Engine noise largely contributes to the overall sound level, causing noise pollution in the areas where the turbine engines are widely used. This problem has raised a necessity to develop the technologies that would minimize noise while maximizing the productivity of the engine. The noise reduction technologies are derived from the transformations in the cycle parameters of the engine and the features of low-noise design. The sources of engine noise are the exhaust (is referred to as jet), fan (stator), the turbine, the compression, and the combustor,
Fan Noise Reduction
The fan noise reduction is achieved by reducing the pressure ration and the tip speed. The optimization study demonstrates that the best fan speed is reached when the rotational tip speed remains under Mach=1 so to eliminate shock related noise. If this speed is reached, the pressure ratio of fan becomes a controlling component for the broadband noise. The source for this type of noise is the turbulence which takes place in the fan wakes and strikes the stators, causing unstable pressure field. It is turned into acoustic waves that are radiated from the fan duct of the engine.
One more reason to reduce pressure ratio and fan tip speed is that it reduces multiple noise sources, thus making the features of noise reduction design more effective. One of the models of fan noise reduction is called the ADP or the Advanced Ducted Propulsor of the UHBR engine. The results have also shown that the noise reduction can be achieved by adding various combinations of acoustic treatment. Geared Turbofan is one more engine which contributes to noise reduction (Huff, 2007). A ‘scarf inlet” is utilized for the reduction of the inlet fan noise through redirection of the forward radiated sounds away from the community.
Jet Noise Reduction
The jet noise reduction is achieved through the lowering of the jet exhaust velocity. In the newer engines, the engine cycle is used to derive energy from the engine core, thus reducing the mixed velocity of the fan ducts and core. It is recommended to reduce the jet noise but avoid changes in the engine cycle. Chevron nozzles are currently used to reduce the jet noise. While being tested, the jet noise was reduced by mixing the bypass flows and core so to reduce low frequency (Huff, 2007). It appears to be the first test where the reduction of jet noise did not affect the thrust.
Lip Treatments, Smart Distribution of the Liners, and “Soft” Stator Vanes
Two sorts of de-icing techniques (either thermoelectric or pneumatic) have been invented to contribute to the noise reduction. Treated lip technologies with integrated pneumatic anti-ice systems are successfully introduced as a noise reduction technique (Leylekian, Lebrun, & Lempereur, 2007). The positive results are expected from the use of smart liner distribution. For instance, the air intake is treatment is separated by longitudinal splices that border the treated parts and entail azimuthal variations that limit acoustic performance. This problem has been addressed by the development of zero-splice liners that reduce noise. One more option for noise reduction is called “Soft Stator Vanes.” It aims at the reduction of the noise from rotor-stator interaction by the reduction of fluctuation of vane pressure (Huff, 2005). These technologies have improved the noise reduction system which is widely used in aircraft.
Evidently, noise pollution currently remains one of the greatest challenges of the contemporary world. Noise reduction technologies are based on the changes of the engine design and its components. Although the progress in noise reduction techniques is observed, their implementation cannot cause any errors in the work of the engine. It means that the noise reduction techniques require the highest level of optimization.
- Huff, D. (2005). Engine noise reduction technologies and strategies for commercial application. Pratt & Whitney, United Technologies.
- Huff, D. (2007). Noise reduction technologies for turbofan engines. Glenn Research Center.
- Leylekian, L., Lebrun, M., & Lempereur, P. (2007). An overview of aircraft noise reduction technologies. Journal of Aerospace Labs.