A propfan assembly includes a plurality of blades that each include an internal cavity containing a noise attenuation structure. Acoustic energy is communicated to the internal cavity through a plurality of openings in the blade surfaces. The cavities include features for attenuating noise energy to reduce generation of noise emitted from the propfan assembly.

BACKGROUND OF THE INVENTION

This invention generally relates to a propfan assembly. More particularly, this invention relates to a propeller blade for a propfan assembly that includes noise attenuating features.

A gas turbofan engine includes fan blades that are disposed within a nacelle housing. The nacelle housing includes noise attenuating features to quiet select frequencies of noise generated by the rotating fan blades. A propfan includes blades that are not disposed within a duct and can provide performance improvements over ducted fan blades. However, un-ducted propfan blades can be noisy. Without surrounding nacelle mounted noise attenuation structures and features; noise generated by the prop-fan can be greater than is desired.

Accordingly, it is desirable to design and develop a prop-fan assembly with reduced noise emissions.

SUMMARY OF THE INVENTION

An example propfan assembly includes a plurality of blades that each include an internal cavity containing a noise attenuation structure. Acoustic energy is communicated to the internal cavity through a plurality of openings in the blade surfaces.

The example blades for the propfan assembly each include a plurality of openings on either the suction side, pressure side or both sides to communicate acoustic energy with cavities within each blade. The cavities include features for attenuating noise energy.

Accordingly, the example propfan assembly provides reduced noise emissions without sacrifice of performance improvements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, a propfan assembly10includes a hub12and a plurality of blades14attached to the hub12. The hub12and blades14rotate as one assembly. The propfan assembly10is only one example of a propeller assembly. It is within the contemplation of this invention that any propeller assembly and configuration would benefit from application of the disclosed noise attenuation features.

Each of the plurality of blades14includes a plurality of small openings16that are schematically shown as the gray areas. The openings16communicate noise energy to an internal cavity22containing a noise attenuation structure28. Noise energy communicated to the internal cavity22is dissipated to reduce the overall acoustic signature emitted by the propfan assembly10. The example blades14include a plurality of cavities22that each include a noise attenuation structure28.

Referring toFIGS. 2 and 3, a single blade14is illustrated in an untwisted simplified schematic representation. The plurality of openings16communicate acoustic energy into the cavities22but are of a size that does not interfere with airflow over each of the pressure and suction sides18,20. The example openings16are disposed on both the suction and pressure sides18,20of each of the blades. However, the openings16can be disposed on only one of the suction and pressure sides18,20. The openings16cover a portion of the blade sides18,20that overlie portions of the cavities22, disposed within each of the blades14.

Referring toFIG. 4, the example noise attenuation structure28comprises a honeycomb structure that dissipates acoustic energy. The honeycomb structure is orientated such that at least one of the plurality of openings is in communication with each individual cell. The example honeycomb structure can be a separate structure that is installed within each of the cavities22, or a integral structure of the cavity22itself. Further, although a honeycomb noise attenuation structure is disclosed, other noise attenuation structures that dissipate and absorb acoustic energy could also be utilized.

Referring toFIGS. 5 and 6, a single blade14includes a plurality of cavities22. The cavities22are of a defined length24. The length24is defined to correspond with the frequency of noise desired to be reduced. Noise generated from the propfan assembly10is often in a low frequency range requiring long cavities to absorb and attenuate the acoustic energy as desired. The shape of the blade14may require a specific orientation of the cavity22so that the desired length corresponding to the desired frequency can be installed. This may require that each cavity be uniquely positioned along the chord and span of each blade14. The example cavity22is orientated within the blade14at a compound angle including a first angle30relative to the blade chord, and a second angle32relative to span of the blade. The resulting overall length of the cavities22corresponds to the targeted noise frequency. Further, each of the blades14can include cavities22of different lengths to target several different noise frequencies for attenuation.

The example propfan assembly10reduces overall acoustic emissions by attenuating the most prevalent frequencies. Further, the structure of each blade14reduces the amount of noise that is generated. The cavities22disposed within the blades14reduce unsteady pressures on each of the blades14that generate the acoustic energy. The reduced noise that is generated is then attenuated by the internal features of each blade14.

Each individual blade14will attenuate noise generated by adjacent blades during rotation. In other words, one blade14will attenuate noise generated by the preceding blade. Further, for propfan assemblies that include multiple rows of blades14, a rearward row of blades14will attenuate noise generated in the forward row of blades.