Computational study on aeroacoustic fields of a transitional supersonic jet

Area of Science:

• Computational fluid dynamics
• Aeroacoustics
• Turbulence research

Background:

• Supersonic jets generate noise through complex flow phenomena.
• Understanding transitional flow regimes is crucial for noise reduction.
• Previous studies often focused on subsonic jets, with less data on supersonic transitional conditions.

Purpose of the Study:

• To computationally investigate the aeroacoustic fields of supersonic free jets under transitional conditions.
• To analyze the effects of shear layer thickness and disturbances on jet noise.
• To compare noise generation mechanisms in supersonic versus subsonic jets.

Main Methods:

• Employed large-eddy simulations (LES) for computational fluid dynamics.
• Investigated supersonic jets at Mach 2.1 and Reynolds number 70,000.
• Varied shear layer thickness and introduced disturbances for comparative analysis.

Main Results:

• Shear layer thickness and disturbances significantly impact transition position and turbulence intensity.
• Decreasing shear layer thickness or adding disturbances attenuates turbulent fluctuations and Mach wave intensity.
• Observed a 5 dB increase in sound pressure level, lower than in subsonic jets.

Conclusions:

• The transition process in supersonic jets, driven by spiral modes, differs from the axisymmetric modes in subsonic jets.
• This difference explains the lower sound pressure level increase in supersonic jets.
• Linear stability analysis, proper orthogonal decomposition, and vortex structure visualization confirm the findings.