MULTISECTION LINERS FOR NOISE REDUCTION OF COUNTER-ROTATING FAN

It has been found that multisection liners not only attenuate the sound waves in ducts,but also to suppress sound wave thorugh the wave reflection at impedance discontinuities.As a consequence,the maximum noise reduction in a duct of given length can be realized by designing each section liner and different combination.In the present investigation,different combinations of multisection liners have been designed to suppress the discrete noises generated by a counter-rotating fan.The experimental results testified that,the noise was reduced by 9 dB in far field under the conditon of 60 cm liner length.