Relaminarization in a short acceleration zone on a convex surface (NAL PD EA 0511)

Mukund, R (2002) Relaminarization in a short acceleration zone on a convex surface (NAL PD EA 0511). PhD thesis, Indian Institute of Science.

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    Abstract

    This thesis is essentially an experimental study investigating two-dimensional relaminarizing turbulent boundary layer flows under the combined influence of acceleration and convex surface curvature at low speeds. Relaminarization of turbulent flow is a process by which the mean flow reverts to an effectively laminar state. The phenomenon of relaminarization in severely accelerated turbulent boundary layers on a flat plate has been studied in the past by several investigations and reviews can be found in Narasimha & Sreenivasan [1979] and Sreenivasan [1982]. Narasimha & Sreenivasan [1973] have proposed that relaminarization is an asymptotic process involving a large ratio of the streamwise pressure gradient to a characteristic Reynolds stress, and developed a two-layer integral model (called the quasi-laminar equations, QLE) for predicting the boundary layer mean flow parameters in the latter part of the relaminarization process. While early work on relaminarization was largely motivated by scientific curiosity, interest in the problem has recently revived because of aircraft design applications involving relaminarization at swept leading-edges at high-lift, both in flight and in wind tunnels. The boundary layer near the leading edge of a swept wing, following attachment line transition, encounters not only strong streamwise acceleration but also convex surface curvature. It is well known that convex curvature can have a considerable stabilizing effect on a turbulent boundary layer (Bradshaw [1969]), so it is possible that relaminarization at a swept wing leading edge is influenced by streamwise convex curvature in addition to strong acceleration; such combined effects on relaminarization have not been studied before. A complete understanding of relaminarization phenomena relevant to swept wings would further involve study of the effects of additional parameters like threedimensionality and transition to turbulence by different mechanisms preceding relaminarization. Flow measurements on a swept wing, particularly in the leading edge zone, are difficult due to the relative thinness of the boundary layers in the zone. Two dimensional building block experiments, systematically investigating the different effects on relaminarization, can therefore prove to be useful for understanding many features of 3D relaminarization such as those at a swept wing leading edge.

    Item Type: Thesis (PhD)
    Uncontrolled Keywords: Relaminarization;Acceleration zone;Convex surface
    Subjects: AERONAUTICS > Aeronautics (General)
    AERONAUTICS > Aerodynamics
    Division/Department: Experimental Aerodynamics Division
    Depositing User: Ms. Alphones Mary
    Date Deposited: 28 Jun 2011 13:29
    Last Modified: 28 Jun 2011 13:29
    URI: http://nal-ir.nal.res.in/id/eprint/9248

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