As a rough estimate, given the speed of sound as *ā* = 340 m/s, the wavelengths, *λ* = *ā*/*f*, of the external excitations at frequencies of 2, 5, and 10 kHz are 17.0, 6.8, and 3.4 cm, respectively. The diameter of the jet, 1.27 mm, is much smaller than these wavelengths, and even the computational domain is not long enough to cover an acoustic wavelength. This means that the computational domain is acoustically compact, and acoustic-induced variations are expected to be indiscernible in space. Therefore, visualization of the acoustic effects is only presented based on the temporal evolution of the flow field. The oscillations are activated for 2.5 ms in all forcing cases, corresponding to 5.0, 12.5, and 25.0 forcing cycles for the 2, 5, and 10 kHz cases, respectively.