An Investigation of Vortex-based Hydropropulsors: Effect of Nozzle Contractility

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ABSTRACTPROPOSAL NO.: CTS-0309672PROPOSAL TYPE: INVESTIGATOR INITIATEDPRINCIPAL INVESTIGATORS: MORTEZA GHARIBINSTITUTION: CALIFORNIA INST. OF TECH.AN INVESTIGATION OF VORTEX-BASED HYDROPROPULSORS: EFFECT OF NOZZLE CONTRACTILITYWhat do jellyfish and the human heart have in common? They both use a simple but reliable method to pump fluid, a process that is the focus of this research program. State-of-the-art experimental hydrodynamics techniques to uncover how these pumping systems are designed by Nature. Such advances will help in detecting malfunctions in these biological systems, potentially leading to earlier diagnosis of certain heart diseases. In addition, the researchers have created computer algorithms to rapidly "evolve" the naturally-occurring designs for use in biologically-inspired machines with specific performance requirements. The relative simplicity of the pulsed jet mechanism and its apparent success in nature suggests serious consideration of these principles for use in man-made systems. Studies of this question to date have relied on experimentation and modeling of a piston ejecting fluid from a rigid cylindrical orifice to generate vortex rings. This paradigm alone is insufficient for understanding the governing processes of vortex formation in biologically relevant cases, due to the paramount importance of wall deformation in their propulsive mechanisms. It is proposed to examine the general case of a wall-contracting vortex generator of arbitrary shape. Experiments will be conducted using a piston-cylinder arrangement with a modified nozzle designed to facilitate time-variation of the orifice exit area. A time-dependent parameter space consisting of piston velocities and orifice exit areas will be interrogated to determine an optimal parameter set for a given cost or fitness function (e.g. maximum thrust, efficiency, etc). The objective is to discover the fundamental physical processes governing thrust generation in variable-area pulsed jet propulsion systems. With this technology, the researchers are aiming to develop new strategies for designing systems ranging from artificial heart valves to advanced underwater vehicle concepts. The research team combines resources from the Aeronautics and Bioengineering departments at Caltech.