Based on the low of the eighth power of speed of M.J. Lighthill this article has derived the calculating formula for the air dynamic noise power in the compressor, and analysed the factors to affect the noise, also indicated that the dynamic noise in the compressor mainly comes from the valve jet noise; the principle to reduce the dynamic noise is to get a small Reynolds number Re; the emphasis...

The study of core noise from turbofan engines has becomemore important as noise from other sources such as the fan and jet were reduced. A multiple-microphone and acoustic-source modeling method to separate correlated and uncorrelated sources is discussed. The autoand cross spectra in the frequency range below 1000Hz are fitted with a noise propagation model based on a source couplet consisting...

A global noise reduction of a high-subsonic jet is achieved by experimental use of an impinging microjets system. The microjet velocity relative to the main jet velocity, the longitudinal distance of injection and the number of microjets are the three parameters examined in order to obtain the maximum noise reduction. This optimized microjet configuration is obtained by a balance between low-fr...

The concepts studied during Offset Stream Technology (OST) test were all designed to produce directional jet noise reduction in a separate flow engine configuration by redirecting the fan stream relative to the core stream, creating a thicker fan flow on one side of the jet. Previous studies, conducted at bypass ratios of five or less showed that lower noise levels would result on the thickened...

Despite almost 60 years of active research on jet noise, the noise generated by expulsion of hot gases at the exhaust of aircraft engines remains an important part of the total aircraft noise. This is particularly true in the case of supersonic aircrafts, where the high speed of the exhaust gases yields extremely high noise. In the framework of the development of future civil supersonic aircraf...

A 3-D microphone array was developed and used to locate the origins of individual sound waves that were created within a high-speed and high Reynolds number turbulent jet. In previous work by the authors, a linear array of microphones and simultaneous temporally resolved flow visualizations were used to determine the origin of individual sound waves and their generation mechanisms within the je...

Structural fatigue, hearing damage, and community disturbances are all consequences of rocket and jet noise, especially as they become more powerful. Noise-reduction schemes require accurate characterization of the noise sources within rocket plumes and jets. Nearfield acoustical holography (NAH) measurements were made to visualize the sound field in the jet exhaust region of an F-22 Raptor. Th...

This experimental investigation examined the potential of pylon-based deployable flaps to reduce jet noise of separate-flow turbofan engines with a bypass ratio of eight. The main function of the flap deflectors is to thicken the low-speed region surrounding the core jet in the downward and sideline directions. The study encompassed acoustic measurements, noise-source imaging, mean-velocity sur...