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Visar resultat 1 - 5 av 6 avhandlingar som matchar ovanstående sökkriterier.

  1. 1. Flow control of boundary lagers and wakes

    Författare :Jens H. M. Fransson; KTH; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Laminar-turbulent transition; asymptotic suction boundary layer; free stream turbulence; Tollmien-Schlichting wave; stability; flow control; cylinder wake; Engineering mechanics; Teknisk mekanik;

    Sammanfattning : Both experimental and theoretical studies have beenconsidered on flat plate boundary layers as well as on wakesbehind porous cylinders. The main thread in this work iscontrol, which is applied passively and actively on boundarylayers in order to inhibit or postpone transition toturbulence; and actively through the cylinder surface in orderto effect the wakecharacteristics. LÄS MER

  3. 2. Stability analysis and transition prediction of wall-bounded flows

    Författare :Ori Levin; KTH; []
    Nyckelord :Boundary layer; wall jet; algebraic growth; exponential growth; lift-up effect; streamwise streaks; Tollmien-Schlichting waves; free-stream turbulence; roughness element; transition prediction; Parabolized Stability Equations; Direct Numerical S;

    Sammanfattning : Disturbances introduced in wall-bounded .ows can grow andlead to transition from laminar to turbulent .ow. In order toreduce losses or enhance mixing in energy systems, afundamental understanding of the . LÄS MER

  4. 3. Topology optimization of transitional flows

    Författare :Harrison Nobis; Dan Henningson; Philipp Schlatter; Paolo Luchini; KTH; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Direct Numerical Simulation; Topology Optimization; Laminar– Turbulent Transition; Spectral Element Method; Direkt numerisk simulering; topologioptimering; laminär–turbulent omslag; spektralelementmetod; Teknisk mekanik; Engineering Mechanics;

    Sammanfattning : This thesis is concerned with the application of topology optimization in thedesign of structures that control fluids. A framework is developed in the high-order Spectral Element Method (SEM) code Nek5000, extending Nek5000 fromits original capabilities, performing Direct Numerical Simulations (DNS), toperforming density-based topology optimization. LÄS MER

  5. 4. Laninar-turbulent boundary layer transition influenced by free stream turbulence

    Författare :Jonas Westin; KTH; []
    Nyckelord :;

    Sammanfattning : Laminar-turbulent transition in a flat plate boundary layerhas been considered, with a special emphasis on the influencefrom free stream turbulence (FST)First, experiments on linear stability ofTollmien-Schlichting (TS) waves in a Blasius boundary layer wasstudied. This is a well-known example from hydrodynamicstability theory, which has hitherto suffered from unresolveddiscrepancies between experiments and linear theory. LÄS MER

  7. 5. Stability and transition in the suction boundary layer and other shear flows

    Författare :Niklas Davidsson; Luleå tekniska universitet; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Strömningslära; Fluid Mechanics;

    Sammanfattning : Bypass transition has been studied by theoretical and numerical procedures, with the asymptotic suction boundary layer (ASBL) in focus. As reference cases the Blasius boundary layer (BBL) and a free shear flow have been studied. In order to reduce energy losses associated with flow systems, it is a wish to avoid turbulence in these flows. LÄS MER