Feasibility Study of Obtaining Oscillatory Airfoil Control Using a Bump

Michal Raviv Sayag
Work towards M.Sc. degree under the supervision of Prof. O. Rand, Prof. R. Arieli and Dr. Y. Elimelech
Faculty of Aerospace Engineering
Technion – Israel Institute of Technology

This study aims at investigating the feasibility to control aerodynamic characteristics of a lifting surface using an oscillating bump. The bump is obtained through a flexible membrane patch placed on the airfoil surface and inflated periodically by pneumatic pressure. This simple device can be easily implemented on a range of small air vehicles flying at low Reynolds numbers. The main two advantages of the suggested method are: Eliminating the need for complex mechanisms, and avoiding large hinge moments usually required for deflecting a control device.

To examine the feasibility of such a device, the study was conducted using two techniques: Numerical simulations, and water tunnel experimental tests. The numerical study included simulations of a bump located on a flat plate, subjected to laminar incompressible flow. The bump, with a maximum height of one percent chord, was inflated from a flat form to a parabolic arc shape and back. The bump was activated in a sinusoidal mode at various frequencies. The unsteady flow field and aerodynamic coefficients were examined in the range of  0 < St < 2 and Re = 2,500 based on bump chord and freestream velocity. To validate the calculated results, a series of experiments were conducted at the Technion water tunnel. A visualization of the flow behind the oscillating bump was conducted using diluted paint, and flow structures were filmed and compared with calculations.

Results showed a good agreement between numerical predictions and experimental results at low frequency while significant interference with the flow was observed at high frequencies.

The numerical results show that the flow surrounding the bump is highly influenced by the oscillation frequency. For example, a bump fluctuating at a frequency of 1Hz generated a maximal increase in lift coefficient of approximately 0.3.  Hysteresis of the aerodynamic coefficients and flow separation patterns were found even at low frequencies.

The talk will be given in Hebrew

Mon, 26-05-2014, 16:30 (Gathering at 16:00)

Classroom, ground floor, Library, Aerospace Eng.

Light refreshments will be served before the lecture

Feasibility Study of Obtaining Oscillatory Airfoil Control Using a Bump