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Fluid/Structure Interaction

Fluid/structure interaction can be applied to different areas, our current research is motivated by out interests in MAVs.  As MAVs reduce the size, they can operate with lower stalling speeds, defined as the minimum speed at which sufficient lift is produced for flight. However, the correspondingly low Reynolds number degrades the aerodynamic performance, such as the lift-to-drag ratio. Furthermore, the vehicle becomes more sensitive to the wind effect, considering the wind speed can often be comparable to the flight speed. It has been demonstrated that flexible membrane wings are appropriate for the MAVs  because they can adapt their shapes in response to the flight environment, and the stalling margin can be extended because of such a passive control capability.

 

   

    Membrane wing MAV              Lift coefficient vs AoA                          Lift-to-drag ratio vs AoA


Unlike a rigid wing, a membrane wing exhibits self-initiated unsteady response even in a steady state freestream. Such response and associated shape changes affect the wing aerodynamics, which in turn affect the membrane dynamics, resulting in a fluid-and-structure interaction problem. Through the interaction with its surrounding flow, an aeroelastic flexible wing is capable of delaying the stall angle and adapting to the flow environment to stabilize the vehicle under gusty conditions. Our research has shown that a flexible wing can enhance the lift by increasing the wing camber. Further study shows that the flexible wing vibration energizes the separated flow and prompts laminar-to-turbulent transition. This eventually leads to the flow reattachment and better aerodynamic performance. Evidences show that both fixed wings and flapping wings can benefit from flexible structure.

 

 

                    The flexible wing shows reduced effective AoA

 

Other applications include the interaction between the cardiovascular vessel/oral airway with its internal flow. The phenomena are governed by complex fluid/structure interactions within short, curved, branching, elastic tubes that undergo lateral dynamic motions while interacting with propagating and reflecting pressure waves. These interactions often underlie the vessel’s biological function or dysfunction, and can cause nonlinear pressure-drop or flow rate relations. Moreover, the internal flow can undergo all flow regimes, from laminar to fully turbulence. And transitional and turbulent flows are intrinsically related to endothelial cell injury and the origin of vascular disease. Understanding the nature of these phenomena is challenging because it involves unsteady transitional flow, large deformation, and complex three dimensional motion.

 

Click here for the simulation of tandem wings in synchronized motion


References

Lian, Y., Shyy, W., Viieru, D., and Zhang, B. N., "Membrane Wing Aerodynamics for Micro Air Vehicles," Progress in Aerospace Sciences, Vol. 39, 2003, pp. 425-465.

 

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