Abdul Aziz, Mohd Sharizal
(2012)
Numerical And Experimental Investigations Of 2d Membrane Airfoil Performance.
Masters thesis, Universiti Sains Malaysia.
Abstract
The characteristic feature of a mammalian flight is the use of thin compliant
wings as the lifting surface. This unique feature of flexible membrane wings found in
flying mammals such as bats and flying squirrel was studied in order to explore its
possibility as flexible membrane wings in aerodynamics performance study. The
unsteady aspects of the fluid-structure interaction of membrane wings are very
complicated and therefore did not receive much attention compared to the rigid wing.
Motivated by this, a membrane airfoil consisting of latex sheet mounted on a NACA
643-218 airfoil frame was developed to study effect of membrane flexibility on
laminar separation bubble (LSB), effects of membrane thickness, Reynolds number
(Re), and membrane rigidity on the aerodynamic performance (lift and drag), meant
for low Re applications. Unsteady, two dimensional (2D) simulations were also
carried out on rigid and membrane airfoils with the air flow modeled as Laminar and
the turbulent cases being modeled using Spalart-Allmaras viscous model. FLUENT
6.3 was employed to study the fluid flow behavior, whereas ABAQUS 6.8-1 was
utilized as structural solver, both of which were coupled in real time using the
MpCCI 3.1 software. It has been established that, the LSB is greatly influenced by
the membrane flexibility, and the membrane airfoil has superior flow separation
characteristics over rigid one. Besides that, the effects of skin thickness and Re on
the aerodynamic performance are investigated. In general, it was observed that, as
the membrane thickness decreases, the lift increases and drag decreases, thereby
improving the aerodynamic performance; with similar observation reported for the
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case with increase in Re. Moreover, using experiment, the studies on the effect of
ribs on aerodynamic performances were also presented. The results showed that the
rigidity of the membrane skins could significantly affect the performance of the
membrane airfoils; as the number of rigid ribs decreases, the lift increases and drag
decreases. Finally, the displacement and stress of membrane airfoil with incoming
flow has been studied by simulation technique. It was found that the membrane
airfoils have deformed by the incoming flow and the Von Mises stress was found
fluctuating around the membrane airfoil. The current simulation techniques were also
validated by suitable wind tunnel experiments and close agreement was obtained.
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