OJFD  Vol.3 No.4 , December 2013
Near Wake of a Horizontal Circular Cylinder in Stably Stratified Flows
ABSTRACT
The near wake of a circular cylinder in linearly stratified flows of finite depth was experimentally investigated by means of flow visualization and measurements of vortex shedding frequencies, at Reynolds numbers 3.5 × 103-1.2 × 104 and stratification parameters kd 0-2.0. The non-dimensional parameter kd is defined as kd = Nd/U, where N is the Brunt-Vaisala frequency, d, the diameter of the cylinder, and U, the approaching flow velocity. The study demonstrates that as kd increases from zero, the vortex shedding from a circular cylinder progressively strengthens, while the Strouhal number gradually becomes lower than that for homogeneous flow. This phenomenon can be explained by the effect of the increasingly stable stratification which enhances the two-dimensionality of the near-wake flow of the circular cylinder; the enhanced two-dimensionality of the flow strengthens the roll-up of the separated shear layer. Above a certain value of kd, however, vortex formation and shedding are strongly suppressed and the Strouhal number rises sharply. This observation is attributable to the development of stationary lee waves downstream of the circular cylinder because the lee waves strongly suppress vertical fluid motions.

Cite this paper
Y. Ohya, T. Uchida and T. Nagai, "Near Wake of a Horizontal Circular Cylinder in Stably Stratified Flows," Open Journal of Fluid Dynamics, Vol. 3 No. 4, 2013, pp. 311-320. doi: 10.4236/ojfd.2013.34038.
References
[1]   W. Blumen, “Atmospheric Processes over Complex Terrain (Meteorological Monographs),” American Meteor Society, Vol. 23, No. 45, 1990, pp. 1-323.

[2]   W. H. Snyder, “Fluid Modeling of Pollutant Transport and Diffusion in Stably Stratified Flows over Complex Terrain,” Annual Review of Fluid Mechanics, Vol. 17, 1985, pp. 239-266.

[3]   H. Honji, “Stratified Flow Experiments,” Nagare, Vol. 6, 1987, pp. 276-284.

[4]   H. Honji, “Vortex Street in the Stratified Fluids,” Reports of Research Institute for Applied Mechanics, No. 60, 1984, pp. 393-401.

[5]   H. Honji, “Vortex Motions in the Stratified Wake Flows,” Fluid Dynamics Research, Vol. 3, No. 1-4, 1988, pp. 425-430. http://dx.doi.org/10.1016/0169-5983(88)90104-9

[6]   J. T. Lin and Y. H. Pao, “Wakes in Stratified Fluids,” Annual Review of Fluid Mechanics, Vol. 11, 1979, pp. 317-338. http://dx.doi.org/10.1146/annurev.fl.11.010179.001533

[7]   D. L. Boyer, P. A. Davies, H. J. S. Fernando and X. Zhang, “Linearly Stratified Flow Past a Horizontal Circular Cylinder,” Philosophical Transactions of the Royal Society of London. Series A, Vol. 328, 1989, pp. 501-528. http://dx.doi.org/10.1098/rsta.1989.0049

[8]   S. N. Wei, T. W. Kao and H. P. Pao, “Experimental Study of Upstream Influence in the Two-Dimensional Flow of a Stratified Fluid over an Obstacle,” Geophysical fluid Dynamics, Vol. 6, No. 4, 1975, pp. 315-336. http://dx.doi.org/10.1080/03091927509365802

[9]   H. Hanazaki, “Upstream and Advancing Columnar Disturbances in Two-Dimensional Stratified Flow of Finite Depth,” Physics of Fluids A, Vol. 1, No. 12, 1989, pp. 1976-1987.

[10]   R. R. Hwang and S. H. Lin, “On Laminar Wakes behind a Circular Cylinder in Stratified Fluids,” Transactions of the ASME, Journal of Fluids Engineering, Vol. 114, No. 1, 1992, pp. 20-28. http://dx.doi.org/10.1115/1.2909993

[11]   N. Boulanger, P. Meunier and S. Le Dizes, “Structure of a Stratified Tilted Vortex,” Journal of Fluid Mechanics, Vol. 583, 2007, pp. 443-458. http://dx.doi.org/10.1017/S0022112007006416

[12]   N. Boulanger, P. Meunier and S. Le Dizes, “Tilt-Induced Instability of a Stratified Vortex,” Journal of Fluid Mechanics, Vol. 596, 2008, pp. 1-20. http://dx.doi.org/10.1017/S0022112007009263

[13]   P. Meunier, “Stratified Wake of a Tilted Cylinder. Part 1. Suppression of a von Karman Vortex Street,” Journal of Fluid Mechanics, Vol. 699, 2012, pp. 174-197. http://dx.doi.org/10.1017/jfm.2012.92

[14]   P. Meunier, “Stratified Wake of a Tilted Cylinder. Part 2. Lee Internal Waves,” Journal of Fluid Mechanics, Vol. 699, 2012, pp. 198-215. http://dx.doi.org/10.1017/jfm.2012.123

[15]   Y. Ohya and Y. Nakamura, “Near Wakes of a Circular Cylinder in Stratified Flows,” Physics of Fluids A, Vol. 2-4, No. 4, 1990, pp. 481-483.

[16]   Y. Ohya, S. Ozono and Y. Nakamura, “A Wind Tunnel for Studying Density-Stratified Flows,” Atmospheric Environment, Vol. 28, No. 11, 1994, pp. 1895-1900. http://dx.doi.org/10.1016/1352-2310(94)90329-8

[17]   M. Funakoshi and M. Oikawa, “Non-Linear Waves in Stratified Flow,” Nagare, Vol. 8, 1989, pp. 311-335.

[18]   Y. Yokoi and K. Kamemoto, “Initial Stage of a Three-Dimensional Vortex Structure Existing in a Two-Dimensional Boundary Layer Separation Flow: Observation of Laminar Boundary Layer Separation over a Circular Cylinder by Flow Visualization,” JSME International Journal. Ser. 2, Fluids Engineering, Heat Transfer, Power, Combustion, Thermophysical Properties, Vol. 35-II, No. 2, 1992, pp. 189-195.

 
 
Top