A wind tunnel study of the aerodynamic characteristics of a scaled, aeroelastic, model tree

Abstract

Tree crowns, unlike most bluff bodies, are both porous and flexible, so frontal area and crown deflection vary with wind speed. The former leads to aerodynamic force characteristics that vary with frontal area and wind speed while the latter is related to energy transfer between wind and tree. In order to investigate aerodynamic force characteristics and energy transfer, an approach to constructing an aeroelastic model of a tree, which satisfies geometric similarity, dynamic similarity and dimensionless parameters including Froude number, Cauchy number and density ratio, was developed and wind tunnel tests were carried out. The model was designed with eight distinct crown configurations according to different quantities of leaves. Aerodynamic forces, wind speed and frontal area were measured synchronously. The results showed that crown sheltering effects effectively limited mean crown deflection, which limit the mean base overturning moment coefficient. In addition, the energy transfer of the model with different crown configurations were investigated, and the characteristics of energy transfer were identified. It was shown that the crown frequency effectively controls the response via mechanical admittance, which amplified the response at the crown frequency.