Small scale intermittency and bursting in a turbulent channel flow

Area of Science:

• Fluid Dynamics
• Turbulence Research
• Experimental Physics

Background:

• Turbulent channel flow exhibits complex statistical properties.
• Intermittency, characterized by intermittent bursts of activity, is a key feature of turbulence.
• Understanding intermittency is crucial for modeling and predicting turbulent flows.

Purpose of the Study:

• To experimentally investigate the statistical properties of streamwise velocity fluctuations in fully developed turbulent channel flow.
• To analyze the intermittency features and their dependence on wall distance.
• To develop and apply a wavelet-based method for identifying organized motion and its relation to intermittency.

Main Methods:

• Single hot-wire anemometry for velocity measurements.
• Extended self-similarity for scaling velocity structure function moments.
• Wavelet transform for analyzing probability density functions and educing coherent structures.
• Conditional averaging based on educed events.

Main Results:

• Intermittency effects are strongly dependent on the distance from the wall.
• Maximum intermittency is observed in the buffer and inner logarithmic regions.
• A wavelet-based eduction technique successfully identified organized motion.
• Intermittent events are linked to high velocity gradients and occur near the wall.

Conclusions:

• The study confirms the wall-distance dependence of intermittency in turbulent channel flow.
• Coherent structures, particularly those associated with bursting phenomena, play a significant role in intermittency.
• The developed wavelet-based method is effective for analyzing turbulent signals and identifying intermittency-related events.