Dr. Williams et al., 3-DIMENSIONAL SUBHARMONIC WAVES DURING TRANSITION IN THE NEAR-WAKE REGION OF A CYLINDER, Physics of fluids, 8(6), 1996, pp. 1476-1485
Detailed quantitative measurements of three-dimensional subharmonic wa
ves have been obtained with a scanning laser anemometer in the near-wa
ke region of a circular cylinder. A spatial decomposition technique ha
s been used to separate the secondary three-dimensional flow from the
primary Strouhal vortex flow. The appearance of subharmonic frequencie
s in the spectrum of the secondary instability field at Reynolds numbe
rs of 300 and above provides experimental evidence consistent with the
scenario of a period-doubling route to turbulence. The basic flow str
ucture of the secondary field responsible for producing the subharmoni
cs is shown to be pairs of counter-rotating streamwise vortices, which
alternate the direction of rotation every Strouhal period. (C) 1996 A
merican Institute of Physics.