Publication Date

2014-06-03

Availability

Open access

Embargo Period

2014-06-02

Degree Name

Master of Science (MS)

Department

Mechanical Engineering (Engineering)

Date of Defense

2014-04-04

First Committee Member

GeCheng Zha

Second Committee Member

Amir Rahmani

Third Committee Member

Hongtan Liu

Fourth Committee Member

Mike Brown

Abstract

The work presented in this thesis includes a detailed study of passive jet flow control as applied to an automotive side-view mirror. Numerical analysis as well as experimental prototype tests are conducted on three models of mirrors: one baseline model and two others with variable jet strength. An open inlet draws a certain amount of flow, passes it through a converging duct, and exhausts the flow as a jet with an angle toward the center of the mirror. The jet forms a boat-tail effect that entrains high energy flow from the free stream to the base area, increasing the base pressure, and reducing the base drag. Throughout this thesis, drag reduction compared to the conventional automotive mirror is proven and detailed through computational fluid dynamics (CFD) simulation validated with wind tunnel experiments. The CFD algorithm employed is high order large eddy simulation (LES) and the code is produced by the CFD research group at the University of Miami. The jet 1 model has an inlet area that is 10% of the base area and is shown to have a drag decrease of 29.41% in CFD. In the jet 2 model, which has a four times larger inlet, we see a 40.91% drag decrease in CFD. This drag decrease is primarily due to wake reduction. The jet is observed as pulsing into the base area. The jet pulsation on the mid vertical and horizontal plane has a phase lag. The pulsing jet introduces coherent structures that enhance the entrainment of the main flow to the base area. An interesting phenomenon is observed that the jet generates negative entropy, which means the jet is energized by the free stream. The passive flow control is thus similar to an active jet flow control in this way. The mechanism of the negative entropy is not fully understood yet at this stage; more study are needed. The following are some task that warrant investigation: LES with refined grid to resolve the wake better in order to match the experimental PIV measurements, study the effect of different jet flow angle, study the inlet and outlet ratio effect on the mixing and entrainment, and scaling for the drag reduction with the geometric parameters.

Keywords

Mirror; Aerodynamics; Automotive Engineering; Mechanical Engineering; Turbulent Flow; Base Flow

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