The Acoustic and Instability Waves of Jets Confined inside an Acoustically Lined Rectangular Duct

An analysis of linear wave modes associated with supersonic jets con ned inside an acoustically lined rectangular duct is presented. Mathematical formulations are given for the vortex-sheet model and continuous mean ow model of the jet ow pro les. Detailed dispersion relations of these waves in a two-dimensional con ned jet as well as an uncon ned free jet are computed. E ects of the con ning duct and the liners on the jet instability and acoustic waves are studied numerically. It is found that the e ect of the liners is to attenuate waves that have supersonic phase velocities relative to the ambient ow. Numerical results also show that the growth rates of the instability waves could be reduced signi cantly by the use of liners. In addition, it is found that the upstream propagating neutral waves of an uncon ned jet could become attenuated when the jet is con ned. ||||||||||||||||| This work was supported by the National Aeronautics and Space Administration under NASA Contract NAS1-19480 while the author was in residence at the Institute for Computer Applications in Science and Engineering, NASA Langley Research Center, Hampton, VA 23665, USA.