On the development of turbulent wakes from vortex streets
Wave development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low speed wind tunnel. Standard hot-wire techniques were used to study the velocity fluctuations. The Reynolds number range of periodic vortex "shedding" is divided into two distinct s...
| Summary: | Wave development behind circular cylinders at Reynolds numbers from 40 to 10,000 was investigated in a low speed wind tunnel. Standard hot-wire techniques were used to study the velocity fluctuations.
The Reynolds number range of periodic vortex "shedding" is divided into two distinct sub-ranges. At R = 40 to 150, called the stable range, regular vortex streets are formed and no turbulent motion is developed. R = 150 to 300 is a transition range to a regime called the irregular range, in which turbulent velocity fluctuations accompany the periodic formation of vortices. The turbulence is initiated by laminar-turbulent transition in the free layers which spring from the separation points on the cylinder. This transition first occurs in the range R = 150 to 300.
Spectrum and statistical measurements were made to study the velocity fluctuations. In the stable range the vortices decay by viscous diffusion. In the irregular range the diffusion is turbulent and the wake becomes fully turbulent in 40 to 50 diameters downstream.
It was found that in the stable range the vortex street has a periodic spanwise structure.
The dependence of shedding frequency on velocity was successfully used to measure flow velocity.
Measurements in the wake of a ring showed that an "annular" vortex street is developed. |
|---|