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Evolution of turbulent spots in a parallel shear flow.
1Fachbereich Physik, Philipps-Universität Marburg, D-35032 Marburg, Germany.
Summary
Turbulent spots in shear flow evolve with distinct regions and a large-scale induced flow. Spot growth is linked to this outside flow, influencing streak lift-up and front propagation.
Area of Science:
- Fluid dynamics
- Turbulence research
Background:
- Turbulent spots are localized disturbances in laminar flows.
- Understanding their evolution is key to predicting turbulent behavior.
Purpose of the Study:
- Investigate the dynamics of turbulent spots in parallel shear flow.
- Characterize the interaction between turbulent spots and the surrounding laminar flow.
Main Methods:
- Full three-dimensional numerical simulations.
- Analysis of flow regions, streak dynamics, and front velocity.
Main Results:
- Identified three distinct regions within the spot cross-section: turbulent interior, interface layer, and laminar exterior.
- Observed lift-up of streamwise streaks due to non-normal amplification near the interface.
- Spot front exhibits exponential decay and moves independently of cross-stream or spanwise velocities.
Conclusions:
- Spot growth is intrinsically linked to the large-scale flow induced by the spot.
- The induced flow creates a linear instability, but its velocity is insufficient to fully explain spot spreading.