Sökning: "streamwise streaks"

Visar resultat 6 - 10 av 31 avhandlingar innehållade orden streamwise streaks.

1. 6. Numerical studies of transtion in wall-bounded flows

   Författare :Ori Levin; Dan Henningson; Nikolaus Adams; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; boundary layer; suction; wall jet; streaks; waves; periodic disturbance; localized disturbance; turbulent spot; algebraic growth; exponential growth; stability; transition thresholds; transition prediction; PSE; DNS; Fluid mechanics; Strömningsmekanik;

   Sammanfattning : Disturbances introduced in wall-bounded flows can grow and lead to transition from laminar to turbulent flow. In order to reduce losses or enhance mixing in energy systems, a fundamental understanding of the flow stability and transition mechanism is important. LÄS MER

3. 7. 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

4. 8. Boundary layer streaks as a novel laminar flow control method

   Författare :Sohrab Sattarzadeh Shirvan; Jens H. M. Fransson; Edward B. White; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; boundary layer stability; laminar to turbulent transition; laminar flow control; drag reduction; Tollmien-Schlichting waves; oblique waves; streaky boundary layers; miniature vortex generators; discrete suction;

   Sammanfattning : A novel laminar flow control based on generation of spanwise mean velocity gradients (SVG) in a flat plate boundary layer is investigated where disturbances of different types are introduced in the wall-bounded shear layer. The experimental investigations are aimed at; (i) generating stable and steady streamwise streaks in the boundary layer which set up spanwise gradients in the mean flow, and (ii) attenuating disturbance energy growth in the streaky boundary layers and hence delaying the onset of turbulence transition. LÄS MER

5. 9. 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

7. 10. Orientation of elongated, macro and nano-sized particles in macroscopic flows

   Författare :Karl Håkansson; Danel Söderberg; Fredrik Lundell; Lisa Prahl Wittberg; Jean-Yves Cavaillé; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Orientation; fibre; fibril; turbulent channel flow; particle streaks; flow focusing; cellulose nanofibrils; extensional flow; Smoluchowski; rotary diffusion;

   Sammanfattning : Non-spherical particles are present all around us, in biological, industrial and environmental processes. Making predictions of their impact on us and systems in our vicinity can make life better for everyone here on earth. LÄS MER