DID YOU KNOW? DTIC has over 3.5 million final reports on DoD funded research, development, test, and evaluation activities available to our registered users. Click
HERE to register or log in.
Accession Number:
ADA048629
Title:
Visualization Study of Vorticity Amplification in Stagnation Flow.
Descriptive Note:
Technical rept.,
Corporate Author:
PURDUE UNIV LAFAYETTE IND PROJECT SQUID HEADQUARTERS
Report Date:
1977-10-01
Pagination or Media Count:
77.0
Abstract:
A visualization study of stagnation flow round a circular cylinder was carried out in order to gain a physical insight into its model put forward by the vorticity-amplification theory. The visualization was conducted at a Reynolds number of 8000 utilizing white smoke composed of titanium dioxide for an approaching flow containing turbulence at scales larger than the neutral wavelength. An in-depth dynamic qualitative apperception of the flow events was obtained by means of motion pictures taken from three different viewpoints. In addition, a frame by frame examination of selected movie strips led to the acquisition of a reasonably quantitative interpretation of the gross flow structure. The analysis of the flow events focused on tracing the temporal and spatial evolution of a cross-vortex tube outlined by the entrained smoke filaments. The visualization supplied striking evidence concerning 1 the selective stretching of cross-vortex tubes which is responsible for the amplification of vorticity and, hence, of turbulence 2 the streamwise tilting of stretched cross-vortex tubes 3 the existence of a coherent array of vortices near the stagnation zone 4 the interaction of the amplified vorticity with the body laminar boundary layer and, finally, 5 the growth of a turbulent boundary layer. These are basically the flow characteristics and events advanced by the vorticity-amplification theory. It is thus apparent that the amplification of turbulence in stagnation flow around a bluff body and its effects upon the body boundary layer are satisfactorily explained by the vorticity-amplification theory. Author
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
