Date of Award

Spring 5-13-2017

Level of Access

Campus-Only Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Advisor

Xudong Zheng

Second Committee Member

Zhihe Jin

Third Committee Member

Wilhelm Friess

Additional Committee Members

Mohsen Shahinpoor

Abstract

Impulsively started, low-speed, incompressible jets observed in nature, are commonly found as starting flows through a moving valve. Similar flows are found in the human heart where blood is transported from the left atrium, through the mitral valve, and into the left ventricle. During this process, a vortex is formed around the lip of the moving valve before propagating into the left ventricle. We use a sharp-interfaced, immersed boundary method based, CFD solver to run a series of numerical simulations to investigate the vortex dynamics of starting flows through an axisymmetric nozzle with time varying exit geometry. The incompressible fluid field, contained within a cylindrical tank, is subjected to a temporally specified volumetric flow rate, held at the nozzle inlet, while the nozzle is treated as a rigid body with motion independent of fluid forces. We show that nozzle motion affects both vortex formation time and pinch-off time, as well as the size, circulation, and energy associated with the leading vortex ring. By parametrically ranging over a variety of prescribed flow rates and exit diameter frequencies, the independent contributions of the nozzle motion on the developing vortex structures and the distinctive characteristics of their formation processes are presented and subsequently assessed.

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