Investigation of Large-Scale Cooling System Fan Blade Vibration

Fans operating at the edges of large-scale air-cooled steam condensers often do so under distorted inlet air flow conditions. These conditions create variations in the aerodynamic loads exerted on a fan blade during rotation which causes it to vibrate. In order to isolate the sources of the unsteady aerodynamic loads as well as their effects on blade vibration, a potential flow fluid dynamics code was written to determine the aerodynamic loads exerted on a fan blade as a function of its rotation. The lift and drag forces were exported to a finite element code approximating the fan blade as a cantilever beam. With these two sets of code the response of the blade when subjected to varying aerodynamic loads could be determined. Furthermore, the effect of changing certain parameters such as blade stiffness or damping can be investigated. It was found that the blade’s response closely resembles that which was measured at the full-scale facility and that slight changes to the blade’s stiffness can potentially reduce the vibrational amplitude but may also lead to resonance.