TITLE:
A Study on Broad Band Noise Emitted from Underexpanded Radial Jet
AUTHORS:
Yuichi Hiramoto, Hiromasa Suzuki, Masaki Endo, Yoko Sakakibara
KEYWORDS:
Broadband Noise, Shock Wave, Underexpanded Jet, Visualization
JOURNAL NAME:
Open Journal of Fluid Dynamics,
Vol.9 No.1,
March
14,
2019
ABSTRACT: This study focuses on a noise emitted from a radial underexpanded jet. The
underexpanded jet is well known as one of supersonic jets and it is formed
when the pressure ratio across a convergent nozzle is more than the critical
value. The underexpanded jet has been used in many fields, such a propulsion
of rocket, laser cutting and a glass tempering process. Such jet is exhausted
from a circular nozzle. The expansion wave, the compression wave and the
shock wave are periodically formed in the jet, which leads to quasi-periodical
shock-cell structure. On the other hand, an underexpanded jet radially issues
from intake and exhaust valves of an internal combustion engine and a pressure
control valve. The radial underexpanded jet does not have the quasi-
periodical shock-cell structure such as the jet from the circular nozzle, its
cell length decreasing along jet axis. In this study, an underexpanded jet radially
discharged from a circular slit nozzle, which consists of two circular
tubes, is experimentally examined for different nozzle pressure ratios. The jet
structure is visualized using Schlieren method and a noise emitted from the
jet is measured. Typically, the shock associated broadband noise is analyzed
and a relation between the jet structure and the radiation noise frequency is
discussed. As a result, it is found that the broadband noise lies on lower frequency
than a screech tone and that the 1st cell length plays an important role
in broadband noise radiation.