Azimuthal Variation of Instabilities Generated on a Flared Cone by Laser Perturbations

Area of Science:

• Fluid dynamics
• Aerodynamics
• Boundary-layer theory

Background:

• Boundary-layer instabilities are crucial for aerodynamic design.
• Understanding transition mechanisms is key to predicting drag and heat transfer.
• Azimuthal variations in boundary layers can significantly impact flow behavior.

Purpose of the Study:

• To investigate the azimuthal development of boundary-layer instabilities.
• To analyze the impact of controlled freestream perturbations on flared-cone models.
• To determine how offset perturbations affect wave packet generation and transition onset.

Main Methods:

• Utilized a Mach 6 Quiet Tunnel with a laser-generated freestream perturbation.
• Employed a flared-cone model with pressure transducers arranged in azimuthal arrays.
• Varied the position of the freestream perturbation (centerline, 1.5 mm offset, 3.0 mm offset).

Main Results:

• An offset freestream perturbation generated a larger wave packet on the offset side.
• Earlier boundary-layer transition was observed on the side of the offset perturbation.
• The effect of offset perturbations was less significant on a sharp flared cone compared to one with a larger nose radius.

Conclusions:

• Freestream perturbation location significantly influences azimuthal boundary-layer development.
• Offset perturbations can lead to asymmetric transition, impacting overall flow characteristics.
• Nose radius plays a role in the sensitivity of boundary layers to external disturbances.