ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

5aEA3. Symmetrical mode of rectangular choked jet screech.

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