Numerical study of flow structure and aerodynamic noise characteristics of rectangular jets with different nozzle shapes at low Mach number

Abstract

This study numerically investigates the flow and aeroacoustic characteristics of rectangular jets with different nozzle geometries but with the same mass flow rate. Turbulence statistics in the near field are compared, and the influence of nozzle shape on jet dynamics and associated noise is assessed. The configurations analyzed include a planar nozzle and orifice-type nozzles with square, beveled, and filleted edges. The Reynolds number based on the nozzle height is 1:1 × 10 ⁴ and the maximum Mach number is approximately 0.17. Flow fields are computed using Delayed Detached Eddy Simulation with the Spalart–Allmaras turbulence model, while far-field noise is obtained using Farrasat’s 1A formulation from permeable integration surfaces. The numerical framework is validated against experimental data. Results demonstrate that square and beveled orifices induce the vena contraction effect by their sharp edges, resulting in higher exit velocities and elevated near-field turbulence. In contrast, planar and filleted nozzles exhibit weaker turbulence, delayed shear layer roll-up, and longer potential cores. The beveled orifice in particular exhibits pronounced tonal noise peaks at 4.3, 8.5, and 12.7 kHz in the turbulent velocity spectrum. Spectral proper orthogonal decomposition identified dominant energetic modes near the potential core boundary where vortex roll-up and shear-layer interaction occur. The sharp-edged orifices produce overall sound pressure levels approximately 10 dB higher when integrating across the full frequency spectrum (including the tones) and 7 dB higher for the broadband component, compared to the planar and filleted nozzles. These findings underscore the trade-off between jet mixing and noise mitigation in nozzle design, offering insights for optimizing rectangular jets for engineering.

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