Coupling of twin supersonic jets of complex geometry

Fundamental issues about the coupling of twin supersonic jets of complex ge ometry are examined. It is shown that screech tones from twin rectangular n ozzles with double-beveled exit geometries can couple. Unlike coupling of t win rectangular jets of uniform geometry, the coupling here is more intrica te because simultaneous multiple frequencies with a different spanwise moda l structure are present. The coupling produces two frequencies, one of whic h is lower than the screech frequency of either jet. Although many coupling modes are kinematically permissible, the twin jets prefer two specific mod es, and in some cases these two coupling modes coexist at different frequen cies. Despite the geometric complexity we can effectively predict frequenci es of tones from both single and twin coupled jets using the waveguide appr oach. It is hoped that these results and insights will assist those simulat ing screech for the purpose of tailoring shock-containing complex twin jets that minimize sonic fatigue failure of aircraft structures.