Accession Number : ADA268419


Title :   Laboratory Measurements of the Evolution of a Vortex Pair in a Nonstratified Fluid


Corporate Author : NORTHWEST RESEARCH ASSOCIATES INC BELLEVUE WA


Personal Author(s) : Delisi, Donald P ; Greene, George C ; Altman, Donald B ; Piper, Lee E ; Singh, Raminder


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a268419.pdf


Report Date : Apr 1992


Pagination or Media Count : 47


Abstract : New measurements of the evolution of a vortex pair from a lifting wing in a nonstratified fluid are presented. The new feature of these measurements is the use of nearly neutrally buoyant particles as the primary flow visualization tool. Using dye, as in previous studies, we show that our results are consistent with observations of other researchers. Using particles, however, organized vorticity is shown to persist for significantly longer times and to migrate significantly longer distances than observed in previous studies. The vortex motion is observed in three stages: (1) a two-dimensional line vortex pair. (2) transition from two-dimensional to three-dimensional vorticity via a mutual induction, or Crow, instability, and (3) vortex rings. Unlike previous studies, the third stage of vortex rings is shown to be very stable and robust. In nondimensional units of time, T, the first stage is shown to last until T approx. 5, the second stage from T approx. 5 to approx. 11, and the third stage from T approx. 11 to at least 100. Characteristics of the flow are measured for each stage in the evolution. Practical implications for commercial aircraft wakes are also discussed.


Descriptors :   *AIRCRAFT , *VORTICES , *WINGS , *FLOW VISUALIZATION , *AERODYNAMIC LIFT , MEASUREMENT , THREE DIMENSIONAL , AERODYNAMIC CHARACTERISTICS , FLUID FLOW , INSTABILITY , TRANSITIONS , WAKE , PARTICLES , COMMERCIAL AIRCRAFT , TWO DIMENSIONAL , MOTION


Subject Categories : Aerodynamics


Distribution Statement : APPROVED FOR PUBLIC RELEASE