Random vortex-street model for a self-similar plane turbulent jet

Area of Science:

• Fluid dynamics
• Turbulence research
• Aerodynamics

Background:

• Turbulent jets exhibit a characteristic spreading angle.
• The precise mechanisms governing this angle remain an area of active investigation.
• Previous models often struggled to quantitatively predict jet angles.

Purpose of the Study:

• To elucidate the factors determining the small angle of turbulent jets.
• To develop a predictive model for jet angle based on fundamental principles.
• To reconcile theoretical models with experimental observations of jet spreading.

Main Methods:

• Construction of a deterministic vortex-street model for self-similar plane turbulent jets.
• Quantitative comparison of model predictions with experimental data for velocity profiles and vortex positions.
• Analysis of the interplay between vortex dynamics and jet angle evolution.

Main Results:

• The vortex-street model accurately reproduces mean velocity profiles and large-scale structure positions without adjustable parameters.
• Deterministic models alone predict jet angle collapse, contradicting experimental observations.
• A competition between vortex sweeping (collapsing) and structural randomness (spreading) explains the observed small jet angle.

Conclusions:

• The small angle of turbulent jets is not solely determined by ordered vortex structures.
• Randomness in vortex structure is crucial for jet spreading, counteracting the collapsing effect of vortex sweeping.
• This finding offers a more comprehensive understanding of turbulent jet dynamics.