Much of my research has focused on analyzing the replicating the locomotion of jellyfish, squid, octopuses, and other cephalopods. These animals propel themselves with a form of unsteady jet propulsion which is fundamentally different from continuous jetting used in recreational watercraft. Unlike continuous jet flows, the thrust generated by expelling unsteady jets is heavily dependent on vortex ring formation.
Characterizing these complex dynamics required fluid velocity measurement techniques like digital particle velocimetry (DPIV), laser doppler velocimetry, and more qualitative flow visualization practices. I have not only developed an expertise on these experimental techniques, but I have designed and constructed large scale measurement equipment like the 700 gal jet flow visualization tank shown on the right.
In order to explain discrepancies between measured forces of unsteady jetting (both in squid and engineered systems) and momentum transfer calculations, I developed higher accuracy analytical models. Starting from governing principles I derived the evolution of circulation, impulse, and energy in jets from domain boundary kinematics, yielding notable results,
- The increased thrust (or overpressure) in unsteady jets can be explained by a radial velocity gradient induced by vortex ring formation at the nozzle
- Thruster performance at high frequencies is degraded for high stroke ratio jets due to trailing wake re-ingestion.
In addition, I developed a model for pressure inside jetting bodies in order to model/predict work required to generate propulsion. The modeling relates surface pressures to evolution of circulation in the jet-cavity system. The advantage of this type of modeling is that unsteady pressure dynamics can be predicted in terms of the 4 types of vorticity sources that I identified in the cavity-jet system. Through this analysis I have shown that,
- There are 4 unique vorticity generation mechanisms in cavity-jet systems
- Impulsive jet flows (those with fast increase in jet velocity from rest) actuall require less energy to generate
I have created a movie to illustrate this relationship between pressure and circulation dynamics, which is included in my Video Gallery for the interested viewer.