Numerical Investigation on Wide-Chord Fan Blade Forced Response due to Vortex Ingestion

Abstract

When a turbofan engine is taxing or taking-off, a vortex can form between ground surface and the intake. As the diameters of engines increase, intakes are closer to the ground and as a result the possibility of vortex ingestion is increasing. The vortex starts from the ground surface and enters the inlet at high rotating speed. It is likely to draw in hard material or dust from the ground, which leads to blade erosion or impact damage. This is harmful to the engine durability and safety. Besides the vortex, inlet flow separation could induce high level of blade vibration, or aerodynamic instability, such as rotating stall. Cross wind may also lead to both vortex and flow distortion, which is more challenging for engine stability. Therefore, vibration characteristics and forced response under vortex ingestion should be evaluated to ensure the stability and safety of the engine in design phase. This paper presents a computational study of the forced response of a wide-chord fan blade under vortex ingestion. A finite element model was built, and modal analysis was conducted to characterize the vibrating characteristics of the fan blade with a corresponding Campbell diagram. Transient simulations of vortex passing over the fan blade were conducted with and without the blade pre-vibration at the natural frequency of the first bending mode. The forced response level was evaluated under various conditions, including different hitting time and increasing intensity of vortex. Results showed that the ingested vortex is able to amplify the displacement and vibratory response to a significant level of 18% at most. Linear relation between vortex intensity and blade response was found. The results give a comprehensive prediction of forced response for a better blade design against vortex ingestion.