CFD Analysis of Effects of Damage Due to Bird Strike on Fan Performance

Abstract

Bird ingestion has been a hazard that affects the structural integrity and survivability of turbofan engines. It can result in deformation of one or more fan blades, in which case, the engine is likely to surge and not recover. Numerical studies and simulations of bird strikes have become essential to optimize the design of engine components simultaneously to increase the engine capabilities for acceptable damage tolerance. Good understanding of these phenomena and the implications on the behaviour of the flow field with respect to the damage affecting the fan blades are usually investigated using computational techniques and/or experimental methods. The purpose of this paper is to present a Computational Fluid Dynamics (CFD) method for the analysis of the aerodynamic behaviour of an aero-engine fan affected by a bird strike. NASA rotor 67 was used as a test case because of the availability of experimental data that can be used to calibrate the model for the undamaged fan. The undamaged fan characteristic was mapped using a modification to the methodology developed by Sayma (2007). In this method a downstream variable throttle is added which allows changing the operating point on the speed characteristic without having to change downstream boundary conditions. This approach allows for changes in fan operating point to come out of the calculation as opposed to those dictated by the downstream static pressure boundary conditions used in typical computations. The methodology is automated allowing for a sweep along a speed characteristic or along a working line in one calculation in the same way as a rig test is conducted. Agreement with experimental data when available was excellent. This provided the base line for the undamaged blades. A damaged blade was inserted among undamaged blades in the fan assembly and the fan characteristic was mapped for a range of rotational speeds. Two different degrees of damage were analysed in an attempt to establish a correlation between the extent of the damage and the locus of the stall boundary. It was found that small increments on the damage lead to significant reduction in stall margin particularly at higher rotational speeds.

Effect of open crack on axial compressor performance

“…17,18 Among the typical damage forms, the bird striking on aero-engine is always a concern, which results in the damage to blade shape and influents the working stability. [19][20][21] When the blade is subjected to the extreme aerodynamic load, centrifugal load, and vibration alternating load, the crack will appear at any position of the blade. When the crack develops to a certain extent, it will cause bad effects on the aerodynamic performance and noise.…”

Procedure for Analyzing, Manipulating and Meshing of Compressor Blades to Simulate their Flow

“…The aerodynamic influence of fan blades damaged by foreign object damage (FOD) was investigated by Bohari et al [2]. Therefore, Bohari changed the geometry of one blade in row by rotating its leading edge.…”

Unsteady Aerodynamic Analysis of a Bird-Damaged Turbofan

“…Despite its importance, few computational studies have examined the aerodynamic behavior and aeroelastic response of a bird-damaged fan. Bohari and Sayma 19 present a CFD method to analyze the aerodynamic characteristics of a bird-damaged NASA rotor 67 containing a single blade with "assumed" leading edge damage. An automated procedure is used to map the characteristic curve of the damaged fan, and the stall boundary is determined at three engine operating speeds.…”