In this study, turbulent flow through an orifice was numerically modeled using delayed detached-eddy simulations to clarify transient flow dynamics and coherent flow structures. Three inlet pressures (Pin = 1 bar, 2 bars, and 3 bars) were selected for comparative analysis under a typical orifice porosity (orifice hole area to pipe area ratio) of β = 28.4%. The numerical results agreed well with the previous experimental measurements. The unsteady jet characteristics were first investigated regarding the time-averaged flow quantities, statistical quantities, and density schlieren. Subsequently, spectral proper orthogonal decomposition analysis was utilized to effectively assess the coherent flow structures present in wavepackets. The results demonstrate that the inlet pressure significantly affects the flow characteristics. In particular, jet morphology variations manifest as an increased shear layer angle at the orifice throat and changes in the spacing of shock cells. The jet core and the wake dissipation region are significantly extended with the rise of the inlet pressure. For Pin = 3 bars, a distinct subsonic region with complex vortex structures is found behind the Mach disk. When Pin = 1 bar, the noise originates from the Kelvin–Helmholtz (K–H) instability and vortex shedding, with the K–H instability dominating at high frequencies. When Pin = 2 bars, the K–H instability is the dominant contributor to the noise. In contrast to the previous two conditions, the low-frequency double-layer wavepacket structure dominates when Pin = 3 bars, exhibiting positive and negative antisymmetric alternating motion.
Li et al. (Sun,) studied this question.