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

• Oscillation of a nuclear fuel rod elastically supported in an axial flow was studied.
• A rod oscillates nearby its natural frequency, not at the fluid excitation frequency.
• Rod oscillation is slightly affected by hydrodynamic lift in a low Re domain.
• At Re = 2500 higher frequency components were added to the primary lift frequency peak.
• Higher frequency components in the lift showed no effect on the rod motion.

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–yx–y plane orthogonal to the flow direction zz. 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=1000and2500. Under Re=1000Re=1000, the Fourier power spectra of the time variations in the xx-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 fpeak=8.9fpeak=8.9, that is sufficiently apart from the fluid dynamic excitation Strouhal frequency peak fpeak∗≈0.1 numerically obtained in the previous studies for a rigidly fixed cylindrical rod under the identical flow condition. The above fpeakfpeak deviated a little to the higher side of the natural Strouhal frequency f0=8.5f0=8.5 of the cylindrical rod under the influence of alternating lift acting on the rod. In case Re=2500Re=2500, Fourier power spectrum of the time variation in the lift acting on the rod showed the dominant peak at the same Strouhal frequency fpeak=8.9fpeak=8.9 as in the case of Re=1000Re=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.