Sökning: "streamwise vortices"

Visar resultat 1 - 5 av 30 avhandlingar innehållade orden streamwise vortices.

  1. 1. Attenuation of boundary layer disturbances by means of streamwise vortices

    Författare :Sohrab Sattarzadeh Shirvan; Jens H. M. Fransson; Valery Chernoray; KTH; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; boundary layer stability; Tollmien-Schlichting waves; oblique waves; transition to turbulence; streamwise vortices; miniature vortex generators; instability control; drag reduction;

    Sammanfattning : The stability of the boundary layer developed on a flat plate is studied in the presence of streamwise streaks where disturbances of different types are introduced in the wall-bounded shear layer. The experimental investigations are aimed at flow control by means of passively damping the energy growth of the disturbances in the streaky boundary layer and furthermore delay the onset of the transition in the streamwise direction. LÄS MER

  3. 2. Study of generation, growth and breakdown of streamwise streaks in a Blasius boundary layer

    Författare :Luca Brandt; KTH; []
    Nyckelord :Fluid mechanics; laminar-turbulent transition; boundary layer flow; transient growth; streamwise streaks; lift-up effect; receptivity; free-stream turbulence; streak instability; secondary instability; Direct Numerical Simulation.;

    Sammanfattning : Transition from laminar to turbulent flow has beentraditionally studied in terms of exponentially growingeigensolutions to the linearized disturbance equations.However, experimental findings show that transition may occuralso for parameters combinations such that these eigensolutionsare damped. LÄS MER

  4. 3. Receptivity of Boundary-Layer Flows over Flat and Curved Walls

    Författare :Lars-Uve Schrader; Luca Brandt; Dan Stefan Henningson; Gregoire Casalis; KTH; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Boundary-layer receptivity; laminar-turbulent transition; swept-plate boundary layer; Görtler flow; leading-edge effects; swept-wing flow; crossflow vortices; Görtler rolls; disturbance streaks; wall roughness; free-stream turbulence; Fluid mechanics; Strömningsmekanik;

    Sammanfattning : Direct numerical simulations of the receptivity and instability of boundary layers on flat and curved surfaces are herein reported. Various flow models are considered with the aim to capture aspects of flows over straight and swept wings such as wall curvature, pressure variations, leading-edge effects, streamline curvature and crossflow. LÄS MER

  5. 4. An experimental study on streamwise streaks in transitional boundary layers

    Författare :Shahab Shahinfar; Jens Fransson; Yury Kachanov; KTH; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY;

    Sammanfattning : The present experimental study focuses on two topics, a passive transition-delay method for different types of wave disturbances and the effect of free-stream turbulence characteristics on boundary layer transition over a at plate. In the investigations, hot-wire anemometry was employed and the experiments were performed in a well-controlled wind tunnel facility. LÄS MER

  7. 5. Experimental studies of turbulent boundary layer separation and control

    Författare :Kristian Angele; KTH; []
    Nyckelord :turbulence; boundary layer; separition; adverse pressure graddient;

    Sammanfattning : The object ofthe present work is to experimentally study thecase ofa turbulent boundary layer subjected to an AdversePressure Gradient (APG) with separation and reattachment. Thisconstitutes a good test case for advanced turbulence modeling. LÄS MER