Dan Lin
Alan Powell
Dept. of Mech. Eng., Univ. of Houston, TX 77204-4792
The screech and edge tones of rectangular jets had always been considered
to be due to asymmetric (sinuous) jet instabilities, with out-of-phase sound
fields across the jet plane. Kozu's 1991 screech measurements showed a
discontinuity at 2.12 (less than or equal to)R[sub d]<2.16, R=pressure ratio,
the wavelengths (lambda) below this being about 25% less than the empirical
(lambda)/h=k[radical (R-R[inf c])[radical , h=small dimension of rectangular
nozzle, k=constant=5.2 (Powell),=5.0 (Krothapali), R[sub c]=critical value.
However, Lin's 1992 schlieren photographs showed a symmetric (varicose) mode
for edge tones at a pressure ratio R=2.36 and small nozzle-to-edge distances
for the same nozzle, aspect ratio 4.8, with wavelength about half that for
(asymmetrical) screech. Lin's 1992 investigation of screech for R