Directionality and pulsing of acoustic propagation to the far-field of a supersonic jet flow

We analyze simultaneous data in the near- and far-field of a 2-stream supersonic jet. The flow combines a rectangular jet at Ma = 1.6 and a rectangular wall jet at Ma = 1.0 separating the primary jet from a deck plate. We treat simultaneous data from deck- mounted kulite sensors and far-field microphones sampled for 10 s at 100 kHz. Aside from a clear 33kHz tone, traced previously to Kelvin-Helmholtz instability at the trailing edge of the splitter plate between the jets, a number of weaker pulses are identified at lower frequencies of the order of 1 to 5 kHz. The pulse frequencies are active in correlations between the sensors. In particular, the cross-correlation between near- and far-field shows bands of activity that differ for the various pairs of sensors (6 kulites and 12 microphones); the lags between near- and far-field are also frequency and direction-dependent. Significant departures from the expected propagation time (about 11 ms) are discussed. In addition to directional dependencies of most statistics, the modulation of the 33 kHz tone by near-field pulsing is documented.