Hydrophysics

Hydrophysics

Experimental Study of Internal Waves Due to the Movement of a Cylindrical Body in a Density Stratified Fluid

Document Type : Original Article

Authors
Mohammad AkbarnejadBaie 1
abbasali aliakbaribidokhti 2
mohammad akbarinasab 3
mojtaba Ezam 1
sara allahyari 1
1 Department of physical oceanography, Science and Research Branch,Islamic Azad University, Tehran,Iran
2 Space Physics, Tehran University,tehran,Iran
3 department of physical oceanography,mazandaran University,Babolsar,Iran
Abstract
In the case of an internal force in stratified fluid, internal waves are one of the most important phenomena that occurs in the stratified oceanic environment. This study was conducted to investigate internal waves and turbulent wake effect behind a cylindrical body in a linear stratified environment in laboratory. In this work, in a glass tank with dimensions of 3×1×0.5 (m), a linear stratification with buoyancy frequency (N) of 0.51 (s-1), was set up. Then a cylindrical body of 6 cm diameter and 45 cm long was towed in the fluid, while changing the Froude and Reynolds numbers of the flow and the effect of these changes on the formation of the internal waves and wake of the cylinder, at speeds of 5 mm/s to 4.5 cm/s, using a computer controlled system, were examined. In this work shadowgraphs technique was used to capture the flow. The results show that the presence of internal waves depend on changes of Froude and Reynolds numbers of the flow, and maximum internal waves activities were found when Froude number was tended to the critical values of one; the wavelength of the internal waves  was also increased with Froude number. In the range of the supercritical Froude number the flow consisted of a turbulence wake in the environment, also relatively increasing irregular shorter waves were observed around the cylinder. Detection of such waves at a distance from the cylinder was one of the objective of the present work.
Keywords
stratified fluid tank
internal waves
buoyancy frequency
shadowgraph technique
Froude number

Subjects

[1] Nansen F, editor. The Norwegian North polar expedition, 1893-1896: scientific results. Longmans, Green and Company; 1905.
 [2] Sutherland BR, Linden PF. Internal wave excitation by a vertically oscillating elliptical cylinder. Physics of Fluids. 2002 Feb;14(2):721-31.
[3] Aguilar DA, Sutherland BR, Muraki DJ. Laboratory generation of internal waves from sinusoidal topography. Deep Sea Research Part II: Topical Studies in Oceanography. 2006 Jan 1;53(1-2):96-115.
[4] Glushko GS, Gumilevskii AG, Polezhaev VI. Evolution of the turbulent wakes of spherical bodies in stably stratified media. Fluid dynamics. 1994 Jan 1;29(1):10-6.
[5] Bidokhti AA. Flow Visualization of Internal Waves and Wakes of a Streamlined Body in a Stratified Fluid. Journal of Applied Fluid Mechanics. 2016 Apr 1;9(2).
[6] Thorpe SA. The turbulent ocean. Cambridge University Press; 2005 Oct 27.
[7] Garrett C, Munk W. Internal waves in the ocean. Annual Review of Fluid Mechanics. 1979 Jan;11(1):339-69.
[8] Dotsenko SF, Savoskin VM. Generation of internal waves by moving non-stationary disturbances in a real stratified ocean. Physical Oceanography. 1994 Sep 1;5(5):335-47.
[9] Stevenson TN, Kanellopulos D, Constantinides M. The phase configuration of trapped internal waves from a body moving in a thermocline. Applied scientific research. 1986 Jun 1;43(2):91-105.
[10] Swain SK, Trinath K. Non-Acoustic Detection of Moving Submerged Bodies in Ocean. International Journal of Innovative Research and Development. 2012 Dec 1;1(10):361-72.
[11] Abdilghanie AM, Diamessis PJ. The internal gravity wave field emitted by a stably stratified turbulent wake. Journal of Fluid Mechanics. 2013 Apr;720:104-39.
[12] Ohya Y, Uchida T, Nagai T. Near wake of a horizontal circular cylinder in stably stratified flows. Open Journal of Fluid Dynamics. 2013 Nov 1;3(4):311.
[13] Wong AB, Griffiths RW, Hughes GO. Shear layers driven by turbulent plumes. Journal of Fluid Mechanics. 2001 May;434:209-41.
[14] Mitkin VV, Chashechkin YD. Experimental Investigation of the Velocity Field near a Cylinder in a Contonuously Stratified Fluid. Fluid Dynamics. 2000 Sep 1;35(5):642-51.
[15] Gill A. Atmospheric-ocean dynamics. International Geophysics Series. 1982;30:662.
[16] Hopfinger EJ, Flor JB, Chomaz JM, Bonneton P. Internal waves generated by a moving sphere and its wake in a stratified fluid. Experiments in Fluids. 1991 Jul 1;11(4):255-61.

  • Receive Date 23 September 2017
  • Revise Date 25 January 2018
  • Accept Date 29 January 2018