吊挂安装效应对热喷流噪声影响实验

利用位于全消声室中的热喷流噪声实验台对涵道比为5.5的分开式排气系统进行了吹风实验，研究了在起飞工况下吊挂的安装效应对喷流噪声和锯齿型喷管降噪效果的影响。结果表明:吊挂的安装效应改变了喷流噪声周向的频谱特性；安装效应降低了喷流噪声低频段的噪声并导致高频噪声增加；安装效应对吊挂上方位置低频段噪声降噪量最大，其最高频谱降噪量为3.7dB；带吊挂锯齿型喷管对吊挂上方喷流噪声影响较小，但是会降低吊挂下方和侧面的低频段噪声，其中对吊挂下方低频段噪声降噪量最大，频谱降噪量最大约1.3dB；锯齿型喷管对侧面位置的高频噪声影响最大；吊挂的安装效应对喷流噪声远声场总声压级指向性影响不大。 

Experimental of the pylon installation effect on hot jet noise

This experiment was made to study the installation effect on the radiated noise from separate flow nozzles with a bypass ratio of 5.5 at take-off condition, as well as the jet noise reduction of pylon-based chevron nozzles. All the experiments were conducted on the hot jet noise rig located in the anechoic chamber. The results indicated that the pylon made an azimuthal dependence on the far field radiated jet noise frequency spectrum. The pylon was effective at low-frequency with reducing noise but produced an increase of noise at high-frequency. The most significant low-frequency noise reduction was observed in position located above the pylon where the peak noise reduction was 3.7dB on frequency spectrum. There was little effect of chevron nozzles on the jet noise radiated from the top of the pylon. The low-frequency noise reduction on the pylon was observed below and laterally while the position below the pylon had the best low-frequency noise reduction whose peak noise reduction was about 1.3dB on frequency spectrum. The largest impact of pylon on high-frequency noise was only on the side. The installation had little effect on the far field overall sound pressure level directivities.