High-Speed Flash Photography of Jets and Study of Noises of Aerodynamic Origin

In the study of noises coming from gaseous supercritical jets the waves were investigated by four separate methods in order to cross check the results. With the use of an electronic camera a film was made showing the evolution of acoustic waves. A sound analysis was made using a narrow passband analyzer and a microphone sensitive to high frequency. Schlieren photographs show that the waves on one side are out of phase relatively to those on the other side. Convergent-divergent nozzles were used giving Mach numbers from 1 to 4 comparable to sonic nozzles. The jet has a cellular structure at the exit as shown on shadowgraph pictures. “Screeches” occur when the jet is overexpanded. A specific ratio of pressure exists for each nozzle which brings about maximum screech. Frequency of oscillation was determined from 16 views filmed by the schlieren and shadowgraph methods. Two schlieren photographs demonstrate that a reflector at the origination of the jet diminishes jet screech by 20 dB.

Print ISSN

0361-4573

Published

1971-04

Content type

Original Research

DOI

10.5594/J08903