are generally used to coat surfaces (such as turbine blades) with very hard materials (such as ceramic) in a process called plasma spraying. The extreme environment of the plasma creates a jet that mixes very rapidly while at the same time being extremely difficult to interrogate. If the plasma can be recreated using gases at room temperature, several diagnostic techniques can be used to shed light on the underlying fluid mechanics in hopes of reducing mixing - thereby creating a better plasma spray.
The work was quite successful on a fundamental level and allowed us to shed new light on instabilities inherent to low density flows. In short we have shown that certain features of the global mode in a low-density jet can be predicted very accurately using conditions at the exit of the jet. Recent nonlinear theoretical work (from people such as J-M Chomaz, P. Huerre, B. Pier among others) based on parallel wakes reveal a remarkable connection between the nonlinear evolution of the flow and the underlying linear stability. This theory is well tested in the parallel wake and provides an answer to the long-studied question of singing wires first investigated more than a century ago by V. Strouhal. However, extension to real wake flows (nonparallel) has been somewhat less convincing. The present work provides evidence that the same theoretical underpinnings may apply to the low-density jet; which is possibly a better candidate due to the very nearly parallel nature near the nozzle exit.
University of Minnesota
Mechanical Engineering
ME162
612-625-8058
Last modified: 8/13/08