Abstract
The results of the experimental study into the damping of flexural vibrations in turbofan blades with trailing edges tapered according to a power-law profile are reported. Trailing edges of power-law profile (wedges), with small pieces of attached absorbing layers, materialise one-dimensional acoustic black holes for flexural waves that can absorb a large proportion of the incident flexural wave energy. The experiments were carried out on four model blades made of aluminium. Two of them were twisted, so that a more realistic fan blade could be considered. All model blades, the ones with tapered trailing edges and the ones of traditional form, were excited by an electromagnetic shaker, and the corresponding frequency response functions have been measured. The results show that the resonant peaks are reduced substantially once a power-law tapering is introduced to the blade. An initial study into the aerodynamic implications of this method has been carried out as well, using measurements in a closed circuit wind tunnel. In particular, the effects of the trailing edge of power-law profile on the airflow-excited vibrations of the fan blades have been investigated. It has been demonstrated that trailing edges of power-law profile with appropriate damping layers are efficient in reduction of the airflow-excited vibrations of the fan blades. The obtained results demonstrate that power-law tapering of trailing edges of turbofan blades can be a viable method of reduction of blade vibrations.
Highlights
One of the major causes of turbofan blade failure in jet engines is the flow-induced vibrations of the blades resulting in their high cyclic fatigue [1]
This paper describes the results of the experimental investigation of damping flexural vibrations in model turbofan blades with their trailing edges modified to have the power-law shapes, following the idea proposed in [10]
The results of this work show that modifying trailing edges of turbofan blades according to the power-law profile along with the attaching thin strips of damping layers, which materialises one-dimensional acoustic black holes for flexural waves, represents an effective method of damping flexural vibrations in the blades
Summary
One of the major causes of turbofan blade failure in jet engines is the flow-induced vibrations of the blades resulting in their high cyclic fatigue [1]. With the addition of small pieces of absorbing materials helping to overcome problems associated with the geometry of real manufactured wedges, this constitutes the acoustic black hole effect It has been established theoretically [8,9] and confirmed experimentally [10,12,13,14,15] that this method of damping structural vibrations is very efficient. This paper describes the results of the experimental investigation of damping flexural vibrations in model turbofan blades with their trailing edges modified to have the power-law shapes, following the idea proposed in [10] Such trailing edges materialise onedimensional acoustic black holes for flexural waves, and they are expected to result in substantial reduction in wave reflections from the edges and in efficient suppression of resonant vibrations of the blades. The effects of the trailing edge of power-law profile on the airflow-excited vibrations of the fan blades have been investigated
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