Fluidelastic instability is a self-excited aeroelastic runaway mechanism governed by Connors’ equation. When crossflow velocity exceeds the critical threshold (vc > vcrit), energy fed into the vibrating tubes by fluid forces exceeds the structural and viscous damping dissipation. Amplitudes grow exponentially until neighboring tubes violently collide, sawing against baffle holes and fracturing within hours of startup.

In gas cooling services, periodic vortex shedding behind tubes occurs at Strouhal frequency (fv). If this frequency matches the natural acoustic standing wave frequency of the cylindrical shell cavity (fa = c / 2Ds), a powerful acoustic resonance locks in. This produces intense, ear-splitting screeching (>125 dB) that can crack shell nozzle welds even if tubes do not physically touch.

De-resonating baffles are thin longitudinal divider plates installed parallel to the flow direction inside the tube bundle. They divide the shell cavity into two or more narrower acoustic chambers, doubling the acoustic natural frequency (fa) and shifting it far above the vortex shedding excitation frequency, completely extinguishing the standing wave.

Tubes passing through the baffle cut window are supported only by alternate baffles, doubling their unsupported span length (Lu). Because beam natural frequency scales inversely with length squared (fn ∝ 1 / Lu²), window tubes have only one-fourth the stiffness of non-window tubes, making them the primary point of failure.

When tubes vibrate submerged in dense liquids, they accelerate the fluid surrounding them. This displaced fluid acts as an additional mass attached to the tube (added mass), which can equal or exceed the weight of the metal tube itself. Ignoring hydrodynamic added mass artificially inflates calculated natural frequency by 25% to 40%, masking dangerous flutter risks.