Date of Award

Fall 2006

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Osama A. Kandil

Committee Member

Oktay Baysal

Call Number for Print

Special Collections; LD4331.E535 D36 2006

Abstract

Flow separation over lifting aerodynamic components, such as airfoils and wings, occurs during stall conditions which are caused by adverse changes (i.e.; high angle of attack, inflow conditions, etc.) in the operating conditions of aerodynamic components. During stall conditions, the flow over airfoil loses its momentum, creating high pressure zones on the upper surface of the airfoil and even a small increase in pressure causes the fluid particles to stop and separate to a low pressure zone. In order to eliminate the flow separation, the low momentum flow should be removed in order to maintain the high momentum and low pressure zones over the airfoil.

The present study is conducted to investigate the performance limitations of synchronized, alternating-angle direction, oscillatory (SAADO) synthetic jets for high angles of attack. It also introduces the concept of multiple frequency application of SAADO jets for flow control for a NACA 0012 airfoil at post-stall conditions. The synthetic jet is designed such that the jet direction angle changes its sign during suction and blowing phases of the oscillation cycle of diaphragm. The diaphragm oscillation isdriven using the fundamental frequency of the separated flow which is found by computationally sensing the separated flow at points downstream of the separation location and using a Fast Fourier Transform (FFT) analysis to obtain it. Single and double synthetic jets are located at control ports which are placed at the leading edge and at the middle of the airfoil upper surface, respectively. The effect of the locations and the operation sequence of synthetic jets, direction angle for suction and blowing phases, driving frequency, phase angle and maximum amplitude for the controllers are investigated. After obtaining the optimum combination of flow control parameters, the concept of multi-frequency flow control is introduced. It is based on adding a second sinusoidal function to mass flow rate of the SAADO synthetic jets, to overcome the adverse effects of the flow.

Computational results showed that the performance of SAADO synthetic jets is better for a variety of cases. Multiple frequency flow control applications increased the C1/CD ratio to remarkable values and results indicate that it appears to be promising.

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DOI

10.25777/bwj5-8412

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