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FLOW STABILITY IN THE PRESENCE OF FINITE INITIAL DISTURBANCES
ADVISORY GROUP FOR AERONAUTICAL RESEARCH AND DEVELOPMENT PARIS (FRANCE)
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Descriptions of some theoretical and experimental studies of the behaviour of finite amplitude disturbances in viscous flow are presented. An analysis is developed for disturbances 1 which are oscillatory and grow with streamwise distance between parallel planes until a possible equilibrium state is reached, or 2 which depart from an unstable equilibrium state of finite amplitude with streamwise distance these two possibilities correspond to disturbances under supercritical and subcritical conditions respectively, and in both the solution is a perturbation from linearized theory. An experiment is described by which it is proposed to check the above theory. Some details are also given of results of a parallel experiment on finite disturbances in flow in a straight pipe in which the growth of artificially introduced disturbances and the generation of harmonics is described qualitatively, and limited support is found for some of the theoretical concepts. Breaking patterns similar to those found by Klebanoff and Tidstrom in a boundary layer are shown to be horseshoe vortices. Author
APPROVED FOR PUBLIC RELEASE