Experimental Study of Aerodynamic Damping in Arrays of Vibrating Cantilevers

Cantilever structures vibrating in a fluid are encountered in numerous engineering applications. The aerodynamic loading from a fluid can have a large effect on both the resonance frequency and damping, and has been the subject of numerous studies. The aerodynamic loading on a single beam is altered when multiple beams are configured in an array. In such situations, neighboring beams interact through the fluid and their dynamic behavior is modified. In this work, aerodynamic interactions between neighboring cantilever beams operating near their first resonance mode and vibrating at amplitudes comparable to their widths are experimentally explored. The degree to which two beams become coupled through the fluid is found to be sensitive to vibration amplitude and proximity of neighboring components in the array. The cantilever beams considered are slender piezoelectric fans (approximately 6 cm in length), and are caused to vibrate in-phase and out-of-phase at frequencies near their fundamental resonance values. Aerodynamic damping is expressed in terms of the quality factor for two different array configurations and estimated for both in-phase and out-of-phase conditions. The two array configurations considered are for neighboring fans placed face-to-face and edge-to-edge. It is found that the damping is greatly influenced by proximity of neighboring fans and phase difference. For the face-to-face configuration, a reduction in damping is observed for in-phase vibration, while it is greatly increased for out-of-phase vibration; the opposite effect is seen for the edge-to-edge configuration. The resonance frequencies also show a dependence on the phase difference, but these changes are small compared to those observed for damping. Correlations are developed based on the experimental data which can be used to predict the aerodynamic damping in arrays of vibrating cantilevers. The distance at which the beams no longer interact is quantified for both array configurations. Understanding the fluid interactions between neighboring vibrating beams is essential for predicting the dynamic behavior of such arrays and designing them for practical applications

Numerical Investigation of Flexible Airfoil Aerodynamics

A commercial CFD solver is used to simulate the unsteady aerodynamics performance of rigid and flexible wing airfoils for a high-performance jet trainer aircraft. The configuration used in the computational analysis is NACA 64012. In the numerical simulations the turbulence is modeled by enhancing Spalart-Allmaras turbulence model. To simulate the fluttering motion of the upper surface, an algorithm written in C computer language is integrated with the Fluent. The program controls the oscillation of the upper suction surface to specific defined displacement and the mesh dynamic that adjacent to the moving surface of the airfoil. The numerical experiments for both, rigid and flexible airfoils are carried out at flight speed of 85 m/s and angle of attack from zero to 18 degree. In order to verify the results of numerical simulation, the solver is validated against prior experiment of a lift coefficient. In comparison between rigid and flexible airfoils, the aerodynamic forces produced by a flexible airfoil shows that the lift coefficient is increased by 10% for angle of attack ranging from the incidence degree to 10 degree and then decreased slightly till the stall angle located at 16 degree. The flow separation in rigid airfoil is predicted at 7.5% of airfoil chord, whereas in the flexible airfoil it is at 59% of the airfoil chord