| A two-part experimental study was conducted in order to investigate and then reduce the noise generated by high-temperature supersonic jets. The first part of the study focused on the noise generated by supersonic jets at Mach numbers ranging from 1.2 to 2.2 and temperatures ranging from 290 K to 1366 K. Through the use of a newly defined Mach number, it was found that the jet noise in the peak radiation direction is a function of the velocity to the eighth power for subsonic jets. For supersonic jets, the noise is a function of the velocity cubed. In the normal direction, the jet noise demonstrates a dependence on the velocity to the sixth and fourth powers. Based on these results, a simple scheme was developed for predicting the directivity of the jet noise in the aft quadrant. A universality of the frequency spectra was also observed in the peak radiation and normal directions. The second part of the study was focused on the use of microjet injection as a means of supersonic jet noise reduction. It was determined that the primary effect of microjet injection is the reduction of Mach wave radition clue to the generation of strong streamwise vortices in the shear layer of the jet. However, through the use of water-based microjets additional reductions in the turbulence levels were obtained. It was found that the effectiveness of the microjets in the peak radiation direction is dependent on the momentum ratio between the microjets and the main jet. The results from two full-scale jet engine tests were used to validate the results that were obtained in the laboratory. |
