Mechanical Engineering ETDs

Publication Date

2003

Abstract

The ''snapshot" proper orthogonal decomposition (POD) was used to analyze the turbulent characteristics of a plane mixing layer. A two-dimensional (2-D) Hartmann wavefront sensor measured optical tilt propagation through a flow field downstream of a splitter plate. The velocity difference across the splitter plate produced roller vortices via the Kelvin-Helmholtz instability. Refractive-index fluctuations were produced by slightly heating the flow on the low-speed side of the splitter plate. The Hartmann sensor detects gradients in refractive index (and thus temperature) in directions perpendicular to its direction of propagation. The measured field of two-dimensional tilt (or optical deflection) is proportional to the gradient integrated along the path from the laser diode source, through the mixing layer, and onto the receiving optics. The flow was generated upstream in a suction tunnel to produce a velocity differential across the splitter plate. Small temperature differences enabled the sensor to capture fluctuations within the mixing layer resulting from large-scale turbulent structure. An ensemble of 2000 measurements (or snapshots) acquired at 30 Hz was subjected to POD analysis to identify turbulent structures within the mixing layer.

The POD results show that the most energetic tilt fields can be represented by relatively few eigenmodes. Eight POD modes capture nearly 77% of the energy within 600 of 2000 snapshots. The tilt fields characteristic of these dominant modes can be related to the large-scale turbulent structure in agreement with an earlier analysis based on conditional averages.

Degree Name

Mechanical Engineering

Level of Degree

Masters

Department Name

Mechanical Engineering

First Committee Member (Chair)

C. Randall Turner

Second Committee Member

Marc S. Ingber

Third Committee Member

Illegible

Document Type

Thesis

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