Accession Number : ADA262281


Title :   Studies of Origin of Three-Dimensionality in Laminar Wakes


Descriptive Note : Final technical rept. 1 Dec 1989-31 Jan 1993


Corporate Author : CALIFORNIA UNIV SAN DIEGO LA JOLLA OFFICE OF CONTRACT AND GRANT ADMINISTRATION


Personal Author(s) : Gharib, Morteza


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a262281.pdf


Report Date : 17 Feb 1993


Pagination or Media Count : 31


Abstract : Wind tunnel experiments, using hot-wire anemometry and smoke-wire flow visualization, were conducted to study the process of transition from laminar to turbulent flow of parallel and oblique vortex streets from circular cylinders. It was found that the origin and scale of three-dimensionality which appears at Reynolds numbers just below the transition from laminar to turbulent flow are dependent on the vortex shedding geometry in the near-wake. Oblique vortex streets develop large scale three-dimensional structures and undergo an early transition, i.e. at lower Reynolds numbers, when compared to parallel vortex streets. This is due to the presence of three-dimensionality in oblique wakes at pretransition Reynolds numbers, whereas parallel wakes remain laminar until the vortices themselves develop three-dimensional features. The downstream evolution of these two wake geometries from the primary Karman vortices to the far-wake vortical structures was also investigated. The far-wake structures are parallel to the cylinder axis for parallel shedding. For oblique shedding, these structures are initially parallel to the cylinder axis, but further downstream they develop a strong spanwise modulation whose wavelength is the spanwise distance between two consecutive Karman vortices of the same sign of vorticity.


Descriptors :   *TURBULENT FLOW , *FLOW VISUALIZATION , *WAKE , *LAMINAR FLOW , *VORTEX SHEDDING , VELOCITY , TRANSITIONS , REYNOLDS NUMBER , HOT WIRE ANEMOMETERS , WIND TUNNELS , MODULATION , GEOMETRY , VORTICES , THREE DIMENSIONAL , WIND TUNNEL TESTS


Subject Categories : Fluid Mechanics


Distribution Statement : APPROVED FOR PUBLIC RELEASE