Generation of acoustic tones in round jets at a Mach number of 0.9 impinging on a plate with and without a hole

The generation of acoustic tones in four round jets at a Mach number 0.9 impinging on plate distance $L=6r_0$ from the nozzle exit, where $r_0$ is radius, has been investigated by large-eddy simulation. Three plates are perforated holes diameters $h=2r_0$ , $3r_0$ and $4.4r_0$ centred jet axis, whereas fourth no hole, order to study effects hole flow fields. In all cases, emerge near field, upstream but also downstream for plates. Their frequencies similar close those predicted aeroacoustic feedback loops establishing between plate, involving disturbances convected waves propagating ambient speed sound. levels, however, decrease with diameter, few dB $h\leqslant 3r_0$ approximately 40 $h=4.4r_0$ . features identified computing two-dimensional space–time correlations frequency–wavenumber spectra pressure fluctuations mixing layers. These found be closed free-stream upstream-propagating guided waves, produced impingement vortical structures scattering aerodynamic edges Finally, an analogy used show that contributions radiated noise dominant.