一様流中の一方向吊屋根の自励振動についての風洞実験

Abstract

Characteristics of the responses of elastic one-way type suspension roof models and characteristics of the fluctuating pressures on the corresponding rigid roof models in a smooth flow have been examined by wind tunnel tests. Main findings are : 1) The internal volume much influences dynamic properties of elastic models. Symmetric mode oscillations, which need change of the internal volume, do not occur to models with the internal volume V_i =25×25×80 cm^3. 2) Suspension roofs in the smooth flow do exhibit self-excited oscillations. Model A, both in the cases of V_i =∞ and V_i〓∞, has exhibited self-excited oscillation in the anti-symmetric first mode in the flow velocity range U_h/f_2L〓1.1, where U_h is the flow velocity at the wall height, f_2 the natural frequency of the anti-symmetric first mode oscillation and L the span. Model B, V_i =∞, has exhibited self-excited oscillation in the symmetric first mode in the flow velocity range 2.1<U_h/f_1L<〓2.6, where f_1 is the natural frequency of the symmetric first mode oscillation, and self-excited oscillation in the anti-symmetric first mode in the flow velocity range U_h/f_2L〓1.2. Model B, V_i 〓∞, has exhibited self-excited oscillation in the anti-symmetric first mode in the flow velocity range U_h/f_2L>1.0. 3) The spectra of the fluctuating pressures on the rigid roof models do not have any distinct peak. It shows that the shear layers, which develop from the windward edges of the rigid roof models, do not become vortices. Thus, the self-excited oscillations mentioned above is not the vortex-excited oscillation, though a few researchers claim that they are.