3D numerical evaluation on Strouhal frequency associated with flow-induced lift acting on an elastically supported cylindrical rod under axial flow with different velocity

摘要

Influence of the motion of a cylindrical rod under the axial flow on the Strouhal frequency of the flow-induced lift was numerically investigated where the cylindrical rod was elastically supported and movable in the x-y plane orthogonal to the flow direction z. For typical examples, realistic input data in engineering aspects such as the damping coefficient, the mass per unit length of the cylindrical rod and the stiffness of the elastic spring supporting the rod were chosen in the numerical analysis with Re = 1000 and 2500. Under Re = 1000, the Fourier power spectra of the time variations in the x-directional cylindrical rod displacement and the associated lift acting on the cylindrical rod under the axial flow showed a sharp peak at the Strouhal frequency f(peak) = 8.9, that is sufficiently apart from the fluid dynamic excitation Strouhal frequency peak f(peak)* 0.1 numerically obtained in the previous studies for a rigidly fixed cylindrical rod under the identical flow condition. The above f(peak) deviated a little to the higher side of the natural Strouhal frequency f(0) = 8.5 of the cylindrical rod under the influence of alternating lift acting on the rod. In case Re = 2500, Fourier power spectrum of the time variation in the lift acting on the rod showed the dominant peak at the same Strouhal frequency f(peak) = 8.9 as in the case of Re = 1000 with minor intensity peaks in the higher frequency domain due to the flow transition, however these higher frequency components showed no significant effect on the motion of the cylindrical rod. (C) 2014 Elsevier Ltd. All rights reserved.