Publication Date

2014-08-11

Availability

Open access

Embargo Period

2014-08-11

Degree Name

Master of Science (MS)

Department

Mechanical Engineering (Engineering)

Date of Defense

2014-06-26

First Committee Member

Gecheng Zha

Second Committee Member

Na Li

Third Committee Member

Wangda Zuo

Abstract

This study is focused on the experimental investigation of an extended rear view mirror and the development of near-wake flow in an effort to reduce the overall base pressure drag of the model. The passive flow control technique was employed through a circumferential slot of the rearward facing edge of a bluff body to deliver a passive jet in the direction of the free stream. The passive jet employs the surrounding high energy free stream air through an intake slot in the front of the model in order to enhance the mixing layer of the immediate wake region in addition to energizing the wake area flow through entrainment. These effects subsequently caused a reduction of the effects of adverse pressure gradients that are associated with separation of the free stream shear layer over the over the passive jet model surface. The jet produced along the rear surface not only increased the turbulence of the mixing layer, but can also be directly tied to the coherent nature of the wake area flow. Using Two Dimensional Two Component (2D2C) in addition to Two Dimensional Three component (2D3C) Particle Image Velocimetry applied to our model in an open circuit wind tunnel, results show a substantial reduction in the overall wake area for which we attribute to the enhancements due to mixing effects of the passive jet interacting with the free stream shear layer. Flow entrainment from enhanced vorticity through the production coherent structures are believed to initiate the mixing layer earlier, in addition to increase the growth rate of the mixing layer while also attributing to the increase in the overall shear layer thickness as well. Particle Image Velocimetry (PIV) was carried out on an automobile mirror model with three configurations in order to investigate the effects of a baseline model including the absence of a passive jet mixing, a modified model including a small area circumferential jet and a heavily modified model including a large circumferential slot area jet. In combination with PIV, Partial Orthogonal Decomposition (POD) also referred to as the Karhunen Loeve expansion, was also applied in order to analyze the underlying large scale structures and dominant behaviors that would otherwise be hard to identify in the immediate wake flow structure. The mirror models used for testing was designed and produced to provide three specific testing configurations, baseline, Jet 1 and Jet 2. In order to proceed with the testing of the mirror models, the design and manufacturing of a reinforced force balance mounting apparatus was necessary in order to provide a more rigid and secure platform to measure aerodynamic loads of the mirror and future designs. The nature of the new design includes multiple support location in order to more equally distribute the loading in addition to bearings to assist in experiments that require a rotation of the model in order to increase the angle with respect to the free steam flow.

Keywords

Passive Flow Control, Bluff Body, Drag Reduction, Automotive Mirror, Particle Image Velocimetry

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