Turbulent jet manipulation using two unsteady azimuthally separated radial minijets

Area of Science:

• Fluid Dynamics
• Turbulence Control
• Experimental Aerodynamics

Background:

• Turbulent round jets are fundamental in various engineering applications.
• Controlling jet behavior is crucial for performance enhancement and noise reduction.
• Previous methods for jet manipulation often lack efficiency or precise control.

Purpose of the Study:

• To experimentally investigate the active manipulation of a turbulent round jet.
• To explore the effects of injecting radial unsteady minijets on jet characteristics.
• To understand the influence of minijet parameters on jet velocity decay and flow structures.

Main Methods:

• Experimental investigation of a turbulent round jet.
• Injection of two radial unsteady minijets upstream of the main jet exit.
• Parametric study varying mass flow ratio (Cm) and frequency ratio (fe/f0).
• Azimuthal separation angle (θ) of minijets was systematically varied (60° and 180°).

Main Results:

• A significant increase in jet centerline mean velocity decay rate was observed.
• The optimal azimuthal separation angle for enhanced decay was found to be θ=60°.
• This enhanced decay is attributed to the induced flapping motion of the jet column.
• The formation process and generation mechanism of the flapping motion were analyzed.

Conclusions:

• Active manipulation using radial minijets is an effective method for controlling turbulent round jets.
• Minijet azimuthal placement critically influences jet behavior, with 60° separation promoting significant velocity decay.
• The study elucidates the flapping motion mechanism responsible for enhanced jet decay, offering insights for flow control strategies.