Abstract
This work, through a series of forced-vibration wind tunnel experiments, investigates the aerodynamic characteristics of square prisms subject to the transverse inclination. An aeroelastic prism was tested under different wind speeds, inclination angles, and oscillation amplitudes. Through analysis on the mean pressure distribution, local force coefficient, force spectra, and aerodynamic damping coefficient, the unsteady aerodynamic characteristics of the configuration were revealed. Empirical observations discovered the Base Intensification phenomenon, which refers to a fundamental change in the structure’s aerodynamic behaviors given any degrees of transverse inclination. Specifically, it is the intensification of the aerodynamic loading, vortical activities, and aerodynamic damping on only the lower portion of an inclined structure. The phenomenon, being almost impactless to the upper portion, is also insensitive to changes in inclination angle and tip amplitude once triggered by the initial inclination. Analysis also revealed that the origin of Base Intensification phenomenon traces back to fix-end three-dimensional effects like the horseshoe vortex, instead of the predominant Bérnard-Kármán vortex shedding. Moreover, results showed that wind speed is the decisive factor for the structure’s crosswind motions. Inside the lock-in region, structure loadings, vortical activities, and the effects of Base Intensification are significantly amplified. Beyond the range, the configuration gradually resorts to a quasi-steady linearity. Finally, results from the force-vibration tests were used for the prediction of structure response. Experimental comparison revealed that the predictions notably outperform those based on rigid tests, forecasting the actual responses with a markedly improved accuracy.
Unsteady aerodynamic characteristics of a bionic flapping wing in three-dimensional composite motion
