Rotary kinetic fluid motors or pumps – With sound or vibratory wave absorbing or preventing means...
Reexamination Certificate
1999-01-14
2001-06-12
Verdier, Christopher (Department: 3745)
Rotary kinetic fluid motors or pumps
With sound or vibratory wave absorbing or preventing means...
C415S914000
Reexamination Certificate
active
06244817
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to noise control, and more particularly, to methods and apparatuses for controlling noise and vibrations generated by rotating blades of a fan.
2. Background of Invention
Virtually all large modern transport aircraft, especially civil aircraft, use turbofan engines. A turbofan engine essentially comprises a turbojet with a large low-pressure compressor, in which airflow is discharged as a relatively cool and slow propulsive jet. The turbofan exhibits superior propulsive efficiency and fuel consumption characteristics over ordinary turbojets. Perhaps the most important advantage of turbofan engines over turbojets in civil aviation, however, is the dramatically lower noise level.
Despite the improvement over conventional turbojets, however, turbofan engines still produce a powerful roar. The sound of turbofan engines continues to generate animosity among the public towards the aviation industry. Noise concerns produce resistance to the construction of new, more convenient airports, and promote strict noise control regulations. Compliance with these regulations often presents an enormous expense to aircraft owners because engines or even entire aircraft may require replacement.
In some cases, compliance may even be impossible. Current solutions for reducing engine noise have met with limited success. Although a turbofan produces less jet noise than a turbojet, the fan itself has become a source of considerable noise. Much of the fan noise may be produced by interaction between unsteady fluid flows and solid surfaces. Such interactions may be attributed to inflow disturbances, such as the inlet boundary layer interacting with the blades of the fan, or the fan wakes and blade tip vortices interacting with the stator vanes or support struts downstream from the fan. In addition, as fans become larger and more powerful, the contribution of the fan to the overall noise of the engine becomes more pronounced.
A typical acoustic spectrum for a fan includes both broadband noise and higher amplitude noise at particular frequencies relating to the fan rotation rate. The higher amplitude noise associated with the fan rotation rate, referred to here as blade-passing noise, is generated, in considerable part, by aerodynamic interaction between blade load or blade thickness disturbance flows and solid surfaces. This interaction occurs, for example, when the downstream stator vanes or support struts respond to flow fluctuations caused by the upstream fan blades. Under high loading conditions, the most significant of such disturbances to the flow downstream are caused by the development of blade leading edge vortices and stronger blade tip vortex shedding. Consequently, fan blade-passing noise is typically most severe under high load conditions.
Broadband noise, on the other hand, is generated from multiple sources. Some broadband noise sources depend on three-dimensional unsteady flows within a rotor or stator blade row. Such three-dimensional flows may comprise a vortex at the blade tip adjacent to the surface, due to the leakage of fluid through the tip clearance gap. Also, three-dimensional flow may include blade tip vortices which are generated by the deflection of the flow streamlines within the annular wall boundary layer. Such leakage and blade tip vortex flows may increase the fan broadband noise.
To minimize fan noise, a noise control system should attenuate both the blade-passing noise as well as the fan broadband noise. Absorbing the fan noise with acoustic wall treatments or engine hushkitters is somewhat effective, but only produces relatively small reductions in fan noise and often adversely affects engine performance. Active noise control solutions, on the other hand, show promise, but the techniques are not fully developed, require precise and costly control systems, and typically address only blade-passing noise corresponding to the rotation rate of the fan.
Furthermore, fan noise presents a problem in many applications other than aircraft engines. For example, cooling fans are very common as household appliances, in computers, and in other applications. In many of these applications, controlling the noise generated by the fan is a common design objective. As fans become more powerful, however, noise control often becomes more difficult.
SUMMARY OF THE INVENTION
A system according to various aspects of the present invention comprises a fan noise control system for reducing noise associated with a fan system. The system includes components for controlling broadband noise and blade-passing noise associated with the rotation rate of the fan. In particular, a fan noise control system according to various aspects of the present invention suitably includes a pre-swirl generator configured to provide a layer of fluid upstream from the fan blades which is swirling in the direction of the fan's rotation. The layer of swirling fluid reduces the angular velocity differential between the fan blades and the incident fluid.
In addition, the fan noise control system may further include a fluid seal generator configured to generate a barrier between the blade tips of the fan and the interior surface of the fluid flow channel. The fluid seal or barrier may comprise a layer of fluid between the fan blade tips and the interior surface which rotates in the same direction as the fan blades. Consequently, the fluid seal inhibits leakage flow between the fan blade tips and the interior surface, as well as formation of blade vortices.
Thus, a system according to various aspects of the invention reduces noise associated with a rotating fan. The pre-swirl generator tends to reduce the blade-passing noise component. In addition, the fluid seal generator tends to diminish the broadband noise associated with leakage flow and blade vortices. Because the pre-swirl generator and fluid seal generator provide force in the direction of the fan rotation, both components also tend to unload the fan, thus improving performance of the fan system and further reducing noise.
These and other advantages of a system according to various aspects of the present invention will be apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.
REFERENCES:
patent: 4692091 (1987-09-01), Ritenour
patent: 5308225 (1994-05-01), Koff et al.
patent: 5707206 (1998-01-01), Goto et al.
patent: 5762034 (1998-06-01), Foss
patent: 55-35173 (1980-03-01), None
patent: 58-202399 (1983-11-01), None
Xin Zhang and John A. Edwards, Experimental Investigation of Supersonic Flow over Two Cavities in Tandem, pp. 1182-1190, AIAA Journal, vol. 30, No. 5, May 1992.
Richard G. Holz and Ahmed A. Hassan, Numerical Model for Circulation-Control Flows, pp. 701-707, AIAA Journal, vol. 32, No. 4, Apr. 1994.
Englar et al., Development of the Circulation Control Wing to Provide STOL Potential for High Performance Aircraft, pp. 1-11 (No Date).
McDonnell Douglas Corporation
Snell & Wilmer L.L.P.
Verdier Christopher
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