Roshko number
In fluid mechanics, the Roshko number (Ro) is a dimensionless number describing oscillating flow mechanisms. It is named after the American Professor of Aeronautics Anatol Roshko. It is defined as
- valid over [ 50 <= Re < 200]
- valid over [200 <= Re < 2000]
where
- St is the dimensionless Strouhal number;
- Re is the Reynolds number;
- U is mean stream velocity;
- f is the frequency of vortex shedding;
- L is the characteristic length (for example hydraulic diameter);
- ν is the kinematic viscosity of the fluid.
- Note: Linear relation between Ro# and Re# from Roshko's Caltech Thesis (figures 9-10); tested in air [over range Re=50 to Re=2000]
The kinematic viscosity of air at 15 °C is 1.48×10−5 m2/s. at 20 °C, the kinematic viscosity is 1.525×10−5 m2/s. at 25 °C, the kinematic viscosity is 1.57×10−5 m2/s.
References
- Olim, A. M.; Riethmuller, M. L.; Gameiro da Silva, M. C. (2002). "Flowfield characterisation in the wake of a low-velocity heated sphere anemometer". Exp. Fluids. 32 (6): 645–651. Bibcode:2002ExFl...32..645O. doi:10.1007/s00348-001-0403-6.
- Ormieres, D.; Provansal, M. (1999). "Transition to turbulence in the wake of a sphere". Phys. Rev. Lett. 83 (1): 80–83. Bibcode:1999PhRvL..83...80O. doi:10.1103/PhysRevLett.83.80.
External links
- On the Development of Turbulent Wakes From Vortex Streets PhD. Thesis by Anatol Roshko (hosted on Caltech Site).
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