00-05: Evaluation of the Unsteady Loads on a Fan Blade

The knowledge of the unsteady loads is fundamental for the fan blade fatigue design and for the evaluation of the cooling tower vibration level. The most significant unsteady loads are generated by the effect of the aerodynamic interference between the fan-gearbox supporting beams and the fan blades. This paper discusses the origin and the effect of the aerodynamic interference, presents a methodology for calculating the unsteady loads and the relevant stress on the fan blade, and shows the experimental results and their correlation with the theory. A simple method for reducing the unsteady loads is also discussed.