Date of Award

Summer 2005

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

Committee Member

Chuh Mei

Call Number for Print

Special Collections; LD4331.E535 K36 2005

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 closed-loop active flow control using SAADO synthetic jets 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 is driven 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, double and triple synthetic jets are located at control ports which are placed at leading edge, middle and trailing edge 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 closed-loop flow control is introduced. It is based on computational sensing of separated flow at discrete times and at the control ports, using FFT analysis to obtain the corresponding fundamental frequency and applying the new frequency to the corresponding SAADO synthetic jet. Five schemes were introduced to apply the closed-loop flow control. It is investigated for the purpose of adaptation of the flow control to varying flow conditions.

Computational results showed that the performance of SAADO synthetic jets is even better and they are also applicable for high angle of attack. Closed-loop flow control applications increased the average lift coefficient to remarkable values and results indicated that it appears to be promising.

Rights

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

DOI

10.25777/fsvf-d137

Share

COinS