Acoustic characteristics of annular jets

Annular jets are widely used in gas turbines and burner due to stability over free jet; it introduces highly strained, recirculated turbulent flows and low NOx emissions. Present article compares acoustic features of annular jets formed with different blockage area and free jet. This study is carried out for nozzle pressure ratio (NPR) varying from 1.5 to 5. Various noise parameters such as turbulent noise, broadband shock associate noise and screech are compared separately. It is found that increase in blockage area reduces the overall noise except small region and occurrence of screech shifts to higher NPR. Addition to this directivity study is carried out for specific NPR. Further flow visualization is carried out to support acoustic data.