# Particle image velocimetry of a low-Reynolds-number separation bubble

## Authors

- First Online:

- Received:
- Revised:
- Accepted:

DOI: 10.1007/s00348-010-0887-z

- Cite this article as:
- Boiko, A., Dovgal, A., Hein, S. et al. Exp Fluids (2011) 50: 13. doi:10.1007/s00348-010-0887-z

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## Abstract

Boundary-layer separation at a backward-facing step of a flat plate has been investigated in a low-turbulence wind tunnel with high-speed Particle Image Velocimetry (PIV). The experiments focused on the flow pattern behind the step at the Reynolds number based on its height of about 1,000. Under quiet environmental and low-Re-number conditions, laminar-flow separation was observed behind the step subjected to a small amount of the shear-layer instability. Examination of natural and controlled velocity perturbations in the separation region indicated that the version of PIV used in the present study is an appropriate tool to deal with linear instability details that is normally done through hot-wire measurements.

### List of symbols

*f*Oscillation frequency

*h*Step height

*H*Shape factor

- Re
Reynolds number

*U*Streamwise component of the mean-flow velocity

*U*_{0}External-flow velocity at the step position

*u*Amplitude of the streamwise velocity perturbations

*V*Normal component of the mean-flow velocity

*v*Amplitude of the normal velocity perturbations

*x*Streamwise coordinate

*y*Normal-to-wall coordinate

*z*Transverse coordinate

### Greek symbols

*α*_{i}Spatial growth rate of velocity disturbances

*β*_{H}Hartree parameter

*δ**Displacement thickness

*θ*Momentum thickness

*ν*Kinematic viscosity

### Subscripts

- r
Reattachment

- s
Separation

### Superscripts

- ′
Root-mean-square (rms)